Zot \Ji~ Abstract

H.d eHee r

Measurementsan dcomputation s onth e behaviouro fth einsecticide s azinphos-methyl anddimethoat ei nditche s

Centre for Agricultural Publishing and Documentation

Wageningen - 1979 zot \ji~ Abstract

Heer,H .d e (1979).Measurement san dcomputation so nth ebehaviou ro fth einsecticide s azinphos-methyl anddimethoat e inditches .Agric .Res .Rep . (Versl.landbouwk .Onderz . 884.Pudo cWageningen . ISBN9 022 0069 56.(xiv )+ 176p. ,5 5figs ,5 5tables ,14 2refs ,Eng .an dDutc hsummaries . Also:Doctora l thesisWageningen .

Theunintentiona lpollutio no fsurfac ewate rwa sstudie ddurin gsprayin go fth einsec ticidesazinphos-methy lan ddimethoat eo ntw ofrui tfarms .Spra ydrif tdepende d closelyo n theloca lsituation sa tth efrui tfarm s (windbreaks,distanc efro mtree st oditches ,paths ) ando nwa yo fapplication . Duringapplication , theconcentration so fbot hinsecticide s inwate ran di nditc h bottomswer emeasured .Method swer eadapte do rdevelope d forsampling ,extraction ,clean - -upan dgas-chromatography .Shortl yafte rspraying ,concentration swer esevera lhundred s ofm gm~3 .Th ehalf-live so fazinphos-methy lrange d from3 t o4 d ;thos efo rdimethoat e ranged from4 t o 13d . Waterflo wfro man dt oditc hsection swa sestimate d onbot hfrui tfarm sdurin gappli cation.Flo wthroug hth editc hbotto mwa sestimate d asa closin gite mi na balanc eequa tion.Al litem so fwate rbalanc ewer eintroduce d intocomputatio nmodel so fth ebehaviou r ofpesticide s insurfac ewate ran dbotto mmaterial .Th ese to fdifferentia lequation swa s solvednumericall yafte rprogrammin g inth ecompute rlanguag eCSM PIII .Simulatio no fa trialwit h lowdischarg efro ma siphon-linke d ditch indicated thatconversio no fbot hcom poundsi nwate rwa s 70-90%o fth emateria lbalances .Penetratio nint oth editc hbotto mwa s slow.Durin gwate rflo wthroug hth editches ,convectiv e transportan ddispersio nwer epre dominant. Declineo fazinphos-methy l anddimethoat ewa sals omeasure d inoutdoo rtan ksystem s witha botto mlayer .Fluctuation s inp Han dvariation s inligh tpenetratio ninfluence dde clinerates .Computation sfo rth etan ksyste mindicate d thatconversio ni nth ewate rcom partmentwa sth emajo rite mi nmateria lbalance .Th ecompute dan dmeasure dmasse so fth e insecticidesi nth ebotto mlaye rwer eles stha n 10%o fth eamoun tadded . Conversionrate si nsurfac ewate ran di nsystem swit hanaerobi cbotto mmateria lwer e measured inth elaborator ya t 10an d2 0°C .Conversio ni nwate r inth edar kwa sslow ,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 t tentime sthos ei nsurfac ewater . Copperion swer 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 . ISBN 90 220 06956

The author graduated on 30Ma y 1979 asDocto r ind e Landbouwwetenschappen at the Agricultural University, Wageningen, the Netherlands , on a thesiswith the same title and contents.

No part of thisboo kma y be reproduced or published inan y form, by print, photoprint, microfilm or any othermean swithou t written permission from thepublishers . Contents

List of symbols and units

1 Occurrence and origin of pesticides and herbicides in the aquatic environment 1 1.1 Chlorinatedhydrocarbo npesticide san d ijelatedcompound s 1 1.2 Cholinesteraseinhibitor s 2 1.3 Herbicides 4 1.4 Directapplicatio no fpesticide st osurfac e waters 5 1.5 Origino funintentiona lcontaminatio no i surfacewate rwit hpesticide s 7

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

3 Review of the use and properties of azin\ tphos-methyl and dimethoate 13 3.1 Applicationo fazinphos-methy lan d dimeljhoatei nfrui tfarmin g 13 3.2 Physico-chemicalpropertie so fth ecompound s 14 3.3 Conversionrate san dpathway so fth eco npound s 14 3.4 Adsorptionan dleachin go fth e compoundsi nsoi l 18 3.5 Volatilizationo fth e compoundsfro mwate rbodie s 19 3.6 Sometoxicologica ldat ao fth ecompound s 21

4 Sampling of water and bottom material in ditches for analysis of pesticide residues 23 4.1 Shortrevie wo fdevice san dprocedure sflor watersamplin g 23 4.2 Watersamplin gi nth epresen tstud y 24 4.3 Shortrevie wo fdevice san dprocedure sfior samplingbotto mmateria l 25 4.4 Samplingo fbotto mmateria li nth epresen t study 26

S Procedures for chemical analysis for azinphos-épthyl and dimethoate in surface water and bottom material 28 5.1 Introduction 28 5.2 Methodsfo rextractio no fpesticide s frem surfac ewater s 28 5.3 Extractiono fazinphos-methy l fromwate i samples 29 5.4 Extractiono fdimethoat e fromwate rsample s 30 5.5 Methodsfo rextractio no fpesticide sf re m bottommateria l 30 5.6 Extractiono fazinphos-methy l frombotto m samples 31 5.7 Extractiono fdimethoat efro mbotto msa npie s 31 5.8 Methodsfo rclean-u po fextract s 31 5.9 Clean-upfo razinphos-methy lextract sfrja nwate r 32 5.10 Clean-upfo rdimethoat eextract sfro mwate r 32 5.11 Clean-upfo razinphos-methy lextract sfro mbotto mmateria l 32 5.12 Clean-upfo rdimethoat eextract sfro mbotto mmateria l 33 5.13 Concentrationmeasurement sb ygas—liqui dchromatograph y 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 l inaqueou ssolution skep ti ndarknes s 36 6.3 Conversionrat eo fdimethoat ei naqueou ssolution skep 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 rtan ktrial s 57 7.3 Measuredrate so fdeclin ei nwate r 63 7.4 Measuredpenetratio nint obotto mmateria l 68 7.5 Generaldiscussio no noutdoo rtan ktrial s 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 Fieldtrial so nth efat eo fazinphos-met^iy lan ddimethoat ei nditche s afterspra ydrif t 89 9.3.1 Introduction 89 9.3.2 Datao nth etria lfield si nth eLopikerw^ar d Polder 89 9.3.3 Measurementan dapproximatio no fth e iteiis ofth ewate rbalanc e 91 9.3.4 Surfacean dgroundwate r quality 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 h water 102 9.3.8 Directmeasuremen to fspra ydrif tint od: . tches 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 fconcentratioil s ingroundwate r 111 9.3.12 Penetrationo fazinphos-methy lint obottcp m: material 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 fequatioi s 116 10.3 Designo fth ecomputation san dvalue so fparameter s 120 10.4 Computedresult sfo rth efiel dtrial s 123 10.5 Designo fth esimulatio n experiments 132 10.6 Resultso fth esimulatio n experiments 132 10.7 General discussion 136

11 Measurements and computations on the behaviour of\ substances in ditches with flowing water 137 11.1 Introduction 137 11.2 Derivationo fequation sfo rone-dimensiorja lconvectio nan 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 f parameters 144 11.4.3 Resultso fsimulation sfo rth etrace r expsriment irimentss 146 11.4.4 Designo fth esimulatio nexperiment swit h pesticides 148 11.4.5 Resultso fsimulatio nexperiment swit h pesticides 148 11.5 Generaldiscussio n 149

Summary 151 Samenvatting 156 Appendices 161 References 171 List of symbols and units

a dispersionconstan t (Equation40 ) 1) A averagewette dcross-sectiona lare ao fditc h m2) surfaceare ao ffirs tbotto mcompartmen ta tsediment—wate r m2)

D.dif.l b diffusioncoefficien to fsubstanc ei nliqui dphas eo fbotto m m d material (interm so fvolum eo fliqui dphas ean ddept hi n bottommaterial ) 2 ,-1 diffusioncoefficien to fsubstanc ei nwate r 0.di f ,w m d longitudinaldispersio ncoefficien t 2j- 1 A labyrintho rtortuosit yfactor :rati oo fsurfac eare ao f mD d bottommateria lt oliqui dphas e -1 • s,wd flowrat eo fsubstanc eint odownstrea mditc hsectio nduring : mgd intakeperio d -1 flowrat eo fsubstanc eint owate rcompartmen tdurin gintak e mgd period flowrat eo fsubstanc eou to fwate rcompartmen tdurin g mgd " s,wo pumpingperio d flowrat eo fsubstanc eint owate rcompartmen tfro mupstrea m mgd -1 ditchsectio ndurin gpumpin gperio d areicmas sflu xacros sgas—liqui d interfaceb yvolatiliza mgm d ) tion accelerationdu et ogravit y m d"2) :Henry' s constant (Equation5 ) (1) :heigh to fgroundwate r levelabov editc h bottom (m) 1heigh to fwate r levelabov editc hbottop i (m) :averag ewate rdept h (m) ! inde xnumbe ro fbotto mcompartmen t (1) ;arei cmas s fluxb yconvectio n into bottammaterial :mas s (mgm d conv.lb fluxdivide db yare ao fbotto mmateria l •arei cmas s fluxb yconvectio ni nwater : mass fluxdivide db y (mgm d conv.w wetted cross-sectional areao fditc h •arei cmas s fluxb ydiffusio ni nbotto m material:mas s flux (mgm " d ^dif.lb dividedb yare ao fbotto mmateria l ;arei cmas s fluxb ydiffusio ni nwater : massflu xdivide db y (mgm d dif, w wetted cross-sectional areao fditc h : arei cmas s fluxb yconvectiv edispers i 51011 (mgm d disp.lb intobotto mmate - rial:mas s fluxdivide db yare ao fbott|o m material areicmas s fluxb yconvectiv edisper : (mgm d disp.w rsion inwater : massflu xdivide db ywette d cross- -sectiona l areao fditc h totalarei cmas s fluxint obotto mmateria l mass fluxdivide d (mgm d s.lb byare ao fbotto mmateria l totalarei cmas sflu xi nwater :mas s fluxdivide db ywette d (mgm d cross-sectional areao fditc h dispersion constant (Equation41 ) (1) ratecoefficien t forconversio no f 1 c,b substancei nbotto m Cd" ) material rate coefficientfo r conversiono f substancei nwate r Cd"1) exchange coefficientfo rga sphas e (md" 1) exchange coefficientfo rliqui dphas e (md -1) 1 1 Mannings coefficient forbotto mroughn i (m /3d -1j first-order ratecoefficien tfo rdeclini e (d"1) distributionquotien tsolid/liqui d phase •• adsorption (m3 kg-1) coefficient (interm so fvolum eo fliqui d phasean dmas s ofsoli dphase ) -1 t,l overall liquidphas e transfercoefficien t (rnd ) lengtho fditc h compartment (m) dispersion distance (m) m initial injectedmas so fsubstanc e (mg) M, firstmomen t (Equation51 ) (d) masso fslic eo fwe tbotto mmateria l (kg) masso fslic eo fdr ybotto mmateria l (kg) multiplication factorfo rdownwar di incrsas e in thickness (D ofbotto m compartments measuredmas so fpesticid e inwate r compartment before (mg) Sampling n masso fpesticid ei nwate r compartment correctedfo r (mg) volumeo fsample swithdraw n areicrati oo fcontaminatio no fwater :rati oo fmas s (1) 'r,A ofsubstanc eintroduce d intowate rdivide db yare ao fwate r tomas so fsubstanc eapplie dt olan ddivide db ylan dare a integer,Samplin gN o (intim eseries ) (1) wettedperimete ro fditc h (m) rateo fflo wthroug hwette dperimete ro fditc h (m d" ) 3 rateo fdischarg efro mwate rcompartmen t (tm d" ) 3 rateo fdischarg efro mupstrea mditc hsectio n (rm d" 'd,u ) flowrat ethroug hdrain s (rm 3 d" ?dr ) rateo fevaporatio nfro mwate rcompartmen t (rm 3 d" ) rateo fintak eint owate rcompartmen t (t m3 d" ) rateo fintak eint odownstrea mditc hsectio n (f m3 d" ) 'i,d rateo fprecipitatio nint owate rcompartmen t (m 3 d" ) R hydraulicradiu s (m) rateo fconversio ni nbotto mmateria l (mg m" 3 dJ-1 )> c,b i -1 rateo fconversio ni nwate r (mg m d 'j R c,w slopeo flowe rpar to fditc hwall s (tga = horiz./vert. ) (1) 1 t time (d) At timeste p (insimulatio nexperiments ) (d) half-life (d) *• 2 volatilizationhalf-lif e (d) 5.V timea twhic hth emaximu mmas sconcentratio ni sreache d (d) ata samplin gpoin t averageflo wvelocit yo fwate r (md" 1) shearvelocit y (md" 1) volumeo fslic eo fwe tbotto mmateria l (m3) 1 Flb filtrationvelocit ythroug hbotto mcompartment s (interm s (md" ) ofvolum eo fwate ran dare ao fbotto mmaterial ) filtrationvelocit ythroug hth efirs tbotto mcompartmen t 1 "lb (1) (md" ) (interm so fvolum eo fwate ran dare ao fbotto mmaterial ) 3 : f Ï V volum eo fwate rsampl e (intim eseries ) (m) s n v ' :volum eo fwate rcompartmen t (ra3) w dV làt ;chang ei nstorag eo fwate rcompartmen t 3 -1 w (m d ) œ ;downstrea mdistanc ealon gditc haxi s (m) : 2 dept hi nbotto m (m) a arctg s-, (1) e arctg (1/sp (1) -2,- 1 Y drainageresistanc e (kgm d ') e. volumefractio no fliquid :volum eo fliqui dphas edivide d (1) byvolum eo fbotto mmateria l (dry)bul kdensit yo fbotto mmaterial :mas so fsoli dphas e (kgm ) dividedb yvolum eo fbotto mmateria l densityo fsoli dphas eo fbotto mmaterial :mas so fsoli d (kgnf 3) phasedivide db yvolum eo fsoli dphas e densityo fwate r (kgm" 3) shearstres sa tditc hwall s (kgm" 1 d"2) 1 Occurrence and origin of pes :icides and herbicides in the aquatic environment

Theproble mo fth eoccurrenc eo fpesticide s and herbicidesi nsurfac ewate rha ss o manyaspect s thata researc hprogra mi nthi s field Jiiist needsb erestricte dt opar to fit . Tose tth epresen t researchprogra mi ncontex tan d allowa bette revaluatio no fth e results,Chapte r1 give sa genera l sketcho fth e problem spherebefor eth eresearc hap - proachi sdescribe di nChapte r 2.Fo rth edescripti i ofconcentration s thatca noccu ri n surfacewate r (mainlyi nth elarge rwatercourses) , tie resultso fextensiv e monitoring research couldb eused .Onl ya fe wdat ahav ebee n publishedo nth esiz eo fth esourc e ofspecifie d contamination.I nsevera l cases,a n emissio n tosurfac ewate rcoul dwel l occur,howeve r littlei sknow nabou tth esiz eo fth e source.Som epossibl esource so f pesticides andherbicide si nsurfac ewater sar e discussedi nSectio n1.5 .

