•>&p r. v / WSÔ2PI I .D EHE E

MEASUREMENTS AND COMPUTATIONS N08201,760 ON THE BEHAVIOUR >F THE INSECTICIDES INPHOS-METHYL AND DIMETHOATE ; - IN DITCHES H. de Heer

Measurements and computations on the behaviour of the insecticides azinphos-methyl and dimethoate in ditches

Proefschrift terverkrijgin gvan d egraa dvan doctori nd elandbouwwetenschappen , op gezagvan d erecto rmagnificus , dr.H.C .va nde rPlas , hoogleraari nd eorganisch e scheikunde, inhe topenbaa rt everdedige n opwoensda g3 0me i 1979 desnamiddag st evie ruu ri nd eaul a vand eLandbouwhogeschoo l teWageninge n

Centre for Agricultural Publishing and Documentation

Wageningen - 1979 Abstract

Heer H.d e (1979).Measurement san dcomputation so nth ebehaviou ro fth einsecticide s azinphos-methylan ddimethoat ei nditches .Agric .Res .Rep .(Versl .landbouwk .Onder«. ; 884.Pudo cWageningen . -„varies ISBN9 022 0069 56 .(xiv )+ 17 6p. ,5 5figs ,5 5tables ,l « refs,Eng .an dDutc hsummaries . Also:Doctora lthesi sWageningen .

Theunintentiona lpollutio no fsurfac ewate rwa sstudie ddurin gsprayin g of theinsec ­ ticidesazinphos-methy lan ddimethoat eo ntw ofrui tfarms .Spra ydrif tdepende d closelyo n theloca lsituation sa tth efrui tfarm s (windbreaks,distanc efro m trees toditches ,patns ; ando nwa yo fapplication . , Duringapplication ,th econcentration so fbot hinsecticide s inwate r and inditct i bottomswer emeasured .Method swer eadapte do rdevelope d forsampling ,extraction ,^ lean_ -upan deas-chromatography .Shortl yafte rspraying ,concentration swer e severalhundred s ofm gm~3 .Th ehalf-live so fazinphos-methy lrange dfro m3 t o4 d ; thosefo rdimethoat e rangedfro m4 t o1 3d . ._ Water flowfro man d toditc hsection swa sestimate d onbot h fruitfarm sdurin gappli ­ cation.Flo wthroug hth editc hbotto mwa sestimate d asa closin g itemi na balanc eequa ­ tion.Al litem so fwate rbalanc ewer eintroduce d intocomputatio nmodel so f thebehaviou r ofpesticide si nsurfac ewate ran dbotto mmaterial .Th ese to fdifferentia l equationswa s solvednumericall yafte rprogrammin gi nth ecompute r languageCSH PIII .Simulatio no fa trialwit hlo wdischarg efro ma siphon-linke dditc hindicate d thatconversio no fbot hcom ­ poundsi nwate rwa s70-90 %o fth emateria lbalances .Penetratio nint o theditc hbotto mwa s slow.Durin gwate rflo wthroug hth editches ,convectiv etranspor tan ddispersio nwer epr e dominant. Declineo fazinphos-methy lan ddimethoat ewa sals omeasure d inoutdoo r tanksystem s witha botto mlayer .Fluctuation si np Han dvariation si nligh tpenetratio n influencedd e clinerates .Computation sfo rth etan ksyste mindicate d thatconversio ni nth ewate rcom ­ partmentwa sth emajo rite mi nmateria lbalance .Th ecompute d andmeasure dmasse so fth e insecticidesi nth ebotto mlaye rwer eles stha n 10%o fth eamoun tadded . Conversionrate si nsurfac ewate ran d insystem swit hanaerobi cbotto mmateria l we*e measured inth elaborator ya t1 0an d2 0°C .Conversio ni nwate r inth edar kwa s slow,wit h half-liveso fbot hcompound sa tabou t 100d a t2 0°C .Th econversio nrate so fazinphos - -methyli nanaerobi cbotto mmateria la t2 0° Cwa sabou tte ntime s thosei nsurfac ewater . Copper ionswer ecatalyti ci nth econversio no fbot hinsecticide s inwater .

Freedescriptors :adsorptio ncoefficient ,clean-up ,gas—liqui d chromatography,botto m material,conversion ,insecticides ,azinphos-methyl ,dimethoate ,watercourse ,ditch ,sam ­ pling,spra ydrift ,diffusion ,dispersion ,computations ,half-life ,rate-constant .

Thisthesi swil lals ob epublishe da sAgricultura lResearc hReport s884 .

© Centrefo rAgricultura lPublishin gan dDocumentation ,Wageningen ,1979 .

Nopar to fthi sboo kma yb ereproduce do rpublishe d inan yform ,b yprint ,photopri n, microfilmo ran yothe rmean swithou twritte npermissio nfro mth epublishers . Stellingen

1. De toetsingva ne nd evoorlichtin g overd emogelijk e gevolgenva nhe tgebrui k vanbe ­ strijdingsmiddelen voorhe tmilie udiene nster k teworde n geïntensiveerd.

2. Demat eva nverontreinigin g vanoppervlaktewate r metbestrijdingsmiddele n isster kaf ­ hankelijk vand e lokale situatie end ewerkwijz e vand e gebruiker.

3. Infruitteeltgebiede nme tvee lslote nka nd everontreinigin g vanoppervlaktewate r met bestrijdingsmiddelen verminderdworde n door sloten tevervange n door een drainagesysteem, doorhe tplaatse nva nwindsingel s rondom fruitteeltpercelen of doorhe taanlegge n vanpa ­ den tussend eboomgaar d enhe t oppervlaktewater.

4. Bijonderbemalin gva nslote nverdien the t aanbevelingee nlag ewaterstan d aant ebrenge n vóór debespuitin g metbestrijdingsmiddele n enn a debespuitin g zolangmogelij k tewachte n metbemalen .

5. Gezienhe t grote aantal chemische verbindingen end euiteenlopend e veldsituaties is het gebruik vanrekenmodelle n als denkraam inmilieustudie s onontbeerlijk.

6. Onzekerheden inaanname se nbasisgegeven sbeperke n totn u toed evoorspellend e waarde vanrekenmodellen .Aa nhe t ontwikkelenva nrepresentatiev e laboratoriumexperimenten terbe ­ paling vanafbraaksnelhede n inoppervlaktewate r zalmee r aandachtmoete nworde nbesteed .

7. Het inzicht ind e relatie tussenmilieu-toxicologisch e gegevensva n bestrijdingsmiddelen enecologisch e effecten inhe tmilie udien t sterkverdiep t teworden ,opda tee n zinvolle beoordeling kanplaatsvinde nva nd ekan s oponaanvaardbar e schadelijke nevenwerkingen van bestrijdingsmiddelen voorhe tmilieu .

8. Nietallee nchemische ,maa roo kbiologisch e enmechanisch ebestrijdingsmethode ndiene n involdoend emat e teworde n getoetst ophu naanvaardbaarhei d voorhe tmilieu .

9. Beschaduwingva nwaterlope nka nongunsti gwerke no p deomzettingssnelhei d vaninsekti - ciden inoppervlaktewater .

10. Hetster k terugdringenva nd eeutrofiërin g vanoppervlaktewate r kan de afbraak van toxische stoffen inoppervlaktewate r vertragen. 11. Belangrijkeverschille ni nhe ttoelatingsbelei d ind everschillend eEuropes elande n werkthe tgebrui kva nniet-toegelate nbestrijdingsmiddele n ind ehand .

12. Debepalin gi nd eschouwplich tva nsommig ewaterschappe nove rhe tverwijdere nva n fluitekruidui twegberme ndien tgeschrap tt eworden .

13. Doord enadru kdi edoo rpubliciteitsmedi ao pd erelationel ee nsocial eoorzake nva n kwalenword tgelegd ,dreige nd ezuive rmedisc hlichamelijk e aspectenal sonbelangrij kter ­ zijdet eworde ngeschoven .

Proefschriftva nH .d eHee r Measurements andcomputation s onth ebehaviou ro fth einsecticide s azinphos-methylan d dimethoate inditche s Curriculum vitae

Deauteu rwer d geboreno p8 jun i 1946t ePurme r (Gem. Edam).N ahe tbehale nva nhe t einddiplomaHBS- Baa nd eRHB St ePurmeren dwer dd emilitair e dienstplicht vervuld.I n 1968bego nhi j zijnstudi eaa nd eLandbouwhogeschoo l teWageningen .Va nfebruar i 1972to t juni 1972brach thi j zijnpraktijktij d dooro pd eafdelin g Gronde nWate rva nhe tAdvies ­ bureauArnhem .I nseptembe r 1974studeerd ehi j (metlof )a fi nd erichtin g cultuurtech­ niekme tal shoofdvakke n cultuurtechniek,bodemscheikund ee nbodemnatuurkund ee nal s bij­ vakwiskunde .Vana fseptembe r 1974i shi jwerkzaa mbi jhe tLaboratoriu m voor Insekticiden Onderzoeki nWageninge naa nonderzoeksprojecte n betreffendehe tgedra gva nbestrijdings ­ middeleni noppervlaktewater . Woord vooraf

Bijhe tgereedkome nva ndi tproefschrif twi li kgraa giederee nbedanke ndi eaa nd e totstandkoming ervanheef tbijgedragen . Allereerstwi li kU ,prof.dr.ir .W.H .va nde rMole nbedanke nvoo rd eagrohydrologisch e opleidingdi ei kva nU ontving.Aa nU wcollege she bi kmij ninteress ei nd ewaterkwaliteits - enwaterkwantiteitsmodelle nvoo ree nbelangrij kdee lt edanken .Voo rU wwaardevoll eadvie ­ zenal spromoto rtijden she twerke naa ndi tproefschrif tbe ni kU zeererkentelijk . Dr.A.F.H .Besemer ,U wbijzonder egrot ekenni so phe tgebie dva nd ebestrijdingsmiddel ­ eni sva ngrot ewaard e geweestvoo rd esamenstellin gva ndi tproefschrift .I kbe nU al s promotor zeerdankbaa rvoo rd eopbouwend ekritie ke nd estimulerend ediscussie s tijdenshe t doorwerkenva nhe tmanuscript . Mijnbijzonder ewaarderin ggaa tui tnaa rmij ncollega ,dr.ir .M .Leistra .Minze ,d e energiekee nenthousiast ewijz ewaaro pj emi ji nvel efase nva nhe tonderzoe kheb tgehol ­ pen,doo rt eadvisere nbi jd eopze tva nd erekenmodelle ne ni nhe tbijzonde rdoo rhe tkri ­ tischbestudere ne ncorrigere nva nmij nconcepten ,i sva ngrot ebetekeni sgewees tvoo rd e totstandkomingva ndi tproefschrift . Dedirekteu rva nhe tLaboratoriu mvoo r InsekticidenOnderzoek ,dr.ir .A.M .va nDoorn , beni kzee rerkentelij kda thi jmi ji nd egelegenhei dheef tgestel ddi tproefschrif tsame n testellen .Graa gbetui ki kU mij nhartelijk edan kvoo rd eadvieze ntijden she tonderzoek . Eengroo tgedeelt eva nhe twer kwer dmogelij kgemaak tdoo r financiëlebijdrage nva n deCentral eOrganisati eTN Oi nhe tkade rva nd eactiviteite nva nd eContactgroe pWate rva n de Commissievoo rOnderzoe k inzakeNevenwerkinge nva nBestrijdingsmiddele ne nAanverwant e Verbindingen.I kbe nhiervoo r zeererkentelijk . CockJ .Schut ,voo rd eprettig ee nnauwkeurig ewijz ewaaro pj ed evel eanalyse si nhe t laboratoriumheb tuitgevoer dhe bi kvee lwaardering . JohanH . Smeltdan ki kvoo r zijnmedewerkin gbi jdivers eexperimenten .Drs .N.W.H . Houxbe ni kzee rerkentelij kvoo rd ewaardevoll e adviezenbi jd eanalyses . Mijnerkentelijkhei d gaatui tnaa rd ehee rM .d eWitt evoo r zijnbijdrag ebi jd ekeuz e vangeschikt ebemonsteringspunte ni nd eProvinci eUtrecht .Verde rdan ki kd ehere nE.A.J . Zwanenburge nA . Stigtervoo rhe twelwillen d toestaanva nvel eexperimente no phu nbedrijven . Iemedewerker sva nhe tRekencentru mva nd eLandbouwhogeschoo l danki kvoo rhu n advie­ zene nvoo rhe tbiede nva nd emogelijkhei do md ecomputerberekeninge nui tt evoeren . MevrouwHed yWessels-va nBlijenburg hbe ni kzee rerkentelij kvoo rd esnell ee nzorg ­ vuldigewijz ewaaro p zijd edivers econcepte ne nhe tuiteindelijk emanuscrip theef tgetypt . De redacteurenva nhe tPudo ct eWageningen ,J.C .Rig ge nJ .Castelei ndan ki kvoo rhu n redactionelebijdrag eaa ndi tproefschrift .D ehee rM .Janse ndan ki kvoo rzij nverdienste ­ lijktekenwerk . Milly,i kwi loo kvoora ljo ubedanke nvoo rd esteu ne nmotivati edi ei kva nj ekree g tijdensd evel eure ndi ei kthui sbestee dhe b aanmij nproefschrift . Contents

List of symbols and units

Occurrence and origin of pesticides and herbicides in the aquatic environment 1.1 Chlorinatedhydrocarbo npesticide san drelate dcompound s 1.2 Cholinesterase inhibitors

1.3 Herbicides 5 1.4 Directapplicatio no fpesticide st osurfac ewater s 7 1.5 Origino funintentiona lcontaminatio no fsurfac ewate rwit h pesticides

10 2 Introduction to the present research program 10 2.1 Agriculturalemissio no fpesticide st osurfac ewate r 11 2.2 Lay-outo fth epresen tresearc hprogra m

13 3 Review of the use and properties of azinphos-methyl and dimethaate 13 3.1 Applicationo fazinphos-methy l anddimethoat ei nfrui t farming 14 3.2 Physico-chemicalpropertie so fth ecompound s 14 3.3 Conversionrate san dpathway so fth ecompound s 18 3.4 Adsorptionan dleachin go fth ecompound si nsoi l 19 3.5 Volatilizationo fth ecompound sfro mwate rbodie s 21 3.6 Sometoxicologica ldat ao fth ecompound s

23 4 Sampling of water and bottom material in ditches for analysis of pesticide residues 23 4.1 Shortrevie wo fdevice san dprocedure s forwate r sampling 24 4.2 Watersamplin gi nth epresen tstud y 25 4.3 Shortrevie wo fdevice san dprocedure sfo rsamplin gbotto mmateria l 26 4.4 Samplingo fbotto mmateria li nth epresen t study

5 Procedures for chemical analysis for azinphos-methyl and dimethoate in surface 28 water and bottom material 28 5.1 Introduction 28 5.2 Methods forextractio no fpesticide s fromsurfac ewater s 29 5.3 Extractiono fazinphos-methy l fromwate r samples 30 5.4 Extractiono fdimethoat e fromwate rsample s 30 5.5 Methods forextractio no fpesticide s frombotto mmateria l 31 5.6 Extractiono fazinphos-methy l frombotto m samples 31 5.7 Extractiono fdimethoat e frombotto msample s 31 5.8 Methodsfo rclean-u po fextract s 32 5.9 Clean-upfo razinphos-methy lextract s fromwate r 5.10 Clean-upfo rdimethoat eextract s fromwate r 32 5.11 Clean-upfo razinphos-methy lextract s frombotto mmateria l 32 5.12 Clean-upfo rdimethoat e extracts frombotto mmateria l 33 5.13 Concentrationmeasurement sb ygas—liqui d chromatography 33 5.14 Measuremento fazinphos-methy l 33 5.15 Measuremento fdimethoat e 35

6 Conversion rate and adsorption of azinphos-methyl and dimethoate in aquatic systems 36 6.1 Introduction 36 6.2 Conversionrat eo fazinphos-methy li naqueou s solutionskep ti ndarknes s 36 6.3 Conversionrat eo fdimethoat ei naqueou s solutionskep ti ndarknes s 43 6.4 Conversionrat eo fazinphos-methy li nsystem so fbotto mmateria lan d surfacewate r 46 6.5 Conversionrat eo fdimethoat ei nsystem so fbotto mmateria lan d surfacewate r 49 6.6 Adsorptiono fazinphos-methy lo nbotto mmaterial s 51 6.7 Adsorptiono fdimethoat eo nbotto mmaterial s 54 6.8 Generaldiscussio n 55

7 Measurements in outdoor tanks: decline in water and penetration into bottom material 57 7.1 Introduction 57 7.2 Designo fth eoutdoo r tanktrial s 57 7.3 Measuredrate so fdeclin ei nwate r 63 7.4 Measuredpenetratio n intobotto mmateria l 68 7.5 Generaldiscussio no noutdoo r tank trials 70

8 Computation model on the behaviour of pesticides in a tank of water with a bottom layer 72 8.1 Introduction 72 8.2 Derivationo fth eequation s 72 8.3 Designo fth ecomputation s 74 8.4 Resultso fth esimulation so ftan ktrial s 75 8.5 Designo fth esimulatio nexperiment s 79 8.6 Resultso fth esimulatio nexperiment s 80 8.7 Generaldiscussio n 83

9 Measurements of azinphos-methyl and dimethoate in watercourses and farm ditches in the Kromme Rhine area and in the Lopikerwaard Polder 84 9.1 Introduction 84 9.2 Monitoringo fazinphos-methy lan ddimethoat ei nwatercourse san di n ditcheso nfrui tfarm sdurin g 1975 84 9.2.1 Descriptiono fsamplin gpoint san dprocedure s 84 9.2.2 Resultsan ddiscussio n 86 9.2.3 Preliminaryconclusion s 88 9.3 Field trialso nth efat eo fazinphos-methy lan ddimethoat ei nditche s afterspra ydrif t °9 9.3.1 Introduction 89 9.3.2 Datao nth etria l fieldsi nth eLopikerwaar dPolde r 89 9.3.3 Measurementan dapproximatio no fth eitem so fth ewate rbalanc e 91 9.3.4 Surfacean dgroundwate rqualit y 96 9.3.5 Characterizationo fditc hbottom s 96 9.3.6 Sprayingdate san dprocedure si n197 6 101 9.3.7 Concentrationso fth einsecticide si nditc hwate r 102 9.3.8 Directmeasuremen to fspra ydrif tint oditche s 106 9.3.9 Estimateo frat ecoefficient sfo rdeclin e 109 9.3.10 Concentrationso fth einsecticide si nsurfac ewate rnea rBenscho pan d Jaarsveldi n197 6 110 9.3.11 Preliminarymeasurement so fconcentration si ngroundwate r 111 9.3.12 Penetrationo fazinphos-methy l intobotto mmateria l 112 9.3.13 Generaldiscussio nan dconclusion s 115

10 Computations on the behaviour of pesticides in a ditch compartment 116 10.1 Introduction 116 10.2 Ditchgeometr yan dderivatio no fequation s 116 10.3 Designo fth ecomputation s andvalue so fparameter s 120 10.4 Computedresult sfo rth efiel dtrial s 123 10.5 Designo fth esimulatio nexperiment s 132 10.6 Resultso fth esimulatio nexperiment s 132 10.7 Generaldiscussio n 136

11 Measurements and computations on the behaviour of substances in ditches with flowing water 137 11.1 Introduction 137 11.2 Derivationo fequation s forone-dimensiona l convectionan ddispersio no f substancesi nflowin gwate r 138 11.3 Dispersionmeasurement swit hdye s 140 11.4 Computationmode lfo rth ebehaviou ro fsubstance si nditche swit h flowingwate r 143 11.4.1 Derivationo fth eequation s 143 11.4.2 Lay-outo fth ecomputation san dvalue so fparameter s 144 11.4.3 Resultso fsimulation sfo rth etrace rexperiment s 146 11.4.4 Designo fth esimulatio nexperiment swit hpesticide s 148 11.4.5 Resultso fsimulatio nexperiment swit hpesticide s 148 11.5 Generaldiscussio n 149

Summary ir-i Samenvatting •>r g

Appendices 1fi1

References 171 List of symbols and units

a =dispersio nconstan t (Equation40 ) (1) A =averag ewette d cross-sectional areao fditc h (m2) 2 Ub)z_Q =surfac eare ao ffirs tbotto mcompartmen ta tsediment—wate r (m ) interface

bl =widt ha tbotto mo fditch ;widt ho fcompartmen t1 (m) 3 oa =mas sconcentratio no fsubstanc e infre eai r (mg m " ) 3 cb =mas sconcentratio no fsubstanc e inbotto mmaterial :mas so f (mg m"" ) substancedivide db yvolum eo fbotto mmateria l

C£ =equilibriu mmas s concentrationo fsubstanc e at gas—liquid (mg m' 3 • ) interface:mas so fsubstanc edivide db yvolume.o fai r 3 C£w =equilibriu mmas sconcentratio no fsubstanc e atgas—liqui d (mg m" • ) interface:mas so fsubstanc edivide db yvolum eo fwate r 3 clb =mas s concentration ofsubstanc e inliqui dphas eo fbotto m (mg m" ) material:mas so fsubstanc edivide db yvolum eo f liquidphas e J 3 ow =mas s concentrationo fsubstanc e inwate r orwate rcompartmen t (mgm ) (mg m" ) a.,. • =mas sconcentratio no fsubstanc ei nintak ewate r (mg m" 3) = 1 1mSiSS °wma x roa^i- ™ concentrationa ta samplin gpoin t (mg ra 3) 7 3 ew =mas sconcentratio no fsubstanc e inupstrea mditc hsectio n (mg m ) d2 =dept ho fuppe rsurfac eo fsecon dbotto m compartment (m) ß = difl b diffusioncoefficien to fsubstanc e inliqui dphas eo fbotto m (m2 d" 1) material (interm so fvolum eo fliqui dphas ean ddept hi n bottom material) D = dif w diffusioncoefficien to fsubstanc e inwate r (m2 d" C-L =longitudina l dispersion coefficient (m2 d" 1) fI =labyrint ho rtortuosit y factor:rati oo fsurfac eare ao f CD bottommateria l toliqui dphas e Fsw d =flo wrat eo fsubstanc eint odownstrea mditc hsectio ndurin g (mg d" b intakeperio d 1 Fs w£ =flo wrat eo fsubstanc eint owate r compartmentdurin g intake (mg d" ) period F =flo wrat eo fsubstanc eou to fwate rcompartmen tdurin g (mg d" 1) pumpingperio d F =flo wrat eo fsubstanc eint owate r compartment fromupstrea m (mg d' b ditchsectio ndurin gpumpin gperio d 2 -1, fv =arei cmas sflu xacros sgas—liqui d interfaceb yvolatiliza ­ (mg ra d tion a =acceleratio ndu e togravit y (m d-2 ) Henry'sconstan t (Equation5 ) CD heighto fgroundwate rleve labov editc hbotto m (m) heighto fwate rleve labov editc hbotto m (m) averagewate rdept h (m) indexnumbe ro fbotto mcompartmen t CD areicmas sflu xb yconvectio nint obotto mmaterial: ;mas s (mgm d conv,lb fluxdivide db yare ao fbotto mmateria l; areicmas sflu xb yconvectio ni nwater :mas sflu xdivide db y (mgm d conv.w wettedcross-sectiona lare ao fditc h areicmas sflu xb ydiffusio ni nbotto mmaterial :mas sflu x (mgm d Jdif,lb dividedb yare ao fbotto mmateria l "2 j- areicmas sflu xb ydiffusio ni nwater :mas sflu xdivide db y m d dif, w wettedcross-sectiona lare ao fditc h areicmas sflu xb yconvectiv edispersio nint obottjo mmate ­ (mgm " disp.lb rial:mas sflu xdivide db yare ao fbotto mmateria l areicmas sflu xb yconvectiv edispersio ni nwater : (mgm " disp.w massflu xdivide db ywette dcross-sectiona lare ao fditc h

J totalarei cmas sflu xint obotto mmaterial :mas s fluxdivide d (mgm d s,lIKb byare ao fbotto mmateria l totalarei cmas sflu xi nwater :mas sflu xdivide db ywette d (mgm d J s,w cross-sectionalare ao fditc h k dispersionconstan t (Equation41 ) CD ratecoefficien tfo rconversio no fsubstanc ei nbotto m 1 c,b Cd" ) material ratecoefficien tfo rconversio no fsubstanc ei nwate r 1 k c,w Cd" ) exchangecoefficien tfo rga sphas e Cmd" 1) exchangecoefficien tfo rliqui dphas e (md _1) Manningscoefficien tfo rbotto mroughnes s (m1'3d' 1) first-orderrat ecoefficien tfo rdeclin e Cd"1) 3 -1 s/l distributionquotien tsolid/liqui dphas e= adsorptio n Cm kg ) coefficient(i nterm so fvolum eo fliqui dphas ean dmas s ofsoli dphase )

1 t,l overallliqui dphas etransfe rcoefficien t Cmd" ) lengtho fditc hcompartmen t Cm) ;dispersio ndistanc e Cm) :initia linjecte dmas so fsubstanc e m Cmg) ;firs tmomen t (Equation51 ) M, (d) :mas so fslic eo fwe tbotto mmateria l Ckg) =mas so fslic eo fdr ybotto mmateria l Ckg) s multiplicatio nfacto rfo rdownwar dincreas ei nthicknes s CD ofbotto mcompartment s

=measure dmas so fpesticid ei nwate rcompartmen tbefor e (mg) Sampling n •-mas so fpesticid ei nwate r compartmentcorrecte dfo r Cmg) volumeo fsample swithdraw n =arei crati o ofcontaminatio n ofwater :rati o ofmas s (1) r,A ofsubstanc e introduced intowate r dividedb y areao fwate r tomas s ofsubstanc e applied to landdivide db y land area =integer ,Samplin g No (intim e series) (1) =wette dperimete r ofditc h (m) =rat eo f flowthroug hwette dperimete r ofditc h (m3 d" ') =rat eo fdischarg e fromwate r compartment (m3 d~ ) =rat eo fdischarg e fromupstrea mditc h section (m3 d" Hà,M ) 3 (interm so fvolum eo fwate ran d areao fbotto mmaterial ) (m3) •volum e ofwate r sample (intim e series) : 3 Vw volum eo fwate r compartment (m ) ; 3 -1 dV w/d * chang ei nstorag eo fwate r compartment (m d ) •downstrea mdistanc e alongditc h axis (m) 2 depth inbotto m (m) a arctg L 0) arctg/(1/s.|) drainage resistance (kg m" d-') volume fractiono f liquid:volum e ofliqui dphas e divided CD byvolum eo fbotto mmateria l (dry)bul kdensit y ofbotto mmaterial :mas so f solidphas e (kg m-3) dividedb yvolum eo fbotto mmateria l p =densit yo fsoli dphas eo fbotto mmaterial :mas so fsoli d (kgm ) phasedivide db yvolum eo fsoli dphas e _3 p =densit yo fwate r (kgm ) w -1 -2 xn =shea rstres sa tditc hwall s (kgm d ) 1 Occurrence and origin of pesticides and herbicides in the aquatic environment

Theproble mo fth eoccurrenc eo fpesticide san dherbicide si nsurfac ewate rha ss o many aspects thata researc hprogra mi nthi s fieldmus tneed sb erestricte dt opar to fit . Tose tth epresen t researchprogra mi ncontex tan dt oallo wa bette r evaluationo fth e results,Chapte r1 give sa genera lsketc ho fth eproble m spherebefor eth eresearc hap ­ proachi sdescribe di nChapte r 2.Fo rth e descriptiono fconcentration s thatca noccu ri n surfacewate r (mainlyi nth elarge rwatercourses) ,th eresult so fextensiv e monitoring research couldb eused .Onl ya fe wdat ahav ebee npublishe do nth esiz eo fth esourc e ofspecifie d contamination. Insevera l cases,a nemissio nt osurfac ewate r couldwel l occur,howeve r littlei sknow nabou tth esiz eo fth esource . Somepossibl e sourceso f pesticides andherbicide si nsurfac ewater sar ediscusse di nSectio n1.5 .

1.1 CHLORINATEDHYDROCARBO NPESTICIDE SAN DRELATE DCOMPOUND S

Monitoringo fsurfac ewater san dbotto m sediments startedi nth eUnite d States aboutte nyear s afterth eintroductio no fth eorganochlorin e insecticides.I tsoo nbecam e evidenttha tsmal lamount so fthes e insecticideswer epresen ti nman y surfacewaters . Sincethen ,extensiv e surveyshav ebee nmad ei nsevera l countries.Mos tattentio nwa s paidt oth echlorinate d hydrocarbons,sinc e thesewer ewidel y usedan dcoul db erathe r easilymeasure dwit h gaschromatograph sequippe dwit ha nelectron-captur e detector.Sever ­ alchlorinate d hydrocarbonsar eonl y slowly degradedi nwater .Review so forganochlorin e residuesi nwate rwer e given,fo rinstance ,b yWestlak e& Günthe r (1966),Nicholso n (1969) andEdward s (1973).Thei rsummarize d datasho w thatth eresidu e levels inwate rar e rel­ atively low,rangin gfro ma fe wmicrogram st oa fe wmilligram spe rcubi cmetre ,excep t nearpoin t sources likedischarg eo findustria l effluent,direc t applicationo raccidaita l contamination. Chlorinatedhydrocarbon s were detectedi nwate r samplesi nman y European countries (Grève,1972 ;Herzel ,1972 ;Lowde ne tal. , 1969;Sörensen , 1973).Thes emeasurement s show that lindane,havin gth ehighes twate r solubilityo fth egenera lchlorinate d hydrocarbon insecticides (Kinge tal. , 1969),wa smos tcommonl y foundi nEurope . Most chlorinated hydrocarbons showa lo wsolubilit yi npur ewate ran dthe yma yb e readily adsorbedt ohumi csubstances ,organo-cla ycomplexe san dothe rparticulat e matter insuspension .I nlaborator y experiments,th ereleas eo fthes ecompound s from sediments intowate rwa s foundt ob eslo w (Choi& Chen , 1976). Chlorinatedhydrocarbo n residuesma y longpersis ti nth ebotto mmaterial .Fo rinstance ,Dimon de tal . (1971)showe dtha tth e average contento fDD Tan dit smetabolite si ndr ymu dfro mth ebotto mo fsmal l streams decreased from 1.08m gk g ,on eyea rafte ra singl e applicationt o0.5 9m gk g after fiveyears .Afte rte nyears ,th econten tha ddecline dt o0.0 7m gk g .Th ebotto m sediment mayb estirre du pb ystron gcurrent san dth etranspor to fDD Ti nwate rma ythu soccu r whilestil l largelyadsorbe do nsuspende dmateria l (Nicholson, 1969). Sincesom eorganochlorin einsecticide sar e knownt ob epersisten tan dten dt oaccumu ­ latei norganisms ,especiall yi nadipos etissu eo fanimals ,thei rus eha sbee n restricted orbanne di nsevera lcountries .I nth eNetherlands ,th elas tapplication so fDD Twer eban ­ nedo n1 Jul y 1973.

Monitoring of chlorinated hydrocarbons in Dutch surface waters

Thefirs tmonitorin gi nth eNetherland sdate sbac kt o196 7an dsinc eMa y 1969,wate r hasbee nsample da tman ypoints .Thes esamplin gpoint swer edistribute dove rth eRive r Rhinewit hit stributaries ,intake sfo rdrinkin gwate r suppliesan dlarg e agricultural areas (Grève, 1971). Grève (1972)an dMeijer s (1973)foun dtha ta-hexachlorocyclohexan e (a-HCH), lindane (y-HCH)an dhexachlorobenzen e (HCB)wer enearl yalway spresen ti nRhin ewater .Th einsec ­ ticideendosulfa nha dbee nfoun di ntha trive ri nsevera lwave sdurin gth eyear s 1969an d 1970,bu twa srarel yfoun dafte rJul y 1970.Othe rorganochlorin epesticide san dthei r conversionproduct s (heptachlor,it sepoxide ,aldrin ,dieldrin ,endri nan dDD Tplu s related compounds)wer eoccasionall ydetecte di nrathe rlo wconcentrations .Th eaverag econ ­ centrationove rth eperio d1 Septembe r 1969t o1 Apri l 1972,amounte dt o0.1 5m gn f for a-hexachlorocyclohexane,0.1 0m gm forlindan ean d0.1 3m gm forhexachlorobenzen e (Grève, 1972).Th e concentrationso fth eby-produc ta-hexachlorocyclohexan e were thus found tob ehighe rtha nthos eo fth epesticid elindan eitself .I nvie wo fth elimite dus eo fpesti ­ cidescontainin ga-hexachlorocyclohexan ei nagricultur ealon gth eRhine ,industr yha sprob ­ ablybee nth emai nsourc eo fpollution .Th ehig hconcentration so fhexachlorobenzen e could notb eexplaine db yth elimite dus eo fthi scompoun da sa nagricultura l fungicideo rb yit s presencea sa nimpurit yi na fungicid elik equintozene .Hexachlorobenzen ei sa nintermedi ­ atecompoun do ffrequen toccurrenc ei nindustria l syntheses.Thi scompoun di sals ouse da s a flameretardant . Since 1972,al lmonitorin gdat ameasure dfo rth elarge rDutc hwaterway s administered bynationa lauthoritie shav ebee ntabulate di nth equarterl y surveyso fRijkswaterstaa t (1973-1978).Thes enewe rdat a (Table 1)sho wtha tth econcentration so fa-HC Han do flin ­ danedecrease dconsiderably .A sther ewa sn osystemati c trendi nth e dischargeo fth eriv ­ er,whic haverage d 1890m 3s" 1 overthi sS yea rperiod ,th edischarg eo fth elatte rtw o chlorinatedhydrocarbon smus thav eactuall ydecreased .

1.2 CHOLINESTERASE INHIBITORS

Themonitorin gprogra mstarte di nth eNetherland si n196 7an dals oinclude dth e measuremento fCholinesteras einhibitor s (mainlyorganophosphoru san dcarbamat epesticides ) insurfac ewaters .Grèv ee tal . (1972)showe d thatrathe rhig hconcentration so fCholin ­ esteraseinhibitor swer epresen ti nth eRhin ean dit sdistributaries .The yanalyse d some watersample sfro mthi srive rsyste mi nmor edetail .Fiv einsecticide swer edetecte db y thin-layerchromatograph y (TLC)an dgas-liqui d chromatography (GLC),whil e theirpresenc e Table 1. Average mass concentrations of a few chlorinated hydrocarbons inRhin e water sampled near Lobith, the Netherlands. (After Rijkswaterstaat, 1973-1978).

Compound Quarter Mass concentrations (mg m"3) in different years

1973 1974 1975 1976 1977

Hexachlorobenzene 1st 0.18 0.11 0.04 0.10 0.07 (HCB) 2nd 0.11 0.12 0.07 0.12 0.07 3rd 0.08 0.17 0.08 0.16 0.14 4t h 0.09 0.06 0.10 0.13 0.04 a-Hexachlorocyclohexane 1st 0.28 0.25 0.06 0.04 0.02 (a-HCH) 2nd 0.13 0.35 0.10 0.06 0.02 3rd 0.15 0.21 0.05 0.06 0.03 4t h 0.22 0.04 0.04 0.04 0.01 Lindane 1st 0.26 0.13 0.04 0.03 0.02 (Y-HCH) 2nd 0.10 0.17 0.05 0.04 0.03 3rd 0.09 0.13 0.03 0.03 0.03 4t h 0.14 0.02 0.03 0.02 0.04 was confirmedwit ha mas s spectrometer (MS) (Table 2).Th epresenc eo fCholinesteras e inhibitorsi nsurfac ewate ri sunfavourable ,becaus e Cholinesterase activityi sintimatel y relatedt olif ei nth eaquati cenvironment . Littlei sknow nabou tth esignificanc eo fsub - -lethal concentrationsfo raquati corganisms . The average concentrationo fCholinesteras e inhibitors,expresse di nparaoxo n equivalent,measure d during 1970,197 1an d197 2wa sbelo w1 m gm (Grèvee tal. , 1972). However,th econcentration s inth eRhin enea r Lobith increased fromth efirs t quartero f 1973onwards .Occasionall yth econcentration s were fairlyhig hi n1976 ,whic h couldno t be explainedb yth erelativel ylo wdischarg eo fwate ri nth e Rhinei ntha tyea r (Table3 ; Figure1) . In 1976,a nimportan t industrial effluent sourcewa s tracedb yth eInstitu tfü r Wasser,Boden -un dLufthygien ede s Bundesgesundheitsamtes (BGA)i nth eRive rMain .Afte r thecomplaint so fth eBG Aan dth e National Instituteo fPubli c Healthi nth e Netherlands, theconcentratio no fparaoxo n equivalentnea r this sourcediminishe dwithi na fe wweek s froma maximu mo f300 0m gm toabou t1 0m gm (Fritschie tal. , 1978). Inothe rsurfac ewater si nth eNetherlands ,th eleve lo fCholinesteras e inhibitors was foundt ob esubstantiall y lowertha ntha ti nth e RiverRhine ,eve nbelo w thedetectio n limito f0.0 5m gm (Wegman& Grève , 1978). Inothe r countries too,smal l amountso forganophosphoru s pesticideswer e foundi n

Table 2.Mas s concentration of a few Cholinesterase inhibitors in Rhine water. (After Grève et al., 1972). _ ____ Cholinesterase Mass concentration (mg m ) inhibitor November 1971 January 1972

Dimethoate 0.07 0.08 Malathion 0.01 0.01 Diazinon 0.02 0.05 Parathion 0.03 0.07 Carbaryl 0.40 0.20 Table3 .Averag emas sconcentratio no fCholinesteras einhibitor si n Rhinewate rsample dnea rLobith .Concentration sexpresse d inm g paraoxonequivalen tpe rm 3water .(Afte rRijkswaterstaat ,1973-1978) .

Quarter Mass concentration (mgm ) in different years

1973 1974 1975 1976 1977

1st 5.73 •0.92 4.5 31.0 5.9 2nd 1.52 0.95 2.9 21.0 5.4 3rd 2.42 2.74 10.1 2.2 3.8 4t h 3.27 1.64 12.1 3.8 1.9 Annual avei age 3.24 1.56 7.4 14.5 4.3

surfacewater .Fo rexampl ei nBritis hrivers ,Lowde ne tal . (1969)foun dcarbophenothio n 0.01-1,diazino n0.01-0.03 ,demeto no rdemeton- S0.01 ,malathio n0.0 1 andphorat e0.0 1 -3 mgm .InWes tGermany ,Sörense n(1973 )foun dsevera lorganophosphoru spesticide si nsur ­ facewaters ,wit ha stron gvariatio ni nconcentratio ndependen to nth esamplin gpoints . Hisresult sar erepresente di nTabl e4 .I nth eRive rMain ,dimethoat ewa sregularl ypres ­ enti nconcentration sbetwee n1 an d1 0m gm ~ (Kussmaul,1978) . Extensivereport so nCholinesteras einhibitor si nsurfac ewater si nItal ywer egive n byDe lVecchi oe tal . (1970),wh omeasure dchlorpyriphos ,diazinon ,fenchlorphos ,mala - thion,methy l-par athio nan dparathio ni na rang efro mles stha n0.0 1 mgm toabou t 0.70m gnf 3.

1.3 HERBICIDES

Monitoringstudie si nvariou sarea so fth eUnite dState sshowe dtha tunintentiona l presenceo fherbicide si nnatura lwater swa sinfrequen tan da tlo wlevel s (Frank,1972) . Duringextensiv emonitorin go fstream si nth ewester nUnite dStates ,concentration so f

concentration ( mg m ) 50

19691 1970 I 1971 I 1972 I 1973 I 1974 I 1975—I' 1976 I Figure 1.Cholinesteras einhibitor si nRhin ewate r (Lobith)i nm gparaoxo n equivalentpe rm3 .(Afte r Fritschie tal. , 1978). Table4 .Organophosphoru spesticide s insurfac ewate r inWes tGermany . (AfterSörensen , 1973).N.A .= no tanalysed ;- = $ 0.0 1 mgm ~. . . -^ Samplingpoin t Mass concentration (mgm )

bromophos dimethoate disulfoton parathion methyl- sulfotepp parathion

Rhinenea r Ingelheim 0.15 N.A. - 0.12 Wuppernea r Friedenstal - - 113 23.5 0.45 18.8 Wuppernea r Leverkussen - - 2.0 0.12 1.08 Rhinenea r Leverkusen- -Hitdorf - N.A. 2.0 - - 1.95 Rhinenea r Diisseldorf- -Benrath - 10.8 0.1

2,4-Dwer eusuall yles stha n1 m gm .In thosestreams ,lo wresidue so f2,4,5- Twer e foundto o(Schulz ee tal. , 1973).Fo rsevera lyears ,atrazin eha sbee nuse do na larg e scalefo rwee d control inth eCor nBel ti nth eUnite dStates .Thi scompoun dwit ha solu ­ bilityi nwate ro f3 3g m ismos tfrequentl ydetecte d inth erecen tmonitorin gstudies . Richarde tal . (1975)foun dtha tth eatrazin econcentration si nrun-off ,i ndrainag e ditches,an di na fe wriver si nIow awer emor etha n1 m gm afe wday safte rintensiv e rainfall. Waldron (1974)investigate dth econtributio no fagricultural ,municipal ,residentia l andindustria lactivitie st opesticid epollutio no fLak eEri ei n1971-1972 .Durin gthi s study,residue so fseve norganochlorin einsecticides ,thre etriazin eherbicides ,thre e chlorophenoxyaci dherbicide san d fiveorganophosphoru s insecticideswer emonitored .Thes e analyseso frive rwate ran dbotto mmu dindicate donl ysporadi coccurrenc eo fminut econ ­ centrations.H efoun datrazin et ob eth emos tfrequentl ydetectabl eherbicide .I nte nsam ­ pleso frive rwate rwit hpea kresidu elevels ,th econcentration srange dfro m3 t o7 0m gm . Sometimessimazin ewa sdetected . Littleinformatio ni savailabl eabou tunintentiona loccurrenc eo fherbicide s inDutc h surfacewaters .Th eapplicatio no fherbicide sfo raquati cwee d controli nth eNetherland s willb ebriefl ydiscusse d inSectio n1.4 .

1.4 DIRECTAPPLICATIO NO FPESTICIDE ST OSURFAC EWATER S

Probablyth egreates tdirec tsourc eo fpesticide s inwate rha sbee nth eten so f thousandso fton so fDD Ttha twer eapplie dannuall yt osurfac ewate r (Westlake& Günther , 1966)an destuarin esal tmarshe sove rtw odecade st ocontro lmosquitoe s (Butler,1969) . Sometimespesticide swer euse di nprogram st oeradicat etras hfish .Fo rexample , camphechlor (Toxaphene)wa suse dt oeliminat eundesire d fishspecie si nman yfresh-wate r fishinglake si nth eUnite d States (Veith& Lee ,1971) . Arecen texampl eo fpesticid eapplicatio ni nsurfac ewate ri sth eus eo ftemefo s (Abate)a slarvicid eagains t Simulium insom earea so fAfrica ,an dSout han dCentra l America.Certai nspecie so fSimuliida ear evector so fa nimportan tfilaria ldiseas eo fman , onchocerciasis.DD Twa sformerl yuse da sa larvicid eagains t Simulium. Inrecen tyears , temefosha sbee nrecommende db yth eWorl dHealt hOrganizatio na sa comparativel ysaf eal ­ ternativet oth echlorinate dhydrocarbon s (Dalee tal. , 1975).Anothe rexampl ei sth eprom ­ isingmolluscicid etrifenmorp h (Frescon)applie di nwarm ,slowl ymoving ,wate rfo rth e controlo fsnails ,whic har eintermediat ehost so ftrematode scausin gschistosomiasi s (bilharziasis)i nma n (Osgerby,1970) . Inth eNetherlands ,n opesticid ei sapplie di ntha twa yt osurfac ewater .

Application of herbicides

Onlya fe wherbicide sar eapprove di nth eNetherland sfo rth econtro lo faquati c weedsunde rspecia lcondition s (PlantenziektenkundigeDienst ,1978) . Inthi ssection ,a shortdescriptio n isgive no fth esituatio ni n1978 .A fe wcharacteristic so fth ephysico - -chemicalbehaviou ro fthes eherbicide si nwatercourse sar eindicate dan dsom eremark sar e madeabou tpossibl eside-effects .

Dalapon

Thisherbicid ei suse do na rathe rlarg escal eagains tgrass yweed slik eree d (Phragmites communis) andfloa tgras so rree d sweetgrass {Glycevia maxima) inwatercourses . Applicationsar eonl ypermitte dafte r1 5July .Dalapo n (salt)i shighl ysolubl ei nwater : >80 0k gm at2 5 C.I tdecompose squickly .Th emajo rdegradatio nproduc to fdalapo ni s pyruvicacid ,whic hi subiquitou si norganisms .N osignifican tenvironmenta lproblem shav e beenobserve dove rman yyear so fwide-scal eus e (Kenaga,1974) .

Paraquatan ddiqua t

Theseherbicide sar euse dfo raquati cwee dcontro lo na fairl ylarg escale ,particu ­ larlyparaquat .The ysho whig hactivit yagains tsubmerge dweed slik ewate rthym eo r Canadianpondwee d (Elodea canadensis) andpondwee d {Potamogeton species). Applicationi s onlyallowe dafte r1 June .Th eperio dwit hdistinc therbicida lactivit y iscomparativel y short:usuall ya fe wday so rless .Thes ecompound sar estrongl yadsorbe dont osuspende d particulatematte ran dbotto mmaterial ,an dthe yar erapidl ytake nu pb yaquati cplant s andalga e (Simsiman& Diesters ,1976) .Ther ema yb esom ephotochemica ldegradation ,depen ­ dento nfactor slik etim eo fapplication ,sola rradiatio nan dexposur eo fth ewate rt oso ­ larradiation .Fran k& Come s (1967)showe dtha tparaqua tan ddiqua tadsorbe d tobotto mmud s ofponds ,persiste di nhig hconcentration sfo rmor etha n8 5an d 160days ,respectively .

Side-effectsan dalternative s

Thecontac therbicida lactivit yo fa compoun dlik eparaqua tcause srapi ddeat ho f submerged aquaticvegetation ,resultin gi nchange si nth ephysical ,chemica lan dbiologica l natureo fa treate d stretcho fwater .Th eremova lo fcompetitio nb ycertai nweed sma y resulti nabundan t growtho falga esom etim eafte r treatment.Th ebreakdow nb ymicro - -organismso frapidl ydyin gplan tmateria lrequire sa lo to foxygen ,whic hma y decrease theconcentratio no fdissolve d oxygent over ylo wlevel s (Brooker& Edwards , 1975). Such changesi nlivin g conditionsma yals o indirectly reducepopulation so faquati canimals . Invie wo fth eside-effect so fherbicide si nsurfac ewater , improvementst omechanica l ditchcleanin gha sbee n studied.I nrecen tyears , thepracticalit yo fsom ebiologica lmeth ­ odso faquati cwee d controlha sbee n investigated (vanZon , 1974). Forth econtro lo fundesire dplan t growtho ftemporaril ydr yditc hbottoms ,othe r herbicides like diuron,dichlobeni lan dsimazin ear eapproved ,a slon ga sn owate r flow throughthes editche si st ob eexpecte d during thenex ttw o months (Plantenziektenkundige Dienst, 1978).A nimportan tquestio nwit h these applications ist owha t extent thesecom ­ poundsma yb erelease d intowate ran dtransporte dwhe nwate r startst oflo wthroug hth e ditchagain .

1.5 ORIGINO FUNINTENTIONA LCONTAMINATIO NO FSURFAC EWATE RWIT HPESTICIDE S

Industrial, domestic and agricultural waste

Point sourceso fcontaminatio no fsurfac ewate rwit hpesticide s outside agriculture mayb eth e dischargeo findustria lo rdomesti cwast ewate ran dsewag eplan teffluents . Thewast e frompesticid e factoriesma yb ehighl y contaminated.A wel lknow n incident wasth egenera ldeat ho ffis hi nth e Rhinei nJun e 1969cause db ylarg e amountso fendo - sulfan (Grève& Wit , 1971). Recentlya majo r industrial discharge,highl y contaminated with Cholinesterase inhibitors,wa strace di nth eRive rMai nb yFritsch ie tal . (1978) (Section 1.2). Inth eundilute d effluento fa factor yfo rorganophosphoru san dcarbamat e pesticides inKansa s City,Coppag e& Braidec h (1976)foun dconcentration sa shig ha s200 0t o400 0m gm fordisulfoton ,fensulfothion ,azinphos-methy l andpropoxur .The y reported that about 3.2k go fazinphos-methy l enteredth erive r eachda y(correspondin g witha concentratio n ofabou t0.1 6m gm atlo wrive r flows). Some industriesus einsecticide si nthei rprocesses .Lowde ne tal . (1969)showed , forexample ,tha tth eeffluen t frommot hproofin g inwoo lan dcarpe t factories contained lindane 0.14,dieldri n1. 8an dDD T0. 8m gm ". Agricultural 'point sourceso fcontamination ' canb e accidental spill from equipment, cleaningo fequipment ,carelessnes si nhandling , transportan ddisposa lo fempt ycontain ­ ers, andinadverten t disposalo fremainin g spray liquido rdippin gbaths .

Surface run-off from agricultural land

Oneo fth etw oprincipa l sourceso fsurfac ewate r contaminationb ypesticide s inth e UnitedState si sprobabl y run-offfro magricultura l land (Nicholson, 1969;Bail ye tal. , 1974). After treatmento fa watershe di nArizon awit hth e herbicidepicloram ,th econcen - trationsi nstrea mwate ra tth eoutle to fth ewatershe dwer emeasure db yDavi s& Ingeb o (1973). Theyfoun dmaximu mconcentration so f350-37 0m gm ", whic hoccurre ddurin gth e firstthre emonth s aftertreatmen tan dwer eassociate dwit hheavy rainfall . Miles& Harri s (1971)showe da correlatio nbetwee nrainfal l ratean dconcentratio n ofDD Tan dmetabolite si ncree kwate rflowin gint oLak eErie . Ina stud yo fdieldri nmovemen t fromsoi lt owate ri ntw owatersheds ,onl y0.07 e»o f theamoun tapplie dt osoi lappeare di nrun-of fwate rwit hth elarges t lossesoccurrin gi n thefirs ttw omonth safte rapplicatio n (Caro& Taylor , 1971).Man yothe rworker s reported seasonalpeak si nresidue s thatcoincide dwit hperiod so fextensiv e agriculturaluse . Thesurfac erun-of ffro magricultura l landi nth efla tarea so fth eNetherland si s likelyt ob eo fmino rimportance .

Control of ditehside vegetation

Whenherbicide sar euse dfo rth econtro lo fditehsid eweeds ,par to fth espra yma y reachth ewater .Jus ta sfo rth econtro lo faquati cweed s (Section 1.4),onl ya fe wher ­ bicidesar eapprove dfo rth econtro lo fditehsid evegetatio ni nth eNetherlands .Applica ­ tionso fparaqua tar eallowe donl yafte r1 June .I npractice ,thes erestrictiv emeasure s willpartl ydiminis hth eus eo fherbicide sfo rcontro lo fditehsid evegetation .Furthe rb y applicationso fdalapo nan dparaquat ,ther ema yb ea ris ko finstabilit yo fth editc h slopeso ra ris ko fdisturbanc eo fth ecompetitiv eequilibriu mbetwee nherb san dgrasses . Atpresent ,mechanica lwee dcontro lo fditehsid evegetatio ni shighl yrecommende d (PlantenziektenkundigeDienst ,1978) .

Leaching of pesticides through the soil

Afterapplicatio no fpesticide st oplant so rt oth esoi l surface,variou sdeclin e processeswil lstar tsuc ha svolatilizatio nan dconversion ,includin gphotochemica lcon ­ version.A fractio no fth eamoun tdeposite do nth eplant sma yreac hth esoi lsurfac ea ta laterstage ,fo r exampleb ywashin gof fb yrain .I ti so finteres tt okno wwha t fraction ofth eamoun treachin gth esoi lsurfac ei sleache d intoth esubsoil .Especiall ypesticide s combiningwea kadsorptio ni nsoi lwit ha lo wdecompositio nrat ear eap tt ob eleache d from therootin gzone .Movemen to fsuc hcompound st oth esubsoi lbecome ssubstantiall y greater whenther ei sn oplan tgrowt ho rwhe nthe yar eapplie di nth eautum n (Leistra, 1975). A Dutchworkin ggrou pi sconcerne dwit h systematicevaluatio no fpesticide san dher ­ bicidesfo rris ko fleachin gt ogroundwater .Substance stha tma ygiv eris et oresidue si n thegroundwate rar eno tpermitte di ngroundwate rprotectio narea saroun dpumpin g stations fordomesti csupply . Duringmovemen tthroug hsoil ,ther ei susuall yconsiderabl etim eavailabl efo r con­ versiono fth epesticides .O fcourse ,rathe rpersisten tan dmobil econversio nproduct sma y alsob eleached .Concentration sar edecrease db yspreadin gprocesse slik econvectiv e dis­ persionan ddiffusion ,a swel la sb ydecompositio nan duptake . Fewquantitativ eresult sar eavailabl eo ntranspor to fpesticide s throughth esubsoi l tosurfac ewaters .Mos to fth egroundwate rha st omov eove rconsiderabl edistance san d witha rang eof ,generall y long,residenc etime s throughth esubsoi lt otile-drain so r ditches. Basicdat ao nmovement san drate so fconversio ni nsubsoi lar efew .Onl y recently didi tbecom epossibl et oestimat e- b ycomputationa l models- th eamount s thatma yb eex ­ pectedt oleac h fromth eroo t zoneunde rvariou s conditions (Leistra& Dekkers , 1976).

Drift from application by aircraft or by tractor-drawn spraying machines

Applicationsb yaircraf tmainl yoccu ro nlarg e fieldso fth esam e cropi narabl e farm­ ing. Themetho di smainl yuse dfo rfungicides ,fo rexampl eo fth ebenzimidazol egroup , dithiocarbamates,an dorganoti n compounds.T oa lesse rextent ,insecticide sar espraye d fromaircraft ,mos to fthe mbein g organophosphorus compounds sucha sfenitrothion ,dime - thoate,bromofos-ethyl ,thiometo nan dfosalone .Onl y rarely canherbicide sb eapplie di n thisway ,becaus eo fth eris ko fdamag et ocrop so nadjacen t fields.A revie wo fpossibl e pesticide applicationsb yaircraf twa s givenb yth ePlantenziektenkundig e Dienst (1975), withadvantage san ddisadvantage so fthi smethod . Possibleundesirabl e consequenceso f spraydrif tfro mth etarge tfield swer eclearl y shown.Wit h application fromaircraft ,i t ishardl ypossibl et oavoi d contaminationo fth ewatercourse s borderingo nth e treated fields.I ti sthu s advisablet oselec tth ecompound swit hth elowes t toxicityt oaquati c organisms.Dat ao nth ebehaviou ro fpesticide si nsurfac ewate ran dthei rtoxicit yt o aquatic organismsar eessentia li nselectio no fcompound s suitablefo raeria lapplication . Whenapplyin g insecticides,acaricide so rfungicide sb ytractor-draw nsprayer st o high crops like fruit trees,spra y driftma yoccu rove rconsiderabl e distancess oals ot o neighbouringwatercourses . Withcarefu l applicationso fpesticide san dherbicide st oth esoi l surfaceo rt o fieldswit h lowvegetatio n- mainl yb ytractor-draw nsprayin g equipmentwit ha lo wspra y boom- an dals o adequatedrople t size littlespra ywil l driftan dthu s also littleconta ­ minationo fwate rwil loccur .

Relative importance of the various contaminations sources

Inspit eo fth enumerou s studieso nth eoccurrenc ean dorigi no fpesticide si nsur ­ facewaters ,th erelativ e importanceo fth evariou sunintentiona l sourceso fcontaminatio n isdifficul tt oassess .Whe nsample sar ecollecte dnea rknow nsource so fpesticid epollu ­ tion,th elevel s tendt ob ehigh .O nth eothe rhand ,analysi so fsample s collectedi nmo ­ nitoring programs indicatecomparativel ylo wlevel so fcontaminatio n becauseo fth estron g dilution thatoccur s aftera pollutan ti sintroduce d intoa naquati c system. Unintentional introductiono fpesticide s fromagricultur e into surfacewate rstil lre ­ quiresconsiderabl e attention.I nth epresen t study,spray-drif t fromorchard st odrainag e ditcheswa s investigatedi nmor edetail . 2 Introduction to the present research program

2.1 AGRICULTURALEMISSIO NO FPESTICIDE ST OSURFAC EWATE R

Theliteratur edat acollecte di nChapte r1 sho wth epresenc eo fvariou spesticide s insurfac ewaters .Th ereporte dconcentration svar ywidely ,depending ,fo rinstance ,o n thesiz eo fth esource ,th edistanc efro mth esourc ean dth edilution . Oneaspec to fth eresearc hprogra mo fou rlaborator yi sth e contributiono fagricul ­ turet ocontaminatio no fsurfac ewater swit hpesticides .A numbe ro fsituation swit h pos­ sibleemissio no fpesticide sfro magricultur et osurfac ewate rwer edescribe di nChapte r 1. Ifunintentiona l introductiono fpesticide s intosurfac ewate rb eexpected ,variou s questionshav et ob eanswered .Thes equestion sca nb edivide d intothre egroups : 1.Wha tar eth esources ?Wha ti sth eexten to fcontamination ?Wha ti sth efrequenc yo f emission?Ho wca nemission sb eprevente do rreduced ? 2.Wha ti sth ephysico-chemica lbehaviou ro fspecifi cpesticide s afterthe yhav e reached openwater ?Wha twil lb eth eresultin gconcentration-tim e relationshipsi nsurfac ewaters ? 3.Wha t areth econsequence so fthes econcentration sfo raquati corganism san dfo rth e qualityo fth ewate ri nvie wo fth eintende duse ;fo rexampl ea sdrinkin gwate r forma n and animals,a sirrigatio nwate ran da srecreationa lwater ? -Source so fagricultura lcontaminatio no fsurfac ewate rb ypesticide sca nb echaracterize d byinspectio nan db ycarefu lmeasurement si fnecessary .Loca lcircumstance sar eimportant . Contaminationo fsurfac ewil ldepen dheavil yo nth ewa ypesticide sar eapplie dan do nth e caretake nb yth euser . Contaminationsshoul db efirs to fal lb ereduce db yeduction ,an db ymakin g theuser s moreconsciou so fth eproblems .Preventiv eadvisor yactivitie sshoul db edirecte dt oth e peopleworkin gwit hpesticide si nth efield .Thi saspec t lendsitsel fonl yt oa limite d extentfo rphysico-chemica lresearch . Inth epresen tinvestigation ,spra ydrif to fpesticide sfro morchard st odrainag e ditcheswa sinvestigate di nsom edetai lo na fe wfrui tfarm si nth eLopikerwaar d Polder (Chapter9) . -Physico-chemica lbehaviou rwa s themai naspec to fstud yi nsurfac ewater .Attentio nwa s paidt oth eadsorptio no fpesticide so nditc hbotto mmateria lan dt oth epenetratio no f pesticides intoditc hbottoms .Conversio nrate so fpesticide swer estudie di nsurfac ewa ­ terunde rdifferen tcondition san di nbotto mmaterial .Transpor tan dconversio nwer eals o investigatedi nfiel d trials.Computatio nmodel swer edevelope d andused .A mai nobjec t ofth epresen tstud ywa st oobtai na quantitativ edescriptio no fth e concentration-time relationshipsfo rpesticide si nwatercourses . -Th econsequenc efo raquati corganism so fth eexposur et obiologicall yactiv ecompound s ismainl ya toxicologica lproblem .Thi sfiel do fresearc hi srathe rcomple xs otha tspecia l

10 researchprogram sar erequired .I nth epresen t investigation,onl ya shor t compilationo f literature datao nth etoxicit yo ftw omode lpesticide sfo raquati corganism swa smad e (Section 3.6). Otherpotentia lproblem sassociate dwit hpesticid e residuesdepen do nth e local situationan dth especifi cus eo fth ewater .

2.2 LAY-OUTO FTH EPRESEN TRESEARC HPROGRA M

Invie wo fth eman yquestion st ob eanswere d (Section 2.1), this investigationwa s restrictedt oa fe wpesticide san dt oa fe wagricultura l situationsi nwhic h contamination ofsurfac ewate rb ypesticide swa s likely. Atpresent ,aquati cherbicide sar e only appliedo na limite d scalei nth e Netherlands. Somode l pesticideswer e selectedwhic hma yunintentionall y contaminatesurfac ewaters . Sinceth eus eo fchlorinate dhydrocarbo n insecticidesha sbee ndrasticall y reduced,mainl y organophosphorusan dcarbamat e insecticidesar eapplie di nhorticultur ean darabl e farming. Someo fthes e compoundsar erathe r toxict ovariou s aquatic organisms.Althoug hsuc hcom ­ poundsar egenerall y lesspersisten t thanth echlorinate dhydrocarbons ,ther ewa s evidence thatsom eo fthe mma yb erathe rpersisten ti nsurfac ewaters .Condition si naquati cmedi a ares odifferen t from thosei nplants ,i nsoi lo ro nartificia l surfaces,tha tspecia l measurementso nconversio nrate si nsurfac ewate rar eneeded . The importantorganophosphoru spesticide s azinphos-methylan ddimethoat ewer e selected asmode l compounds.Th erate so fconversio nunde raquati c conditionswer e largely lacking. A general characterizationo fth eus ean dpropertie so fazinphos-methy lan ddimethoat ei s giveni nChapte r3 . Ina norientatio n stageo fth einvestigation ,variou s surfacewater swer e sampledi n theKromm e Rhineare aan di nth eLopikerwaar d Polder (Provinceo fUtrecht) . Initiallymuc h attentionwa s needed toth edevelopmen to fexperimenta lmethod san danalytica lprocedures . Samplingo fwate r andbotto mmateria l required special techniques (Chapter 4). Manyprob ­ lemsha dt ob esolve di nga schromatograph ya tlo wlevel so fth ecompounds .Larg eamount s ofinterferin g substancesi nal l extractso fbotto mmateria lha dt ob eremove d (Chapter5) . Thedevelopmen to fsuitabl e clean-upprocedure sfo rthes eextract s required muchattention . Lateri tbecam e evident thatattentio nha dt ob efocuse do na fe wsituation si n whichbot hmode l compoundswer eapplied .Tw ofrui t farmswer e selected formor e detailed study,on e near thevillag eo fBenscho pan don enea r thevillag eo fJaarsveld ,bot hi nth e Lopikerwaard (Chapter 9).A criterio ni nth eselectio no fsamplin gpoint swa s thato nthes e farmsth edrainag e ditchescontaine dwate r throughoutth egrowin g season.Furthermor eo n both farms,th editc h systemswer e occasionallydischarge db ysmal lpumpin gstations , whichmad ei tpossibl et oestimat eth ewate rbalanc eo fth editche s (Chapter10) . Inth esituation s selectedfo rth efiel d trials,considerabl edrif t fromth eorchard s intoditche s couldb eexpected .Th efarm swer e traversedb ysevera l farmditches .Severa l treesgro wjus talongsid e theditche swit h theircrown s above thewater ,s otha tinevitabl y a certain amounto fth espra ydescende d into thewater .Althoug h suitableobject sfo rth e present study, thesesituation sar eno tcommo ni nfruit-growin g areas.Loca l situations varywidel yan dshoul d thusb econsidered .I nmos t fruit-growing areas,th eproportio no f openwate ri sfa rless ;ditche sma yb edr ydurin gth e growing season.Ofte nfrui t trees

11 areseparate d fromth editche sb ya wind-brea k of trees,b ya path ,o rb ya sizablebor ­ der.Thu s itma yb e expected thatcontaminatio n onth etw ofarm swoul d represent anuppe r limito fcontaminatio n rathertha na naverag evalue . At anearl y stageo fth eresearch ,i tbecam e clear that field situations canb e quite complex.S osimple r trialswer emad e inoutdoo r tanks,measurin g the rateo fdeclin e in water and penetration intobotto mmateria l (Chapter 7). Thedeclin e trials inthes e out­ door systemswer e carriedou tunde rtemperatur e andligh t conditions similar to those in thefield . Invie wo fth elarg enumbe ro fcompound s andcondition s ofapplications ,ther e is a need fora ninitia l characterization ofth ecompound s inwel l defined laboratory tests. Inlaborator y tests,conversio nrat ean dadsorptio no fazinphos-methy l anddimethoat ewer e measuredunde rcontrolle dcondition s (Chapter6) . Theevaluatio n ofth ebehaviou r ofman ypesticide s undervariou s conditions insur ­ facewate rwoul d require anenormou s research capacity. Iti sno tfeasibl e tostud y all relevant compoundsunde ral lpossibl e environmental conditions.Severa l principles in the behaviouro fpesticide s insurfac ewate rar eo fgenera l nature;the y canb e applied tovar ­ iouscontaminant s underdifferen t circumstances.Therefore ,computationa lmodel s for the quantitativedescriptio no fphysico-chemica l behaviouro fpesticide s insurfac ewate r are considered good toolsi nthi sresearch .Thes emodel s aima tth equantitativ e description ofconcentratio n asa functiono fpositio nan d time (Chapters 8, 10an d 11). Detailed in­ vestigations formode lpesticide s couldthu syiel d informationo fmor egenera l validity on thephysico-chemica l behaviouro fpesticide s insurfac ewater . Invie wo fth ecomplexit y ofaquati csystem s and of thenee d for flexibility, the differential equationswer esolve dnumerically . The computer simulation language CSMP III (IBM, 197S)wa suse d forprogrammin g themodels . Thecomputatio nmodel swer eprimaril yconsidere d tob e research toolsb ywhic h areas ofto o limited knowledgecoul db e tracedmor eclearly .Th eresult s ofmode l computations provide astartin gpoin tfo rfurthe rinvestigations .Computatio nmodel sma ybecom e more suitablefo rmakin gpredictions ,startin g froma limited seto fbasi c datao n the com­ pound and from thehydrologica l situation.

12 3 Review of the use and properties of azinphos-methyl and dimethoate

3.1 APPLICATION OFAZINPHOS-METHY LAN DDIMETHOAT EI NFRUI TFARMIN G

Forth econtro lo fharmfu l arthropodsi narabl e farming,horticultur ean dlandscap e management,variou spesticide sar eavailabl e (Gidsvoo r Ziekten-e nOnkruidbestrijdin gi n Land-e nTuinbouw , 1977).Th e model compoundsi nth e present studyar eapprove dfo rvar ­ iouspurposes . Azinphos-methyl canb euse di nappl ean dpea rorchards ,an di nflowe rcrops .Th e situation that receivedparticula r attentioni nthi s studywa s applicationi nappl ean d pear orchards,wher e azinphos-methyla s25 1 (w/w)wettabl epowder ,ma yb euse d especially against caterpillars,an dfurthe ragains tpsyllids ,appl eblosso mweevils ,sawflie san d pearblosso mweevils . Dimethoatei sapprove d forus e againstharmfu l insectsi nvariou s fruits.Further , this compoundma yb euse do noutdoo rvegetables ,potatoes ,sugar-bee tan dcereals .Th e compoundi sals ouse dt osom eexten to nornamentals ,flowe rbulb san do nnurser y stock. The applicationso fdimethoat ei norchards ,subjec to fth epresen t investigation, aredi ­ rected against aphids,psyllids ,wooll y aphids,capsid san dsawflies .Dimethoat ei suse d indifferen t formulations,namel ya s20° s(w/w )wettabl epowde ran da sliquid so fmas scon - _3 centration20 0an d40 0k gm . Combinationso fazinphos-methy lan ddimethoate ,formulate da sa wettabl epowde rwit h 20°6+ 10 ?oactiv e ingredient,ar e approved forus e against some insectso napples ,pears , cabbagesan dpotatoes .Th enumbe ro fapplication so fbot h insecticideso rth emixtur ede ­ pendso nth eexten to foccurrenc eo fth einsects ,bu tofte nsevera l applicationsma yb e necessaryt ocontro l them.Nowaday s sexpheromone sca nb euse da sa warnin g systemfo rth e presenceo fpopulation so fsumme r fruittortri xmoths .B yusin g this systemo f'supervise d control',th enumbe ro fapplication sca nsometime sb ereduce d (Minks& d eJong , 1975).Fo r thewettabl epowde ro fazinphos-methyl ,th erecommende ddos eo fproduc ti s0. 3g m (3k g -1 3-2 -1 ha )an dtha tfo r40* odimethoat ei s0. 1c m m (1litr eh a) . Inth e Netherlands,th emaximu mpermitte d residueo fazinphos-methy lo nappl ean d peari s0. 4m gk g ;tha t fordimethoat ei s0. 6m gk g ,bu ta nincreas et o1. 5m g kg" is underconsideration . Safetyperiod sbetwee napplicatio nan dharves t forbot h insecticides onappl ean dpea rar ethre eweeks .Becaus eo fth etoxicit yo fbot hcompound st obees , ap­ plications during floweringo ffrui ttree sar eno tallowe d (Gidsvoo rZiekten -e nOnkruid ­ bestrijdingi nLand -e nTuinbouw , 1977).

13 3.2 PHYSICO-CHEMICALPROPERTIE SO FTH ECOMPOUND S

Physico-chemicalpropertie so fazinphos-methy lan ddimethoat ear etabulate d inTabl e 5 andTabl e6 ,respectively .Thes edat asho wtha tbot hcompound shav ea rathe rlo wvola ­ tility,an dtha tdimethoat ei sfa rmor esolubl ei nwate rtha nazinphos-methyl .Furthe rin ­ formationca nb efoun di nhandbook slik etha to fMarti n& Worthin g (1977).

3.3 CONVERSIONRATE SAN DPATHWAY SO FTH ECOMPOUND S

Theconversio nrate so fpesticide si nsoil san dwate runde rconstan to runde ronl y slightlyvaryin genvironmenta lcircumstance sca nofte nb echaracterize db yon erat econ ­ stant.Th efollowin gfirst-orde rrat eequatio nca nofte nb eused :

de/dt = -k a (1) inwhic h o =mas sconcentratio no fsubstanc e (mgm ") t =tim e Cd) =rat ecoefficien tfo rconversio n 1 ka Cd" )

Integrationo fEquatio n1 yield s

ko =-I n (o/oo)/t C2)

Table5 . Physico-chemicalpropertie so fazinphos-methyl .Sources : (1)Baye rA.G .(1971) ;(2 )Cavagno l &Talbot t (1967); (3)Marti n& Worthing (1977);(4 )Spence r (1973); (5)Wäcker s (1977).

Chemicalnam e (3) 0,Ö-dimethyl S-[(4-oxo- l,2,3-benzotriazin-3 - (4H)-yl)methyl]phosphorodithioat e Tradename s (3) Gusathion (Bayer);Guthio n(Chemagro ) Structuralformul a (1)

Molecularformul a (1) C10H12N303PS2

Molecularmas s (1) 317.3 Meltingpoin t (1) 73-74 C (purecompound ) (2) 65-68 C (technicalmaterial ) Vapourpress'ur e (3) <5 1mP aa t2 0° C (5) ca0. 5mP aa t2 5° C Solubility (4) inwate rabou t3 3g m" 3 atroo mtemperature ; solublei nman yorgani csolvent s

14 Table6 . Physico-chemical propertieso fdimethoate .Sources : (1)Marti n& Worthin g (1977); (2)Spence r (1973); (3)Wagne r &Frehs e (1976).

Chemicalnam e (1) 0,0-dimethylS-[2-(methylamino)-2-oxoethyl ] phosphorodithioate Tradename s (1) Cygon (AmericanCyanamid) ;Fostio nMM , Rogor (Montecatini); Roxio n (Cela); Perfekthion (BASF) Structural formula (2)(2 ) CH3\j fi CH„ ^SP-S-CH-C-N : CH( T

Molecularformul a (1) C5H12N03PS2

Molecular mass. (1) 229.2 Meltingpoin t (1) 51-52° C Boilingpoin t (3) 117° C (13.3Pa ) Vapourpressur e (3) 1mP aa t2 0° C (1) 1.1.1mP 1mP aa ta 2 t52 " 5C° C Solubility (1),(2) inwate r 25k gm at2 1 C;mos t solublei n polarsolvent ssuc ha smethanol ,ethano lan d otheralcohols ;ketone s sucha saceton ean d cyclohexanone;lowe r solubility in apolar solvents sucha sxylen ean daliphatic ssuc h ashexan e

inwhic h a =concentratio na ttim e zero (mgm )

Thehalf-lif eo fa compoun d (i,)i ssimpl y relatedt oit srat ecoefficient ,accordin g 2 the following relationship:

0.693/fe (3)

Half-liveso fazinphos-methy lan ddimethoat ei nvariou smedi aunde r different environ­ mental conditionsa sreporte di nliteratur ewil lb ebriefl ydiscusse d inth efollowin gsec ­ tions.Th eliteratur e datao nrat e coefficientso fbot h compoundsi nsurfac ewate r under various circumstanceswil lb ediscusse di nrelatio nt oou row nexperiment si nwate r from outdoor tanks,whic hwil lb edescribe di nChapte r6 .

Conversion rates and pathways of azinphos-methyl

The conversion rateo fazinphos-methy lo ncrop san dtre e fruitsi sdependen to nvar ­ ious climatic conditionsan do nth e natureo fth e plantmaterial .O nvegetables ,forag e cropsan dtre e fruits grownunde r field conditions,th eaverag ehalf-lif efo r azinphos- -methyl ranges from3 t o8 day s (ChemagroDivisio n Research Staff, 1974). However,unde r certain circumstancesth e half-lifema yb esubstantia l longer.Fo rexample ,Günthe re tal . (1963)foun d thati nCaliforni ath ehalf-lif eo nan di nth e peelo fValenci aorange swa s

15 Table7 .Structura lformula eo fidentifie d conversionproduct so f azinphos-methyl (afterWienek e& Steffens , 1976).

(I) Azinphos-methyloxyge nanalogu e CH,0 0

p:P-S-CH2-R CH0 ' (II) Mercaptomethylbenzazimid e H-S-CH2-R (III) Dimethylbenzazimid esulfid e R-CH-S-C H- R (IV) Dimethylbenzazimid edisulfid e R-CH-S-S-C H- R (V) Benzazimide H-R (VI) AHnethylbenzazimid e (VII) Anthranilicaci d

340-400days .

T,bl 7 ereldoatifM p»t,e„ „ter-solubl„ptodu * ^imZnTJ z : " - of the difficulties in ,„«„.„*• , entitled. This can be seen as an indication version products of azin^ ^1 ^^ " ^ "* *"» ^ »^-soluble =»"'

that lT22s°l\7eT?22f :ZinPh0S-methyl 3S deSCrib^ - the literature show f tent of the sou, so ^ b " ? ^. —, such as foliation, moisture con- , cuij. cype, biological activity of thp <=nii ,„,i various tions. Schultz et al (1970) found ^ • ^ climatic condi- as an emulsion on a silt-loan, soil SOWas l^T^H "^ "^""t*1 WaS aPPlied /S Ap lication followed by rotary tillage to a denth nf n 1 ' P ™ granular form /ear, 131 of the applied granules! "^ M *** f°r a 50°6 loss' After1 w "" granules was recovered in tha -r„ j- version products II, III or IV V and VI f azinphos-methyl. The con- ? W6re identifie compounds were found. Yaron et'al no7A ™ ^^ d- Four unidentified 3 Sil loam s "-«er content lower than II pH' 84 ! ^^ ^ *" ^ °^ (organic fraction of water SOI) the rate coUfilZT'^^ ^^ W mno1 k^ ^d v°lume d"1 at 25 °C. Lower rate coefficient w2Y^/™^ ™* 0.011 d" at 6 °C and 0.053 - sieved soils. *. approve ^ f ^t ! ^ " ^ ^ * *" ^ """ overhead iltaination frQm ^^ ^^*^~ « 30 °C with constat S rrom u.07 d for acla y and a silt 16 loamsoi lt o0.00 87 d fora sand y loaman da loa msoil .Th emoistur e contentwa s 401o f themaximu mretentiv ecapacity ,a sdetermine dfo runsieve dsoils . Recently,th ephotodecompositio no f [ cjazinphos-methyli na thi nlaye ro fsoi l (of2 kgmois t silt-loampe rsquar emetr eo fglas ssurface )wa sstudie db yLian g& Licntenstei n (1976).The y foundthat ,afte r8 h exposur et osunlight ,abou t80 %o fth eorigina l dose wasrecovere db ybenzen eextraction .Nearl y 3.5%wa sconverte dt onon-insecticida lwater - -solubleconversio nproduct san dapproximatel y 16%wa s founda sboun d residue.I nthei r controlmeasurement si nth edark ,n odegradatio nan dn oboun d residueswer e found. Theeffect so fligh tan dp Ho nth econversio no f [ CJazinphos-methy l ina naqueou s solutiono f2 g m " were investigatedb yLian g& Lichtenstei n (1972).Th econversio no f azinphos-methyli nth eaqueou s solutionexpose dt oultraviole t lightwa sver y rapid.Afte r twohour s exposure,the y found that56 %o fth edos ecoul db erecovere db ychlorofor mex ­ traction;thi sphas econsiste dmostl yo fbenzazimid e (V)o rth eoxyge nanalogu eo fazin ­ phos-methyl (I)(45 %o f Capplied) ,4 %anthranili c acid (VII)an donl ya fe wpercen to f compounds II,II Io rIV ,an dV I(Tabl e 7). About 25«»o fth edos e remainedi nth ewate r phasean dth e missingradioactiv emateria lwa s assumedt ob evolatilized . Theconversio no fazinphos-methy li nwate ri shighl ydependen to npH ,a swil lb edis ­ cussedi nmor edetai li nChapte r6 .Lian g& Lichtenstei n (1972)foun d thata tp H1 0an dp H 11afte r7 day sa t2 5°C , 18%an d97% ,respectivel yo fth edos eo f [cjazinphos-methy l wasconverte dt owater-solubl econversio nproducts .A tp H1 0th echloroform-solubl econ­ versionproduct s (82%o f Capplied )consiste dprimaril yo fcompound sII Io rIV ,an dVI , totalling 34%o fth e Capplied ; 30%o fth e Cwa s convertedt ocompound sV o rI , and 18%o fth e14 Cwa s recovereda sazinphos-methy lo rcompoun dII .

Conversion rates and pathways of dimethoate

Dimethoateshow sa rathe rhig h rateo fconversio ni nan do ncrops .Fo rexample ,Bach e & Lisk (1965)reporte d thatth erat ecoefficien tfo rconversio no fdimethoat ei nfield - -sprayed lettucewa sabou t0.1 7d ~. Pre ee tal . (1976)foun d that 50%o fdimethoat eo n apple-tree leavesdisappeare di n2.3-7. 2d ,dependen to ntim eo fapplicatio nan dformula ­ tion.Possibl econversio npathway s thatma yoccu ri nplant swer esummarize db yMenzi e (1969; 1974). Bohn (1964)investigate dth edeclin erat eo fdimethoat ei na sand y loamsoi l (pH5.5 ) -2 afterapplicatio no f1 k go factiv eingredien tpe rhectar e (0.1gm )a semulsifiabl e concentrate.Th esamplin gdept hwa s7. 5cm .Unde r dryingconditions , k^ was0.1 7d "an d after3 3m mo frainfal l k was0.2 8d ~. I nincubatio nstudies ,Bach e& Lis k (1966)foun d 1 ° a k of0.4 3d ina moist silt-loa msoi l(p H5.8) .Whe ndimethoat ewa smixe di na mois t loamsoi l (2.3%organi cmatter ,p H5.7 ,75 %o ffiel dcapacity )an dplace di na ligh troo m at20-3 0°C ,th erat ecoefficien tfo rconversio nwa s foundt ob e0.02 1 d (Bro-Rasmussen et al., 1970). Significantconversio no fdimethoat et oit soxyge nanalogu e (VIII,Tabl e8 ) wasmeasure di ndifferen tsoil sb yBach e& Lis k (1966)an db yDuf f& Menze r (1973). Radioactive p2p]dimethoat ewa s rapidlyhydrolyse di nwate ra tp H11 .I n2 h , 87% ofth edimethoat ewa s convertedt owater-solubl ematerials ,whic h remainedi nth eaqueou s phaseupo n extractionwit h chloroform.Th ewater-solubl e conversionproduct swer epredomi -

17 Table8 .Structura lformula eo fconversio nproduct so fdimethoate .

(VIII)Dimethoat eoxyge nanalogu e( =omethoate , CH-J<\ 0 ° /CH1 dimethoxon)Tradenam eFolima t \J „„ J) /

CH0 XH (IX) Des-methyldimethoat e CH„0 0 0 CH, 3\l l II/ 3 ^>-S-CH-C- N

(X) Dimethoatecarboxyli caci d CH.O S 0 3\ H S P-S-CH- C / 2 \ CH30 OH (XI) Dimethylthiophosphori caci d CH0 S 3\l l P-OH CH3°y

nantlydes-methy ldimethoat e(IX )(49.31 )dimethy lthiophosphori caci d (XI)(32.81 )an d imethoatecarboxyli caci d (X)(9.5. )(Tabl e8) .Mor etha n97 .o fth elabelle dmateria l 32 m thechlorofor mextrac t (about13 4o fth P PI ,,,r- c J * * t 0 UnChanged dimethoate (Brady& Arthur,1963) . ' ' ^

3.4 ADSORPTIONAN DLEACHIN GO FTH ECOMPOUND SI NSOI L

tion Imcient'0 ^ "iT^ '" '^ * ^ iS ""^ det™d * adsorp- m eld"t C° rient f°r CmVerSi0n °f the COmpOUnd' characteristics ofThe L 1 °nS T Pl3nt gr0Wth- ^ ™ °f groundwater pollution through l^Z, ZZ 10m Can bS aPPr0Ximatal Wlth Rational models (LeistraS e-;: ^1;:::^::::! rhosTbyiarereporte da s— by —- • -phos-methyi2 ub e -^^rivjrrr: tedmTshow* a; « :r^fc^-^T of ther ~^ ~ «"- . redin s 0,sr:—z:z ^ —:;r ~ :r— phos-methyl was not transported deeper than n / • C } ^ that &Z™~ content of 0.6. and pH8 4) aft.. • • m '" * ^^ l0am SOil ^or8anic "«tter days. P 8,4) after lrrigatl0n at * »te of 0.28 mirrigatio n water over 38

The systemic insecticide dimethoate is highly solnhi«.•

sorbed to only a limited extent on soi! ^ZÎ^ ~£ ?** » ** ^ *" °nto a sxlt loamsoi l (organic matter content of 2 1TT ' " T? Cf fi"ent

-Bryce, 1969). whether groundwater pollutieL 2il ^ " "* ^ «**»* factors. The leaching of dimethoat/f d^thoate „m occur depends onman y est™ from the result^ ^ - & ^ ^ **" ** * *°toto "op «n be s-ing a rate coefficient for cJ^ToTP^T " ^ & ^ ^ *" (bection 3.3), an adsorption coeffi- 18 Table9 .Soi l characteristics andadsorptio n coefficientso fazinphos-methy l asmeasure db yBaye r A.G. (1978).

Soil %Cla y 1 Silt %Organi c PH s/1 (<2pm ) (2-50pm ) matter (water) (m3kg"' ) Sandyloa m 10.5 33.1 1.1 6.4 3.3 \0~* Silt-loam 20.5 62.8 1.8 5.5 11.0 10~^ Highlyorgani c 19.0 56.8 4.6 5.4 28.51 0 silt-loam

cient zeroan da nannua l infiltrationo frainfal l0.6 6m ,th eexten to fleachin g froma toplaye r1 m thic kwa scompute dt ob eles stha nO. H ofth edose .

3.5 VOLATILIZATIONO FTH ECOMPOUND SFRO MWATE R BODIES

Therat eo fvolatilizatio no fpesticide s fromwate rbodies.t oth eatmospher eca nb e estimatedb yprocedure so fLis s& Slate r (1974)an do fMacka y& Leinone n (1975). They useda two-laye rmodel ,compose do fa liqui d filman da ga sfil mseparate db ygas—liq ­ uid interface.Th emai nbod yo feac hflui dwa sassume dt ob ewel lmixed .Transfe ro fth e pesticides throughth elayer swa sb ymolecula rdiffusion ,whic hca nb edescribe db yPick' s -2- 1 firstlaw .Th earei cmas s fluxF (mgm d )acros sth egas—liqui d interfaceb y volati­ lizationca nthe nb eexpresse da sa functio no fth econcentratio ndifferenc e acrossth e layersan dth eexchang econstant sfo rth eliqui dan dga sphases ,respectively ,a sshow ni n Equation4 .

Fv = klK - ci,w)=yci,a- °a ) (4)

inwhic h e and a aremas sconcentration so fsubstanc ei nope nwate ran di n w a _7 freeai r (mgm ) a. and a- areequilibriu mmas sconcentration so fsubstanc ea t i,w i,a n _3 gas—liquid interface (mgm ) k, and k areexchang e coefficientsfo rliqui dan dga sphase s (md ~) Ifth eexchangin g compound obeysHenry' s law,then ,a tth eequilibriu m presumeda t the interface

a. = ü a. (5) i,a i,w inwhic h H =Henry' sconstan t 0)

Thisconstan tca nb eestimate d fromth equotien to fmas sconcentratio no fsaturate d vapour (viavapou rpressure )o fth ecompoun dan dth esolubilit yo fth ecompoun di nwater . Eliminationo f a. i,ana dc . i,inwEquation s4 an d5 yield s 19 Fv = (ow - oJS)/ {\/kx + 1/(27 feg)] (6) which can be written as

F = k„ Ac - aIn) (7) v t, 1 *• w a ' and

lAt)1= \l\ +1/C »y C8) inwhic h

fe., = overal l liquidphas etransfe rcoefficien t (id)

Themas stransfe rcoefficient sca nb econsidere d tob econductivitie s and theirre ­ ciprocals tob eresistance sb yanalog yt oOhm' slaw . Combining thearei cmas sflux, F ,acros sth einterfac e ina balanc e equation ina n unsteadystat emode l (andassumin gn oothe rpathway so floss )lead s toth e differential Equation9 :

d(Äs cj/dt =-* t>1(<,w- oJS) (9) inwhic h

hy =wate rdept h (m)

Ife a isnegligible ,whic hmean stha tth ebackgroun datmospheri c levelo f thecom ­ pound islow ,the nEquatio n9 ca nb esimplifie dan da half-lif e t, canb e simplyderive d fromEquatio n9 : 2>v

*i, ,=0.69 3 hik*. s,v \/ t,l (10) inwhic h

*},v= vola tilizationhalf-lif e (d) 10 us^/rlT °f;:latiliZati0n f°r ^ m0del ""*»** -s estimated by Equation M be 2 em „rfr an7. Î o "* ^ *"" *** ^ * °" »• *» transfer 3 2S C Were eStimted by ^ v 1L L^ i " s methy **mdi P™«*dimethoat ™ »f Lise s & Slater (1974). ^:^T:^ZZ rr" - ™*- * - tions),th evolati iZ iT , "" ^^^ (Prevailingunde r fieldcondi -

& ™ey foundth/ tafte ro n da m acT^-s ^ ******* *** * **»»• Y onlytrace so fradioactiv eazinphos-methy lwer e found inva - pourtraps .Th epreliminar y conclusioni stha tth erat eo fvolatilizatio no fth emode lcom ­ poundsfro msurfac ewater swil lb eo fmino rimportance .

3.6 SOMETOXICOLOGICA LDAT AO FTH ECOMPOUND S

Azinphoa-methyl

Theacut eora lLDV 0o fazinphos-methy lfo rfemal ean dmal erat svarie sbetwee n10-2 0 mgpe rkilogra m liveweight (BayerA.G. , 1971).Th etoxicit yo fmetabolite so fazinphos-me ­ thylha sbee nindicate db yth eWH Oa sa nare afo rfurthe rresearc h (WHO/FAO, 1974). Theacut etoxicit yo fazinphos-methy lt oa variet yo faquati corganism sha sbee nre ­ viewedb yU SEnvironmenta lProtectio nAgenc y (1973).Howeve rth ereporte dAmerica nspe ­ cieso faquati corganism sar eno tfull ycomparabl ewit hth especie soccurrin gi nDutc hsur ­ facewaters .Nevertheless ,som edat aar eshow ni nTabl e 10.Thes edat esho wth ehig hacut e toxicityo fazinphos-methy lt ocrustaceans ,severa l fishspecie san dsom esalt-wate rorga ­ nisms.Th edifference si nth eacut etoxicit yt oaquati corganism sar efirs to fal ldeter ­ minedb yth esusceptibilit yo fth especies .However ,material san dtes tmethod sma ycaus e substantialvariatio ni nth eacut e toxicity.I ti swel lknow ntha tacut e toxicityca nb e modifiedb yfactor s likeformulation ,temperature ,wate rhardness ,anima l sizean dage , previousexposure ,physiologica l condition,an doccurrenc eo fothe rpesticides . Moreresearc ho nsemi-chroni can dchroni ceffect san dno-effec t levelso fazinphos -

Table 10.Toxicit yo fazinphos-methy lt oaquati corganisms .Sources :(1 ) Referencesi nU SEnvironmenta lProtectio nAgenc y (1973); (2)Adelma net,al . (1976);(3 ) BayerA.G . (1971); (4)Portman n& Wilso n (1971). Organisms Acute toxicity (LC^)1 Noeffec t Source masscon e exposure level (mgm~ 3) time(h )

Crustaceans 0.10 96 (O Gammarua faseiatus Asellus bvevioaudus 21 96 (U

Insects: Ophiogomphusrupinaulensia 12 .5 969 6 1.73(3 0d ) (1) (0 Pteronaraya californiaa 1•' Fishes: Pevoa flaveaoens 13 96 (O Iotaluvua punotatua 329 0 96 (1) Mioropterua aalmoides 5 96 y) Pimephales promelaa 195 0 96 0.51(tes to n (2) Lebiatea reticulatus 100 96 fecundity) (3) Caraaaius ouratua >1 00 0 96 (3) Saltwaterorganisms : Pondalua montogui 0.3-1 48 y' Cvangon orangon 0.3-1 A8 \ ) Carcirtua maenaa 33-100 48 )*]_

1.LC 50 isth emas s concentrationo ftoxican t thatkill s 50%o f the organisms exposedt oi tdurin ga specifie d exposure time.

21 -methylo naquati corganism swil lb enecessar yt orecommen d criteriafo rwate rquality .

Oimethoate

Theacut eora lLD 50o fdimethoat efo rwhit erat si s60 0m gkg " (Dautermane tal. , 1959).Thos efo rth eoxyge nanalogu eo fdimethoat e (omethoate),des-methy ldimethoate ,an d dimethoatecarboxyli caci d (Table8 )wer efoun dt ob e55 ,1500-200 0an d2500-300 0m gk g , respectively (Dautermane tal. , 1959). Thusth eoxyge nanalogu ei sth emos t toxic compound. Toxicitydat ao fdimethoat et oaquati corganism sar epresente di nTabl e 11.Thes eda ­ tasho wtha tdimethoat ei shardl ytoxi ct ofish ,bu t somesalt-wate rorganism swer e shown tob ever ysensitiv et odimethoate .Omethoat e appearedt ob emuc hmor e toxict o Daphnia magna thandimethoate .

Table 11.Toxicit yo fdimethoat et oaquati corganisms .Sources :(1 ) Canton (1977); (2)Marti n& Worthin g (1977); (3)Portman n& Wilso n (1971).

Organisms Acutetoxicit y (LC50) Source

masscon e(m gm ) exposure time(h )

Crustaceans: Daphnia magna 640 0 48 (1) (Samespecies , 31 48 (O omethoate)

Fishes: Gambusia affinis 40000-5 000 0 96 (2) Salmo gairdneii 1000 0 48 (0 Lebistes retioulatus 57000 0 96 (1)

Saltwaterorganisms : Pandalus montagui 33 48 (3) Crangon orangem 0.3-1 48 (3) Caroinus maenas >3 30 0 48 (3)

22 4 Sampling of water and bottom material in ditches for analysis of pesticide residues

4.1 SHORTREVIE WO FDEVICE SAN DPROCEDURE SFO RWATE RSAMPLIN G

Variousprocedure s havebee n describedfor th ecollectio no fsample s from surface waters.A syet ,method san dterminolog y forwate r sampling haveno tbee n standardized (Josephson, 1974). Forpesticides ,th eselectio no fmethod si sdetermine db yth eobjective s ofth estud yan dth esamplin g situation (Monitoring Panelo fFWGPM , 1974;U SEnvironmenta l ProtectionAgency , 1974). One shouldalway sb eawar eo fpossibl e interactionsbetwee npesticide san dsample r components.Man ypesticide s showstron gadsorptio no nth e surfaceo fmaterial s like rubber andplastics ,whic har ecommonl yuse dfo rcollectin gwate r samples.Par re tal . (1974) sometimes founda considerabl e adsorptionb ysample rcomponents .Variou sadmixture sma yb e released frompolymers ,whic h interferewit hchemica l analysiso fth epesticides .There ­ forea siner ta materia la spossibl e (preferably glasso rstainles s steel)shoul db euse d for sampling.Poly(tetrafluoroethylene ) (Teflon)wil lpresumabl y oftenno tcontaminat eth e sample (Feltze tal. , 1971). Waterca nb esample db ylowerin g someglas so rstainles s steelcontaine r intoth ewa ­ terbody . Fillingo fth econtaine rwhil ehel d justbeneat h thewate r surface avoids skim­ mingof fa floatin g film, throughwhic ha sampl ewoul dno tb erepresentative . Feltz &Cul - bertson (1972)pointe d out thata hig hpercentag eo fal lwate r samplesi npesticid e moni­ toringprogram swa s obtainedb yshallo wemersio no fcontainers .Suc h samplesar ecommon ­ lyreferre dt oa sdi po rgra bsamples . Especiallypesticide s showinga hydrophobi c character,fo rinstanc emos to fth echlo ­ rinated hydrocarbons,ma yno tb eequall ydistribute d overth edept ho fa watercourse .Th e highest concentrationso fthes epesticide sma yoccu ra tth esurface ,especiall y ifthi si s coveredb ya noil y film. Ifwate r samplesnee dt ob ealmos tfre e fromfloatin gmaterials , bottle-samplers canb eimprove db yconstructin ga spring-loade d cap.Thes e spring-loaded capsca nb eopene da tan ydesire ddept hb ypullin go na line .A recen t constructionwa s describedb yGum pe tal . (1975). Mitchell& Dicke y (1973)develope da sample rwit ha spring-loaded lockinguni t thatallowe d samplingo fwate rfro msmal lpond so rlagoon sb y oneperso n standingo nth ebank . Besidesth edi psamplers ,tw oothe r groupso fsamplin g devicesar ei ncommo nuse ,par ­ ticularlyi nautomati cwater-samplin g programs,namel ypum pan dvacuu m samplers.A disad ­ vantageo fthes e typesi sth eris ktha tth eorifice so fth esuctio npip ema yge tplugged . Mosto fth eautomati cwate rsampler snee delectri cpowe r supply forpumpin gan dfo rcool ­ ingth esamples .A nexceptio ni sa vacuum-typ eo fsample r composedo fbottle s evacuated before samplingan dequippe dwit hpinc hvalve s (Hergert& Gall , 1973). Thesevalve sar e openedi ntur nb ya time d trigger.Thi s samplerha s separate tubesfo reac hsampling .A

23 disadvantageo fthi ssample ri sagai npossibl eadsorptio no nan dreleas e fromth ePV C tubesan dth erubbe rclosin gtubes .Modificatio nwil lb enecessar y forth e samplingo f watersi nstudie so npesticides .

4.2 WATERSAMPLIN GI NTH EPRESEN TSTUD Y

Dipsample sfro mth esmal ldrainag editche swer ecollecte dwit ha smal lbarre lat ­ tachedt oa telescopi cfishin grod ,wit ha maximu mlengt ho fnearl y4 m .Th evolum eo fth e 3 stainlessstee lbarre lwa s0. 4d m (Figure 2b).B ybulkin gth edi psamples ,averag econ ­ centrationsi nditche sca nb emeasured .Te nsubsample swer etake nan dcollecte d ina glas s bottleo fvolum e2 d m whichwa sclose dwit ha ground-glas sstopper .Befor eusin gthes e bottles,the ywer ethoroughl ycleane db yalkal itreatment ,rinse dwit hdistille dwate ran d re-distilledaceton ean doven-drie da t11 0°C . Tocollec twate rsample sfro mwide ran ddeepe rwatercourses ,a samplin gdevic ewa s constructedo fa telescopi cfishin gro dwit ha removabl eglas sbottle ,volum e 1d m ,fit -

Figure2 .Wate rsamplin gdevice suse d inth epresen tstudy . a.Stainles sstee ltub euse d forsamplin go fdrainag e ditchesan dgroundwater . b.Stainles s steeldi psample ruse dfo rsamplin go f drainageditches . c Glassdi psample ruse dfo rsamplin go f largewater - courses.

24 teda tth eend .Th eextende d lengtho f thisfishin gro dwa smor e than5 m (Figure2c) . Frombridge s over suchwatercourses ,th e glassbottl ewa srepeatedl y loweredt oth e bottom andslowl yraise d toth ewate r surfacedurin g filling.Thi sprocedur ewa s repeated atdif ­ ferentplace s acrossth ewate rbod y toge ta sampl e representative forth eentir e cross- -section. Fordetaile dmeasuremen t ofth edistributio n ofpesticid e residues inditche s after spray-driftcontamination ,a simpl evacuum-typ e samplerwa s developed. This sampler con­ sisted ofa stainles s steel tube (innerdiamete r 6mm )fitte dwit h acoppe rwir e netting filtera tth een d (openingso f0.3 3mm )an dconnecte d toa glas sbottl e of2 d m with stopperan d cock (Figure 2a).Thi sbottl ewa sevacuate dwit ha hand-operate d vacuumpump . The same samplingequipmen twa suse d forsuckin gu p groundwater samples from groundwater tubes (Section 9.3.11). Thisvacuum-typ e ofwate r samplerwa s alsouse dfo rtakin g samples during dispersion measurements inwatercourse swit h flowingwate r (Chapter 11).Fo rthi spurpose ,th e suc­ tioncapacit ywa s enlargedb y addinga vacuu mreservoi r ofglass ,volum e 10d m .Fou r seperate stainless steel tubeswer e installedwit hth e loweren da tdifferen tposition s in thewette d cross-section ofth editc han deac hwa s connected toa glas sbottl eo f 0.25 dm. These smallbottle swer econnected ,b ypolyethylen e tubesan dglas s cocks,t oth e evacuated glassreservoir .Thu s foursample s couldb e suckedu pnearl y simultaneously withina few seconds.

4.3 SHORTREVIE W OFDEVICE SAN DPROCEDURE S FOR SAMPLING BOTTOM MATERIAL

Wateran dbotto msedimen tmus tb e sampledalmos tsimultaneousl y forstud yo f thephys ­ ico-chemicalbehaviou ro fpesticide s inditches .I nman y instances,pesticid e concentra­ tionsi nth editc hbotto mdecreas e stronglywit hdepth .Fo raccurat e sampling ofbotto m material,goo dmethod sar eneede d giving leastdisturbanc e andallowin gdivisio no fth e sample intothi nlayers . Littleprogres s hadbee nmad e indevelopin g equipment tocollec t representative sam­ plesnea r the liquid—solid interface,whic h isdifficul t tosampl ewithou t disturbance (Monitoring Panelo fFWGPM , 1974). Sampling ofth ebotto mmateria l inpond san dditche s foranalysi so fpesticid e resi­ duesusuall y involves dredging orcorin gdevices .Th ewell-know nEkma n dredge (Lamotte& Bourlière, 1971),widel yuse d forbiologica l surveying, isals ouse d forsof tbottom s in pesticidemonitorin gprograms .Th emai ndisadvantag e ofth eEkma ndredg e andothe rdredgin g devices istha tpar to fth ewate r andbotto mmateria l issqueeze d outo fth edredg ewhe n iti sclosed . Further,man y grabsample s arecollecte dfro munascertainabl e depth (Aarefjord, 1972;Larimore , 1970).T oovercom e thisproblem ,Jackso n (1970)constructe d a controlled-depthvolumetri cbotto msampler .Concentration s ofcamphechlo r (Toxaphene)i n samples of lake sedimentsobtaine dwit ha nEkma ndredg ewer e generallymuc h less thanthos e insample s obtainedwit h acore r (Veith& Lee , 1971).Thes e authorsmeasure dcontent sex ­ pressed indr ymu do f6. 2 mgk g indredg e samplesan do f90. 0m gkg " inth e0 t o0.0 5 m sectiono fcor esamples . Coringdevice s allowmor edetaile dmeasuremen t ofpesticid edistributio nwit hdept h

25 inmu dbottom so fwatercourses .However ,th esedimen tcolum nca neasil yb edisturbe ddurin g sampling,fo rexampl ewhe nobstacle slik etwig so rleave sobstruc tth ecuttin gedg eo fth e coringdevice .Moreover ,mos tcor esampler slac keffectiv eseal st ohol da sampl ei nplac e whenth esample rleave sth ewate r (Feltz& Culbertson , 1972).Seriou sdisturbanc e canoc ­ curwit hsom esamplers ,whic hmus tb eturne dove rbefor eliftin gfro mth ebotto msurfac e (Thayere tal. ,1975) .

Inrelativel ydee pwatercourse swit ha sof tbottom ,nearl yundisturbe dmu dcore sca n betake nwit ha Jenki nmu dsample r (Mortimer,1942) .Thi ssample rconsist so fa removabl e coretub ei na framework ,wit ha spring-loade dlockin gsyste mtha tslowl yclose sa botto m lidjus tbefor ea to pone .

4.4 SAMPLINGO FBOTTO MMATERIA LI NTH EPRESEN TSTUD Y

Tosampl ebotto mmateria l inrelativel yshallo wditche swit hlittl edisturbance ,a coringdevic ewa sconstructe db yth eTechnica lan dPhysica lEngineerin gResearc hServic e inWageningen .Thi score rconsist so fa poly(methy lmethacrylate ) (Perspex)sampl eholde r (innerdiamete r8 0mm )wit ha shar pstainles sstee lcuttin gedg eo nth elowe ren dan da closingsyste mo nto p (Figures3 an d 4). Adsorptiono fbot hmode lcompound so nPerspe x wasmeasure dt ob ever ylow .

Toobtai na mu dsample ,th eholde r (withbot hside sopen )wa sgentl ylowere dvertical ­ lythroug hth ewate rint oth editc hbottom ,til lth euppe ren do fth eholde rnearl yreache d thewater-sedimen tinterface .Next ,th eto po fth eholde rwa s tightlyclose db y turning amille dkno ba tth eto po fth ero d (Figure 4). Theholde rcontainin g thecolui mo fmu d andwate rwa sslowl yraise dan dth elowe ren do fth eholde rwa sstoppere dwit ha poly ­ ethylenecap ,whil ei twa sstil lunde rwater .Afte rremovin gth ero dsection ,th eto po f theholde rwa sals ostoppere dwit ha polyethylen eca n qi™-»i* «- u ... p"j./cuiyienecap .binc eth etube swer etransparent , immediatevisua linspectio no fth eintac tmu dcor ewa spossible . nitmc™, Theuholde i, rstoppere •, da tbot hend swa splace pj-dcedvertica averticall ll v -i^y, i na crate * - ,mx.- whic^ •h si xcol ­ umnscoul db ecarrie dt oth elaborator ywithou tdisturbance . Theoverlyin gwate rwa sslowl yremove dan dfo ra fe wday sth ecola ™wa splace dver ­ ticallyi na deep-freeze ra t-2 0°C .B ypourin gwar mwate ralon gth eoutsid eo fth etubes , thefrozen-mu dcolum ncoul db equickl yremoved .Thi scola ™wa sagai nplace d inth edeep - -freezera t- 0 C,pendin gdivisio nint othi nslices ,extractio nan danalysis .

Undisturbedmu dcore st otes tfo rpesticid eresidue si ntan kexperiment swer etake n bevi f rl haCrylate)tUb6 (imeS dlamr - 4"° ^diam -5 0»» J length41 0 mm), mle S 1 T T'^ SamPling'th e h°lde^rSl0Wl y> UShe-d t0th e b0«°m r ub1 1 St°PPeWar SPUShe "d *th el0We r «*' *»* beforeliftin g rfoth e lab rat0lyth e COlUmS d th2 editch-botto Hh It rmcolumns ' ,removin° g'th eoverlyin —gwate P—ran dfreezin -« -»g a »tW-2 a0s° C

26 •ir-

Figure3 .Sample rfo rbotto mmaterial . a.Poly(methy lmethacrylate )tube . b.Stainles sstee lro dwit hclosin gsystem . c.Th etub econnecte d toth eclosin g systemwit htw o b adjustablecatches .

Figure4 .Cross-sectio no f thesample rfo rbotto mmaterial . 1Mille dknob .2 Handgrip .3 Stainles sstee l tube,inne r diam. 19mm ,oute rdiam .2 5mm .4 Stainles s steelrod , diam. 12mm ,wit h screwthreadbelow .5 Cove rplat ewit h sixbor eholes ,diam . 12mm .6 Rubbe rwashers .7 Tw oadjust ­ ablecatches .8 Stainles s steelflange .9Poly(methy l methacrylate)sampl eholder ,inne rdiam .8 0mm ,oute rdiam . 90mm . 10Stainles s steelcuttin gring .1 1Rubbe rring . 12Polyethylen ecover . Workingprinciple : Before lowering intoth editch ,th eflang e8 mus tb e screweddow nwit h themille dkno b 1.Whe n lifting,th e flange8 mus tb eclose dagains t thestainles sstee ledg e of thecove rplat e5 .

27 5 Procedures for chemical analysis for azinphos-methyl and dimethoate in surface water and bottom material

5.1 INTRODUCTION

Theprocedur e forth eanalysi so fpesticide si nsample so fwate r andbotto m material involvesvariou s stages.Firstly ,th epesticid eo rit sconversio nproduct mustb eextracte d asselectivel y andefficientl ya spossibl e from thewater o rmu d sample intoa suitabl e solvent.Th eextrac twil l thenusuall yb ecleane du pt oeliminat e compounds interfering withdetection .Man ypesticide s andsometime s also theirconversio nproduct sca nthe nb e measured quantitativelyb ygas-liqui d chromatography. Finally,a nadditiona l identifica­ tionma yb enecessar yt oconfir mresults .

5.2 METHODSFO REXTRACTIO NO FPESTICIDE S FROM SURFACE WATERS

Two typeso fextractio nmethod sma yb euse d forextractio no fpesticide s from surface water.Ove rsevera lyears ,mainl y liquid-liquid extractionmethod shav e beenused .I n recentyears ,technique s involving adsorptiono nvariou s solid adsorbents incolumn s have received growing attention. The liquid-liquid extractionmethod s canb edivide d intobatc h equilibrationan d con­ tinuous extractionprocedures .A limitin g factor for liquid-liquid extraction methodsma y be thepamtionin go fth epesticid ebetwee nsolven tan d aqueousphase .Repeate d extraction wth comparativelylarg evolume so fsolven tma yb e requiredt oget acceptable recoveryo f ratterpola rsubstance s fromwater .Example sar eth e ratherpola ran dthu s water-soluble metaboliteso fvariou s organophosphoruspesticides .

batCheqU libratl0n/eXtracti hiBh~ ; -technique ,usin ga separatox y funnel,ofte n yields P rt 0Sli8htl yP lar0 rTa T ;6; ? ° «^- «* organophosphoruspesticide s e ofs i I' ? 'T' 1972'Rlple y6 ta1 -'""> • *»Vantag e istha ta larg enum - c u171 h0! , f eXtraCted'A diSadVantag e° fth eorator yfunne lenactio n procdu r mayb eth elimrte dvolum eo fwater thatca nb eextracte da ton e time. Continuous P2t;r 1 rtraCti°teClmiqUen S all°W eXtraCti°n °^f volumes of water, thusi n Canb e deLe r^ 6 T' ^^^ —d (Goldberge tal. , W1; Meijers ava n toZLersZ',:!: : °i ' ™St° £ the r:C°oflargenuni5ersntinU0US ^"°fs^^ ies-tractio-***»**»»**<*»*<*nproc eure sar e -- nîstiller C S S ^ heatlng °f tHe S°1Vent in C01*™ -tractors with »lu^r^raXe^™^ 7^ " ^ ^ ^^ «*°» •*»*«*i n a terials will bT^LJd ^ ^^ ** "*" ^ ** « «-*»* ~ Activated carbon is highly suitable for adsorption of severa! pesticides from water,

28 butadsorbe dpesticide sar edifficul tt oelut ecompletely .Extractio no forganophosphoru s pesticidesfro mth eactivate dcarbo nusuall ygive slo wrecoverie s (Eichelberger& Lichten ­ berg, 1971a). Polymericresi nAmberlit eXAD- 2( apolyme ro fstyren ean ddiviny lbenzen ewit hlo w polarity)ma yb euse dfo rextractio no fsevera lorganochlorin epesticide san dpolychlori - natedbiphenyl s fromnatura lwater s (Coburne tal. , 1977).A disadvantag e ofsuc hresin s istha tbefor euse ,extensiv ecleanin go fth eresin swit hsolvent si snecessar yt oreduc e thebackgroun do finterferin gcompound st oacceptabl elevels . Polyurethane foamsar eonl yadequat efo radsorptio no fapola rorganochlorin epesti ­ cidesan dpolychlorinate dbiphenyl s (Musty& Nickless ,1974) . Preliminaryresult sdescribe db yLeon ie tal .(197S )indicat etha tth eus eo fTena x (aporou spolyme rbase do n2,6-diphenyl-p-phenyleneoxid emad eb yAKZO ,Arnhem )i sprom ­ isingfo rextractio no fpesticide s fromwater .Particularl y theextractio no forganophos - -3 phoruspesticide syielde dreasonabl eresults ,eve na tlo wconcentratio n (1m gm ). Theadsorptio no fpesticide s fromsurfac ewater sma yb eadversel yaffecte db yth epres ­ enceo fothe rcontaminant san dnatura lsubstance si nwate r (sucha ssurfactants ,fatt y substancesan dalgae) . Extractiono flarg evolume so fsurfac ewate rwit hadsorbent sma y alsoyiel dhig hconcentration so finterferin gcompounds .Furthe rdetaile d investigations arenecessar ybefor eth eadsorptio ntechnique sma yb eutilize dfo rextractio no forgano ­ phosphoruspesticides .

5.3 EXTRACTIONO FAZINPHOS-METHY LFRO MWATE RSAMPLE S

Azinphos-methyl andit soxyge nanalogu ewer eextracte dfro msample so fsurfac ewate r witha liquid—liqui dextractio nmetho d (Grève, 1972).Th eunfiltere dwate rsample s(0. 1 3 3 dm fromth etank san dusuall y 1d m fromwatercourses )wer eextracte di na separator y funnelwit hconsecutivel y 100,5 0an d5 0c m portionso fdichloromethan eb yhandshakin g

eachtim efo ron eminute .Th ecombine dextract swer edrie do ncalcinate dgranula rNa 2S04, concentratedt oa fe wcubi ccentimetre si na Kuderna—Danis hequipmen tan devaporate dt o drynessa troo mtemperatur ewit ha gentl estrea mo fnitroge ngas .Th eresidu ewa sdissolve d ina know nvolum e (0.5cm 3o rmore )o fa suitabl esolven t (acetone,hexan eo rethy l acetate)correspondin gt oth esolven tuse dfo rth ereferenc esolution .Th esolution swer e immediatelyplace di na deep-freeze rt oavoi dchemica lconversio nan devaporatio no fth e solvent,befor eclean-u pan dga schromatography .Th eprocedur ewa ssufficientl yrapi dt o allowextractio no fu pt o2 4wate rsample si na day . Themea nrecoverie so fazinphos-methy lan dit soxyge nanalogu efro mspike dwate rsam ­ plesar epresente d inTabl e 12.Th elevel so fspikin g (induplicate )wer e 1,1 0an d10 0 -3 -3 mgm forazinphos-methy l in6 drinkin gwate rsample san d10 0m gm forazinphos-methy l andit soxyge nanalogu ei n1 2surfac ewate rsamples .A tth ethre espikin glevels ,n osig ­ nificantdifference swer efoun di nth erecover yo fcompounds .Th eeffect so fshakin g intensitywa sinvestigate dbecaus esom esurfac ewater scontainin gman yalga etende dt o formheav yemulsion sdurin gvigorou sshaking .Nearl yal lsurfac ewate rsample swer eex ­ tractedb y 'normal'shakin g (about8 0shake spe rminute )yieldin ggoo drecoverie sfo r azinphos-methylan dit soxyge nanalogue . 29 Table12 .Recoverie so fazinphos-methy lan dit soxyge nanalogu efro m spikedwate rsamples . Coefficiento f Compound Typeo f Detailso n Numbero f Recovery (%) water procedure1 extractions variation (%)

Azinphos- drinking normalshakin g 6 100 4 -methyl water slowshakin g 6 87 7 vigorousshakin g 6 96 9 doublevolum e 6 104 2 ofsolven t surface normalshakin g 12 99 3 water Azinphos- surface normalshakin g 12 101 5 -methyl water oxygen analogue

1.Th eslow ,norma lan dvigorou sshakin g waswit h about 40, 80 and 120shake spe rminute ,respectively .

5.4 EXTRACTIONO FDIMETH0AT EFRO MWATE RSAMPLE S

Withth eprocedur efo rextractio no fazinphos-methy lfro msurfac ewate r (Section5.3J , dimethoatecoul dals ob eextracte dwit hacceptabl erecoverie s (Table 13).Th e comparative­ lypola rdimethoat ewa sonl ymoderatel yextracte db yslo wshaking .Th epola roxyge n analogueo fdimethoat ewa spoorl yextracte dwit hth evolum eo fdichloromethan euse di n thestandar dextraction .Hig hrecover yo fth eoxyge nanalogu ecoul db eobtaine db yextrac ­ tiono fsmal lwate rsample s(S Oc m)wit hconsecutivel y 100,50 ,S Oan d5 0c m portionso f chloroform,whic hresulte di na naverag erecover yo f9 H (coefficiento fvariatio n5*o) .

5.5 METHODSFO REXTRACTIO NO FPESTICIDE SFRO MBOTTO MMATERIA L

Pesticidesca nb eextracte dfro msoil san dbotto mmateria lb yavariet yo ftechnique s sucha sshaking ,tumbling ,blending ,Soxhle trefluxin gan dultrasoni cvibration .Th e choice ofth esolvent so rsolven tcombination sdepend smainl yo nth enatur eo fth esubstanc e

Table 13.Recoverie so fdimethoat efro mspike dwate rsamples .

1 Typeo f Detailso nprocedure Numbero f water Recovery(% ) Coefficiento f extractions variation(% ) Drinking normalshakin g 6 water slowshakin g 7 6 69 vigorousshakin g 11 6 90 8 doublevolum eo fsolven t 6 96 2 Surface normalshakin g 12 water 94 3

01 1 3nd vigorous shaki anand^olhlvp"d 120shake s pe™r minute, respectively". 8 »as with about 40,8 0

30 tob eextracte d (Caro &Taylor , 1976). Little informationwa s available onth eeffec t of thespikin g methodo requilibratio n conditions onth eextractabilit y ofpesticide s from bottommaterials . Inman y instances,rathe rpola r solventshave tob eused ,whic hwil l co-extract com­ paratively large amountso finterferin g substances from thebotto mmaterials .Consequently , theextractio nwil lnearl y alwayshav et ob e followedb y cumbersomeclean-u pprocedures .

5.6 EXTRACTION OFAZINPHOS-METHY LFRO MBOTTO M SAMPLES

Several combinations oforgani csolvent swer e tested tominimiz eth eamoun to fco - -extractants,whic h interfere inth ega s chromatography ofazinphos-methyl . Finally,a 3 3 3 mixtureo f20 0c m n-hexane, 25c m dichloromethanean d 25c m acetonitrileprove d tob e suitable.Thi nslice so fbotto mmateria lwere extracte d oncewit h thismixtur e of solvents by shakingmechanicall y for 2h .Th e liquidphas e ofth eextractio nslurr ywa s collected witha pressurize dmembran e filter,equippe dwit h aniner tsilicate-fibr e filter. Then-hexane—dichloromethan e fractionwa s separated from thewater—acetonitril e layer ina separator y funnel,the ndrie dwit hanhydrou s sodium sulphate and filtered over aPyre xglass-filte r (averagepor esiz e90-15 0 ym). The finalvolum eo f then-hexane - -dichloromethane fractionwa snote d toallo wcorrection s forlosse sdurin g the different manipulations.Th e latter solutionwa s concentrated inKuderna—Danis hequipmen t toa few cubiccentimetre s andevaporate d todrynes swit ha gentl y streamo fnitroge n gas.The n theresidu ewa s dissolved ina smal lvolum eo fhexan e (0.5c m )read y for furtherclean-up .

5.7 EXTRACTION OFDIMETHOAT EFRO MBOTTO M SAMPLES

Sliceso fbotto mmateria l fromth eoutdoo rtank s (Section7.4 )wer eextracte d once •7 "7 byshakin gmechanicall y for 2h wit h 25c m ofdistille dwate r and 50c m of ethylacetate . The liquidphas eo fth eextractio nslurr ywa s filtered offthroug ha Büchne r funnelwit h 15g o fCelit eHyfl oSupergel .Th eethy l acetatephas ewa s separated from theaqueou s phase ina separator y funnel anddrie dwit hanhydrou s sodiumsulphate .Th e losses ofethy l acetatedurin g theprocedur ewer enote d toallo w thenecessar ycorrections . Theextract swer e concentrated ina rotar y evaporator and,afte rclean-up ,measure d bygas—liqui d chromatography. Themetho dyielde d agoo drecover y ofspike d samples of bottommateria l (Section 5.12)bu t theus eo fHyfl ohampere drapi d estimationo fdr ymas s ofth ebotto mmaterial .

5.8 METHODSFO R CLEAN-UPO F EXTRACTS

Various clean-upprocedure s inestimatin g residues ofpesticide s inwate rhav ebee n described (Chesters et al., 1974;Fishbein , 1975). Co-extractedmaterial s interfering in theanalysi s areusuall y removedb yadsorptio n chromatography, inwhic h theadsorben t Florisil iswidel yused .Thi smateria lretain s thepola rco-extractive s verywell ,where ­ asapola rchlorinate dhydrocarbo npesticide sma yb e easilyelute dwit ha napola rsolvent . Withth emor epola rorganophosphoru spesticides ,suc hseparation s aremor edifficult .

31 Moreover,i tseem stha tsom einsecticide sma yb efirml yboun do nFlorisi l (Kadoum,1967) . Anotherwidel yuse dadsorbent ,silic agel ,ha sbee nsuccessfull yuse d toseparat echlori ­ natedan dorganophosphorou spesticide sfro mco-extractive s (Kadoum,1967 ;Leoni , 1971). Theinterferin gcompound si nextract sfro mbotto mmaterial sar eusuall yremove dals o byadsorptio nchromatography .Fo rexample ,La w& Goerlit z (1974)separate dPCBs ,DD Tan d relatedcompound san dchlordan ei nsuc hextract sfro minterferin gsubstance sb yusin gtw o chromatographiccolumn sfille dwit haluminiu moxi dan dsilic agel ,respectively .Littl e informationi savailabl eo nsuitabl eclean-u pprocedure sfo rorganophosphoru spesticide s inextract sfro mbotto mmaterial . Clean-upprocedure softe nnee dt ob echecke dan dmodifie dfo reac hcombinatio no f pesticidean dsamplin gplace ,becaus ebotto mmateria lma ycontai nvaryin gamount so fspe ­ cificinterferin gcompounds .

5.9 CLEAN-UPFO RAZINPHOS-METHY LEXTRACT SFRO MWATE R

Theliquid-chromatographi csyste mconsiste do fa glas scolum no flengt h8 0m man d innerdiamete r1 0m mfille dwit h4 g dr ysilic age l (KieselgelWoelm ,32-6 3ym ,non-acti ­ vatedan duse da sreceived) . Theextract ,dissolve di n0. 5cm 3ethy lacetate ,wa sapplie d toth ecolumn ,whic h waselute dwit hethy lacetat esupplie dfro ma glas sreservoi rmounte da ta heigh to fabou t 0.5m abov eth eto po fth ecolumn .

3 3 Thefirs teluat efractio no f5 cm (yellow)wa sdiscarded .Th esecon dfractio n( 7 cm) o fth eeluat econtaine dazinphos-methyl .Th eaverag erecover y from6 spike dextract s

ofwate rsample swa s96» 6,wit ha coefficien to fvariatio no f31 .Thi ssimpl eclean-u p procedureallowe dquic kremova lo fman yinterferin gsubstance sfro mextract so fsurfac e water.

5.10 CLEAN-UPFO RDIMETHOAT EEXTRACT SFRO MWATE R

Theprocedur edescribe di nSectio n5. 9wa sals ouse dfo rclean-u po fdimethoat ei n extractso fsurfac ewater .Dimethoat eelute di na fractio no f2 2cm 3,Mediatel y after thefractio ncontainin gazinphos-methyl .Th eaverag erecover yo fdimethoat e from7 spike d extractswa s92 1wit ha coefficien to fvariatio no f31 .

5.11 CLEAN-UPFO RAZINPHOS-METHY LEXTRACT SFRO MBOTTO MMATERIA L

quired rUreH °f aZinph0S"meth>'1 inib°«om Serial ft» the tanks and ditches re- Tys 1 0^Zi rUP t0 eliminate SeVeral high* Bering Stances. Various iulTbe deveC " ^^ M » ^ *«- before an acceptable method

n SS tUb 20 l0ng Wlth m imer diameter of 8 silicsilicaa geeel waTs pouredV, to a° heigh"* t o "*f isn ™, TU -0 2.« g non-activated - the top of the col™, ^J^ZTZ^ " •**"—* *» *** f in „-hexane. This gradient was made by H2 t^a """ ***** ° «*^oxc«tb«. y constructing a gravity flow system, using a measur- 32 ingcylinde r (with5 0c m n-hexane)an da conica lflas k (with8 0c m dichloromethane). Thefirs teluat efractio n (80c m) wit hman yinterferin gsubstance swa sdiscarded ; thesecon deluat efractio n (23c m) containe dazinphos-methyl .Th eaverag erecover y (16 runsdistribute dove rvariou smeasurin gseries )fro mbotto mmateria lextract sspike dwit h azinphos-methylwa s91 %wit ha coefficien to fvariatio no f 7%. Sometimesai rbubble sappeare di nth egravit ysystem ,whic hinfluence dth eelutio n process.Therefor ethi ssyste mwa sreplace db ya pumpin gsystem .Th esam esolvent s wereused ,resultin gi nnearl yth esam eelutio npattern .Thi simprove dsyste mwa squicker , yielded somewhathighe rrecoverie san dshowe dles svariatio nthe nth egravit ysyste m (Section6.4) .

5.12 CLEAN-UPFO RDIMETHOAT EEXTRACT SFRO MBOTTO MMATERIA L

Forclean-u po fdimethoat eextract sfro mbotto mmateria l fromth etanks ,a glas stub e 200m mlon go finne rdiamete r2 0m mwa sfille dwit h17. 3g non-activate d silicage lt oa heighto f12 0mm .Th eextract so fth ebotto mmateria l wereadde do nto po fth esilic age l columnan delute dwit ha mixtur eo fethy lacetat ean dn-hexan e (4:1b yvolume) .Dimethoat e 3 wasrecovere d fromth ecolum ni nth e 100-170c m fractiono fth eeluate .Th erecover yfro m 5spike dextract saverage d95% ,wit ha coefficien to fvariatio no f6% .

5.13 CONCENTRATIONMEASUREMENT SB YGAS—LIQUI DCHROMATOGRAPH Y

Thefina lassessmen to fpesticid econcentration si nth ecleane dextract sca nb eac ­ complished indifferen tways .However ,som emethod ssuffe rfro mlac ki nsensitivit yan d specificity.Th emetho dusuall ypreferre dfo rmeasuremen to forganophosphoru spesticide s isgas—liqui dchromatograph y (GLC).Th eapparatu sma yb eequippe dwit hon eo fth esevera l availableselectiv ean dsensitiv edetector sfo rcompound scontainin gP o rS .Severa ltype s ofcolum npackin gwit hdifferen tstationar y (liquid)phase shav ebee nuse dunde rvariou s chromatographic conditions,fo risotherma lo rtemperature-programme d gaschromatograph yo f phosphorus-containingpesticide s (Zweig,1972) . Evenafte rpreviou sclean-u pb yadsorptio nchromatography ,i ti softe nfoun dtha t peakso fco-extracte d substancescoincid ewit hth epeak so fpesticida l compoundsi nth e gaschromatograms .S oi ti softe nnecessar yt oanalys eth esample swit h twoo rthre egas - -chromatographiccolumn scontainin gstationar yphase so fdifferen tpolarit y (Cochrane, 1976). Massspectrometry ,especiall yi ncombinatio nwit hGLC ,i son eo fth ebes tmethod sfo r furtherconfirmatio no fth eidentit yo fpesticide sresidues .

5.14 MEASUREMENTO FAZINPHOS-METHY L

Thequantitativ emeasuremen to fazinphos-methy lha sbee nth eobjec to fsom especia l studies.Th eavailabl eanalytica lmethod swer ereviewe db yth eChemagr oDivisio nResearc h Staff (1974).Th ebes tavailabl etechniqu efo rmeasuremen to fazinphos-methy l isgas - -liquidchromatograph y (GLC).Howeve ra selectiv ean dsensitiv emeasuremen to fazinphos -

33 -methylca nb ecarrie dou tb yGL Conl yo na fe wcolum npacking s (Zweig, 1972). Inth epresen tstudy ,th eazinphos-methy lextract swer eanalyse dwit ha Traco r55 0 gasChromatograp hequippe dwit ha flame-photometri cdetecto r (FPD)operatin g inth ephos ­ phorusmode .Azinphos-methy lan dit soxyge nanalogu ewer emeasure do ntw odifferen tcol ­ umns.Th egas-chromatographi ccondition san dcolum nspecification sar epresente d inTabl e 14. Thecleane dextract so fwate ran dbotto mmateria lwer eevaporate dan dthe ndissolve d ina nappropriat evolum eo fsolven t (acetoneo rethy lacetate) .Referenc esolution so f insecticidei nth ecorrespondin gsolven twer emad efro manalytical-grad eazinphos-methy l (98%purity )an dit soxyge nanalogu e (991),obtaine dfro mChrompac k &Nederlan dB.V. , Middelburg.Wit ha 1 0m m injectionsyringe ,5-1 0m m ofth eextract san do freferenc eso ­ lutionswer einjecte dalternatel yint oth ega sChromatograph .Th elinearit yo fth erespons e ofth esigna lwit hdifferen treferenc esolution swa squit ereasonable ,bu tafte rinjectio n ofsom eextract swit ha nunknow namoun to fco-extractives ,ther ewa ssom evariatio ni n responset oreferenc esolutions .Fo rthi sreason ,th eextract swer einjecte d twoo rthre e times,alternatel ywit hreferenc esolutions .Th econcentration so fth eextract swer eprop ­ erlydilute dafte ra preliminar ymeasuremen ts otha tth erespons eo fth eextract swa si n therang eo fth erespons eo freferenc esolutions . Thepesticid econcentration si nth eextract swer emeasure db ycomparin gpea kheight s withthos efro mth ereferenc esolutions .B yifein gColum nII ,packe dwit h 1%Apiezon- L (Table14 )azinphos-methy lan dit soxyge nanalogu ecoul db emeasure dsimultaneousl yan d rathersensitively .Th eretentio ntime so fazinphos-methy lan dit soxyge nanalogu ewer e relativelysmall .Th edetectio nlimit sse ta tthre etime sth enois ewer ecomparativel ylo w forbot hcolumn s (Table14) .

Table 14.Gas-chromatographi c conditionsfo rmeasuremen to fazinphos - -methylan dit soxyge nanalogue . ColumnI :glas scolumn ;4 0c mlong ;0. 3 cminne rdiam. ;packe dwit h4 % SE-30/6%SP-240 1 coatedo nSupelcopor t 100-120mesh ,obtaine dfro m SupelcoInc .(Pleuge rNederland ,Amstelveen) . ColumnII :glas scolumn ;6 0c mlong ;0. 3 cminne rdiam. ;packe dwit h3 % Apiezon-Lo nChromosor bW-AW-DMCS ,80-10 0mesh ,obtaine d fromChrompac k NederlandB.V. ,Middelburg .

ColumnI ColumnI I azinphos- oxyge n azinphos- oxygen -methyl analogu e -methyl analogue

Carrierga sN 2 180 180 92 (cm3min -1) 92 Detectorgase s H2(cm3 min-1) 150 150 150 0 (cm3 min-1) 150 2 10 10 10 air(cm3min -1) 10 30 30 30 30 Temperature(°C ) column 180 150 200 200 injectionpor t 210 210 210 detector 210 210 210 210 210 Detectionlimi t (ng) 0.4 5 0.2 2 Retentiontim e( min) 2.3 1.8 3.4 2.2

34 5.15 MEASUREMENTO FDIMETHOAT E

Dimethoatema yb emeasure db yGL Cwit hvariou s columnpacking s (Zweig, 1972). Inth e presentstudy ,th eextract so fsurfac ewate ran dbotto mmateria lwer e analysedfo rdimetho ­ atean dit soxyge nanalogu ewit ha Traco r55 0(containin gColum nI o rII )an da Py eUnica m GCVga sChromatograp h (containingColum n III). Bothga schromatograph swer e equippedwit h flame-photometric detectors.Th ecolum nspecification ,gas-chromatographi cconditions , re­ tentiontime san ddetectio n limitsar etabulate di nTabl e 15.Th einjectio nan dcalcula ­ tionprocedur ewa sth esam ea sfo razinphos-methyl . Thediversit yo fth einterferin g substancesi nsurfac ewate r extracts sometimes necessitated theus eo fthre echromatographi c columnswit hdifferen tpolarit yo fth e sta­ tionaryphas et oobtai ncertaint yabou tth eidentit yo fdimethoate .B yusin gColum n III, dimethoatean dit soxyge nanalogu e couldb emeasure d simultaneously.

Table 15.Gas-chromatographi c conditionsfo rmeasuremen t ofdimethoat ean d omethoate. ColumnI an dI Iar eth esam ecolumn s asuse d forazinphos-methyl ,alread y specified inTabl e14 . ColumnIII :glas s column;9 5c mlong ;0. 2 cminne rdiam. ;packe dwit h3 % Carbowax 20Mo nChromosor bW-AW-DMCS ,80-10 0mesh ,obtaine d fromChrompac k Nederland B.V.,Middelburg .

Column I ColumnI I Column III dimeithoat e omethoate dimethoate dimethoate omethoate

Carrierga sN 2 100 80 66 80 80 (cm3mi n* ) Detectorgase s 3 -1 H2(cm min ) 150 150 150 40 40 3 -1 02(cm min ) 10 10 10 air(cm3 min-1) 30 30 30 40 40 Temperature(s C 'C) column 135 135 170 190 190 injectionpor t 210 210 210 210 210 detector 210 210 210 210 210 Detectionlimi t :(ng ) 0. 1 0. 3 0.0 1 0. 2 1 Retentiontim e (min) 2. 0 1.6 0.6 3.5 2.7

35 6 Conversion rate and adsorptiono f azinphos-methyl and dimethoate in aquatic systems

6.1 INTRODUCTION

Laboratorytest swer eneede dfo rth efollowin g threereasons . -Becauseo fth elarg enumbe ro fpesticide san dcondition so fapplication ,ther ei snee d fora ninitia lcharacterizatio no fpesticid ebehaviour .Attempt sar eneede dt odesig n quicklaborator ytests ,th eresult so fwhic hca nb euse dt opredic tth ebehaviou ro fpes ­ ticidesi nth eaquati cenvironment .Howeve rther ei sn oconsensu so nth eexperimenta lmeth ­ odst ob eused ,an dther ei smuc hdiscussio no nth ewa yi nwhic hsuc htest smus tb edone . Consequently therei snee dfo rcomparativ eresearc ho nth econversio nrat ei ndifferen t aquaticsystems .Persistenc edat aobtaine di nth elaborator yha st ob ecompare d withthos e obtainedunde rfiel dconditions .Muc hattentio nha st ob epai dt oth echaracterizatio no f aquaticsystems ,bot hi nth elaborator yan di nth efield . -Becauseth econversio nrat eo fpesticide si nth efiel dma yvar yconsiderabl ywit hplac e andtime ,dat ai sneede do nth efactor sinvolved .Th eeffec to fseparat efactor sca nofte n bestudie donl yadequatel yunde rwel lcontrolle d laboratoryconditions .Th erelationship s predictlr^ beintr0dUœ dint °COmPUte rSimlati0 nmodel st 0™* equantitativ e -Therat eo fdeclin eunde routdoo rcondition si sth eresul to fvariou sprocesse s thatma y

Tele! T°USly" ^ fi6ldStUdi6S ' il 1Sdif£iCUl tt 0 **«"» ^ contributiont o f Pr0CeS Slik emiCr0bial Chemica l ztion ad!° t r ' «* Photo-chemical conversion,volatili - riÏr;;" ?Penetrati °n-FUrth ™ "i s<^ul t toextrapolat eth eresult s toTcl „ r T." an0ther'Relati0nShi *S0bt *-d underwel lcontrolle dcondi - field"S £ lnt°«-l-te rsimulatio nmodel st ob echecke db ywel ldefine d

*.2 «ON MTK0 FA.INPHOS- ™I NAQUE0U SSOYON SKEP „T DARKNES S

Literature data

hydraiysis f aqueo^rîr;::!:ÏLT« ° •«-»*« »^^ *

Paust & Conea (1972) and ahT . 3^ ^T "^ *** " ^ ^' aquatic media than their phosBhorotv Ph°sphoro-dithioates are more stable in «t instances c^t^ T^ ******>** ***»" « * *» conversion rates of p T* "^ "*"««" <*** * Go^a, 1972). bya rate coefficient (k ï ^^ SOlutions ca* beusuall y characterized TMsrat e coefficient for^rsTnly T'^l ""^ ^^ ^ **»"*» 1)' ersion may be composed of several partial coefficients, which represent thevariou s catalytican denzymi cinfluence so nth ereaction s (Grahl, 1973). However,th emechanism so fth ereaction s aremostl ypoorl yunderstoo dan dmor eresearc hi s requiredo nth e factors affectingdecompositio n rateso forganophosphoru s pesticidesi n aqueous solutions. Theconversio nrate so fazinphos-methy lan dit soxyge nanalogu e arehighl y dependent onpH .Th erelationship sbetwee nrat eo fhydrolysi sa t7 0 Can dp Hobtaine db yMühlman n & Schrader (1957)ar eshow ni nFigur e5 .Azinphos-methy lwa shydrolyse d sloweri naqueou s solution thanit soxyge nanalogu ean dbot hcompound swer e less stablewit h increasingpH . Thetemperatur edurin g thesehydrolysi s testswa shig h (7.0°C ); thu sth erate so fhydrol ­ ysisunde renvironmenta l conditionsma yb eexpecte dt ob emuc h lower. Rateso fhydrolysi sa tmor e realistic temperatureswer emeasure db yBaye rA.G . (1978), Liang& Lichtenstei n (1972)an dHeue re tal . (1974).Th erat e coefficientsfor conversiona tvariou sp Hvalue sassesse di nthes estudie s arepresente di nFigur e6 . The strong increasei nth erat ecoefficien t forhydrolysi so fazinphos-methy lwit h increasing pHi sclearl y shown.Th elarg edifference sbetwee nth erat ecoefficient s foundi nth edif ­ ferentstudie s canprobabl yb eattribute dt odifference si nth etes tmaterial san di nth e chemical compositiono fth ebuffere d aqueoussolutions . Obviously literaturedat ao nth erat eo fhydrolysi so fazinphos-methy li nth ep Hrang e 7-8.5 atsurface-wate r temperatures (10-20°C )prevailin gi nth eare ao fstud yar ever y scarce.N odat acoul db efoun do nth ehydrolysi s rateo fth eoxyge nanalogu eo fazinphos - -methyla tsuc htemperatures .Moreove rconversio nrate so fazinphos-methy l ando fit s wettablepowde ri nsurfac ewate rwer eno tfoun di nth eliterature .

rate coefficient for conversion(cf 1) 100 a

Figure5 .Effec to fp Ho nhydrolysi s rateso fazinphos - "1—'—'—' ' I -methyl(•-• ) andit soxyge n analogue (x-x)i naqueou s 5 1p01 S solutiona t7 0°C . (AfterMühlman n& Schrader , 1957).