1.1 CHLORINATED HYDROCARBON PESTICIDES ANDRELATE D COMPOUNDS

Monitoringo fsurfac ewater san dbotto msedimevt sstarte di nth eUnite d States aboutte nyear s afterth eintroductio no fth eorgan odilorin einsecticides .I tsoo nbecam e evident thatsmal l amountso fthes e insecticideswer îpresen ti nman y surfacewaters . Sincethen ,extensiv e surveyshav ebee nmad ei nsevera lcountries .Mos tattentio nwa s paidt oth echlorinate dhydrocarbons ,sinc e thesew e: ewidel yuse dan dcoul db erathe r easilymeasure dwit hga schromatograph sequippe dwit ha nelectron-captur e detector.Sever alchlorinate dhydrocarbon sar eonl y slowlydegrade di nwater .Review so forganochlorin e residues inwate rwer egiven ,fo r instance,b yWestliik e& Günthe r (1966),Nicholso n (1969) andEdward s (1973). Theirsummarize d datasho w thatth eresidu e levelsi nwate rar erel atively low,rangin g froma fe wmicrogram st oa fe wiiilligram spe rcubi cmetre ,excep t nearpoin t sources likedischarg eo findustria l effluent,direc t applicationo raccidenta l contamination. Chlorinatedhydrocarbon swer edetecte di nwate fsample si nman yEuropea n countries (Grève, 1972;Herzel ,1972 ; Lowdene tal. , 1969;Sörensen , 1973). Thesemeasurement s show that lindane,havin gth ehighes twate r solubilityo f thegenera lchlorinate d hydrocarbon insecticides (Kinge tal. , 1969),wa smos t commonly Jtoundi nEurope . Most chlorinatedhydrocarbon s showa lo wsolub ]lit yi npur ewate ran dthe yma yb e readilyadsorbe dt ohumi csubstances ,organo-cla ycomplexe san dothe rparticulat e matter insuspension .I nlaborator y experiments,th e release ofthes ecompound s fromsediment s intowate rwa sfoun dt ob eslo w (Choi& Chen , 1976). Chlorinatedhydrocarbo nresidue sma 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 c fromth ebotto mo fsmal l streams decreased from 1.08m gkg ", on eyea rafte ra singl e applicationt o0.5 9m gk g after -1 fiveyears .Afte rte nyears ,th econten tha ddécliné e to0.0 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 llargel yadsorbe do nsuspende dmateria l (Nicholson,1969) . Sincesom eorganochlorin e insecticidesar eknow nt ob epersisten tan dten dt oaccumu latei norganisms ,especiall y inadipos etissu eo fanimals ,thei rus eha sbee nrestricte d orbanne di nsevera lcountries .I nth eNetherlands ,th elas tapplication so fDD Twer eban nedo n1 Jul y1973 .

Monitoring of chlorinated hydrocarbons in Dutch surface waters

Thefirs tmonitorin g inth 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 rsupplie san dlarg eagricultura l areas (Grève,1971) . Grève (1972)an dMeijer s (1973)foun dtha ta-hexachlorocyclohexan e (a-HCH),lindan e (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 s196 9an 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 srelate d compounds)wer eoccasionall ydetecte di nrathe rlo wconcentrations .Th eaverag econ centrationove rth eperio d 1Septembe r 1969t o1 Apri l 1972,amounte dt o0.1 5m gm for a-hexachlorocyclohexane, 0.10m gm forlindan ean d0.1 3m gm ~ forhexachlorobenzen e (Grève,1972) .Th econcentration so fth eby-produc ta-hexachlorocyclohexan ewer ethu sfoun d tob ehighe rtha nthos eo fth epesticid elindan eitself .I nvie wo fth elimite dus eo fpesti cidescontainin ga-hexachlorocyclohexan e inagricultur ealon gth eRhine ,industr yha sprob ablybee nth emai nsourc eo fpollution .Th ehig hconcentration so fhexachlorobenzen ecoul d notb eexplaine db yth elimite dus eo fthi scompoun da sa nagricultura lfungicid eo rb yit s presencea sa nimpurit yi na fungicid elik equintozene .Hexachlorobenzen ei sa nintermedi atecompoun do ffrequen toccurrenc ei nindustria lsyntheses .Thi scompoun di sals ouse da s aflam eretardant . Since1972 ,al lmonitorin gdat ameasure dfo rth elarge rDutc hwaterway sadministere d bynationa lauthoritie shav ebee ntabulate di nth equarterl ysurvey so fRijkswaterstaa t (1973-1978).Thes enewe rdat a (Table1 )sho wtha tth econcentration so fa-HC Han do flin danedecrease dconsiderably .A sther ewa sn osystemati ctren di nth edischarg eo fth eriv - 3 -1 er,whic haverage d 1890m s overthi s5 yea rperiod ,th edischarg eo fth elatte rtw o chlorinatedhydrocarbon smus thav eactuall ydecreased .

1.2 CHOLINESTERASE INHIBITORS

Themonitorin gprogra mstarte di nth eNetherland s in196 7an dals oinclude dth e measuremento fCholinesteras e inhibitors (mainlyorganophosphoru san dcarbamat epesticides ) insurfac ewaters .Grèv ee tal .(1972 )showe dtha trathe rhig hconcentration so fCholin esterase inhibitorswer epresen ti nth eRhin ean dit sdistributaries .The yanalyse dsom e watersample sfro mthi srive rsyste mi nmor edetail .Fiv einsecticide swer edetecte db y thin-layerchromatograph y (TLC)an dgas—liqui dchromatograph y (GLC),whil ethei rpresenc e Table 1. Averagemas s concentrations of a few chl>rinated hydrocarbons inRhin e water sampled near Lobith, theNetherlands . (After Rijkswaters taat, 1973-1978).

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

1973 1974 117 5 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 4th 0.14 0.02 0,03 0.02 0.04

wasconfirme dwit ha mas sspectromete r (MS)(Tabl e 2). Thepresenc eo fCholinesteras e inhibitorsi nsurfac ewate ri sunfavourable ,becaus eCholinesteras eactivit yi sintimatel y relatedt olif ei nth eaquati cenvironment .Littl e isknow nabou tth esignificanc eo fsub - -lethalconcentration sfo raquati corganisms . Theaverag econcentratio no fCholinesteras e inhibitors,expresse di nparaoxo n equivalent,measure ddurin g 1970,197 1an d197 2wa s below 1m gm (Grèvee tal. , 1972). However,th econcentration s inth eRhin enea rLobiti iincrease d fromth efirs tquarte ro f 1973onwards .Occasionall yth econcentration swer e fairlyhig hi n1976 ,whic hcoul dno t beexplaine db yth erelativel ylo wdischarg eo fwat2 ri nth eRhin ei ntha tyea r (Table3 ; Figure 1). In1976 ,a nimportan tindustria leffluen tsour: ewa strace db yth eInstitu tfü r Wasser,Boden -un dLufthygien ede sBundesgesundheitsamte s(BGA )i nth eRive rMain .Afte r thecomplaint so fth eBG Aan dth eNationa l Institut;o fPubli cHealt hi nth eNetherlands , theconcentratio no fparaoxo nequivalen tnea rthi s sourcediminishe dwithi na fe wweek s -3 -3 froma maximu mo f300 0m gm toabou t 10m gm (Pritschie tal. , 1978). Inothe rsurfac ewater si nth eNetherlands ,th eleve lo fCholinesteras einhibitor s wasfoun dt ob esubstantiall ylowe rtha ntha ti nth oRive rRhine ,eve nbelo wth edetectio n limito f0.0 5m gm~ 3 (Wegman& Grève ,1978) . Inothe rcountrie stoo ,smal lamount so forgan«>phosphoru spesticide swer efoun di n

Table2 .Mas sconcentratio no fa fe wCholinesterase -inhibitor s inRhin ewater .(Afte rGrèv ee tal. , 1972). -3 Cholinesterase Massconcentratio n (mgm ) inhibitor NovembeNovei r 1971 January 1972

Dimethoate 0.07 0.08 Malathio n 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 e inhibitorsi n Rhinewate r samplednea rLobith .Concentration s expressed inm g paraoxonequivalen tpe rnr 'water . (AfterRijkswaterstaat , 1973-1978),

Quarter Massconcentratio n (mgm )i ndifferen tyear s

1973 1974 1975 1976 1977

1st 5.73 0.92 4.5 31. 0 5.9 2nd 1.5 2 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 average 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 mgm .InWes tGermany ,Sörense n (1973)foun dsevera lorganophosphoru spesticide si nsur facewaters ,wit ha stron gvariatio n inconcentratio ndependen to nth esamplin gpoints . Hisresult sar erepresente di nTabl e4 .I nth eRive rMain ,dimethoat ewa sregularl ypres - enti nconcentration sbetwee n1 an d 10m gm (Kussmaul,1978) . Extensivereport so nCholinesteras e inhibitors insurfac ewater s inItal ywer egive n byDe lVecchi oe tal . (1970),wh omeasure d chlorpyriphos,diazinon ,fenchlorphos ,mala thion,methyl-parathio nan dparathio n ina rang efro mles stha n0.0 1 mgm toabou t 0.70m gm .

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 ' 1971 Î972 I 1973 I 1974 I 1975 I 1976 I Figure 1.Cholinesteras e inhibitors inRhin ewate r (Lobith)i nm gparaoxo n equivalentpe rm3 . (After Fritschie tal. , 1978). Table4 .Organophosphoru spesticide s insurfac ew a :eri nWes tGermany . (AfterSörensen , 1973).N.A .* no tanalysed ;- - < 0.01m gm~ 3.

Samplingpoin t Massconcentratio n (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 Düsseldorf- -Benrath 10.8 0.1

J -3 2,4-Dwer eusuall y less than1 m gm .I nthos e stiearns ,, lo wresidue so f2,4,5- Twer e foundto o(Schulz ee tal. , 1973).Fo rsevera lyear s ,atrazin eha sbee nuse do na larg e scale forwee d controli nth eCor nBel ti nth eUnite d States.Thi s compoundwit ha solu - bility inwate ro f3 3g m ~ ismos t frequently det«cte d inth erecen tmonitorin g studies. Richarde tal . (1975)foun d thatth e atrazine concentrationsi nrun-off ,i ndrainag e ditches,an di na fe wriver si nIow awer emor ethai , 1m gm afe wday safte r intensive rainfall. Waldron (1974)investigate d the contribution ^fagricultural ,municipal ,residentia l andindustria l activitiest opesticid epollutio no i LakeEri ei n1971-1972 .Durin g this study,residue so fseve norganochlorin e insecticides ,thre etriazin eherbicides ,thre e chlorophenoxy acid herbicidesan dfiv eorganophosp h torusinsecticide swer emonitored . These analyseso frive rwate r andbotto mmu d indicated or.ly sporadic occurrenceo fminut econ - centrations.H efoun d atrazinet ob eth emos tfrequentl y detectableherbicide .I nte nsam - pieso frive rwate rwit hpea k residue levels, the doncentrationsrange dfro m3 t o7 0m gm~ 3 Sometimessimazin ewa s detected. Littleinformatio ni savailabl eabou tuninteniiiona l occurrenceo fherbicide si nDutc h surfacewaters .Th e applicationo fherbicide sfo r aquaticwee d controli nth e Netherlands willb ebriefl ydiscusse di nSectio n1.4 .