37 rate coefficient for conversion (d~1) 10-3

0.1

Figure6 .Effec to fp Ho nrat ecoefficien tfo rhydrol ­ ysis ofazinphos-methy li naqueou ssolution sa t differ- -,—,—r—j—,—,—, enttemperatures .Dat afro m•- •(2 0°C )Baye rA.G . 6 9 12 (1978),+- +(2 0°C )Lian g& Lichtenstei n (1972) and PH x-x(2 5°C) ,o- o( 6°C )Heue re tal .(1974) .

Procédures for measuring the hydrolysis ofazinphos-methyl in buffer solutions

Hydrolysisrate so fazinphos-methy la sanalytica lgrad e(98 *purity )wer emeasure di n aqueoussolution sbuffere da ttw op Hvalues .A buffere daqueou ssolutio no fP H7. 7wa s preparedx nde-ionize dwate rwit hphosphate ,borat ean dhydrochlori cacid .Anothe rbuffere a aqueoussolutio no fp H8. 9wa sM dei nde-ionize dwate rwit hbori cacid ,potassiu m EMc n SOd7,hydrOXide- CB0t"f*h "Wer e ^^ ^ Titrisol®solution so f 0! 1 h"" h!A VOlUm e° f5 ^ °fth ebU£fere d^ SOluti- raining to e tlS"tle f;adde dt0t6S ttUb6 S° ^5 WhlC h™ » ^^* * onfn U6 SWer !PlaC6 dl n^ darkl na Wat6 rbat ha t1 S° C Afterth econ ­ centronsx nth etube swxt hP H8. 9ha ddecrease dt ohal fthei rinitia lvalu e the tem­ peratureo fth ewate rbat hwa sraise dfro m1 5t o2 0°C Af, Il rth econcen A agaiK nl(2 U L0° CH D8 H8 8 1 ththe »* trationwa shalve d 'P - J temperaturewa sraise dt o2 5° r m,0- „ • duringth etest swer eles stha n0. 5°C . temperaturefluctuation s

timelnterValS tW tUb6 S fb thP HValU6 S *TJLT^T°\\T°*5 JlfTT^ , ' ° extracts° ° wer — e conecte extractedind twic a *ewit «** h • «*« * aJrsL:: 1:/^;L~^.T ^ Thed — wasremove dwit h analyseswer eb y*^W<^^^*£« * T^?* * ^ * unnI Ifo rth eothe rtemperature s(Tabl e w2 15 'S6rie S "* °"' ciento fvariatio no fH . ' aV6rage"^ ^ was 98°'wi *ha coeffi -

38 Procedure for measuring the conversion of azinphos-methyl in surface water

Conversionrate swer emeasure do fazinphos-methy l (98%purity) ,it soxyge nanalogu e (99%purity )an dazinphos-methy lw.p . (25%wettabl epowder )dissolve di nsurfac ewater . Thesolution swer eno tbuffered .Th eincubatio njar swer eplace di ntemperature-controlle d cabinetsa t 10an d2 0 C. Inth ecabinets ,th efluctuatio no ftemperatur ewa sabou t 1°C . Thesurfac ewate rwa sobtaine dfro muntreate dTan k III (Chapter7 )an dwa sfiltere d overa niner tsilicate-fibr e filter (size0 )t oremov esuspende dparticles .Th echemica l compositiono fthi saqueou ssolutio ni sshow ni nTabl e 16.Th einitia lp Hwa sadjuste dt o 7.0b yadditio no fa smal lvolum eo fsulphuri caci dsubstanc econcentratio n0. 5kmo lm . Duringtests ,th ep Hwa smeasure dbefor eth eextractions . -3 -3 Aqueoussolution swer eprepared ,concentration s 10g m and5 g m ofazinphos-me ­ thyl,2 0g m ofit soxyge nanalogue ,an d2 0g m ofazinphos-methy lw.p .Volume so f5 0 cm ofthes esolution swer eadde dt oglas sjar s (250c m ),whic hwer eclose dwit hpoly -

Table 16.Chemica lcharacteristic so fwate rfro muntreate d outdoor tankII I (Chapter 7), used forth econversio ntest swit hazinphos-methy li nth elaboratory . Analysesb y theEaster nLaborator y forWate rTesting ,Doetinchem .Samplin gdate : 15Augus t 1977.Dat ao fanalyses : 19Octobe r1977 .

Characteristics Mass concentration (gm )

COD 110

N03 <1 NH* <0.0 5 TotalN 2.5 Orthophosphate (as POO 5.2 Totalph ( Dsphate(a s iP(\ ) 5.5 CI 345 1) 2+ Ca 212 1) HCO3 77

C02 3 C02- 3 0 S02- 12

Hardness (asCaO ) 301 1) Cu2+ -3 <5 m gm

Conductivity 113.4m Snf ' 1)

1)Fo ra bette rprecipitatio no fsuspende dmateria ldurin g centrifuging,55 5g o f calciumchlorid ewa sadde dpe rcubi cmetr eo faqueou s solutiona tth estar to fth e test.

39 ethylenecaps .Fo reac hcombinatio no fcompoun dan dconcentration ,1 8 jarswer e incubated. Inoutdoo rtrial s (Chapter 7),coppe rsulphat ewa suse dt osuppres sa nalga lbloo m inth ewate ro fth etanks .Th eeffec to fcoppe rsulphat eo nth econversio nrat eo fazin - phos-methyli nwate rwa smeasure di na nincubatio nstudy .Coppe rsulphat ewa s addedt o waterfro muntreate dTan kII It oa mas sconcentratio no f3. 2g m" 3. Intha t test, the aqueoussolutio nwa sspike dwit hazinphos-methy lw.p .a t1 6g m -3. Theglas s jarswer e placedi nth edar ki ntw otemperature-controlle d cabinetsa t1 0an d 20°C . Triplicatesample swer eextracte d ina separator y funnelwit h consecutively 100,5 0 and5 0c m ofdichloromethan ea sdescribe d inSectio n5.3 .Analysi swa sb yGLC ,usin gCol ­ umn II (Table 14)fo ral lcompounds .Th erecoverie so fazinphos-methy lan d itsoxyge n

analoguewer ealmos t 100°s,wit hlo wcoefficient so fvariatio n (Table12) .

Measured conversion rates of azinphos-methyl in aqueous solution

Theeffec to fp Ho nth erat eo fhydrolysi so fazinphos-methyl ,a sanalytica lgrade , inbuffere daqueou ssolution sa tdifferen ttemperature s isshow n inFigur e 7.Th edeclin e patternswer eapproximate dwit ha first-orde rreactio nrat eequation .Th ehydrolysi srat e coefficientsan dhalf-lif evalue sar etabulate d inTabl e17 . Therat ecoefficient sfo rhydrolysi san dth ecoefficient so fdeterminatio n (r2;squar e ofcorrelatio ncoefficient )wer ecalculate dwit ha standar dregressio nprogra mo na Hewlet t Packarddes kcalculator .Tabl e 17show slowe rcoefficient so fdeterminatio na t lowerpH ; thiscoul dhav ebee nimprove db ymeasurin gconcentration s overlonge rperiods .Durin gth e hydrolysistests ,th edifference sbetwee nduplicat esample so nth esamplin gdate swer eles s than2 6 ofthei raverag econcentrations .

Therat ecoefficient swer ehighl ydependen to nP H and temperature.Th e averagerat e IncI™ 11" PH8 '7t 08 '9W " ab0Utf0U rtimS Sa SfaS ta s thata tp H7. 6t o 7.7. Increasingth etemperatur e inbot hbuffere dsolution sresulte d ina considerabl e increase

™ ist°r "ff0 rMr0lySi S ^ ^ 6ffeCt0 f*»*««ur eo n* inth e ZZ Ar •Wa V ^ * theW 20"25° C-Thi Seffe - «uld not^'describe d Lr Z neTnr UOnShip'SlnC eaPl0 t° lf g^ w^ 1/T didno tyiel da straigh t SOlUtimS (f0r eXmPle ad6CreaS ei n timeli)mighZ thhav v ^ e disturbe TT: dth eArrheniu srelationship . «* « P^ential with

•• olazinphos-methyl (ug)

-e^'analytica^ grad^ ""„l^0*'" <* azinphos-

6 2 ; PH8 9 ,5 C;B = PH8.8:2^:V!JH 8.7 !2 O-; - ' ° 40 Table 17.First-orde r ratecoefficient san dhalf-live sfo rth e hydrolysiso fazinphos-methyl ,analytica lgrade ,i nbuffere d aqueoussolutions .

Temperature pH Rateco e iff. Half-life Coeff.o f (°C) (d"1) (d) determ.

15 8.9 0.0419 16.6 0.99 20 8.8 0.0541 12.8 0.98 25 8.7 0.114 6.1 0.95 15 7.7 0.0090 77 0.86 20 7.6 0.0126 55 0.90 25 7.6 0.0424 16 0.88

Measured conversion rates of azinphos-methyl in surface waters

Theresult so fth econversio ntest swit hazinphos-methyl ,it soxyge nanalogu ean d azinphos-methylw.p .i nsurfac ewate rar eshow ni nFigur e8 .Th ecalculate dfirst-orde r ratecoefficient s (k )ar epresente di nTabl e18 . Althoughth esample so fsurfac ewate rwer eno tbuffered ,th evariatio n inp Hdi dno t disturbth eapproximat efirst-orde rconversio npattern sshow ni nFigur e8 .N odistinc t trendsi np Hwer eobserve ddurin gth etests .Th ecoefficient so fdeterminatio nwer erela ­ tivelyhig hfo rtest si nunbuffere dsolutions . Thedifference sbetwee nth econcentration s inth ethre esample so neac ho fth esam -

masso fsubstanc e(ug ) 1000-n

1O0O

100d

°time(d ) Figure8 .Mas so fsubstanc e insurfac ewate r againsttim edurin g laboratory incubationsa t 10(above )an d 20° C (under).. - azinpho sm e thyl(analytica l grade);x = th esame ,wit h azin hos_methy half theinitia lmass ;o = P \ncme. (25%w.p.) ; A= azinphos-methy loxyge nanalogue , += azinphos-methy l (25%w.p. )an dcoppe r sulphateadded . 41 Table 18.First-orde rrat ecoefficient san dhalf-live sfo rth econversio no fazinphos - -methylan dit soxyge nanalogu ei nsurfac ewate rdurin g incubationi n thedar ka t 10an d2 0°C .

Compound Temperature pH,averag e Rate Half Coeff. Averaged (°C) (andrange ) coeff. life of difference3 (d-') (d) determ. (%)

1 Azinphos-methyl 10 7.5 (6.7-8.1) 0.0011 624 0.87 4 2 (analyticalgrade ) 10 7.4 (6.4-7.9) 0.0011 613 0.89 3 1 20 6.6 (5.7-7.5) 0.0064 109 0.99 6 202 6.8 (6.4-7.6) 0.0057 122 0.97 6 Azinphos-methyl 10 7.5 (7.1-8.1) 0.0016 427 0.87 2 (25%w.p. ) 20 7.6 (6.1-8.4) 0.0077 91 0.97 11 Azinphos-methyl 10 7.7 (7.3-8.2) 0.013 54 0.97 12 oxygenanalogu e 20 7.7 (7.4-8.3) 0.045 16 1.00 21 1.Dos e0. 5mg . 2.Dos e0.2 5mg . 3.Se etext .

Plmgdate swer eexpresse da sa percentag eo £th eaverag econcentration so ntha tsamplin g date.Afte rthat ,thes epercentage swer eaverage dfo ral lsamplin gtime sfo reac hincuba ­ tiontes t(Tabl e18) .Th eaverage ddifference swer erelativel ysmall ,wit ha nexceptio n forth eoxyge nanalogu eo fazinphos-methy la t2 0°C ,wher edifferenc eaverage d211 . Therat ecoefficient sfo rconversio no fth ecompound swer ehighl ydependen to ntem ­ perature.A t1 0C ,thes ecoefficient swer eonl yabou ta thir dt oa sixt ho fthos ea t2 0 LIZ" w?° Se °faZinph °S-meth^ «»lyticalgrade ,hardl yaffecte dhalf-live s Table18) .Wit ha w.p . formulation,azinphos-methy lshowe da somewha tfaste rconversio n thanwhe napplie da spur ecompoun d(Tabl e 18). consiLb^TT11T °f^ 0Xygenmal0gU e° fazin Ph—thyl insurfac ewate rwa s "S uf °faZinph0S -meth^"»If .»-in gincubatio no fazinphos - tntherapi - icd nconversio e" 6 7no \f th eoxyge0Xyge nnanalogue anal°gUe. C0U Un0 tb ed6teCted '^ becauseo f Addingcoppe rsulphat et oth esurfac ewate r nn °r\ -,, . azinphos-methylshortl yafte rth estar to ft W ™ "** C°™YSi°n °£ version(Figur e8 1 JL 'teSt ' f°lloWedb ya P eri°dwit hslo wcon - Anexp 11ZZlI' Z d:: PaUem C°Uldn0 tb edeSCrib6 da Sa ^-oxda rreaction . p tem couupossibi yb e f d tionS hadbe : iintz ^zr °- -—*»— A comparison of the results: nf *•»,„ • ,_ .

20 °C (Table 18) with those id Z^T " •**"-** * «*«»« ~ " difficult invie w of the low coeffi i»t 0 T™ ^^ ^ ^ ™ ^ 6teimnatl0n the view of the variations inP H in the t *? buffered tests and in thyl in aqueous solutions in the dar^s5?1^51^6 ""^ C°nVersion of azinphos-me- out of doors. Ta slow Pr°cess at temperatures prevailing

42 6.3CONVERSIO NRAT E OFDIMETHOAT EI NAQUEOU SSOLUTION SKEP TI NDARKNES S

Literature data

Therate so fhydrolysi so fdimethoat ean dit soxyge nanalogu e (omethoate)i naqueou sso ­ lutionsa tdifferen tp Hvalue swer e examinedb yGrimme re tal . (1968). Their resultsa t2 5° C arepresente di nFigur e9 .Th erate so fhydrolysi so fdimethoat ean dit soxyge nanalogu ear e highlydependen to npH .Th erat ecoefficien tfo rhydrolysi so fdimethoat e increasesb ya factoro falmos t 100whe np Hincrease s from7. 0t o10.0 .Dimethoat ewa s foundt ob ede ­ gradedmor e slowly thanomethoate .Dimethoat ei sdegrade d slowlyi naci daqueou ssolutions . Eichelberger& Lichtenber g (1971b)incubate ddimethoat ei nrive rwate rplace di nth e laboratoryunde rsunligh tan dfluorescen t light.Th ep Hwa s7. 3a ttim e zeroan dincrease d to8. 0afte reigh tweeks .I ntha ttime ,hal fo fth einitia lamoun twa sconverte d (onaver ­ age, k =0.01 2d ).Brad y& Arthu r (1963)measure d therat ecoefficien to fhydrolysi s ofdimethoat ei na sodiu mcarbonat e solution,substanc econcentratio n0.0 5kmo lm (ad­ justedt op H11) ,i nflask so na shaker .The ymeasure da k of2 8d .Unfortunately , temperatureswer e notspecifie di nthes epapers .Wagne r& Frehs e (1976)referre dt oindus ­ trialdat a indicating thathydrolysi s rateso fdimethoat ean domethoat ea t2 1 Can dp H 9wer e0.1 2an d2. 3d ,respectively .Thes evalue s agree fairlywel lwit hth e resultsi n Figure9 . Conversion rateso fdimethoat ei nsurfac ewate ra tlowe rwate r temperatureswer eno t foundi nth eliterature .Furthe r testswer edon et omeasur e conversion rateso fdimethoat e insurfac ewate ra tlowe rwate r temperatures,an dwit h additiono fcoppe r sulphatean dcal ­ ciumchlorid et oth eaqueou ssolution .

rate coefficient for hydrolysis (d_1) 100^,

0.1

0.01

Figure9 Effecto fp Ho nth erat e coefficient forhydrolysi s 0.001• I' '• ' I ofdimethoat e (•-•) andomethoat e (x-x),i nbuffere d aqueous 5 pH solutionsa t2 5°C . (AfterGrimme re tal. , 1968).

43 Procedures for measuring the' conversion of dimethoate in surface water

Theconversio nrat eo fdimethoat edissolve di nuntreate dwate rfro mTan k Iwa sstudied . Thewate rwa sfiltere d (Section6.2 )an dno tbuffered .Th echemica lcompositio no fthi s aqueoussolutio ni sshow ni nTabl e19 .Th ep Ha tth estar to fth eexperimen twa sadjuste d to7. 0b yaddin go fa smal lvolum eo fsulphuri caci d0. 5kmo lm ~ .Durin gth etests ,p H wasmeasure dbefor eeac hextraction . Dimethoatewa sapplie da sanalytica lgrad e (98%purity) . Initiallyth econcentratio n inth eaqueou ssolutio nwa s2 0g m .Detail so fincubatio nwer esimila rt othos efo r azinphos-methyl(Sectio n6.2) .Th eaqueou ssolution swer eincubate da t10 ,1 5an d2 0 C. Ina separat eserie so ftests ,th eeffect so faddin gcalciu mchlorid eo rcalciu m chlorideplu scoppe rsulphat eo nth econversio nrat eo fdimethoat ewer einvestigated .Th e calciumchloride ,whic hi susuall yadde di nadsorptio nstudies ,wa sapplie dt oa mas scon ­ centrationo f5.5 5k gm .Th econcentratio no fcoppe rsulphat ei nth erelevan tincuba ­ tionsolution swa s3. 2g n f .Thes elatte rsolution swer eonl yincubate da t2 0°C . Theextractio nprocedure swer eth esam ea sfo rconversio ntest swit hazinphos-methyl . Analysiswa sb yGL Cwit hColum nII I(Tabl e 15).Averag erecover yo fdimethoat efro m1 2 spikedwate rsample swa s961 ,wit ha coefficien to fvariatio no f 2%.

Table 19. Chemicalcharacteristic so fth ewate rfro muntreate d outdoorTan kI (Chapte r7 )use dfo rth econversio ntest swit h dimethoatei nth elaboratory .Analyse sb y theEaster nLaborator y forWate rTesting ,Doetinchem .Samplin gdata :1 5Marc h1978 . Dateo fanalysis :1 1Apri l1978 .

Characteristics Massconcentratio n (gm~ 3)

COD 15 NO3 < 1.0 NH+ 0.19 TotalN 0.19 Orthophosiphat e 0.20 Totalphosphat e 0.30 Cl" 11 2+ Ca 33 HCO3 59 C02 2 COf 0 SC-2- 57 Hardness (asCaO ) 47 Cu2+ -3 < 5m gm Conductivity 19m Sm -1

44 Measured conversion rates of dimethoate in surface water

Theeffec to ftemperatur eo nrat eo fconversio no fdimethoate ,analytica l grade,i n surfacewate ri sshow ni nFigur e 10.Th edeclin epattern sa t2 0° Ccoul dno tb echaracter ­ izedfo rth ewhol eperio do fincubatio nb ya first-orde r reactionequation . Initially thedeclin ewa s relatively slow,late rconversio nrate s increased (Figure 10).Th ein ­ creasei nconversio nrate sma yb edu et ochang ei nth echemica lo rmicrobia l conditions inth esurfac ewate rdurin g incubation.Ther ei sa napparen t inconsistencyi nth eeffec t oftemperature . Thedifference sbetwee nconcentration si nth etriplicat e samplesa tth estar to f incubationswer erathe r small (Table 20). However thesedifference sbecam e rather large atth een do fth etests .Thi sphenomeno ncoul db epartl yrelate dt ochange si np Hi nth e unbuffered surfacewater .I nsom esample s incubateda t2 0 C,relativel yhig hp Hvalue s weremeasured ,whic h correspondedt olo wconcentrations ;relativel y lowp Hvalue scorres ­ pondedt ohig hconcentrations .O naverage ,p Hchange sdi dno tsho wa clea rupwar do fdown ­ ward trend. The firstpar to fth edeclin ecurve sfo rdimethoat ei nsurfac ewate r (Figure 10)wa s approximatedwit ha first-orde rrat e equation.Th erat ecoefficient s arepresente di n Table 20.Th erat ecoefficien to fdimethoat efo rth efirs tpar to fth edeclin ecurv ea t 15° Cwa somitte di nvie wo fth efe wdat ai ntha tpar to fth ecurve .First-orde r rate coefficientsfo rth esecon dpar to fth edeclin ea t2 0° Cwer eomitte di nvie wo fth e large deviationsi nconcentration sfo rtriplicat e samplesa tth een do fth etest s (Table20) . The decline curveo fdimethoat ei nsurfac ewate rwit hcalciu mchlorid ei sshow ni n Figure 11.Th econversio n ratesfo rth efirs tperio do fincubatio na t2 0 Cwit han d withoutadditio no fcalciu m chloridewer enearl yth esame .Th ewid escatte ro fpoint si n thesecon dperio dmad ean ycompariso nbetwee nconversio nrate si neithe rmediu mimpossible . Adding coppersulphat et oth eaqueou ssolutio nresulte di na grea t increasei nth e conversionrat eo fdimethoate .Th elimite dnumbe ro fsample sdi dno tallo wassessmen to f theshap eo fth edeclin e curve.Assumin ga first-orde r conversionrat eequatio nfo rth e firstfou rpoints ,a naverag e ratecoefficien to f0.1 2d (t,= 5. 9d )wa scalculate d (Figure11) .

mass of dimethoate (ug) 1000^»

100-

Figure 10.Mas so fdimethoat ei nsurfac ewate r against timeo fincubatio na t1 0(o) ,1 5(x )an d2 0° C(•) .

45 Table20 .First-orde rrat ecoefficient san dhalf-live s forconversio no fdimethoat e insurfac ewate r inth edar ka t10 ,1 5an d 20°C .

Additive Temp. Period1 pH,averag e Rate Half Coeff. Averaged (°C) (andrange ) coeff. life of difference (cT1) (d) determ. a) None 10 I,II 7.4 (7.1-7.6) 0.0012 592 0.93 2 15 I 7.1 (6.9-7.2) _3 _3 _3 1 II 6.2 (5.8-6.8) 0.020 34 0.97 30 20 I 7.2 (6.6-7.5) 0.0071 97 0.94 13 II 6.6 (5.8-7.6) _3 _3 _3 65 CaCl? 20 I 7.1 (6.6-7.4) 0.0061 113 0.95 3 II 7.1 (6.4-7.8) _3 _3 _3 13 CaCl2+ CuSOi , 20 I,II 7.1 (6.7-7.7) 0.12 5.9 0.98 19 1.1= firstperiod ;I I= secon dperio d (see text). 2.Se eSectio n6.2 . 3.Omitte dvalue s (seetext) .

Theconversio nrat eo fdimethoat eincubate d insurfac ewate ri nth edar ka tp Haroun d 7wa srathe rslow ,especiall ya tlo wtemperatures .I ngeneral ,thes erate swer esomewha t highertha nthos eo fazinphos-methy l (Tables2 0an d18) . Duringincubatio no fdimethoat ei nsurfac ewater ,th eformatio no fth eoxyge nana ­ logueo fdimethoat e (omethoate)coul dno tb edetected .Thi smigh tb erelate d toth efas t conversiono fomethoat ei nhydrolysi stests ,a sreporte di nliteratur e (Figure9) .

6.4 CONVERSIONRAT EO FAZINPHOS-METHY L INSYSTEM SO FBOTTO MMATERIA LAN D SURFACEWATE R

Datao nth econversio nrat eo fazinphos-methy lan dit soxyge nanalogu eunde ranaero ­ biccondition si nbotto mmateria lcoul dno tb efoun di nth eliterature .Mor eresearc hwa s thusneede do ndecompositio nrate si nsuc hmedia .T osimulat enatura lconditions ,i twa s decidedt oinvestigat eth econversio nrat ei na syste mo fbotto mmateria l incontac twit h surfacewater .

masso f dimethoate (uq) 1000^j i > -A

Figure 11.Mas so fdimethoat e insurfac e wateragains ttim eo fincubatio na t2 0°C . A =calciu mchlorid eadded ;o = calciu m chlorideplu scoppe r sulphateadded . 46 Procédures for measuring the conversion of azinphos-methyl in systems with bottom mate­ rial

Theconversio n rateo fazinphos-methy lwa s studied ina mixtur eo fwate ran dbotto m material from theuntreate d Tank III.Th ewate rwa s filtereda si nSectio n6. 2an dwa sno t buffered.Th echemica l compositiono fthi saqueou s solutioni spresente di nTabl e16 . Thep Ha tth estar to fth etes twa s adjustedt o7. 0a sdescribe di nSectio n 6.2.Th ebot ­ tommateria lwa s collected fromuntreate dTan kII Ian dthoroughl ymixe dbefor eth estar t ofth etest . About2 5g o ffres hbotto mmateria lwa s introduced intoa centrifug e tube (70c m) equippedwit ha ground-glas s stopper.The n5 0c m ofsurfac ewate rspike dwit hazinphos - -methyl (analytical grade,0. 5o r0.2 5 mg),it s oxygenanalogu e (1mg )o razinphos-methy l w.p. (0.5mg )wa sadded .Fo reac hcombinatio no fcompoun dan dconcentration , 18centrifug e tubeswere incubated. These tubeswer eplace di na controlled-temperatur ecabine ta t2 0 C +1 C.A t1 0 C,onl yon eserie swa sse tu pwit ha dos eo f0. 5m go fazinphos-methyl , analytical grade.Durin g incubation,th etube swer eplace d twicea wee ko na shake rfo r5 min.Redo xpotential si nth ebotto mmateria lwer emeasure da tinterval so f2 weeks . At appropriate time intervals,thre e tubeso feac hserie swer e centrifugedfo r5 mi n at3 3H z(200 0min " ).Th esupernatan t liquidwa smeasure dan dextracte da sdescribe di n Section6.2 .Th ebotto mmateria lwa squantitativel y transferred intoa glas sja ran dex ­ tracteda sdescribe di nSectio n 5.6.Afte rextraction ,th edr ymas so fth ebotto mmate ­ rialwa sdetermine db ydryin gt oconstan tmas sa t10 5C . The extractso fth ebotto mmateria lwer ecleane du pb ycolum nchromatograph y using theimprove dpumpin g systemfo rth eelutio nsolven ta sdescribe di nSectio n 5.11. The firsteluat e fraction (60cm 3)coul db ediscarded ;th esecon d eluate fraction(2 8c m) 3 contained azinphos-methyl.Nex t2 0c m ofa mixtur eo fdichloromethan ean daceton e(2:1 , v/v)wa spumpe d throughth ecolum nan dwa sdiscarded .Afte r thatth eoxyge nanalogu eo f azinphos-methyl couldb ecollecte di nth efollowin g2 0c m. Theextract so fth eaqueou ssolution san dth e cleanedextract so fbotto mmateria l wereanalyse db ygas—liqui dchromatograph yo nColum nI I(Tabl e 14).Th erecoverie so f azinphos-methylan dit s oxygenanalogu e fromth eaqueou ssolution swere almos t 100°s (Ta­ ble 12).Th erecoverie so fthes e compounds from spikedbotto mmateria lwer e 103%(coeffi ­ ciento fvariatio n3% )an d59 % (coefficiento fvariatio nals o 3°s),respectively .Th erel ­ ativelylo wrecover yo fth eoxyge nanalogu ewa sprobabl ydu et olo wefficienc yo fextrac ­ tionbecaus eth erecover yfo rth eclean-u pprocedur e alonewa s 96%,wit ha coefficien to f variationo f 6%.N ocorrection swere made fo rrecovery .

Measured conversion rates of azinphos-methyl in systems with bottom material

Theconcentration so fazinphos-methy li nsystem swit hbotto mmateria la tvariou s times during incubationa t1 0an d2 0° Car eshow ni nFigure s1 2an d13 ,respectively .Th e calcu­ lated first-order ratecoefficient sfo rth econversio no fazinphos-methy li nthi ssyste m arepresente di nTabl e21 . Theaverag eredo xpotentia li nth ebotto m layero fth esyste mwa sabout -0.1 2V .

47 mass of substance (ug) 1000 -,

100-d

Figure 12.Mas so fazinphos-methy l (analyt­ icalgrade )i nsystem swit hbotto mmateria l againsttim eo fincubatio na t 10°C .

Duringth eincubatio nperiod ,th estandar ddeviatio no f1 3measurement swa s0.0 4V .Th e bottommateria lca nb eclassifie da sanaerobic . Theaverage ddifference sbetwee ntriplicat esample swer erelativel ysmall ,excep t forincubatio na t1 0° C (Table21) .Raisin gth etemperatur efro m 10t o2 0° Cincrease d theconversio nrat eo fazinphos-methy lb ya facto r3.4 .Halvin gth eamoun to fazinphos - -methylresulte di nnearl yth esam econversio nrate s (Figure 13;Tabl e21) . Theconversio nrat eo fth eoxyge nanalogu eo fazinphos-methy l inbotto mmateria lwa s slightlyhighe rtha nth econversio nrat eo fazinphos-methy l itself.Durin g incubationo f azinphos-methyli nthi ssyste mwit hbotto mmaterial ,n ooxyge nanalogu ecoul db efound . Althoughth eaverag ep Hi nth ebotto mmateria lwa sslightl ylowe rtha nth eaverag e pHi ntest swit hsurfac ewater ,th econversio nrate so fazinphos-methy l inth eanaerobi c bottommateria lwer egenerall y1 0t o2 0time sa sfas t (Tables 18an d 21).Howeve rth e

mass of substance(ua) 1000 tq '

100

10 d

time(d ) Figure 13.Mas so fsubstanc ei nsystem swit hbotto m materialagains ttim eo fincubatio na t2 0°C .• = azinphos-methyl (analyticalgrade) ;x = th esam e compoundwit hhal fth einitia ldose ;o = azinphos - -methyl(25 %w.p.) ;A = azinphos-methy loxyge n analogue.

»8 Table21 .Rat ecoefficient san dhalf-live sfo rth econversio no fazinphos-methy lan d itsoxyge nanalogu eincubate d insystem swit hanaerobi cbotto mmateria la t1 0an d2 0 C.

Compound Temperature pH, average Rate Half Coeff. Averaged (°C) (andrange ) coeff. life of difference3 (d-1) (d) determ. (%)

Azinphos-methyl 10 6.9 (6.8-7.2) 0.020 34 0.88 25 (analytical grade) 201 6.8 (6.6-7.1) 0.068 10 1.00 11 202 6.8 (6.6-7.1) 0.078 8.9 1.00 5 Azinph os-m ethy 1 20 6.8(6.6-7.1 ) 0.079 8.8 0.99 14 (25%w.p. ) Azinphos-methyl 20 6.8 (6.6-7.1) 0.10 7.0 0.98 13 oxygenanalogu e

1.Dos e0. 5mg . 2.Dos e0.2 5mg . 3.Se etext .

differencesbetwee nth econversio nrate so fth eoxyge nanalogu eo fazinphos-methy li n bothmedi awer eno ts olarge .

6.5 CONVERSION RATEO FDIMETHOAT EI NSYSTEM SO FBOTTO MMATERIA LAN DSURFAC EWATE R

Nodat ao nth econversio n rateo fdimethoat ei nanaerobi cbotto mmateria lwer e found inth eliterature .

Procedures for measuring conversion of dimethoate in systems with bottom material

Theincubation swer ecarrie dou ti ncentrifug etube swit hground-glas s stoppers (Section6.4) .Abou t2 5go ffres hbotto mmateria l fromuntreate dTan kI wa sintroduce d intoth etubes .T otha twa sadde d5 0cm o3 fsurfac ewate r (fromTan kI ;fo rchemica l characteristicsse eTabl e 19)spike dwit h1 m go fdimethoat e (analytical grade).Thes e tubeswer eplace di nthre econstant-temperatur ecabinet sadjuste dt o10 ,1 5an d2 0C . Redoxpotential si nth ebotto mmateria lwer emeasure dmonthly . Atappropriat e time intervals,thre etube swer e centrifugedan dth esupernatan t liquidwa s extractedi nth esam ewa ya sdescribe dfo razinphos-methy li nSectio n6.4 . The extractiono fdimethoat efro mth ebotto mmateria ldescribe di nSectio n5. 7w a modified. Afterremovin gth esupernatan t liquid,5 cm 3o fde-ionize dwate ran d4 0c m ofethy lace ­ tatewer eadde dt oth ebotto mmateria li nth ecentrifug etube .Th etube swer eplace do na shakerfo r1h ,thereafte rth etube swer ecentrifuge dan dth esupernatan tsolutio nwa s collected.Th eextractio nprocedur ewa srepeate d twicewit h3 0c m ofethy lacetate .Th e combinedextract swer edrie dwit hanhydrou ssodiu msulphat ean devaporate dt odrynes s m arotar yevaporator . Theextract so fth ebotto mmateria lwer ecleane du pa sdescribe dfo rextract so fwa ­ ter(Sectio n 5.10).Th eonl ydifferenc ewa stha tth eelutio nliqui d (ethylacetate )was^alf - -saturatedwit hwate r (mss fractiono fwate r 1.61).Th efirs teluat e fractiono f1 0o nwa s discarded.Th enex t1 0an 3o feluat econtaine dth e dimethoate.Th efraction swer eanalyse d

49 by GLCwit hColum n III (Table 15).Th eaverag e recoveryo fdimethoat e from 25 spikedsam ­ pleso fbotto mmateria lwa s90°a ,wit ha coefficien to fvariatio no f

Measured conversion rates of dimethoate in systems with bottom material

Theresult so fincubatio no fdimethoat ei nsystem swit h anaerobicbotto mmateria la t 10,1 5an d2 5° Car epresente di nFigur e 14.Initiall yth econversio n rateso fdimethoat e wereslow ,becomin gconsiderabl yhighe r later.Th edeclin epattern swer e approximatedwit h a first-order rateequatio nfo reac ho fthes etw otim eperiods . Theaverag ep Han drange so fp Hi nth esystem swit hbotto mmateria lwer e nearlyth e samefo rdifferen ttemperatures .Th eaverage d differencesbetwee nth econcentratio no f dimethoatei ntriplicat ebotto msample swer e relatively small (Table 22).Th eincreas ei n conversionrat efo reac ho fth eincubation si nth e secondperio d couldb erelate dt oa changei nchemica lo rmicrobia l conditions.Th eredo xpotentia li nth ebotto m material droppedfro m-0.0 3V a tth estar to fth e testt o-0.1 2V a tth eend . As temperature increased,th e durationo fth efirs tperio dwit h comparatively slow conversion decreased.A sth etemperatur e increasedconversio n rates considerably increased insystem swit hbotto mmaterial . Theconversio no fdimethoat ei nth e anaerobicbotto mmateria l systemwa s considerably faster thani naqueou ssolution s (Tables2 0an d22) .Th econversio n rateso fdimethoat ei n thefirs tperio do fincubatio nwer eslowe r thanthos eo fazinphos-methyl .I nth esecon d periodo fincubation ,th erate so fdeclin eo fdimethoat e (Table 22)seeme dto b econsi ­ derably fastertha nthos efo razinphos-methy l (Table21) .

mass of dimethoate (ug) 1000— '

100 d

Figure 14.Mas so fdimethoat e (analvtir*! insystem swit hbotto mmateri a1SSns t îi£ ' g bation du^ (:r tests at 10 (0*f ;---

50 Table 22.First-orde r rate coefficientsan dhalf-live sfo rconversio n ofdimethoat e incubated insystem swit h anaerobicbotto mmateria l at 10,1 5an d2 0°C .

Temp. Perilod 1 pH, average Rate Half Coeff. Averaged (°C) (andranges ) coeff. life of difference2 (d"1) (d) determ. m 10 I 7.0 (6.9-7.0) 0.0044 157 0.99 2 II 6.9 (6.8-6.9) 0.055 13 0.97 14 15 I ' 7.0 (6.9-7.1) 0.010 68 0.99 1 II 6.9 (6.8-6.9) 0.11 6.2 0.94 7 20 I 7.1 (7.0-7.1) 0.054 13 1.0 6 II 7.0 (6.9-7.1) 0.23 3.0 0.86 5

1.1= first period,I I= secon d period( seetex t )• 2.Se e text.

6.6 ADSORPTIONO FAZINPH OS-METHY LO NBOTTO MMATERIAL S

Adsorptiono fpesticide so nagricultura l soilsunde rvariou s conditionsha sbee n studiedb yman yworkers .Thes estudie s showtha tpesticid e adsorptioni sa comple xphe ­ nomenon,dependen to nth echemica lan dphysica lpropertie so fth epesticide sa swel la s ofth esoil . Inth efield ,adsorptio ni ninflucence db yman y environmental factorsan d especiallyb ysoi lpropertie s likeorgani cmatte rcontent ,cla ycontent ,cation-exchang e capacity,surfac eare aan dpH .O fthes epartl y interrelatedproperties ,organi cmatte r contentan dcla y contentar eusuall y considered themos timportant .Th ecompositio no f soilsan dbotto mmaterial s should thereforeb especified . Datao nadsorptio no fazinphos-methy lont obotto mmaterial s richi norgani cmatte r andcla ywer eno tfoun di nliteratur e (Table9) .

Procedures in adsorption tests with azinphos-methyl

Adsorptiono fazinphos-methy lwa s studiedb yth ebatch-equilibratio n techniquefo r bottommaterial s fromth etank san dfro mth ewatercourse so nfrui t farms.Fo r characteris­ ticso fth ebotto mmaterial sse e Table23 . Solutionso fazinphos-methy l (analyticalgrade )i nde-ionize dwate rwer eprepare d withCaC la t55 5g m" 3.Th econcentration so fazinphos-methy lwer e1 ,3 ,5 ,7 ,9 an d 13.5 gm" 3, respectively.O feac ho fthes esolutions ,1 0cm 3wer e equilibratedi nquadruplicat e with2 g o fbotto mmateria l (airdry )i n13-cm 3centrifug etube swit hground-glas s stoppers Thetube swer e turned overnight (15h )c ma nincline dturntabl ea ta frequenc yo f0.2 2H z (13mi n )a troo mtemperatur e (18t o2 1C) . Aftercentrifuging ,5 on 3o fth esupernatan taqueou sphas ewa s»^ * ** concentrations.I n1 4tubes ,th eremainin gbotto mseria l wasa s oextr a , t^r whichth eextrac twa s cleanedu paccordin gt oth eprove d proceduredesc r edin*.on 6-4.Th erecove ro fth eamount so fazinphos-methy lsupplie dt owate ran dbotto mmateria l wasabou t 100°*wit ha coefficien to fvariatio no f7a• 4.;™ .Correction ,« f7 ? Correction* sfo rrecover yo rdecom - positionwer eno tmade . 51 nn csl ^! eu 4-» ronn n n H cü 1 I 1 1 1 •^^ o o o o o O rH d JJ u h QJ O-N J>= , rt, 00 •3 _0 ° m 00 4-1 ü 1 X u Ö a 'H iw O 0 « ÜH 3 eu •H J5 cd O •H T3 4-1 ci a g r~ en o o en C >. cd X to g co CM r^ m ~ XI cd W CU CJ ^-< •* co in cN n dj O o CO CO u 3 M « B n. co cce) uo H U J 4-1 o co M 01 co C\| *-• m co m m CN CN Ä M) 0) 4J 01 4J cd x! ni S g >" 2. n m oo in r^. oo _, a> S >10> C e xi o r-l CN fî-S ro <}• -i co o ai *r-i u 4J u cj ai • « 4J U u cd al cd B xi e Sec t rptio n o f cati ' X! rH CO 'H r» — cN LT) H e ja u cd ü O O'rl a u u u u i-H i-M £ a tfl CU 0) 0) CJ & 0) Ö . t-l o co co en cu B > 0 AJ m tö >H en oi j G ^! ^ 4J CO 4J T3 CM g 0 O CJ e M cfl cU •r4 CU U etf ctj o CJ 1U i—t 01 0) T! XI r-l 4J ut 14-1 xi ^ u zi O O) n) XI T) In Pi & H) C C 14 10 •a H cd -H W t/) en s s • • • o B H« wcq M h h H iMlY)

52 Checkswer emad eo nth epossibl e effecto fair-dryin go fbotto mmateria l beforeth e experiment.Adsorptio n testsfo r azinphos-methyl were alsodon ewit ha suspensio no f freshbotto mmaterial ,a suse dfo rth econversio n tests (Section6.4) .Thes e suspensions wereals oequilibrate d inth elarg e tubes (70c m) fo r1 5h .Th eextractio nprocedur ewa s thesam ea sdescribe di nSectio n 6.4.

Measured adsorption coefficients of azinphos-methyl

Themas s fractiono fazinphos-methy l adsorbed onto thebotto mmateria l (expressedo n drymatte rbasis )wa splotte di nFigur e 15agains tth econcentratio n remainingi nth eso ­ lution.Linea r adsorption isothermswer e calculatedwit ha regressio nprogra m fromth e pointsfo rth efiv e lowest concentrations.Th eadsorptio n coefficients (K ,,), whichre ­ presentth eslop eo fth e isotherms,ar e giveni nTabl e 23.A tth ehighes t concentration, asmal ldeviatio n from the linear adsorption isothermwa s sometimes observed, especially whenadsorptio nwa s comparatively low. Theadsorptio n coefficientso fazinphos-methy l forth evariou sbotto mmaterial s were muchhighe r thanth ecoefficient s reported forsilt-loa m soils (Section3.4 ,Tabl e9) . Theadsorptio n coefficientso fazinphos-methy lfo rth evariou sbotto mmaterial scorres ­ pondwel lwit h theorgani cmatte r contentso fthes ebotto mmaterial s (Table23) . The averaged differences betweenth efina l concentrationso fazinphos-methy l inqua ­ druplicate sairpleswer e less than 5%o fth eaverag evalue sfo ral lconcentrations .

massfractio n adsorbed(m akg" 1) 80-,

-\—i—i—i—i—i—i—i—i i r 0.5 10 « mass concentration in solution (g m ) Figure 15. Adsorption of azinphos-methyl on various bottom materials. The linear adsorption isotherms were derived from the points for the lowest five concentrations. • = Benschop, siphon- -linked ditch, back section; o = Benschop, siphon-linked ditch, front section; x = Bottom material used in tank trial; A= Jaarsveld, middle ditch, front section.

53 Adsorptiono fazinphos-methy lont ofres hbotto mmateria l fromth eoutdoo r tanksre ­ sultedi na nadsorptio ncoefficien to f0.07 3(m 3kg -1),whic hwa sonl yslightl yhighe r thantha tfo rair-drie dbotto mmateria l (Table 23).Thu sa clea reffec to fair-dryin go f bottommateria lo nadsorptio no fazinphos-methy lcoul dno tb edemonstrated .

6.7 ADSORPTIONO FDIMETHOAT EO NBOTTO MMATERIAL S

Values for the adsorption of dimethoate on bottom material were lacking in the lit­ erature.

Procedures in adsorption tests with dimethoate

Four bottom materials were used as characterized in Table 23. Solutions of dimetho­ -3 ate (analytical grade) in de-ionized water with CaCl2 at 5550 g m were prepared. The initial concentrations of dimethoate were 1.06, 2.25, 5.0, 10.1, and 19.5 g m"3. Of each of these solutions, 10 cm were added in triplicate to 2 g of bottom material (air dry) in centrifuge tubes, which were then rotated overnight as in Section 6.6. After centrifuging, 5 cm3 of the supernatant liquid was extracted with consecutively 10, 5 and 5 on of dichloromethane (Section 5.4). Again, the material balance was checked

by extracting the bottom material fSection fi -n -n,Q r ,. , „. "«-eiidi section 6.5). The recovery of dimethoate applied to 11 adsorption systems with water and bottom material was QI» ,,*«.» , «•• * • • nf ,o r „. i'idLeriai was 91s, with a coefficient of variation of 2.. Corrections for recovery or decomposition were not made. S £feC drying f b0tt0m material n the adS0 ti0n the Zwaäy describel df-" m Sectioe n 6.6 ° . ° ^ ***hem was checked in

Measured adsorption coefficients of dimethoate

tod,i, ha re8ression p er «, an „.P01nt , r^ " s:™;:™ ™ * F coetticientso fdimethoat eont oth evariou sbotto m

massfractio n adsorbed (mgkg"' ) 25-,

Figure 16.Adsorptio no fdimethoat eo n variousbotto mmaterials .Linea r adsorption isothermscalculate d using thepoint s foral l concentrations.• = Benschop ,siphon-linke d ditch,bac ksection ;o = Benschop ,siphon - -linkedditch ,fron tsection ;A « Benschop , massconcentratio n insolutio n( grrf 3) supplementallydraine dditch ,bac ksection ; x= Botto mmateria luse d intan ktrial . 54 materialsar egive ni nTabl e23 .Thes ecoefficient sar eabou ta hundredt ho fthos efo r azinphos-methyl. Therelationshi pbetwee nth eadsorptio ncoefficient san dth eorgani cmatte rcontent s wasquit eclear ,jus ta sfo razinphos-methy l (Table 23).Th edifference sbetwee nth econ ­ centrationso fdimethoat ei ntriplicat esample swit hth esmal lcentrifug etube swer eles s than4 4o fthei raverages .Wit hth elarg ecentrifug etube s (70c m ), thedifference sbe ­ tweentriplicat esample swer eles stha n 2%o fth eaverag econcentrations . Theadsorptio no fdimethoat ea trelativel y lowconcentration so nfres h (notdried ) bottommateria l ando npreviousl ydrie dbotto mmateria li spresente di nFigur e 17.Th e adsorptioncoefficien to fdimethoat eont ofres hbotto mmateria lwa s0.003 2m kg". Tha t forth edrie dbotto mmateria lwa shal fo ftha tvalue .Th ereductio ni nadsorptio ndu et o previousdryin gma yb ecause db ya partl yirriversibl echang ei nth eorgani cmateria ldur ­ ingair-drying .

6.8 GENERALDISCUSSIO N

Thehydrolysi srate so fazinphos-methy lan ddimethoat ea tp Haroun d7 ar erathe rlow . Theserate sincreas estrongl ywit hpH .Thi si son eo fth emos tessentia lcharacteristic s ofthes ecompound s insurfac ewate ran dca nb esee na sconfirmatio no fearlie rinvestiga ­ tions. Conversionrate sca nb estudie dwit hvariou stype so fwater ,includin gdistille dwa ­ ter,de-ionize dwater ,ta pwater ,groun dwate ran dsurfac ewater .Clos ecompariso no fth e resultso fincubatio no fazinphos-methy l insurfac ewate rwit hthos eobtaine d inbuffere d aqueoussolution swa srathe rdifficul ti nvie wo fvariation si np Hi nth esurfac ewate r tests. Remarkable isth ecatalyti ceffec to fCu 2+o nconversio nrate so fazinphos-methy lan d dimethoatei nsurfac ewater .S oi nconversio nstudies ,coppe rconcentration s insurfac e

mass fractionadsorbe d (mg kg")

Fleure 17.Adsorptio no fdimethoat eo nbotto m „Jerialo foutdoo rtanks .Isotherm swer ecal ­ culatedwit hlinea rregressio nprogra mfo ral l relativelylo wconcentrations .. -fres h (un- dried)botto mmaterial ,x = starte dfro mair - -drybotto mmaterial . mass concentration in solution (g m ) 55 water must be measured. Possibly other ions that mayb y present insurfac e water can also catalyse conversion reactions of both compounds. Higher temperature accelerated conversion ofbot h compounds. The Arrhenius relation­ ship sometimes gavea poo r discription ofth e relationship between the first-order rate coefficients and temperature. More research isneede d to clarify this relationship. Manyothe r factors mayinfluenc e the conversion rates ofpesticide s insurfac e waters, but study ofthe mha s only just started. Light appears to be an important factor in con­ version. Laboratory tests by Liang * Lichtenstein (1972) showed that only ultraviolet ight was effective inth e photo-chemical conversion ofazinphos-methy l in water (fc =

*e I vV ?8 7' WhereaS yell°W °r red li8ht yi6lded version «tes aslo wafi n If, \ ? ! at0ry' the inflUenœ °f li8ht °n COnversion -tes ofpesticide si n tens" 6r be StUdled mder llght C°nditi0nS «tentative for the field. 1 a" 1Zr 7 *" Ph0t°-ChemiCal —- -es ofpesticides ; therefore ex- trapolauon ofrate s from the laborator toth e field is extremely difficult (Howard et

e r a St Peri Sl0W C nVerSi0n a Str ng inCrease tuthe merate offconversio co? n of°dimethoate Î f °. This may'b e relat° e ,„ v, "»• ™**Y / observed in further research will be needed to clarify Z7 1 ^ " ° ^^ ** aerobic conditions also need LZ^ t"riT ' •^ ^ ** ^^ ""** -poundsi nsystem s with~j£££^ £ Z Ï^ "^ " ** version rates oforramnWrf , material is remarkable. Literature data oncon - S P6StlCldeS b UOm mteTials are Sti11 scarce but conversi n1 / ™ ^^ ° ' S US Chl0rimted hydr Carb0n ud e" r ;™ id T ° *»***» * biologically active

rTreTan ob "^ "»"^ *» ^er aerobic conditions (Hill & McCarty, 1967). ^rz^rz^from s^anl H 0US * ^ r^ -r *" C°nVerSie~ °nie »to s°ifs ******to take —* the fiel d rial species and numbers isa seriou s 'r bl 7 " *" "* *»"* *" ^ ter systems by inoculating ^7^ ^ ^ t0 US6 standardizedwa - comparative data on such yÜ a 7 " ^^ "* ^ ^unately,

- anBactiVe-sludge system^f™ 17 ~ ^ ^ " *~ insuSr:^ :sri^^ns r r:rof •**»-** - *-*•• sionrate sunde rfiel dcondition s Th ,\ "^ ^^ t0prediC t C0nV6r" systemsi sdiscusse di nChap t "and1 Ü TdVb ^ ^ """"* " °Utd°°r 9. Pr / an dtha ti nditche si nth efiel di sdiscusse di nChapte r

56 7 Measurements in outdoor tanks: decline in water and penetration into bottom material

7.1 INTRODUCTION

Rate coefficients forth edeclin eo forganophosphoru spesticide si noutdoo r aquatic systemsunde r temperaturean dligh tcondition s comparablet othos ei nfiel d situations arescarc ei nliterature .Onl yon eoutdoo r trialwit h azinphos-methyl ina wadin g pool filled withpon dwate ran da botto m layero fsil tha sbee nstudie d (BayerA.G. , 1978). They found thata ta wate r temperatureo fabou t2 9° Can da tp H7 th erat eo fdeclin eo f azinphos-methyl inpon dwate rwa s0.5 8d~ 1 {t =1. 2d) . Thehig hwate r temperaturean d near-neutralp Har eno trepresentativ efo rsurfac ewater si nth eNetherlands .Rat ecoeffi ­ cientsfo rth edeclin eo fdimethoat ei noutdoo rwater s couldno tb efoun di nth e litera­ ture. Togai nmor e insight intoth edeclin eo fazinphos-methy lan ddimethoat e insurfac e water,outdoo r trialswer e setu pi ntanks .Th eimportanc eo fa laye ro fbotto m material inth etank so nth ephysico-chemica l behaviouro fth emode l compoundswa sals o investiga­ ted. Theexten to fpenetratio no fazinphos-methy lan ddimethoat e into thebotto mmateria l inth etank swa s studiedo na limite dscale . Some attentionwa spai dt odifference si nrat eo fdeclin ewhe nth ecompound s were applieda sanalytica l gradeo ra sformulate dproducts .

7.2 DESIGNO FTH EOUTDOO R TANK TRIALS

Setting up the tanks

Sixbat h tubswer edu gint oth esoi lnea rth eLaboratory .Th erim sprotrude d approxi­ mately5 c mabov eth esoi l surfacet oavoi dcontaminatio n fromsurroundin g soxl Stainless- steelwire-netting s (meshsiz e 11mm )wer eplace do nth etank st oreduc e disturbance.Th e sideswer eo fenamel . , ... Infou r tanks,a botto m layer0. 1m thic kwa s introduced; theothe rtw otank sdx dno t containbotto mmaterial .Al lsi xtank swer e filledwit h tapwater ,originatin g fromdee p *. •i , fille d inAugus t 1975;thos ewxthou tbot - groundwater.Th etank swit hbotto mmaterxa lwer e txlieBTO ax n«ugu s tornmateria lwer e installedi nsprin g 1976. , , , „„maa c u A»t nn Hm31 theris e inwate r levelwa s meas- Aftereac h additiono fwate rwxt h•a bucke • -u t (10d m) , tuerx s *v,oraiibratio ncurve ,th evolum ex neac ho tth e uredwit ha stainless-stee l rule.Fro mth ecalxbratio nciu v, tankscoul db einferre da tan ytim efro mth ewate rlevel . Thebotto mmateria lwa s collected froma comparativel y clean-™^ ^ Slg" nificanturba n influences,calle dth e-Tutenburgs e Wetering',sxtuate dnea rGxesbee k

57 (Provenceo fGuelderland) .Th ewatercours ewa s enlarged threeyear sbefor e samplingdurin g landconsolidatio nwork .Th euppe r 10c mo fth ebotto mmateria l fromth ewatercours ewa s collectedwit ha basket-typ e cutterhavin ga fine-meshe dwire-nettin g insideth e basket. Thismateria lwa spartiall y driedi nai ran dthe nsterilize d duringon eda yb ysteamin g undera sheet . Toobtai na simila rdevelopmen to fbiologica l activityi nth efou r tankswit hbotto m material,the ywer einoculate dwit h2 dm 3wel lmixe d freshbotto mmaterial ,fo rinstanc e withcyclops ,daphnias ,snail san dtubifex .Furthermore ,thes e tankswer epartl yplante d witha fe wsmal lplant so fCanadia npondwee d [ßlodea canadensis) collected fromth esam ­ plingditch .

Application of pesticides

TanksI an dII Iwer ekep tuntreate d duringal ltrials .Th etank swithou ta laye ro f bottommateria lwer edesignate dTank sV an dVI .Fo rquic kreferenc eth evariou s treatments areindicate dwit habbreviation s consistingo fth echaracter sA fo razinphos-methyl ,D fo r dimethoatean dFfo rformulate dproduct .Arabi cnumeral s indicateth evariou s trials( 1 to5 )an dTplu sRoma nnumera lrefer st oth etank s (It oVI ) (Table 24).Afte r application, theinsecticid edos ewa smanuall ymixe dwit h thewate rusin ga skimmer .Th einitia lwa - ervolum ei nth etank si nth efirs ttria lwa sabou t0. !m 3an dwa s0.1 5m 3 inal lothe r trials.

and TT flm tanktria lStart6 dl nSeptembe r197 SWit h di-thoate applied toTank sI I andI Va sanalytica l grade (981purity )a ta concentratio no f1 0m g m"3 neons!"T °thertan ktrialS ' b°th azinPh0ST«Vi ** dimethoatewer e applied simulta- w h L H3 C™ti0n °f ab°Ut 10°" *m" 3-* June 1976,th esecon d trial started 7 dimeth ate b thanalytlCa lgrade ly „ ra t P Wde° r 'faZil ° h0S - ** ***tria lstarte di n m foZZ 7: ° ° * -^ (Gusathion,25 . (w/w)w. P.)an da 1* - uidformulatio no fdimethoat e (Rogor,40 * w/v).

aziiys^a^^^^^^^^^drSrpuritvv'Al8;Abbre -"i°ns:A fo r formulatedproduc t (Gusathion,25 ZV ) B^ M ^««Phos-methyl,

Trial Tankswit ha lave rn fi, nff ". ' " ~ • __Jfy«_ofbotto mmateria l Tanksw iM , I idmcswit honl ywate r TI TI1 Till TIV ' ' ' TV TVI i B A2Tn I D1TI V A

Characteristics of the water

Somechemica l characteristicso fwate r samples fromth eoutdoo r tankswer emeasure d byth eEaster nLaborator y forWate rTesting ,Doetinchem .Th eresult s forwate r samples fromth esecon dan dth efift h trialar egive ni nTabl e 25.Th ewate rsample sma yb eclas ­ sifieda seutrophi c surfacewate rdu et oth erelativel yhig hconcentration so fphosphate . Duet oth estron g sunshine during 1976,a stron galga lbloo moccurre di nth eeutrophi c

watero fal l tanks.Th ealga e takeu pC0 2 duringphotosynthesi si nth edaytim ean dreleas e

C02a tnight .Th eCO ,uptak e disturbed equilibriumo fcarbo ndioxid ean dcalciu mbicarbo ­ nate,causin ga ris ei np Hdurin gth eda y(Figur e18) .

Table25 .Chemica l characteristicso fwate rsample sfro moutdoo rtan k trials,measure db y theEaster nLaborator y forWate rTesting ,Doetinchem . Samplingdat efo rTria l 2,1 5Jun e 1976;fo rTria l5 ,2 1Septembe r1976 .

Characteristics Trial2 Trial 5

T U T IV TV T VI T IV TV

pH 9.7 9.6 8.7 9.1 7.6 8.1 CODCgm-3) 110 125 95 65 180 125

NO3 (g m-3) 1 1 < «

Total N(g m-3) 3.1 3.2 1.9 1-4 0.68 1.4 Orthophosphate (g m-3) 0.60 2.4 < 0.03 < 0.03 0.25 0.08 Total phosphate (g m-3) 1.» 5.5 0.49 0.36 0.46 0.20

CI" (g m-3) ,8 16 15 20 15 12 W\ 29 Ca2+ (g m-3) 127 87 H C03 (g m-3) 9 C02 (g m-3) C°l- <* T') Hardness (as CaO) (g m"3)

Conductivity (mS m-1) 28.8 23.2 2CK9 20.5 25.3 .7.6

59 pH 11

I—i—i—i—|—i—i—i—|—i—i—i—, , , , , , | Figure 18.p H in thewate r compartment (average of 8 12 16 sixwate r tanks) against time of day. Measurements timeo fth eda y(h ) on 16 July 1976.

Thep Hin'th ewate rcompartment swer eoccasionall ymeasure dsevera l times duringth e daywit ha digita lp Hmeter .Th ep Hwa sals omostl ychecke da tinterval so f2day sa t 08:30an d16:0 0h .A sth erelationship sbetwee np Han dth ehydrolysi s rateso fth emode l compoundsar eno tlinear ,th eassessmen to fa naverag ep Hi nth ewate r compartmenti son ­ lyo flimite dimportance .

Characteristics of bottom material

InApri l 1977,th eyea rafte rth etrials ,wate rwa sslowl yremove d fromTank sI Ian d W withoutdisturbin gth esedimen tlayer .Sample so fbotto mmateria lwer e takenwit ha skimmer.Th ecompositio no fth euppe rfe wcentimetre so fth emu dlaye ran dsom ephysica l andchemica lcharacteristic so fth emu dlaye rwer emeasure db yth eLaborator yfo rSoi l andCro pTestin gi nOosterbee k (Table 23).Th eminera l fractiono fth ebotto mmateria l canb eclassifie d intoth e'clay 'textura lclass .Th eorgani cmatte r contenti srathe r highi ncompariso nwit hmos tagricultura lcla ysoils . Formeasuremen to fth evolum efractio no fliqui dan dbul kdensit yo fth ebotto mmate ­ rial,mu dcore swer etake ni ntriplicat e fromTank sI Ian dIV ,accordin gt oprocedur edes ­ cribedi nSectio n4.4 .Th ecolumn so fbotto mmateria lwer efroze na t-2 0° Can dsubse ­ quentlydivide dint oslice so fequa lthicknes s (0.01m )wit ha mechanica l saw,normall y usedfo rresearc ho nsoi lslide sa tth eSoi lSurve y Institutei nWageningen .Th eslice s werewei ghed_( %) anddrie da t10 5° Ct oconstan tmas s( ^ Thevolum eo fth eslice so f bottommateria l V wascalculate d fromEquatio n 11,assumin gcomplet e saturationo f ofth e 2 "yer"1 ^ "^ ^^ * ^ ****^ in* » "*" **«nti»t» »

%- H - md^w+ Vps OD inwhic h

Pw= densit yo fwate r -3

Ps= densit yo fsoli dphas eo fbotto mmateria l [^^ j

Th,M« , lmtlm ofUqni d(h )an dth o irf Mk ^ ^ ^ ^^

60 from Equations 12 and 13, respectively

(12) 0*b - md)/(Vw) (13) ?b = md/7b

Theprofil eo fvolum e fractionso fliqui dan do fbul k densityi nth ebotto mmateria l areshow ni nFigur e 19.Compare dwit hagricultura l soils,th evolum e fractionso fliqui d arehig han ddr ybul k densitiesar elow ,especiall yi nth euppe r layers.Dat aar esimila r tothos efo rditc hbottoms .

Sampling of water and GLC analysis

Rainfallan devaporatio nresulte di na variatio no fth ewate rvolum ei nth etanks . Beforeeac hsampling ,th eheigh to fth ewate r surfacewa smeasured ,afte rwhic h thevolum e couldb erea d fromth ecalibratio ncurve . Atth e sampling dates,th erang eo fwate r temperaturei nth eprecedin gperio dwa s readfro mminimum—maximu mthermometer s immersed inTank sI ,II Ian dV . Duringth efirs t trials,composit ewate r samples totalling 1d m werecollecte dwit h astainles sstee l ladle.A tth ebeginnin go fal lothe r trials,composit ewate r samplesto ­ talling0. 1dm 3wer e collectedwit ha pipett eo f1 0cm 3 anda ta late rstage ,whe ncon ­ centrationsbecam e low,composit e samplestotallin g1 dm 3wer e againtake nwit hth e ladle. Allwate r sampleswer e extractedwit hdichloromethan ei nseparator y funnelsa sdes ­ cribedi nSectio n5. 3an d5.4 .Azinphos-methy li nth eextract so fth ewate r samples from Trials3 an d4 wa smeasure db yGL Co nColum n I;th eextract s fromTrial s2 , 3an d5 wer e analysedwit hColum nI I(Tabl e 14).Th econcentration so fdimethoat ei nth eextract so fwa ­ tersample s fromTrial s 1,3 an d4wer emeasure do nColum n I;thos e fromTrial s3 an d5 wereanalyse do nColum nI Ian dthos e fromTria l2 wer emeasure do nColum nII I(Tabl e15) . Someserie swer e thusmeasure do ntw odifferen tcolumn sa tdifferen t times,whic h sometimes gavesligh tdifference si nth econcentration sbu tonl y smalldifference si nth eslop eo f

volume fraction of liquid(m 3m3) bulk densitytkg m" ) 0 400 800 ofV-0.6 08 10 /" V

\

0.054

Correction for sampling of water

Sinceth evolum eo fwate r inoutdoo r tanksvarie dwit h rainan devaporation , total masso fth ecompound sa tth esamplin g dateswer euse dfo rplottin g thedeclin e ofth ecom ­ poundswit htime . Becauseth ewate r sampleswithdraw n fromth etank swer e sometimes rather large (espe­ cially duringTria l 1wit h dimethoate),a correctio nfo rvolum e removedwa snecessar ybe ­ forecontinuou s declineplot s couldb emade . The discontinuities duet owate r sampling inth erelationshi p between themas s ofpes ­ ticidei nth ewate r compartmento na logarithmi c scaleagains t time couldb e eliminated withth efollowin g equations:

m = c x V n w,n w,n t = 0, n = 1 : m'. = m. n = 2 *1 : m'2 = m2/(1 n >, 3 : m' = m /(1 4 Vi n n K v ,/V ,)x ( 1- V IV ) U ) s.M-1'w,n-l JA "- ' s,l'w ,1 J in which

= integer,Samplin gN o(i ntim eseries ) (1) =measure dmas so fpesticid e inwate r compartment before Sampling n (mg) n 3 ow,n =mas s concentrationo fpesticid e inwate r compartment (intim eseries )(m gm" ) Vw,n= volum eo fwate r compartmentbefor e Sampling n (m3)

m'n =mas so fpesticid e inwate r compartment corrected forvolum eo f (mg) sampleswithdraw n Vs,n =volum eo £wate r sample (intim eseries ) (m3)

The correction steps (Equation 14)wer e introduced intoa nadapte d linear regression programo na Hewlet t Packard deskcalculator .Th efirst-orde r rate coefficients(*, . in d )fo rth edeclin eo fth esubstance s correspond toth eabsolut e valueo fth eregressio n coefficients ofth eregressio n lines forI n m'nagains t time. The differencesbetwee nth emeasure dmasse san dth ecorrecte d masses ofazinphos-me - thylan ddnnethoat e inth ewate rcompartmen to fth etanks ,du et owithdrawals , couldb e neglected inTrial s 2,3 an d4 becaus eth evolume swithdraw nwer e relatively small(0. 1 dm ) However,i nTrial s ^an d5 ,a correctio nwa snecessary ,becaus e thesampl e volume was dm Moreoveri nTria l Ï, samplingwa srathe r frequentan di nTria l5 als o water sampleso f2. 5d m were collectedfo rassessmen to fwate r quality.