1.4 DIRECTAPPLICATIO NO FPESTICIDE ST OSURFAC EW/TER S

Probably thegreates tdirec tsourc eo f pesticides inwate rha sbee nth eten so f thousandso fton so fDD Ttha twer eapplie d annually tosurfac ewate r (Westlake& Günther , 1966)an destuarin e saltmarshe s overtw odecade s to controlmosquitoe s (Butler, 1969). Sometimespesticide swer euse di nprogram st o eradicate trashfish .Fo rexample , camphechlor (Toxaphene)wa suse dt oeliminat e undesired fishspecie si nman y fresh-water fishing lakesi nth eUnite d States (Veith& Lee , 1971 )• A recentexampl 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 d inwarm ,slowl ymoving ,wate rfo rth e controlo fsnails ,whic har eintermediat ehost so ftrematode scausin g schistosomiasis (bilharziasis)i nma n (Osgerby,1970) . Inth eNetherlands ,n opesticid e isapplie d intha twa yt osurfac ewater .

Application of herbicides

Onlya fe wherbicide sar eapprove d inth eNetherland sfo rth econtro lo faquati c weedsunde rspecia lcondition s (PlantenziektenkundigeDienst ,1978) . Inthi ssection ,a shortdescriptio n isgive no fth esituatio n in1978 .A fewcharacteristic so fth ephysico - -chemicalbehaviou ro fthes eherbicide s inwatercourse 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 r 15July .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& Chesters ,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 d inhig hconcentration s formor etha n8 5an d16 0days ,respectively .

Side-effectsan dalternative s

Thecontac therbicida lactivit yo fa compoun dlik eparaqua tcause srapi ddeat ho f submergedaquati cvegetation ,resultin gi nchange s inth ephysical ,chemica lan dbiologica l natureo fa treate d stretcho fwater .Th eremova l of competitionb ycertai nweed sma y resulti nabundan tgrowt ho falga esom etim eafte r treatment.Th ebreakdow nb ymicro - -organismso frapidl ydyin gplan tmateria l require^ alo to foxygen ,whic hma y decrease theconcentratio no fdissolve doxyge nt over ylo w evels (Brooker& Edwards , 1975). Such changesi nlivin gcondition sma yals o indirectly reducepopulation so faquati canimals , Invie wo fth e side-effectso fherbicide si nsurfac e water, improvementst omechanica l ditchcleanin gha sbee nstudied .I nrecen tyears , Jiepracticalit yo fsom ebiologica lmeth - odso faquati cwee dcontro lha sbee n investigated vanZon , 1974). Forth e controlo fundesire dplan tgrowt ho f temporarilydr yditc hbottoms ,othe r herbicides likediuron ,dichlobeni lan dsimazin ea approved,a slon ga sn owate r flow through theseditche si sto b eexpecte d duringth e next twomonth s (Plantenziektenkundige Dienst, 1978).A nimportan tquestio nwit h thesea ] pjklicationsi sto wha texten tthes ecom - poundsma yb erelease d intowate ran dtransporte d vhenwate rstart st oflo wthroug hth e ditchagain .

1.5 ORIGINO FUNINTENTIONA LCONTAMINATIO NO FSURFAC EWATE RWIT HPESTICIDE S

Industrial, domestic and agricultural waste

Pointsource so fcontaminatio no fsurfac e wateirwit hpesticide soutsid e agriculture mayb eth edischarg eo findustria lo rdomesti c wateran dsewag eplan teffluents , Thewast efro mpesticid e factoriesma yb e highlycontaminated .A wel l known incident wasth e generaldeat ho ffis hi nth eRhin ei nJun e 1969cause db ylarg eamount so fendo - sulfan (Grève& Wit , 1971). Recentlya majo r industlrialdischarge ,highl ycontaminate dwit h Cholinesterase inhibitors,wa strace di nth eRive r Mainb yFritsch ie tal . (1978) (Section 1.2). Inth eundilute deffluen to fa factor yfo r oijganophosphorusan dcarbamat epesticide s inKansa sCity ,Coppag e& Braidec h (1976)foun d ationsa shig ha s200 0t o400 0m gm fordisulfoton ,fensulfothion ,azinphos-methy lan d jropoxur.The y reported thatabou t 3.2k go fazinphos-methy l entered therive reac h dav (correspondingwit ha concentratio n ofabou t0.1 6 mgm atlo wrive r flows). Some industriesus e insecticidesi nthei rprocesse s Lowdene tal . (1969)showed , forexample ,tha tth eeffluen t frommot hproofin gi< i woolan dcarpe t factories contained lindane 0.14,dieldri n1. 8an dDD T0. 8m gm~ 3. Agricultural 'pointsource so fcontamination ' canb e accidentalspil l fromequipment , cleaningo fequipment ,carelessnes si nhandling , transportan ddisposa lo fempt ycontain - ers,an dinadverten tdisposa lo fremainin gspra y liquido rdippin gbaths .

Surface run-off from agricultural land

Oneo fth etw oprincipa lsource so fsurfac e watercontaminatio nb ypesticide si nth e UnitedState si sprobabl y run-offfro magricultura l land (Nicholson,1969 ;Bail ye tal. , 1974). After treatmento fa watershe di nArizon awit h theherbicid epicloram ,th e concentrationsi 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 safte rtreatmen tan dwer eassociate dwit hheav yrainfall . Miles& Harri s (1971)showe da correlatio nbetwee nrainfal lrat ean dconcentratio n ofDD Tan dmetabolite s incree kwate rflowin gint oLak eErie . Ina stud yo fdieldri nmovemen tfro msoi lt owate ri ntw owatersheds ,onl y0.07 %o f theamoun tapplie dt osoi lappeare di nrun-of fwate rwit hth elarges tlosse soccurrin gi n thefirs ttw omonth safte rapplicatio n (Caro& Taylor ,1971) .Man yothe rworker sreporte d seasonalpeak si nresidue stha tcoincide dwit hperiod so fextensiv eagricultura luse . Thesurfac erun-of ffro magricultura l landi nth efla tarea so fth eNetherland si s likelyt ob eo fmino rimportance .

Control of ditchside vegetation

Whenherbicide sar euse dfo rth econtro lo fditchsid eweeds ,par to fth espra yma y reachth ewater .Jus ta sfo rth econtro lo faquati cweed s (Section1.4) ,onl ya fe wher bicidesar eapprove dfo rth econtro lo fditchsid evegetatio ni nth eNetherlands .Applica tionso fparaqua tar eallowe donl yafte r 1June .I npractice ,thes erestrictiv emeasure s willpartl ydiminis hth eus eo fherbicide sfo rcontro lo fditchsid 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 fditchsid evegetatio ni shighl yrecommende d (PlantenziektenkundigeDienst ,1978) .

Leaching of pesticides through the soil

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

Drift from application by aircraft or by tractor-ct'awn spraying machines

Applicationsb yaircraf tmainl yoccu ro nlarg ^ fieldso fth esam ecro pi narabl e farming. Themetho di smainl yuse dfo rfungicides , for exampleo fth ebenzimidazol egroup , dithiocarbamates,an dorganoti ncompounds .T oa lesser extent,insecticide s arespraye d fromaircraft ,mos to fthe mbein g organophosphorus compounds sucha sfenitrothion ,dime - thoate,bromofos-ethyl ,thiometo nan dfosalon e On:.y rarely canherbicide sb eapplie di n thisway ,becaus eo fth eris ko fdamag et ocrop s adjacent fields.A revie wo fpossibl e pesticideapplication sb yaircraf twa s givenb yth ^ Plantenziektenkundige Dienst (1975), withadvantage san ddisadvantage so fthi smetho d possibleundesirabl e consequenceso f spraydrif t fromth etarge t fieldswer e clearly shown.Wit happlicatio nfro maircraft ,i t ishardl ypossibl et oavoi dcontaminatio no fth e watercoursesborderin go nth e treated fields.I ti sthu sadvisabl et oselec tth ecompoun d swit h the lowesttoxicit yt oaquati c organisms.Dat ao nth ebehaviou ro fpesticide si n iurfacewate ran dthei rtoxicit yt o aquaticorganism sar eessentia li nselectio no fc < oripoundssuitabl e foraeria lapplication , Whenapplyin g insecticides,acaricide so rfun^ : icidesb ytractor-draw nsprayer st o highcrop s like fruittrees ,spra ydrif tma yoccu r overconsiderabl edistance ss oals ot o neighbouringwatercourses . Withcarefu lapplication so fpesticide san d herbicidest oth esoi lsurfac eo rt o fieldswit hlo wvegetatio n- mainl yb ytractor-drave n sprayingequipmen twit ha lo wspra y boom- an dals oadequat edrople t sizelittl espra y willdrif tan dthu sals olittl econta - minationo fwate rwil loccur .

Relative importance of the various contaminations sources

Inspit eo fth enumerou s studieso nth e occurience andorigi no fpesticide si nsur - facewaters ,th erelativ e importanceo fth evariou s unintentional sourceso fcontaminatio n isdifficul tt oassess .Whe nsample sar ecollecte d nearknow nsource so fpesticid epollu - tion,th elevel sten dt ob ehigh .O nth eothe rhand) , ,analysi so fsample scollecte di nmo - nitoring programs indicatecomparativel ylo wlevel s ofcontaminatio nbecaus eo fth estron g dilutiontha toccur s aftera pollutan ti sintroduce d intoa naquati csystem , Unintentional introductiono fpesticide s from agricultureint osurfac ewate rstil lre - quires considerableattention .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 d inChapte 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 y isth econtributio no fagricul turet ocontaminatio no fsurfac ewater swit hpesticides .A numbe ro fsituation swit hpos sibleemissio no fpesticide sfro magricultur et osurfac ewate rwer edescribe di nChapte r1 . Ifunintentiona l introductiono fpesticide sint osurfac 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 l behaviouro fspecifi cpesticide safte rthe yhav ereache d openwater ?Wha twil lb eth eresultin gconcentration-tim e relationships insurfac ewaters ? 3.Wha tar eth econsequence so fthes econcentration s foraquati corganism san dfo rth e qualityo fth ewate ri nvie wo fth eintende duse ;fo rexampl ea sdrinkin gwate rfo rma n andanimals ,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 s ifnecessary .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 gth euser s moreconsciou so fth eproblems .Preventiv eadvisor yactivitie sshoul db edirecte dt oth e peopleworkin gwit hpesticide si nth efield .Thi saspec tlend sitsel fonl yt oa limite d extentfo rphysico-chemica lresearch . Inth epresen tinvestigation ,spra ydrif to fpesticide sfro morchard st odrainag e ditcheswa s investigatedi nsom edetai lo na fe wfrui tfarm si nth eLopikerwaar dPolde r (Chapter9) . -Physico-chemica lbehaviou rwa sth emai naspec to fstud yi nsurfac ewater .Attentio nwa s paidt oth eadsorptio no fpesticide so nditc hbotto mmateria lan dt oth epenetratio no f pesticidesint oditc hbottoms .Conversio nrate so fpesticide swer estudie di nsurfac ewa terunde rdifferen tcondition san di nbotto mmaterial .Transpor tan dconversio nwer eals o investigated infiel dtrials .Computatio nmodel swer edevelope d andused .A mai nobjec t ofth epresen tstud ywa st oobtai na quantitativ edescriptio no fth econcentration-tim e relationships forpesticide 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 e required. Inth epresen t inv;stigation,onl y ashor tcompilatio no f literature datao nth e toxicityo ftw omode lpest i Ides foraquati corganism swa smad e (Section 3.6). Otherpotentia lproblem s associated withpesticid e residuesdepen do nth e localsituatio nan d thespecifi cus eo fth ewate r

2.2 LAY-OUTO FTH EPRESEN TRESEARC H PROGRAM

Invie wo fth eman yquestion s tob eanswere d |Section 2.1), this investigationwa s restricted toa fewpesticide san d toa fewagricu]tura lsituation s inwhic h contamination ofsurfac ewate rb y pesticideswa s likely. Atpresent ,aquati cherbicide s areonl yapplie do na limited scalei nth eNetherlands . Somode l pesticideswer eselecte dwhic hma yunintertionall ycontaminat esurfac ewaters . Sinceth eus eo fchlorinate dhydrocarbo n insecticides hasbee ndrasticall y reduced,mainl y organophosphorus andcarbamat e insecticides areapplie d inhorticultur e and arablefarming . Someo fthes ecompound s arerathe r toxic tovariou s aquatic organisms.Althoug h suchcom poundsar egenerall y lesspersisten t thanth echlorinate dhydrocarbons ,ther ewa s evidence thatsom eo fthe mma yb e ratherpersisten t insurfa; ewaters .Condition s inaquati cmedi a ares odifferen t fromthos e inplants ,i nsoi lo ro nartificia l surfaces,tha t special measurements onconversio n rates insurfac ewate r areneeded . The important organophosphoruspesticide s azinphos-methylan ddimethoat ewer e selected asmode l compounds.Th e rateso fconversio nunde raquati c conditionswer elargel y lacking. A generalcharacterizatio no fth eus ean dpropertie « ofazinphos-methy lan ddimethoat e is giveni nChapte r3 . Ina norientatio n stageo f the investigation,lariou ssurfac ewater swer e sampled in theKromm eRhin eare aan d inth eLopikerwaar d Poldei (Provinceo fUtrecht) . Initiallymuc h attentionwa sneede d toth edevelopmen t ofexperimerta lmethod s andanalytica lprocedures . Samplingo fwate ran dbotto mmateria l requiredspec ia ltechnique s (Chapter 4). Manyprob lemsha d tob e solved inga schromatograph ya t lowlevel so fth ecompounds .Larg eamount s ofinterferin gsubstance s inal l extracts ofbotto m naterialha d tob eremove d (Chapter5) . Thedevelopmen t ofsuitabl eclean-u pprocedure s for theseextract s required muchattention . Lateri tbecam eeviden t thatattentio nha d tob î focusedo na fe wsituation s in whichbot hmode l compoundswer eapplied .Tw ofrui tfirm swer e selected formor e detailed study,on enea rth evillag eo fBenscho pan don enea rth evillag eo fJaarsveld ,bot hi nth e Lopikerwaard (Chapter 9). A criterion inth eselectio no fsamplin gpoint swa s thato n these farms thedrainag e ditchescontaine dwate r throughout thegrowin g season.Furthermor e on bothfarms ,th editc hsystem swer e occasionally discharged by smallpumpin gstations , whichmad ei tpossibl e toestimat e thewate rbalanc e ofth editche s (Chapter10) . Inth esituation sselecte d forth efiel dtrials , considerabledrif t fromth eorchard s intoditche s couldb e expected.Th efarm swer e traversed bysevera l farmditches .Severa l treesgro wjus talongsid e theditche swit h theircrovn s aboveth ewater ,s o that inevitably a certainamoun t ofth espra ydescende d into thewater .Althoug h suitableobject s forth e present study,thes esituation s areno t common infruit-growin g areas.Loca l situations varywidel yan dshoul d thusb econsidered . Inmos t frait-growingareas ,th eproportio no f openwate r isfa rless ;ditche sma yb edr ydurin g the growing season.Ofte nfrui t trees