62 Sampling of bottom material and GLC analysis

Thepenetratio no fdimethoat e into thebotto m layerwa smeasure ddurin gTria l 1. Bot­ tomsample swer e takenwit h tubesi ntriplicat eo n2 4Septembe ran d1 5Octobe r 1975 (Section4.4) .Th epenetratio no fazinphos-methy lwa s investigateddurin gTria l2 b ytak ­ ingmu dcore si nduplicat eo n1 0Jun e ando n1 5Jun e 1976.Th ecross-sectiona l areao f thebotto mmateria l columnswa s about 12.3c m. Themu d coreswer e storedi na deep-freeze ra t-2 0°C .A sth edevelopmen to fa suita ­ bleclean-u pmetho dfo razinphos-methy l tooksevera lmonths ,th estorag e timewa s nearly halfa year .Th estorag e time forbotto m coreswit hdimethoat ewa s lesstha non emonth . Thefroze nmu d columnswer e divided intoslice s1- 2c mthic kwit ha carborundu mhandsaw . Theslice swer eweighe d before extraction.Afte r extractionan ddryin ga t10 5 C,th edr y masso fth ebotto m materialwa s estimated.Th evolume so fth ewe tbotto mmateria lwer e calculatedfro mEquatio n 11.Th edept hbelo w the sediment-water interfacewa s calculated fromth evolum eo fth eslice ,an dth esurfac eo fth ebotto m column.Th esaw-cu twa s2 m m forth ehand-saw nmu dcolumns . Theprocedure sfo rextractio nan dclean-u po fth eextract sfo razinphos-methy lan d dimethoatear edescribe di nSection s 5.6, 5.7,5.1 1an d5.12 ,respectively .Th ecleane d extractswer e analysedb yGL Co nColum nI Ifo r azinphos-methylan do nColum n IIIfo rdime ­ thoate(Table s1 4an d 15). Ina separat e testth eeffec to fstorag e timeo nrecover yo fazinphos-methy l from frozenmu dcolumn swa s studied .Mu dsample swer eprepare d from1 0go fair-dr ybotto m ^ materialan d5 0cm 3o fwate ri na polyethylen e cup.Tnes esample swer e spikedwit hanalyti ­ cal-gradeazinphos-methy lan dstore da tabou t-2 0 °C.The ywer e extractedan danalyse daf ­ ter1 ,10 5an d24 2day si nth esam ewa ya sth eslice so fbotto mmateria l fromth e tank trials. Recovery from 16sample so fbotto mmateria l spikedwit hazinphos-methy lwa s 9U, »itha coefficien to fvariatio no f 1%(Sectio n 5.11).Afte r 105an d24 2days ,abou t90 . ** 102*o fth e initial amountswer e recovered,wit h coefficientso fvariatio no fabou t «*« , respectively. These results showtha ta correctio n factorfo rstorag e timewa sno t Pessary.Als on ocorrection swer emad efo rth erecovery .Th eaverag erecover yo fdime - thoatefro mbotto mmateria lwa s 95*.so no correction swer emad e forrecover yo fdimetho - ateeither . Asa resul to fth eproblem ,encountere di ndevelopmen to fsuitabl eclean-u pprocedure , «y afe wmeasurement s couldb edon eo npenetratio no fth ecompound s intoth ebotto mlaye r ofth etanks . 71 MEASUREDRATE SO FDECLIN EI NWATE R

^e plotso fth ecorrecte d masseso fazinphos-methy li nth ewate r «^^ ^ forTrial s2 to 5 ar eshow ni nFigur e 20.Plot s fordimethoat em Trials

Panted inFigur e 21. -nth etank swit hbotto mlaye r Differencesi ndeclin e rateo fth emode l compounds inth e tan* *« -d TIV)i nth e first three experiments (withoutadditio no fcoppe r sulphate) 63 mass of azinphos-methyl (mg) B mass of azinphos-methyl (mg) 20-h 20-

AF3 TZ(pHa2-*U)

. AF3 TXZ(pH76-10.S)

AF3 Tü{pHa8-iaa} A2 Ttt(pH89-103)

>2 TIEtpH9.1-11Û )

\AF3 TXL(pH04-10.7) I • | • • • I | I 10 15 tlme(d)

mass of azinphos-methyl (ma) 20-

mass of azinphos-methyl (mg) 20-1

AFC4 T2(pH7.8-a3) AFC4 TEt(pH7.7-8.3)

0.14 AC5 TlI(pH7.7-«2)

ACS ra

S Zin h methyll nWate r lytical^; adp ^f/ /' f" ««»Partnento foutdoo rtanks .A .Tria l2 : ana- Iddf n8"Juî y!976 nC 'ELlT " V^?1 3=f °™lated P^uct (Gusathtn25 2w.p. ) 5A gUSt ,976 C er sul hate tomas sconce nran"of" Cu^ S/Ä"! A^ T " ' °" ? ^ 8 31 20Septembe r1976 -coone r,„i nw. ^ ^^S" - D.Tria l5 :analytica lgrad eadde do n

SeptemberandTLthe T "^ nfoftobeTl nTr^W ^ 1 ^ ''" * *" °* '\ forvolum eo fsample swithdrawn .Fo rcoding" flin Lse fS e g.*"^ *"COrreCt 6 distinct.Th esam ehold sfo rrate so fdeclin ei nth etank swithou tbottom'materia l(T Van d WI)(Figure s20A ,B ;21A ,B,C) .Suc hdifference sca nprobabl ypartl yb eascribe dt odif ­ ferencesi nalga lbloom ,resultin gi ndifferen tp Han dligh tpenetration .I nTrial s4 an d S.wit hadditio no falgicide ,p Hfluctuation swer esmal l(Tabl e26) . Consequentlyth edif ­ ferencesi nth edeclin epatter no fth ecompound swer esmal l(Figure s20C ,D ;21D , E). betwel T fClln\Canb e d6SCribedWit ha first-orde rrat eequation ,th erelationshi p foTl s T *"' BS9° fth ePeStlCid em d time is "*«• Asca nb esee n 6 Pl tS the ^t f! ° ' «lationrixi pi salmos tlinea rfo ronl ypar to fth eperio do f dS Lr 7 PartS° fth ed6Clin ePl0tS 'linea rpressio n lineswer e calcula- 'dSL föS 6 fFigUre S 2°3n d21 -^ —P^ing rate'coefficientsfo r thl edeclin eo fbot hcompound sar egive ni nTabl e2 6

alsorathe rfas t T„L I S Wlth°Ut bottom layer> ^ decline waS lied same nk dL f " ^ ^ ^^ ™" ^ simultaneouslyt oth e M tank,declin eo fazinphos-methy lwa sfaste rtha no fdimethoat e(Tabl e26) ! mass of dimethoate (mg) 1.0' t«*Kte. I=i=.=4—*_•_ D1 TtttpH7.6-9.6 )

D1 TIZ(pH7.5-9.5)

35 40 time (d)

mass of dimethoate (mg) 20- mass of dimethoate (mg) 20-

DF3 TI(pHa2-10i)

DF3 TiKpHaa-ioe)

DF3 TÏKPH9.4-10.7: D2 TIZ(pHft1-110>

1 ' I ' ' ' ' | ' ' ' ' I 5 10 15 time(d)

mass of dimethoate (mg) 20>6- mass of dimethoate (mg) 20 DC5 TJZ(pH75-0.1)

DC5 TEI(pH7.0-a2) DFC4 mtpH7>ej)°- I •' ' ' I I ' ' i i I i T 20 25 5 10 15 20 25 tlme(d) time(d)

Hgure21 .Mas so fdimethoat e inwate rcompartmen to foutdoo rtanks .A Trial 1. nalyti "Igrad eadde d on2 3Septembe r 1975.B .Tria l 2:analytica lgrad eadde do n4 Jun e1976 . C Trial3 :formulate d product (Rogor40 %liquid )adde do n 15Jul y 1976 D ^ial4. as Wal 3adde do n5 Augus t .976;coppe rsulphat eadde dt o ^^^^ ££r ^^ gm 3o n4 August .E .Tria l5 :analytica lgrad eadde do n2 0Septembe rjy/e , PP V addedt omas sconcentratio n ofCu " 1.5g m" 3 on 19Septembe ran da f u her3^ » ™ I.October,m Trials 1(Fig .A )an d 5 (Fig.E) ,masse swer ecorrecte d forvolum eo fsample s withdrawn.Fo rcodin go f linesse eTabl e24 .

ïnfluence of pH and temperature on the decline rates

Therange so fp Hi nth ewate rcompartmen to fth edifferen ttanks ,measure di nperiod s

*h approximatelylinear'decline ,ar epresente di nTabl e26 .Th erange so fP Hduring^ac h J- areshow ,agains tth eregressio niine si nFibre s 20£ ^ÏZZÎl I in

ureasei nth edeclin erat ea tincreasin gp Hrange .Thi sindicate stna t * watercomparan ti sprobabl ya majo rfacto ri nth erat eo fdeclin eo f ^* ** thisreason ,rat ecoefficient sfo rdeclin eo fazinphos-methy lan d *£^»^ &st threetan ktrial s (withoutcoppe rsulphate )wer eplotte dagains tth e«™I * «

*W 22.a e scatteri nFigur e2 2result s fromth einfluenc eo fothe rma^o rfactor s ^erature,alga lbloo man dligh t (externalan di nth ewate rcompartment) .

65 Table 26.First-orde r rate coefficients fordeclin e of azinphos-methyl and dimethoate in water compartment of outdoor tanks.Derive d forperiod s with approximately linear rela­ tionships between mass of insecticide (logscale ) and time.Abbreviations : A for azinphos- -methyl,D fordimethoate ,F forformulate d compound, Cfo r copper sulphate addition and T for tank.

Time Information on water sy stems Azinphos-methyl Dimethoate period tank pH water code rate half code rate half No temp.( C ) for coeff. life for coeff. life trial (d-1) (d) trial (d-1) (d) 8:30h 16:00h av. range minimum maximum

1975 09-23/ II 8.2 9.6 16 12-17 Dl TII 0.14 5.0 09-27 IV 8.2 9.5 16 10-18 Dl TIV 0.12 5.6 09-28/ II 7.8 9.3 12 3-18 Dl TII 0.021 34 10-28 IV 7.5 9.1 12 5-17 Dl TIV 0.032 22 1976 II 8.9 9.7 19 10-24 A2 Til 0.23 3.0 D2 TII 0.22 3.2 06-04/ IV 9.3 10.6 21 10-28 A2TI V 0.72 1.0 D2 TIV 0.67 1.0 06-10 V 7.7 8.4 20 10-25 A2T V 0.19 3.7 D2 TV 0.013 53 VI 8.8 9.7 20 10-25 A2 TVI 0.26 2.7 D2 TVI 0.12 5.6 II 9.0 10.3 20 13-27 A2 TII 0.49 1.4 D2 TII 0.57 1.2 06-10/ IV 9.1 11.0 22 14-28 A2TI V 0.39 1.8 D2 TIV 0.59 1.2 06-30 V 8.1 9.5 20 14-26 A2T V 0.27 2.6 D2 TV 0.20 3.5 VI 8.9 9.7 20 14-26 A2TV I 0.40 1.7 D2 TVI 0.31 2.2 II 8.8 10.8 21 15-28 AF3 TII 0.59 1.2 DF3 TII 0.50 1.4 07-15/ IV 7.6 10.5 21 15-29 AF3TI V 0.41 1.7 DF3 TIV 0.25 2.8 07-30 V 8.2 10.2 21 15-30 AF3T V 0.17 4.0 DF3 TV 0.17 4.1 VI 9.4 10.7 21 15-30 AF3 TVI 1.1 0.63 DF3 TVI 0.80 0.87 08-05/ 7.8 \l 8.3 17 14-21 AFC4T V 0.25 2.8 DFC4 TV 0.036 19 08-09 VI 7.7 8.1 17 14-21 AFC4TV I 0.21 3.3 DFC4 TVI 0.010 67 08-09/ 8.2 v 8.3 20 17-24 AFC4T V 0.31 2.3 DFC4 TV 0.14 5.0 08-16 f\V I 8.2 8.3 20 17-24 AFC4TV I 0.36 1.9 DFC4 TVI 0.18 4.0 08-16/ v 8.2 8.3 19 11-24 AFC4T V 0.29 2.4 DFC4 TV 0.078 8.9 08-30 l VI 8.1 8.3 19 11-24 AFC4TV I 0.28 2.5 DFC4 TVI 0.11 6.5 II 7.7 8.8 15 11-24 AC5TI I 0.16 4.4 DC5 TII 0.055 13 09-20/ IV 7.5 8.0 16 12-23 AC5TI V 0.13 5.5 DC5 TIV 0.038 18 10-01 V 8.1 8.3 16 12-23 AC5T V 0.17 4.0 DC5 TV 0.089 7.8 VI 8.1 8.2 16 12-23 AC5 TVI 0.17 4.0 DC5 TVI 0.067 10 II 7.7 9.2 15 12-18 AC5TI I 0.095 7.3 DC5 TII 0.059 12 10-01/ IV 7.5 9.1 17 12-19 AC5TI V 0.14 5.0 DC5 TIV 0.052 13 10-13 V 7.9 8.1 15 12-19 AC5 T V 0.17 4.1 0.083 8.4 VI 7.9 8.1 DC5 TV 15 12-19 AC5 TVI 0.18 3.8 DC5 TVI 0.12 5.8

Extrapolationso fth erat ecoefficient sfo rdeclin eo fbot hcompound si nwate rt op H below8 ar erathe runcertain .Th ecoefficien tfo rdeclin eo fazinphos-methy li nsurfac e watera tp H7ma yb eles stha n0. 1d" 1 (t,> 7 d) .Th erat ecoefficien to fdimethoat ei n surfacewate rwit hp H7 coul db eles stha n0.0 1 d"1 (t >7 0d ) (Figure22) . Thetemperatur efluctuation si nth ewate rcompartment swer e rather large,rangin g from1 0t o3 0 Cdurin gth esumme ran dfro m3 t o2 4° Ci nth eautum n (Table 26). Average watertemperature swer ecalculate dfro mth ehighes tan dlowes twate r temperatures read

66 rate coefficient for decline (d~') 1.0-

0.1• 10

& i

1 A *

Figure22 .First-orde rrat ecoefficient sfo rdeclin e ofth emode lcompound si nth ewate r compartmento f outdoor tanksagains tmaximu mp Hdurin gTria l 1 to 3.Averag ewate r temperaturerange d from1 6t o2 2 °C. o= azinphos-methyl ,analytica lgrade ;• = azinphos - methyl25 %w.p. ;A = dimethoate ,analytica lgrade ; 0.01 "I 1 1 9 10 11 dimethoate,40 %liqui d p H A = fromminimum-maximu m thermometers.Th eaverag ewate rtemperatur ei nsumme rrange dfro m 17t o2 2° Can dthos ei nth eautum nfro m1 2t o1 7 C.

Thehighes trat eo fdeclin eo fazinphos-methy l (fcr= 1. 1d ", * ,= 0.6 3d )wa sfoun d ata combinatio no fth ehighes taverag ewate rtemperatur e2 1°C )an da hig hp Hranging ^ from9. 4t o10. 7(Tabl e 26).Th elowes trat eo fdeclin eo fazinphos-methy l (fcr= 0. 1d , h - 7.3d )wa smeasure di nth eTria l5 (wit hcoppe rsulphate) ,a ta naverag ewate rtemper ­ atureo f1 5° Can da p Hrang eo f7. 7t o9. 2(Tabl e 26).Th erat eo fdeclin eo fazmphos - -methylthu svarie db yabou ta facto rten . Therat eo fdeclin eo fdimethoat ei nth etrial svarie db yabou ta facto r80 .Th elow ­

estrat eo fdeclin e( *=0.0 1d" \ tL - 67d )wa sfoun da ta naverag ewate rtemperatur e of1 7° Can da ta P Hrang efro m7. 7t o8.1 ,i nth epresenc eo fcoppe rsulphat e (Table26) . 1 ^e declinewa sfastes t C*r= 0.8 0d" ,* ,= 0.8 7d )fo rth ehighes taverag ewate rtermper - ature(2 1°C )an dth ehig hp Hrang e (9.4-10.7).

Effeet of formulation

Therate so fdeclin eo fth emode lcompound sapplie da sanalytica lgrad eo r«.formula ­ tedproduct si nth ewate rcompartment ,durin gTrial s1 t o3 ma yb ecompare d nJ^J' * cleardifferenc ei nrat eo fdeclin ecoul db eobserve dbetwee nazxnphos-,^ s a^yt -I gradean d23 ,w. ,Th e« holdsfo r^ -^„^^^i^ aPPlieda sanalytica l gradeo ra s m liquid.Fo rpossibl eeffect s ^itiont ocoppe rsulphat eo nth edelin erate so fbot hcompounds ,n oclea rtrend s found.

67 Effect of copper sulphate

Additiono fcoppe rsulphat et oth ereplenishe dwate r compartments strongly retarded growtho falgae ,s otha tp Hfluctuation swer estrongl y suppressed (Table 26,Trial s4 an d 5). Howeverdurin gTria l5 i nTank sI Ian dI V(wit hbotto m layer), this suppressionwa s onlytemporary ,probabl y duet oadsorptio no fcoppe r sulphateo nth ebotto mmaterial . In Trial5 ,rate so fdeclin eo fbot hcompound si ntank swit hbotto mmateria lwer e slowertha n thosei ntank swithou tbotto mmaterial ,despit eth econsiderabl y higherp Hi nth e tanks withbotto mmateria l (Table 26). Oneexplanatio nmigh tb ea decreas ei nth e catalyticac ­ tivityo fcoppe rsulphate ,b yadsorptio no nbotto mmaterial .Anothe r explanationmigh tb e thatth ecleane dan dreplenishe d tankswithou tbotto mmateria l alloweda greate r lightpen ­ etrationtha nth e tankswit ha botto mlayer ,containin g alsosom e algaei nth ewate rcom ­ partment.I nvie wo fth efaste rconversio nrat eo fbot hcompound si nsurfac ewate r after additiono fcoppe rsulphat ei nlaborator y tests (Sections6. 2an d 6.3),th eforme rexpla ­ nationseem s tob emor elikely .

Effects of adsorption onto bottom material

Insituation swit ha fas tadsorptio no fth e insecticides onto thebotto mmaterial ,a fastdeclin ea tth ebeginnin go fth etrial sma yb eexpected .I nsuc hcases ,th eintercep t attim e zeroi slower .Th eplot s forth edeclin eo fdimethoat edi dno t show suchlo w intercepts.Som eo fth edeclin eplot s forazinphos-methy lclearl y showeda lowe r intercept thanth eamoun tintroduce d (linesA 2TIV ,AF 3TI Ian dAF 3TI Vi nFigure s 20A,B) .Howeve r theregressio nline s forA 2TII ,AC STI Ian dAC STI Vdi dno t clearly indicatea fas tad ­ sorptiono fazinphos-methy lo nth ebotto mmaterial . Becauseo fth e largefluctuation s inp Hi nth e tank trials,i ti sdifficul tt odra w conclusionso nth eeffec to fbotto mmateria lo nth erat eo fdeclin eo feithe r compound. Therate so fdeclin eo fbot hmode lcompound sdurin gTrial s2 an d3 wer e fasteri ntank s witha botto mlaye rexcep tfo rAF 3TV Ian dDF 3TV I (Figures 20Ban d21C) .However ,th eex ­ tremely fastdeclin eo fazinphos-irethy lan ddimethoat ei nTan kV Idurin g Trial3 ca nb eex ­ plainedb yth eextremel yhig hp Hrang eo f9. 4t o 10.7 (Table26) .

7.4 MEASUREDPENETRATIO N INTOBOTTO MMATERIA L

Masseso fazinphos-methy lmeasure di nextract so fslice so fbotto mmateria l during Trial2 ar epresente di nTabl e27 . Themasse so fazinphos-methy li nth euppe rslice swer egenerall y muchhighe r thani n thelowe rslices .Ove rth edept h investigated (0-6 cm),a distinc tpenetratio no fazinphos - -methylwa sfound .Th edifference si nth emasse s forduplicat e columnswer e large.Th edif - TWkS lrmd IVWer e alS°larg e(Tabl e »"Al -unts ofazinphos - ZZl Tl iaye ro fTm ki vca nparti ybe ^- ^ £ ZT^ZT:: —- *•** —- ° ted anTcoT1 T*- f aZlnph°S-methyl in «" b°"om compartment of the tanks was calcula- and compared with nasses of azinphos-methyl in the water compartment (Table 28). After 68 Table 27. Measured penetration of azinphos-methyl in the bottom layer during outdoor tank Trial 2 started on 4 June 1976. Masses of azinphos- ethyl per column slice.

Date Tank Slice1 Layer inbotto m Masso fazinphos - No No (m) -methyl(ng )

10Jun e TI I la 0 - 0.023 860 lb 0 - 0.020 1650 2a 0.025 - 0.047 81 2b 0.022 - 0.038 320 3a 0.049 - 0.066 65 3b 0.040 - 0.056 30 _2 TI V la 0 - 0.017 lb 0 - 0.017 130 2a 0.019 - 0.037 44 2b 0.019 - 0.041 28 3a 0.039 - 0.054 26 3b 0.043 - 0.064 26 15Jun e TI I la 0 - 0.017 820 lb 0 - 0.019 300 2a 0.019 - 0.035 160 2b 0.021 - 0.035 36 3a 0.037 - 0.051 10 3b 0.037 - 0.051 33 TI V la 0 - 0.020 190 lb 0 - 0.026 48 2a 0.022 - 0.044 33 2b 0.028 - 0.047 23 3a 0.046 - 0.079 <1 0 3b 0.049 - 0.062 < 9

1.Slic eN o1 , 2an d 3 arefirst , second and thirdslice ;a an db refert oduplicat es amples. _2-Failur ei nanalv s is.

5-5 days, the mass fractions of azinphos-methyl in the bottom compartment of T^ks I and IV were 17 and 27». respectively in the total masses recovered in the tank. Af r 1 days, these values were 55 and 111, respectively. They indicate that the rate of dec no ,„ „ fnctpr than the rate oi decline in azinphos-methyl in the water compartment was probably K1taster the bottom material.

Ia^e 28. Mass of azinphos-methyl in the water compartment (m^) a "d bottom compartment (m. b) of Tanks II and IV during the sec°nd tank experiment started on 4 June 1976. __

Azinphos-methyl

m7,A,b" Km.' A, w + w,A, ,) b

69 Masseso fdimethoat ei nextract so fslice so fbotto mmateria ldurin gTria l 1ar e showni nTabl e29 . Themasse so fdimethoat ei nth euppe rslice swer ehighe rtha ni nth elowe rslices , butno ta sdistinc ta sfo razinphos-methyl .Th edifference sbetwee nth ethre ecolumn sfo r eachtan kwer erathe rsmal lan dth edifference sbetwee nTank sI Ian dI Vwer eals osmal l (Table 29). After2 2days ,th etota lmas so fdimethoat ei nth ebotto mlaye rwa s6 1y g fo rTan k IIan d3 8y gfo rTan kIV .Th emasse so fdimethoat emeasure di nth ewate rcompartment so f TankI Ian dI Vwer ethe nabou t28 0yg .Th emas sfractio no fdimethoat ei nth ebotto mlaye r wasthu s18 %o fth etota lrecover yi nTan kI Ian d 12%i nTan kIV .Thes evalue sar econsid ­ erablylowe rtha nth epercentage sobtaine dfo razinphos-methyl .Th emai nreaso nfo rth e behaviouri sth emuc hlowe radsorptio no fdimethoate .

7.5 GENERALDISCUSSIO NO NOUTDOO RTANK STRIAL S

Outdoortrial si nwate rtank sma ysho wth erat eo fdeclin eunde rfiel dcondition s andit svariation .However ,wel ldefine dan dmor eeasil ycontrollabl e testsunde rlabora ­ torycondition sar eneede dt oanalys ei nmor edetai lth erelativel yimportanc eo fth evar ­ iousprocesses . Thedeclin eo fazinphos-methy lan ddimethoat ei nth ewate rcompartmen to foutdoo r tankswa smuc hfaste rtha nth econversion ,measure di nth elaborator yi nth edark .Th e effecto fligh to nth erat eo fdeclin eo fbot hcompound swa sthu sconsiderable .Therefor e laboratorytest si nth edar khav eonl ylimite dvalu efo rpredictin gth edeclin erat eo f pesticidesi noutdoo raquati csystems .I nth elaboratory ,mor eresearc hi sneede dt oas ­ sessth eeffec to flight .

Table29 .Measure dpenetratio no fdimethoat ei nth ebotto mlaye r duringoutdoo r tankTria l1 starte do n2 3Septembe r 1975.Masse so f dimethoatepe rcolum nslice .

Date Tank Slice1 Layer in Masso f No No bottorti dimethoate (m) (ng)

15Octobe r TI I la 0 -0.01 1 81 lb 0 -0.01 0 79 lc 0 -0.01 0 _2 2a 0.013 -0.02 4 41 2b 0.012 -0.02 3 50 2c 0.012 -0.02 3 42 TI V la 0 -0.01 1 43 lb 0 -0.01 2 61 lc 0 -0.01 3 52 2a 0.013 -0.02 5 31 2b 0.014 -0.02 5 28 2c 0.015 -0.02 6 18 1.Slic eN o] an d2 arefirs tan dsecon ds i ice;a ,b an dc ' refert otriplicat e columns. 2.Failur ei nanalysis .

70 Tank trials are useful in studies on the decline of pesticides in the field. However, even tank trials are rather complex. Algal bloom can easily occur and causes, for instance fluctuation in pH and, variation in light penetration. Tank systems with almost the same initial situation may develop differently. The pH of the water was a major factor in decline of both model compounds. The pH in many surface waters will not be as high as in these trials, and in general the decline will probably be slower. In shallow, relatively small ditches, however, the same kind of development may occur. More detailed measurements of pH and temperature (preferably con­ tinuous) are needed in future tank trials. A bottom layer in the tank did not determine the decline of compounds in the water compartment. Aclea r effect of formulations of both compounds on the rates of decline could not be found. Copper sulphate suppressed algal bloom and prevented pH fluctuation. However, the influence of Cu2+ on the decline rate of both compounds in light could not yet be analysed. With a bottom layer, Cu2+ seemed to be inactivated rapidly. A distinct penetration of the compounds into the bottom layer was detected. The con­ centration patterns measured would result from diffusion in combination with adsorption, with unknown contributions from mixing by organisms and disturbance of the bottom layer during sampling. Another mechanism for the transfer of pesticides to the bottom may be the deposition with phytoplankton and suspended solids. The measurements on azinphos-methyl indicated that the decline in the bottom compart­ ment was probably slower than in the water compartment. By using computer simulations on the behaviour of pesticides in aquatic systems with a bottom layer, the contribution of a bottom layer on the rate of decline can be better evaluated (Chapter 8). The results of these outdoor tank trials will be compared with those from measure­ ments in the field, especially in ditches with standing water (Chapter 9).

71 8 Computation model on the behaviour of pesticides in a tank of water with a bottom layer

8.1 INTRODUCTION

A computationmode lwa sbuil t todescrib eth ebehaviou ro fpesticide s ina wate r tankwit ha botto m layer.Suc ha mode lca nb ehelpfu l inevaluatin g theresult so fth e tank trials (Chapter 7)i nmor edetail .Besides ,thi s model canb ea goo d starting point forth ecomputation so nditc hsections . Inth ecomputatio nmodel ,som e simplifying assumptions were made. Introductiono fth e pesticideswa sassume d tob einitiall y mixed evenly throughout thewate r compartmento fa tank.Pesticide s movementh y diffusion from thewater-sedimen t interface intoth ebotto m layerwa sdescribe d ina one-dimensiona l system.Adsoxptio n equilibriumwa s assumed tob e established instantaneously. Therate sfo rdecompositio no fth einsecticide s inwate ran d inbotto m materialwer e different.Th emos t reliable data availablewer e introduced into themodels . By comparingth eresult so fcomputation swit h thoseo fmeasurement s inth eoutdoo r tanks themos t important shortcomingsi nth ecomputatio n modelan di nth edat aca nb e traced. Finally,th ecomputatio nmode li suse dfo ra fe wsimulatio n experimentso nth ebehav - Zl Î V7-TdeS ln m aqUatlCSySt6 mWlt ha b°tt0m la^- Pesticide characteristics nt l TZ COeffiCientl nth ellqUi dPhaS e° f ** b0ttOm> *» ^«ptioncoeffi - v iedt COnVerSi0nl n b°tt0m material «*th erat eo f —ion inwate r were tatl0nS behelPfU ll neValUatln gth erelativ e I 'iTTh T ^ Stanc e ofpara ­ metersi nth ebehaviou ro fpesticide si nwate rsystems .

8.2 DERIVATIONO FTH EEQUATION S », z1^f*B "tr throushbot,o m- ,eriai* diffci»* * •"* "*-•

c 3c /3s "dif.ib- " dif,ib ib (15) inwhic h j-rii .= arei cmas s fluxb ydiffusio ni nbotto mmateria l (mgm a J dif.ib 2,-1- , ödifl b= diffusion coefficiento fsubstanc e inliqui d phaseo f [m a j bottom material c,, =mas s concentrationo fsubstanc ei nliqui d phaseo fbotto m (mgm J material z =dept hi nbotto m W 72 The diffusion coefficient of substance in liquid phase (Graham-Bryce, 1969; Frissel et al., 1970) D,.~ ,, was calculated from

Ddif,lb = h El Ddif,w ™ inwhic h ƒ, =labyrint ho r tortuosityfactor :rati oo fsurfac eare ao fbotto m 0) materialt oliqui dphas e

e1 =volum e fractiono f liquid:volum eo fliqui ddivide db yvolum eo f (1) bottommateria l 2- 1 ödif =diffusio ncoefficien to fsubstanc ei nwate r (md )

Forth econversio no fth esubstanc e inwate ran di nbotto mlayer ,first-orde rrat e equationswer eused :

(17) c,w~ c,w cw

J Ä, =rat eo fconversio ni nwate r W* _1 fcc'w= rat ecoefficien t forconversio no fsubstanc ei nwate r (d ) ° '= mas s concentrationo fsubstanc e inwate r (m2m •>

A similarequatio ni suse d forth ebotto mlayer :

(18) *"c,. bu-= *c,k _u b a % m which -3-1 Ä •i (mgm d ) cu =rat eo fconversio ni nbotto mmateria l , k' =rat ecoefficien t forconversio no fsubstanc ei nbotto mmateria l (d ) % =mas s concentrationo fsubstanc ei nbotto mmateria l

T*erelevan tconservatio nequatio n forth epesticid ei nth ewate rcompartmen twit h volume vwa s (19) 3^w

Forth ebotto mmaterial ,th econservatio nequatio no fth epesticid ewa s (20) V3t =-^if.ih/ 8s -R, dif,lb/8s" Ä c,b 73 Theadsorption—desorptio nequilibriu mwa sassume dt oestablis h instantaneously, whileth eadsorptio nisother mwa stake na slinear .Th erelationshi pbetwee nth econcentra ­ tiono fth esubstanc ei nth eliqui dphas e (c^)an dtha ti nbotto mmateria l (c) i s then:

clb" V( £l +p b*s/l } (2D

inwhic h = dl bul k _ Pb ( y) densityo fbotto mmateria l (kg m 3^ *s/l= distributi °nquotien tsolid/liqui d (oradsorptio ncoefficient ) (m3kg" 1)

8.3 DESIGNO FTH ECOMPUTATION S

These to fequation s (15t o21 )wa ssolve dnumericall y afterprogrammin gi nth ecom ­ puterlanguag eCSM PII I (IBM,1975) .Th eprogra mwa sru no nth eDECsystem-1 0compute ro f theAgricultura lUniversity ,Wageningen .Th elistin go fth ecompute rprogra mo nth ebehav ­ iouro fazmphos-methy lan ddimethoat ei ntank swit hwate ran dbotto mmateria li sshow n m AppendixA . Inth erun ssimulatin gTan kTria l2 i nJun e 1976,th einitia lmas swa s 13.2m go f azinphos-methyli nTan k IIan d 13.1m gi nTan k IV.Th einitia lmas so f1m go fdimethoat e

corresponded toth edos eapplie dt oTank sI Ian d IVdurin gTria l1 i nth eautum no f197 5 (Chapter7) .Th edos ewa sassume dt ob eimmediatel yevenl ydistribute di nth ewate rcom ­ partment,whil eth einitia lmasse si nth ebotto mcompartment swer e zero.Th edownwar d areicmas sflu xfro mth elowes tbotto mcompartmen t (wallo fth etank )wa sse ta t zero. Sincevolatilizatio no fth emode lcompound sfro mth ewate rsurfac ewa sver yslow ,thi s processwa sno tintroduce d intoth ecomputatio nmode l (Section3 5 ) Thevolum eo fwate ri nth etank swa s introduceda sa functio no ftim eaccordin gt o ^measurementsdurin gth etan ktrials .Th esurfac eare ao fth ebotto mwa s0. 6

a I,V mthiCk )Wa SdiVid6 d int°1 0 C°TOi0n cements,wit hgraduall y TZZIT:5 fr°mt0 Pt 0b0tt0 m^^ ^ **»• VI."«.Th ethicknes l COmPartmentWa S 01m 6ffeCtS f opltb t °-° -^ ° *««« * thicknesso fth e nZ a TtCOmPartmenweret8n checked ddlfferen atemUlti bui kdensitP licatiy- retorso nth eaccurac yo fth e rb rr: - • * *»^ f^ono fL ^ of the bottoms ofTank s „and IV were both introduced as a function of depth (Figure 19).

04 1Tn*y?l Tnt °f aZinph0S-me^ in -ter at 20 °C was estLSd to be CalCUlati n methods am va !e 2 ,' TZ " * ° *™ by Reid & Shenvood (1966). The same value was calculated for dimethoate ata wate r temperature of 15° C introd^edlTfl7 T"f1 *T ^^ ^ ** ^ ^ ^ ^ *>«« - o. r ,. o :rn ° 3ï3ztwa s °-°3> °^ »•». °.« - o. ^ - , , 2 0 r6SpeCtlVely acCordin 50 m fcr E l 0 0 Leisr a( 17 FQ „ ' ' S toa literatur ecompilatio nb y £r n ta nth e t0rtU Sity faCt0r t Tnin etortuosit uo L ktyfactor ' sTi nth e °rane eabov p ° - r, an ™ .. *» * * thelitera - lationwit hth emaximu mvalu e* =n o /j -0.5 wereobtaine db ylinea rintexpo - stancei nth elimn dr*n c K * * diffusioncoefficien to fth esub - theliqui dphas ebetwee ntw obotto mcompartment swa scompute db ylinea rinterpo - 74 lation. Themeasure d adsorption coefficient K, ,o fazinphos-methy lont obotto mmateria li n •7 i s/i 3 _1 thetank swa s 0.073m kg-1.Th ecoefficien t K^ fordimethoat ewa s0.003 2m kg as measuredfo rfreshl y sampled bottommateria l (Chapter6) . Therat e coefficients k ,fo rconversio no fbot h compounds inth ebotto mo fTank s IIan dI Vwer e derived fromth evalue smeasure di nincubatio n testswit h systemso ffres h bottommateria li nwate ri nth elaborator y (Chapter 6).Th ecoefficien t kQ^ ofazinphos - 1 -methyla t2 0° Cwa s 0.073d" (Table 21).Th ek Qb for dimethoatea t1 5° Cwa s0.0 1d (Table22) . The rate coefficients k forconversio no fbot h compoundsi nth ewate r compartments c w ofTank sI Ian dI Vwer ei nth éfirs t instancese tequa lt oth emeasure d rate coefficients fordeclin eo fbot h compoundsa stabulate d inTabl e 26.Bu tth elatte rcoefficient s include theprocesse so fadsorptio n ontoan ddiffusio n into thebotto m layer,s otha tth eactua l ratecoefficien tfo rconversio ni nth ewate r compartmentwoul d havebee n lower thanth e ratecoefficient s fordecline ,especiall y duringth efirs tperio do fth e outdoor trials. Therefore,als o lower rate coefficients forconversio ni nth ewate r compartmentwer ein ­ troduced whichwer e0. 9time s themeasure d rate coefficients for decline (Table 26).Thes e lowerrat e coefficients were introduced toestimat eth erelativ e contributiono fconver ­ sion,penetratio nan dadsorptio nt oth edecline . The computations were carried outwit h Runge-Kutta's (RKS)integratio n methodove ra periodo f2 7days .Th eintegratio n procedure useda variabl e time-stept ominimiz eth e integration error.A tregula r intervals during computations,th esimulate d material bal­ anceo fth epesticid ei nth etan k systemwa s checked.

8.4 RESULTSO FTH ESIMULATION SO FTAN K TRIALS

Amounts in water compartment and bottom compartments

The computed andmeasure d masseso fazinphos-methy l inth ewate r compartmentan di n thebotto m compartmentso fTank sI Ian dI Va sa functio no ftim ear egive ni nFigur e23 . The samekin do fplot s for dimethoatear eshow ni nFigur e 24.Th efigure s show thatth e differences between themeasure dan dcompute dmas so fbot h compoundsi nth ewate rcompart ­ mentwer eusuall y small.Whe n the rate coefficientso fconversio no fth ecompound swer e seta t90° ,o fth emeasure d coefficientso fdecline ,onl y slightlyhighe rmasse si nth e wateran dbotto m compartment were computed (Figures2 3an d24) .Th econtributio no fpene ­ tration intoth ebotto m layert odeclin eo fbot h compoundsi nth ewate r layerwa s only lim­ ited. Forbot h outdoor trials,th ecompute d masso fsubstanc ei nth ebotto mlaye rwa s nearly always less than 10%o fth e dose.Th emateria lbalance so fbot hpesticide s inth e tank systemafte ra computatio n timeo f2 7d ar e showni nTabl e 30.Decreasin gth erat e coefficiento fconversio nb y10 »resulte d innearl yth esam emateria l balance forazinphos - -methyl.Howeve r fordimethoate ,i tresulte di nsomewha thighe rmasse si nth ewate ran di n thebotto m (Table 30). , The limitedmeasurement so nazinphos-methy lan ddimethoat ei nth ebotto m layerd o not allowdetaile d comparisonbetwee nmeasure dan dcalculate d resultsfo r thebotto m layer. Inal l trials,th ecalculate d masseso fazinphos-methy lan ddimethoat ei nth ebotto m mass of substance in water mass of substance in bottom material 15-1 t5-i

i I i i i i I• i i i I 10 20 30

15-1

T°| II I• | I 10 20 n 30 Figure23 .Mas so fazinphos-methy li nwate ran d inbotto mmateria lo fTank s IIan d IV. = computedmas s (fecw =0. 9 fer); =compute d mass (kc w = kr); o= measure d datao fTan kTria l 2i nJun e 1976 (Chapter 7).Vertica lbar sar e rangei nmas so fsubstanc ei nth ewhol ebotto m materialestimate d fromduplicat ebotto mcolumns .

layerwer ehighe rtha nth emeasure dmasse s (Figures2 3an d24) . Thismigh tb ecause db y anincomplet emixin gi nth ewate rdurin gth e outdoor trials.Anothe r reasoncoul db ea fasterrat eo fconversio ni nbotto mmateria lunde rth eoutdoo rsituation s thanunde rth e laboratory conditions.Furthe rto o higha valu eo fth etortuosit y factora thig h e,wil l resulti na noverestimat eo fth emasse spenetratin g thebotto m layer. Comparisonsbetwee nth emeasure dan dcompute d concentrationso fazinphos-methy lan d dimethoatea tvariou s depthsi nth ebotto m layerar eshow ni nFigure s2 5an d26 ,respec ­ tively.Th ecompute ddept ho fpenetratio no fazinphos-methy lwa sver y small.Afte r 11d nearly allth eremainin g azinphos-methylwa s computedt ob estil li nth e upper 0.02m o f thebottom .Howeve ri nth e tanktrials ,smal lamount so fazinphos-methy l were recovered frombotto mmateria lbelo w0.0 2m dept h (Figure 25). Thisma yb ecause db ydisturbanc e ofth ebotto m layerb ysamplin go rb yorganisms . The calculatedpenetratio n deptho fdimethoat ewa s largertha no fazinphos-methy l (Figures2 5an d26) , themai nreaso nbein g themuc h loweradsorptio no fdimethoate . Thecalculate ddept ho fpenetratio n fordimethoat ewa s significantlymor e thansam ­ pleddurin gth etrial .Fo rth ecompariso no fcompute dan dmeasure dmasse si nth ebotto m layer (Figure 24),a correctio nwa snecessar yfo rth emas so fdimethoat e thatpenetrate d belowth e sampleddept ho fabou t0.02 5m .Thes emasse swer e calculatedwit hth ecomputa ­ tionmode lt ob eabou t 251o fth ecompute dmas si nth ebotto m layer forbot h tanksI Ian d IV (Figure 24,crosses) .Thes ecorrecte dvalue s showa smalle rdeviatio nfro mth ecompu ­ tedmasse spenetrate d thanth emeasure dvalues .

76 masso tsubstanc e in water mass of substance in bottom material (mg) 0.15-*

0.10H

0.05

• | < i i i | i i i i | 0 | i i i i | i i i i | i i l i | 10 20 30 0 10 20 30

1.5- 0.15-

W-, 0.10H V TET 05- OOS- ^ï^ï=B*=o=o*-

Q 1 i I i i i i I i i ' 1 ' I ' ' • ' I (3 30 10 20 30 10 20 time (d) Figure24 .Mas so fdimethoat e inwate ran di n bottommateria l ofTank s IIan d IV. =com ­ putedmas s (fe w =0. 9 fcr); =compute d mass (fec„= ii'); o= measure d datao f theTan k Trial li nSeptembe r 1975 (Chapter 7); X= valu e corrected forpenetratio n lossesbelo wsample d depth (Section8.4) .Vertica lbar sar erang ei n masso fsubstanc e inth ewhol ebotto mmateria l estimated from triplicatebotto mcolumns .

Comparisono fth efe wpenetratio nmeasurement swit hth ecompute dresult sindicat e thati nfutur epenetratio ntrial sfo rcompound swit hrelativel yhig hadsorptio ncoeffi ­ cients,thi nslice so fbotto mmateria lshoul db eanalyse da tappropriat etim eintervals . Withlo wadsorption ,penetratio nmus tb estudie dt ogreate rdepth stha ni nthi sstudy .

Table30 .Compute d itemso fth emateria lbalanc eo fazinphos-methy lan d dimethoate ina simulate d tanksyste mafte r 27d .

Compound Tank Ratecoeff . Fractiono f initialamoun t (%) k 1 • _ c,w remaining converted

in in in in water bottom water bottom

0.0 0.8 90.8 8.4 Azinphos- II k 8.9 -methyl 0Ï9 k 0.1 0.9 90.1 96.3 3.4 IV k 0.0 0.3 95.9 3.8 0Ï9 k 0.0 0.3 r 63.2 2.2 Dimethoate II 25.0 9.6 k 60.2 2.3 0^9 k 27.2 10.3 r 66.7 2.1 IV k 22.6 8.6 25.1 9.3 63.4 2.2 0Ï9 k 0.9 k i. k k r (Table26 )o r k c,w

77 mass concentration (mg m ) 400 J

TECafte r lldays

depth inbotto m (m) Figure25 .Mas sconcentration s ofazinphos-methy l inth ebotto mmateria lo fTank s IIan d IV. = computedmas sconcentratio n (kc w =0, 9 kv); = computedmas sconcentratio n (kc w =fe r);o = meas ­ ureddat ao fTan kTria l2 i nJun e 1976(Chapte r7) . Horizontalbar sar erang ei nconcentratio no fsub ­ stancei nslice so fduplicat ebotto mcores .Verti ­ calbar sar eaverag e thicknesso fth ebotto mslices .

mass concentration (mg ni* ) c 0 5 ?„'. • —i • ' i i 'Vi. - T IJl

/ TK 0.05J 005-

depth in bottom (m)

Figure26 .Mas sconcentration s ofdimethoat ei n thebotto mmateria lo fTank s IIan d IVafte r2 2 days. =compute dmas sconcentratio n (k c c'.y c,w fer);o » measure ddat ao fTan kTria l2 i nJun e 1976(Chapte r 7).Horizonta lbar sar erang ei n concentrationo fsubstanc ei nslice so fdupli ­ catebotto mcores .Vertica lbar sar eaverag e thicknesso fth ebotto mslices .

78 Thecompute dresults ,showe dtha ti nsituation swit hhig hconversio nrate si nth e watercompartmen tonly ,comparativel y smallamount spenetrate dth ebotto mlayer ,eve nfo r substanceslik eazinphos-methyl ,whic har estrongl yadsorbed .Furthe rtrial so npenetra ­ tionwil lb eneede dt overif y thevariou sassumption san dt oimprov eth eapproximation s ofth ecomputatio nmodel .

8.5 DESIGNO FTH ESIMULATIO NEXPERIMENT S

Simulationexperiment so nth econversio no fpesticide s inth ewate rcompartmen tan d thepenetratio nint oa botto mlaye rwer ecarrie dou twit hth esam ecomputatio nmode la s describedi nSectio n8.3 .The ywer eintende dt otes tth esensitivit yo fth emode lsyste m tochange si nvariou sparameters ,especiall yfo rthos ewhic hvar ystrongl y inpractic e andthos ewhic hwer equit euncertain .Th eparameter s thatwer evarie di nth edifferen t computerrun sar egive ni nTabl e31 . Foral lrun sth einitia lmas si nth ewate rcompartmen twa sse ta t10 0m go fpesticid e anda tzer ofo rth ebotto mcompartment .Th evolum eo fwate ri nth etan kwa shel dconstan t andth esurfac eare ao fth ebotto mlaye rwa stake nt ob e 1m .I nRun s10 ,1 1an d 12,th e effecto fdifferen twate rdepth so nth erelativ eamoun to fpesticid etha tpenetrate dth e bottomlaye rwa scomputed .Th ebotto mlaye rwa sdivide d into1 0compartment swit hincreas ­ ingthickness .Th ethicknes so fth euppe rbotto mcompartmen twa s0.00 1 man dth emulti ­

plicationfacto r Of)wa s 1.5.I nsituation swit hhig hrat ecoefficien t forconversio no f thesubstanc ei nth ebotto mlaye ro rwit hhig hadsorptio ncoefficients ,th ethicknes s ofth euppe rbotto mcompartmen twa sse ta t0.000 5m .Th ebul kdensit y increasedlinearl y from20 0k gm~ 3 atth esediment—wate rinterfac et o68 0k gm " at0. 2m depth .Th evolum e

Table31 .Parameter s introduced intoth ecompute rrun so fth esimulatio nexperiments .

Ruri Wate r Diffusion Maximum Adsorption Bottom material Water No depth coeii tortuosity coeff. (m) ini «ater factor (m3 kg-1) rate coeff. half rate coeff. half (m2 d--1) (1) of conversion life of conversion life (d-1) (d) (d"1) (d)

0.0 1 0.4 0.2 X >°1 1.0 0.0 0.0 2 0.4 0.3 X lu"* 1.0 0.0 0.0 0.0 3 0.4 0.4 X 1.0 0.0 0.0 0.0 4 0.4 0.4 X '°1 0.75 0.0 0.0 0.0 5 0.4 0.4 X >°">°1A 0.5 0.0 0.0 0.0 6 0.4 0.4 X lu"* 1.0 0.001 0.0 0.0 7 0.01 0.0 0.0 0.4 0.4 X >0"A 1.0 8 0.4 0.4 X 10-* 1.0 0.1 0.0 0.0 9 0.4 0.4 X lu"* 1.0 1.0 0.0 0.0 10 0.3 0.4 X IQ"* 1.0 0.1 0.0 0.0 11 0.2 0.4 X ID"* 1.0 0.1 0.0 0.0 12 0.1 0.4 X 1.0 0.1 0.0 0.0 13 0.4 0.4 X IQ">°1* 1.0 0.1 0.00693 100 0.0 14 0.4 0.4 X lu"* 1.0 0.1 0.0693 10 0.0 15 0.4 0.4 X 10"* 1.0 0.1 0.693 1 0.0 0.00693 16 0.4 0.4 X 10* 1. 0 0.1 0.0693 10 100 0.0693 17 0.4 0.4 X -4 1.0 0.1 0.0693 10 10 -4 0.693 18 0.4 0.4 X 1i0o; 1.0 0.1 0.0693 10 1

79 fractiono fliqui ddecrease dlinearl yove rth esam edistanc efro m0.9 2 to0.74 . InRun s1 t o3 ,differen tdiffusio ncoefficient so fth epesticid e inbul kwate rwer e introduced.Ther ewa sn oconversio no fth esubstanc ei nth ebotto mmateria lan dwater ,an d adsorptioni nth ebotto mwa szero .I nRun s4 an d5 ,differen trelationship sfo rth etor ­ tuosityfactor ,ƒ, ,wer eobtaine db yinterpolatin glinearl yt oth evalue s f^ =0.7 5 (Run4 )an dƒ .= 0. 5(Ru n5 )a tvolum efractio no fliqui de =1.0 .I nfou rrun s (No6 to9) , adsorptioncoefficient so fpesticide so nth ebotto mmateria lrange dfro mfairl y low (0.001m 3kg" 1)t over yhig h (1m 3 kg"1). Therat ecoefficient sfo rconversio no fth esubstanc ei nth ebotto mlaye rwer evarie d fromlo wt ohig hi nRun s1 3t o15 .Finall yth emos trealisti csituation swer esimulate di n Runs1 6t o18 ,introducin gals ovariou srat ecoefficient sfo rconversio ni nth ewate rcom ­ partmento fth esystem .

8.6 RESULTSO FTH ESIMULATIO NEXPERIMENT S

Masses in water compartment and bottom compartments

Theresult swit hdifferen tvalue so fth ediffusio ncoefficien to fth esubstanc ei n bulkwate rar eshow ni nFigur e27A .Diffusio nint oth ebotto mlaye rwa sonl yslow :afte r 27day s5. 4 to7.5 1o fth einitia ldos ewa stransporte dint oth ebotto mlayer .I nth e nexttw orun s (No4 an d 5),wit hdifferen textrapolation so fth etortuosit yfactor ,th e

masso f substancei nwate r masso f substance in bottom material 00- (mg) (mg) G kN 96- ^ ;> •<=^ 92- ~~i w i i ! i i

Figure27 .Mas so fsubstanc ei nwate rcompartmen t andbotto mcompartment scompute dwit h thetan k model.Number srefe rt oth ecompute rrun sliste d inTabl e31 .

80 penetrationwa s only slightly slower thancompute di nRu n3 (Figure s 27B).Thu s theuncer ­ taintiesi nth evalue sfo rth ediffusio ncoefficien t D . andfo rth etortuosit y factor ƒ,a thig h e,value s seemt ob eo fmino rimportance . The resultso fRun s6 t o9 wit hdifferen tadsorptio n coefficients (X /,)o nth ebot ­ tommateria lar epresente di nFigur e 27C.The y showa considerabl e contributiono fadsorp ­ tiont oth edeclin eo fth esubstanc ei nth ewate rcompartment .Man ypesticide s havemoder ­ ateadsorptio nvalue so nsoil s (X. .< 0.0 1m kg ),bu tadsorptio no nditc h bottom materialsma yb ehighe rb ya facto r1 0(Section s6. 6an d6.7) .Wit ha adsorptio ncoeffi - 3 -1 ciento f0. 1m kg ,29.6 s»o fth einitia l dosewa s computedt odiffus eint o thebotto m ina 27-da yperio d (Run8) . Bydecreasin g thewate rdepth ,th einitia lmas sconcentratio ni nth ewate rcompart ­ mentincreased . This induced greaterpenetratio no fth esubstanc e into thebotto m layer (Figure 28A,Run s 10t o12) .A ta wate rdept ho f0. 1m an dusin gth esam eadsorptio n coefficienta si nRu n8 , 66%o fth edos eha ddiffuse d intoth ebotto m layerafte r2 7day s (Run 12). Especiallyi nditche swit h smallwate rdepths ,adsorptio no fpesticide so nth e bottom layerca nthu sb eo fgrea timportance . The resultsobtaine dwit h various ratecoefficient sfo rconversio ni nth ebotto m layerar e showni nFigur e28 B(Run s1 3t o15) .Conversio no fth esubstanc ei nth ebotto m

mass of substance in water mass of substancei n bottom material 100-1 (mg) (mg)

„f ^-~i* i i i i i 11 i • i i ° i'iii i i 11i 11 i i i i o K) 20 30

100-1 ^^ 60- *==: =3? 20- ^ \^ v ^ 17 0- Vi» I I I I 1 I'f'f I I -i i |. i c> 10 10 20 30 20 30 time Id) Figure 28. Mass of substance in water compartment and bottom compartments computed with the tank mod­ el. For the parameters used in the different com­ puter runs see Table 31.

81 layeraccelerate dsubstantiall yth edecreas ei nth ewate rcompartment ,especiall yafte r thefirs tfe wweeks .Wit ha fas tconversio nrat ei nth ebotto mlaye r (Kun15 ,tj >b =1 d), thetota lamoun ti nth ebotto mlaye rremaine dlow :th emaximu mvalu e (6.31o fth edose ) wascompute dafte rthre edays .Further ,th etota lmas so fsubstanc edecompose d inth ebot ­ tomlaye rafte r2 7day swa s74.3° so fth edose . Theresult so fth erun swit hvariou srat ecoefficient sfo rconversio ni nth ewate r compartmentar epresente di nFigur e28C .Compariso no fRu n1 4wit hRun s 16t o1 8show sth e greateffec to fth erat eo fconversio ni nth ewate rcompartment .I nsituation swit ha rel ­

ativelyhig hconversio nrat ei nth ewate rcompartmen t (Run18 ,t^ w = 1d )penetratio n intoth ebotto mlaye rwil lno tb eimportant .Afte r4 day si nRu n18 ,90 4o fth edos ewa s convertedi nth ewate rcompartment .I nthi scompute rrun ,th earei cmas sflu xint oth e firstbotto mcompartmen teve nbecam enegativ eafte r1. 5days . Inal lruns ,halvin gth ethicknes so fth euppe rbotto mcompartmen tha donl ya ver y smalleffec to nth ecompute dmas so fsubstanc ei nth ebottom .

Depth of penetration into the bottom

Theconcentratio npattern si nth ebotto mlaye rafte r9 an d 27day scompute d intw o ofth esimulatio nexperiment sar epresente di nFigur e29 .Withou tadsorptio nont o thebot ­ tommateria l (Run3) , concentrations inth euppe r0.0 1 mwer emuc hlowe rtha nwit hadsorp ­ tion (Run 8). Theslope so fth econcentratio ncurve si nRu n8 wer emarkedl ysteepe rtha n inRu n3 .Wit hadsorption ,n osignifican tpenetratio nint oth ebotto mwa scompute dbelo w adept ho fabou t0.0 2m i na 27-da yperiod .

mass concentration (mg m ) 100 200 i i i I i i i i j.

0.05-

Run8 0.02

depth inbotto m (m )

Figure29 .Mas sconcentratio no fsubstanc ei n bottomlaye rafte r9 d ( )an d 27d ( ).Fo r theparameter suse d inth esimulatio nexperiment s seeTabl e31 .

82 8.7 GENERALDISCUSSIO N

Formode l computationso nth ebehaviou ro fpesticide si naquati csystem swit hbotto m material,severa lparameter sar eneeded .Th e mostimportan tparameter sar eth erat ecoeffi ­ cientsfo rconversio ni nth ewate r compartmentan di nth ebotto m layer (k and k , c,w c,b respectively).Diffusio n intobotto mlayer si sa fairl yslo wphenomenon .Th eadsorptio n coefficienti sals oneede dt odescrib eth erat eo fdeclin eo fa substanc e inwater .Th e adsorptioncoefficien thighl yaffect s thepenetratio ndept ho fsubstance si nth ebotto m layer. Unfortunately,i nalmos tan ypublicatio no fexperimenta lwor ko nth ebehaviou ro fpes ­ ticidesi naquati c systems,on eo rmor eo fth eessentia lparameter sar elacking .Conse ­ quently,i twa sno tpossibl et ochec k thedevelope d computationmode li ndetai lagains t datafro mth eliterature .Hamelin k& Waybran t (1973)studie dth edistributio no fDD E( a conversionproduc to fDDT )an dlindane ,whic hwer e addedt oth eepilimnio no fa thermall y stratified flooded limestonequarr y (15m deep) ,fo r oneyear .Afte r threemonths ,85° so f therecovere dDD Ewa spresen ti nbotto msediments ,whil e 72°so fth emeasure d lindanewa s stilli nth ewater .Thei rresult s indicate thatth edeclin eo fver y slowlyconverte d pes­ ticidesi naqueou ssystem sma yb eprimaril ydu et oadsorptio nont obotto mmaterial .Mos t ofth estrongl y adsorbed DDEwa s foundi nth eto p0.01 5m i nal lbotto msamples .Lindan e wasfoun dt oa dept ho f0.05 5m . The contributiono fth evariou smechanism so fdeclin eo fherbicide si nwate rbodie s ofaqueou s systemsi shighl ydependen tupo n thephysico-chemica lpropertie so fth eherbi ­ cides.Organi ccation s likediqua tan dparaqua tar eadsorbe do nth ebotto mmateria lwithi n afe wdays .Th eweakl y adsorbed compound 2,4-Di srapidl y convertedi nwate r (Frank, 1970). However,suc h informationi sonl yo fqualitativ enatur ean dthu sno tsuitabl efo rtestin g computationmodels . Comparisono fth elimite dnumbe ro fmeasure d datao nth emasse so fazinphos-methy l anddimethoat ei nslice so fbotto mmateria ldurin goutdoo rtan ktrial swit hth ecompute d masseso fbot h compoundsyielde d encouraging results.Th ecalculate d deptho fpenetratio n was small;therefor e themetho do fsamplin gth euppe rcentimetr eo fth ebotto m layeri n aquaticsystem si sextremel y important.Samplin go fbotto mmateria lwit hdredge-typ ebot ­ tomsampler swil lmostl y giveerroneou s results (Chapter4) . Furtherexperiment swit h improvedprocedure s areneede dt otes tth evalidit yo fth e various assumptionsan dapproximation si nth ecomputatio nmodel .I nfutur eexperiment so n penetration intobotto mmaterial ,ver y thinslice so fbotto mmateria l shouldb eanalysed . More informationi sneede do nth eeffec to faerobi can danaerobi ccondition so nth e rateo fconversio no fth esubstanc ei nth euppe r fewmillimetre sbelo wth esediment—wate r interface.Furthe rcomplication s liketh eexistenc eo fdifferen tperiod si ndegradatio ni n watero rbotto m layermigh toccu r (Chapter 6). Alsomor e informationi sneede do nth eef ­ fecto fligh to nth erat eo fconversio no fpesticide si nshallo wwatercourses . Onlya fe wfirs tstep shav ebee nmad ei ndescribin gpesticid ebehaviou ri naquati c tank-like systemsquantitativel ywit hcomputatio nmodels .Muc h experimentalan d computa­ tionalwor k remainst ob edone.

83 9 Measurements of azinphos-methyl and dimethoate in watercourses and farm ditches in the Kromme Rhine area and in the Lopikerwaard Polder

9.1 INTRODUCTION

Inth ewate ro fth eKromm eRhine ,flowin gthroug ha nare ao ffrui tfanning ,concen ­ trationso fazinphos-methy lwer emeasure db yPon s (1972),wh ofoun dtha tth econcentratio n ofthi scompoun dincrease ddownstrea man dascribe d thistren dt oth eus eo fazinphos-me ­ thyli nfrui tfarming .Th econcentration so fazinphos-methy lwer emeasure di nthi sstud y bythin-laye rchromatograph y (TLC),whic hma ylea dt oerroneou sresult si fver ylo wcon ­ centrationso fpesticide sar epresen ti nwater scontainin gvariou spollutant s andnatura l substances.Mor equantitativ edat ao nth eoccurrenc eo fazinphos-methy l inwatercourse s canb eobtaine db yusin gclean-u pan dGL Ctechniques .I nlarg ewatercourses ,includin g theKromm eRhine ,a fe wsamplin gpoint swer eselecte dfo rmeasuremen to fchange sdown ­ stream. Toinvestigat eth eunintentiona lcontaminatio no fwatercourse sfro mfrui tfarm si n moredetail ,carefu lselectio no fothe rsamplin gpoint san dmor efrequen tsamplin gwer e feltnecessary .Durin gthi sreconnaissance ,samplin gpoint swer e selectedi n197 5i nditche s onfrui tfarm swit hth eai mt oinvestigat eth eoccurrenc ean dbehaviou ro fazinphos-methy l anddimethoat ei nfar mditches .Th eselecte dfarm sha dthei row npumpin gstation ;th ewate r balanceo fpumpe dditche scoul db eestimate dmor eeasil ytha ntha tfo rwatercourse swit h freedischarge . Sinceconsiderabl econcentration swer efoun di n197 5i nth editche so ntw ofrui t farms,mor edetaile dmeasurement swer ese tu pi n 1976t oestimat eth ewate rbalanc ean d pesticidebalanc eo fpumpe dditche so nthos efarms .Th edeclin eo fazinphos-methy lan ddi ­ methoatei nthes epumpe dditche swa smeasured .I n1977 ,spra ydrif tt oditche swa smeasure d indetai lo nth esam efarm st oestimat emor eaccuratel y theinpu to fpesticide s intothes e ditches. Theditc hsyste mwa scharacterize db yvariou smeasurements .Man yo fth edat aassesse d wereals ouse di nsimulatio nmodel sfo rpesticid ebehaviou ri nditche s(Chapte r 10).Th e investigatedditc hsystem scoul dthu sb euse dt oderiv emode lsystem sfo rth ecomputation s andt ocompar ecompute dan dmeasure dresults .

9.2 MONITORINGO FAZINPHOS-METHY LAN DDIMETHOAT E INWATERCOURSE SAN DI NDITCHE SO NFRUI T FARMSDURIN G197 5

9.2.1 Description of sampling points and procedures

Appropriatesamplin gpoint swer eselecte di nth eProvinc eo fUtrech ti nconsultatio n withth eregiona lcro pprotectio nextensio nofficer ,wh owa sfamilia rwit hth efiel d

84 Situation.Th eselecte d samplingpoint sar eshow ni nFigur e30 .Thre eo fthe mwer ei nlarg e watercourses inth eKromm eRhin earea .Th eKromm eRhin ei sa distributar yo fth eNethe r Rhine.Th eKromm eRhin eflow sthroug ha nare awit hfrui tfarmin gsituate dmainl yo n thenatura llevee salon gth eriver san dgrasslan dfarmin gmainl yo nth eheav ybackswam p clays.However ,frui tfarmin go nsom eo fth elatte rsoil si spossibl eb ylowerin gth e groundwaterleve lb ypumpin gth editches ,especiall ydurin gth ewinte rseason .A nexampl e ofthi ssituatio ni sSamplin gPoin t5 nea rBunnik .Pumpe dditche sar eals ofoun do nloam y soils,wher esom eseepag ewate rfro mth eRive rLe k (thecontinuatio no fth eNethe rRhine) , flowinga ta highe rleve lmus tb eremoved .Thes econdition soccurre da tSamplin gPoin t6 nearSchalkwyk .A tPoint s5 an d6 ,windbreak sstoo drigh tnex tt oth editche so non eside , whileo nth eothe rsid ewer einspectio npath sfo rditc hcleaning .A tthes ePoint s5 an d6 , thefrui ttree swer eno timmediatel ynex tt oth ewatercourse .Thi si squit ea usua lpat ­ terno fplanting .

Figure30 .Ma po f thesamplin gpoint si nth eKromm eRhin eare aan di n theLopikerwaar dPolder .Samplin gpoints : 1= Kromm eRhin enea rth einle tfro mth eNethe rRhin enea rWy kb y Duurstede. 2 =Langbroeke rCana lfro mth ebridg enea rSterkenbur gCastle . • KrommeRhin efro mth ebridg enea rOdyk . =Lopike rCana lnea r theBiezendy kbend . • Drainageditc ho nfrui tfar mnea rBunnik . =Drainag editc ho nfrui tfar mnea rSchalkwyk . =Drainag editche so nfrui tfar mnea rBenschop . =Drainag editche so nfrui tfar mnea rJaarsveld . =Drainag editche so nfrui tfar mnea rLopikerkapel .

85 Somemor e exceptional Sampling Pointswer e selectedi nth eLopikerwaar dPolder .A t Sampling Points7 an d8 ,man y fruit trees grewjus t alongside theditches ,s otha t during applicationso fpesticide sa par to fth espra y inevitably descended into thewater .Th e Lopikerwaardi sa nare awit h relatively high groundwater levels.Th e various soil types aremainl yuse dfo rgrasslan d farming.Ditc hwate r levelsi ngrasslan d areas tendt ob e ratherhigh ,especiall yi narea swit h peaty soilo rwit h loamyan dclaye y layerso na peaty subsoil.I fsupplementar y pump-drainage isavailable ,frui t farmingi spossibl eo n some loamyan dclaye y soils,a saroun d Sampling Point7 nea r Benschop,o nth enatura l lev­ eesnea rJaarsvel d (Sampling Point 8)an dnea r Lopikerkapel (Sampling Point 9).Aroun d all samplingpoint si nth eLopikerwaard , somedee p seepagema yb eexpecte d (Studiegroep Lopikerwaard, 1973).Moreove ra tPoint s8 an d9 ,shallo w seepage occursdurin g high river water levels.Th eSamplin g Point4 i nth eLopike r drainage canalwa s selected asa repre ­ sentativewater-inle tpoint . Thepoint si nth ewatercourse san dth edrainag e ditcheswer e sampled beforean daf ­ terspra y operationso nth efrui tfarm s accordingt oth eprocedur e describedi nSectio n 4.2.I n1975 ,sample swer e taken5 times .Th esample so fwate rwer e extracteda ssoo na s possible (Sections5. 3an d5.4) .Som e surfacewate r extractswer e cleanedu pfo rmor e accuratemeasuremen to fazinphos-methy lan ddimethoat e (Sections5. 9an d5.10) . During themonitorin g activities in1975 ,th econcentratio no fazinphos-methy li n allwate r sampleswa smeasure do non eGL Ccolumn ,sinc ea ttha t time onlyon eappropriat e columnwa s available (Table 14,Colum n 1).Dimethoat e concentrations weremeasure do ntw o columns (Table 15,Column sI an d III).

9.2.2 Results and discussion

Theaverag e apparent concentrationso fazinphos-methy lan ddimethoat ei nextract so f water samples from the largewatercourse san dth evariou s farmditche so n5 samplin g dates in 1975ar egive ni nTable s3 2an d33 ,respectively .Mos to fth econcentration sar e presentedwit h 'smaller than'marks .Thes emark s arenecessary , sinceth eapparen t con­ centrationso fazinphos-methy lan ddimethoat ei nth eextract swer eusuall y much loweraf ­ terclean-up ;especiall yfo rsample s from largewatercourses .Th eextract so fwate r sam­ pleswer e cleanedu pabou t twomonth s later,afte rstorag efo rsevera l dayso na labora ­ torybenc han di na refrigerato ra t5 °C .Muc ho fth ereductio ni nconcentratio n after clean-upo fth esample s fromDitche s6 ,7 an d8 (Tabl e 32)ma yresul t from decomposition during storage.Evidently , interfering substancesha donl ya mino r effecta tthes erela ­ tivelyhig h concentrationso fazinphos-methyl . Small amountso fazinphos-methy l anddimethoat ewer e found afteron e single clean-up ofwate r samples from theKromm eRhin eo n2 9July .Thes e datad ono tsho wa significan t increasei nconcentratio nfo reithe rcompoun d during flow throughth eKromm e Rhine area (Tables3 2an d33 ,Samplin g Points 1an d3) .Fo rmeasuremen to fth eactua l amountso f both compoundsi nth elarg ewatercourses ,large rwate r samples,mor e extensive clean-up and analysiswit hmor eGL Ccolumn swoul dhav ebee nnecessary . Duringmonitorin gi n1975 ,apparen t concentrationso fdimethoat ei nwate r samples from the largewatercourse so fth e farmditche swer e only small (Table 33).Lo wconcen -

86 Table32 .Averag eapparen tmas s concentrations ofazinphos-methy lmeasure d inextract so f watersample sfro m largewatercourse s (Points 1-4)an dfro mfar mditche s (Points 5-9) during 1975.Fo rpositio no fsamplin gpoint sse eFigur e30 . s-methyl (mgm 3 Samplin gpoin t Number Average concentrationo f azinpho; ) of 19Augus t samples 14Marc h 6Ma y 2Jun e 29Jul y before after before after clean- clean- clean- clean- -up -up -up -up

1 <0.5 <0.09 <0.9 1. Wykb yDuursted e : 2 <0.5 - <0.5 <0.02 <0.1 <0.9 2. Sterkenburg 2 <0.08 <0.2 <0.2 <0.6 <0.07 <1.1 3. Odyk 2 <0.4 <0.4 <0.7 <0.4 <0.05 <0.1 4. Biezendyk 2 <0.1 <0.3 <0.3 2 <0.4 5. Bunnik 2 <0.02 <1.1 <0.3 3 <0.4 <0.2 0.3 6. Schalkwyk4 4 <0.06 <0.2 1.3 l 9° <0.1 0.5 7. Benschop 4 <0.1 <0.2 18 0.3 5 <0.2 10.5 6 43 <0.2 8. Jaarsveld 4 <0.2 9. Lopikerkapel 3 <0.5 <0.03 <0.4 <0.2 -3 1. Thedetectio n limitwa sabou t0.0 1 mgm 2. Nowate r inth e drainage ditch. 3. Clean-up twomonth s latero non es ampleo f water. k. Azinph os-m ethy 1 spraya t theen do fMa yan d June. 5. Azinphos-methyl sprayo n 30Ma y and 25Jun e 7July . 6. Azinphos-methyl sprayo n 30April , 16May , 28May , 26June ,

7. Azinphos-methyl sprayon ] Lya tth e endo fJune . _ • trationo £dimethoat ei nth efar mditche scoul db eexpecte dsinc ei ntha tyea rth ecom ­ poundwa sno tapplie do nth eneighbourin gfields . Thecomparativel yhig hconcentration so fazinphos-methy l canb erelate dt oth e sprayingdate so nth efrui tfarms .

Table33 .Averag eapparen tmas sconcentration so fdimethoat e--ure^i^extract^of^a- ^ tersample s fromlarg ewatercourse s (Points 1 H)an arru m 1975.Fo rpositio no fsamplin gpoint sse eFigur e30 . . • ..i Sampling Number Averageconcentratio no fdimethoat ei nm gm Point of 19Augus t samples 14Marc h 6Ma y 2Jun e 29Jul y before after before after before after clean- clean- clean- clean- clean- clean- -up -up -up -up "UP "UP <0.04 _1 <0.1 <1 <0.11 <0.5 1.Wy kb y <0.4 Duurstede <0.03 <0.5 <0.6 <0.2 <0.2 2.Sterkenbur g 2 <1.9 <0.09 <0.5 <0.2 3.Ody k 2 _1 <0.5 <0.3 <0.5 <0.2 <0.1 <1.5 <0.1 4.Biezendy k 2 <0.1 <0.2 <0.4 _2 <0.04 <0.05 <0.04 5.Bunni k 2 <0.3 <0.1 <0.03 6.Schalkwy k 4 <0.05 <0.06 <0.3 <0.02 <0.02 <0.02 7.Benscho p 4 <0.06 <0.07 <0.3 <0.01 3 <0.1 <0.2 <0.1 8.Jaarsvel d 4 <0.1 <0.01 <0.3 <0.2 <0.04 <0.3 9.Lopikerkape l 3 <0.3 <0.02

!.Highl y interferingsubstances . 2.N owate r indrainag editch . 3.Th edetectio n limitwa sabou t0.01_mg_m _

87 Before the flowering of the fruit trees, the compound was only applied in Jaarsveld. After flowering, fruit trees were sprayed with azinphos-methyl near Sampling Points 6, 7 and 8. The concentrations were highest in drainage ditches near Benschop and Jaarsveld, as would be expected for situations in which fruit trees grow just alongside the ditches. The• concentration s of azinphos-methyl in water samples taken at Jaarsveld on 6 Mayrange d from 9.5 to 11.4 mgm ; those in the samples from Benschop (2 June) ranged from 10.4 to 22.5 mg m . With a windbreak and an inspection path alongside the ditches (Schalkwyk, Point 6, 2 June) the concentration was much lower. At the end of July, comparatively low concentrations were found in the ditches of all fruit farms, perhaps because of the large rainfall in that month. For example at Points 6, 7 and 8, nearly 100 mmo f rainfall was measured within a few days in July. Three days of continuous pumping were necessary to discharge this extreme rainfall.

9.2.3 Preliminary conclusions

From the monitoring during 1975 of azinphos-methyl and dimethoate in watercourses and in ditches on fruit farms, a few preliminary conclusions could be drawn. -Measurement of small amounts in large watercourses without adequate clean-up procedures will mostly give too high a value. - At least two GLC column packings with different polarity have to be used. - Good GLC analysis is rather difficult and very time-consuming. Continuous attention had to be paid to the quality control. - Further monitoring of the larger watercourses would yield only limited information. There is always a certain 'background' of pollution, probably by intake of polluted water from the main river. Even with rather frequent sampling at several points, it mayb e dif­ ficult to trace the sources of instantaneous contamination and concentration waves may be overlooked.

- On the whole, the concentrations in the larger watercourses seem to be quite lowan d there are no indications for an increase downstream. This is probably due to factors like

Tribut T10n: the SCatter °f ** °rChards be*een P»tuie and arable lands, the dis­ tribution of applications in time or also the relatively rapid decline rate in surface wa-

eS ln SUraner e5 iall in the K S "s'u^ r TJTTZ;: :::::rr ^ istinc ^ tdischarg ' ^ ye °f——™«- Khin—*»e — ditche° *"** s «ÏTc^ÏZIZ: Sitmted JUSt al°ngSide *• ***». «»t« contamination of dit* - Onmos t modern fruit fame ,,-!„.«- i , - and the introduction of eTje ^7' ^^ ^ "*» ^^ ** ""£ - The systematic tracingof a" f^ "«*"* *"** SP™ WiU * ** reliable quantitative Resits. ^ ** ^ ^ ^^ ^ ^ **»* *" - Attempts are needed to redur^ +w number of water sampies for "ach? TT" " ^^^^ analyses for an enormous neous development of computation models ^ intGreSt* ™S ^ ^ *** * ^^ -Fo rmor edetaile d investigations,ditche s areneede d forwhic hwate rbalanc eca neasil y bemeasure dan dt oa certai nexten t controlled.

9.3 FIELDTRIAL SO NTH EFAT EO FAZINPHOS-METHY L AND DIMETHOATEI NDITCHE SAFTE R SPRAY DRIFT

9.S.1 Introduction

Invie wo fth erelativel y high concentrationso fazinphos-methy li nsample so fwate r fromth edrainag editche si nBenscho p andJaarsvel di n197 5 (Table32 ,Point s7 an d 8), thesefar mditche swer e selectedfo rfurthe r investigationi n1976 . Theconcentration s in197 5raise d the followingquestions . -I si tpossibl et omeasur eth einpu to fbot h compounds intoditche sdu et ospra y drift duringanplication so nfrui t farms? -Ho wquickl ywil lth econcentratio nb emixe dove rth ecross-sectio no fth ewate rbod y in the ditch? - Is it possible to estimate the rates of decline of the compounds in ditches for periods without discharge or intake of water? - What will be the effect of adsorption on rate of decline? - How far and how fast will the compounds penetrate the ditch bottom? Before the pesticide balance in the field ditches can be solved, the water balance of these ditches must be assessed. The circumstances were far from ideal for solving this water balance, since the soils were heterogeneous and hydrological conditions were rather complexes is often so in practice). _ was mde During the period of pesticide application on both farms in is/o, an v to approximate the various items of the water and pesticide balances for the pumped ditches. Before and after spraying azinphos-methyl and dimethoate, ^^^ •measured in many water samples. Penetration of azinphos-methyl into the ditch bottom ma terial was also measured. The ditch bottom material was characterized to ^**w o simulation models. Profiles of the volume fraction of liquid and the bulk density were measured at several points in the drainage ditches. s-3-2 Data on the trial fields in the Lopikerwaard Voider

- ditch sections, which were selected in 197, f^^^^Z «* on pesticide behaviour are shown in ***-']£££ ^ su lementarily drained *ere selected, a siphon-linked ditch (designated BSL) and the PP^ ^ ^ ^ ditch section before the water pump (designated BSD) Figure • ^ s*face in Benschop varied from 0.60 mbelo w sea-level (Standard ms -r Ditch Section 1 to about 1 mbelo w NAP in the Mediate surround o *e ^ 1-st water level of the pumped ditches on the farm in Benschop « b •»• At this water level, the electric pump was automatically switched

SWltCh" i nniv three of the many ditches Hydrological conditions in Jaarsveld were quite complex. Only three 89 10 *T1f I f ui © ©ll

BSL BSD

M b(Z JP_ 7 9 L

•^ ^ A«

108had supplementaryadraiiaIePaiherda«LHiit-heS ^ * fruit fam in Bensch°P" Secti°nS '." these sections were filler! ?„ „J 7 ?, s rePresent ditches which were not pumped, detail. They are indicated as siuhon r ^ i^" SeCti°nS 8 and 10 were Studied ^ ^l (BSD), respectively. Abbreviate ? Z I dltCh (BSL> and supplementally drained ditch Key:^= siphon, ©= groundwater'tubes' 2* *"* f f°r fr°nt part of a dUch SeCti°n' °es' • = water pump.

LTaJo™ 7*eTT (Fi§Ure 32)- ™eSe dltCh SeCti0nS - heated withth e ab- md JF f r baCk middle and f t; * ° ' h — tparditc tho sectionfth e £a, respectivelyabou t r. I n Jaar, level ratwhic £h :r:; th ™™ n :;: :: ™ ::rL Vel" ^ abour t °-10 ™ aboveNAP ™.Th ewate •• r* - atwnic nth ePpum pwa snormall ystorm t ,,„ u y St ed Datao n t, ,. . °PP '«a sabou t0.7 9m belo wNAP . uatao nth edimension sn ftb oj; « which includescalculat e «t 7\ ! dlff^ent ditchsection sar eshow ni nTabl e34 ,

tion.I» ,variatio n1 „th l« , ™ «»»e,e„tso fth edept han d»idt hpe rditc hs « ,ouerpa n ot a dit 8 ter «ü. «op, „ : Ld « r:Ie T tC Cl° * -"*- - '**•" I»opscho pth « »« X t "™f f " ™^- area of the ditches, it was assum d draina8e system. To calculate the catchment between ditches and'drains TheTt TT ^ Wat6rsheds were halfwa/ between ditchf ^ that for Jaarsveld was about 7 000 Ï. ^ "** " BenSCh°P WaS ab°Ut 135 °°° m ^

90 b

JB

9 X 5 E 2 IL.- J Te 1> 10 0 JM EZ ©

10 f

» b

JF

— 4

Figure 32. Position and flow pattern of ditches on a fruit farm in Jaarsveld. All sections w«e pumped. The left dashed line represents a ditch at polder level. The right dashed line is a ditch d , a windpump of an adjoining fruit farm. Dashed-dotted lines are f°rmer ditches, filled with old trees and top-soil. Sections 9, 10 and 11 were studied in f « detail. They are indicated with abbreviations as JB, JM and JF for back, middle and fr°nt sections, respectively. Abbreviations: b for back and f for front part of the ditch sections. x Key:^<:= siphon, © = groundwater tubes, • = water pump, y= windpump.

9-s-S Measurement and approximation of the items of the water balance

Measurements on items of the water balance were set up in 1976 for a period of about 2 "»nths, from the beginning of May to the beginning of July. After that, uncontrolled a- mou*ts of water were taken in on both farms for sprinkler and furrow irrigation, and it be- Came lmP°ssible to measure the water balance. For the approximation of the various rates of water flow in the ditch sections, a sun- Ple ««putativ model was used (Chapter 10). The water balance of a ditch water compart- mei* is in words: rate of change in water volume = rate of precipitation - rate of evapo­ ration - rate of outflow + rate of in£low + rate of flow through the wetted perimeter of e ditch + rate of flow from the drains (Equation 24). *> rate of evaporation from a free water surface was estimated by averaging the data °f De But and Naaldwyk meteorological stations (KNMI, 1976) (Figure 33). In the dry and 91 rate of evaporation from the water surface (mm d") 7-, 6 5H 4 3 2H 1 I I I I I I I I I I I I I I I H [ I I I I I II I I | I I I I I I II I | I I U I I I I I |I I I I I I I I I 11 I I Q 10 20 30 40 50 |60 [ | time(d) 3May Uune Uuly Figure 33. Rate of evaporation from open water. Averaged data of De Bilt and Naaldwyk mete­ orological stations (KNMI, 1976). sunny year 1976, the rate of evaporation was high. During the period of pesticide application, the ditch water-level was measured on sampling dates. The ditch water-levels above the reference levels (at which the pumps nor­ mally stopped, Table 34) are shown in Figure 34C and 35C. In view of the relatively dry period, the farmers had raised the switch-off level of the pump a few centimetres above the reference level. The water level before the pumping period on 21 June at Benschopwa s read from a high-water mark, manifested by a duckweed ring around the pumping tube. The water levels during the pumping periods were estimated by using a computation model (Chap­ ter 10). At Jaarsveld, the fluctuations of the water level could only roughly be approxi­ mated. The amounts of rain were read daily by the farmers at 08:00 h. This daily rainfall on both farms is shown in Figures 34A and 35A. The total rainfall in May was 37 m in Benschop and 42 mmi n Jaarsveld. In the Netherlands, the 30-year average rainfall inMa y is 51 mm (KNMI, 1976). In June, 48 mmo f rain was measured on both farms (30-year average is 54 mm).

On both farms the electric water-pump was equipped with a pumping-time meter. Thedu ­ ration of pumping was read by the farmers at 08:00 h each day. Normally the water pumps were equipped with a float switch, which kept the ditch water-level within narrow limits- After the spraying dates in the trial period, the water pumps were not used for some time in order to study the decline in the pesticides in the watercourses. They were switchedo n by hand when necessary, which resulted in a rather discontinuous pattern of pumping (Fig­ ures 34B and 35B).

The approximation of the rate of discharge of the different ditch sections will be discussed in Chapter 10. At the beginning of the trials in Jaarsveld, unknown amounts of water were taken in redVromTr "V*™™* * * *** "" *» back dit<* (Figure 32). This intake occur- riod in Jaar,«.!^ "**** °f W3t6r taken in durin« Ae £irSt ^ ^ Z w 7 mt direCtly meaSUred' * C0Uld be -ly roughly estimated ft- * o 2 L;: ln :ditchwd ** risei n ^-~> »^ - -eragestorag e Peri d lnJaarSVeld ^L^Z^l h "*** ° 'J« * ^fore theheav y rainfall, no I, ^X^::^Z^- * — -r andgrondwater . O-^ pproximateth eamoun to fwate r taken in. 92 Cf» — — iTl — O — O CM

— O O O O O

/—S +1+1+1+1+1 + m O

— O O O O

+1+1+1+1+1

r-l J3 o o — o o o o •a u o o + CTi CM

co CM r- oo — o — o — o o o o +1+1+1+1+1

N IN VU »o CJ J2 a-H 0 -o n cj *o CM cr« m u — o o o * S r-l CO — o o o o rH 4J h CJ +1+1+1+1+1 O n 4J M -0 •o .o •u •rl ^ *^/ »^ **• *^f O c •o CJ CJ CM — CS CM co o S T) ffl u ai 01 CS~OOOCMOOOOCm CM co* Q. •-I m 0 i *w tNO>00 J3 4J CJ CJ O c co V) CO u u al ai CJ & co u u M 3g U CO P. Q) P, p. 4J fl fi fi }_t +i 4J 4-1 « M •rl a) 3 CJ CJ •H •H fi P. s 3 3 4-1 s P. CJ o cO co m ,£ 3 al ai CJ CJ CJ M u u •rl 5^ j! cO cO 10 fi CJ 4-> ? +1 +1 u CJ CM 4-1 -d 4-1 T) U-l »4-1 C co « c c ai CO ai o ai 9i o g S u e r-l 3 CJ CJ J= fi CA p. P« 5 CJ Cl CJ o +1 4-> co o cO aJ .e +> s a a ÇJ r-t CJ t-l ,—4 ni co S en en O o u rJ U J3£ CÜJ2 Ol J3 X! •£ CO | ^ CM m J- m iß <"-

tU'HCÜrHCiJrHCOCOCOSP •JSacnMcnuOUWCM

93 Groundwaterlevel swer eneede dt oestimat eth ewate rflo wthroug h theditc hbottom . Somegroundwate rtube swer eplace di nth efrui ttre erow sa tvariou sdistance s fromth e selectedditc hsection s (Figure3 1an d32) .Th elevel so fth etub ehead swer e takenwit h alevellin ginstrument .Durin gpesticid eapplication ,th egroundwate rlevel swer emeasure d

rainfall (mm d ) 20- 15- 10- 5- 1111111111111111111111111111111 1 111 'I'M'" Ó 10 20 30 40 3May Uune Uuly

cumulative pumping time (d) 1.0- 08- 0.6 0.4 0.2-

u- it HI 11m i i| 111 ii i O 10 20 30 4Ö 3 May Uune Uuly

water level (m) 0.30-

0.20-

i J*" \ 0.10 \ S' / 11111111I I I 111 11111 1111 1 111III1 1 1111 11 111 1 I 111 1I 111111 1 I I II I O 10 20 pO 40 50 pO 3Ma y Uune Uuly

averaged groundwater level (m) 0.4-

0.3- -o o a-- —-- » v \ 0.2 o ./I \ \ \V

0.1-

1111 11111111 11111111111111111111 [ 11111 111 11111II1111 III ' 9 10 20 30 40 50 60 3Ma y Uune Uuly time(d) Figure34 .Fiel dobservation so nth efrui tfar mi n Benschop,durin g thetria li n1976 . A.Rainfal lagains ttime . B.Cumulativ epumpin g timeagains ttime . C.Ditc hwater-leve labov elowes tpumpin gleve l againsttime ;x = measure d levels, =approxi ­ matedlevels . D.Average d groundwater levelabov elowes tpum p levelagains ttime ;• an do ar emeasure dground ­ waterlevel saroun d thesiphon-linke d ditch (BSL) and thesupplementall ydraine d ditch (BSD),re ­ spectively; =approximate dlevels .

94 rainfall (mm d-1) A 25-1 20- 15- 10- 5- • 1 Q IMUI, il ll 1 r 111 1 I • 11111111 ftfiiilTirfH TTTTTTTTTTTTTTTTT M 1 1 1 1 II II Mil 10 20 3Ö 40 50 J50 3 Ma? y Uune Uuly

cur nulative pumping time (d) B 3- 2- I ^_ r 0- 1 1 | 1 1 1 1 1 1 1 M | 1 1 1 1 1 1 1 1 1 | 1 1 1 1 1 1 1 1 1 | 1 1 ' 1 1 M 1'I'lllMIIMII I \? - 10 20 30 40 50 ^0 3 May Uune Uuly

water level m) C 0.50-

040- / ]

030- / / ƒ• / / 020- ( / / / I/" \ I 0.10- / \ i 1 i ,1 0- \ ƒ^j x%/ 11 [ 111111111111111111 j 111111111111111x 1 1' ' » 9 10 20 .30 40 50 BO 3K lay Uune Uuly

averaged groundwater level (m) 0.4-

--2 o 0.3-| 'o-o'' /H I \> i* \ Q2

0.1- lb \ . >^j( 0-

T'l I I I I I I I 1M I IT'TT T I 'II I' 1111111111 M pi ? >0 30 40 50 J60 3Ma y Uune Uuly time(d)

Figure 35. Field observations on the fruit farm in Jaarsveld, during the trial in 1976. A.Rainfal lagains ttime . B.Cumulativ epumpin g timeagains ttime . c- Ditch water-level above lowest pump level against time; x = measured levels, = approximated levels. D.Average d groundwater levelsabov e lowestpum p levelagains t time;o (aroun d frontditch) ,• (aroundmiddl editch )an d k (aroundbac kditch ) aremeasure d levels, =approximate d levels.

95 onsamplin gdates .Thos eo fTube s III,IV ,VI Ian dVII Ii nBenscho pwer e usedt ocalculat e anaverag egroundwate r level aroundth esiphon-linke d ditch;thos eo fTube s I,II ,I Xan d Xwer euse d fora naverag egroundwate r level around thesupplementall y drained ditch (Fig­ ure 34D).Average d groundwaterlevel saroun d theditc hsection sa tJaarsvel d areshow ni n Figure35D .I nbot h fieldsituations ,th egroundwate r rosestrongl y afterth e heavyrain ­ falla tth een do fJune .A tJaarsveld ,th egroundwate r levelsaroun d themiddl ean dbac k ditch rosesignificantl ywit h thewate r intakea tth ebeginnin go fMay . Thewate r fluxthroug hth editc hbotto man dth erat eo fflo w fromdrain swer ecalcu ­ latedfro m thewate rbalanc ea sa closin gentry .A detaile d discussiono nth edesig no f thecomputatio nmode lan dth erelevan tparameter swil lb egive ni nChapte r10 .

9.3.4 Surface and groundwater quality

Forth echaracterizatio no fwate rqualit yi nth evariou s ditch sectionsan dground ­ watertubes ,som ewate rsample swer esucke du pwit ha vacuu m sampler (Section4.2) .Thes e sampleswer e analysedb yth eEaster nLaborator y forWate rTesting ,Doetinchem .Th eresult s aregive ni nTabl e35 . Therelativel yhig hchlorid e concentrationi nth editche si nJaarsvel dca nb eex ­ plainedb yth eintak eo fwate r froma large rwatercours ewit ha hig h chloride concentra­ tion.

9.3.5 Characterization of ditch bottoms

Forth echaracterizatio no fth ebotto mmateria lo fth editches ,abou t1 0c mo fth e upperlaye rwa s sampledwit ha faun ashovel .Sample swer ecollecte di nBenscho pa tfou r placesi nth efron tan dbac k sectionso fbot hditche san di nJaarsvel d fromtw oplace s m thefron tan dbac ksectio no fth emiddl e ditch (Figure3 1an d 32). Witha Perspe xbotto msampler ,provide dwit ha stainless-stee l closing unit (Section 4.4),mu dcore swer e collecteda tabou tth esam eplace si nth editches .Th elowe rpart so f thecolumn s (from2 2t o3 0c mbelo wth esediment—wate r interface) taken from thefron t andbac ksection so fth edifferen tditches ,wer epu ttogether .Thes e sampleswer euse dfo r thechemica lan dgranula r characterizationo fth e 'sub-bottom'o fth editc hbottoms . Thegranula ran dchemica lanalysi so fth ebotto mmateria l (Table36 )wa sdon eb yth e Laboratoryfo rSoi lan dCro pTestin ga tOosterbeek ,accordin gt ostandar d methodsdescribe d byHofste e& Fie n (1971).Th epH(KCl )o fth ebotto mmateria li nth efron tan dbac k sectionso fth edifferen tditche swa s nearly equal.Th ep Ho fth esub-botto mwa sdistinct ­ lylowe rtha ntha to fth euppe rlayer so fbotto mmaterial .Wit h thepeat y subsoila tBen ­ schop,th eorgani cmatte rcontent so fth euppe r layerso fbotto mmateria l therewer emuc h highertha na tJaarsveld .Thi swa s also foundfo rth esub-botto mo fth e ditcheso nbot h farms.Th eorgani cmatte rconten twa smeasure db y'los so nignition ' andb ytota lelemen ­ tarycarbo nanalysis .Organi cmatte ri nto psoil si nth eNetherland s containso nth e aver­ ageS8 ?ocarbon .Th eorgani cmatte rconten twa scalculate d fromth emeasure d elementary carbonconten tb ymultiplyin gb ya facto r 1.724.Th eorgani cmatte r contenti nth ebotto m

materialmeasure db yth e'los so nignition 'metho dwa s correctedfo rcla yan dCaC0 3,ac -

96 c O •r4 S ^ CO V \D CS U IJ CJ g 0 •mü •H w B. H J 0. T

C tü •rf .o

r-*irj

u s •H -a in o ON o m — 3 S NO-om-in^co u 3 r^ v oo CT> u a) M

§g I-.LT> —• o —t o -"O M

^ es m en ^ O o o S S

3 ~ 0 en U M co U< D •sOOOOC^OO-JCTt 'S in a* — v v m co «J to

— Li-i

o > 11 » u ON-JCO co v co o> W C C3 0 «

i r^u^—'O—'OOvO-J O

•—\ M 's ^ 1 'e .C l_ •C » . s 60 S 60 ° tj CA ^^ co S ° "(u en l m a> u i * e

•H .H /-v ÖO x: o- oo • • U tu CO 00*—' M- P-MV-. o . S O .13 O 3 SX O.TJ m ° ^ 60 4-> •rJ o. "4 97 « 0. » C r-l O r-l M " n Vi O « J! « O g Jj *J 4J i-I fis-g B3 O •-! | O U O J= CU •U B U-t o u o M co Ol •o o —• «-« CO CM *3" O vo — o> r-l AJ 0 CM CN CN •a u a oinwNtncoNo CO B 3 o u u — — co CM CA CU -

•Hfi J3 4J CO a eu a XI •a U 4-1 •r4 B •a u 'HN'srco^^nro

o -o c 2 c eu XÎ C CO 0CU « oCM CM O O sf -tf co a) '- « fi (NNO CN O en CO co o CM — CM N M CM CM ^o CM CM ".a •r4 in w ,4 CM II eu c 4J cd co co , 4J T3 •i-l o >, O M r-l fi o CO i-H -H •J ao O O cO ctf bp O o o en H« r» g , # ,

98 cording to factors described by Hofstee & Fieri (1971], The difference in organic matter content between the two methods was small (Table 36). The mineral fraction of the bottom material from the-ditches in Benschop can be clas­ sified as clay, in Jaarsveld as sandy clay-loam to clay-loam (Soil Survey Staff, 1975). The bottom material was classified according to the organic fraction following the classi­ fication system given by de Bakker &Schellin g (1966). In Benschop, it can be classified as peaty clay and clayey peat to rich in humus, in Jaarsveld as very humous to rich in humus. The cation-exchange capacity (CEC) of the bottom material was high, as could be expec­ ted in view of the high organic matter contents and the high clay contents. In all samples, calcium was the major exchangeable cation. The solid phase density of the bottom material was determined for calculation of the volume of the solid phase in slices of bottom material in penetration trials (Section 9.3. 12). This solid phase density varied from 2180 kg m"3 for the 'peaty clay' to 2500 kgm for the 'loam y bottom material '.

Profiles of volume fraction of liquid and bulk density

In April 1977, mud cores were collected in triplicate from the various ditch sections for measurement of volume fraction of liquid and bulk density. The cores were taken with the bottom-material sampler, provided with a closing unit on top. The frozen mud columns were divided mechanically into slices about 2 cm thick, as described in Section 7.2. The volume fractions of liquid in the slices are shown in Figure 36. The plots show the averages obtained from three columns per sampling site. The differences between the three columns were rather small. Near the sediment-water interface, the volume fraction of liquid was nearly the same in all samples. With increasing depth, the volume fraction decreased gradually. At one sampling point, in the front section of the supplementary drained ditch, there was only a very small decrease. For the lowest slices of bottom ma­ terial, sometimes relatively high volume fractions of liquid were found, which may be due to disturbance during sampling. The bulk densities of the bottom material are presented in Figure 36. The differences between the triplicate values per sampling site were rather large. The bulk density of the attorn material near the sediment-water interface was very low. The pattern of increase <*th e bulk density with depth was rather irregular. The distinct difference between the front and back section of the supplementally drained ditch in Benschop can be explained hy the presence of a peat layer in the sub-bottom of the front section of this ditch This ^ confined during sampling, since brown pieces of peat were visible through the clear Perspex wall of the sampling tube.

Elementary carbon

ïhe organic matter content is an important characteristic because it is highly rel*ed with the adsorption of pesticides (Section 6.6). Organic matter ™*°«*™J» Reallnicallyy sawn slices of frozen bottom material shown in Figure 37 were ^ * ƒ •"easured contents of elementary carbon of pooled material from two bottom columns. volume fraction ofliqui d (m3 m-3) 0.70. 8Q 9 1.0 0.70. 8 0.9 10 0.7 0.8 0.91 0 o-rfr' ' '> ' -r4' ' ' -' -rt' ' ' '

0.10H

J BSLb//BSLf Q20- BSDb/ BSDf JMb'IjMf i V' 030->

bulk density (kgm ) 0 200 400 20040 0 6000 200 400 0 | I^I l I_ ^ u_J l__J l l_ j I I IL _ J

0.10 BSDf \BSDb 0.20H

Q30

elementary carbon i.°/ó) c) 5 10 15 20 n i i i 10 152 02 5 303 5 0 5 10 15 \j ' J I I L ' J "l 0.10- [V BSLf X jBSLb BSDbi BSDf Q20- 1 JJMb.'JM f t

0.30- depth inbotto m(m ) lïfZMt $havTerirtl0n° fditC hb0tt0ra si n theLopiker - vaardPolder .Volum efraction so fliquid ,bul kdensitie san d elementary carboncontents .Abbreviation sfo rsam p n^ iS B- Benscho p J-Jaarsveld ,S D=siphon-linke d ditch!S D- supplementallydraine dditch ,M= middl editch ,b - bac k TL"£Tpart ofth edifferen tditc hsecti °- Ä- ueeper layers, more slices fahnm- •> ? ^- ,, increase with depth was r ^ ^ "*"*> *™ ""-*"*• ^ pattern of dec, VariaWe 6 f Peat ] sub-botto. ofth e front se tSn f 1 ' - ^ P^ ° ^ the wide variability in carbon. T Jn a^ T^^ ^^ ^ ^ ^ a dep* of about 10en » of the^f f ^ ^ch" ^ "T* *" *" ** ^ '^ " eiementa. carbon profits shl in P^T ^ * ^ * ^ ^ ^ ^ " -i^^isit^frr* ditchbotto m- thes -iementariiydrain :d* into 2o n slxces. Large variations in carbon contents were found 100 elementary carbon (%) 4 8 12 16 20 24 J i I \, I i I i L

0.04

Figure 37. Mass fraction of elementary carbon in 2 cm bottom slices for two ditches in Benschop ( — = 024j siphon-linked ditch and = supplementally depth in bottom(m ) drained ditch).

(Figure 37). This variability shows that it will be difficult to take representative sam­ ples of the ditch bottom.

S.3.6 Spraying dates and procedures in 1976

The siphon-linked ditch in Benschop was surrounded by a full-grown apple orchard (standard tree). Along one side of the supplementally drained ditch was an old pear or­ chard (standard tree) and on the other side a young apple orchard (spill trees). No paths were present along those ditches. The trees along the ditches were sprayed «ice, once on the nonnal way, and once with only one side of the spray heads (of a Kinkelder low-vo urne sprayer) operating, spraying only in the direction of the trees just alongsidetfie ditch Azinphos-methyl was applied in Benschop in apple and pear orchards on 3 May 21 June,

2-l y and 9 August 1976. T* last application was - investigated. On^the A^ ^ a spraying dates, azinphos-methyl, applied as Gusathion 25. »•?;' » t ^ ^athoate, applied as Rogor 40. li.uid. The spray "^^^ Lnts of

about 2.7 kg B"3 £or azinphos-methyl and a out 1. * »*rd^ ^^ water used for spraying were 15 cm3 m l and 25 cm m for the young

"TnanLd apple tree orchard was situated near the front ditch in Jaarsveld^ At one side of the middlfditch, a young spill tree plantation was planted an on ^J « this ditch stood standard trees. Alongside the front and middle ditch, there -d. The apple trees along the other side of *ese ^^^J^f ^orchard

-d by .spraying over, ^ ditdl. At both sides of the ^^^J^ ditch, (standard tree) was planted, very close to the ditch. In 19// on

tte old plantation was replaced by a new spill plantation. ^ ^ ^ ^ ^ 21June,

In Jaarsveld, azinphos-methyl was applied to apple trees on ' inyes_ 1 Aûy. 6 August and ^August (the effects of the last two ^"^J^ ingredient a. ttgated). Azinphos-methyl 25i w.p. was sprayed with a concentration ^ b 3 °«t 2.5 kg m" using a Kinkelder low-volume sprayer. Tne amounts of water sP ab 3 2 -t 20 to 30 cm m" for the young and old trees, "^^.^ areaS; they As mentioned before such situations are unusual in most ir representcondition stha tgreatl yfavou rth epollutio no fope nwate rwit hpesticides .

9.3.7 Concentrations of the insecticides in ditch water

Sampling,extractio nan dGL Canalysi s

Beforeapplicatio no fth epesticide so nbot hfarms ,dip-wate rsample swer ecollecte d fromth editc hsections ,b yth eprocedur edescribe di nSectio n4.2 .Shortl yafte ran dbe ­ tweenapplication so fazinphos-methy lan ddimethoate ,wate rsample swer e collected.O nth e firstfou rsamplin gdates ,composit edi psample swer ecollected .Late rdee pan dshallo w watersample swer etake nto owit hth evacuum-typ esample r (Section4.2) . Azinphos-methylan ddimethoat ewer eextracte dfro mth ewate rsample swit hdichloro - methanei na separator y funnel.Som eo fth eextract so fwate rsample swer ecleane du po n silicage lcolumns ,a sdescribe di nSectio n5. 9an d5.10 .Analysi so fazinphos-methy lwa s mostlyo ntw oGL Ccolumn s (Table 14).Dimethoat ewa smostl ymeasure do ntw ocolumn san d sometimeso nthre ecolumn s (Table15) .

Concentrationsi n 1976

Theconcentration so fazinphos-methy lan ddimethoat emeasure d inwate rsample stake n fromth edrainag editche si nBenscho par eshow ni nTable s3 7 and 38.Th econcentration s ofazinphos-methy li nth editc hsection si nJaarsvel dar epresente d inTabl e 39.Th ere - concenf°T &t COnCentrati0nSWer e «WH/ verylo wbefor espraying .Afte rspraying , concentrationswer einitiall yhig han ddecrease dgradually . Theconcentration so fbot hcompound si nwate rsample stake nbefor e sprayingwer ebe - „3^ " (n°Clean "Up)-M option was thesupplementall ydraine dditc hi nBenscho p LiItLST /"Tu Par t° f^ famWa SSpraye d °n1 »V "* thewate rpum pwa sno t ^l^Z^T ~tso ttef co — «***• »- «*-intoth e

in 1h .Beside sth epum^ sw ?" ^ ^ "*"^ ^ *"***" ^ used. e operationan ddifferen tsamplin g techniqueswer e

Effecto fdifferen tGL Ccolumn san dclean ­ up

Theconcentration so fth ecnmm,,^ , theris ko ferror scause db yLtel' f "T "^ " ^^ ^ "^ t0 "^ urements.Th edifference sbetwee n g tmces^ t0 urease theaccurac yo fmeas - 10115 faz GLCcolumn swer erelativel ysmal l l^™" ° inphos-methylmeasure d ondifferen t Column IIwer ei nmos tsample ssomewh^TT^ 0"5 °fazinphos -meth>'1measure d° n ^ maticdifference scoul db efound betw e h ^ ^"^ *' V°T dimethoaten 0SySt6 ~ columns. ^ concentrationsmeasure dwit hdifferen tGL C Theclean-u pprocedures ,a sdescrilw i • c eal naction s5. 9an d5.1 0wer euse do n1 0sam - 102 Ci ui -F to K> to — — Ni — co O o" ca H ^ to tu fD (D to t-H S S S 3 rt f-' 3 O* Ci •O (D O en M > o n w H Ö Ci CH C S K P 0) 1 < ir" t-1 x) C c C C 3 » to Fs ^j Vtoi I- « O fD (DOOI rr 13 3 3 3 ID *< ~< •< H- O 3* ro (ti ^ 3 tti nou tu o o << fi H« 00 3"T3 ~J fD a C C cu i-l rt gacnOcnwööOcnOcn H a u a a CO SCS B rt • ro H* p* H' H« H' tu to n to 3 cncncncncna'ü'öcncncncn T3 •a •Ö 13 •o o o O o rt H- (n en cn 00 cn CCCCCP- e e e C ' H« 3 1 3 fD 3 en oonnntj onoo T) rt o n oo H o o 3 n sou en — o 3 i- öc/iac/ioc/iüc/i a o H a cd rt en B C vo s » H' H* H- H' M- M. ~j n Ml o fD l 3 O en cncocncncncncncn •a •O •a B 0 rro> CL K C eeeeeecc 3 l a. tu • 3 P. » HBO onooooon P- 3 i-ti a HV: a 3 00 rt CO ff H- h1- h1* h" H* t— m u (D I (0 w en cn w w 'O'OBitiidirai/ioiœTj'O'a 0 a. 3 o o CL M« en t-i C C C G C CCCCCCC 3 i rt HC *- fD 13 w tu 3 n o n o o ooooono fD O a (D o* ro •O en Hi H> fD h-1 , , a rt ro tu NINJ^^^C^NI^^NI^^^^^C^C^C ^O""'NJ»-SJ VJNINJ en 3 ru OH 3 re d (T) » 3 to — a, MvJOOtO^DOOO-lJi^tOW-COCOCOCO-WOOO g H- H* ff Js DUS « H. « O i-ti o (_i «« 13 ro ro o CD 3- n t_ O A A W O o o 3 in en rt — C oo^ooooooooororo 3 en I O rt •O NI £•- vß .(> ho O si «^ CT' Ol O o » B O • ^ O ff 3 B ro h-> CA O T3 rt C (D cn U •-• 3" S O C f3" fD >< « yvlsiyj A S rr 3 O l-1 j> -*4 ^. vu — O < " . VO *-0 O m O I NJ -J LO Ln fD U t» 00 Ni x a rt fD (X O* er t'­ h- 0- en fD B (^LnOO-E>NtOO O to It Hl ffl a o ON a> — oo -P- \0 N! o f H (D tu J3 UID — M- — o Cr< -O — — l^n.0— j> — -P> .S3 B *< N: —* NI U> O — rt H- fD 3 n a* H OO o (u A N) -P- h- n — 4>- K£) — Ln

CO 0> O 1 i*" O * Ni 3 m fD tl Ml

A U) JS MI «; fD » ri rt S en ft> O I UiC^-P-CoUiCO-JO » M 00 Ni rt g O MI O M M- H W N) Ln - W O - C1 f O X o S

*• N) ÜTsl (?> C? W

(u 13 Ml - co ro c^ y o , g t- MI W W N K) *• W •O fD fD ' M LO —• O fD Ml 3 rt N) (O -t> Ni O A 3" C \D si O OJ W O to en O O rt ID Je ID r> O Ui O ^D ^O si N) •-- loo n rt o CA O o g . _ C 3 O H- c — — W W Ni Ui -1 00 !-• P. 6 P- ,. n o o\ œ M co IÛ u > B M* 0 (D p- a. MI (D oo to C rt u *• u ^ n — tD 4> Ui si -F> o en en en O A en en 3" CO o o — w ho ro \o - ro -P> UJ CT* *-J — (T> ,r'HH o u I ° 2 S' ro o o n 4> O <-<•> O - E'S- V£> | | Ni tO <- CA P" H K* 0 (D rt ONl-fc-UiNlC0O"*0-P-V/iU>Nl o Ln Ln Iji «Xî ro to -P- h" rt O M- .— t— ro w ro O 0 O ONii»o^>a>NiroOo — -c-—* <-n o c^ ro — o *- o — C^ o *— vo cy. .p> ro -P- vo NI es o r^. en o —• CM o- no t VU cr\ co Is- es a\ s-vr^^m-Noci^o o —

en r-» es rn a» «

es m co vu r«. vo es coinofoocooino

es o> en m es

« CO o

o>

CS — vO u"ï u™i o u u S ai a 3 S O —1 fsm en o coc o o • H u o •o WH O

U W ca 0 M .C c -a 3 01 i-l -o —I S •H O & S o •H S -a co 10 C U-l 10 o °î ™ ° °1 "î " ^ -3- -N 1—( u 4-» C o — —'Ooomoomino* co o S Ä 3 u. PJv m es es es •u 4-t (U u C 0 0) a) £ U-l u c >n o \o wf c o u ^ ^ °^ °; ^ -; ^ ^-3- * o o u o ) v£> r-«. es cO • J3 «W O o-oooomdovocses H C? ai 3 C B O T) a o. 3 S C *H .H M• o T3 H o a Q Q 01 P.CO C H o o r-l S _, cO Ö) U P. o e I UJ oi U w B u o O 3 a a Q - a 3333 "ÜOUUOOU co .S 5- °- o- 10 60 CO 10 « x Ä .H*.5'MM°>I«<010!0!0 C ai « o S 3 « S 01 'r4 4J M •PU"c o 3 3 as c co ai i3 O 4-1 o -H •H H >• ai £ 01 o 01 <-i 01 CO r-l U > SN co ja u S S c c O.U M a a 3 3 C D- a g •1 3 O H 00 cjd 13

— — CM ,-( cvl m j- Table 39. Mass concentrations of azinphos-methyl in samples of water from the different ditches in Jaarsveld during 1976. For codes for way of sampling see Table 37. Abbre­ viations f and b refer to the front and back sections of the different ditches.

3 iphos-methyl( i ngm -3) Dateo f Way of sampling pH Concen tration of azii sampling ditch backd i Ltch front middle back front ditch middle ditch ditch ditch I2 II I II I II

<1.0 <0.1 <0.3 5May 1 B Dip B Dip B Dip 7.0 <0.6 <0.8 <1.4 118 108 119 Dip Dip Dip 7.0 153 155 113 74 18 18 7Ma y Dip Dip Dip 7.2 15 14 61 2.9 1 1 2.4 12Ma y Dip Dip Dip 7.0 7.9 10 2.8 1• 1 f D suc 7.0 21 28 17Ma y Dip 7.2 7.8 8.6 3.7 4.5 Dip 1.4 2.1 f S f S suc 7.2 14 13 suc 1.8 2.4 f D suc 7.2 13 12 f D suc 1.6 2.2 24Ma y Dip Dip Dip 7.2 56 77 36 48 f S suc f S suc 7.1 214 264 19 20 f D suc f D suc 7.2 309 388 40 36 b S suc 7.2 55 63 b D suc 7.2 53 62 7.1 7.8 1.2 1.6 1Jun e f Dip Dip Dip 7.8 52 58 b Dip 7.8 11 15 0.4 0.6 14Jun e Dip Dip 7.5 3.3 2.7 0.3 0.4 f M suc f M suc 7.5 17 16 329 406 58 59 21Jun e f S suc f S suc f S suc 7.0 315 217 72 57 48 50 f D suc f D suc f D suc 7.0 12 15 12 64 73 5.5 23Jun e f S suc f S suc f S suc 7.0 62 66 98 79 5.0 8.1 f D suc f D suc f D suc 7.0 71 66 b S suc 7.0 80 68 7.0 58 60 b D suc 19 27 105 114 132 1Jul y f S suc f S suc f S suc 7.1 94 24 175 203 20 f D suc f D suc f D suc 7.1 28 29 b S suc 7.4 11 12 b D suc 7.4 24 27 2.5 2.6 5Jul y b S suc f S suc 7.2 8.8 8.6 2.0 1.9 b D suc f D suc 7.2 8.0 7.1 2.9 2.8 f M suc f M suc 7.4 24 26 —. • July 1976 (Section 9.3 i.6). '•Spra ydate s on 5May . 24 May, 21 June and 1 . 2-GL CColum n I and II. . see :Tabl e \l 3-Averag eva : lue for d: Lfferent ditch sections. —

i *• differences in concentration of Pies of water from the farm ditches. The average relative din ^ ^ ^ ^ azinphos-methyl and dimethoate before and after clean-up were on y ^ ^ ^ ^ Pounds. These differences were even smaller at concentrations above JJ^ ^ ^ , *e relatively high concentrations in the farm ditches, clean-up w

Effect of sampling and estimation of mixing time bout 0 to 6 cm below the water In 1976, many shallow water samples were sucked up, a ou interface. This gives s sediœn "rface, and deep samples, about 0 to 6 cm above the ^s_section o£ ^e water body

an indication on the distribution of the compounds over the cross ^^ ^ greatest « the ditch. The differences in concentration in shallow an ^ ^ ^ respectively). after spraying on 21 June in Benschop and Jaarsveld (Tables , compounds A„A fnr romolete mixing or uw v ,~ It is difficult to estimate the time needed for compie 105 through thewette d cross-sectiono fth editch .Transvers emixin gmainl y occursb ywate r circulationresultin g fromtemperatur edifference s inth ewater ,b ywin d actionan db y dispersiondurin g longitudinal flow.I nthes e field situations,som e other factorslik e local growtho fduckwee d andshar pvariatio ni nwate rdept hmad e itdifficul t toestimat e therat eo fmixing . Inth editche sa tJaarsveld ,mixin gwa s almost completeafte rtw odays , as canb e seenfro mth econcentration s inshallo wan d deepwater so n2 1 June and 23Jun e (Table 39). During thatperiod ,considerabl emixin g occurred in the ditches atBenscho p although itseeme d tob eincomplete . Anexceptio nwa s aftersprayin go fazinphos-methy lo n2 4Ma y 1976 inJaarsveld .I n thefron tsectio no fth e frontditch ,ver yhig h concentrations ofazinphos-methy lwer e foundbot h indee pan dshallo wsample so fwater .Thi s exceptionwa s due toa defec ti nth e sprayera tth estar to fspraying .

Variationi nconcentration swit hplac e

Besidesa stron gvariatio ni nconcentratio no fth ecompound swit h depth andtime , variationwit hplac eca nb esee ni nTable s 37t o39 .A tBenschop ,th econcentration s inth e middle sectiono fth esiphon-linke d ditchwer ehighe r than in its front andbac ksections . Thisca nb e explainedb y thepresenc eo fcomparativel y small trees alongsidepar to fth e middle sectiono fth editch .Durin gspraying ,i twa s clearlyvisibl e thata large rpar t ofth espra ypasse dacros sth esmalle rtrees . InJaarsveld ,th econcentration so fazinphos-methy l inth e frontan dmiddl editc hwer e muchhighe rtha ni nth ebac kditch .Thi scoul db edu e toth ewa y of spraying acrossth e first twoditc hsection s (Section9.3.6) .

9.3.8 Direct measurement of spray drift into ditches

In 1977,spra y driftt oth esam editche sa sstudie di n197 6wa smeasure ddirectly .

Before spraying Tempex (expandedplastic )float s (0.25m^ )wer e installed on thewate r 09m l rtanCeSl n* *ditCh6S -* th6Se floats> «I««» Petridishe s (diameter 0.09 m)wer eplaced .Afte rspraying ,th ePetr idishe swer e removedwithi n 1h fro mth e floats andplace d indar kcoole dboxe s Tnt u ,, • 0A threeti™> svrii- ha * ,, . ? laboratory, thePetr i disheswer e rinsed tnreetime swit haceton e fah mi ti çt « m 3-, „, ble usual!v„ - ,T ; 1St 0 20c m ). Thisrinsin gwa s done as quickly aspossi - Die,usuall ywith itJl m3 h o fsrirav-m n TK« • , tP^tpA in spraying.Th erecoverie so fazinphos-methy l and dimethoate(a s

iked water5 ies (o s -e« **d »I«,, „I,«« t„r s p ' vi ""•* - - °" ,k a „ph„s-,«hvl sh«d , fel « T "" PUCed " * "" °Ut °f tor8' In 2i f M < th0it8d8Cre Sed b b t vi« „f tüe Lt e^o»« "à/ .I ri "Î "" " c' " ™oum '"''" oi ,fc . **,« Tr.„ o^ LT^CS;:r r *•" ° * Spray driftwa smeasure d twiceduri ™ e • Qecilne- Benschopan dJaarsveld .Spra ydrif t 7^ ^^ ** azinPh°s"-thyli n1977 ,bot ha t otdimethoat ewa s onlymeasure d atBenschop .Thes e 106 simple measurements can replace calculation of spray drift into ditches from concentration in the water. There were no interfering compounds, extraction was Very fast and contamina­ tion could be measured accurately.

Results of measuring spray drift in Benschop

The methods of spraying and the amounts sprayed were the same as in 1976 (Section 9.3.6). Distances between standard apple trees around the siphon-linked ditch were 3 to 4 m. Around the supplementally drained ditch, the distances between the standard pear trees were 4.5 m and between the spill apple trees were 1.5 m. The distance between floats was 14.3 m for both ditches. The amounts of azinphos-methyl and dimethoate detected in the Petri dishes in Benschop are shown in Table 40. Differences between the duplicate samples were usually small and averaged 5% (0-28%) of the observed amounts. The variation in the longitudinal direction was much larger than in the transverse direction (Table 40, Sam­ pling Sites 3, 4 and 5 in the siphon-linked ditch on 26 August). The coefficient of varia­ tion in the average amounts in the longitudinal direction of the different ditches ranged from 29 to 45%. The amounts of dimethoate in the dishes were lower than those for azinphos-methyl which corresponded fairly well to the initial concentration in the sprayer (Section

Table 40. Masses (ug) of azinphos-methyl (A) and dimethoate (D) measured after at surf Ce spray drift in Petri dishes (diam. 0.09 m) placed on floats on the » «- ^ « ditches at Benschop in 1977. Mean values of duplicate samples. The floats were '.^•3 m'apart. ^^^^^__^_

SamPling Siphon-linked ditch Supplementally Ditch Section 51 site drained ditch

31 May 26 August 31 May f A"8ust ADA AD A 1.7 78 49 17 21 13 27 16 1.6 58 35 41 0.8 2 27 16 29 17 27(30)(26) 0.9 49 29 25(29)(35)2 35 15 34 23 26(26)(28)2 25 22 27 16 15 36 20 54 32 43 29 17 42 27 47 32 21 57 34 57 27 17 46 28 59 19 13 25 16 59 24 31 36 22 43 46 29 33 19 30 15 10 35 22 68 32 21 25 15 28 17 15 K3 42 26 38 28 18 (36) (35) (45) (29) (38) <38>

Ditch Section 5 was behind a windbreak on the fruit farm at Benschop Wlgure 31). y sin!"1"63 °£ the distributiono fth ecompoun d over thewidt ho fth e ^P^inked ditch. 107 Theaverag eamount so fbot hcompound si nth edishe so fth esupplementaril ydraine d ditchwer elowe rtha nthos eo fth esiphon-linke dditch .A ton esid eo fth esupplementari ­ lydraine dditch ,a spil lappl etre eorchar d receiveda smalle ramoun to fbot hcompound s thanth estandar dtree saroun dth esiphon-linke dditc h (Section9.3.6) . Ina ditc hsec ­ tionbehin da windbreak ,th emasse so fazinphos-methy l inth ePetr idishe swer emuc hles s thani nth eothe rsection s (Table40) .

Resultso fmeasurin gspra ydrif ti nJaarsvel d

Azinphos-methylwa sapplie dt oth eappl etree saccordin gt oth eprocedur edescribe d inSectio n9.3.6 .Th edistanc ebetwee nappl etree srange dfro m8. 5m forstandar dtree s to2 m fo rspil ltrees .Th edistanc ebetwee nth efloat swit hPetr idishe srange dfro m 16t o18. 7m .Th emasse so fazinphos-methy lmeasure di nPetr idishe si nJaarsvel d are.pre ­

sentedi nTabl e41 .Th eaverag edifferenc ebetwee nth eduplicat esample swa s6° 6 (0-491). Theamount si nth edifferen tditc hsection si nJaarsvel dwer emuc hhighe rtha nthos e inBenschop .Th elarg eamount si nth efron tan dmiddl editche sca nb eexplaine db yth e procedureo fsprayin gove rthes editc hsection s (Section9.3.6) .Th eamount si nth ebac k ditchwer eals ohigh ,probabl ybecaus eth etree sstoo dver yclos et oth editch . Thevariatio ni ntransvers edirectio nwa ssmaller ,jus ta sa tBenscho p (Sites8 an d 9 inth efron tditc ho n6 July) .Th ecoefficien to fvariatio no fth eaverag eamount smeas ­ uredi nth elongitudina ldirectio no fth editche si nJaarsvel drange dfro m2 3t o55°s .

Table41 .Masse s (ug)o fazinphos-methy l (A)measure d after spraydrif t inPetr idische s (diam.0.0 9m )place do nfloat so nth ewater-surfac ei n ditchesa tJaarsvel d in 1977.Mea nvalue so fduplicat esamples .

Sampling Frontd i .ten Middle ditch1 Backditch 1 site 25Ma y 6Jul y 25Ma y 6 July 25Ma y

1(front ) 218 186 169 178 89 2 138 153 74 246 86 3 102 139 110 170 73 4 76 219 121 157 46 5 61 261 137 135 66 6 199 108 321 137 39 7 119 184 125 113 207 8 117 183(180)2 75 81 9 85 220(149)(214)2 92 110 10 51 169 95 65 1I (back ) 218 209 93 Average 126 185 128 162 86 Coefficiento f (48) (23) (55) (27) (55) variation(% )

1.Par to f theol dappl eplantatio no non esid eo f theditc hwa scleare d inJune. . 2.Value so fth edistributio no fth ecompoun d over thewidt h ofth efron t ditch.

108 Estimate of drift of the insecticides into ditches \\V. Theaverag emas so fazinphos-methy li na Petr idis ho fare a63. 6cm 2i nth esiphon - -linkedditc hwa s4 2y go r6. 6 mgm ofevaporatin gsurfac eo fth editch .Th emas sdos e ofazinphos-methy ldivide db ygroun dsurfac eapplie do nth estandar dtree saroun dth e siphon-linked ditchwa s6 8m gm (Section9.6.3) . Torelat econtaminatio nt odose ,a n 'areicrati oo fcontamination ' m .coul db edefine da sth erati obetwee nth emas so fin ­ secticidefallin go na nare ao fwate rdivide db ytha tare aan dth emas sdos edivide db y groundare ao fth espraye dorchard .O n3 1Ma yan d2 6August ,afte rspra ydrif tint oth e siphon-linkedditc hthi srati owa sabou t0.1 . Forth epumpe dditch ,th earei cratio , m ., forazinphos-methy lwa scalculate dt o be0.08 .Th ecorrespondin gratio sfo rdimethoat eint obot hditche swer enearl yth esam ea s forazinphos-methy lnamel y0. 1 and0.09 ,respectively . On2 5Ma yi nJaarsveld ,th earei cratio sfo razinphos-methyl ,wer eabou t0.2 6 forth e frontditch ,0.3 2 forth emiddl editc han d0.1 8 forth ebac kditch .O n6 Jul ythes eratio s forth efron tan dmiddl editche swer eabou t0.3 9 and0.41 ,respectively . Forth editc hsectio nprotecte db ya windbreak ,th erati o m wasonl y0.003 . r,/L 9.3.9 Estimate of rate coefficients for decline

Themas so fth ecompound si nth ewate rcompartmen tafte rth efirs tapplicatio ni n Benschopo n3 Ma y 1976wer eobtaine dfro mth eproduc to faverage dconcentration s in'dip ' samplestake nfro mth efront ,middl ean dbac ksection s (Tables3 7an d38 )an dwate rvol ­ umeso nsamplin gdates .Sinc eth eamount sshortl yafte rsprayin gwer eno tye tmixe dove r thecross-sectio no fth ewate rbody ,thes einitia lmasse swer econsidere dto ouncertai n forestimatio no frat ecoefficients . Adeclin eplo t (logconcentratio na tvariou stimes )wa smad efo ra perio dwithou t infiltrationo rdischarg eb yth ewate rpum pfro m5 t o1 8Ma yfo rbot hcompound si nbot h ditchesa tBenscho p (Figure38) .Linea rregressio nline swer edraw n (Chapter7) .Th erat e coefficientsfo rdeclin eo fazinphos-methy lan ddimethoat ei nditc hwate rar epresente di n Table4 2 (Period I).Th erat ecoefficient sfo rdeclin eo fdimethoat ewer edistinctl ylowe r thanthos efo razinphos-methyl .

mass of pesticide (g)

Figure38 .Mas so fpesticide s inth ewate rcom ­ partmento fditche sa tBenscho pa tvariou stime s afterapplicatio no n3 Ma y 1976.A = azinphos - -methyli nsiphon-linke dditc h (BSL);• = dime ­ thoatei nsiphon-linke dditc h (BSL); A= azinphos - -methyli nsupplementall ydraine dditc h (BSD); o= dimethoat e insupplementall ydraine dditc h (BSD).

109 Table42 .First-orde r ratecoefficient sfo rdeclin eo fazinphos-methy l anddimethoat ei ndrain ­ ageditche sa tBenschop .Perio dI fro m5 t o1 7May ,an dPerio d IIfro m2 1Jun e to1 Jul y1976 .

Period PH1 Watertemp . Azinpho s-methyl Dimethoate °C,av. ,s.d . andrange 2 rate half coeff.o f rate half coeff. of coeff. life determ. coeff. life determ. (d-1) (d) (a"1) (d)

Siphon-linked I 7.0 14+2(11-19) 0.25 2.8 1.00 0.056 12 0.95 ditch II 7.0 19+2(15-21) 0.25 2.8 0.99 0.052 13 0.97 3 Supplementärily I 7.1 14+2(11-19) 0.18 3.9 0.91 0.061 11 0.98 drainedditc h II 7.0 19+2(15-21) 0.26 2.6 0.98 0.19 3.6 1.00

1.p Hwa smeasure d inth efield . 2.Calculate d fromdail yminimu man dmaximu m temperatures inth ewate r compartmentnea rth e waterpump . i 3.Valu eo n5 Ma yfo rdimethoat ewa srejected .

Afterth esecon dapplicatio no fbot hcompound sa tth eBenscho pfar mo n2 1Jun e1976 , theaverag emasse so fbot hpesticide so n2 3Jun ean d1 Jul ywer ecalculate dfro mth eaver ­ ageconcentratio ni nshallo wan ddee psample so fwate ran dth ewate rvolum eo nbot hdates . Shortlyafte rth esecon dspraying ,shallo wsample so fwate rwer etaken .Durin gth espray - -driftexperiment si n1977 ,th erelationshi pbetwee nshallo wsamplin gan darei crati oo f contaminationwa smeasured .B ytakin gint oaccoun tth ewate rsurfac eare ai n1976 , the initialmasse scoul db eestimated .Fo ra perio dwithou tinfiltratio no rdischarg efro m2 1 Junet o1 July ,th edeclin epattern sa tBenscho par eshow ni nFigur e39 .Th erat ecoeffi ­ cientsfo rdeclin eo fbot hcompound sar epresente di nTabl e4 2(Perio dII) . Therat ecoefficient sobtaine ddurin gbot hperiod so finvestigatio nar ecomparabl et o therat ecoefficient s foundi nth eoutdoo rtank sfo rperiod swit hsimila rcondition s (compareTable s2 6an d42) .

9.3.10 Concentrations of the insecticides in surface water near Benschop and Jaarsveld in 1976

Concentrationso fbot hcompound si nsurfac ewate routsid ebot hfarm swer emeasure do n a limitedscale .Th eresult sar eshow ni nTabl e43 .Thes edat awer eobtaine do ndifferen t

masso f pesticide (g) 10-a

Figure39 .Mas so fpesticide s inth ewate r compartment ofditche sa tBenscho pa tvariou s timesafte rth e2n d applicationo n2 1Jun e 1976.1 = azinphos-methy li n siphon-linked ditch (BSL);• = dimethoat e insiphon - -linked ditch (BSL); A= azinphos-methyl insupplemen ­ tally drainedditc h (BSD);o = dimethoat e insupple ­ mentallydraine d ditch (BSD).

110 Table 43. Mass concentrations of azinphos-methyl and dimethoate in samples of surface water in the Lopikerwaard Polder, in 1976. Date of Site pH Concentration (mg m-3) sampling azinphos-methyl dimethoate

r3 II I II III 7 May Intake, Jaarsveld 7.2 0.4 0.8 24Ma y Discharge, Benschop1 7.6 1.6 1.8 17 16 1Jun e Discharge, Benschop 7.8 0.4 0.7 5.8 9.3 9.7 Benschopper Canal2 7.6 0.6 1.1 0.2 8.2 0.1 14Jun e Discharge, Benschop 7.0 0.3 0.4 6.2 5.6 7.4 1. Discharge, Benschop: surface water receiving water from the fruit farm at Benschop.i ' 2. Benschopper Canal: near the bridge in Benschop village. 3. GLCColumn s (see Tables 14 and 15). .

GLC columns without clean-up procedures. The discharge ditch at Benschop received water from the water pump. The high concen­ trations of dimethoate in this discharge ditch was possibly due to cleaning of the spray équipent near the sampling point. The deviant high value for dimethoate in surface water ('Benschopper Canal', 1 June) measured on Column II showed that using only one GLC column packing involved a risk of overestimating the concentration. 9-Z-U Preliminary measurements of concentrations in groundwater

Before spraying in 1976, some groundwater tubes (length 2m; diam. 0.06 m) were placed in bore holes (diam. 0.08 m) (Figures 31 and 32). The lower part of the PVC groundwater **e was perforated, with filter length of 0.5 m. The top of the tube protruded about 0.15 m above the surface. On top of the tubes, screw-caps were placed. See groundwater samples were sucked up from these tubes with the vacuum- yp sa»ï>ler (Chapter 4) for analysis. Concentrations of both compounds in samples o g ter «e presented in Tables 44 ^ 45. With one exception, the concentrations were JT low- Without clean-up, the azinphos-methyl concentrations in groundWf ^"^ _ ^ Sd»P -re usually below 1 mg m"3. Although the tubes were emptied a few day b ** deling, contamination caused by leakage along the groundwater tubes might be poss , becau*e the diameter of the bore hole was greater than the diameter of the t . ^ iMring investigation in 1976 at Benschop, hardly any water flow occur *«* into the subsoil. However at Jaarsveld, a considerable *«««^- £ ^

«*** ditch was measured after water intake (rising ^^wf in Table 35). At hl°ride concentrations in Groundwater Tube VI on 17 m and 14 June 197 ^ ^ ;arsveld, the azinphos-methyl concentrations in Groundwater Tubes an *• orations in Tubes V and VI, which showed a much stronger rep ns 0^ ^ ^el to raising of the ditch water than Tubes I and II ^^^ in areas Uon <* groundwater from contaminated surface water probably cannot be 111 Table44 .Mas sconcentration s ofazinphos-methy lan ddimethoat ei nsample so f groundwater atBenscho p in1976 .

3 Dateo f Ground pH Concentration (mgm ) sampling water tube azinphos-methy l dimethoate

il II I II III

17Ma y III 6.9 0.2 0.3 0.2 0.05 IX 4.2 0.07 0.1 0.2 0.03 14Jun e III 7.5 0.6 0.8 7.3 7.9 8.2 IX 6.2 0.1 0.04 0.2 0.03 1Jul y II 7.4 0.6 0.6 0.3 0.4 0.08 III 7.4 0.2 0.3 0.7 0.8 0.4 VIII 7.4 0.3 0.4 1.0 1.7 1.2

1.GL CCo l umns(se e TabLe s1 4 and15) .

whereinfiltratio ni scommo nan dwher eresidenc etime sar erelativel yshort . Theconcentratio no fdimethoat ei nGroundwate rTub e IIIo n 14Jun e 1976a tBenscho p washighe rtha no fothe rmeasurement s (Table44) . Formor edefinit econclusion so npossi ­ blegroundwate rcontamination ,mor emeasurement sar enecessary . Inth efuture ,an yleakag e alongth etube sshoul db eprevented .

9.3.12 Penetration of azinphos-methyl into bottom material

Proceduresfo rmeasurin gpenetratio n

Duringth emeasurin gperiod si n197 6som emu dcore swer ecollecte d inBenscho pa t fourplace si nth efron tan dbac ksection so fbot hditche san di nJaarsvel di nth efron t sectionso fth efront ,middl ean dbac kditc h (Figures3 1an d 32).Thes emu dcore swer e takenwit hth ePerspe xbotto mmateria lsample rwit ha stainless-stee lclosin guni to pto p (Chapter 4). Themu dcolumn swer estore d ina deep-freeze rfo rabou thal fa year .Th efroze n mudcolumn swer ea tfirs tdivide d intoslices ,wit ha carborundu mhandsaw ;late rth ecolumn s weremechanicall ysaw n (Chapter7) .

Table45 .Mas sconcentration so fazinphos-methy l insample so fground ­ watera tJaarsvel d in1976 .

Dateo f Ground pH , Concentration nf3) sampling water tube II

17Ma y II 6.9 0.3 0.7 VI 7.0 1.0 1.1 14Jun e I 7.0 0.3 0.4 V 7.0 4.0 2.3 1Jul y I 7.4 0.8 0.6 V 7.4 0.8 1.3 VI 7.4 0.9 1.1

1.GL CColumn s (seeTabl e14) .

112 The volumes of the wet mud slices were calculated with Equation 11, using the data on the density of the solid phase (Table 36). The depth below the sediment—water interface was obtained by dividing the volume of the wet mud sample by the average surface area of the frozen mud column (49 cm ). The saw cut was about 2 mmfo r both hand-sawn and mechani­ cally sawn columns. The slices were extracted with a mixture of solvents and the extracts were cleaned on silica gel columns in the same way as the extracts from the bottom material in the outdoor tanks (Sections 5.6 and 5.11). The cleaned extracts were analysed by GLC on Column II (Ta­ ble 14). Asignifican t decrease in concentration during storage of the mud columns was not detected, and no correction factor was introduced (Chapter 7).

Results for penetration

The masses of azinphos-methyl in bottom materials from Benschop and Jaarsveld are pre­ sented in Tables 46 and 47, respectively, unfortunately, several mud columns, including the samples of bottom material taken before the spraying period were lost during storage byfailur e of one of the deep-freezers. Therefore in the next year (March 1977), new un-

Table 46. Penetration of az inphos-methyl into the bottom of the siphon-linked ditch and the supplementally draineinpd Hditc Hit-rh hin i nBenscho Benschop pdurin during g 1976. f, front of the ditch; b» back of the ditch.

Dateo f Siphon-linked ditch Supplementallydraine dditc h sampling masso f site depthi n masso f site depthi n bottom(m ) azinphos- andslic e bottom (m) azinphos- andslic e -methyli n number -methyli n number slices(ug ) slices (ug) 0 -0.008 0.14 17 May fl 0.67 fl 0 -0.010 0.010-0.023 <0.01 f2 f2 0.012-0.023 0.44 0.025-0.036 <0.01 f3 f3 0.025-0.036 0.16 0 -0.011 0.54 bl bl 0 -0.012 0.34 0.013-0.024 0.24 b2 b2 0.014-0.025 0.17 0.026-0.037 0.15 b3 0.027-0.039 0.07 b3 0.07 M May 0 -0.009 fl 0 -0.009 _1 fl 0.09 0.05 f2 0.011-0.026 f2 0.011-0.021 0.028-0.043 0.08 0.09 f3 f3 0.023-0.033 0 -0.021 0.15 bl 0 -0.007 0.13 bl 0.17 b2 0.023-0.034 b2 0.009-0.028 0.24 0.036-0.047 0.08 b3 0.030-0.049 0.01 b3 21 0 -0.011 0.04 June bl bl 0 -0.010 0.29 0.013-0.023 <0.01 b2 b2 0.012-0.023 _1 0.025-0.036 <0.01 b3 b3 0.025-0.036 0.18 0.038-0.050 0.04 b6 0.063-0.073 0.04 b4 blO 0.112-0.123 0.01 0.86 23 June 0 -0.011 fl 0 -0.011 0.30 fl 0.013-0.024 0.09 f2 0.013-0.022 0.29 f2 0.026-0.037 0.05 f3 0.024-0.034 0.18 f3 0 -0.010 0.38 bl 0 -0.010 1.84 bl 0.012-0.022 0.24 b2 0.012-0.022 0.22 b2 0.024-0.036 0.11 b3 0.024-0.034 0.14 b3

substances;clean-u pfaile d

113 Table47 .Penetratio no fazinphos-methy l inth ebotto mo ffron tditc h (JF), middleditc h (JM)an dbac kditc h (JB)i nJaarsvel d during 1976.Al lsample s were collected fromth efron tpart so fth edifferen tditches .