11 areseparate dfro mth editche sb ya wind-brea ko ftrees ,b ya path ,o rb ya sizabl ebor der.Thu si tma yb eexpecte d thatcontaminatio no nth etw ofarm swoul drepresen ta nuppe r limito fcontaminatio nrathe rtha na naverag evalue . Ata nearl ystag eo fth eresearch ,i tbecam eclea rtha tfiel dsituation sca nb equit e complex.S osimple rtrial swer emad ei noutdoo rtanks ,measurin g therat eo fdeclin ei n wateran dpenetratio nint obotto mmateria l (Chapter 7). Thedeclin etrial si nthes eout doorsystem swer ecarrie dou tunde rtemperatur ean dligh tcondition ssimila rt othos ei n thefield . Invie wo fth elarg enumbe ro fcompound san dcondition so fapplications ,ther ei sa needfo ra ninitia lcharacterizatio no fth ecompound s inwel ldefine dlaborator ytests . Inlaborator ytests ,conversio nrat ean dadsorptio no fazinphos-methy lan ddimethoat ewer e measuredunde rcontrolle dcondition s (Chapter6) . Theevaluatio no fth ebehaviou ro fman ypesticide sunde rvariou scondition si nsur facewate rwoul drequir ea nenormou sresearc hcapacity .I ti sno tfeasibl et ostud yal l relevantcompound sunde ral lpossibl eenvironmenta lconditions .Severa lprinciple s inth e behaviouro fpesticide si nsurfac ewate rar eo fgenera lnature ;the yca nb eapplie dt ovar iouscontaminant sunde rdifferen tcircumstances .Therefore ,computationa lmodel sfo rth e quantitativedescriptio no fphysico-chemica lbehaviou ro fpesticide s insurfac ewate rar e consideredgoo dtool si nthi sresearch .Thes emodel sai ma tth equantitativ edescriptio n ofconcentratio na sa functio no fpositio nan dtim e (Chapters8 ,1 0an d 11).Detaile din vestigations formode lpesticide scoul dthu syiel d informationo fmor egenera lvalidit yo n thephysico-chemica lbehaviou ro fpesticide s insurfac ewater . Invie wo fth ecomplexit yo faquati csystem san do fth enee dfo rflexibility ,th e differentialequation swer esolve dnumerically .Th ecompute rsimulatio nlanguag eCSM PII I (IBM,1975 )wa suse dfo rprogrammin g themodels . Thecomputatio nmodel swer eprimaril yconsidere dt ob eresearc htool sb ywhic harea s ofto olimite dknowledg ecoul db etrace dmor eclearly .Th eresult so fmode lcomputation s providea startin gpoin tfo rfurthe rinvestigations .Computatio nmodel sma ybecom emor e suitablefo rmakin gpredictions ,startin gfro ma limite dse to fbasi cdat ao nth ecom poundan dfro mth ehydrologica lsituation .

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

3.1 APPLICATIONO FAZINPHOS-METHY LAN DDIMETHOAT E [NFRUI T FARMING

For thecontro lo fharmfu l arthropodsi narabl p farming,horticultur ean dlandscap e management,variou spesticide sar eavailabl e (Gids voor Ziekten-e nOnkruidbestrijdin gi n Land-e nTuinbouw , 1977). Themode lcompound si nth ^ presentstud y areapprove d forvar - iouspurposes . Azinphos-methyl canb euse di nappl ean dpea r orchards,an di nflowe rcrops .Th e situationtha treceive dparticula r attentioni nthi ^ studywa s applicationi nappl ean d pearorchards ,wher eazinphos-methy la s25 % (w/w) wettablepowder ,ma yb euse d especially againstcaterpillars ,an dfurthe ragains tpsyllids , appleblosso mweevils ,sawflie san d pearblosso mweevils . Dimethoatei sapprove d forus e againstharmfu l insectsi nvariou s fruits.Further , thiscompoun dma yb euse do noutdoo rvegetables , poi:atoes ,, sugar-bee tan dcereals . The compoundi sals ouse dt osom eexten to nornamental s flowerbulb san do nnurser y stock, Theapplication so fdimethoat ei norchards ,subjec t ofth epresen t investigation,ar edi - rectedagains t aphids,psyllids ,wooll yaphids , cap;id s and sawflies.Dimethoat ei suse d indifferen t formulations,namel ya s20 1 (w/w) wettablepowde ran da sliquid so fmas scon - centration 200an d40 0k gm ". Combinationso fazinphos-methy lan ddimethoat e formulateda sa wettabl epowde rwit h 20%+ 10 1activ e ingredient,ar eapprove d forus eajjains t someinsect so napples ,pears , cabbages andpotatoes .Th enumbe ro fapplication s oi- both insecticideso rth emixtur ede - pendso nth eexten to foccurrenc eo fth einsects , but oftensevera l applicationsma yb e necessaryt ocontro l them.Nowaday s sexpheromone s (Janb euse da sa warnin g system forth e presenceo fpopulation so fsumme r fruittortri xmoth s .B yusin g this systemo f'supervise d control',th enumbe ro fapplication sca nsometime st ereduce d (Minks& d eJong , 1975).Fo r thewettabl epowde ro fazinphos-methyl ,th erecommerde ddos eo fproduc ti s0. 3gm (3k g -1 3-2 (1 litre ha-1). ha )an dtha tfo r 40%dimethoat ei s0. 1c m m Inth eNetherlands ,th emaximu mpermitte d resi idueo fazinphos-methy lo nappl ean d peari s0. 4m gk g ;tha tfo rdimethoat ei s0. 6m g 1g ,bu ta nincreas et o1. 5m gkg " underconsideration . Safetyperiod sbetwee napplica t ionan dharves t forbot h insecticides onappl ean dpea rar ethre eweeks .Becaus eo fth e toxicityo fbot hcompound st obees , ap- plications during floweringo ffrui ttree sar eno t allowed (Gidsvoo r Ziekten-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 s liketha to fMarti n& Worthin g [1977).

3.3 CONVERSIONRATE SAN DPATHWAY SO FTH ECOMPOUND S

Theconversio nrate so fpesticide s insoil 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 :

da/dt = -k a 0) inwhic h a =mas sconcentratio no fsubstanc e (mg m ) t =tim e Cd) k =rat ecoefficien tfo rconversio n (d"1) a

Integration of Equation 1 yields

ko = -in {c/oo)/t (2)

Table5 . Physico-chemical propertieso 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) 0,0-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) 0

CH.O^ S r 3\ IIÏP-S-CH „

CH30

Molecular formula (1) C10H12N303PS2 Molecularmas s (0 317.3 Meltingpoin t (O 73-74 C (purecompound ) (2) 65-68 C (technicalmaterial ) Vapourpressur e (3) <5 1mP aa t2 0° C (5) ca0. 5mP aa t2 5° C Solubility (4) inwate rabou t3 3g m atroo mtemperature ; soluble inman y organic solvents

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

Chemicalnam e (1) 0,0-dimethylS-[2-(methy l ,imino)-2-oxoethyl] phosphorodithioate Tradename s (1) Cygon (AmericanCyanamid ) FostionMM , Rogor (Montecatini);Roxio n (Cela); Perfekthion(BASF )

Structuralform i la (2) CH,0V S 0 .CH., 3 \n II

^>P-S-CH2-C-N

Molecularformu ! a (0 CH5(H T12 N03PS2

Molecular mass (1) 229.2 Meltingpoin t (0 51-52° C Boilingpoin t (3) 117° C(13. 3Pa ) Vapourpressur e (3) 1mP aa t2 0° C (1) 1.1mP aa t2 5° C Solubility (0 ,(2) inwate r2 5k gm at2 1 Z;mos tsolubl ei n polarsolvent ssuc ha smetianol ,ethano lan d otheralcohols ;ketone s su:ha saceton ean d cyclohexanone;lowe rsolub i Llityi napola r solventssuc ha sxylen ean ! >.i aliphaticssuc h ashexan e

inwhic h

o o =concentratio na ttim ezer o (mgm ")

Thehalf-lif eo fa compoun d (£,)i ssimpl y related toit srat ecoefficient ,accordin g thefollowin grelationship :

t,= 0.693A c (3)

Half-liveso fazinphos-methy lan ddimethoat ei n variousmedi aunde rdifferen tenviron - mentalcondition sa sreporte di nliteratur ewil lb e brieflydiscusse d inth efollowin gsec - tions.Th eliteratur edat ao nrat ecoefficient so f both compoundsi nsurfac ewate runde r variouscircumstance swil lb ediscusse di nrelatio n ta ourow nexperiment si nwate rfro m outdoortanks ,whic hwil lb edescribe di nChapte r6 .

Conversion rates and pathways of azinphos-methyl

Theconversio nrat eo fazinphos-methy lo ncrop siin dtre efruit si sdependen to nvar ious climaticcondition san do nth enatur eo fth eplin tmaterial .O nvegetables ,forag e cropsan dtre efruit sgrow nunde rfiel dconditions ,th eaverag ehalf-lif efo razinphos - -methylrange sfro m3 t o8 day s (ChemagroDivisio nResearc hStaff ,1974) .However ,unde r certaincircumstance sth ehalf-lif ema yb esubstantia l longer.Fo rexample ,Günthe re tal . (1963)foun dtha ti nCaliforni ath ehalf-lif eo nan di nth epee lo 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-S-CH2-R

CH30 (II) Mercaptomethylbenzazimid e H-S-CH- 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) ff-methyl benzazimide (VII) Anthranilic acid

N%,

340-400days . Theconversio nproduct so f L CJazinphos-methylo nbea nleave swer einvestigate db y Wieneke& Steffen s (1976).The yfoun dtha t1 6radioactiv ecompound scoul db eextracte d withorgani csolvents .Th ecompound sI ,II Io r IV,an dV fro mTabl e7 wer eidentified . Fourteenwater-solubl eproduct scoul dno tb eidentified .Thi sca nb esee na sa nindicatio n ofth edifficultie s inseparatio nan danalyse so fpola ran dthu shighl ywater-solubl econ versionproduct so fazinphos-methyl . Studieso nsoi lpersistenc eo fazinphos-methy la sdescribe di nth eliteratur esho w thatth econversio nrat ei sdependen to nman yfactors ,suc ha sformulation ,moistur econ tento fth esoil ,soi ltype ,biologica lactivit yo fth esoi lan dvariou sclimati ccondi tions.Schult ze tal .(1970 )foun dtha ti nfiel dtrial swher eazinphos-methy lwa sapplie d asa nemulsio no na silt-loa msoi l S0%wa slos ti n1 2days .Applicatio ni ngranula rfor m followedb yrotar ytillag et oa dept ho f0. 1 mrequire d 28day sfo ra S0%loss .Afte r1 year,13 1o fth eapplie dgranule swa srecovere d inth efor mo fazinphos-methyl .Th econ versionproduct s II,II Io rIV ,V an dV Ifro mTabl e7 wer eidentified .Fou runidentifie d compoundswer efound .Yaro ne tal . (1974a)reporte dtha ti na silt yloa msoi l (organic matterconten tlowe rtha nH , pH8.4 ,cation-exchang ecapacit y 134mmo lk g andvolum e fractiono fwate r50% )th erat ecoefficien tfo rconversio nwa s0.01 1d at6 Can d0.05 3 d"1 at2 5°C .Lowe rrat ecoefficient swer efoun db y Iwatae tal . (1975)i ndus tfro msever alsieve dsoils .Th eapproximat erat ecoefficien tfo rconversio na t3 0° Cwit hconstan t overhead illuminationfro mfluorescen ttube srange dfro m0.0 7d fora cla yan da sil t