Dateo f Sitean d Depth inbotto m Masso fazinphos - sampling slicenumbe r (m) -methyl inslice s (ug)

24Ma y JF1 0 -0.019 1.80 JF2 0.021-0.032 0.49 JF3 0.034-0.046 0.23 JM1 0 -0.015 1.55 JM2 0.017-0.024 0.10 JM3 0.026-0.033 0.10 JB1 0 -0.013 0.80 JB2 0.015-0.024 0.12 JB3 0.026-0.033 0.09 21Jun e JB1 0 -0.010 0.65 JB2 0.012-0.023 0.22 JB3 0.025-0.035 0.09 JB6 0.061-0.071 0.08 JB10 0.109-0.120 0.11 23Jun e JM1 0 -0.010 3.24 JM2 0.012-0.022 0.78 JM3 0.024-0.035 0.43 JB1 0 -0.011 2.53 JB2 0.013-0.023 2.04 JB3 0.025-0.035 0.94 1Jul y JF1 0 -0.009 0.15 JF2 0.011-0.022 0.04 JF3 0.024-0.034 0.02 JM1 0 -0.010 0.64 JM2 0.012-0.022 0.21 JM3 0.024-0.034 0.15 JM6 0.061-0.071 0.06 JM10 0.109-0.120 -

1.Interferin g substances;clean-u pfailed .

treatedbotto msample swer ecollected .Th emasse so fazinphos-methy li nth euppe r layer werebelo wth edetectio nlimi tfo rextract so fbotto mmaterial ,whic hwa s 1n gpe rslic e (50c m) . Sopresumabl yals oi n1976 ,n omeasurabl eamount swer epresen tbefor espraying . Afterspraying ,th emasse si nth e upperslice swer ehighe rtha ni nth elowe rslices . Thedifference sbetwee nth efron tan dbac k sectionso fth editche si nBenscho pwer e large (Table 46).Th elarges tamount so fazinphos-methy lwer e foundi nbotto mslice s fromth e middlean dbac kditc hi nJaarsvel do n2 3June ,2 d afte rspraying .O ntha tdat eth ewate r concentrationswer elikewis ehig h (Tables4 7an d 39). Inspit eo fth esmal lnumbe ro fbotto m cores,som eapproximation swer emad eo nth e totalmasse so fazinphos-methy li nth e differentditc hbottom si nBenscho po n2 3June .Thes e totalmasse swer eestimate d fromth eaverag emasse si nth ethre euppe rslice so fbotto m materialan dth esurfac eare ao fth editc hbottom .The ywer ecompare dt otota lmasse so f azinphos-methyli nth ewate rcompartment so fbot hditche si nBenscho p (Figure39) . Thetota lmas so fazinphos-methy li nth ebotto mcompartmen to fth esiphon-linke dditc ho n 23Jun ewa sestimate da t13« .o fit smas si nth ewate rcompartment .Th ecorrespondin gper ­ centagei nth esupplementall ydraine dditc hwa sonl y 2%.

114 The penetration of azinphos-methyl in the bottom layer will be discussed in more de­ tail under computer simulation for these situations (Chapter 10).

9.S.1S General discussion and conclusions

The hydrological circumstances on both farms in the Lopikerwaard Polder were highly complex. Moreover the soil surface was rather uneven, the soil was very heterogeneous and data on the water-conducting substratum were lacking. Consequently, the usual drainage for­ mulae could not be used to estimate water flow through the ditch bottoms. Intake of uncon­ trolled amounts of water made estimation of the items of water balance difficult. For ac­ curate measurement of water balances, simpler field situations and automatic measuring e- quipment will be necessary. The characterization of ditch bottoms showed high organic matter contents, low bulk densities and corresponding high volume fractions of liquid. Data of this kind are rather scarce and need more attention in the future. Introduction of the insecticides into surface water by spray drift could be measured quickly with Petri dishes. Its extent is highly influenced by local situations (windbreaks, Position of trees, paths) and ways of application. Windbreaks (and probably also paths a- longside the ditches) reduce the areic ratio of contamination, but more researches needed toasses s their effect in different situations. In such measurements of spray drift, the tossesb y photochemical conversion and volatilization should be measured. There may be other sources of contamination into watercourses, for example the clean- lng of spray equipment after use. The concentration of the compounds in the farm ditches were fairly high and other substances did not interfere during the GLC analysis. The calculated half-lives of azm- Phos-methyi in the ditches in Benschop were about 3 to 4 days, and those for diinethoate t0 13days. These half-lives corresponded to the half-lives measured in outdoor tank trials (Chapter 7). Mixing of the compounds throughout the cross-section of the ditch occurred within a few days. The rate of adsorption and penetration into the bottom material may be lower n ouations with slow mixing. More research is needed to investigate the mixing process TOre detail. me data on penetration of azinphos-methyl into the bottom layer were ^ 1^ to est«te accurately the fraction of the substance introduced that penetrated. " ^-sion in bottom material under field conditions was not known, but ^^V "*** that it may be fairly high (Chapter 6). The contributions of «™^J^ ^ion, and biological mixing to penetration of the insecticide into *eJ£« ™ " ***• ^se aspects will be discussed in more detail under the computer simulation

^ situations t -hu t. * the basis of these field trials alone, it is difficult to estate *-J^_ S ;t°; « different decline processes. In Chapters 10 and 11, « ^.^ system- These 3te «a effects of the various processes by computer simulation of ^f^ ticides ^er studies should enlarge the transferability to other stations and other pe different physico-chemical properties. 115 10 Computations on the behaviour of pesticides in a ditch compartment

10.1 INTRODUCTION

Thecontributio no fth evariou sprocesse st oth edeclin eo fazinphos-methy l anddime - thoatei nditche swa sdifficul tt oassess ,especiall yi nperiod so fwate rintak eo rpump ­ ing.Th eexten to fpenetratio no fbot hpesticide s intoth editc hbotto mwa sals odiffi ­ cultt oevaluat e fromth efiel dexperiment s (Chapter 9). Toovercom e theseproblem sat ­ temptsar emad et odescrib eth ebehaviou ro fazinphos-methy l anddimethoat ei na ditc h systemmor equantitativel ywit hcomputatio nmodels . Firstlyth erelevan twate rflo wi nth editc hsystem swer e approximated. Secondly, pesticidemovemen tan dconversio nwer ebuil tint oa computatio nmodel .Th emode l includes flowo fth epesticid e throughth eboundar ysurface so fth ewate ran dbotto mcompartments . Muchattentio nwa spai d toth eeffect so fadsorptio no nan dpenetratio no fth epesticide s intoth editc hbottom . Ina simulatio nexperiment ,th esignificanc ewa s studiedo finfil ­ trationthroug hth editc hbotto mo nexten to fpenetratio no fpesticides . Comparisonso fth eresult so f thecomputation swit h thoseo ffiel dmeasurement swer e onlymad e forth etw oditche si nBenschop .Th e largevariatio ni nth ewate r levelsi n ditchesa tJaarsvel dan dth euncontrolle dwate r intakea tth ebeginnin go fMa yan da tth e endo fJun e 1976presente d insurmountableproblem s forth eapproximatio no fth ewate rbal ­ ance.

10.2 DITCHGEOMETR YAN DDERIVATIO NO FEQUATION S

Thecross-sectio no f theditc hwa s assumed toconsis to fstacke d trapezia (Figure 40). Theslope so f thewall s inth elowe rpar to fth editche swer estee p (Table 34). Thewet ­ tedperimete ro fth editc h (P) wa s calculated from

P, = b, + Ih Ja1,+ 1 (22) I 1 w 1 *• inwhic h

b] =width a tbotto mo fditc h (m) &w =averag ewate rdept h (m)

s} ortgc e= slop eo flowe rpar to fditc hwall swit hrespec tt overtica l (1) (tga= horiz./vert. ) (Figure40 ) Thepesticide swer eassume d tob ecompletel ymixe d through theditc hwate rcompart ­ ment.Th editc hbotto mwa sdivide d intotwent ycomputatio ncompartments . Thesurfac eare ao fth efirs tbotto mcompartmen ta tth esediment-wate r interface (Vz=owa s comPuted from theproduc to fth ewette dperimete r (p,)an d thelengt ho fth e

116 4MUSXMS.

Figure40 .Cross-sectio no fa ditc hwit h / JéJÎ theshap eo fstacke d trapezia.Fo rsymbol s seetext .

ditchcompartmen t (I ).Th esurfac eare ao fth esecon dbotto mcompartmen twa sobtaine d fromth eproduc to f 'interface'perimete r P and I .Th eperimete r p wascompute dfro m Equation23 :

P2 =2» ,+ 2d2 tgUfO +2 {hv +d 2) /s^+ 1 * C23)

inwhic h ß =arct g (1/sj)(Figur e40 ) (1) cL= dept ho fuppe rsurfac eo fsecon dbotto mcompartmen t (m)

Thesurfac earea so fth eothe rbotto mcompartment swer eobtaine di na simila rway .

Water flow

Waterflo wi nth ewate rcompartmen t (Figure41 )wa scombine dint oth efollowin gcon ­ servationequation :

(24) dVw /it = q - qe - qd + q^ + ^ - q^ • <7b *

ID "•

Figure41 .Sketc ho fa ditc hcompartment .Fo r theitem so f thewate rbalanc eo f theditc hcompartment ,se eEquatio n24 .

117 inwhic h àV/àt =chang e instorag eo fwate r compartment (m3 d" ) q =rat eo fprecipitatio n intowate r compartment (m3 d" ) q =rat eo fevaporatio n fromwate r compartment (m3 d" ) e 3 q =rat eo fdischarg e fromwate r compartment (m d" ) 3 q =rat eo fdischarg e fromupstrea m ditch section (m d" ) i 3 - q. =rat eo fintak e intowate r compartment (m dA ) 3 q. , =rat eo fintak e into down stream ditch section Cm d" ) 3 q =rat eo fflo w through wetted perimetero fditc h (m d" ) 3 q =flo w rate through drains (m d" ')

•z _2 -i Thefiltratio nvelocit y( ^ inm m d )throug hth edifferen tbotto m compartments wascalculate d from

inwhic h 2 A, =surfac eare ao fbotto mcompartmen t (m) 3 =inde xnumbe ro fbotto mcompartmen t (1)

Pesticide movement and conversion

The total areicmas s fluxo fpesticid e into bottom material (

Js,lb= ^conv.lb+ ^disp.l b+ ^dif.l b (26) inwhic h j =arei cmas s fluxb yconvectio n into bottommateria l (mem d ) -2 "1 conv.lb -2-1 J,. , =arei cmas s fluxb yconvectiv e dispersion into bottom mate- (mgm " d ) disp.lb r *•Ä rial Jdif,lb =arei c mass fluxb ydiffusio n inbotto m material (mgm " d ) The areicmas s fluxb yconvectio nwa s describedb yth eproduc to ffiltratio n veloci­ ty 0lb)an dmas s concentrationo fth epesticid e inth eliqui d phaseo fth e bottom 0lb inm gm) :

J conv,lb = "ib "ib (27)

The areic mass fluxb yconvectiv e dispersionwa s calculated with

J = 3e /3z 2fJ disP,lb -*dhb| lb ( ) inwhic h

118 l& =dispersio ndistanc e (m) z =dept h inbotto m (m)

Thearei cmas s fluxb ydiffusio ni nbotto mmateria l («7..., ,) wa scompute di nth e samewa ya sdescribe d inChapte r8 [Equations 15an d16) . Therat eo fconversio ni nth editc hwate r {R )an dth erat eo fconversio ni nth e ditchbotto mmateria l (i? )wer ecalculate dwit h first-orderrat eEquation s 17an d 18, respectively. Theflo wrat eo fsubstanc e intoth ewate rcompartmen tdurin ga nintak eperio d (F inm gd )wa s calculated from

Fc •= a. a . (29) S,W1 H1 W,l v ' inwhic h °w i=mas s concer>trationo fsubstanc ei nintak ewate r (mgm )

Theflo wrat eo fsubstanc eint odownstrea mditc hsectio n duringa nintak eperio d

(fsw d inm gd )wa scompute dfro m

F • = q. . o (30) s,wd *

Theflo wrat eo fsubstanc eou to fth ewate rcompartmen tdurin ga pumpin gperio d (FSs,w oi nm gd ~ )wa scalculate dfro m

s,wo ^d w

Theflo wrat eo fsubstanc eint oa wate rcompartmen tfro mupstrea mditc hsectio n dur­ inga pumpin gperio d (F inm gd ") wa scompute d from

F =a , a (32) s.wu Hd,u w,u inwhic h _3 c =mas s concentrationo fsubstanc e inupstrea mditc hsectio n (mgm )

Theresultin gconservatio nequatio nfo rth epesticid ei nth ewate rcompartmen twit h 3 volumef w (m )wa s

S(V a 1/3f = -(A ,T 1 + F . + F -F . - F - V R (33) n w

119 dcjdt =-3J - ../3s- i? „, (34) b s,lb c,b

The relationship betweenmas sconcentratio ni nth ebotto mmateria l Ob)an dth e con­ centrationi nth e liquidphas e (c )wa scompute dwit h Equation 21.Th eadsorption—desorp - tionwa s assumedt ooccu rinstantaneously ,whil eth eisother mwa s assumedt ob elinea ri n therelevan t concentration range.

10.3 DESIGNO FTH ECOMPUTATION SAN DVALUE SO FPARAMETER S

Thedifferentia l equations,boundar y conditionsan dbasi c relationshipswer e program­ medi nth ecompute r language CSMPII I(IBM , 1975).Th eprogra mwa sru no nth eDECsystem-1 0 computero fth eAgricultura l University,Wageningen .Th elistin go fthi s computationmode l isgive n'i nAppendi xB . The initialmasse so fth esubstanc ei nth ewate r compartmentan di nth e bottom com­ partmentswer e assumedt ob ezero .Th espray-drif twa sse ta ta constan t rate duringth e dayo fspraying .Thi s inputwa s assumedt ob ecompletel ymixe d through thewate r compart­ ment.Th etota lmasse sa tBenscho po nth efirs tsprayin g datewer e derivedb ybackwar d extrapolationo fth eregressio n linesi nFigur e3 8t oth eordinat eo nth edat eo fth e spraying.Th emasse s applied duringth esecon d sprayingwer e obtained fromth evalue sa t theintercep twit hth eordinat ei nFigur e39 . InBenschop ,n owate rwa s takeni ndurin gth einvestigation , thusth erat eo fintak e into thewate r compartment (q.) andth erat eo fintak e into downstream ditch sections (q. ,)coul db ese tt ozero .Becaus eth esiphon-linke d ditchwa sa branc ho fth e discharge system (Figure 31),n odischarg e fromupstrea m ditch sections occurred {q, = 0). During periodswit h discharge,th econcentratio no fth esubstanc e inwate r flowing from upstream ditch sections intoth esupplementall y drained ditchi nBenscho pwa s assumedt oequa lth e concentration discharged fromth esiphon-linke d ditch. Thedimension so fth editc h sectionswer e introduced fromTabl e 34.Th enumbe ro f computation compartments inth e bottomwa s twenty.Th ethicknes so fth e firstbotto mcom ­ partmentwa s0.00 1m .Th emultiplicatio n factorfo rth ethicknes so fth ebotto m compartments

(mf)wa s1.1 .Th etota l thicknesso fth ebotto m layerwa s thencompute da t0.0 6m .Th epara ­ meterso fth editc hbotto m like thebul k density (p,) an dth evolum e fractiono fliqui d b

(e.)a sshow ni nFigur e3 5wer e introduceda sfunction so fdepth .

Description of the water flow Theflo wrate so fevaporatio n {q )an drainfal l (q )wer e calculated fromFigure s3 3 and 34Ab ymultiplyin gth efluxe s (inm md )b yth ewate r surfacearea .I nth ecomputa ­ tionmodel ,th e rateo frainfal lwa sdistribute d evenly overth eda yprecedin gth etim eo f observation. Therat eo fdischarg eo fth ewate rpum pwa smeasure ddurin g dispersion experiments (Chapter 11).Th erat eo fdischarg e from thewate r compartment (q) durin ga da ywit hpump ­ ingwa s obtainedb ymultiplyin gth efollowin g quantities:a )dail ypumpin g times (Figure 34B);b )rat eo fdischarg eo fth ewate rpump ;c )rati obetwee nth ecatchemen t areao fth e

120 ditchcompartmen tan d the totalcatchmen t areao fth ewate rpum p (Table 34). This resulted indischarg e rates inBenscho p ofq d(BSL)= 135an d

inwhic h (kg m-3} p =densit yo fwate r . ^-2. g =acceleratio ndu et o gravity h =heigh t ofgroundwate r levelabov e ditchbotto m ^

hv =heigh t ofwate r levelabov editc hbotto m ^.2 ^ Y =drainag e resistance

Valueso fdrainag e resistance M were calculated fromvalu eo f^(D , *?an d h °n thefirs t foursamplin gdates . (Inthi sperio dn owate rwa sp^e d outo rle tint oth e ditches;thu s ^(1) was reasonably known).Thes edrainag e resistanceswer euse d toestimat e thechang e inwate r leveldurin ga da ywit hwate rpumping . First,th echang e inwate r leveldurin gpumpin gwa s roughly estimate ,- *- ™ tionvelocit y ,(1) couldb e obtainedwit h< „ inconservatio nEquatio n24 .The . ***** of .(I) were Introducedi nth eresistanc eEquatio n35 ,b yassumin g aconstan t W resistancean dwit h* „th epatter ,o fth egroundwate r leveldurin gt e inves gUo ^ becalculated . By comparingth ecalculate d andmeasure dgroundwate r levels,i t* », toge tbette r approximations for thechang e inwate r leveldurin g thepumpin gperiods . 121 Diffusion, dispersion, adsorption and conversion parameters

Theaverag ewate r temperaturei nth editche swa sabou t 15 C.Th ediffusio ncoeffi - o -4 2 cient (o,.. )o f azinphos-methy r li nwate ra t1 5 Cwa s calculatedt ob e0.3 5x 1 0 m 1 dif.vr _4 7 _i d andtha t fordimethoat ewa scalculate d tob e0.4 1x 1 0 m d (Reid& Sherwood , 1966). The same tortuosity relationshipwa sintroduce da sdescribe di nSectio n8.3 . The dispersion distance (Z.)i nth ebotto m materialwa sunknown . Foragricultura l soils, ratherwid e rangeso fdispersio n distance have been found, forexample ,a rang e from 0.01 to0.0 6m (Frissele tal. , 1970). Thedistanc e introduced inthi s studywa s0.01 5m . The adsorption coefficients (K ..) ofazinphos-methy lo nth ebotto m materialo fth ediffer ­ ent ditch sectionswer e measured (Table 23). The rate coefficients forconversio no fazinphos-methy l anddimethoat e inth ewate r compartments (k )o fbot h ditchesa tBenscho pwer e approximated tob e0. 9time s therat e coefficients measured forth edeclin e (k )o fbot h compounds fortw operiod si nthos e ditches (Table 42).Thi s assumptionwa sbase do nth eresult so fth ecomputation s forth e tank trials (Chapter 8),whic h showed that conversion inwate r mayb eexpecte d tob eth e dominant process outo fdoors .Th erat e coefficients forconversio no fth ecompound si nth e bottom material (k )wer e derived from rate coefficients obtainedi nincubatio n tests c,b .. (Chapter 6).A t1 5°C , k forazinphos-methy l wasestimate d tob e0.03 8 d (Table21 ) C, D ,. and fordimethoat et ob e0.0 1d (Table 22).

Details on the computation method The computations forazinphos-methy l inbot h ditchesa tBenscho p were doneb yEuler' s integration method (RECT)usin ga tim e stepA to f0.00 5d ,ove ra perio do f5 9days . Fordi ­ methoatei nbot h ditches thetim e stepha dt ob ereduce dt o0.00 2d .Th e computations were checkedb yhalvin g thetim e step andb yusin g theRunge-Kutt a (RKS)integratio n method, which automatically selects small time intervals when rateso fchang e arehig h (IBM,1975 )• For theconvectiv e flowi nth ebotto m (Equation 27),th econcentratio ni nadjacen t compartments were averaged,whic h minimized numerical dispersion (Goudriaan, 1973). In situations with upwardwate r flow through theditc h bottom andwit ha stee p con­ centration gradient (decreasingi ndownwar d direction)a nartificia l downward mass flux, duet odispersion ,wa ssimulated . This artefactwa smainl y suppressedb ysettin g themas s flux into thebotto m layer (Equation 26)smalle r thano requa lt oth eflu xo fdiffusio ni n such situations (limited flux equation,Appendi x B).Thi s working method still givesa slight overestimateo fdownwar d transporti nth editc h bottom compared with what would have been computed under these conditions witha correc t model.A second methodwa s tested, whereby forupwar d liquid flow thedispersio n termwa sse tal lth etim ea tzero . This meth­ od givesa nunderestimatio no fth epenetratio n into thebotto mi nrelatio nt oa correc t model forsuc h conditions. At regular intervals during computations,th ewate r balance andth emateria l balance of thepesticid ei nth editc h systemwer e checked.

17.2 10.4 COMPUTEDRESULT SFO RTH EFIEL DTRIAL S

Results of computation of the water balance

Theheight so fth ewate rleve labov eth editc hbotto mi nth esiphon-linke dditc han d thesupplementaril ydraine dditc ha tBenscho par eshow ni nFigure s42 Aan d43A ,respective ­ ly.Th echange si nwate rleve ldurin gpumpin gwer eapproximate db ycomparin gth ecalcu ­ latedgroundwate r levelswit hth egroundwate rlevel smeasure do nsamplin gdate s (Figures 42Ban d43B) . Invie wo fpossibl evariatio ni nth edrainag eresistanc edurin gth eperio d ofinvestigation ,a smal ldifferenc ebetwee nth ecalculate dan dmeasure dgroundwate rlevel s wasconsidere dacceptable .Durin gth efirs ttw opumpin gperiod s (Day1 7an dDa y 24),a sig ­ nificantris ei nth ecalculate dgroundwate rleve lwa sobtained . Inthes eperiods ,n osig ­ nificantincreas ei nth efiltratio nvelocit ythroug hth ewette dperimete ro fth editc h

(^lbO))wa scompute d (Figures42 Can d43C) .

height of the ditch water (m) 0.5- 0.4- 0.3- x 0.2-*^ 1P 0.1- P, 2

11111111 1 u )1111111 1'1111 '

height of the groundwater (m) 1.0-,

1111 I 'I I

filtration velocity through the ditch bottom (m3m"2d~ ) C 0.02-,

0.0H

T 50 60 time (d) Figure42 .Result so fth eapproximatin gwate r balancecalculation s forth esiphon-linke dditc h atBenscho p in1976 . A.Heigh to f thewate r levelabov eth editc h bottom.x,wate rheigh ta tsamplin gdates ;P , pumpingperiod . B.Calculate dheigh to f thegroundwate rleve l aboveth editc hbottom ,o ,groundwate r level onsamplin gdate s. C.Filtratio nvelocit y calculated fromEquatio n 25. 123 height of the ditch water (m) 0.5-1 0.4- 0.3- 0.2- 0.1- I 11111111111111 1 11 i| i 11 M•

height of the groundwater (m) 1.0

0 11111 • i• • • I filtratioItrc n velocity through the ditch bottom (m'm^d"') C 0:02

0O1

1 50 60 time(d ) Figure43 .Result so fth eapproximatin gwate r balance calculations forth esupplementall y drainedditc ha tBenscho pi n1976 . A.Heigh to fth ewate r levelabov eth editc h bottom,x ,wate rheigh ta tsamplin gdates ; P,pumpin gperiod . B.Calculate d heighto fth egroundwate rleve l aboveth editc hbottom ,o ,groundwate rleve l onsamplin gdates . C.Filtratio nvelocit y calculated fromEquatio n 25.

Duringth elas tpumpin gperio d (afterth eheav yrainfal lo n2 0Jun ean d2 1June )(Da y 48), theincreas ei nth ecalculate dgroundwate rleve lwa ssubstantiall y largertha nth ein ­ creasei nth emeasure dgroundwate rlevel .Thi si sattributabl et oa reductio ni ndrainag e resistancedurin gth eheav yrainfall . 1 Duringth einvestigation ,usuall ysmal lvariation si nth efiltratio nvelocit y(^ lb( )) werecalculated .However ,muc hfaste rflo wthroug hth editc hbotto moccurre d duringth e heavyrainfall .Th epositiv evalue so f^„(1 )indicat ea continuou sdischarg eo fgroundwa ­ terint oth editch-wate rcompartment .Inflo wo fgroundwate rcomin gfro melsewher ema yoccu r toa smal lexten ti nthi sare a ('upward seepage').Howeve rth einflo wo fgroundwate ri n thisare acoul dno tb eaccuratel yassesse dfro mdee pan dshallo wgroundwate rlevel s (Hey& Kester,1977) . Divisiono fth erat eo fflo wthroug hth ewette dperimete ro fth editc h (q,) b yth e surfaceare ao flan ddrainin gint oth editc hgive sth eflo wrat ei nwate rlaye rpe rda ya s usedi nsom edrainag eformulae .Thi sflo wrat ewa srathe rlo wan drange dfro mabou t 0.0003 m d atth ebeginnin go fMa ydow nt oabou t0.00 01 id" 1 justbefor eth eheav y

124 rainfall.Thes e flow ratesar ei nth esam e rangea sth eestimate so fth eupwar d seepage rateo f0.00 02 m d~ 1,mentione db yth eStudiegroe p Lopikerwaard (1973)fo r comparable sit­ uations. The itemso fth ewate r conservation Equation2 4fo rbot hditches ,cumulate d overth e periodo finvestigatio n from3 Ma yt o2 Jul y 1976,ar eshow ni nTabl e48 .Th edischarg e fromth esiphon-linke d ditchwa s relatively smalli nth edr yyea r 1976.Th etota l discharge fromth esupplementaril y drained ditchwa s equalt oth edischarg eo fth ewate rpump . The substantial discharge fromupstrea m ditch sections intoth esupplementaril y drained ditch waso fgrea t importance forpesticid e movement during theperio dwit hwate rpumping .Th e totaldischarg e from this sectionwa smor e thante ntime sth eaverag e volumeo fwate ri n theditc h compartment. Thecomputation s withth eRunge-Kutt a integrationmetho d (RKS)produce dnearl yth e sameresult sa sthos ewit h Euler's integrationmetho d (RECT).Th edifference si nth evalue s ofth ewate r fluxeswhe n halvingth ecomputatio n time-stepwer e alsosmall .

Pesticide movement and conversion

Pesticidei nth ewate r compartment

Thecompute d andmeasure dmasse so fazinphos-methy li nth ewate r compartmento fth e siphon-linked ditchan dth esupplementaril y drained ditcha sa functio no ftim ear egive n inFigure s4 4an d46 .Th evalue sfo r dimethoatei nbot h ditchesar eshow ni nFigure s4 5 and47 .Th emeasure d masso fsubstanc ei nth editc hwate r compartmentswa s derived from theproduc to faverag e concentrationi nth editc h sectionsan dth ewate rvolum ea tsamplin g dates.Th erange si nth emeasure d mass showni nFigure s4 4t o4 7indicat eth e highestan d lowestaverag e concentrationi nth efront ,middl eo rbac k sectiono fth editc h (Tables3 7 and38) . With k =0.9 k (Table 42),th edeclin eprocesse si nth ewate r compartmentwer e des­ cribed fairty'well.Tn e samehold sfo r setting kc w equalt o^ Thisconfirm sth e assump­ tiontha tconversio ni nth ewate r compartmentwas'th epredominan tproces si nth edeclxn e underoutdoo r conditions. The computed curvesfo rth edeclin ei nth ewate r compartment (logscale )wer e some- Table48 .Item si nth ewate r balance (m3)o fth editche si n »e»"ho^n^ed overth eperio do finvestigatio n from3 Ma yt o2 Jul y 1976.Durin g theperiod , nowate rwa s taken in. . Siphon-linked Supplementarily ditch drained ditch Changei nstorag e 33 Total rainfall 29 36 Total evaporation 95 ii7 Totaldischarg e HI ^ Total discharge fromupstrea m 0 129j> Total flow through the 53 39 ditch bottom Total flow throughth edrain s 157 17b . . — 125 masso f azinphos-methyl (g)

10

0.01-

0001 1 I I I I I I M | I I I I I I I < I | I I I I I I I I I | I I I I I I I I I | I I I I I I I I l| I I I I I I I M I 0 10 20 30 40 50 60 time(d) Figure44 .Compute d andmeasure dmas so fazin ­ phos-methyl inth ewate r compartmento fth e siphon-linked ditcha tBenscho p from3 Ma y 1976. =compute dmas s (fcC(W= 0. 9 kr); =com ­ putedmas s (kc w =fe r);o = average dmeasure d masses;S = sprayin gdate s (Chapter 9);P = pumpingperio d (Chapter 9). Verticalbar sar e rangeo fmeasure dmass .

mass of dimethoate (g) 10-1

0.01

Figure45 .Compute d andmeasure dmas so fdime ­ thoate inth ewate rcompartmen to fth esiphon - -linkedditc ha tBenscho pfro m3 Ma y1976 . - computedmas s (kc w 0.9 kr); computedmas s (kc w '" kT); o= average dmeas - uredmasses ;S sprayingdate s (Chapter9) ; P =pumpin gperio d (Chapter 9). Verticalbar s arerang eo f themeasure dmass .

126 mass of azinphos-methyl (g)

0.01

0.001 | I t I I I I I M | I I I I I I I I I | 40 50 60 time(d)

Figure46 .Compute d andmeasure dmas so fazin ­ phos-methyl inth ewate r compartmento fth e supplementarilydraine d ditcha tBenscho pfro m 3Ma y 1976. =compute dmas s (kCjW =0. 9fe r); o= average dmeasure dmasses ;S = sprayin gdate s (Chapter 9);P =pumpin gperio d (Chapter9) . Verticalbar sar erang eo f themeasure dmass .

mass of dimethoate (g) 10^

'I 50 60 time(d ) Figure47 .Compute d andmeasure dmas so fdime - thoatei nth ewate r compartmento fth esupple ­ mentarily drainedditc ha tBenscho pfro m3 Ma y 1976. =compute dmas s (fec>w= 0. 9 kr); o- averagedmeasure d masses;S = sprayin gdate s (Chapter 9);P =pumpin gperio d (Chapter9) . Verticalbar sar erang eo f themeasure dmass .

127 whatconcave .Thi s canb epartl y explained froma sligh tadsorptio nan dpenetratio n into thebotto m layer,whic hwil lb e simulated tob e fastest at thebeginnin g of theexperiment . Becauseo fth ecomparativel y smallconversio n rateo fth ecompoun d inth ebotto m layer,th e mass fluxa t thebottom—wate r interface evenbecam enegativ e (upward flux)afte ra fe w days.Thi s contributed to theconcav epatter no fdeclin e inth ewate rcompartment . During thethre epumpin gperiods ,a decreas e inth emas so fth e compoundswa scompu ­ tedfo r thesiphon-linke d ditch.Shortl ybefor e the thirdpumpin gperio d asligh t increase inth emas so fazinphos-methy li nth ewate rcompartmen twa s calculated due toupwar ddrain ­ agefro m theditc hbotto m duringa da ywit hmuc hrainfal l (Figure44 ,Da y 48). Duringth e firstpumpin gperio d inth esupplementaril ydraine d ditch,relativel y strong increasei n themas s ofbot hcompound s inth ewate r compartmentwa s computed (Figure 46,Da y 17).Thi s resulted from therelativel yhig h concentration inth ewate r discharged fromupstrea m ditch sections.Th eassumptio n thatth econcentratio n inth esiphon-linke d ditchwa srep ­ resentative forth econcentratio n in theinflowin gwate rma yno thav e beencorrect .Th e spray-drift into theupstrea mditc h Section 2 (Figure 31)coul dhav ebee n lower due to thepat halongsid e thatditc h section. Inditc hsection swit h a contaminatedwate r flow fromupstrea msections ,i ti srathe rdifficul t toasses sa pesticid ebalance . The itemso fth esimulate dbalanc e forbot hcompound s inth editches ,cumulate d over theperio do finvestigatio nfro m3 Ma y to2 Jul y 1976ar epresente d inTabl e 49,whic h shows that conversion inth ewate r compartmentwa s themos t important item.Th e different conversion rates inth ewate rha donl y asmal l effect. Increasing the conversion rateo f azinphos-methyl inwate rb y 1H (toth edeclin e rateitself ;Tabl e 42), resulted inonl y anextr a 1.51o fth emas s appliedbein gconverte d inwater .Fo rdimethoat e the correspond­ ingvalu ewa s somewhathighe r (31).Th emasse s ofbot hcompound s discharged from the supplementarily drainedditc hwer ehighe r thanthos edischarge d fromth e siphon-linked ditch.Durin g the threepumpin gperiods ,a considerabl emas s ofsubstanc ewa s transported fromupstrea m ditch sections into thesupplementaril y drained ditch (Table49) .

Pesticide in theditc hbotto m

The computed andmeasure dmasse s ofazinphos-methy l inth ebotto m layero f thesiphon - -linked ditch and ofth esupplementaril y drainedditc ha tBenscho p are given inFigur e48 . Inbot hditches ,th ecalculate d amounts are considerably higher thanmeasured . Inthes e computations,i twa sassume d that thecompoun d iscompletel ymixe d throughout thewate r compartment.However ,i npractic e therear e considerable differences betweenconcentra ­ tionsa tvariou sdepth s inth ewate rbod y inth efirs tfe wday s aftercontaminatio n (Ta­ bles 36an d 37). Theeffec to fpenetratio n into theditc hbotto m is thus likely tob eover ­ estimatedwit h themodel .Th erat eo fconversio n ofth epesticid e inth editc h bottom (K J under fieldcondition s isquit euncertain .Th evalu eo f k ,i nfiel d situations L' c,b maydeviat e fromth evalu eo f k^fc measure d in laboratory incubation studies and introduced intoth ecomputations . Themeasure d andcompute d concentrationpattern s ofazinphos-methy l inbot hditc h bottoms arepresente d inFigure s 49an d 50.Th e computed concentration inth euppe rcen ­ timetreo fth editc hbotto mwa smuc hhighe rtha nth emeasure d concentration in theuppe r

128 -H W 4J I CO ^3 U 3

O O O O O O o o o o o o o o o o

T) h 0) 0J 00 W u cO S« J= CJ 6 CT»O\r^I~»CT\C0 00 CN 01 o S&

-a a CU o 4-) U u u 0) o > J3 o *J n co N r^ CM m C O Ö e^ 00 00 — — — VOO Cj -H

T) m m KP. CO — CO CM CM CM N S 01 S A; 3 O c> 3 o C -a u •H

o oo r~ oo

CN — — — — —- ino

0) u .o 3

co co H -.-I 00 co in io >ï *û r-^ r-* __-_- — — o m

C •H r-H

0) 01 +J 4J o o o o

H C 4-" O •.- 1 S T3 4J ni en i-t CO 01 c3 en oo 0) 3 •H O" — r* CU W e •H X I U) 3 M r-l CO M U-)

P. CM •o e o r^ e o w TJ CO T4 M ^ï co XI I M U CU co O. rH T3 CO O -H ss J>S , •H T3 u U 01 CU CU PH £ a1 «u 4J CO CO .£ o o *J SS Si J= SS O O P. O. 4J XI -H C CU SS e •H B u S N •<-! o CO -o . .¥ - •H o\ > U • o O i-l 4«J 14H •a s H CU M a -o »3 CU CU «-I r-l C cj p. P..H Ä: - p. co 3 V C^ T3 r* CM 129 masso f azinphos-methyl (g) 4~\

0.1-

10^i

0.1-

0.01 | I I I 1 I I I I I | I I I I I I I M | I I I I | II I I I I I I I | II I I I I I I I | M I I I I I I I | 0 10 20 30 40 50 60 time (d)

Figure48 .Mas so fazinphos-methy l inth editc h bottomo fA .th esiphon-linke d ditchB .th esup - plementarilydraine d ditcha tBenschop ,startin g from3 Ma y 1976. =compute dmas s (k c c,w 0,9 kr); * computedmas s (kc measuredmass ;S = sprayin gdate s (Chapter9) ; P =pumpin gperio d (Chapter 9). Verticalbar s arerang eestimate d fromduplicat ecolumns .

slice.Th ecompute dpenetratio nint oth ebotto mwa sdistinctl yles stha nth emeasure dpen ­ etration.Biologica lmixin gan da smal ldisturbanc edurin gsamplin gma yhav eha dsom ein ­ fluence. Thecompute dmasse so fdimethoat ei nth ebotto mlaye ro fbot hditche sa tBenscho p shortlyafte rth esprayin gdate swer emuc hlowe rtha nthes efo razinphos-methyl .Thi sca n bepartl yascribe dt oth ehighe razinphos-methy lconcentration si nth ewate rcompartmen t andfurthe rt oth emuc hlowe radsorptio no fdimethoat eo nth ebotto mmaterial . Thecompute dconcentratio nprofile so fdimethoat ei nth editc hbotto mwer eles sstee p thanthos eo fazinphos-methyl .Th epenetratio ndept hfo rdimethoat ewa sreduce db yth e slowupwar dwate rflo wthroug hth editc hbottom . Byomittin gth edispersio nter m (Equation26 )fo rfiel dsituation swit ha nupwar d

130 mass concentration (mg rfr) 50 100 150 200 250 _L _L

0.04

rf 0.02-

0.04- eiepth in bottom im) Figure49 .Mas s concentrations ofazinphos-methy li n thebotto m (mgm~ 3)o f thesiphon-linke d ditcha t Benschop. =compute dmas sconcentratio n (kc w = 0.9fe r);o = averag emeasure d concentrations.Horizon ­ talbar sar erang eo fconcentration smeasure d indupli ­ cate.Vertica lbar sar eaverag e thickness ofth ebotto m slices.

mass concentration (mg nrT3) c 50 150 200 250 ) I «JO L l 0— T -

0.02- l=14.5d _ 004- t

depth: 0.0005:571 00016 =36 2

depth in bottom (m)

Figure50 .Mas s concentrationso fazinphos-methy li n thebotto mo f thesupplementall ydraine d ditcha t Benschop. =compute dmas sconcentratio n (fec,w= 0.9fe r);o = averag emeasure d concentrations.Horizon ­ talbar sar erang eo fconcentration smeasure d indupli ­ cate.Vertica lbar sar eaverag e thicknesso fbotto m slices.

131 waterflow ,a 'plugflow 'situatio nwa s simulated.Thi s resultedi nsomewha t smallerfluxe s intoth ebotto mtha nwit hth elimite dflu xequatio n (Appendix B), especiallydurin g thefirs tfe wday safte rth estar to fcomputations .Howeve ri nth efiel dsituation , the fluxint oth ebotto mcompartment sbecam enegativ e (upwardflux )afte ra fe wdays .I nsuc h a situation,th e'plug-flo wmodel 'wil l transportth e penetratedpesticid eto ofas tou to f thebotto mcompartments .Wit hplu gflow ,th ecompute dmas so fth ecompound sconverte di n thebotto mwa s somewhatlowe rtha nwit hth elimited-flu xequation .Bot hcompute ddistri ­ butions ('limited-fluxequation 'an d'plug-flow 'model )ca nb econsidere da sextremes : theactua ldistributio nwil lb eintermediate .Th edifferenc ei nth eitem so fth emateria l balanceo fazinphos-methy lan ddimethoat e forbot hmode lsituation swer erelativel ysmal l (Table 49). Themode la sshow ni nAppendi xB wa spresumabl yth e mostacceptabl eon ebe ­ causeth elimitatio no fth e fluxesworke donl ya tth e beginningo fth ecomputations .

10.5 DESIGNO FTH ESIMULATIO NEXPERIMENT S

Insimulatio nexperiments ,th eeffec twa s studiedo fdrainag ean dinfiltratio no n theamount so fazinphos-methy lan ddimethoat epenetratin g intoth editc hbottom .A sim ­ plifiedditc hsyste mwa sderive dfro mth ebac kditc hi nJaarsveld .I nthes esimulatio n experiments,rainfal lan devaporatio nwer eassume dt ob eequal ,an dth ewate rdept hwa s heldconstant .Th erate so fdischarg ean dintake ,whic hwer evarie di nth edifferen tcom ­ puterruns ,ar egive ni nTabl e50 . Theinitia lmas so fpesticid ei nth ewate rcompartmen twa s 10g fo ral lruns ;tha t forth ebotto mcompartment swa s zero.I nth edrainag e (V.,> 0 )an ddiffusio n (7„ =0 ) situations,th ethicknes so fth euppe rbotto mcompartmen twa s 0.001m an dth emultiplica ­ tionfacto rfo rth edownwar d increasei nthicknes so fbotto mcompartment s (m) wa s 1.1. Forth einfiltratio nsituation s (.V,.< 0),th ethicknes so fth efirs tbotto mcompartmen t

was0.00 2m ,an dm f =1.2 .Th ebul kdensitie san dvolum efraction so fliqui dwer e taken forth ebac kditc ha tJaarsvel d (Table36) . Therat ecoefficient sfo rconversio no fth e pesticidesi nth e watercompartmen twer e seta t0. 9time sth eaverag erate so fdeclin ea smeasure di nfiel dtrial s (Table 42).Th e ratecoefficien tfo rth econversio ni nwate ro fazinphos-methy lwa s0.2 1d ,tha tfo r dimethoatewa s0.0 8d .Th erat ecoefficient sfo rconversio no fth ecompound si nth e ditchbotto mwer e0.03 8d " and0.0 1d ,respectively .Th eadsorptio ncoefficien to f azinphos-methylwa s0.07 7m 3kg -1 (Table 23), thatfo rdimethoat ewa sassume dt ob e0.00 1 3, -1 m kg . Thecomputation swer ewit hEuler' sintegratio nmethod .Th etime-ste p (At)fo rth e experimentswit hazinphos-methy lwa s0.00 5d ;i nth ecomputation sfo rdimethoat ea smalle r timeste po f0.00 2d ha dt ob eused .Th emode lsystem swer esimulate dfo r2 7d .Th ecom ­ putationswer echecke dwit ha Runge-Kutt aintegratio nprocudur ewhic h selectsa variabl e time-step.

10.6 RESULTSO FTH ESIMULATIO NEXPERIMENT S

Thecompute dmas so fth esubstance si nth ewate rcompartmen tan di nth ebotto mlaye r areshow ni nFigur e51 .Th edeclin eo fth ecompound si nth ewate rcompartmen ti na situa -

132 masso f substance in water mass of substance in bottom 10-, (g) 1.0-1 (g)

Figure 51.Mas so fsubstanc ei nwate ran d inbotto m layer computed inth esimulatio n experiments.Number s refert oth e comput­ errun s listedi nTabl e 50.A ,azinphos - -methyl;D ,dimethoate ;Ru n1 ,drainage ; T—i"~T~T~~i—i—i °~f—i—i—i—c—i—i—L Run 3,diffusio n(n oflow) ;Ru n5 ,infil ­ 0 4 4 8 12 16 20 24 28 0 4 8 12 16 20 24 28time(d ) tration.

tionwithou twate r flow (onlydiffusion ,Run sA 3an dD3 )wa sslowe rtha nm situations withwate r flow (drainageo rinfiltration) .Durin gdrainage ,a certai namoun to fth ecom ­ poundsi stransporte d outo fth ewate r compartment (RunsA 1an dD1) . During infiltration, afractio ni stransporte d into thebotto m layer (RunsA 5an d D5).A scoul db eexpected , themas so fsubstanc ei nth ebotto m layerwa smuc hhighe rwit hdownwar dwate r flow (in­ filtration)tha nwit hupwar dwate r flow (drainage). Thedeclin eo fazinphos-methy li nth ewate r compartmentwithou twate r flowwa smuc h faster thantha tfo rdimethoate .Thi s differencewa s causedprimaril yb yth erelativel y fastconversio n rateo fazinphos-methy l inwater .Th eadsorptio ncoefficien to fazmphos - -methylwa smuc hhighe r than that fordimethoat ean dthu s thepenetrate d masso fazinphos - methyli nth ebotto m layerwa shighe r thantha tfo rdimethoate .However ,th epenetrate d masso fbot h compoundsi nth ebotto mha d onlya limite d influenceo nth edeclin ecurve s inth esituatio nwit hn owate r flow (Figure 51,A 3an dD3) . Ina drainag e situation the masso fazinphos-methy l inth ebotto m layerwa smuc hhighe rtha ntha tfo rdimethoat e (Fig­ ure 51,A 1an dD1) ,du et oit srelativel yhig h adsorption.However ,durin g infiltration (A5an dD5) ,th e maximummas so fdimethoat ei nth ebotto m layerwa scompute dt ob ehighe r thantha tfo razinphos-methyl .Thi sdifferenc ewa s causedb yth erelativel ylo wconversio n rateso fdimethoat ei nwate ran dbotto mmaterial . Themateria lbalance so fbot hpesticide si nth editc h systemafte ra computationtin e of2 7d ar eshow ni nTabl e 50.I ndrainag e situations,th eeffec to fpenetratio nan d con­ versioni nth ebotto m layero fbot h compoundso nth etota lmateria lbalanc ewa s ryli m ited.Considerabl e amountso fth esubstanc ewer edischarge d fromth ewate r compartment

(Table 50). . an,_, _ The infiltration simulationexperiment s showed thatth ebotto mlaye rma yb ea ni m portant sink forpesticide s inwatercourses .Onl yi nth e ^«^/^"^"^ a considerable fractiono fth einitia l^s s ofdimethoat ewa s computedt ob etransporte d outo fth e lowestbotto mcompartmen t (atdept ho f0.3 5 m). 133 0> r- O O O O O O O O es co

T3 VJ tu 01 4->• 00 4-1 £ U ei] 01 +EJ Ü g P« r-» co a\ CT\ n w o S n) -H )_, o \D CS O O O O CS O O O *Ü MH u co CS vO vj" s& o •o S Ol o 4J 4-1 tl 4-> CU o ^j. cvJ « — ^o CO <ƒ CN — CO o e o o ~ oo o>

u 4-1 o « vo r~ « s o c Ofl N Ol N o •H ^o r^ cri ^D m

es m — o — O N l^\D h e o 00û •M .D

~- CO r-. UO CO iT| is vu N \j3 c ca OOOOO OCN^-CSO •H ?

a i o .e •* s>> o. 4-1 4-1CN1 e M -H I IJ O e •u o CU g O O O O O OOOOO I I

c O a i •H ^ TJ

ai o C 3 3 3 —

o o. i- s

134 Penetration depth

Theconcentratio nprofile si nth ebotto mlaye rafte r9 ,1 8an d2 7d fo rSimulatio n Runs1 ,3 an d5 ar epresente di nFigur e52 .Whe nwate rflo wwa supwar d (drainage),th e penetrationdept hwa slimite dt oa fe wcentimetres .Th epenetratio ndept hwa sslightl y overestimated,a sth eartificia ldispersio nflu xi nth ecomputatio nmode lcoul donl ypart ­ lyb esuppresse d (AppendixB )(Sectio n 10.4).Fo rsituation swithou twate rflo w(diffu ­ sion), th econcentration si nth ebotto mwer econsiderabl yhighe rtha ni ndrainag esitua ­ tions.Bu twit hdownwar dwate rflo w (infiltration)considerabl epenetratio nwa scompute d downt o0. 4m fordimethoate .Th epenetratio nfo razinphos-methy l inth einfiltratio ncom ­ putationswa sabou t0.1 5m .Howeve rth esimulatio nexperiment swer ewit ha rathe rlo wad ­ sorptioncoefficien t {K .) o fazinphos-methyl ,a smeasure dfo rth editc hi nJaarsveld . Witha highe radsorptio ncoefficient ,a smeasure dfo rth esiphon-linke dditc hi nBenschop , thedifferenc ebetwee nth epenetratio ndepth so fazinphos-methy lan ddimethoat ewoul dhav e beenmor epronounced . Thesesimulatio nexperiment s indicateth epossibl econtaminatio no fgroundwate rdur ­ inga ninfiltratio nperiod . Inth einvestigate darea ,period so fdrainag ean dinfiltra ­ tionoccu ralternatel ybu tove rth ewhol eyear ,drainag ei spredominant .Durin ginfiltra ­ tionperiods ,th ebehaviou ro fpesticide s inth editc hbotto man dsubsoi lshoul dthu sb e furtherstudied .

mass concentration (mg m J) 100 0 50 -I 1 I, I L, 1 1 I 1 1 I

Pi

0.04-1

O 50 100 150 200 250 0 50 100 150200 0- T ^• L i—i—• T • _ZL •—i A I'I 'i'—'—'—'—'—' 1270 1180/9.0 0.02-

0.04H

50 100 150 2Q0 250 50 100 150 200 i i I i I i—I I i T . I i I i—I 57qT^>1a0 0.1

0.2-

Q3-

0.4-I depth in bottom (m) Figure52 .Compute dmas sconcentration so fth esu b stancesi nth ebotto mmaterial .Number srefe rt oth e computerrun sliste d inTabl e50 .A ,azinphos-methyl , D,dimethoate ;Ru n 1,drainage ;Ru n3 ,diffusio n (noflow) ; Run5 ,infiltratio n.

135 10.7 GENERALDISCUSSIO N

Thesimulatio no fpesticid ebehaviou ri na ditc hsyste mrequire sa naccurat edescrip ­ tiono fwate rflo wi nth editc han dthroug hth ebottom . Inth efiel dsituatio na tBenschop , therat eo fwate rflo wthroug hth ewette dperimete ro fth editc hwa sdifficul tt oascer ­ tain.Furthe rth edistributio no fth etota ldischarg erat eo fth ewate rpum pove rth evar ­ iousditc hsection scoul donl yb eroughl yestimated . Infurthe rexperiment s inditc hsys ­ tems,th echang ei nditch-wate rlevel san dgroundwate rlevel sshoul db erecorde dcontinu ­ ouslyt oimprov eth echaracterizatio no fwate rflow . Thecomputatio nmode lo nth ebehaviou ro fpesticide si na ditc hcompartmen t issuit ­ ablefo restimatio no fth econtributio no fvariou sphenomen at odeclin e inth efield .Fo r theditche sa tBenschop ,conversio ni nth ewate rcompartmen twa sfoun dt ob eth emos tim ­ portantproces sfo rdecline ,especiall yi nperiod swithou tpumping . Ina norma lsituation ,i nwhic hwate rlevel sar ekep twithi nnarro wlimits ,consider ­ ableamount so fsubstanc eca nb edischarge dfro mth editc hsyste mint olarge rwatercourses , especiallywhe npumpin gstart swithi na fe wday so fspraying . Thecomputatio nmode ldevelope dcoul dno tb echecke dagains tth eliterature .Unfor ­ tunatelyi nalmos tan yarticl eo nth efat eo fpesticide s inditc hsystems ,on eo rmor eo f theessentia lparameter sar elacking . Inth efiel dsituatio na tBenschop ,th econtributio no fth ebotto m layert oth ede ­ clineo fth ecompound si nth ewate rcompartmen tdi dno tsee mimportant .I nothe rfruit - -growingarea si nth eNetherlands ,man yditche sfal ldr yo rnearl ys odurin gsummer .I n suchditches ,th edeclin eproces si nth editc hbotto mma ypredominate . Thecalculate dan dmeasure dconcentratio nprofile si nth ebottom ,sho wtha ti nfur ­ therexperiment sver ythi nslice so fbotto mmateria lshoul db eanalysed .Fo ra naccurat e predictiono fconcentratio nprofile s inth editc hbotto mi ninfiltratio nsituations ,mor e researchi sneede do nth edispersio ncoefficient si nth ebotto mmaterial .I ndrainag esit ­ uations,penetratio ndept hi sslightl yoverestimate dwit hth ecomputatio nmodel ,an d thusa mor eaccurat emode li sneeded .Fo rcompound swit hlo wconversio nrate si nwate r andhig hadsorptio ncoefficients ,penetratio nint oth ebotto mma yb ea majo rprocess .Espe ­ ciallyfo rsuc hsituations ,mor ecomputationa lan dexperimenta lresearc h isneede dt o improvedescriptio no fpenetratio nint oth editc hbottom .

136 11 Measurements and computations on the behaviour of substances in ditches with flowing water

11.1 INTRODUCTION

Thebehaviou ro fpesticide si nditche swit h flowingwate ri sdetermine db yman ypro ­ cessessuc ha sconvection ,dispersion ,diffusion ,adsorption ,volatilization ,microbia l andchemica l conversion.I nflowin gwater ,dispersio ni sa nimportan tphenomenon ,becaus e ofth evelocit y distributionove rth ecross-sectio no fth ewatersour ei sno tuniform . A shortrevie wo fsom eequation snormall yuse dfo rdescriptio no fconvectiv eflo w anddispersio ni nflowin gwate ri sgive ni nthi sChapter .U pt oabou t1 6empirica lequa ­ tionshav ebee ndevelope dfo rcomputin gth elongitudina ldispersio ncoefficien t (Bansal, 1971).Howeve ri tremain sdifficul tt opredic tth edispersio ncoefficien tm surfacewa ­ ter.Th evariou s empirical equations givevalue s thatdiffe rwidel yfo ra particula rflo w system.Althoug hman y empiricaldispersio ncoefficient sar egive ni nth e literature,hard ­ lyan ydat ao nth edispersio no fsubstance si nsmal lwatercourse s canb efound .Fo rthi s reason,a fe wdispersio n experimentswer e carriedou tfo rth esupplementar y drained ditchi nBenscho pan dfo rth efron tditc hi nJaarsveld . Invie wo fth etoxicit yo fth estudie dpesticides ,the ycoul dno tb euse di ndisper ­ sionmeasurements .Therefor etw ofluorescen t dyes,fluorescein-sodiu man dRhodanun eWT , wereuse da stracers .Th ebehaviou ro fbot hcompound swa s investigateddurin ga pumpin g periodafte rmomentar yplacin ga sa ban dacros sth elas tditc hsectio nbefor eth etw owa -

t6rTenion s indispersio nexpert s insm.l lditche sar ea sfollow s Howquidcl)^wil l. substance spreadb ydispersion .Wha tdispersio ncoefficien tapplie sm ^^^ watera tvariou s times during theyea runde rdifferen t conditionso fveg eatio n» ttad Will spreadb esymmetrica lo rasymmetrical ?Ho wgrea tar eth edeviation s fro,,th e ymme ricalpatter ,an dho wca nthe yb eexplained ?Kna twil lb eth einfluenc eo fothe rd cUn e processes?Wil l thereb ea considerabl e differencebetwee nth espreadin gproces so f pounds,tha tar eeithe rstrongl yo rweakl yadsorbe d onto theditc hbotto m All thesequestion s cannotb esolve dwit honl ya fe wrelativel ysimpl ed^i n ex periments.Therefor e thebehaviou ro fth edye si nflowin gwater ,wa sals os ^ aten computationmodel ,whic h includedconvectiv e flow,dispersion ,adsorptiona n — oTthe compounds.Th eresult so fth ecomputation swer ecompare dwit hthos e **^" persionmeasurement sfo rth editc hsection si nfron to fth ewate rpump sm B«*** an Jaarsveld.T, edispersio nbehaviou ro fazinphos-methy lafte ra ninstantaneou s input simulatedwit hth edevelope d computationmodel .

137 11.2 DERIVATIONO FEQUATION SFO RONE-DIMENSIONA L CONVECTIONAN DDISPERSIO N OF SUBSTANCES INFLOWIN GWATE R

Theone-dimensiona ldispersio ncoefficien t (o) i sdefine db ydescribin g theconvec ­ tionan ddispersio no fa substanc e ina give nditc hb y thebasi cdifferentia lequatio nfo r one-dimensional convectionan ddispersion .Th edispersio ncoefficien tdepend so n theve ­ locitydistributio nove rth ecross-sectio nan dhenc eo nth egeometr yo fth editch .Unde r steadyflo wcondition san dwithou tconversio nan dadsorptio no fth ecompound ,th ediffer ­ entialequatio nma yb ewritte na s

3c/3 t= D ,3 e /dx -â 3c hx (36) w 1 w w inwhic h a =mas sconcentratio no fsubstanc ei nwate r (mgm ) w 2-1 D =longitudina ldispersio ncoefficien t (m d ) u =averag e flowvelocit yo fwate r (md ) x =downstrea mdistanc ealon gditc haxi s (m) t =tim e (d) Thedispersio ncoefficien tca nb ecalculate d fromexperimenta ldat ao fdispersio ni n agive nditc husin gEquatio n36 .Thi sequatio nca nb esolve dfo rth econditio no fa nin ­ stantaneouspoin tsource ;th esolutio ni sthe n

2 n/(AÄw~t) exp [-{x -ui) /^*)] (37) w inwhic h m =initia l injectedmas so fsubstanc e (mg) 7 A =averag ewette d cross-sectional areao fditc h (m)

Multiplyingbot hside so fEquatio n3 7wit h /Fan dtakin g thedecadi clogarith mo f bothside so fth eequatio nyield s

2 Ig(V't)= 'l g [m/(A /üöp]' - [{x - üt) /(4D1i)]l ge (38)

Ifthi smode lholds ,a straigh tlin ewil lb eobtaine dwhe nplottin g lg(c /£)agains t {x - ut) If, theslop eo fwhic hi sequa lt o| _1/(4 0) J lge . Forsymmetrica lconcentra ­ tionpattern s ('Gaussiandistribution') ,th elongitudina l dispersioncoefficien t (öj can beobtaine d fromth eslope .Fo rasymmetrica lconcentratio ncurves ,differen tstraigh tline s willb eobtaine d forth efron tan d thetai lo fth econcentration—tim erelationship .Thi s resultsi nrathe rdifferen tdispersio ncoefficient s forth efron tan d thetai lo fth econ ­ centrationcurve . Equation3 8ca nals ob euse dt oestimat e D inanothe rway .Whe nth emaximu mconcen ­ trationo fth ecompoun dpasse s thesamplin gpoin t x - üt =0 an dafte rrearrangin gth e max ° termsm Equation38 , D^ canb ecompute d fromth efollowin gequation : 138 D,= m2/(Ä2 C2 M ) (39) 1 *• w.max maxJ *• ' inwhic h c =th emaximu mmas sconcentratio na ta samplin gpoin t (mgm ) timea twhic h themaximu mmas sconcentratio n isreache da ta (d) t max a samplingpoint .

Thedispersio ncoefficien t (calculatedwit hEquatio n39 )lie sbetwee nth evalue sob ­ tainedfro m theslope so fth efron tan dth etai lo f theconcentratio ncurve .

Relationship between dispersion coefficient and water depth

Various investigatorshav etrie dt ofin drelationship s forpredictin gth elongitudi ­ naldispersio ncoefficien t innatura lstreams .Th ecomparativel y simpleequation sinclud e termslik eaverag ewate rdept h (^), shearvelocit yu,(i nm d" 1)o rth eaverag e flowvelo ­ cityo fwate r u (inm d -1)- Exampleso f suchequation sar e

(40) D.,= a h u. _, , 1 _w_ * (413 and D, = k h u 1 w inwhic h a and kar edimensionles sdispersio nconstant s (1)

Theshea rvelocit y («„)ca nb erelate d toth eaverag e flowvelocit y (Ü)b y thefol - lowingequations :

r-r r-B-V6„-i (42) u*= /T°/P„= Jg " R Km inwhic h „ -1,-2- , ,- ,_ ii (kgm dJ

T0 =shea rstres sa tditc hwall s _3 0 (kgm ) p =densit yo fwate r -2-, w ' . (md ) q =acceleratio ndu e togravit y y (m) R =hydrauli cradiu s 1/3 -1 K =Manning scoefficien tfo rbotto mroughnes s ^ The relationshipbetwee n« .an d« i nEquatio n4 2show stha tEquation s4 0an d4 1ar e analogous. . . .._ TT,_ Awid e rangeo fvalue s isreporte d forth edimensionles sdispersio n constants^ constant a ranged from2 t o750 0 (Day, 1975).A syet ,onl ya fe wdispersio n ^er­ inriver s inth eNetherland shav ebee ndescribe d (Table 51). Forthes erivers ,th edime n sionlessdispersio nconstan t krange d from 1.5 to6 . .,-••„„% Ifth eone-dimensiona ldescriptio no fth econvectio nan ddispersio nE,ua Un 3 6 holds,th emaximu mconcentratio no fa substanc e ^^ ona downstrea mdistanc e 139 Table 51.Result so fdispersio n experimentsfo rriver si nth e Netherlands. (Aftervan d eBei d& van Straten , 1976).

River Average Average Dispersion Dispersion flow water coefficient constant k velocity depth (m2d" 1) (1) (md-1 ) (m)

GroenloseSling e 4320 1 7200 1.7 OudeYsse l 6000 4 144000 6.0 HupselseStrea m 4800 0.5 3600 1.5

aninstantaneou s inputca nb eestimate d fromth efollowin g equation (43),whic hwa sob ­ tainedafte rrearrangin g Equations3 9an d41 .

m/{2A A k h x) (43) w,max

Forsymmetrica l dispersioncurves ,th emaximu mconcentratio ncan easil yb epredicte d withEquatio n43 ,assumin gtha tth erelationshi p betweenth edispersio n coefficient, waterdept han daverag e flowvelocit y (asuse di nEquatio n41 )i svalid .

11.3 DISPERSIONMEASUREMENT SWIT HDYE S

Inth editc h sectionsi nfron to fth ewate rpumps ,fou rdispersio n experiments were carried outwit h fluorescenttracers .Thre e experimentswer e carried outi nth esupplemen - tarily drained ditcha tBenscho pan d onei nth efron tditc ha tJaarsveld . Threeexperi ­ mentswer ewit h fluorescein-sodium.I nvie wo fth erapi d conversiono fthi s compoundi n sunlight,Rhodamin eW Twa suse di non eexperiment ;i ti sslowe r decomposedi nsurfac ewa ­ terunde r sunny conditions.Detail so fth e various dispersion experimentsar etabulate di n Table 52.Durin gth efirs tthre eexperiments ,i nwhic h fluorescein-sodiumwa sused ,th e skywa s completely cloudy.Th elas texperimen t (withRhodamin eWT )wa si nbrigh t sunny weather. Mosto fth ewate r sampleswer e suckedu pwit hth evacuu m sampler (Section 4.2).How ­ ever,durin gth ethir ddispersio n experiment,wate rwa s continuously pumped througha spectrophotometeran dth eresult swer e recorded simultaneously. Invie wo fa rathe rlo w maximumpumpin g speed,smal lsuctio ntube swer e usedt oreduc eth etravellin g timet oth e spectrophotometer.A difficult yo fsmal lsuctio n tubeswa sth echanc eo fth esuctio nmout h blocking.On eo fth etube ssituate da fe wcentimetre s aboveth esediment-wate r interface becameblocke d duringth econtinuou smeasurements . The sampleso fth efirs ttw oexperiment swer emeasure dwit ha spectrophotomete r (Beck- man,Act a CV)a t50 4nm .I nth ethir dexperiment ,wate rwa s continuously pumped througha spectrophotometer'(Bausc h& Lomb ,Spectroni c 88)unde rcomparabl e circumstances.Th esam ­ pleso fth edispersio n experimentwit hRhodamin eW Twer emeasure do na fluoromete r (Perkin Elmer,Mode l 204),excitatio na t48 4nm ,analysi sa t51 3nm .Th ewate r sampleso fth e firstexperimen twer eals omeasure dwit hth efluorometer .Th eaverag e difference between 22measurement swit hth efluoromete ran dwit hth espectrophotomete rwa s only 34.

140 00 •d — ö . C • •«H CO o co O r-l Xi P. u m m £ 10 oio ^ o O u o — o y cao eau ^-«. . • o . . . o en T3 Jj O O ,û O O O rû

X) T) •r-l •r-l 0) ca CU CO i-i CU rH T3 u •a •O r-l -o co •I-I T3 <0 CU •H a CU to •H CU •H x> 4-1 i-i C rH B e U 3 •H TJ a •Ö u -r-l *J T3 •O X X •O ni X X CO •H •r-l CU O <4-t C CM CNl B c CN CN CM o -H a

UH o c u •H cu i-H CO XI P. 0) a B XI

CO H X! l-l CU 4J OJ 4-1 P.^ > CO eu B < s -o ~~-

en ÖO CU e o •i-*t aco O, -U S co CO -H _B C/j -ü

••-I O V4 r-l CU P« CO CJ 3 co M 60 en g 4-1 —

r-l rH r-l Xj Pu fn Pu B5

js eu CJ •a X! u o 4-1 •r-l Xi P o Cs CO t*4 C/J •o a ca ^ ca •a II ou CU U-4 c Xi •H ei •o CO eu u u •o S 3 T3 CO 3 CO 43 S-, •H rH CU 4J r-. m 00 •O CN ~ ro 'rH o B CO e 1 1 o1 1 U o CU > o> CT» Cï cr. 1-4 CU •H CL u •o o. o 3 3 M co r-H c 14-4 •H II r-l II O. O cfl i-H C§O ca Pu en

141 Before thestar to fth edispersio nexperiments ,th edischarg erat eo fth ewate rpump s wasmeasure dwit hth e 'Purduetrajector ymethod 'a sdescribe db yBo s (1976).Wit hthi smeth ­ od,th ecurv eo fa je to fwate rfro ma horizonta ldischarg epip ei srelate dt oth edis ­ chargerat ethroug hth epip e (analogoust oth eprincipl eo fa projectile) .B ymeasurin g thedro pi nth eje to fwate r0.1 5m fromth een do fth epipe ,th ecorrespondin gdischarg e rateca nb erea dfro ma nomograp h (Bos,1976) .Th emeasure ddischarge drat eo fth ewate r 3-1 3-1 pumpi nBenscho pwa sabou t 1705m d andi nJaarsvel dabou t 1440m d . Duringth edispersio nexperiments ,wate rdepth swer emeasure dfrequentl ynea rth e injectionpoint ,nea rth esamplin gpoin tan dnea rth ewate rpum pt oasses sth eaverag ewa ­ terdept hdurin gth eexperiments . Results of dispersion experiments

Theconcentration—tim erelationshi pi nth efou rdispersio nexperiment sar eshow ni n Figure53 .Durin gth esecon dexperiment ,th edifference sbetwee nth econcentration smeas ­ ured inth emiddl ean dnea rth esid eo fth editc hwer ever ysmall .Fo rtha texperiment , theconcentration s insample stake nwit hth edifferen ttube swer eaveraged . Thecurve sobtaine di nth eExperiment s 1,3 an d4 wer easymmetrical .Suc ha tailin g phenomenonca nb eexplaine db yzone swit hlittl eo rn oflo wnea rth eside so fth editch . Duringth edispersio nexperiments ,i twa sobserve dtha tpar to fth etrace rbecam eentrappe d ina zon eo flo wflo wrate salon gth editc hsides .Afte r themai npar to fth edistri ­ butionpassed ,ther ewa sa smal lgradua lreleas eo ftrace rint oth emai nstream .Th etail ­ ingma yals ob epartl ycause db ya ris ei nbackgroun dleve la tth een do fth eexperiment .

mass concentration in water (mg m ) 2000

1500

1000 Exp3

200-

300-

100 Figure53 .Mas sconcentratio no f thedye smeasure d 50- near side duringdispersio nexperiment s inditche s inth e LopikerwaardPolder .Sample s inth efourt hexper ­ imentwer e takeni nth emiddl eo f theditc han d near theside .Experiment s 1t o4 a sdefine di n Table52 .