16 loamsoi lt o0.00 87 d for,-a sand 1 y loaman da loai i soil.Th emoistur econten twa s 40%o f themaximu mretentiv ecapacity ,a sdetermine d forursieve dsoils. Recently,th ephotodecompositio no f [CJazinplos-methyli na thi nlaye ro fsoi l (of2 kgmois tsilt-loa mpe rsquar emetr eo fglas ssurface )wa sstudie db yLian g& Lichtenstei n (1976).The y foundthat ,afte r8 h exposur et osunlight ,abou t80 1o fth eorigina ldos e wasrecovere db ybenzen eextraction .Nearl y3.5 %wa s convertedt onon-insecticida lwater - -solubleconversio nproduct san dapproximatel y 16%v>a sfoun da sboun d residue.I nthei r controlmeasurement si nth edark ,n odegradatio nan d noboun d residueswer efound , Theeffect so fligh tan dp Ho nth econversio n of L QJazinphos-methy li na naqueou s -3 solutiono f2 g i J wer e investigatedb yLian g& Licfvtenstei n (1972).Th econversio no f azinphos-methyli nth eaqueou s solutionexpose dt oultraviole t lightwa sver yrapid .Afte r twohour sexposure ,the yfoun d that 56%o fth edos e :ouldb erecovere db ychlorofor mex traction;thi sphas econsiste dmostl yo fbenzazimid e (V)o rth eoxyge nanalogu eo fazin phos-methyl (I) (451o f Capplied) ,4 1anthranili caci d (VII)an donl ya fe wpercen to f compounds II,II Io rIV ,an dV I (Table 7). About25 %o fth edos eremaine di nth ewate r phasean dth emissin gradioactiv emateria lwa s assumedt ob evolatilized . Theconversio no fazinphos-methy l inwate ri shighl ydependen to npH ,a swil lb edis cussedi nmor edetai li nChapte r6 . Liang& Lichten s:ei 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[ 14c]azinphos-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 s IIIo rIV ,an dVI , totalling 34%o fth e 14C applied;30 %o fth e14 Cwa s convertedt ocompound sV o rI , and 18%o fth e Cwa srecovere da 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 dtha tth erat ecoefficien tfo r conversiono fdimethoat ei nfield - -sprayedlettuc ewa sabou t0.1 7d ". Pre ee tal .(1 9 16) foundtha t 50%o fdimethoat eo n apple-treeleave sdisappeare 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 d thedeclin erat eo fdinethoat ei na sand y loamsoi l (pH5.5 ) _2 afterapplicatio no f1 k go factiv eingredien tpe rhectar e (0.1g m )a semulsifiabl e concentrate.Th esamplin gdept hwa s7. 5cm .Unde rdry : ingconditions , k was0.1 7d and after3 3m mo frainfal l k was0.2 8d . Inincubatiq nstudies ,Bach e& Lis k (1966)foun d -1 a k of0.4 3d ina mois tsilt-loa msoi l(p H 5.8). Whendimethoat ewa smixe di na mois t loamsoi l (2.3%organi cmatter ,p H5.7 ,75 %o ffiel d capacity)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).Significan tconversio no fdimethoat e tbit s oxygenanalogu e (VIII,Tabl e8 ) wasmeasure di ndifferen tsoil sb yBach e& Lis k (1966)an db yDuf f& Menze r (1973). Radioactive [ PJdimethoat ewa srapidl yhydrolyse d inwate ra tp H11 .I n2 h , 87% ofth edimethoat ewa sconverte dt owater-solubl ematerials ,whic hremaine di nth eaqueou s phaseupo nextractio nwit hchloroform .Th ewater-solubl econversio nproduct swer epredomi -

17 Table8 .Structura l formulaeo fconversio nproduct s ofdimethoate .

(VIII)Dimethoat eoxyge nanalogu e (=omethoate , ^H_0 0 0 /CH dimethoxon)Tradenam eFolima t NP-S-CH-C-N / \ N (IX) Des-methyldimethoat e CH„0C H00 0 CH„ H 3\ il>-S-C Hn-C- /N 3 2 HO' N, (X) Dimethoate carboxylicaci d CH„0 S 0 3 \ll <^ P-S-CH- C / 2 \ CH0 OH (XI) Dimethyl thiophosphoric acid CH^O S 3\,| / P-OH CH30

nantlydes-methy ldimethoat e (IX)(49.3% )dimethy lthiophosphori caci d (XI)(32.81, )an d dimethoatecarboxyli caci d (X)(9.5% )(Tabl e8) .Mor etha n97 %o fth elabelle dmateria l 32 inth echlorofor mextraextrac c t (about13 %o fth e P)wa sfoun dt ob eunchange ddimethoat e (Brady& Arthur ,1963) .

3.4 ADSORPTIONAN DLEACHIN GO FTH ECOMPOUND SI NSOI L

Theexten tt owhic hpesticide sar eleache d insoil si smainl ydetermine db yadsorp tioncoefficient ,rat ecoefficien tfo rconversio no fth ecompound ,characteristic so fth e soil,climati ccondition san dplan tgrowth .Th eexten to fgroundwate rpollutio nthroug h leachingunde rvariou scondition sca nb eapproximate dwit hcomputationa lmodel s (Leistra& Dekkers, 1976). InTabl e9 ,adsorptio ndat ao fazinphos-methy lar ereporte da smeasure db yBaye rA.G . (1978). Theadsorptio ncoefficients ,determine db ya batch-equilibriu m techniquesho wtha t azinphos-methylwil lb erathe rstrongl yadsorbe do nsoils .Thi sca nb eexpecte di nvie wo f itslo wsolubilit yi nwater .Becaus eo fth erelativel yhig hadsorptio ncoefficien tan da considerablerat eo fconversio nunde rsom efiel dconditions ,azinphos-methy lma yb etrans portedi nsoil st oonl ya smal ldepth .Fo rexample ,Yaro ne tal . (1974b)foun d thatazin phos-methylwa sno ttransporte ddeepe rtha n0. 3m i na sand yloa msoi l (organicmatte r contento f0.6 %an dp H8.4 )afte rirrigatio na ta rat eo f0.2 8m irrigationwate rove r3 8 days. Thesystemi cinsecticid edimethoat e ishighl ysolubl ei nwate r (Table6 )an di sad sorbedt oonl ya limite dexten to nsoi lmaterial .Fo rexample ,th eadsorptio ncoefficien t -3 3 -1 ontoa sil tloa msoi l (organicmatte rconten to f2.7% ) isabou t0.2 1 10 m kg (Graham- -Bryce,1969) .Whethe rgroundwate rpollutio nwit hdimethoat ewil loccu rdepend so nman y factors.Th eleachin go fdimethoat efro ma sand y loamfiel dwit ha potat ocro pca nb e estimated fromth eresult so fth esimulatio nexperiment so fLeistr a& Dekker s (1976).As suminga rat ecoefficien tfo rconversio no f0.0 3d (Section3.3) ,a nadsorptio ncoeffi - Table9 .Soi l characteristics andadsorptio n coefficientso fazinphos-methy l asmeasure db yBaye r A.G. (1978).

Soil 1 Clay %Sil t %Organi c (water) ,%\._, . (<2um ) (2-50um ) matter (m->k g' ) Sandy loam 10.5 33.1 1.1 6.4 3.310"i ? Silt-loam 20.5 62.8 1.8 5.5 11.0 \0~\ Highly organic 19.0 56.8 4.6 5.4 28.5 10 silt-loam

cient zeroan d anannua l infiltrationo frainfal l0 66m ,th eexten to fleac h toplaye r1 m thickwa scompute dt ob eles s than0 . %o fth edose .

3.5 VOLATILIZATIONO FTH ECOMPOUND S FROMWATE RBODIE S

Therat eo fvolatilizatio no fpesticide s from \rate rbodie st oth eatmospher e canb e estimatedb yprocedure so fLis s& Slate r (1974)an d ofMacka y& Leinone n (1975). They useda two-laye rmodel ,compose do fa liqui d filmari d aga sfil mseparate db ygas—liq - uid interface.Th emai nbod yo feac h fluidwa s assured tob ewel lmixed .Transfe ro fth e pesticides throughth elayer swa sb ymolecula rdiffi s ion,whic hca nb edescribe db yFick' s -2- 1 first law.Th earei cmas s flux F(m gm d )acros : thegas—liqui d interfaceb yvolati - lizationca nthe nb eexpresse da sa functio no fth e concentrationdifferenc e acrossth e layersan dth eexchang e constantsfo rth eliqui dan d gasphases ,respectively ,a sshow ni n Equation4 .

Fv = V°w -c i,w)=Yöi,a' °a 3 (4) inwhic h ew„an dc a aremas s concentrationso f substaic e inope nwate ran di n freeai r (mg m ) c.i, wan de . i,ara eequilibriu n mmas sconcentration s ofsubstanc ea t gas—liquid interface [mg m" ) k-.an d k areexchang e coefficientsfo r liq|aidan dga s phases (id'1)

Ifth eexchangin g compound obeysHenry' slaw , tien, at the equilibrium presumed at the interface

H a. (5) i,w inwhic h H= Henry' s constant (1)

This constantca nb eestimate d fromth equotien t ofmas s concentrationo fsaturate d vapour (viavapou rpressure )o fth ecompoun dan dth e solubilityo fth ecompoun di nwater . Eliminationo f a. i,ana d a. i,inwEquation ^ s4 an d 5 yields

19 which canb ewritte na s

F =fe . ( c - a /H) (7) and

lAt>1 =V ^ + Miß feg) (8) inwhic h

Themas s transfer coefficients canb econsidere dt ob econductivitie san dthei rre ciprocalst ob eresistance sb yanalog yt oOhm' s law. Combiningth earei cmas s flux,F ,acros sth einterfac ei na balanc e equationi na n unsteady statemode l (andassumin gn oothe rpathway so floss )lead st oth edifferentia l Equation9 :

WwCw)/dt = -kttl{cw-ca/H) (9) inwhic h

h =wate r depth (m)

Ife isnegligible ,whic hmean s that thebackgroun d atmospheric levelo fth ecom poundi slow ,the nEquatio n9 ca nb esimplifie dan da half-lif e i, canb esimpl yderive d 2> v fromEquatio n9 :

*i,v =°- 693 \A,i (10> inwhic h

t, =volatilizatio nhalf-lif e (d)

Thesignificanc eo fvolatilizatio nfo rth emode l compoundswa s estimatedb yEquatio n 10,usin g the data fromTable s5 an d6 .Wate rdept hwa s assumedt ob e0. 2m .Th etransfe r coefficients (k andk ) a t2 5° Cwer eestimate db yth eprocedur eo fLis s& Slate r (1974). Thevolatilizatio n half-liveso fazinphos-methy lan ddimethoat ewer e calculatedt ob e41 3 dan d0.1 7x 1 0 d,respectively .A tlowe rai rtemperatur e (prevailing under fieldcondi tions), thevolatilizatio nhalf-live s couldb eeve n longer.Th evolatilizatio no f [ cj- -azinphos-methyl fromta pwate ra t3 0 Cwa smeasure db yLichtenstei n& Schult z (1970). They foundtha tafte ron eda yonl y traceso fradioactiv e azinphos-methylwer e foundi nva -

20 pour traps.Th epreliminar y conclusioni stha tth e rateo fvolatilizatio no fth emode lcom - pounds fromsurfac ewater swil lb eo fmino rimportanc e

3.6 SOME TOXICOLOGICAL DATAO FTH ECOMPOUND S

Azinpkos-methy I

The acuteora l LD™ ofazinphos-methy lfo r feilal e andmal e ratsvarie sbetwee n 10-20 mgpe rkilogra m liveweight (BayerA.G. , 1971).Th e toxicityo fmetabolite so fazinphos-me - thylha sbee nindicate db yth eWH Oa sa nare afo r urther research (WHO/FAD, 1974). The acute toxicityo fazinphos-methy lt oa varietyo faquati corganism sha s beenre - viewedb yU SEnvironmenta l ProtectionAgenc y (197:i) However the reportedAmerica nspe - cieso faquati c organisms areno t fully comparable with thespecie soccurrin gi nDutc hsur - facewaters .Nevertheless ,som edat aar eshow ni n Table 10.Thes e date show thehig hacut e toxicityo fazinphos-methy lt ocrustaceans ,severa[ l fishspecie san dsom esalt-wate rorga - nisms.Th e differencesi nth eacut e toxicityt o aq^aticorganism sar efirs to fal ldeter - minedb yth esusceptibilit yo fth e species.Howevel r ,material san dtes tmethod sma ycaus e substantial variationi nth eacut e toxicity.I ti s wellknow n thatacut e toxicity canb e modifiedb yfactor s like formulation,temperature , waterhardness ,anima l sizean d age, previous exposure,physiologica l condition,an do c :urrenceo fothe rpesticides . More researcho nsemi-chroni c and chronic effïct s andno-effec t levelso fazinphos -

Table 10.Toxicit y ofazinphos-methy l to aquatic otganisms.Sources :(1 ) References inU SEnvironmenta l Protection Agency (1973); (2)Adelma ne tal . (1976); (3)Baye r A.G. (1971); (4)Portman n &W i ls^n (1971).