142 Inth eliterature ,th ezon eo fflo wrate si susuall yreferre dt oa s'dea dzone ' or 'stagnant zone'.Th e processo ftrappin gan dslowl y releasinga trace ri na dead-zon e modelwa sdescribed ,fo rinstance ,b yHaye se tal . (1966).Simila rmodel swer edevelope d byCoat s& Smit h (1964)fo rion-exchang ei nsoil swit ha dispersiv e systemwit h fluidmov ­ ingthroug h largepore san dstagnan tflui di nblin dpores .Howeve rdifficultie si nth e modelo fHaye se tal . (1966)ar eestimatio no fth efractio no fth edea d zonei nth etota l cross-sectionan dth emas s transfercoefficien tbetwee nth edea d zonean dth emai nstream . Forthes ereasons ,th erelativel y simple differential equationfo rone-dimensiona lconvec ­ tionan ddispersio n (Equation36 )wa sused . The longitudinal dispersioncoefficient swer e calculatedb yEquatio n39 .Th e coeffi­ cientswer e calculatedfo rExperiment s 1t o4 (Tabl e 53). Thedispersio ncoefficient s

(0X)i nth esupplementar y drained ditchwer e largertha nthos efo rth efron tditc h (Ex­ periment 2). Thevariatio ni n Dl forth esupplementar y drained ditchwa sb ya facto r about3 .Thi svariatio nca npartl yb eascribe dt oa variatio ni nth eflo wcondition si n theditch ,cause db ychange si nsid evegetatio no rexten to fduckwee d (Lemna minor) cover. InExperimen t 1, more than5( Uo fth ewate r surfacewa s coveredwit ha duckwee d layer. Ex­ periment2 wa si na recentl y cleanedditch .Durin gExperimen t3 ,th esupplementall ydraine d ditchwa s rather clean.Howeve ri nExperimen t 4,abou tthre eweek s later,ther ewa sa dens e layero fduckwee di nfron to fa gratin gnea r thewate rpump .

Theaverag e flowvelocitie swer e obtained fromth eequation : x - u*max= 0 ,whic h isvali dwhe n themaximu m concentrationi sreache da tth esamplin gpoint .Tn eaverag eflo w velocitieswer e showni nTabl e 53.Th eaverag e discharge rateo fth ewate rpum pwa scalcu ­ latedfro mth eaverag ewette d cross-sectional areao fth editc han dth eaverag e flowvelo ­ city (Table 53).Durin gExperimen t 4,th eaverag e discharge ratewa sconsiderabl y lower thani nth eExperiment s 1an d3 .Thi swa s causedb yth epresenc eo fa duckwee dbarrie ri n fronto fth epump .Durin gExperimen t 4,th ewate r levelaroun d thepum pwa s temporarily loweredb y0.2 7m afte r8 0mi no fwate rpumping .I nExperimen t3 ,th ewate r levelnea r thepum pwa s loweredonl y0.1 1m i nth esam epumpin g time.Th elowe rwate rleve ldurin g Experiment4 gav eris et oa substantiall y lowerpumpin gcapacit y thani nth eearlie rex ­ periments (Table 53).Th eaverag e rateo fdischarg eo fth epump s obtained fromth edis ­ persionexperiment s (Table53 )wer e somewhatlowe rtha nth edischarg e ratesmeasure dwit h the 'Purduetrajector ymethod' .Thes edifference s canb eexplaine dmainl yb ya nincreas e inth eelevatio nheigh tdurin gth edispersio nexperiments ,whic hresulte di na lowerin go therat eo fdischarge .

Table53 .Longitudina l dispersion coefficients (Dx) measuredfo rditche si nth eLopiker - waardPolder . Dispersion Dispersion Experiment Average Average Average Average constant cross- flow rateo f coefficient k (m2d _1) depth -sectional velocity discharge (1) _1 3 (m) area(m 2) (md ) (m d"l ) 22.3 1 0.1 8 0.36 4640 1650 18600 2 4190 1380 5100 0.21 0.33 7.4 3 0.15 0.30 5640 1660 6280 4 0.16 0.32 3950 1250 16000

143 Thedimensionles sdispersio nconstan t k (Equation41 )measure d forditche si nth eLo - pikerwaardPolde rrange dfro m 5.9t o25. 3 (Table 53). Theseconstant swer ehighe r thanth e dispersionconstant smeasure d forriver s inth eNetherland s (Tables 51 and53) .

11.4 COMPUTATIONMODE LFO RTH EBEHAVIOU RO FSUBSTANCE SI NDITCHE SWIT HFLOWIN GWATE R

11.4.1 Derivation of the equations

Thecross-sectio no fth editc hwa sassume d tohav e theshap eo fa trapezium .Th ewet ­ tedperimete ro fth editc h (P)wa s calculated fromEquatio n22 . —2 -1 The totalarei cmas s fluxo fsubstanc e inth ewate r (<ƒ inm gm d )wa scompose d s,w ofcontribution sb yconvection ,convectiv e dispersionan ddiffusion :

J =J * J.. + J..f • (44) s,w conv.w disp,w dil,w Thearei cmas s fluxb yconvectio n (<ƒ inm gm d )wa s describe-2- 1 db yth eaverag e flowvelocit y inth editc han dth emas sconcentratio no fth esubstanc e inth ewater :

J «u a (45) conv,w w Thearei cmas s fluxb yconvectiv e dispersioni nwate rwa s obtained from

J.. =-0 ,3 ahx (46) disp.w 1 w

The areic mass flux by diffusion in water was calculated with

•**•* = "O-,,.. f So7ix (47) dif.w dif.w vr

wa s The areicmas s fluxb ydiffusio ni nth eliqui dphas eo fth ebotto m (J.-f lb) obtained fromEquation s 15an d16 . As inth eearlie rmodels ,th erat eo fconversio n inth editchwate r (R )an dtha ti n ^c, w theditc hbotto m {R^ )wer ecompute dwit hfirst-orde rrelationship s (Equations 17an d18) . Theresultin gconservatio nequatio nfo rth esubstanc ei na wate rcompartmen twit hvol ­ ume Vw was :

V (48) 3(Kw %)/U - -3(Vw<7 s>w)/3*- Vdi f,lb>*- 0- « *c(w

The conservationequatio nfo rth esubstanc e inth ebotto mmateria lwa s thesam ea s described inEquatio n 20.Th erelationshi pbetwee nth econcentratio ni n theliqui dphas e and thati nth ebotto mmateria lwa scalculate dwit hEquatio n21 .A si nth epreviou smodels , theadsorptio nequilibriu mwa sassume d toestablis h instantaneouslyan d theisother mwa s assumed tob elinea ri nth erelevan tconcentratio nrange .

144 11.4.2 Layout of the computations and values of parameters

Thedifferentia l equations,boundar ycondition san ddispersio nrelationship swer e programedi nth ecompute rlanguag eCSM PII I(IEM , 1975).Th elistin go fth ethir dcompu ­ tationmode li sgive ni nAppendi xC . Themas so fdy eo rpesticid etha tarrive di nth ewate ra ttim ezer owa sassume dt o bemixe dthroughou tth efirs twate rcompartment .Th eapplie dmasse swer eequa lt oth emas ­ sesshow ni nTabl e 52.Th econcentratio no fsubstanc ei nth ewate rflowin g intoth efirs t watercompartmen twa stake nt ob ezero . Thedimension so fth esupplementall ydraine dditc ha tBenscho pan dth efron tditc h atJaarsvel dwer e introduced fromTabl e34 .Th eaverag ewate rheight si nbot hditc hsec ­ tionswer e introduced intoth emode la sgive ni nTabl e52 .Th editche swer edivide dint o ahundre dcomputatio ncompartments .Eac hditc hcompartmen t( 2m long )wa scompose do fa ditchwateran da singl ebotto mcompartment .Th ethicknes so fth ebotto mcompartmen twa s 0.005m .Th editc hbotto mparameter s likebul kdensit yan dvolum efractio no fliqui dwer e obtained fromFigur e 36.Chec krun swer emad eb yhalvin gth elengt ho fth e ditchcompart ­ mentsan dals ob yhalvin gth ethicknes so fth ebotto mcompartments . Whenth econcentration-tim e relationshipwa sapproximatel y symmetrical (Experiment 2), theaverag evelocit yo fwate rflo wcoul db eobtaine dfro mth etim ea twhic hth eto po fth e curvepasse dth e measuringpositio n x: (49) u = x/t max Forth e u obtainedwit hEquatio n49 ,se eTabl e53 .Fo rth easymmetrica lcurv efoun d inth efirs tdispersio nexperiment ,th eflo wvelocit yo fwate rwa scalculate dals oi nan ­ otherway .Fo rthi scurve ,th eaverag e flowvelocit yo fwate rwa sapproximate d formth e firstmomen t(^ )(whic hcorrespond st oth eaverag eresidenc etim ei nth editc hwate rcom - partment): (50) u= x/M.

inwhic hth efirs tmomen tM jwa sdefine das :

(51) M=fe t àt/So àt 1 0 w 0 w Theaverag e flowvelocit y Ûfo rth efirs tdispersio nexperimen tcalculate dwit h Equation5 0wa sabou t 2970m «f 1.Sinc eth eflo wvelocitie si nth editc hwer ehig h relativet ofiltratio nvelocitie si nth editc hbotto m (Figure 43),th elatte rwer e assumedt ob ezer odurin gth edispersio nexperiments . Thediffusio ncoefficien to ffluorescei ni nbul kwate ra t1 5° Cwa s **f«*£ 2 0.35x IQ"*m d- \ accordingt oprocedure so fRai d& Sheivood (1966).Th e "*«£" coefficient (K .,)fo rfluorescei nont oth ebotto mmateria lo fth esupplementar y drain«!

ditchwa smeasure di na slurr yexperimen tt ob eabou t0.00 7m kg .Th e. ^ K g/1fo rt n sametrace ri nth efron tditc ha tJaarsvel dwa sextrapolate da s0.00 3m kg . 145 The ratecoefficien tfo rth econversio no ffluorescei ni nth ewate r compartments forbot h ditcheswa sestimate dt ob e0.5 5d ~ (i,= 1. 3d )fro mdat ao fFeuerstei n& Sel - lick (1963).Th erat e coefficientfo rth econversio no ffluorescei ni nth editc h bottom [k )wa sreporte dt ob ever ylo w(va nd eOever , 1972). Therefore k wasse ta tzero , c,b c»b All computationswer ecarrie dou twit h Euler's integrationmethod .Th ecomputation s werechecke db yhalvin gth e time step andb yusin gth eCSM PRunge-Kutt a (RKS)integration ' procedure (IBM, 1975). Asi nth emode l describedbefor e (seeAppendi x B),th econvectiv e fluxi nth ewate r compartmentswa s calculatedb yaveragin gth econcentratio ni nadjacen t compartments,i n ordert ominimiz e numerical dispersion.Th enumerica l dispersiondu et otakin g simplefi ­ nitedifference si ntim ewit hth erectilinea r integrationmetho dwa s suppressedb yaddin g a correction termequa lt o (u) at/2 inth edispersio ncoefficien to fEquatio n4 6(Bell a & Dobbins, 1968). The time step (At) usedwit hth erectilinea r integrationmetho dwa s selected from thestabilit y condition (Bella& Dobbins , 1968):

2 Ai< I /(2 D.) (52) com 1 inwhic h I =th elengt ho fth editc h compartment (m)

Themateria lbalance so fth e tracersi nth editc h systemwer e checked at regularin ­ tervals duringth e computations.

11.4.3 Results of simulations for the tracer experiments

Themeasure d andcompute d concentration patternso fth edye swer e compared onlyfo r Dispersion Experiments 1an d2 .A compute r simulationo fDispersio n Experiment3 wa somit ­ tedi nvie wo fth e severetailin g (Figure 53).Durin gth e Dispersion Experiment 4,a grat ­ ingnea r thewate rpum pbecam e cloggedwit hduckweed ,s oth eexperimen twa s curtailedan d couldno tb echecke di ndetai lwit hth ecomputatio nmodel . The differencebetwee nth ecompute dan dmeasure d concentration patterno ffluorescei n inExperimen t1 wa srathe r large (Figure 54); forExperimen t 2,th ecorrespondenc ewa s rathergoo d (Figure 54).Th ecomputatio nmode l gavebes t resultsfo ra rathe r clean ditch (Experiment 2).Wit ha dens educkwee d covero nto po fa ditc h (Experiment 1),th emeasure d tailingwa smuc h largertha npredicte dwit hth ecomputatio nmodel .Th edifferenc ebe ­ tweenth ecompute dan dmeasure d concentrationpatter ni nth efirs texperimen t couldb ere ­ ducedb yintroducin ga somewha t lower flowvelocit yi nth editc h system (Figure 54).Thi s reducedvelocit ywa sobtaine d from therelationshi p betweenth efirs tmomen to fth econ ­ centrationcurv ean dth eaverag e flowvelocit yo fwate r (EquationsS Oan d51) .Mos tprob ­ ably,th etailin gphenomeno ni nditche swit ha duckwee d coverca nb edescribe d betterb y dead-zonemodels .Bu ti nvie wo fth e changei nwate r level duringth eexperiment san dth e uncertaintiesi nth ereductio no frat eo fdischarg e afterabou t1 h o fwate rpumping ,th e elaborateproces so ffittin gparameter si nth edead-zon emodel swa s omitted.

146 mass concentration in water (mg m ) 2000-, Ä /

ioooH

Figure54 .Measure d andcompute d concentration patternfo rth e 1stan d 2n^dispersio nexper ­ iment inth editche s inth eLopikerwaar dPolder . =measure dmas sconcentration s (Figure 53); =compute dmas sconcentration s(Appen ­ dixC) ;-• -= compute dwit hreduce daverag eflo w velocity.

Thecompute ditem so fth emateria lbalanc e forfluorescei ni nbot hdispersio nexper ­ iments,cumulate dove ra computatio nperio do f0. 1 d,ar eshow ni nTabl e54 .Th etota l masso fdy etha twa sconverte di nth ewate rcompartment swa sonl y2.3-2.6 %o fth emas s supplied.Th etota lmas so fth edy ei nth ebotto mlaye rafte r2 h o fcomputatio nwa sin ­ significant (0.3*).A sexpected ,th edischarge dmas so fdy efro mth editc hwa sth emajo r itemo fth emateria lbalanc e (Table54) . Halvingth elengt ho fth editc hcompartmen tt o1 m whil edoublin gth enumbe ro fditc h compartmentsresulte di nnearl yth esam econcentratio npatterns .Howeve ra sca nb eexpec ­ tedfro mEquatio n52 ,ru ntim ewa sconsiderabl y increased.Th eresult so fcomputation s withEuler' sintegratio nmetho d (RECT)wer enearl yth esam ea sthos eobtaine dwit hth e moresophisticate dRunge-Kutt aintegratio nmetho d (RKS). Halvingth ethicknes so fth ebotto mcompartmen tresulte dtemporaril y inhighe rcon ­ centrations inth ebottom ,whic hca neasil yb eexplaine db yth esteepe rdiffusio ngradient . Althoughth etota lmas so fth edy ei nth ebotto mcompartment s increased,th eeffec to fthi s

Table54 .Compute d itemso fmateria lbalanc eo ffluorescei ni n DispersionExperiment s 1an d 2,cumulate d over0.08 3d (2h) .

Experiment Mass Fractiono fmas ssupplie d (%) (g)P le in in converted converted discharged water bottom inwate r inbotto m fromditc h 97.4 50 0.0 0.3 2.3 0.0 97.1 7.5 0.0 0.3 2.6 0.0

147 diffusiono nth econcentration si nth editc hwate r remained small.Fo rtha t reasonn orun s weremad ewit ha nextende dmodel ,includin g severalbotto m compartmentspe rditc hcompart ­ ment.

11.4.4 Design of the simulation experiments with pestioides

Underflo wcondition sa sshow ni nTabl e5 3fo rDispersio nExperiment s 1an d2 ,a fe w simulationexperiment swer ecarrie dou twit h azinphos-methylan ddimethoate .Th ebehaviou r ofbot hpesticide s aftera sudde ninpu t (forexampl edu et oinsufficien t care during tank cleaning)int oth etw oditc h sectionsi nth eLopikerwaar d Polderwa s simulated. The samediffusio nan dadsorptio nparameter so fazinphos-methy lan ddimethoat e were introduceda sdescribe di nSectio n 10.3.Th erat e coefficientsfo rth econversio no fbot h pesticidesi nth editc hwate ran di nth editc hbotto mwer eth esam ea suse di nSectio n 10.5.Th erelativ e importanceo fth elongitudina l dispersion coefficiento nth emaximu m concentrationo fth epesticide s inwatercourse swa s testedb ydoublin gth ecoefficient .

11.4.5 Results of the simulation experiments with pesticides

The calculated concentration—time relationshipso fazinphos-methy lan ddimethoat e passingth esam e samplingpoint sa sused i nDispersio nExperiment s 1an d2wer e nearlyth e samea sth ecalculate d concentrationpattern so fth e tracer (Figure 54). Inth etw oditc h sectionsa tBenscho pan dJaarsveld ,th edifferenc ebetwee npesticid e concentrationan d trac­ erconcentration ,a tth etim e thatth emaximu mconcentratio npasse d thesamplin gpoints , was about H forbot hpesticides .Th ecalculate d concentrationso fth e pesticidewer e slightlyhighe rtha nth e tracerconcentrations ,whic hwa s causedb yth erelativel y small conversion rateo fth epesticide si nth editc hwater . The computed itemso fth emateria lbalanc eo fazinphos-methy lan ddimethoat efo r both simulationexperiment sar eshow ni nTabl e 55.Fo rshor tperiod so ftim e (2h )th e influenceo fadsorptio nan dconversio nwa s only slight.I nal lsimulatio n experiments more than98° so fmas s suppliedwa sdischarge d from theditc h system (200m length). Comparing theresult so fth e itemso fth emateria lbalanc eo ffluorescei ni nbot hdispersio nexperi ­ mentswit hbot hpesticide s only showed relatively smalldifference s (Tables5 4an d 55). Some simulated concentration—time relationshipso fazinphos-methy la tdownstrea m

Table 55.Compute d itemso fmateria l balanceo fazinphos-methy l(A ) and dimethoate (D)i nsimulatio n experimentso nthei rbehaviou ri n ditcheswit h flowingwater ,cumulate d over0.08 3d ( 2 h).

Experiment Mass Fractiono fmas s supplied (%) suppl:Le d (g) in in converted converted discharged water bottom inwate r inbotto m fromditc h

1 A 50 0.0 0.3 0.9 0.0 98.7 D 50 0.0 0.3 0.3 0.0 99.3 2 A 7.5 0.0 0.4 1.0 0.0 98.6 D 7.5 0.0 0.4 0.4 0.0 99.2

148 distanceso f58 ,11 8an d19 8m i nbot hditc hsystem sar eshow ni nFigur e55 .Th eeffec t ofdoublin gth elongitudina ldispersio ncoefficien ti sals opresente di nFigur e55 .B y increasingth edispersio ncoefficien tb ya facto r2 ,th emaximu mconcentration stha tpasse d thesamplin gpoints ,wer econsiderabl y lower,a swoul db eexpecte dfro mEquatio n43 .Th e maximumconcentration sa tth esamplin gpoint scompute dwit hth esimulatio nmode lwer e nearlyth esam ea sth emaximu mconcentration scalculate dwit hth esimpl eEquatio n43 .Fo r timeperiod si nwhic hth econversio ni nwate ran dbotto mmateria lca nb eignored ,th eef ­ fecto fa sudde ninpu to fazinphos-methy lan ddimethoat eint oa ditc hsyste mca nb eesti ­ mated fromEquatio n43 .Fo rtim eperiod si nwhic hth econversio no fpesticide sma yno tb e ignoredi nrelatio nt odischarg erat ei nth editc hsystem ,th econcentration—tim erela ­ tionshipca nb ebette rpredicte db yusin gth ecomputatio nmodel .

11.5 GENERALDISCUSSIO N

Thedispersio nexperimen ti na clea nditc hshowe da rathe rsymmetrica lconcentration - -timerelationship .Suc hconcentratio npattern scoul db epredicte drathe rwel lwit hth e computationmodel .I nditche swit ha cove ro fduckwee da differen tconcentration—tim e relationshipwa sobserved .Th ecurve sshowe da rathe rstee pfron tan da relativel ylon g tail.Th ecorrespondenc ebetwee nth ecompute dan dth emeasure dconcentratio ncurve swa s

massconcentratio ni nwate r(m gr n) 3000-1

2000 BSD x=198

1000-

800-1

600

400-

200

0.05 time(d) Figure55 .Simulate dconcentration—tim e relationshipso f azinphos-methyla tdifferen tdownstrea mdistance s (xi nm ) inth esupplementall ydraine d ditcha tBenscho p (BSD) and thefron tditc ha tJaarsvel d (JF). =compute d withdispersio ncoefficient s (Table 52); »compute d withdouble d valueso fth edispersio ncoefficient .

149 only reasonable at the top of the concentration curves; at the front and especially at the tail of the curves, there were large deviations between the simulated and measured concentrations. The tailing can probably better be described with dead-zone models. The water flow was relatively fast. Within 2 h of water pumping, nearly all supplied mass of dye or pesticides was transported out of the ditch system (200 m length). In view of the short residence time in both ditch sections, the other processes like conversion and penetration into the ditch bottom were computed to be of minor importance. The physico-chemical behaviour of dyes (fluorescein and also of Rhodamine WT) can be compared with the physico-chemical behaviour of dimethoate. Dye experiments, therefore, can be used to simulate the behaviour of certain pesticides. In view of the far easier analytical methods and the lower toxicity of dyes, such a procedure has advantages. How­ ever, for pesticides with low solubility in water, the concentration over the cross-sec­ tion of a watercourse may be different. For them, dispersion experiments with more apolar tracers may be necessary. The major factor in the maximum downstream concentrations after a sudden input was undoubtly the dispersion coefficient. For many ditch systems, no data on the dispersion coefficients are available. Therefore prediction of the maximum concentration in ditch systems remains difficult. More dispersion experiments are necessary in various ditch sys­ tems under various conditions. Based on these experiments, a classification of dispersive behaviour for different types of ditch system may be possible. In situations with low velocity in the ditch water, the adsorption of pesticides on­ to the ditch bottom can probably not be ignored. For such situations the description of the ditch system with only one bottom compartment per ditch compartment is too rough and the number of ditch bottom compartments should then be increased. Increasing the number of compartments, however, considerably increase computation time. The computation model holds only for rather symmetrical concentration-time relation­ s' ips In dispersion experiments with severe tailing, the dispersion process cannot easi- X e escribed with the one-dimensional computation model. More experimental and computa­ tion research remains to be done to predict such concentration-time relationships. ™v *, ! the COmputation m°dels (Appendixes) can be further elaborated to make them suitable for prediction of the behaviour of pesticides" in an aquatic environment,

given a set of physico-chemical data on a pesticide and of hydrological data, for the field

150 Summary

Theus e ofpesticide s inagricultur e andhorticultur ema y resultunde rspecia lcir ­ cumstances inunintentiona lpollutio no fsurfac ewater .Som esituation s inwhic hsuc hpol ­ lutionca noccu r are described inChapte r 1. Inth eNetherlands ,th eassessmen to fth eex ­ tento fthes e immissions is impededb y theoccurrenc eo fpesticide s inth eRive rRhin e • (Tables 1,2 an d 3). Inth epresen t study,on e ofth esource so fagricultura lpollutio n wasstudie d inmor e detail,i.e . spraydrif tdurin g applicationo fpesticide s infrui t farming.Th emotivatio n forth edesig no fth epresen tstud y isdescribe d inChapte r2 . The studywa s restricted toth ebehaviou ro f twoimportan torganophosphoru sinsecti ­ cidesazinphos-methy l anddimethoat e insurfac ewater .Th egenera lcharacteristic s ofbot h insecticideswit h respect tothei rbehaviou ran deffect s inwatercourse s aregive ni nChap ­ ter3 .Bot h compoundshav e arelativel y lowsaturate dvapou rpressur e (Tables5 an d 6). The rateo fvolatilizatio n from surfacewate rwa s calculated tob ever y lowan dt ob enegligi ­ blewit h respect to theconversio n insurfac ewate r (Section 3.5). The solubilityo fdime ­ thoatei nwate r isconsiderabl e greater thantha to fazinphos-methyl .A nassociate dproper ­ tyi sth econsiderabl y loweradsorptio ncoefficien t ofdimethoat eo nsoi l thano fazmphos - -methyl.Azinphos-methy l israthe r toxicfo rcrustacean s andsom e fishes (Table 10). Dime­ thoatei shardl y toxic forfis h (Table 11). Ina norientatio n stageo fth e investigationvariou s surfacewater swer esample di n theKromm eRhin e areaan d inth eLopikerwaar d Polder (Section9.2) .Fo rsamplin go fwate r andditc hbottoms ,specia l techniqueswer edevelope dfo rth einvestigatio n (Chapter4) . Littledisturbe dsample so fbotto mmateria l couldb e takenwit ha corin gdevic e (Figures and 4). After freezing thebotto mmaterial ,sample swer e slicedan danalysed . The analyticalprocedure s forazinphos-methy l anddimethoat e insurfac ewate ran di n bottommateria l aredescribe d inChapte r 5.Wate r sampleswer eextracte dwit hdichlorome - thane,sometime s followedb y clean-upwit hcolum nchromatography .Th e insecticideswer e measuredwit h agas-liqui d Chromatograph equippedwit ha flame-photomete rdetector .Th e recoverypercentage swer e high (Tables 12an d 13). Oftensevera lcolumn swit hstationar y phaseso fdifferen tpolarit ywer euse d forga schromatograph y (Tables 14an d 15). rge amountso f interfering substances inal lextract so fbotto mmateria lcoul db eremove dw i silicage lcolumns ...... ,„ uPhav- Somebasi cdat afo rbot h insecticideswer eneede d tostud y their ^*™°J£" iouri nsurfac ewater .Dat ao nrate so fconversio no fthes ecompound s insurfac ew a were still toolimited .Conversio n rateso fazinphos-nethy lan ddimethoat e m surfacewa andi nbotto mmateria lwer emeasure dunde rcontrolle dcondition s inth elaborator y ( P ter 6). The rateo fhydrolysi so fazinphos-methy l strongly increasedwit hp H (Figure j. Thisbehaviou rcorresponde dwit h somedat a inth e literature.Th econversio no fazin p -methyl insurfac ewate ran dbotto mmateria l couldb edescribe dwit ha first-order 151 equation (Figures 8,1 2an d 13). Theconversio nplot s fordimethoat e inbot hmedi a followed a first-orderconversio npatter nonl yfo ra limited time (Figures 10,1 1an d 14). Therat e ofconversio no fdimethoat e increased distinctlywit h time (Table22) . Copperion swer ecatalyti c inth econversio no fbot hmode l compounds insurfac ewater . Theincreas eo fth econversio nrate sa tincreasin g temperaturewa s studied. Theconversio nrate so fbot hcompound s inanaerobi cbotto mmaterial ,measure d inin ­ cubation tests inth edark ,wer e considerable greatertha n insurfac ewate r (Tables18 , 20, 21an d 22).Muc hwor kremain st ob edon eo nth edevelopmen to flaborator y tests,th e resultso fwhic hca nb euse d forpredictio no f thebehaviou r ofpesticide s insurfac ewa ­ ter. The conversion rateso fth eoxyge nanalogu e ofazinphos-methy l (Table7 )i nsurfac e wateran dbotto mmateria lwer e greatertha nthos eo fazinphos-methy l (Tables 18an d20) . Theadsorptio no fazinphos-methy l anddimethoat eo ndifferen tbotto mmaterial scoul d bedescribe d reasonablywel lwit h linearadsorptio n isotherms (Figures 15,1 6an d 17). The adsorptioncoefficient so fazinphos-methy lwer eabou t 100time s thato fdimethoate .Th e adsorptioncoefficient s ofbot h substances correlated closelywit h theorgani cmatte rcon ­ tento fth edifferen tbotto mmaterial s (Table 23).Th eadsorptio ncoefficient s ofbot hcom ­ poundso nbotto mmaterial swer emuc h largertha nthos eo nagricultura lsoils . Ina nearl ystag eo fth einvestigation ,i tbecam eclea rtha ttrial s inditche s canb e complicated.Therefor e relatively simple trialswer e also setu p inoutdoo r tanks.Th e rateso fdeclin eo fbot hmode lcompound si nwate ran dth epenetratio n ina layero fbotto m materialwer emeasure d (Chapter 7). Thedeclin eo fbot h compounds inth ewate r compartment of thetank scoul db edescribe d reasonablywit h afirst-orde rrat eequatio n (Figures 20 and21) . Thedeclin eo fazinphos-methy l anddimethoat e inth ewate rcompartmen to fth e tanks wasmuc h faster than thedeclin emeasure d inincubatio n testswit h surfacewate r indark ­ ness (Tables 18,2 0an d 26).Alga lbloo mcause d considerable daily fluctuation inp Ho f thewate r (Figure 18).Th eapproximativ evalue sfo rth efirst-orde rrat ecoefficient sfo r thedeclin eo fbot hcompound swer e closelydependen to nth emaximu mp H (Figure 22).A sig­ nificanteffec to f formulationo fbot hmode lcompound so nrate so fdeclin e inth ewate r compartmentcoul dno tb eassessed .Th epresenc eo fa botto mlaye ri nth etank swa sno ta dominant factori ndeclin eo fth emode lcompound s inth ewate rcompartment . Laboratory testsi nth edar kha donl y limitedvalu e forpredictio no f therat eo fde ­ clineo fbot hcompound s insurfac ewater .Ther e isa nobviou snee d forlaborator y testst o assess theeffec to fligh to nth erat eo fdeclin eo fpesticide s insurfac ewate r ina rep­ resentativeway . Theevaluatio no fth ebehaviou ro fman ypesticide s insurfac ewate runde rdifferen t conditions requiresa nenormou s researchcapacity .Sinc e thephysico-chemica l processes forman ypesticide s isth esame ,computatio nmodel s canb euse d forquantitativ edescrip ­ tiono fbehaviour .Th efirs tcompute rsimulatio nmode l (AppendixA )describe s thebehavi ­ ouro fpesticide s ina tanksyste mwit ha botto mlaye r (Chapter 8). Movemento fpesticide s bydiffusio nfro m thewater—sedimen t interface intoth ebotto mlaye rwa sdescribe d ina one-dimensional system.Adsorptio nequilibri awer eassume d tob e established instantaneous­ ly.Rate so fdecompositio ni nwate ran dbotto mmateria lwer e introduceda s first-order

152 ratecoefficients . The relative significanceo fdifferen tdeclin eprocesse so fpesticide s insurfac ewa ­ terca nb e describedbette rb y thedevelope d computationmodel .Simulation so fth etan k trials showed thatconversio no fbot hmode lcompound swa s themajo r factori nmateria l bal­ ance (Table 30).Th e computedmas so fbot hinsecticide s inth ebotto m layerwa salway s lesstha n 10% ofth eapplie d dose.Th ecompute dmasse swer ehighe r thanth emeasure d mas­ ses (Figures 23an d24) . Thecompute ddept ho fpenetratio no fdimethoat ewa s largertha ntha to fazinphos-me - thyl,mainl ybecaus eo f therelativel y lowadsorptio no fdimethoate . Insimulatio nexperiments ,th e sensitivitywa s testedo fth emode lo fth etan ksyste m tochange s inparameter s (Table 31). Diffusion inth ebotto m layerwa s relativelyslow . Uncertainties inth ediffusio ncoefficien t through theliqui dphas ei nth ebotto mmate ­ rialappeare dt ob e lessimportan t (Figure 27A).Th egradua ladsorptio no fpesticide sont o bottommateria l canb e ofgrea t importance inshallo wditches ,especiall ywhe nth econver ­ sionrat e inwate r is low.Penetratio n intoth ebotto mlaye ri so fmino r importance insit ­ uationswit h relativelyhig hconversio nrate s (half-liveso fsom e days). Measurements ofazinphos-methy l anddimethoat e inwatercourse s and farmditche s inth e KrommeRhin e areaan d inth eLopikerwaar dPolde rar edescribe d inChapte r9 . Ina norien ­ tationstage ,fou rsamplin gpoint s in largewatercourse s and fivei nfar mditche swer e sampled in 1975 (Figure 30). Interferingsubstance s inth eextract so fwate r fromlarg e watercourses couldb e reducedb y clean-upo nsilic age lcolumns .N odistinc tevidenc ewa s found fora n increaseo f themode lcompound s inth ewate ro f theKromm eRhine ,durin g transport throughth earea .Relativel yhig hconcentration swer efoun d inwate ro ffar m ditches on fruit farms inth eLopikerwaar dPolder . These farmditche swer eselecte d for furtherstud y in 1976an d 1977.The yalway scon ­ tainedwate rdurin gth egrowin gseaso nan do nbot h farms therewa sa supplementar ydrain ­ agesystem ,s o thata wate rbalanc e ofthes editche s couldb e approximated (Section9.3.3) . Allkind so fcomplication s came tolight ,suc ha s thestrongl yheterogeneou ssoils ,th e complexhydrologica l situationan d thenecessit y totak e inwate r inth edr yyea r 1976 (Figures3 1 to 35). Theditc hsystem swer ewel l characterizedb ymeasurement s toallo w simulation fora mode lsyste m (Tables3 4an d 36). Thehig horgani cmatte rcontents ,th e lowbul k densities and thecorrespondin ghig hvolum e fractionso fliqui d inth ebotto mmate ­ rialwer e remarkable (Figure36) . In 1976,afte rapplicatio no fbot hmode lcompound so n thetw ofrui tfarm si nth eLo ­ pikerwaard Polder,th econcentration s inth e farmditche swer emor eclosel y studied (Ta­ bles37 ,3 8an d 39). Thesewer erathe rhigh ,especiall y shortlyafte rapplication .Inter ­ feringsubstance s didno t interferedurin g thega schromatography .Th edeclin eo fbot hmod ­ elcompound s inth e farmditche so nth e fruitfar ma tBenscho p (LopikerwaardPolder )coul d bedescribe db y a first-orderrat eequatio nfo ra perio dwithou t intakeo rdischarg eo f water (Figures 38an d 39). Thecalculate dhalf-live so fazinphos-methy l inthes editche s wereabou t3 to4 days ,thos efo rdimethoat evarie d from4 to 13day s (Table 42). These half-lives agreedwit h thehalf-live smeasure d intan k trials (Table 26). Thepenetratio n ofazinphos-methy l inth ebotto mmateria lo fth editche swa s small (Tables4 6an d47) . Introductiono fth e insecticides intoth e farmditche si n 1977wa smeasure d inmor e

153 detailwit hPetr i dishesplace do n floats inth editche s (Section9.3.8) .Th eexten to f introductiondepende d closelyo nloca lsituation sa t thefrui tfarm s (windbreaks,distanc e fromfruit-tree st oth ewatercourses ,paths )an dth ewa yo fapplicatio n (Tables 40an d 41). Therati obetwee nmas so f insecticide introducedpe runi tsurfac e areao fwate ran d massdos epe runi tsurfac eare ao forchar d soil (=arei cmas s ratioo fcontamination )wa s highestb ysprayin gacros s theditc h (0.4), the lowest ratioswer emeasure d forditche s protectedb ya windbrea k (0.003). Estimationo fth evariou s items inth ewate rbalanc e inth editc hwa sno teas y (Fig­ ures 41,4 2an d 43). The fluxo fwate r through theditc hbotto mwa sderive d fromth ewa ­ terbalanc e asa closin gentry .Thi s fluxwa s relatively lowan dmostl y thedirectio no f theflu xwa s into theditc h (positive) (Section 10.4).Th edistributio no fth edischarg e rateo fth ewate rpum pove rth evariou sditc h sections couldb eestimate d only roughly (Tables 34an d 48). Infutur eexperiment s inditc hsystems ,th echang e inlevel so fditc h wateran dgroun dwate rshoul db erecorde dcontinuousl y toimprov e thedescriptio no fwa ­ terflow . A computationmode lfo rth ebehaviou r ofpesticide s ina ditc hcompartmen twit hcom ­ pletelymixe dwate r isdescribe d inChapte r 10.Thi s computationmode l (AppendixB )des ­ cribesfluxe s ofwate ran dpesticid e inth editc h systeman d alsoinclude s fluxes through theboundar y surfaceso fth ewate rcompartmen tan do fth ebotto mcompartments .Th eintro ­ duced ratecoefficien t forconversio n inth editc hcompartmen twa s seta t 0.9 times the measured ratecoefficien t forth edeclin e (Table 42). This resulted ina reasonableagree ­ mentbetwee nth emeasure dan dcalculate dconcentration—tim e relationships inth ewate r (Figures4 4 to 47). For thesiphon-linke d ditch inBenschop ,th econversio no fth emode l compounds in theditc hwate rcompartmen twa s themai ndeclin eprocess .I na perio do f5 9d with lowwate r discharge,6 9t o 88%o fth eintroduce dmode lcompound swa scalculate d to beconverte d inth ewate r (Table 49). Forth esupplementall ydraine d ditch inBenscho p (lastditc hsectio nbefor e thepump) ,calculation s suggested thatdischarg e from thewa ­ tercompartmen t inth esam eperio dmigh tb e several tenths ofth eintroduce d amount (Ta­ ble 49). Thecompute d totalmasse s ofazinphos-methy l inth editc hbottom swer e larger thanth emeasure dmasses ,jus ta sfo rsimulatio n ofth etank s (Figure48) . Insimulatio nexperiments ,th eeffec to fpenetratio n intoth ebotto mwa s very limited inditche swit ha flo wo fwate r fromgroundwate r (drainagesituation ) (Figures5 1 and52) . With infiltrationfro mth editch ,th editc hbotto mca nb econsidere d asa nimportan t 'sink' (Table 50). More researcho nth edispersio nbehaviou r inbotto mmateria l in infiltration situations isneede d toallo waccurat e descriptiono fconcentratio nprofiles .Th epene ­ trationdept hwit hth epresen tcomputatio nmode l indrainag esituation s issomewha tover - -estimated.A technicalproble m inth emodel ,artificia l 'backward'dispersion ,canno tye t be removed completely. Measurementan dcomputatio no nth ebehaviou ro fsubstance s inditche sdurin gwate r flow (forexampl eb ywate rpumping )ar edescribe d inChapte r 11.Althoug hman y empirical dispersionequation sar edescribe di nth eliterature ,dat ao nth edispersiv ebehaviou ro f substances insmal lwatercourse s arescarc e (Table 51). A fewdispersio nexperiment swer e carriedou twit hdye si nditche so nbot h fruitfarm s inth eLopikerwaar d (Table 52). A relatively lowdispersio ncoefficien twa smeasure d ina dispersio nexperimen t ina recent -

154 lycleane d ditch.Th e dispersion coefficient ina ditc hsituatio nwit ha layero fduck ­ weedwa s four times as large (Table 53).I nsuc ha situation,ther ewa s astron g tailing inth econcentration—tim e relationship atth esamplin gpoint s (Figure 53). The dispersion constants (Equation41 )fo rthes e smallwatercourse swer e largertha nthos e forstream s and rivers inth eNetherland s (Tables 51 and53) . A computationmode lwa sbuil t to describe thebehaviou r ofsubstance s inditche sdur ­ ingwate r flow (Appendix C). Themode l includedman yprocesse s likeconvectiv e flow,dis ­ persion,diffusion ,adsorptio n and conversion of the substances.Goo dagreemen t between measurements and computationswa sonl yobtaine d forth econdition s ina clea nwatercours e (Figure 54). The tailingphenomeno n inconcentration—tim e relationships canprobabl y bet­ terb e described with stagnant-phase models.Simulatio n experimentswit hbot hdye san d model compounds inditche swit h ahighe r flowvelocit y showed thatconversio nan dpenetra ­ tion into the ditchbotto m arenegligibl e inth e shortperio d (Tables5 4an d 55). Spread­ ingb ydispersio nwa sb y farth emos t importantproces s insuc hfiel dsituation s (Figure 55). For situationswit h lowflo wvelocitie s inth editc ho r forditche swit hperiod s of nowate r flow,a mode l mayperhap sb e compiled by combination ofth e secondmode l (Appen­ dixB )an d the thirdmode l (Appendix C). Thepresenc e ofvariou sprocesse swit h fardif ­ ferent rateshoweve r gives complications inth erequire d computationtime . Thecomputatio nmodel swer euse d firsto fal la sresearc h tools totrac ean d define areas of too limited knowledge.Th e results ofmode l computations and comparisonwit hre ­ sultso fmeasurement s provide good startingpoint s for future investigations.Afte r further elaboration, thecomputatio nmodel s couldperhap s beuse d inpredictin g thebehaviou ro fpes ­ ticides inth e aquatic environment,startin g froma limited seto fphysico-chemica l data ona pesticid e ando f thehydrologica l data from thefiel d situation.

155 Samenvatting

Het gebruikva nbestrijdingsmiddele ni nland -e ntuinbou wka nonde rbepaald e omstan­ dighedenee nniet-gewenst everontreinigin gva nhe toppervlaktewate r opleveren.Ee naanta l situatieswaari n zulkeverontreiniginge n kunnenoptreden ,worde nbeschreve ni nhoofdstu k 1.He tvaststelle nva nd egroott eva ndeze verontreinigin gword ti nNederlan d nogalbe ­ moeilijktdoo rd eaanwezighei d vanbestrijdingsmiddele ni nd eRij n (Tabellen1 ,2 e n 3). Indez e studiei séé nva nd eagrarisch e emissiebronnenmee ri ndetai lbestudeerd ,n.l .he t overwaaienva n spuitvloeistof tijdens toepassingva nbestrijdingsmiddele ni nd efruitteelt . Demotivati eva nd eopze tva ndi tonderzoe ki sbeschreve ni nhoofdstu k2 . Hetonderzoe kbepaal t zichto the tgedra gva ntwe ebelangrijk e organo-fosfor insekti- ciden (azinfos-methyle ndimethoaat )i noppervlaktewater .Ee nalgemen e karakteriseringva n beide insekticidenme the too go phu ngedra ge neffekte ni nwaterlope ni sgegeve ni nhoofd ­ stuk3 .Beid estoffe nbezitte nee ntamelij k lageverzadigd edampdru k (Tabellen5 e n6) .Be ­ rekeningenove rd esnelhei dva nvervluchtigin gva ndez everbindinge nvanui t oppervlaktewa­ terleverde n zeerlag ewaarde nop ,zoda tdi tproce sverwaarloosbaa r lijkt t.o.v.d eomzet ­ tingi noppervlaktewate r (Sectie 3.5).D eoplosbaarhei dva ndimethoaa ti nwate ri saanzien ­ lijkgrote rda tiien va nazinfos-methyl .Daarme ehang tsame nda td ecoëfficiën tvoo rd ead ­ sorptieva ndimethoaa taa ngron daanzienlij kkleine ri sda ndi eva nazinfos-methyl .Azin ­ fos-methyli snoga l toxischvoo r crustaceeëne nsommig evissoorte n (Tabel 10).Dimethoaa t isrelatie fweini g toxischvoo rvi s (Tabel 11). Inee noriënterend e faseva nhe tonderzoe kwerde nverschillend e oppervlaktewateren inhe t KrommeRij ngebie de ni nd eLopikerwaar d bemonsterd (Sectie9.2) .Bemonsterin gva n watere nslootbodemmateriaa lvereist e speciale techniekendi evoo rdi tonderzoe k verder werdenontwikkel d (Hoofdstuk 4). Wéinig-verstoordeslibmonster swerde n gestokenme tee n kolomsteekapparaat (Figuren3 e n4) .D eslibmonster swerde nn ainvrieze n laagsgewijsop ­ gedeeld engeanalyseerd . Dewerkwijze nbi jd echemisch eanalys eva nazinfos-methy le ndimethoaa ti noppervlak ­ tewatere nslootbodemmateriaa l zijnbeschreve ni nhoofdstu k 5.D ewatermonster swerde nge ­ ëxtraheerdme tdichloromethaan ,som s gevolgd dooree nzuiverin gd.m.v .kolomchromatografie . Deconcentratie sva nd einsekticide nwerde nbepaal dme tee ngaschromatograaf ,uitgerus t metee nvlamfotometerdetektor .D e'recovery'-percentage sware nhoo g (Tabellen1 2e n 13). Debeid emodelstoffe nwerde nvaa kgescheide no pverscheiden e gaschromatografischekolomme n met stationaire fasenva nverschillend epolaritei t (Tabellen1 4e n15) . Grote hoeveelheden storende stoffeni nall ebodemmateriaalextracte nkonde nworde nverwijder d metbehul pva n silicagelkolommen. Voord ekwantitatiev ebeschrijvin gva nhe tgedra gva nbeid e insekticideni nopper ­ vlaktewaterwa see naanta lbasisgegeven snodig .D egegeven sove rd eomzettingssnelhede n vandeze verbindinge ni noppervlaktewate rware nno gt ebeperkt .Omzettingssnelhede nva n

156 azinfos-methyle ndimethoaa t inoppervlaktewate r eni nslootbodemmateriaa l werden o.a. bepaald inhe t laboratoriumonde rbeheerst e omstandigheden (Hoofdstuk 6). Dehydrolyse - snelheidva n azinfos-methyl namster k toeme t toenemende pH (Figuur 7). Dit gedragwa s in overeenstemming metenkel e literatuurgegevens. De afbraakva nazinfos-methy l inoppervlak ­ tewatere nbodemmateriaa l konbeschreve nworde nme tee neerste-ord e snelheidsvergelijking (Figuren 8, 12e n 13). De afbraakcurves voor dimethoaat inbeid emedi avolgde nvoo r een beperkte tijdee neerste-ord e afbraakpatroon (Figuren 10,1 1e n 14). De afbraaksnelheid vandimethoaa t namduidelij k toeme t de tijd (Tabel22) . Koperionenbleke n sterkkatalytisc h tewerke no pd eomzettin gva nbeid emodelstoffe n inoppervlaktewater . Nagegaanwer d hoeveel deomzettingssnelhede n vanbeid e stoffentoene ­ menbi j stijging vand e temperatuur. De omzettingssnelheden vanbeid e stoffen inanaëroo b slootbodemmateriaal,bepaal d in incubatieproeven inhe t donker,ware naanzienlij k groter dandi e inoppervlaktewate r (Ta­ bellen 18,20 ,2 1 en 22). Aanhe t ontwikkelen van laboratoriumexperimenten waarvan dere ­ sultaten kunnenworde n gebruikt voord evoorspellin g vanhe t gedragva n bestrijdingsmid­ delen inoppervlaktewate r moetno gvee lwer kworde n gedaan. De omzettingssnelheden vanhe t zuurstofanaloog vanazinfos-methy l (Tabel 7)i nopper ­ vlaktewater en slootbodemmateriaal warengrote rda ndi eva n azinfos-methyl (Tabellen 18e n 20). De adsorptieva n azinfos-methyl endimethoaa t aanverschillend ebodemmateriale n kon redelijkbeschreve nworde nme t lineaireadsorptie-isotherme n (Figuren 15,1 6e n 17).D e adsorptiecoëfficiëntenva nazinfos-methy l warenongevee r 100maa l decoëfficiënte n gemeten voordimethoaat . De adsorptiecoëfficiënten vanbeid e stoffencorrespondeerde n goedme the t organische stofgehalteva nd everschillend e bodemmaterialen (Tabel 23).D e coëfficiënten vooradsorpti e aan slootbodemmaterialen warenvee lhoge r dand e coëfficiëntenvoo radsorp ­ tieva n dezelfde verbindingen aan landbouwgronden. Inee nvroe g stadium vanhe t onderzoekwer d hetduidelij k datexperimente n in sloten zeergecompliceer d kunnen zijn.Daaro mwerde n ook relatiefeenvoudig e experimentenuitge ­ voerdme tbassin s ind e openlucht .D e afnamesnelhedenva n demodelstoffe n inwate r end e penetratie inee n laagbodemmateriaa l werden gemeten (Hoofdstuk 7). Deafnam eva nbeid e stoffen inhe twatercompartimen t vand ebassin s konredelij k goedbeschreve nworde nme t eeneerste-ord e snelheidsvergelijking (Figuren 20e n21) . De afname vanazinfos-methy l endimethoaa t inhe twatercompartimen t vand ebassin s wasvee l sneller dand eafnam egemete nbi j incubatie inoppervlaktewate r inhe t donker (Tabellen 18,2 0e n 26). Tengevolgeva nalgenbloe i trad eree naanzienlijk e dagelijkse schommeling op ind ep Hva nhe twate r (Figuur 18). Debenaderend ewaarde nvoo rd eeerste - -ordesnelheidscoëfficiënte n voord eafnam eva nbeid estoffe nblee kster kafhankelij kva n demaximu mp H (Figuur 22). Eenduidelij k effectva nverschillend e formuleringenva nbeid e modelstoffen opd eafnamesnelhei d inhe twatercompartimen t konnie tworde nvastgesteld .D e aanwezigheid vanee nbodemlaa g ind ebassin swa s geendominerend e faktorbi jd eafnam eva n demodelstoffe n inhe t watercompartiment. Laboratoriumexperimenten uitgevoerd inhe t donkerhebbe n slechtsee nbeperkt e waarde voorhe tvoorspelle n vand eafnamesnelhei d vanbeid e stoffen inoppervlaktewater . Eri s duidelijk behoefte aan laboratoriummethodieken waarmee op representatievewijz ehe t effekt

157 van lichto pd eafnamesnelhei d vanbestrijdingsmiddele n inoppervlaktewate r kanworde n vastgesteld. Deevaluati eva nhe tgedra gva nvel ebestrijdingsmiddele n onderverschillend e omstan­ digheden inoppervlaktewate rvereis t eenenorm e onderzoekscapaciteit.Aangezie n deaar d vand efysich-chemisch eprocesse nvoo rvee lverbindinge n dezelfde iskunne n rekenmodellen goedbenu tworde nvoo r dekwantitatiev ebeschrijvin g vanhe tgedra gva ndez emiddelen .He t eerste computersimulatiemodel (AppendixA )beschrijf the tgedra gva n bestrijdingsmiddelen inee nwaterbassinsystee m met eenbodemlaa g (Hoofdstuk 8). Bewegingva n bestrijdingsmid­ delen t.g.v.diffusi evana fhe twater-sedimen t grensvlak ind ebodemlaa gwer d beschreven inee néén-dimensionaa l systeem.Adsorptie-evenwichte nwerde nveronderstel d zichonmiddel ­ lijk int estellen .D eafbraaksnelhede n inwate r enbodemmateriaa lwerde n ingevoerd als eerste-orde reactiecoëfficiënten. Het relatievebelan gva nverschillend e afnameprocessenva nbestrijdingsmiddele ni n oppervlaktewater kanme tbehul pva nhe tontwikkeld e rekenmodelbete r gekwantificeerdwor ­ den.Ui t demateriaalbalan s vanbeid emodelstoffe ni nsimulatie s vand e bassinexperimenten bleekda tomzettin gva nd estoffe n inwate rd ebelangrijkst e faktorwa s (Tabel 30).D ebe ­ rekendemass ava n debeid e insekticiden ind ebodemlaa gwa sbijn a altijd lager dan 10°sva n de toegepaste dosering.Dez eberekend emassa' sware nhoge r dand egemete nhoeveelhede n (Fi­ guren 23e n24) . Deberekend e penetratiediepte vandimethoaa twa s groterda n dieva nazinfos-methyl . Dehoofdoorzaa k voordi tverschi l isd e relatief lageadsorpti e vandimethoaat . Simulatie-experimentenwerde nuitgevoer d omd egevoelighei d vanhe tmode l vanhe t bassinsysteem voorveranderinge n inparameter s teteste n (Tabel 31). Diffusie ind ebodem ­ laagblee k eenrelatie f langzaamproce s te zijn.Onzekerhede n ind ecoëfficiën t voordif ­ fusieva nd estoffe ndoo rd ewaterfas e inhe tbodemmateriaa lbleke nminde rbelangrij k te zijn (Figuur 27A). Inslote nme t relatiefgering ewaterdiept e kand egeleidelijk e adsorp­ tieva nbestrijdingsmiddele n aanbodemmateriaa l vangroo tbelan g zijn,voora l alsd eaf ­ braaksnelheid inwate r geringis .I nsituatie sme tee nrelatie fhog eafbraaksnelhei d (hal­ veringstijd vanenkel edagen )i spenetrati e ind ebodemlaa gva nondergeschik t belang. Demetinge nva nazinfos-methy l endimethoaa t inwaterlope n enbedri jfsslote ni nhe t KrommeRij ngebie d en ind eLopikerwaar d zijnbeschreve n inhoofdstu k 9. Inee noriënte ­ rende faseva nhe tonderzoe k in 1975werde nvie rbemonsteringspunte n ingroter e waterlopen envij fbedrijfsslote nbemonster d (Figuur 30). De interferentie doorstorend e verbindingen inextracte nva nwate rui tgroter ewaterlope n konme tbehul pva nsilicagelkolomme naanzien ­ lijkverminder dworde n (Tabellen3 2e n 33). Erwerde ngee nduidelij k indikaties gevonden vooree n toenameva n demodelstoffe n inhe twate r tijdensdoorstromin gva nhe t Kromme Rijn gebied.Relatie fhog econcentratie swerde naangetroffe n inwate rva nbedri jfsslote no p fruitteeltbedrijven ind e Lopikerwaard. Dezebedrijfsslote nwerde nuitgekoze nvoo rverder e onderzoekingen in 1976e n1977 . Dezeslote nbevatte nsteed swate rtijden she tgroeiseizoe ne no pbeid ebedrijve nwa s een onderbemalingaanwezig , zodatee nwaterbalan s van deze slotenko nworde ngescha t (Sectie 9.3.3). Tijdens deduu rva nhe tonderzoe kkwame nallerle i complicaties aanhe t licht,zo ­ alsd esterk eheterogenitei tva nd egronden ,d ecomplex ehydrologisch e situaties end enood ­ zaakto the t inlatenva nwate r inhe trelatie fdrog ejaa r 1976 (Figuren3 1 t/m 35). De

158 slootsysteraenwerde n goed gekarakteriseerd doormetinge no m simulatieberekeningen vooree n modelsysteem mogelijk temake n (Tabellen 34 en 36). Opvallendware nd ehog eorganisch e | stofgehaltes,d e lagevolumiek e massa's end ehierme eovereenkomend e hogevolumefractie s bodemvochti nhe t slootbodemmateriaal (Figuur 36). ' In 1976werden ,n a de toepassing vanbeid e modelstoffen opd etwe e fruitteeltbedrij- ven ind e Lopikerwaard, deconcentratie s ind ebedri jfsslote nnauwkeuri g bepaald (Tabellen 37, 38e n 39). Dezeware n tamelijk hoog,voora l kort na de toepassing. Erwer d geen last ondervonden van storende stoffenbi j degaschromatografisch e analyses.D eafnam eva nbei ­ demodelstoffe n ind ebedrijfsslote no phe t fruitteeltbedrijf i nBenscho p kon (vooree n periode zonderwaterinlaa t enwaterafvoer ) redelijkbeschreve nworde nme tee n eerste-orde snelheidsvergelijking (Figuren 38e n 39). Deberekend e halfwaardeti jde nva n azinfos-methyl indez e slotenware n ongeveer3 tot 4dagen ,di eva ndimethoaa tvarieerde nva n4 tot1 3 dagen (Tabel 42).Dez ehalfwaardetijde nstemde n overeenme t dehalfwaardetijde n gemeten in bassinexperimenten (Tabel 26).D e penetratie van azinfos-methyl ind e slootbodemsblee k relatief gering te zijn (Tabellen 46 en47) . De immissieva nd e insekticiden naard ebedri jfsslote nwer d in 1977mee r indetai l gemetenme tbehul p vanPetrischale n geplaatst op drijvers ind eslote n (Sectie 9.3.8).D e mateva n immissie bleek sterk afhankelijk van lokale situaties opd e fruitteeltbedrijven (windsingels,afstan dva nd evruchtbome n totd ewaterlopen ,schouwpaden )e nd ewijz e van toepassing (Tabellen4 0e n 41). De verhouding tussen dehoeveelhei d insekticide diete ­ recht kwampe roppervlakte-eenhei dwate r end e dosering peroppervlakte-eenhei d boomgaard- grond (=immissieverhouding)wa s hethoogs tbi j zgn.ove rd e slootspuite n (0.4), de laagste immissieverhoudingenwerde n gemeten voorslote n achterwindsingel s (0.003). Het schattenva nd everschillend e posten ind ewaterbalan s vand esloo twa snie teen ­ voudig (Figuren 41,4 2e n 43). Dewaterflu x door deslootbodem ,al s sluitpost afgeleid uit dewaterbalans ,wa s relatief laag (Sectie 10.4)e nwa smeesta lnaa rd e slootgerich t (po­ sitief). D e verdeling van deafvoersnelhei d van depom pove rd everschillend e slootsecties konslecht s globaal geschatworde n (Tabellen 34e n 48). Inverder e experimenten insloot - systemen zouden deveranderinge n insloot -e n grondwaterpeilen continu geregistreerd moe­ tenworde n omd ekarakteriserin g vand ewaterstromin g teverbeteren . Een rekenmodel voorhe t gedrag vanbestrijdingsmiddele n inee nslootcompartimen tme t volledig gemengd waterword tbeschreve n inhoofdstu k 10.Di t rekenmodel (AppendixB )be ­ schrijftnaas td e relevantewater -e npesticidefluxe ni nhe t slootsysteemoo kd efluxe n door de grensvlakken vanhe twatercompartimen t enva nd ebodemcompartimenten . De ingevoer­ de snelheidscoëfficiënt voorafbraa k inhe t slootwatercompartiment werd gelijkgestel d aan 0.9 keerd esnelheidscoëfficiën t voor degemete n afname (Tabel 42). Dit leverde eenrede ­ lijke overeenstemming op tussend egemete n end eberekend e concentratie-tijdrelatie s in hetwate r (Figuren 44 t/m 47). Voor de 'duiker'sloo t inBenscho pwa s omzetting vand emo ­ delstoffen inhe t slootwatercompartiment hetbelangrijkst e afnameproces. Inee n 59-daagse periodeme t geringewaterafvoe rwer dbereken d dat 69 tot 88% vand e geïntroduceerde model­ stoffenwer d omgezet inhe twate r (Tabel 49). Voor de 'onderbemalen'sloo t inBenscho p (laat­ ste leidingvak voord epomp )wer d indez eperiod ebereken d datafvoe rvanui the tslootwa ­ tercompartiment enkele tientallenprocente nva n de geïntroduceerde hoeveelheid kanbedra ­ gen (Tabel 49).Evenal s ind ebassinsimulatie-experimente n waren de totalemassa' s vana -

1S9 zinfos-methyl ind eslootbodem s groterda nd e gemetenwaarde n (Figuur48) . Uit simulatie-experimenten bleek dat inslote nme t eenafvoe rva nwate rvanui t grond­ water (drainagesituatie)he t effektva npenetrati e ind ebode m zeerbeperk twa s (Figuren 51 en 52). Insituatie sme t infiltratie vanuit de slootko nd e slootbodem alsee nbelang ­ rijke 'sink'worde nbeschouw d (Tabel 50).Voo r eennauwkeurig e beschrijving vand econcen ­ tratiepatronenme td ediept e ininfiltratiesituatie s ismee ronderzoe knodi g overhe tdis ­ persiegedrag inslootbodemmateriaal . Indrainagesituatie s wordt depenetratiediept e met hethuidig e rekenmodel (AppendixB )iet soverschat .Ee nmodeltechnisc hproblee m betreffen­ dekunstmatig e 'achterwaartse'dispersi e kanno gnie tgehee lworde nopgelost . Metingen enberekeninge nove rhe tgedra gva n stoffen inslote n tijdens waterstroming (bijv. tengevolge vanpompen )staa nbeschreve n inhoofdstu k 11.Hoewe l er ind e literatuur vele empririschedispersieformule sstaa nbeschreve nware ne rbijn a geengegeven s overhe t dispersiegedrag van stoffeni nkleiner ewaterlope n (Tabel 51).Enkel e dispersie-experimen­ tenwerde nuitgevoer d metkleurstoffe n inslote no pd ebeid e fruitteeltbedrijven ind e Lo- pikerwaard (Tabel 52).I nee nexperimen t inee npa s 'opgeschoonde'waterloo pwer d eenre ­ latief lagedispersiecoëfficiën t gevonden. Inee nsituati eme tee nkroosde kwa s dedisper ­ siecoëfficiënt eenfakto rvie r groter (Tabel 53).I nzo' nsituati e trad eree n flinke staartvormingo p ind e concentratie-tijd relatie opd emeetpunte n (Figuur 53). De disper­ sieconstanten (Vergelijking 41)voo rdez eklein ewaterlope nware ngrote rda ndi evoo rbeke n enriviere ni nNederlan d (Tabellen 51e n53) . Erwer d een rekenmodel ontwikkeld omhe t gedragva nstoffe n inslote n tijdenswater ­ stroming tebeschrijve n (Appendix C). Hetmode l omvattevel eprocesse n zoals convectieve stroming,dispersie ,diffusie ,adsorpti e enomzettin g vand estoffen .E rwa s alleenee n goedeovereenstemmin g metmeetresultaten ,di everkrege nware n inee nschon ewaterloo p (Fi­ guur 54). Hetverschijnse l vanstaartvormin g inconcentratie-tij d relaties kanwaarschijn ­ lijkbete rbeschreve nworde nme t zgn. 'stagnante fase'modellen .Ui t simulatie-experimen­ tenme td ebeid ekleur -e nmodelstoffe n inslote nme tee n relatiefgrot e stroomsnelheid bleek dat deomzettin g enpenetrati e ind eslootbode mverwaarloosbaa r zijn ind ebetref ­ fendekort eperiod e (Tabellen5 4e n 55). Afvlakking vand e concentratieverdeling door dis­ persiewa s verreweghe tbelangrijkst eproce s indez e situaties (Figuur55) . Insituatie sme t lagestroomsnelhede ni nhe t slootwater ofvoo rslote nme tperiode s vanwaterstilstan d kane rwellich t eenmode l samengesteldworde n door combinatie vanhe t tweede rekenmodel (AppendixB )e nhe tderd e rekenmodel (Appendix C). Hetvóórkome nva ndi ­ verseprocesse nme tster kverschillend e snelheden levertechte r enige complicaties ten aanzienva nd ebenodigd e rekentijd. De rekenmodellenwerde nallereers t gebruikt alshulpmidde l bijhe tonderzoek ,waar ­ doorgebiede n met teweini gkenni sduidelijke r kondenworde n opgespoord. De resultatenva n modelberekeningen end evergelijkin gme tmeetresultate n verschaffengoed estartpunte n voor verderonderzoek . Naverder e toetsingkunne n derekenmodelle nwellich tworde n ingezetvoo r hetdoe nva nvoorspellinge n omtrenthe tgedra gva nbestrijdingsmiddele n inoppervlaktewa ­ ter,uitgaand e vanee nbeperk t aantal fysisch-chemischegegeven s overee nbestrijdingsmid ­ dele ngegeven sove rd ehydrologisch e situatie inhe tveld .

160 Appendices

Appendix A

TITLEBSHAVI0U R 0FAZINPHBS-METHY L INTAN K 2 (DIFFUSI0N M0DEL1) * TANK WITH MIXED VATER C0MPARTMEMTAN D C0MPAETIKENTALIZATI0M 0FBeTT0 M LAYER ST0RAGEDPeRL(lO)*KSL(lO)*CAPL(lO)*CAB0TB(lO)*DE30SU(l1 ) ST0RAGETB0TC10)*DIFD<10)*DE30C0(10),BD<10)*VFLC10)*T0RT(10 ) ST0RA3ECLB(10)*FLRS3(1 1)*RDSC3(10)*CM (10 ) FIXED NBC0i:*J*NBC0MP INITIAL N0S0RT * A3BP.SVIATI0NS :C0M P.=C0MPARTMENT(5 ) * BASIC UNITS :MILLIGRA M (MG)* METE R CID *DA Y CD) *** DEFINITIONTAN K SYSTEM 3EBMETRY *VVTT=V0LUME 0FWATE R C0MP. (M3)A S F(TIME) FUNCTI0N VVTT=(0.*0.154)*(3-64*0-148)*(5.64* 0.142 )*( 9.64*0.133)*•• • C13.64*0.120) *(30«*0 .120 ) 1=30SU=SU?.FAC EARE A CFTH EBeTT0 M C0MP. CM2) PAP.AM30S U=O. 6 *TB0T=THICKNES S 0FB0TT0 M C0MP. CM) * N3C0M=N'JMBEP.0 F30TT0 M C0MP. * MFAC=MULTIPLICATI0N FACT0R F0F.T30T,VFAC=VSI3H T FACT0R F0RTB0 T PAP.AMNBC0M=1O*MFA C=1 . 5 WFAC=1.0/(MFAC+l.0) PAP.AMTB0TI=O.OO 1 TB0TC1)=T30T1 00 10J=2*N3C0 M 10 TB0T(J)=MFAC*T30T(J-1) N3C0KP=NBC0M+1 *DE30C0=DEPT H 0F CENTRES eFTH EB0TT0 M C0MP. (M) *DIFD=DIFFUSI0 N DISTANCEBETVEE NB0TT0 M C0MP. (M) * DE30SU=DEPTH 0F UPPER SURFACES 0F30TT0 M C0MP. (M) DE30C0C!)=O.5*T30TC1 ) DIFDC1)=O.5*T30TC1) DEB0SUC1)=O.O 00 11J=2*N3C0 M DIFD(J)=O.5*(TB0T(J-1)+T30T(J)) DEB0C0(J)=DS30C0(J-1)+DIFD(J) 11 DEB0SU(J)=DE30C0(J-1)+O.5*TB0T(J-1> DE30SUCNBC0MP)=DEB0C0(NBC0M)+O.5*TB0T(NBC0M ) VEITE(6*78)(T30T(J)*J=1*NBC0M) 78 F0RMATC1K0**T30T=•*2X*10E10-3 ) VRITE(6*79)(DEB0C0(J)*J=1*NBC0M) 79 F0RMA7(1H *'DE30C0='*10E10•3) *** PHYSICAL CHARACTERISTICS 0FTH EB0TT0 M * 3DT=BULK DENSITY 0F 30LID PHASE (KS/M3(MEDIUM))A S FCDEPTH) FUNCTI0N BDT=C0.*200.) *CO. O1*370.) *CO-02. .54 0. )* C0.03*660.) *• •• CO.04*650.)*CO.05*670.)*(0.20*680. ) * VFLT=V0LUME FRACTI0H 0FLIQUI D CM3(LIQUID)/M3(MEDIUM) )A S F(DEPTH) FUNCTI0N VFLT=(0.*0.92)*(0.01*0-88)*(0.02*0.79)*(0.03*0.74) *•• • (0.04*0.75)*(0.OS*0.75)*(0.20*0-74) * T0RTT=T0RTU0SITY FACT0R (M2(MEDIUM)/M2(LIQUID)) AS F(VFL> FUNCTI0N T0RTT=(O.*O.)*(0.1*0-03)*(0.2*0.1)*(0.3*0.2)*(0.4*0-34)*...