Organisms Acute toxicity (LC,_) Noeffec t Source mass cone exposure level (mg m-3) time CO Crustaceans : Garrmarus fasciatus 0.10 96 (1) Asellus brevicaudus 21 96 (1) Insects: Ophiogomphus rupineulensis 12 96 1.73 (30d ) (1) Pteronaroys oalifovnioa 1.5 96 (O Fishes: Pevoa flavesoens 13 96 (1) Iatalurua punetatus 329 0 96 (1) Micropterus salmoides 5 96 (1) Pvrnephales promelas 1 950 96 0.51 (testo n (2) Lebi8te8 reticulatus 100 96 fecundity) (3) Cavaesiua auratus 100 0 96 (3) Saltwater organisms: Pandalus montagui 0.3-1 48 (4) Crangon orangem 0.3-1 48 (4) Caroinu8 maenas 33-100 48 (4)

1. LC50 i8 themas s concentration of toxicant that kills50 %o fth e organisms exposed toi tdurin g a specified exposure time.

21 -methylo naquati corganism swil lb enecessar y torecommen dcriteri afo rwate rquality .

Dime thoate

Theacut eora lLDr no fdimethoat efo rwhit erat si s60 0m gk g (Dautermane tal. , 19S9).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 gkg" 1, respectively (Dautermane tal. , 1959).Thu sth eoxyge nanalogu ei sth emos ttoxi ccompound . Toxicitydat ao fdimethoat e toaquati corganism sar epresente di nTabl e 11.Thes eda tasho wtha tdimethoat ei shardl ytoxi ct ofish ,bu tsom esalt-wate rorganism swer eshow n tob ever ysensitiv et odimethoate .Omethoat eappeare dt ob emuc hmor etoxi ct o Daphnia magna thandimethoate .

Table 11.Toxicit y ofdimethoat e toaquati corganisms .Sources :(1 ) Canton (1977); (2)Marti n& Worthin g (1977); (3)Portman n& Wilso n (1971).

Organisms Acut etoxicit y (LC50 ) Source

masscon e (mgm ) exposure time (h)

Crustaceans: Daphnia magna 6 400 48 (1) (Samespecies , 31 48 (0 omethoate)

Fishes: Gambusia affinis 40 000-5000 0 96 (2) Salmo gairdneii 10 000 48 (1) Lebistes retiaulatus 570 000 96 (0 Saltwaterorganisms : Pandalus montagui 33 48 (3) Cvangon orangon 0.3-1 48 (3) Cavoinus maenas >3 300 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 RWA'?E RSAMPLIN G

Variousprocedure s havebee ndescribe dfo rth ecollectio no fsample sfro msurfac e waters.A syet ,method san dterminolog y forwate r samplinghav eno tbee n standardized (Josephson, 1974).Fo rpesticides ,th e selectiono: :method si sdetermine db yth eobjective s ofth estud yan dth esamplin gsituatio n (MonitoringPane lo fFWGPM ,1974 ;U SEnvironmenta l ProtectionAgency , 1974). One shouldalway sb eawar eo fpossibl e interactions betweenpesticide san dsample r components.Man ypesticide s showstron gadsorptio no nth esurfac eo fmaterial s like rubber andplastics ,whic har ecommonl yuse dfo r collectir.gwate r samples.Par re tal . (1974) sometimes founda considerabl eadsorptio nb ysample rcomponents .Variou s admixturesma yb e released frompolymers ,whic h interferewit hchemica lanalysi so fth epesticides .There forea siner ta materia la spossibl e (preferably glasso rstainles ssteel )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 i stainless steelcontaine r intoth ewa terbody .Fillin go fth econtaine rwhil ehel d justbeneat hth ewate r surfaceavoid s skim mingof fa floatin g film,throug hwhic ha sampl ewoul dno tb erepresentative .Felt z& Cul - bertson (1972)pointe dou ttha ta hig hpercentag eo fal lwate rsample si npesticid emoni toringprogram swa sobtaine db yshallo wemersio no fcontainers .Suc hsample sar e common lyreferre dt oa sdi po rgra bsamples . Especiallypesticide s showinga hydrophobi c character,fo rinstanc emos to fth echlo rinatedhydrocarbons ,ma yno tb eequall ydistribute d overth edept ho fa watercourse . The highest concentrationso fthes epesticide sma yoccu: -a tth esurface ,especiall yi fthi si s coveredb ya noil y film. Ifwate rsample snee dt ot>< : almostfre e fromfloatin gmaterials , bottle-samplers canb eimprove db yconstructin ga s]>ring-loade dcap .Thes espring-loade d capsca nb eopene da tan ydesire d depthb ypullin g(i na line .A recen tconstructio nwa s describedb yGum pe tal . (1975). Mitchell& Dicke y 1973)develope da sample rwit ha spring-loaded lockinguni t thatallowe d samplingo f waterfro msmal lpond so rlagoon sb y oneperso n standingo nth ebank . Besidesth edi p samplers,tw oothe rgroup so fsamplin g devicesar ei ncommo nuse ,par ticularlyi nautomati cwater-samplin gprograms ,namel ypum pan dvacuu m samplers.A disad vantageo fthes e typesi sth eris k thatth eorifice so fth esuctio npip ema yge tplugged . Mosto fth eautomati cwate rsampler snee delectri cpowe rsuppl yfo rpumpin gan dfo rcool ingth e samples.A nexceptio ni sa vacuum-typ eo fsaiple rcompose do fbottle s evacuated before samplingan dequippe dwit hpinc hvalve s (Hergsrt& Gall ,1973) .Thes evalve sar e openedi ntu mb ya time d trigger.Thi s samplerha s separatetube sfo reac hsampling .A

23 disadvantageo fthi ssample ri sagai npossibl eadsorptio no nan dreleas efro mth ePV C tubesan dth erubbe rclosin gtubes .Modificatio nwil lb enecessar yfo rth esamplin go f waters instudie 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 stainlessstee lbarre lwa s0. 4d m (Figure 2b). Bybulkin 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 di nth epresen tstudy . a.Stainles sstee ltub euse dfo rsamplin go fdrainag e ditchesan dgroundwater . b.Stainles s steeldi psample ruse dfo rsamplin go f drainageditches . c.Glas sdi psample ruse d forsamplin go flarg ewater courses.

24 teda tth eend .Th eextende d lengtho fthi sfishin j rodwa smor e than 5m (Figure2c) . Frombridge s over suchwatercourses ,th eglas sbottl e was repeatedly lowered toth ebotto m and slowly raisedt oth ewate rsurfac edurin g filling . Thisprocedur ewa srepeate d atdif - ferentplace s across thewate rbod y toge t asampl e representative forth eentir ecross - -section. pesticide residues inditche safte r Fordetaile dmeasuremen t ofth edistributio n cf wasdeveloped .Thi s samplercon - spray-driftcontamination ,a simplevacuum-typ esa npie r mm)fitte dwit h acoppe rwir e netting sisted ofa stainless steel tube (innerdiamete r 6 filter atth een d (openingso f0.3 3 mm)an dconnectie d toa glas sbottl eo f2 d m with stopperan dcoc k (Figure 2a).Thi sbottl ewa s evacuated witha 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| d for taking samplesdurin gdispersio n measurements inwatercourse swit h flowingwate r (Chaptie r 11).Fo r thispurpose ,th esuc - tioncapacit ywa senlarge db yaddin ga vacuu mreservoi r ofglass ,volum e 10d m .Fou r seperate stainless steeltube swer e installedwit h the loweren da tdifferen tposition s in thewette d cross-section ofth editc han deac hwa s connectedt oa glas sbottl eo f0.2 5 dm. These smallbottle swer e connected,b ypolyethylen e tubesan dglas scocks ,t oth e evacuated glassreservoir .Thu s foursample s couldb e sucked upnearl y simultaneouslywithi na few seconds.

4.3 SHORTREVIE WO FDEVICE SAN DPROCEDURE SFO R SAMPLING BOTTOMMATERIA L

Wateran dbotto msedimen tmus tb esample dalmos t simultaneously forstud yo f thephys - ico-chemicalbehaviou ro fpesticide s inditches .I n manyinstances ,pesticid e concentrationsi nth editc hbotto mdecreas e stronglywit h de3th . Foraccurat e sampling ofbotto m material,goo dmethod s areneede dgivin g least disturbancean dallowin gdivisio no fth e sample intothi nlayers . Littleprogres sha dbee nmad e indevelopin g equipmentt ocollec t representative sam- piesnea rth e liquid—solid interface,whic hi s difficultt osampl ewithou t disturbance (Monitoring Panelo fFWGPM , 1974). Sampling ofth ebotto mmateria l inpond san d dutches foranalysi so fpesticid eresi - duesusuall y involves dredgingo rcorin gdevices . Tie well-knownEkma ndredg e (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 ean dothe rdredgin g devices istha tpar t ofth ewate ran dbotto mmateria l issqueeze d outo fth edredg ewhe n iti sclosed .Further ,man ygra bsample sar e collected fromunascertainabl e depth (Aarefjord, 1972;Larimore , 1970).T oovercom e this problem,Jackso n (1970)constructe d a controlled-depthvolumetri cbotto msample r Concentration s ofcamphechlo r (Toxaphene)i n sampleso flak e sedimentsobtaine dwit ha nEkma n dn;dg e were generallymuc h less thanthos e insample sobtaine dwit ha core r (Veith& Lee ,197 1 |.Thes eauthor smeasure dcontent sex - pressed indr ymu do f6. 2 mg kg indredg e samples ando f90. 0m g kg inth -1e 0t o0.0 5 m sectiono fcor e samples. • Coringdevice sallo wmor edetaile d measurement 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 s lackeffectiv eseal st ohol da sampl ei nplac e whenth esample rleave sth ewate r (Feltz& Culbertson ,1972) . Seriousdisturbanc eca noc 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 d lockingsyste mtha tslowl yclose sa botto m lidjus tbefor ea to pone .

4.4 SAMPLINGO FBOTTO MMATERIA L INTH EPRESEN TSTUD Y

Tosampl ebotto mmateria l inrelativel y shallowditche 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 d4) .Adsorptio no 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 t interface.Next ,th eto po fth eholde rwa stightl yclose db yturnin g amille dkno ba tth eto po fth ero d (Figure4) .Th eholde rcontainin gth ecolum no 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 ecap .Sinc eth etube swer etransparent , immediatevisua linspectio no fth eintac tmu dcor ewa spossible . Theholde rstoppere da tbot hend swa splace dverticall y ina crate ,i nwhic hsi xcol umnscoul db ecarrie dt oth elaborator ywithou tdisturbance . Theoverlyin gwate rwa sslowl yremove dan dfo ra fe wday sth ecolum nwa 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 scolum nwa sagai nplace d inth edeep - -freezera t-2 0°C ,pendin gdivisio nint othi nslices ,extractio nan danalysis . Undisturbedmu dcore st otes tfo rpesticid eresidue si ntan kexperiment swer etake n withpoly(methy lmethacrylate )tube s (innerdiam .4 0m m; ou tdiam .5 0mm ;lengt h41 0 mm), bevelleda tth elowe rend .Durin gsampling ,th eholde rwa sslowl ypushe dint oth ebotto m materialan dwa sclose da tth euppe ren dwit ha stoppe rbefor elifting .Afte rraisin gth e holderfro mth ebottom ,anothe rstoppe rwa spushe d intoth elowe rend ,jus tbefor eliftin g thetub eabov eth ewater .I nth elaboratory ,th ecolumn swer eprocesse di nth esam ewa ya s theditch-botto mcolumns ,removin gth eoverlyin gwate ran dfreezin ga t-2 0 C.

26 Figure 3. Sampler for bottom material, a. Poly (methyl methac^yl ate) tube. b. Stainless steel roc. with closing system, c. The tube connected to the closing system with two adjustable catches.

Figure 4. Cross-sectidn of the sampler for bottom material. 1Mille d knob. 2Handgrip . 3 Stainless steel tube, inner diam. 19 outer diaW 25mm . 4 Stainless steel rod, diam. 12mm , with screwthread below. 5 Cover plate with six bore holes, diam. 12mm . 6 Rubber washers. 7Tw o adjust able catches. 8 Stainless steel flange. 9Poly(methy l methacrylate) sample holder, inner diam. 80mm , outer diam. 90mm . 10Stainles s stsel cutting ring. 11 Rubber ring. 12Polyethylen e cover. Working principle: Before lowering into the ditch, the flange 8mus t be screwed down with the nilled knob 1.Whe n lifting, the flange 8mus t be close1 agains t the stainless steel edge of the cover plate 5.

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

5.1 INTRODUCTION

Theprocedur efo rth eanalysi so fpesticide si nsample so fwate ran dbotto mmateria l involvesvariou sstages .Firstly ,th epesticid eo rit sconversio nproduc tmus tb eextracte d asselectivel yan defficientl ya spossibl e fromth ewate ro rmu dsampl eint oa suitabl e solvent.Th eextrac twil l thenusuall yb ecleane du pt oeliminat ecompound s interfering withdetection .Man ypesticide san dsometime sals othei rconversio nproduct sca nthe nb e measuredquantitativel yb ygas—liqui dchromatography .Finally ,a nadditiona lidentifica tionma yb enecessar yt oconfir mresults .

5.2 METHODSFO REXTRACTIO NO FPESTICIDE SFRO MSURFAC EWATER S

Twotype so fextractio nmethod sma yb euse dfo rextractio no fpesticide sfro msurfac e water.Ove rsevera lyears ,mainl yliquid—liqui dextractio nmethod shav ebee nused .I n recentyears ,technique sinvolvin gadsorptio no nvariou ssoli dadsorbent si ncolumn shav e receivedgrowin gattention . Theliquid—liqui dextractio nmethod sca nb edivide d intobatc hequilibratio nan dcon tinuousextractio nprocedures .A limitingfacto rfo rliquid—liqui dextractio nmethod sma y beth epartitionin go fth epesticid ebetwee nsolven tan daqueou sphase .Repeate dextractio n withcomparativel ylarg evolume so fsolven tma yb erequire dt oge tacceptabl erecover yo f ratherpola rsubstance sfro mwater .Example sar eth erathe rpola ran dthu swater-solubl e metaboliteso fvariou sorganophosphoru spesticides . Thebatc hequilibration/extractio ntechnique ,usin ga separator y funnel,ofte nyield s highrecoverie so fapola rt oslightl ypola rorganochlorin ean dorganophosphoru spesticide s (Konrade tal. ,1969 ;Grève ,1972 ,Riple ye tal. , 1974).A nadvantag ei stha ta larg enum bero fsample sca nb ereadil yextracted .A disadvantag eo fth eseparator yfunne lextractio n procedurema yb eth elimite dvolum eo fwate rtha tca nb eextracte da ton etime .Continuou s liquid—liquidextractio ntechnique sallo wextractio no flarg evolume so fwater ,thu si n principlemuc hlowe rconcentration sca nb emeasure d (Goldberge tal. , 1971;Meijer s& va n deLeer ,1976) .However ,mos to fth econtinuou sliquid—liqui dextractio nprocedure sar e toocumbersom e foranalysi so flarg enumber so fsamples .Furthe rther ema yb echemica lcon versiono fth epesticid edurin gth eheatin go fth esolven ti ncontinuou sextractor swit h adistiller . Theothe rgrou po fextractio nmethod si sbase do nadsorptio nont oa nadsorben ti na column.Th eextractio nefficienc yo fpesticide sfro mwate rsample swit hsom enon-ioni cma terialswil lb ediscusse dbriefly . Activatedcarbo ni shighl ysuitabl efo radsorptio no fsevera lpesticide sfro mwater ,

28 butadsorbe dpesticide s aredifficul t toelut e completely. Extractiono f organophosphorus pesticides from theactivate d carbonusuall y gives .owrecoverie s (Eichelberger &Lichten - berg, 1971a). Polymericresi nAmberlit eXAD- 2 (apolyme r of styrenean ddiviny lbenzen ewit h low polarity)ma yb euse d forextractio no fsevera lo rgsnochlorinepesticide san dpolychlori - natedbiphenyl s fromnatura lwater s (Coburne t al., 1977).A disadvantage ofsuc hresin s istha tbefor euse ,extensiv e cleaning ofth eresin s withsolvent s isnecessar y toreduc e thebackgroun d ofinterferin gcompound s toacceptabl e levels. Polyurethane foamsar eonl yadequat e foradsorji t iono fapola rorganochlorin epesti - cidesan dpolychlorinate dbiphenyl s (Musty& Nickleï S 1974). Preliminary resultsdescribe db y Leonie t al. (J197S)indicat e thatth eus eo fTena x (aporou spolyme rbase d on2,6-diphenyl-p-phenylen e oxidemad eb yAKZO ,Arnhem )i sprom - isingfo rextractio no fpesticide s fromwate r Particularl y theextractio no forganophos - phoruspesticide syielde d reasonableresults ,eve n Et lowconcentratio n (1m gm ") . Theadsorptio no fpesticide s fromsurfac e wateis mayb e adversely affectedb yth epres - enceo fothe rcontaminant s andnatura l substancesii . water (sucha ssurfactants ,fatt y substancesan dalgae) . Extractiono flarg evolume s cf surfacewate rwit hadsorbent sma y alsoyiel dhig hconcentration s ofinterferin g compounds Furtherdetaile d investigations arenecessar ybefor e theadsorptio ntechnique sma y be utilized forextractio no forgano - phosphoruspesticides .

5.3 EXTRACTION OFAZINPHOS-METHY LFRO MWATE R SAMPLES

Azinphos-methyl and itsoxyge nanalogu ewer e extractedfro msample so fsurfac ewate r with aliquid—liqui dextractio nmetho d (Grève,19721 ) Theunfiltere dwate r samples (0.1 3 3 were extracted ina separatory dm fromth etank san dusuall y 1d m fromwatercourses ) funnelwit hconsecutivel y 100,5 0an d 50c m port ions ofdichloromethan eb y handshaking eachtim e foron eminute .Th ecombine d extractswer e driedo ncalcinate dgranula rhteuSO^ , concentrated toa fewcubi ccentimetre s ina Kudernal ' -Danishequipmen tan devaporate d to dryness atroo mtemperatur ewit ha gentlestrea mo f nitrogengas .Th eresidu ewa s dissolved _3 ina know nvolum e (0.5c m ormore )o fa suitable solvent (acetone,hexan eo rethy l acetate)correspondin g toth esolven tuse d forth e referencesolution .Th esolution swer e immediatelyplace d ina deep-freeze r toavoi dchemida l conversionan d evaporationo fth e solvent,befor e clean-upan dga schromatography .Th e procedurewa s sufficiently rapid to allowextractio no fu p to2 4wate rsample s ina day . Themea nrecoverie so fazinphos-methy l and itsloxyge nanalogu e fromspike dwate rsam plesar epresente d inTabl e 12.Th e levelso fspikin g (induplicate )wer e 1,1 0an d 100 mgm forazinphos-methy l in6 drinkin gwate r samplss and 100m gm fo-r3 azinphos-methy l and itsoxyge nanalogu e in 12surfac ewate r samples At thethre espikin g levels,n osig - nificantdifference swer e foundi nth erecover y of C31impounds .Th e effectso fshakin g intensitywa s investigatedbecaus e somesurfac e water s containingman yalga e tendedt o formheav yemulsion sdurin gvigorou s shaking.Nearl y allsurfac ewate rsample swer eex - tractedb y 'normal'shakin g (about8 0shake spe r minute)yieldin g goodrecoverie s for azinphos-methyl andit soxyge nanalogue .

29 Table 12.Recoverie so fazinphos-methy lan d itsoxyge nanalogu efro m spikedwate rsamples .

Compound Typeo f Detailso n Numbero f Recovery (%) Coefficiento f 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 eslo w ,norma l andvigorou sshakin g waswit h about 40, 80 and 120shake spe rminute ,respectively .

5.4 EXTRACTIONO FDIMETHOAT EFRO MWATE RSAMPLE S

Withth eprocedur efo rextractio no fazinphos-methy lfro msurfac ewate r (Section5.3) , dimethoatecoul dals ob eextracte dwit hacceptabl erecoverie s (Table 13).Th ecomparative 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 (50cm 3)wit hconsecutivel y 100,50 ,5 0an d5 0c m portionso f chloroform,whic hresulte d ina naverag erecover yo f91 % (coefficiento fvariatio n5°s) .

5.5 METHODSFO REXTRACTIO NO FPESTICIDE SFRO MBOTTO MMATERIA L

Pesticidesca nb eextracte d fromsoil san dbotto mmateria lb ya variet yo ftechnique s sucha sshaking ,tumbling ,blending ,Soxhle trefluxin gan dultrasoni cvibration .Th echoic e ofth esolvent so rsolven tcombination sdepend smainl yo nth enatur eo fth esubstanc e

Table 13.Recoverie so fdimethoat efro mspike dwate rsamples .

Typeo f Detailso nprocedure 1 Numbero f RRecovere y (%) Coefficiento f water extractions variation (%)

Drinking normalshakin g 6 88 7 water slowshakin g 6 69 11 vigorousshakin g 6 90 doublevolum eo fsolven t 6 96 Surface normalshakin g 12 94 water

1.Th eslow ,norma lan dvigorou sshakin gwa swit habou t40 ,8 0 and 120shake spe rminute ,respectively .

30 tob eextracte d (Caro& Taylor , 1976). Little informationwa savailabl eo nth eeffec to f thespikin gmetho do requilibratio ncondition so n the extractabilityo fpesticide s from bottommaterials. . Inman y instances,rathe rpola rsolvent shav etj o beused ,whic hwil lco-extrac tcom - paratively largeamount so finterferin g substances from thebotto mmaterials .Consequently , theextractio nwil lnearl yalway shav et ob efollowe d by cumbersome clean-upprocedures .

5.6 EXTRACTIONO FAZINPHOS-METHY LFRO MBOTTO MSAMPL3 S

Several combinationso forgani csolvent swer e tîstedt ominimiz eth e amounto fco - -extractants,whic h interferei nth ega schromatograph yo fazinphos-methyl . Finally,a 3 3 3 mixtureo f20 0c m n-hexane,2 5c m dichloromethane ind2 5c m acetonitrileprove dt ob e suitable.Thi nslice so fbotto mmateria lwer eextra c;e donc ewit h thismixtur eo fsolvent s by shakingmechanicall yfo r2h .Th eliqui dphas eo fth eextractio nslurr ywa s collected witha pressurize dmembran e filter,equippe dwit ha niner tsilicate-fibr e filter. Then-hexane—dichloromethan e fractionwa s separated fromth ewater—acetonitril e layeri na separator y funnel,the ndrie dwit h anhydrous sodiumsulphat ean dfiltere d over aPyre xglass-filte r (averagepor esiz e90-15 0 ym)."h efina lvolum eo fth en-hexane - -dichloromethane fractionwa snote dt oallo wcorrect :.on sfo r lossesdurin g the different manipulations.Th elatte r solutionwa s concentrated :JIKuderna—Danis hequipmen tt oa fe w cubiccentimetre san devaporate dt odrynes swit ha gentl ystrea mo fnitroge n gas.The n theresidu ewa sdissolve di na smal lvolum eo fhexan e (0.5c m) read yfo rfurthe rclean-up .

5.7 EXTRACTIONO FDIMETHOAT EFRO MBOTTO MSAMPLE S

Sliceso fbotto mmateria l fromth eoutdoo r tanks (Section7.4 )wer eextracte d once byshakin gmechanicall yfo r2h wit h2 5c m ofdistille dwate ran d5 0cm' 'o fethy lacetate .. 3 Theliqui dphas eo fth eextractio n slurrywa s filtered offthroug ha Büchne r funnelwit h 15g o fCelit eHyfl oSupergel .Th eethy lacetat ephas e ewa s separated from theaqueou s phasei na separator y funnel anddrie dwit h anhydrous sodium sulphate.Th elosse so fethy l acetatedurin g theprocedur ewer enote dt oallo wth e necessarycorrections . Theextract swer econcentrate di na rotar y evaporator and,afte rclean-up ,measure d bygas—liqui d chromatography. Themetho dyielde da goo drecover yo fspike d sampleso f bottommateria l (Section 5.12)bu tth eus eo fHyfl ohampere drapi d estimationo fdr ymas s ofth ebotto mmaterial .

5.8 METHODSFO RCLEAN-U PO FEXTRACT S

Various clean-upprocedure si nestimatin g residu; s ofpesticide si nwate rhav ebee n described (Chesterse tal. , 1974;Fishbein , 1975).C o extractedmaterial s interferingi n theanalysi s areusuall yremove db yadsorptio n chromatography inwhic h theadsorben t Florisili swidel yused .Thi smateria l retains thepo.a ; r co-extractives verywell ,where - asapola rchlorinate dhydrocarbo npesticide sma yb ee isilyelute dwit ha napola rsolvent , With themor epola rorganophosphoru s pesticides,suc h separations 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 dt oseparat echlori natedan dorganophosphoru spesticide sfro mco-extractive s (Kadoum,1967 ;Leoni ,1971) . Theinterferin gcompound s inextract s frombotto 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 s fororganophosphoru spesticide s inextract sfro mbotto mmaterial . Clean-upprocedure softe nnee dt ob echecke dan dmodifie d foreac 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 d in0. 5 cm ethylacetate ,wa sapplie dt oth ecolumn ,whic h waselute dwit hethy lacetat esupplie d froma glas sreservoi rmounte da ta heigh to fabou t 0.5m abov eth eto po fth ecolumn . Thefirs teluat efractio no f5 c m (yellow)wa sdiscarded .Th esecon dfractio n( 7 cm) o fth eeluat econtaine dazinphos-methyl .Th eaverag erecover yfro m6 spike dextract s ofwate rsample swa s96°* ,wit ha coefficien to fvariatio no f3°s .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 d inSectio n5. 9wa sals ouse dfo rclean-u po fdimethoat ei n 3 extractso fsurfac ewater .Dimethoat eelute di na fractio no f2 2c m ,immediatel yafte r thefractio ncontainin gazinphos-methyl .Th eaverag erecover yo fdimethoat efro m7 spike d extractswa s92 1wit ha coefficien to fvariatio no f 3%.

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

Themeasuremen to fazinphos-methy li nbotto mmateria lfro mth etank san dditche sre quireda thoroug hclean-u pt oeliminat esevera lhighl yinterferin gsubstances .Variou s systemso fliqui dadsorptio nchromatograph yha dt ob eteste dbefor ea nacceptabl emetho d couldb edeveloped . Ina glas stub e (200m mlon gan dwit ha ninne rdiamete ro f8 mm )2. 8g non-activate d silicage lwa spoured ,t oa heigh to f 180mm .Th eextract so fazinphos-methy lwer eapplie d toth eto po fth ecolumn ,whic hwa sthe nelute dwit ha concav egradien to fdichloromethan e inn-hexane .Thi sgradien twa smad eb yconstructin ga gravit yflo wsystem ,usin ga measur -

32 ingcylinde r (with5 0c m n-hexane)an da conica l£.as k (with8 0c m dichloromethane). Thefirs teluat efractio n (80c m) wit hman y interferingsubstance swa sdiscarded ; .3 thesecon deluat efractio n (23c m) containe dazinp b los-methyl.Th eaverag erecover y(1 6 runsdistribute dove rvariou smeasurin gseries )fro n bottommateria lextract sspike dwit h azinphos-methylwa s9 H witha coefficien to f variationo f 7%. Sometimesai rbubble sappeare di nth egravit y system,whic hinfluence dth eelutio n process.Therefor ethi ssyste mwa sreplace db ya purpin gsystem .Th esam esolvent s wereused ,resultin gi nnearl yth esam eelutio n pattern .Thi simprove dsyste mwa squicker , yieldedsomewha thighe rrecoverie san dshowe dles s variationthe nth egravit ysyste m (Section6.4) .