161 (0.5/0.5),(1.0*1.0) DO 20J=1*N3C0 M BD(J)=AFGEN(BDT*DEB0CO(J)) \7FL(J)=AFGEK(VFLT*DEB0C0(J)) 20 T0RT(J)=AFGEK(TORTT*VFL(J)) * DIFW=DIFF'u'SION COEFFICIENT 0F SUBSTANCE IH BULK WATER (M2(LIQUID)/D ) PARAM DIFV= 0 • 4 1 E - 4 * DP0RL=DIFFUSI0N C0EFFICIEMT 0F SUBSTANCE IN LI3UID PHASE CM3CLICUID)/ DP0RL(l)=yFL(l)*T0RT(l)*DIFW (M(MEDIUM)D)) 00 21 J=2*NBC0M 21 DP0P.L(J)=WFAC*(KFAC*VFL(J-1)*T0RT(J-1)+VFL(J)*T0RT(J))*DIFW *** PARTITION 0F SUBSTANCE 0VER BOTTOM PHASES*INSTANTANE0US EQUILIBRIUM * KSL=D1STRI3UTI0N RATI0 SOLID/LIQUID PHASE =ADS0RPTI0M COEFFICIENT * (HG/KGCS0LID PHASE))/CMG/M3CLIQUID PHASE)) * K3LT=KSL AS FCDEPTH) FUNCTION KSLT=CO.*0.073)/(0.2*0.073) * CAPL=SU3STANCE CAPACITY FACT0R RELATING T0 CONCENTRATION IN LIQUID PHASE * (M3(LIQUID)/M3(MEDIUM)) D03 0J=l*N3C01 i KSL(J)=AFGE:KKSLT*DEB0C0(J)) CAPL(J)=VFL(J)+3D(J)*KSL(J) 30 CA30TB(J)=CAPL(J)*3ESU*TB0T(J) *** DECOMPOSITION OF THE SU3STANCE * RCDEVT=RATE COEFFICIEN T( 1/D ) FOR DECOMPOSITION IN VATER AS FCTIME) FUNCTION RCDEWT=(0.*0-23)*(5.64*0.23)*(5.65*0.49)*(30.*0.49) * RCDEBT=RATE COEFFICIENT(1/D) F0R DECOMPOSITION IN BOTTOM AS F(TIME) FUNCTION RCDEBT=(0-*0.073)*(30.*0.073) *** INITIALAN DBOUNDAR Y CONDITIONS * MSW=KASS OF SUBSTANCE IN WATER COMP. CMS) * MSB=MAS5 OF SU3STANCE IN BOTTOM COMP. (MG) * IREFER S TO INITIAL CONDITION INCON IMSW=13.2 TABLE IMSB(1-10 )=10*0. 0 * FLRS3=FL0V RATE 0F SUBSTANCE INTO 30TT0M COMP. (MG/D) FLRS3(NBC0M?)=0.0 DYNAMIC NOSOR T *** 5U3STANCEMOVEMEN T * RMSW=RATE OF CHANGE IN MASS OF SU3STANCE IN WATER COMP. (MG/D) M5W=INTGRL(IMSW*RMSW) * RMSB=RATE OF CHANGE IN MASS 0F SUBSTANCE IN BOTTOM COMP. (MG/D) MS3=I NTGRL(IMSB *RMSB*10 ) * CW=CONCENTRATI0N OF SU33TANCE IN WATER COMP. (MG/M3) VWT=AF3EN(VWTT*TIME) CW=M5W/VWT * CLB=C0NCENTRATION 0F SUBSTANCE IN LIQUID PHASE 0F BOTTOM COMP. (MG/M3) * CM=C0NCENTRATION OF SUBSTANCE IN BOTTOM COMP. (MG/M3(MEDIUM)) DO 50 J=1*NBC0M CLB(J)=MS3(J)/CA30T3(J) 50 CM(J)=CLB(J)*CAPL(J) FLRS3(1)=-DPORL(1)*B0SU*(CLB(1)-CW)/DIFD(1) D0 51 J=2*N3C0M 51 FLRS3(J)=-DP0RL(J)*B0SU*CCLB(J>-CLB(J-1))/DIFD(J) *** DECOMPOSITION OF THE SUBSTANCE * RDECW=RATE OF DECOMPOSITION IN WATER COMP. (MG/D) * RDEC3=RATE OF DECOMP0SITI0N IN BOTTOM COMP. (MG/D) * TRDECB=TOTAL RATE OF DECOMPOSITION IN THE BOTTOM (MG/D) RDECW=AF3EN(RCDEWT*TIME)*MSW TRDECB=0.0 DO 55 J=1*N3C0M RDECB(J)=AF3SN(RCDE3T*TIME)*MSB(J) 55 TRDECB=TRDECB+RDECB(J) * TDECW=TOTAL MASS 0F SU35TANCE DECOMP0SED IN WATER COMP. (MG) * TDEC3=T0TAL MASS OF SUBSTANCE DECOMPOSED IN BOTTOM (MG) TDECW=INTGRL(0.0*RDECW)

162 TDECB=INTGRLCO.O/TRDECB> *** OVERALL RATE EQUATIONS * RMSW=RATE 0FCHANG E INKAS S 0F SUBSTAMCE IMVATE R COMP (MG/D) RMSW=-FLRS3(1)-RDECW * RMSB=RATE 0FCHANG E IMMAS S 0F SUBSTANCE INB0TT0 M C0MP.(MG/D ) D0 60J=1/NBC0 M 60 RMSB(J)=FLRSB(J)-FLRSB(J+1)-RDECB(J) *** 0UTPUT SECTION PRTI K= I MPULS C 0 • 0 , PP.DEL) IF(?RTIM*XEEP .LT. 0.5) 30 T0 103 * TKS3=T0TAL IIASS 0F SUBSTANCE IN B0TT0IÎ M S " J/ • • • THSB/TDECV/TDECB HETH0D RKS 0UTPUT MSW(0.*15.)/TMS3<0.>1.5) TIMER PRDEL=O.5,0UTDEL=O.5>FINTIM=2 7. END ST0P ENDJ0B

Appendix B

TITLEWATE R AND PESTICIDE BALANCES F0R DRAINAGE AND INFILTRATION DITCH *****x***************#***##*x#*x*#****+*%x***************** *********** * DITCH WITH MIXED WATER COMP.AN D C0MPARTIKEN TAL IZATI0Î J0 FDITC HB0TT0I : ST0RAGETB0T(2O)..DIFD(2O),DEB0C0(2O)/3D(2O).,VFL(2O)/T0RT(2O ) ST0RA3EDP0RL(2O)..KSL(2O).,CAPL(2O)..CA3eT3(2O)/DEB0SU(21>,CM(2O ) ST0RAGEB0SUC21),CLB(20) ,FLRSBC21)>RDECB(20),VBOT(20),DT0TB(20) ST0RAGEPUMPT(6O),INTAKT(6O),EVAP0T(6O),RAINT(6O).,SUPST(6O).,FDIFLBC2O ) FIXED NDAY,J,NBC0M.iNBC0MP INITIAL N0S0RT * ABBREVIATIONS :C0MP.»COMPARTMENT(S ) * AZIN.=AZINPH0S-METHYL/DIM.=DIMETH0ATE * BASIC UNITS :MILLIGRA M (MG) , METER CM), DA Y (D) *** DEFINITI0N 0FDITCH-LAN D SYSTEM GE0KETRY * LC0M=LEN3TH 0FTH EDITC H C0KPARTMENT (M) * S=SL0PE 0FDITC H WALLS (H0RZ./VERT.) (->,SI=L0WER,S2=UPPER PART PARAM LC0M=2O4.#S1=O.46/S2=I. * HWS=HEI3HT 0FL0WE R DITCH PART WITH SL0PE SI (M) * W1=WIDTH AT THE B0TT0M 0F THE DITCH CM) * W2=WIDTH 0FTH EDITC H AT HEIGHT HWS (M) PARAM HWS=0.40*Wt=l.42 W2=W1+2.0*S1*HWS * VWDL=V0LUME 0FTH E DITCH (M3> UP T0TH EHWS-LEVE L VWDL=HWS*(W1+S1*HWS)*LC0M * DSA=DRAINAGE SURFACEARE A (M2)ASSIGNE D T0 THEDITCH(D)>T 0TH EDITC HBeTTe M * (DB),DRAINS(DR) PARAM DSADB=2750.*DSADR=8050. DSAD=DSADB+DSADR * ISA=INFILTRATION SURFACEARE A (M2)ASSIGNE D T0TH EDITC H (D)/T0TH E * DITCH B0TT0M(DB),DRAINS(DR) PARAM ISADB=2750./ISADR=0. ISAD=ISADB+ISADR * P=WETTED PERIMETER 0FTH EDITC H (M)/CALCULATED FReMAH W * AHW»AVERAGEHEIGH T 0FTH EWATE R LEVEL (M) PARAM AHW=0.30 P=W1+2.0*AHW*SQRT(S1**2+1.0) * N3C0M=NUMBER 0FB0TT0 M C0MP. * TB0T=THICKNESS 0FB0TT0 M C0MP. (M) * MFAC=MULTIPLICATI0NFACTO R F0R TB0T/WFAC=WEIGHT FACTOR F0RTB0 T 163 PARAM NBC0M=2O/MFA C=1- 1 WFAC=1.O/CMFAC+1.0) PARAM TB0T1=O-OO1 TB0TC1)=TB0TI D0 10J=2/NBC0 M JO T30TCJ)=MFAC*TB0TCJ-1) N3C0MP=NBC0M+1 * DEB0C0=DEPTH 0FCENTRE S 0FTH EB0TT0 M C0MP. CM) * DIFD=DIFFUSI0N DISTANCEBETVEE NB0TT0 M C0MP. CM) * DEB0SU=DEPTH 0FUPPE R SURFACES 0FB0TT0 M C0MP. CM) * B0SU=SURFACE AREA 0FTH EB0TT0 M C0MP. CM2) DSB0C0C1)=O«5*T30TC1) DIFDC1)=O.5*TB0TC1) DEB0SUCJ)=O-O 30SUC1)=LC0M*P BETA=ATANCI.0/51) D0 11J=2,N8C0 M DIFDCJ)=O.5*(TB0TCJ-1)+TB0TCJ)) DE30C0CJ)=DE30C0CJ-1)+DIFDCJ) DEB0SUCJ)=D£B0C0CJ-1)+O.5*TB0TCJ-1) 11 B0SUCJ)=LC0M*CV1+2.O*DEB0SUCJ)*SINCO.5*BETA)/C0SCO.5*3ETA)+... 2.0*CAHW+DE30SUCJ))*SQRTCS1**2+ 1 -0)) DEB0SUCN3C0MP)=DEB0C0CNBC0M)+O.5*TB0TCN3C0M) B0SUCNBC0MP)=LC0M*CVn+2.O*DEB0SUCNBC0MP)*SINCO.5*3ETA)/... C0SCO.5*3ETA)+2.O*CAHW+DEB0SUCNBC0MP))*SQRTCS1**2+1.0)) VRITEC6/78)CTB0TCJ)/J=l/NBC0M) 78 F0RMATC1HO/*TB0T=•.2X/10E10.3) WRITEC6/79)CDE3eC0CJ)/J =l /NBC0M) 79 F0RMATC1H .'DEB0C0='/10E10.3) WRITEC6/80)CB0SUCJ),J=1/NBC0KP) 80 F0RMATC1H , *B0SU='/2X/11E10.3) *** PHYSICAL CHARACTERISTICS 0F THE B0TT0M * BDT=BULK DENSITY 0F S0LID PHASE CKG/M3CMEDIUM)) AS FCDEPTH) FUNCTI0N BDT=C0./90.)/CO.05/210.)/CO.10/2700/CO.15/300.)/... CO.20/350.)/CO . 25/330.)/CO.5/460.) * VFLT=V0LUME FRACTI0N 0FLIQUI D CM3CLIQUID)/M3CMEDIUM))A S FCDEPTH) FUNCTI0NVFLT=C0./0.96)/C0.05/0.91)/CO.10/0.88)/CO.15/0.87)/.. . CO.20/0 .84)/CO.25/0.85)/CO.5/0.80 ) * T0RTT=T0RTU0SITY FACT0R CM2CMEDIUM)/M2CLIQUID))A S FCVFL) FUNCTI0N T0RTT=CO./O.)/CO.1/O.O3)/CO.2/O.1)/CO.3/O.2)/CO.4/O.34)/... C0.5/0.5)/Cl.0/1.0) D0 20J=1/NBC0 M BDCJ)=AFGENCBDT/DEB0C0CJ)) VFLCJ)=AF3ENCVFLT/DEB0C0CJ)) 20 T0RTCJ)=AF3ENCT0RTT/VFLCJ)) * DIF'J=DIFFUSI0NC0EFFICIEN T 0FSUBSTANC E INBUL K VATER CM2CLIQUID)/D) PARAM DlFW=0.35E-4 * DP0RL=DIFFUSI0NC0EFFICIEN T 0FSUBSTANC E INLIQUI D PHASE CM3CLIQUID)/ * fMfMrDIUM)D)> DP0RLC1)=VFL C1)*T0RT C1)*DIF W (HC^uJun»" D0 21J=2/NBC0 M 21 DP0RLCJ)=WFAC*CMFAC*VFLCJ-1)*T0RTCJ-1)+VFLCJ)*T0RTCJ))*DIFW * DISPD=DISPERSI0N DISTANCE CMCMEDIUM)) " PARAM DISPD=0.015 *** PARTITI0N 0F SUBSTANCE 0VER B0TT0M PHASES/INSTANTANE0US EQUILIBRIUM * KSL=DISTRIBUTI0NRATI 0 S0LID/LIQUID PHASE =ADS0RPTI0N C0EFFICIENT * CM3/K3CS0LID PHASE))/CMG/M 3CL IQUI D PHASE)) MCIEW * KSLT=KSLA S FCDEPTH) FUNCTI0N KSLT=C0./0.279)/C0«8/0.279) CAp * L=SU3STANCEiCAPACITYDFACT0R RELATING T0 C0NCENTRATI0» IN LIQUID PHASE D0 30 J=1/NBC0M KSLCJ)=AFGENCKSLT/DEB0C0CJ)) CAPLCJ)=VFL

164 *** DEC0MP0SITI0N 0FTH E SUBSTANCE * RCDEWT=RATEC0EFFICIENTC1/D )F0 R DEC0MP0SITI0N INWATE RA SFCTIME ) FUNCTI0NRCDEWT=C0.,0.225),C60.,0-225 ) * RCDEBT=RATEC0EFFICIENT<1/D )F0 R DEC0MP0SITI0N INB0TT0 MC0MP .A S FCTIME) FUNCTI0NRCDEBT=(0.,0.036)/(60.,0-038 ) *** DEFINITI0N 0FTH E ITEMS 0FTH EVATE R BALANCE * DISRAT=DISCHARGE RATEASSIGNE D T0DITC H SECTI0N +P0SSIBLEUPSTREA M * DITCH SECTI0N CM3/D) PARAM DISRAT=135. *•PUMPT=PUMPIN 3 TIME CD),DAILY VALUES TABLEPUMP TCI-60 )=17*0.,0-2,6*0.,0-258,23*0.,0-367,11*0 . * DISUPD=DISCHARGE RATEFR0 M UPSTREAM DITCH SECTI0N (M3/D) PARAM DISUPD=0-0 * INTRAT=INTAK£RAT EASSIGNE D T0DITC H SECTI0N +P0SSIBL ED0WNSTREA M * DITCH SECTI0N (M3/D) PARAM INTRAT=0.0 * INTAKT=INTAKETIMECD),DAIL Y VALUES TABLE INTAKT(1-60)=60*0« * INTD0D=INTAKE RATE INT0D0WNSTREA M DITCH SECTI0N CM3/D) PARAM INTD0D=O.O * EVAP0T=RATE 0F EVAP0RATI0N FR0M 0PEN WATER CM/D) TABLE EVAP0TC1-60)=18*0-0041,11*0-004 ,10*0.00 47 ,10*0.0044,10*0.0065 ,• • • 0.0066 * RAINT=RAINFAL L INTENSITY CM/D) TABLE RAIN TCI-60)=0.0045,4*0.0,0.0025,3*0.0,0.0035,0.0005 ,• • • 4*0.0,0.0085,0.0005,0.007,0.Q015,3*0.0,0.0005,•.. 0.006,3*0.0,0.0015,0.0,0.011,17*0.0,0.020,0.017,1 1*0. 0 * HWT=HEIGHT 0FWATE R LEVEL INDITC H SECTI0N AS FCTIME) CM) FUNCTI0N HWT=C0.,0.20),C0.5,0.21),C2.5,0-25),C4.5,0.27),C9.5,0.30),.. . C14.5,0.33),C15.5,0.34),C17.,0.35),C18.,0.29),C21.5,0.32),... C24.,0.34),C25.,0.25),C29.0,0.27),C30.0,0.28),C37.,0.30),-.. C42.5,0.30),(47.,0.29),C48.,0.34),C49.,0.29),... C49.5,0.31),C51.5,0.34),C53.,0.34>,C59.,0.30),C60.,0-30 ) *** SUPPLY,INITIALAN DB0UNDAR Y C0NDITI0NS * SUPST=RATE 0FSUPPL Y T0DITC H WATER DUET 0 SPRAY DRIFT CMG/D) TABLE SUPSTC1-60)=10250-,48*0.0,2100.,10*0.0 * MSW=MASS 0FSUBSTANC E INWATE R C0MP. CM3) * MSB=MASS 0FSUBSTANC E INB0TT0 M C0MP. CMG) * IREFER S T0 INITIAL C0NDITI0N INC0N IMSW=0.0 TABLE IMSBCl-20)=20*0.0 * CWINT=C0NCEMTRATI0N 0FSUBSTANC E IN INTAKEWATE R CM3/M3)A S FCTIME) FUNCTI0N CWINT=C0.,0.),C60.,0.) * CWUPDT=C0NCENTRATI0N 0FSUBSTANC E INWATE R FR0M UPSTREAM DITCH SECTI0N CM3/M3) * AS FCTIME) FUNCTI0NCWUPD T=C0.,0.),C60.,0. ) DYNAMIC N0S0RT NDAY=TIME+1+0.05*DELT DAY=NDAY *** RATE 0FCHANG E INTH EDITC H WATER V0LUME .*P REFER S T0TIM EPLU S DELT ,M REFER S T0 TIMEMINU SDEL T * CENTRAL DIFFERENCE SCHEME HWP=AFGENCHWT,TIME+DELT) HW=AFGENCHWT,TIME) IFCTIME .GT.0.0 ) G0T 04 1 IFCHW .GT.HWS )G 0T 04 2 VWD=HW*CW1+S1*HW)*LC0M VWDM=VWD G0T 04 3 42 VVD=VWDL+CHW-HWS)*CV2+S2*CHW-HWS))*LC0M VWDM=VVD G0T 04 4 41 HWM=AFGENCHWT,TIME-DELT) IFCHW .GT.HWS )G 0T 04 5 VWDM=HWM*CW1+S1*HWM >*LC0 M

165 VWD=HW*(W1+S 1*HW)*LC0 M 43 VVDP=HWP*(W1+S1*HWP)*LC0M G0T 04 6 45 VWDM=VWDL+(HWM-HWS)*(W2+S2*(HWM-HWS))*LC0M VWD=VWDL+(HW-HWS)*(W2+S2*(HW-HWS))*LC0M 44 VWDP=VWDL+(HVP-HWS)*(W2+S2*(HWP-HWS))*LC0M * RVWD=RATS0 FCHANG EI NDITC H VATER V0LUME CM3/D) 46 RVWD=(VWDP-VWDM)/(2.*DELT) *** EVAP0RATI0N AND PRECIPITATI0N EVAP0=EVAP0T(NDAY) RAIN=RAINT(NDAY) IF(HW .GT.HWS )G 0T 04 7 * EVASU=EVAP0RATING SURFACE0 FA DITC H WATER C0MPARTMENT (M2) EVASU=LC0M*(W1+2.0*SI*HW ) G0 T04 8 47 EVASU=LC0M** INTRA T * QID0DS=RATE0 FWATE R INTAKE INT0D0WNSTREA M DITCH SECTI0H(M/D ) QID0DS=INTAKT(NDAY)*INTD0D *** FL0W THR0UGH DITCHB0TT0 MAN D DRAINS (CL0SING ENTRY=CLENT) CLENT=RVWD+QEVAP-QPREC+QDISCH-QDUPDS-QINT+QID0DS * IFCLEN TI SP0SITI'>/E:DRAINA3 EAN DI FNEGATIVE :INFILTRA T10 N IFCCLENT .LT.0.0 ) 30T 04 9 * QWB0T=FL0W RATETHR0U3 HTH EWETTE D PERIMETER0 FTH EDITC H (M3/D) QWB0T=DSADB/DSAD*CLENT * QWDR=FL0W RATETHR0UG H DRAINS (M3/D) QWDR=DSADR/DSAD*CLENT G0T 05 0 49 QWB0T=ISADB/ISAD*CLENT QWDR=ISADR/ISAD*CLENT 50 C0NTINUE * FL0DB=FL0W RATETHR0UG H THEDITC H B0TT0M EXPRESSEDI NM/ D FL0DB=QWB0T/DSADB * VB0To2AîSR/LU£Jffi0UQH THE WETTED DITCH PERIMETER (M3(LIQUID )/(M 2(MEDIUM)D )) D0 51« J=1>NBC0 M 51 VB0T MSB=INT3RL(IMSB,RMSB,20) * » * »ra ouru-. Uij/u; * CW=C0NCENTRATI0N 0F SUBSTANCE IN WATER C0KP. CM3/M71 * CW=MSW/VWD «Jj/.-WJ D0 52 J=I!NBC0M SUBSTANCE IN B0TT0M "MP. (MG/M3(MEDIUM)) CLB(J)=MSB(J)/CAB0TB(J) 52 CM(J)=CLB(J)*CAPL(J> CVIN=AFGEN(CWINT.TIME) CWUPD=AF3EN(CWUPDT,TIME) *: FLRSyDT^ff0NA?lR!L?UBM^5E ItIT0 °0™STREAM DITCH SECTI0N (DURING INFIL- FLRSWD=CW*aiDeDS FLRSWI=FL0W RATE 0F SUBSTANCE FR0K WATPB THTAWI. ,~,.„ PERI0D) (MG/D) JATER INTAKE (DURING INFILTRATION

166 FLRSWI=CWIN*QINT * FLRSW0=FL0W RATE 0F SUBSTANCE DISCHARGED 0UT 0FTH EWATE R C0MP. * (DURING PUMPIHG PERI0D) FDIFLB<1)=-DP0RLC1)*B0SUC1)*CCLB<1>-CW)/DIFDC1) FLRSBC1)»AM IN1 CFLRS BC1),FDIFL BCI) ) G0T 0 54 53 FLRSBC1)=-QWB0T*CV-DT0TBC1)*B0SUC1>*CCLBC1)-CW)/DIFDC1) 54 C0NTINUE D0 55J=2,NBC0 M DT0T3CJ)=DISPD*ABSCVB0TCJ))+DP0RLCJ) FLRSBCJ)=-QW30T*WFAC*CMFAC*CLBCJ-1)+CLBCJ))-DT0TBCJ)*... B0SUCJ)*CCLBCJ)-CL3CJ-1))/DIFDCJ) IFCVB0TC1) .LT.0-0 )3 0T 0 56 FDIFLB(J)=-DP0RL(J)*30SU(J)*(CLB(J)-CLS(J-1))/DIFDCJ) FLRSB(J)=AMIN1(FLRSB(J),FDIFLBCJ)) IFCCLBCJ) .LT.0.0001 ) FLRSBCJ)=AMAX1CFLRSBCJ),0.0) G0T 0 55 56 IFCCLBCJ-1) .LT.0.0001 ) FLRSBCJ)=AMINICFLRSBCJ)/0.0) 55 C0NTINUE IFCQWB0T .LT.0. ) G0T 05 9 FLRSBCNBC0MP)=O.O G0T 0 60 59 FLRSB(NBC0MP)=-QWB0T*CLBCNBC0M) 60 C0NTINUE *** DEC0MP0SITI0N 0FTH E SUBSTANCE * RDECW=RATE 0FDEC0MP0SITI0 N INWATE R C0MP. CMG/D) RDECW=AFGENCRCDEWT,TIME)*MSW * RDEC3=RATE 0FDEC0MP0SIT0 N INB0TT0 M C0MP. CM3/D) * TRDECB=T0TAL RATE 0FDEC0MP0SITI0 N INTH EB0TT0 M CMG/D) TRDEC3=0.0 D0 61 J=1,NBC0M RDECBCJ)=AFGENCRCDE3T.»TIME)*MSBCJ) 61 TRDECB=TRDECB+RDECBCJ) * TDECW=T0TAL MASS 0F SUBSTANCE DEC0MP0SSD INWATE R C0MP.CMG ) * TDECB=T0TAL MASS 0FSUBSTANC E DEC0MP0SED IN30TT0 M CMG) TDECW=INTGRLCO.O.»RDECW) TDECB=INTGRLCO«0*TRDECB) *** 0VERALL RATE EQUATI0NS SUPS=SUPSTCNDAY) * RMSW=RATE 0FCHANG E INMAS S 0FSUBSTANC E INWATE R C0MP CMG/D) RMSW=FLRSWI+FLRSWU+SUPS-FLRSBC1)-RDECW-FLRSVD-FLRSW0 * RMSB=RATE 0FCHANG E INMAS S 0F SUBSTANCE IN30TT0 M C0MP.CMG/D ) D0 62J =1.,NBC0 M 62 RMSBCJ)=FLRSBCJ>-FLRSBCJ+I)-RDECBCJ) *** 0UTPUT SECTI0N * TEVAP=T0TAL V0LUME 0FWATE R EVAP0RATED CM3) TEVAP=INTGRLCO.O>OEVAP) * TRAIN=T0TAL V0LUME 0FWATE R FR0M RAINFALL CM3) TRAIN=INTGRLCO.O,QPREC> * TINT=T0TAL V0LUME 0FWATE R TAKEN IN CM3) TINT=INT3RLC0.0*ÜINT ) ..^TTAH (M3> * TID0DS=T0TAL V0LUME 0FWATE R INTAKE IHT0D0WNSTREA M DITCH SECTIO TID0DS=INTGRLCO.O»QID0DS) * TDISCH=T0TAL V0LUME 0FWATE R PUMPED 0UT 0FTH EDITC H CM3) TDISCH=INTGRLCO.O/QDISCH) „,.,„crpTI0 N * TDUPDS=T0TAL V0LUME 0FWATE R DISCHARGED FR0M THEUPSTREA MDITC H itou»» TDUPDS=INTGRLCO.O*QDUPDS ) onTTflM CM3) * TWB0T=T0TALV0LUM E 0FWATE R TRANSP0RTED THR0UGH THEDITC HB0TT0 W 167 TW30T=INTGRLCO.O..QWB0T ) * TDRAIN=T0TAL V0LUME0 FWATE R FR0MTH EDRAIN SCM3 ) TDRAIN=INTGRLCO.O,QWDR) * TST0R=T0TAL V0LUME0 FWATE R ST0RED INTH EDITC H CM3) TST0R=IHT3RLCO.O>RVWD) * TMSINT=T0TAL MASS 0FSUSTANC E TRANSP0RTED INT0TH EWATE R C0MP. (VIAINTAKE)(MG ) TMSINT=INT3RLC0.0*FLRSWI) * TMSUPD=T0TAL MASS 0FSUBSTANC E TRANSP0RTED INT0TH EWATE R C0MP.VI AU PSTREA M * DITCH SECTI0NS (MG) TMSUPD=INTGRLCO.O,FLRSWU) * TMSD0D=T0TAL MASS 0FSUBSTANC ETRANSP0RTE D 0UT0 FTH EWATE R C0MP. INT0 * D0WNSTREAM DITCH SECTI0NSCMG ) TMSD0D=INTGRLCO.O..FLRSWD) * TMS0UT=T0TAL MASS 0FSUBSTANC ETRANSP0RTE D 0UT0 FTH EWATE R C0MP.VIA PUMPCMG ) TMS0UT=INTGRLCO.O,FLRSW0) * TMSINF=T0TAL MASS 0FSU3STANC E INFILTRATED THR0UGHTH EL0WES T B0TT0M C0MP.V30TC1),FDIFLBC1-2 ),CW.,CM C1-20)/FLRSB C1- 10 ),TMSB,MSW *. . . TDECW.,TDECB,TMSINT,TMSUPD.,TMSD0D,TMS0UT,TMSINF/TMSSUP METH0D RECT 0UTPUT CW/MSW/TMSB TIMER DELT=O.OO5,PRDEL=O.5*0UTDEL=O.5,FINTIM=59.O .END

Appendix C

TITLE BEHAVI0UR 0FSUBSTANCE S INDITCHE S WITH FL0WING WATER Ï***************************************,****:**,*** ********** * WITH DIFFUSI0N INT00N EB0TT0 M C0MP.;VARIABLEWATE R LEVELAN DVARIABL EFLZ W ST0RAGE FLRSWC101)JCWC100).CLBC100),FLRSBC100)..RDECWC100),RDECBCI00) FIXED NDC0M*NDC0MPJI INITIAL N0S0RT * BASIC UNITS :MILLIGRA M (MG>, METE R CM), DA YCD ) * ABBREVIATI0NS :C0MP.=C0MPARTMENTCS ) *** DEFINITI0N 0FDITC H C0MPARTMENT GE0METRY * LC0M=LENGHT 0FTH EDITC H C0MP.CM ) * S1=SL0PE 0FTH EL0WE R PART 0FTH EDITC H WALLS CH0RZ./VERT.)C- ) * Wl=WIDTHA TTH EB0TT0 M 0FTH EDITC HCM ) * AHW=AVERAGE HEIGHT 0FTH EWATE R LEVEL INTH EDITC HCM ) PARAM LC0M=2.,SI=O.32,W1=1.92JAHW=O.18 * P=WETTED PERIMETER 0FTH EDITC HCM ) P=W1+2.0*AHW*SQRTCS1**2+1.0) * NDC0M=NUM3ER 0FDITC HWATE R C0MP.C- > PARAM NDC0M=1OO NDC0MP=NDC0M+1 * TB0T=THICKNESS 0FB0TT0 M C0MP.CM ) PARAM TB0T=O.OO5 * B0SU=SURFACE AREA 0FTH EB0TT0 M C0MP.CM2 ) B0SU=P*LC0M *** PHYSICAL CHARACTERISTICS 0FTH EB0TT0 M * BD=BULK DENSITY 0FS0LI DPHAS E CKG/M3CMEDIUM)) * VFL=V0LUME FRACTI0N 0FLIQUI D CM3CLIQUID)/M3CMEDIUM)) * T0RT=T0RTU0SITY FACT0R CM2CMEDIUM)/M2CLIQUID)) 168 * DIFW=DIFFUSI0N COEFFICIENT 0F SUBSTANCE INBUL K WATER (M2(LIQUID)/D) 5 E :^^S!î^îa'S£î«cT=S-ï?'?SS™ = i!! LIQUID PHASE CH3CLia«I0,/MC«D.,D, .„ Z^r^rsullrLc,OVE R Bz^^^^i^^r^gs^^^^ * KSL=DISTRIBUTION RATI0 S0LID/LIQUID PHASE =ADS0R?TI0N COEFFICIENT » (MG/KG(S0LID PHASE))/CM3/M3(LIQUID PHASE)) P A S * CAPL= SUB°STA°CE CAPACITY FACT0R RELATING TOCONCENTRAT E IN LIQUID PHASE * (M3(LIQUID)/M3(MEDIUM)) CAPL=VFL+BD*KSL CAB0TB=CAPL*30SU*TB0T „„..„»„^U-MTC *** DESCRIPTI0N0 FWATE R FL0W THR0U3H THE DITCH COMPARTMENTS * U=AVERA3E VELOCITY 0FWATE R FL0W INTH E DITCH (M/D) * UT=U AS F(TIME) FUNCTION UT=(0.>4640.)/(1.»4640.) * HW=HEIGHT 0FWATE R LEVEL INDITC H (M) * HWT=HWA SF(TIME ) FUNCTION HWT=(0.,0.18),(3.0/0.18) „.„rnsiiiH rniwTiaM(• ) * DISCON=DISPERSI0N C0NSTANT INA NEMPIRICA L DISPERSI0N EQUATION( PARAM DISC0N=22.3 *** DEC0MP0SITI0N 0FTH E SUBSTANCE „„,„,„„ IM „ATFR AS F(TIME) * RCDEWT=RATE C0EFFICIENT(1/D) F0R DEC0MP0SITI0N INWATE R AS FCTIHbJ FUNCTI0N RCDEWT=(0.>0.55)/( 1./0.55 ) „...,„„ ,.,no ,TTOiM f(3MP.A SF(TIME ) * RCDEBT=RATE C0EFFICIENT(1/D) F0R DEC0MP0SITI0N IN B0TT0M C0MP- Ab FUNCTI0N RCDEBT=(0./0.)/(l.0/0•) *** INITIAL AND B0UNDARY C0NDITI0NS * MSW=MASS 0FSUBSTANC E INWATE R C0MP. (MG) * MSB-MASS 0FSUBSTANC E INB0TT0 M C0MP. (MG> * IREFER ST 0INITIA L C0NDITI0N TABLE IMSW(1-100)=50000./99*0. TABLE IMSB(1-100)=100*0.0 DYNAMIC N0S0RT „„,.„,»,- fr e *** C0MPUTATI0N 0FTH E WATER FL0W CHARACTERISTICS. U=AFGEN(UT/TIME) HW=AFGEM(HWT,TIME> * A=WETTED CR0SS-SECTI0NAL AREA 0FTH E DITCH (M2> A=HW*(W1+S1*HW) #k,_ * VWD=VOLUME0 FWATE R INDITC H WATER C0MP. (M3> VWD=A*LC0M ,„,„>•. * Q=FL0W RATE0 FWATE R INT0A DITC H C0MP. (M3/D) * DLDISW=L0NGITUDINAL DISPERSI0N COEFFICIENT INWATE R C0MP. (M2/D) DLDISW=DISCON*ABS(U)*HW ,„,.„, * DT0TW=T0TAL SPREADING COEFFICIENT IN WATER C0MP. (M2/UJ DT0TW=DLDISW+DIFW+U**2*DELT/2.O

*** SUBSTANCE MOVEMENT t mrmr> __M_ ,M-/D) * RMSV-RATEO FCHANG EI NMAS S 0FSUBSTANC EI NWATE R C0MP. * RMSB-RATE BF CHANGE INMAS S 0FSUBSTANC E INBOTTO M C0MP. MSW=INTGRL(IMSW/RMSW,100) MSB=INTGRL(IMSB/RMSB,100) „„,.,.,, * CW=C0NCENTRATI0NO FSUBSTANC E INWATE R C0MP. (Ma/H3) DO3 0I=1,NDC0 M 30 CW(I)=MSW(I)/VVD ,,...-, * FLRSW=FL0W RATEO FSUBSTANC E INTOA WATE R COMP. (MG/D) FLRSW(1)=INSW(Q/Q*CW(1>/0.0 ) FLRSW(NDC0MP)=IHSW(Q/O.O,Q*CW(NDC0M)) DO3 3I=2,NDC0 M ,„„,,, r-ii t- I ) )/LC0 M 33 FLRSW(I)=Q*O.5*(CW(I-l)+CW(I))-DT0TW*A*(CvKI)-CJ(I »" p# (MG/M3) * CLB=C0NCENTRATI0NO FSUBSTANC E INLIQUI D PHASE0 FB0TT0 M C0MP D03 5I=1/NDC0 M 35 CLB(I)=MS3(I)/CAB0TB ,HP/n, * FLRSB=FL0W RATE 0FSUBSTANC E INTOA B0TT0 M COMP- CMG/D) D03 6I=1/NDC0 M 169 36 FLRSB(I)=-D?0RL*30SU*(CL3(I)-CW(I))/(O.5*TB0T> *** DECOMPOSITION 0FTH E SUBSTANCE * RDECW=RATE 0FDEC0MP0SITI0 N INWATE R C0MP. (MG/D) * RDECB=RATE 0FDECOMPOSITIO N INB0TT0 M COMP.(MG/D) * TRDECW=TOTALRAT E 0FDEC0MP0SITI0 N INTH EWATE R CMG/D) * TRDECB=T0TAL RATE 0FDEC0MP0SITI0 N INTH EB0TT0 M (MG/D) RCDECW=AFGEN(RCDEWT,TIME) RCDECB=AFGEN(RCDEBT,TIME) TRDECW=0-0 TRDECB=0.0 D04 0 I=1»NDC0M RDECWd)=RCDECW*MSW (I) RDECBCI)=RCDEC3*MS B TRDECW=TRDECW+RDECW(I) 40 TRDECB=TRDECB+RDECB(I) * TDECW=T0TALMAS S 0F SUBSTANCE DEC0MP0SED INWATE R C0MP. (MG) * TDECB=T0TAL MASS 0F SUBSTANCE DEC0MP0SED INB0TT0 M CMG) TDECW=INTGRL(0.0,TRDECW) TDECB=INTGRL(0.0,TRDECB) *** OVERALL RATE EQUATIONS D0 50 I= UNDC0 M RMSW(I)=FLRSWCI>-FLRSW( I+1)-FLRS 3CI)-RDECV(I ) 50 RMSB(I)=FLRSB(I)-RDECB(I) *** 0UTPUT SECTI0N * TMSWOF=T0TAL MASS 0F SUBSTANCETRANSP0RTE D 0UT 0F FIRST WATER C0MP. CMG) * TMSW0L=T0TAL HASS 0F SUBSTANCE TRANSPORTED BUT 0FLAS T WATER C0MP. (MG) TMSW0F=INTGRL(O-,-FLRSW(t)) TMSW0L=IHTGRL(0.0> FLRSWCND C0MP) ) PRTIM=IMPULS(0.0,PRDEL) IFCPRTIM*KEEP .LT.0.5 ) 30T 0 100 * TMSW=T0TAL MASS 0F SUBSTANCE INWATE R C0MP. (MG) * TMSB=T0TAL MASS 0F SUBSTANCE INB0TT0 M (M3> TMSW=0.0 TMSB=0.0 D0 60 I=1#NDC0M TMSW=TMSV+MSW(I) 60 TMS3=TMS3+MSB(I) CW51=CW(51) MSW51=MSW(5l) MSB51=MSS(51> 100 C0NTINUE METH0D RECT PRINT Q>U»DT0TW,RCDECW,RCDEC3,TMSW,TMSB,TM5W0F#TMSW0L»TDECW.»TDECB.» • • • CW51>MSW5UMSB51 0UTPUT CW51 <0.*2000O*MSV51 (0.* 1000O,MSB51 CO.* 1000.) TIMER DELT=O.OOOO25/PRDEL=O.OO25/0UTDEL=O.OOS5*FIHTIM=O.l END ST0P ENDJOB

170 References

Aarefjord, F., 1972. The use of an air-lift in freshwater bottom sampling. A Ç°mP""on with the Ekman bottom sampler. Verh. int. Verein, theor. angew. Limnol. »f- 7?' "»• Adelman, I.R., L.L. Smith Jr. & G.D. Siesennop, 1976. Chronic Toxicity of Guthion to the fathead minnow (Pimephales promelaa Rafinesque). Bull. Environ. Contam. Toxicol, is.

Bache!2™; D.J. Lisk, 1965. Determination of organophosphorus insecticide residues using

the emission spectrometric detector. Anal. Chem. 37: 1477-14ÖU. B.hnate and Bache, CA. & D.J. Lisk, 1966. Determination of oxidative metabolites of di«thoate and thimet in soil by emission spectroscopic gas chromatography. J. Ass. off. anal. (.neu.

Bailey!:G!Î!"6R!R. Swank Jr., & H.P. Nicholson, 1974. Predicting Pesticide runoff from agricultural land: a conceptual model. J. Environ. Qual. 3: 95 Wi. . Bakker! H. de & J. Schelling, 1966. Systeem van bodemclassificatie voor Nederland. Pudoc,

Wageningen, the Netherlands. 217 p. . Eners, Banaal. M.K., 1971. Dispersion in natural streams. J. Hydraul. Div. Am. Soc. civ. Engrs. Q7* 1R67 —1Rftfi Bayer A'.G., 1971 <È> Gusathion. Technische Information Bayer Pflanzenschutz, Leverkusen. Bayer A.GI, 1978. Unpublished data; personal communication. Bayer A.G., OD0ervlakte- Beld, H. van den & G° van Straten, 1976. Model voor de zuurstof huishouding ^W£^ water in: Rapport no. 1. Modelonderzoek 1971-197 4 Ten behoeve van de "aterhuishou in Gelderland. Commissie bestudering waterhuishouding in Gelderland, p. Bella, D.A. & W.E. Dobbins, 1968. Difference modeling of stream pollution. J. samt. g

Div. Am. Soc. civ. Engrs. 94: 995-1016. 5?. 798_799. 1 Bohn, W.R., 1964. The disappearance of dimethoate from »" J-^; on small hydraulic Bos, M.G., 1976. Discharge measurement structures, (by the working group /aRI p<0. structures). International Institute for Land Reclamation and mprovement/ IL

Box 45, Wageningen, the Netherlands, p. 357 364. „«.,•-„ nr dimethoate and Brady, U.E. Jr. & B.W. Arthur, 1963. Biological and chemical properties of dimetn related derivatives. J. econ. Ent. 56: 477-482. control of wa- Brooker, M.P. & R.W. Edwards, 1975. Review paper aquatic herbicides and the con ter weeds. Water Res. 9: 1-15. . f fhe disappear- Bro-Rasmussen, F., E. Nrfddegaard & K. Voldum-Clausen, 1970. Comparison of^.^Jtl00t ex- ance of eight organophosphorus insecticides from soil in laborat y

periments. Pestic. Sei. 1: 179-182. . „ . ,„, ooQ_aqi Butler, P.A., 1969. Monitoring pesticide Pollution. BioScience I.889 89 ^ p.0. Canton, J.H., 1977. National Institute of Public Health, Laboratory ior Box 1, Bilthoven, the Netherlands. Personal Communication (June »»'''' £. ld condi- Caro, J.H. & A.W. Taylor, 1971. Pathways of loss of dieldnn from soils under tions. J. agric. Fd. Chem. 19: 379-384. «oils: optimizing ldu Caro, J.H. & A.W. Taylor, 1976. Analysis of pesticide ™ " "J"^' Sensing and soil sampling and pesticide ^traction. First Int. Conf. on Envir ^ Assessment, Las Vegas, 1975. Institute of Electrical &Electronic s tnB New York, Vol. 1., Section 7-3. ..„„„rod determination of Cavagnol, J.C. & T.D. Talbott, 1967. Preliminary report of an automatea gtty> Techni- Guthion by the copper chelate method. In: Automation in analytical con Symposium, New York. p. 160-162. .<©,.. mfh„,v oreanophosphorus insec- Chemagro Division Research Staff, 1974. Guthion^ (azinphos-methyl). Organ v ticide. Residue Rev. 51: 123-180. . - „,i„,-4ral techniques for Chesters, G., H.B. Pionke & T.C. Daniel, 1974. Extraction and analytical ^ Ed. U.D. s pesticides in soil, sediment and water. In 'Pesticides "|. °^ f°° „ S.A. p. 451-550. Wl8 n Guenzi, Soil Science Society of America, Inc., Madison, " "°* ith fine particles 10 0 Choi, W.W. & K.Y. Chen, 1976. Associations of chlorinated M "™ "*. Technol. 10: and humic substances in nearshore surficial sediments. Environ, ac • 782-786. 171 Coats, K.H. &B.D .Smith , 1964.Dead-en d porevolum ean ddispersio ni nporou smedia .Soc . Pet.Eng .J . 4:73-84 . Coburn,J.A. ,I.A .Valdmani s &A.S.Y .Chau ,1977 .Evaluatio no fXAD- 2fo rmultiresidu eex ­ tractiono forganochlorin epesticide san dpolychlorinate d biphenyls fromnatura lwa ­ ters.J .Ass .off .anal .Chem .60 :224-228 . Cochrane,W.P. , 1976.Confirmatio no fpesticid eresidu e identityb ychemica lderivatization . First Int.Conf .o nEnviron .Sensin gan dAssessment ,La sVega s 1975,Institut eo f Electrical &Electronic sEngineers ,Inc. ,Ne wYork ,Vol .1 Sectio n7-4 . Coppage,D.L. ,& T.E .Braidech ,1976 .Rive rpollutio nb yanticholinesteras e agents.Wate r Res. 10:19-24 . Dale,W.E. ,J.W .Mile s &G.O .Guerrant ,1975 .Monitorin g ofresidue so fAbat e instream s treated forSimuliu mcontrol .Environ .Qual .Saf. ,Suppl .Vol .Il lPesticides :780 - -783. Dauterman,W.C. ,J.E .Casida ,J.B . Knaak& T .Kowalczyk , 1959.Bovin emetabolism so forgano - phosphorus insecticides.Metabolis man dresidue sassociate dwit hora l administration ofdimethoat e torat san d three lactatingcows .J .agric .Fd .Chem .7 :188-193 . Davis,E.A . &P.A . Ingebo,1973 .Piclora mmovemen tfro ma chaparra lwatershed .Wate rResour . Res.9 :1304-1313 . Day,T.J. , 1975.Longitudina ldispersio ni nnatura l channels.Wate rResour .Res .11 :909 - -918. DelVecchio ,V. ,V .Leon i& G .Puccetti ,1970 .L acontaminazion ed apesticid i deiprinci ­ pal!bacin i indrografici italianidurant e il 1969e nindic iprospost ipe run asu a valutazione igienica.Nuov iAnn .Ig .Microbiol .21 :381-451 . Dimond,J.B. ,A.S .Getchel l& J.A .Blease ,1971 .Accumulatio nan dpersistenc e ofDD T ina lotieecosystem .J .Fish .Res .Bd .Ca n28 :1877-1882 . Duff,W.G .& R.E .Menzer , 1973.Persistence ,mobilit y anddegradatio no f C-dimethoate insoils .Environ .Entomol .2 :309-318 . Edwards,C.A. , 1973.Pesticid eresidue s insoi lan dwater . InEnvironmenta l pollutionb y pesticides,Ed .C.A .Edwards ,Plenu mPress ,Londo nan dNe wYork .p .409-458 . Eichelberger,J.W . &J.J . Lichtenberg, 1971a.Carbo nadsorptio nfo rrecover y oforgani c pesticides.J .Am .Wat .Wks .Ass .63 :25-27 . Eichelberger,J.W . &J.J .Lichtenberg , 1971b.Persistenc e ofpesticide s inrive rwater . Environ. Sei.Technol .5 :541-544 . Ernst,L.F. , 1971.Analysi so fgroundwate r flowt odee pwell s inarea swit h anon-linea r functionfo rth esubsurfac edrainage .J .Hydrol .14 :158-180 . Faust,S.D . SH.M .Gomaa , 1972.Chemica lhydrolysi s ofsom eorgani cphosphoru s andcarba ­ matepesticide s inaquati cenvironments .Environ .Lett .3 :171-201 . Feltz,H.R. ,W.T .Sayer s& H.P .Nicholson , 1971.Nationa lmonitorin gprogra m forth e assessmento fpesticid eresidue s inwater .Pestic .Monit .J .5 :54-62 . Feltz,H.R . &J.K . Culbertson, 1972.Samplin gprocedure s andproblem s indeterminin gpes ­ ticideresidue s inth ehydrologi eenvironment .Pestic .Monit .J .6 :171-178 . Feuerstein,D.L . &R.E .Selleck , 1963.Fluorescen t tracersfo rdispersio nmeasurements . J. sanit.Engng .Div .Am .Soc .civ .Engrs .89 :1-21 . Fishbein,L. , 1975.Chromatograph y ofenvironmenta lhazards .Vol .Il lPesticides .Elsevie r ScientificPublishin gCompany ,Amsterdam ,Oxford ,Ne wYork .82 0p . Frank,P.A . &R.D .Comes ,1967 .Herbicida lresidue s inpon dwate ran dhydrosoil .Weed s15 : 210-213. Frank,P.A. , 1970.Degradatio nan deffect so fherbicide s inwater .Firs tFA O international conferenceo nwee d control.Davis ,California ,Jun e22-Jul y 1,1970 .p .1-21 . Frank,P.A. , 1972.Herbicida lresidue s inaquati cenvironments .I nFat eo forgani cpesti ­ cides in theaquati cenvironment ,Ed .R.F .Gould ,Adv .i nChem .serie s 111.Am .Chem . Soc, Wash.D.C .p .135-148 . Frissel,M.J. ,P .Poelstr a&P . Reiniger,1970 .Chromatographi c transport throughsoil s III.A simulationmode lfo rth eevaluatio no fth eapparen tdiffusio n coefficienti n undisturbed soilswit h tritiatedwater .PI . Soil33 :161-176 . Fritschi,G. ,P.A . Grève,H .Rissmau l& R.C.C .Wegman , 1978.Cholïnesterasehemmend eStoff e imBereic hde sRheins .I nOrganisch eVerunreinigunge n inde rUmwelt .Erkennen ,Be ­ werten,Vermindern ,Eds .K .Aurand ,H .Hässelbarth ,E .Lahmann ,G .Muller ,W .Niemitz . Erich SchmidtVerlag ,Berli np .265-270 . Gidsvoo rZiekten -e nOnkruidbestrijdin g inLand -e nTuinbouw , 1977.Consulentschappe n voorPlantenziektenbestrijding ,Wageningen ,th eNetherlands .41 6p . Goldberg,M.C. ,L .D eLon g& L . Kahn,1971 .Continuou s extractiono f organicmaterial sfro m water.Environ .Sei .Technol .5 :161-162 . Goudriaan,J. , 1973.Dispersio n insimulatio nmodel so fpopulatio ngrowt han d saltmovemen t inth esoil .Neth .J .Agric .Sei .21 :269-281 .

172 Graham-Bryce, I.J., 1969. Diffusion of organophosphorus insecticides in soils. J. Sei. Fd.

8 4 4 Grahl! K!!"l9?3. Zur Ge;-âsSerkontamination durch organische Spurenstoffe. Z. ges. Hyg. 19:

896-902. stoffen in water: voorkomen en betekenis H20. 4: 272-274.

Grève! ï.t\ S!L! S" Vw.Enlsuîfan in the Rhine river. J. Wat. Pollut. Control Fed.

Grève"? .^«"'potentially hazardous substances in surface waters. Fart I. Pesticides Greve^t.TprSn^1; ïï^™™^ hazardous substances in surface waters. II. Cholinesterase inhibitors in Dutch surface waters. Sei. Total Environ.

2 3 2 GrWr, F ; w%edek & E. Leibnitz, .968. Zur Kenntnis der «lhomologen_des Dimethoats I. Mitt.: Hydrolysegeschwindigkeit und -mechanismus. Z. Naturf. 23K HJ Gump, B.H., H.S. Hertz, W.E. May, S.N. Chesler, S.M. Dyszel & D.P. Enagonio, 1*/ sampler for obtaining fresh and sea water samples for organic compound analysis. Anal. Chem. 47: 1223-1224. Barkley, 1963. Persistence of residues of Günther, F.A., G.E. Carman, R.C. Blinn & J.H. hIk'^ ' processed citrus "pulp" Guthion on and in mature lemons and oranges and m laboratory proc

cattle feed. J. Agric. Fd. Chem. 11: 424-427. dvnamics of non-ionic syn- Hamelink, J.L. & R.C. Waybrant, 1973. Factors contre, Un|^e dynamics ot ^^ thetic organic chemicals in aquatic environments, technical Report University Water Resources Research Center West Laf*ye"e'J^anisms in open-channel a 0 Hays, J.R., P.A. Krenkel & K.B. Schnelle, 1966. Mass « ^ "r^f^eering Department ou flow/Technical Report Number 8. Sanitary and f « " e ' ° . of Civil Engineering, Van der Bilt University Nashville Tennessee. .-> P „.uiple Hergert, G.B. & J. Gall, 1973. Modification to an automatic liquid sampler samples. Can. J. Soil. Sei. 53: 483-484. Germany - 1970 and 1971. Herzel, F., 1972. Organochlorine insecticides in surface waters in Germany Pestic. Monit. J. 3: 179-187. aaueous solutions and on glass Heuer, B., B. Yaron & Y. Birk, 1974. Guthion half-life in aqueous 5JZ surfaces. Bull. Environ. Contam. Toxicol. 11: ""'- . ForBatie van Sterksel/ Hey, G.J. & C.G.M. Kester, 1977. De hydraulische weerstand van de Forma Kedichem in West-Utrecht. R.I.D.-mededeling 77-7. Li p. chlorinated hydrocarbon Hill, D.W. & P.L. McCarty, 1967. Anaerobic degradation of selected pesticides. J. Water Pollut. Control Fed. ™*Jl£~S '** water en bodemvocht. Hofstee, J. & H.J. Fien, 1971. Analysemethoden voor grond, gewast Rijksdienst voor de Usselmeerpolders, Lelystad, the Nether1 Environ. Sci. Howard, P.H., J. Saxena & H. Sikka, 1978. Determining the fate of

Technol. 12: 398-407. _ m) Pr0gram Reference Manual I.B.M., 1975. Continuous System Modeling Program III (CSMP ™. M Division, White SH19-7001-2, Program Number 5734-XS9, IBM corporation Data process g

Plains, New York. 206 p. , Behaviour of five organophosphorus Behavl Iwata, Y., M.E. DÜsh, W.E. Westlake & F.A. Günther 1975. ° Contam. Tox. . pesticides in dust derived from several soil types. Bull. Enviro

Jackson! H!W^,970. A controlled-depth, volumetric bottom sampler. Progve. Fish Cult.^

3 1 1 , , Josep hson , j; , '974. Developing water sampling standards. Environ. Sei. Technol. 8.

787. , ,oa„ „_ f0r gas-chromatographic analy Kadoum, A.M., 1967. A rapid micromethod of sample clean «P^or 8 nd water ex_ sis of insecticidal residues in plant, animal, soil and surr tracts. Bull. Environ. Contam. Tox. 2: 264-273. environmental safety Kenaga, E.E., 1974. Toxicological and residue date useful in the en evaluation of dalapon. Residue Rev. ": 109-151. stribution of pesticides in sur King, P.H., H.H. Yeh, S.P. Warren & C.W. Randall, 1969. Distri face waters. J. Am. Water Works Assoc. 61: *83-4öb. =aareang. Uitgave no. 94A. 3 KNMI, 1976. Maandelijks overzicht der weersgesteldheid. 7 " ^Jhe*land8. 1, Royal Netherlands Meteorological Institute De '^™£ foI extraction of «ga Konrad, J.G., H.B. Pionke & G. Chesters, 1969. An improved method to ^ 490-492. y nochlorine and organophosphate insecticides from late wate r^ iUvated Rhine water. Kussmaul, H., 1978. Behaviour of persistent organic compounds in o ^ Hutzinger, LH. In Aquatic pollutants: Transformation ^^f «e ^nd International Symposium van Lelyveld and B.C.J. Zoeteman. Proce^lnf °^h%he Netherlands, September 26 28, on Aquatic Pollutants, Noordwijkerhout (Amsterdam), the Netn 1977. Pergamon Press, Oxford, p. 265-274. Lamotte,M .& F . Bourlière,1971 .Problème sd'écologie :L'échantillonnag e despeuplement s animauxde smilieu xaquatiques .Masso ne tC ie.,Editeurs ,120 ,b d St.Germain ,Pari s VIe. 294p . Larimore,R.W. ,1970 .Tw oshallow-wate rbotto msampler sProgve .Fis hCult .32 :116-119 . Law,L.M .& D.F .Goerlitz ,1974 .Selecte d chlorinated hydrocarbons inbotto mmateria lfro m streams tributary toSa nFransisc oBay .Pestic .Monit .J . 8:33-36 . Leistra,M. , 1975.Compute d leachingo fpesticide sfro msoi la sinfluence d byhig hrainfall , plantgrowt han d timeo fapplication .Agric .Environm .2 :137-146 . Leistra,M .& W.A .Dekkers ,1976 .Compute d leachingo fpesticide sfro msoi lunde rfiel d conditions.Water ,Air ,Soi lPollut .5 :491-500 . Leistra,M. , 1978.Compute d redistributiono fpesticide s inth eroo tzon eo fa narabl ecrop . PI. Soil49 :569-580 . Leoni,V. , 1971.Th eseparatio no ffift ypesticide san drelate d compoundsan dpolychloro - biphenyls intofou rgroup sb ysilic age lmicrocolum nchromatography .J .Chromat .62 : 63-7'• ffi Leoni,V. ,G .Puccett i& A .Grella ,1975 .Preliminar y resultso nth eus eo fTenaj ^ for theextractio no fpesticide san dpolynuclea r aromatichydrocarbon s fromsurfac ean d drinkingwater s foranalytica lpurposes .J .Chromat .106 :119-124 . Liang,T.T .& E.P .Lichtenstein , 1972.Effec to f light,temperature ,an dp Ho nth edegra ­ dationo fazinphos-methyl .J .Econ .Entomol .65 :315-321 . Liang,T.T .&E.P . Lichtenstein, 1976.Effect so fsoil san d leafsurface s onth ephoto - decompositiono f [14c]-azinphos-methyl .'J .agric .F dChem .24 :1205-1210 . Lichtenstein,E .P .& K.R .Schultz ,1970 .Volatilizatio no f insecticides fromvariou ssub ­ strates.J .agric .Fd .Chem . 18:814-818 . Liss,P.S . &P.G . Slater, 1974.Flu xo fgase sacros s theair-se a interface.Natur e247 : 181-184. Lowden,G.F. ,C.L .Saunder s& R.W .Edwards ,1969 .Organo-chlorin e insecticides inwater - -part II.Wate rTreat .Exam . 18:275-287 . Mackay,D .& P.J . Leinonen, 1975.Rat eo fevaporatio no flow-solubilit y contaminants from waterbodie s toatmosphere .Environ .Sei .Technol .9 : 1178-1180. Martin,H . &C.R .Worthing , 1977.Pesticid emanual ,fift hedition .Britis hCro pProtectio n Council.59 3p . Menzie,CM. , 1969.Metabolis mo fpesticides .Spec ,scient .Rep .U.S .Fis hWildl .Serv . 127-WashingtonD.C .48 7p . Menzie,CM. , 1974.Metabolis mo fpesticides ,a nupdate .Spec ,scient .Rep .U.S . Fish Wildl.Serv . 184.Washingto nD.C .48 6p . Meijers,A.P. , 1973.He tvoorkome nva norganisch emicroverontreiniginge n inRij ne nMaas . H20 10:244-249 . Meijers,A.P .& R.Chr .va nde rLeer ,1976 .Th eoccurrenc eo forgani cmicropollutant s in therive rRhin ean d therive rMaa si n 1974.Wate rRes .10 :597-604 . Miles,J.R.W .& C.R .Harris ,1971 .Insecticid eresidue s ina strea man da controlle d drainage system inagricultura larea so fsouthwester nOntario ,1970 .Pestic .Monit .J . 5:289-294 . Minks,A.K .& D.J . deJong , 1975.Determinatio no fsprayin gdate sfo rAdoxophye s oranab y sexpheromon e trapsan d temperaturerecordings .J .Econ .Entomol .68 :729-732 . Mitchell,J.K . &E .Dickey , 1973.Devic efo robtainin gwate rsample s fromsmal lpond so r lagoons.Trans .Am .Soc .agric .Engrs .16 :544-545 . MonitoringPane lo fFWGPM , 1974.Guideline so nsamplin gan d statisticalmethodologie sfo r ambientpesticide smonitoring .Federa lWorkin gGrou po nPes tManagement ,Washington , D.C. Mortimer,C.H. , 1942.Th eexchang eo fdissolve d substancesbetwee nmu d andwater .J .ficol. 30: 147-201. Mühlmann,R . &G .Schrader , 1957.Hydrolys ede rinsektizide nPhosphorusäureester .Z .Naturf . 12b:196-208 . Musty,P.R . &G .Nickless , 1974.Th eextractio nan drecover yo fchlorinate d insecticides andpolychlorinate dbiphenyl sfro mwate rusin gporou spolyurethan e foams.J .Chromat . 100:83-93 . Nicholson,H.P. , 1969.Occurrenc ean dsignificanc eo fpesticid eresidue s inwater .J .Wash . Acad.Sei .59 :77-85 . Oever,M.L .van_de , 1972.He tontwikkele nva nee nmeetmethod eo mmengpatrone ni nbeke nt e bepalen.Div .o fProces sContr .an dEnvironm .Managern. ,Dept .o fChem .Eng. ,Twent e University ofTechnology ,Enschede ,th eNetherlands . 11p Osbergy,J.M. , 1970.Distributio no fa chemica lfollowin g itsapplicatio na ta poin tsourc e ina nirrigatio nsystem .Pestic .Sei . 1:5-9 .

174 Parr, J.F., G.H. Willis, L.L. McDowell, CE. Murphree & S. Smith, 1974. An automatic pump­ ing sampler for evaluating the transport of pesticides in suspended sediment. J. Environ. Qual. 3: 292-294. Plantenziektenkundige Dienst en Consulentschappen in Algemene Dienst voor Plantenziekten en Onkruidbestrijding, 1975. Bestrijding van ziekten, plagen en onkruiden met behulp van het vliegtuig. Bericht No. 1916. Wageningen, the Netherlands. 12 p. Plantenziektenkundige Dienst en Consulentschappen in Algemene Dienst voor Plantenziekten en Onkruidbestrijding, 1978. Chemische Bestrijding van waterplanten. Bericht No. 78- -18. Wageningen, the Netherlands. 4 p. Pons, T.L., 1972. Een toxicologisch onderzoek in het Kromme Rijn gebied betreffende chloor- koolwaterstoffen en organofosforinsekticiden K.R.P.-nr. 23. Instituut voor Veterinaire Farmacologie en Toxicologie, University of Utrecht, the Netherlands. 18 p. Portmann, J.E. & K.W. Wilson, 1971. The toxicity of 140 substances to the brown shrimp and other marine animals. Shellfish Information leaflet, no. 22. Ministry of Agriculture, Fisheries and Food, Fisheries Laboratory Burnham - on - Crouch, Essex, England. 12 p. Pree, D.J., K.P. Butler, E.R. Kimball & D.K.R. Steward, 1976. Persistence of foliar resi­ dues of dimethoate and azinphos-methyl and their toxicity to the apple maggot. J. Econ. Entomol. 69: 473-478. Reid, R.C. & T.K. Sherwood, 1966. The properties of gases and liquids, Mac Graw Hill, New York, 646 p. Richard, J.J., G.A. Junk, M.J. Avery, N.L. Nehring, J.S. Fritz & H.J. Svec, 1975. Analyses of various Iowa Waters for selected pesticides: atrazine, DDE and dieldrin, 1974. Pestic. Monit. J. 9: 117-123. Ripley, B.D., R.J. Wilkinson & A.S.Y. Shau, 1974. Multiresidue analyses of fourteen orga- nophosphorus pesticides in natural waters. J. Ass. off. anal. Chem. 57: 1033-1042. Rijkswaterstaat, 1973-1978. Kwaliteitsonderzoeks in Rijkswateren. Verslag van de resultaten over de le, 2e, 3e, 4e kw. 1972, 1973, 1974, 1975, 1976, 1977 Rijkswaterstaat, RIV, RID. Rijksinstituut voor Zuivering van Afvalwater Mearlant 6, Lelystad, the Nether­ lands . . . f Ruzicka, J.H., J. Thomson & B.B. Wheals, 1968. The gas-chromatographic determination of organosphosphorus pesticides. J. Chromat. 33: 430-434. Schultz, K.R., E.P. Lcihtenstein, T.T. Liang & T.W. Fuhremann, 1970. Persistence and de­ gradation of azinphos-methyl in soils, as affected by formulation and mode of appli­ cation. J. Econ. Entomol. 63: 432-438. Schulze, J.A., D.B. Manigold & F.L. Andrews, 1973. Pesticides in selected western streams - 1968-71. Pestic. Monit. J. 7: 73-84. . Simsiman, G.V. & G. Chesters, 1976. Persistence of diquat in the aquatic environment, ter Res. 10: 105-112. . . . Soil Survey Staff, 1975. Soil Taxonomy. A basic system of soil classification for maKing and interpreting soil surveys. Soil Conservation Service U.S. Department of Agncu ture. Agricultural Handbook No. 436, U.S. Government Printing Office Washington, u. ., 20402. 754 p. SSrensen, 0., 1973. Gaschromatographischer Pestizidnachweis mit gekoppelten Detekto Gas Wasserfach Wasser-Abwasser 114: 224-227. i-'t-ite Spencer, E.Y., 1973. Guide to the chemicals used in crop protection. Research ^stl^u University of Western Ontario. Sub Post Office London, Ontario N 6A 3K0, Canada. bodemgeS d Studiegroep Lopikerwaard, 1973.' De landinrichting van de Lopikerwaard, "J ^naee- en waterhuishouding. ICW Regionale studies 4/II. Institute for land and water ment research, Wageningen, the Netherlands. 49 p. t-ita- Thayer, G.W., R.B. Williams, T.J. Price & D.R. Colby, 1975. A large corer for quatit 4 tively sampling benthos in shallow water. Limnol. Oceanogr. 20: *^ "*"J" R3_73-o33, US Environmental Protection Agency, 1973. Water quality criteria (1972). EPA. March 1973 US Environmental Protection Agency, 1974. Training Manual. Pesticide residue ana ysis water. Water Program Operations. EPA-430/1-74-012. j-mPnts Veith, G.P. & G.F. Lee, 1971. Water Chemistry of Toxaphene - role of lake seairae Environ. Sei. Technol. 5: 230-234. . 1977) J Wackers, R., 1977. Bayer Nederland B.V., Arnhem. Personal communication. ^ . ,zids'und Wagner, K. & H. Frehse, 1976. Methode zur Bestimmung von Rückständen des InseK Akarizids© Folimat. PfISchutz-Nachr. Bayer 29: 54-66. vironmental Waldron, A.C., 1974. Pesticide movement from cropland into lake Erie. U.S. En Protection Agency. EPA-660/2-74-032. 96 p. . and ar0Batic Wegman, R.C.C. & P.A. Grève, 1978. Organochlorines, Cholinesterase inhibitors,^ ^ ^ amines in Dutch water samples, September 1969-December 1975. Pestic. Mom 149-162. 175 Westlake,W.E .& F.E .Günther , 1966.Occurrenc ean dmod eo fintroductio no fpesticide si n theenvironment . InOrgani cpesticide s inth eenvironment ,Ed .R.F .Gould .Advanc ei n Chemistry Series60 ,Washingto nD.C .p .110-121 . WH0/FA0, 1974.197 3Evaluation so fsom epesticid eresidue s infood .FAO/AGP/1973/M/9/1 ; WHOPesticid eResidu eSeries ,No .3 .p .29-32 . Wieneke,J .& W .Steffens ,1976 .Untersuchunge nübe rAufnahme ,Umwandlun g andAbba uvo n '^C-markierten ®Gusathion inBuschbohnen .PfISchutz-Nachr .Baye r 29:18-34 . Yaron,B. ,B .Heue r& Y .Birk ,1974a .Kinetic so fazinphos-methy l losses inth esoi lenvi ­ ronment.J .agric .Fd .Chem .22 :439-441 . Yaron,B. ,H .Bielora i& L ,Klinger ,1974b .Fat eo f insecticides ina nirrigate d field: Azinphos-methyl andTetradifo ncases .J .Environ .Qual .3 :413-417 . Zon,J.C.J ,van , 1974.Th egrascar p inHolland .Proc .Europea nWee dResearc hCounci l4th . Int.Sympos .Aquati cWeeds ,Wie n 1974.p .128-133 . Zweig,G .(Ed.) ,1972 .Analytica lmethod sfo rpesticide splan tgrowt hregulators ,an dfoo d additives.Vol .V IGas-chromatographi canalysis .Ne wYork ,Academi cPress ,p .191-233 .

176