5.12 CLEAN-UPFO RDIMETHOAT EEXTRACT SFRO MBOTTO MMATERIA L

Forclean-u po fdimethoat eextract sfro mbottoi | materialfro mth etanks ,a glas stub e 200m mlon go finne rdiamete r2 0m mwa sfille dwit h 17.3g non-activate dsilic age 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 e ard n-hexane (4:1b yvolume) . Dimethoate _3 wasrecovere dfro mth ecolum ni nth e100-17 0c m fn ctio n ofth eeluate .Th erecover yfro m 5spike dextract saverage d951 ,wit ha coefficien t cf variationo f6$ .

5.13 CONCENTRATIONMEASUREMENT SB YGAS—LIQUI DCHRCMATOGRAPH Y

Thefina lassessmen to fpesticid econcentration s inth ecleane dextract sca nb eac - complished indifferen tways .However ,som emethod s sufferfro mlac ki nsensitivit yan d specificity.Th emetho dusuall ypreferre dfo r measuremento forganophosphoru spesticide s isgas—liqui dchromatograph y (GLC).Th eapparatu s ila yb eequippe dwit hon eo fth esevera l availableselectiv ean dsensitiv edetector sfo r comjoundscontainin gP o rS .Severa ltype s ofcolum npackin gwit hdifferen tstationar y(liquid ] phaseshav ebee nuse dunde rvariou s chromatographicconditions ,fo risotherma lo r temperature-programmedga schromatograph yo f phosphorus-containingpesticide s (Zweig,1972) . Evenafte rpreviou sclean-u pb yadsorptio n chronatography,i ti softe nfoun dtha t peakso fco-extracte dsubstance scoincid ewit hth e psaks ofpesticida lcompound si nth e gaschromatograms .S oi ti softe nnecessar yt o analyse thesample swit htw oo rthre egas - -chromatographiccolumn scontainin gstationar ypha s es ofdifferen tpolarit y (Cochrane, 1976). Massspectrometry ,especiall yi ncombinatio n with GLC, ison eo fth ebes tmethod sfo r furtherconfirmatio no fth eidentit yo fpesticide s residues.

5.14 MEASUREMENTO FAZINPHOS-METHY L

Thequantitativ emeasuremen to fazinphos-methy l hasbee nth eobjec to fsom especia l studies.Th eavailabl eanalytica lmethod swer ereviewe d byth eChemagr oDivisio nResearc h Staff (1974).Th ebes tavailabl etechniqu efo rmeasuremen t ofazinphos-methy l isgas - -liquidchromatograph y (GLC).Howeve ra selectiv earj d sensitivemeasuremen 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 l andit 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 (981purity )an dit soxyge nanalogu e (99$),obtaine dfro mChrompac k& Nederlan dB.V. , Middelburg.Wit ha 10mm 3 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 dtw oo 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 s inth eextract swer emeasure db ycomparin gpea kheight s withthos efro mth ereferenc esolutions .B yusin gColum n II,packe dwit h 3%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 conditions formeasuremen to fazinphos - -methylan d itsoxyge 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- oxyg en azinphos- oxygen -methyl analogu e -methyl analogue

Carrierga sN 2 180 180 92 92 (cm3min -1) Detectorgase s 3 -1 H2(cm min ) 150 150 150 150 3 -1 02(cm min ) 10 10 10 10 air(cm3 min-1) 30 30 30 30 Temperature (C ) column 180 150 200 200 injectionpor t 210 210 210 210 detector 210 210 210 210 Detectionlimi t (ng) 0 4 5 0 2 2 Retention time( 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 eanalyse dfo 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).Bot !ga schromatograph swer eequippe dwit h flame-photometricdetectors .Th ecolum nspecification ,gas-chromatographi cconditions ,re tentiontime san ddetectio nlimit sar etabulate di nTabl e15 .Th einjectio nan dcalcula tionprocedur ewa sth esam ea sfo razinphos-methyl . Thediversit yo fth einterferin gsubstance si nsurfac ewate rextract ssometime s necessitated theus eo fthre echromatographi ccolla ru swit hdifferen tpolarit yo fth esta tionaryphas et oobtai ncertaint yabou tth eidentit yo fdimethoate .B yusin gColum nIII , dimethoatean dit soxyge nanalogu ecoul db emeasure !simultaneously .

Table 15.Gas-chromatographi c conditionsfo rmeasuremen t ofdimethoat ean d omethoate. ColumnI an dI Iar eth esam ecolumn sa suse dfo ra : nphos-methyl,alread y specified inTabl e14 . ColumnIII :glas scolumn ;9 5c mlong ;0. 2 cminne r iam.;packe dwit h3 % Carbowax 20Mo nChromosor bW-Aw-DMCS ,80-10 0mesh , obtainedfro mChrompac k NederlandB.V. ,Middelburg .

ColumnI Coluiin II ColumnII I dimethoate omethoate dime :hoate dimethoate omethoate

Carrierga sN 2 100 80 66 80 80 (cm3mi n* ) Detectorgase s H2(cm3min -1) 150 150 150 40 40 3 -1 02(cm min ) 10 10 10 air(cm3min -1) 30 30 30 40 40 Temperatures (°C) column 135 135 170 190 190 injectionpor t 210 210 210 210 210 detector 210 210 210 210 210 Detection limit(ng ) 0.1 0.3 O.C 1 0. 2 1 Retentiontim e(min ) 2.0 1 6 0.6 3 5 2.7

35 6 Conversion rate and adsorption of azinphos-methyl and dimethoate in aquatic systems

6.1 INTRODUCTION

Laboratory testswer eneede dfo rth efollowin gthre ereasons . -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 . Consequentlyther ei snee dfo rcomparativ eresearc ho nth econversio nrat ei ndifferen t aquaticsystems .Persistenc edat aobtaine d inth elaborator yha st ob ecompare dwit hthos 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 obtainedca nthe nb eintroduce dint ocompute rsimulatio nmodel st omak equantitativ e predictions. -Therat eo fdeclin eunde routdoo rcondition si sth eresul to fvariou sprocesse stha tma y occursimultaneously . Infiel dstudies ,i ti sdifficul tt oseparat eth econtributio nt o thedeclin eo fprocesse slik emicrobial ,chemica lan dphoto-chemica lconversion ,volatili zation,adsorptio nan dpenetration .Furthermor ei ti sdifficul tt oextrapolat eth eresult s fromon efiel dsituatio nt oanother .Relationship sobtaine dunde rwel lcontrolle dcondi tionsca nb eintroduce d intocompute rsimulatio nmodel st ob echecke db ywel ldefine d fieldtrials .

6.2 CONVERSIONRAT EO FAZINPHOS-METHY LI NAQUEOU SSOLUTION SKEP TI NDARKNES S

Literature data

Comparativestudie so nth erate so fhydrolysi so forganophosphoru spesticide si n aqueoussolution shav ebee nmad eb yNîihlman n& Schrade r (1957),Ruzick ae tal . (1968), Faust& Goma a (1972)an dGrah l (1973). Ingenera lphosphoro-dithioate sar emor establ ei n aquaticmedi atha nthei rphosphoro-thionat eanalogues .Organophosphoru spesticide sar ei n mostinstance scomparativel ypersisten tunde racidi ccondition s (Faust& Gomaa ,1972) . Theconversio nrate so fpesticide si naqueou ssolution sca nb eusuall ycharacterize d bya rat ecoefficien t ),assumin ga first-orde rreactio n (Section3.3 ,Equatio n1) . (k c, w

Thisrat ecoefficien tfo rconversio nma yb ecompose do fsevera lpartia lcoefficients ,whic h

36 represent thevariou s catalytican denzymi c influerce so nth ereaction s (Grahl, 1973). However,th emechanism so fth ereaction s aremostl ypoorl yunderstoo d andmor eresearc hi s requiredo nth efactor saffectin gdecompositio n raleso forganophosphoru s pesticidesi n aqueoussolutions . Theconversio nrate so fazinphos-methy lan dit soxyge nanalogu ear ehighl y dependent onpH .Th e relationshipsbetwee nrat eo fhydrolysi s at7 0° Can dp Hobtaine db yMühlman n & Schrader (1957)ar eshow ni nFigur e5 .Azinphos-nethy lwa shydrolyse d sloweri naqueou s solution thanit soxyge nanalogu ean dbot hcompound swer e lessstabl ewit h increasingpH . Thetemperatur edurin g thesehydrolysi s testswa s1 ig h (7.0°C ); thu sth erate so fhydrol ysisunde renvironmenta l conditionsma yb eexpectec .t ob emuc h lower. Rateso fhydrolysi sa tmor e realistictempéraiure swer emeasure db yBaye rA.G . (1978), Liang& Lichtenstei n (1972)an dHeue re tal . (1974).Th erat ecoefficient sfo r 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 odiffeience 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 7-8.5a tsurface-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 h temperatures.Moreove rconversio nrite so fazinphos-methy l ando fit s wettablepowde ri nsurfac ewate rwer eno t foundi nth eliterature .

rote coefficient forconversio n(d~ 1) 100q

K>i

Figure5 .Effec to i pHo nhydrolysi srate so fazinphos - 0.1 ••—i—i—i—|—i—r—i—i—| 0 5 10 -methyl (•-•) and tsoxyge nanalogu e (x-x)i naqueou s pH solutiona t7 0°C . (AfterMühlman n &Schrader , 1957).

37 rate coefficient for conversion (a™ ) 10-

Figure6 .Effec to fp Ho nrat e coefficient for hydrol ysis ofazinphos-methy li naqueou s solutionsa tdiffer ent temperatures. Data from•- •(2 0°C )Baye r A.G. '6 ^ ^2 0978), +-+(2 0°C )Lian g &Lichtenstei n (1972) and pH x-x(2 5°C) ,o- o( 6°C )Heue re tal . (1974).

Procedures for measuring the hydrolysis of azinphos-methyl in buffer solutions

Hydrolysis rateso fazinphos-methy l asanalytica l grade (981purity )wer emeasure di n aqueous solutionsbuffere da ttw op Hvalues .A buffere d aqueous solutiono fp H7. 7wa s prepared inde-ionize dwate rwit hphosphate ,borat e andhydrochlori c acid.Anothe r buffered aqueous solutiono fp H8. 9wa smad ei nde-ionize dwate rwit h boric acid, potassium chloridean dsodiu mhydroxide . (Bothbuffer swer eprepare dwit h Titrisol solutions(So )f 3 E.Merck ,Darmstadt) .A volum eo f5 c m ofth ebuffere d aqueous solutions containing 50u g azinphos-methyl was addedt otes t tubes (15c m) whic hwer e closedwit h ground-glass stoppers.Al ltes t tubeswer e placedi nth edar ki na wate rbat ha t1 5 C.Afte rth e con centrations inth etube swit hp H8. 9ha ddecrease d tohal f their initial value,th etem peratureo fth ewate rbat hwa s raised from 15t o2 0°C .Afte r the concentrationwa s halved again (20 C,p H8.8 )th etemperatur ewa s raisedt o2 5°C .Th etemperatur e fluctuations during the testswer e lesstha n0. 5C . At appropriate time intervals,tw otube so fbot hp Hvalue swer e extracted twice with 5c m ofdichloromethane .Th ecombine d extracts were collectedi na tes ttub ean ddrie d by addinga smal l spoono fanhydrou s sodium sulphate.Th edichloromethan ewa s removed with a gentle streamo fnitroge n gas,afte rwhic h azinphos-methyl was dissolvedi nacetone . The analyseswer eb ygas—liqui d chromatography using ColumnI fo rth e1 5 Cserie san do nCol umnI Ifo rth eothe r temperatures (Table 14).Th e average recoverywa s 98%wit ha coeffi ciento fvariatio no f1% .

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

Conversionrate swer emeasure do fazinphos-m e hyl (981purity) ,it soxyge nanalogu e (995opurity )an dazinphos-methy lw.p . (25%wettabl ^ powder)dissolve d insurfac ewater . Thesolution swer eno tbuffered .Th eincubatio nj ;wer eplace di ntemperature-controlle d cabinetsa t1 0an d2 0°C .I nth ecabinets ,th efluitua t iono ftemperatur ewa sabou t1 °C . Thesurfac ewate rwa sobtaine dfro muntreate d Tank III (Chapter7 )an dwa sfiltere d overa niner tsilicate-fibr efilte r (size0 )t o rei»v e suspendedparticles .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 d substanceconcentratio n0. 5kmo lm -3 Duringtests ,th ep Hwa smeasure dbefor eth e extraction s -3 -3 Aqueoussolution swer eprepared ,concentratioii 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 (2Î0c m ),whic hwer eclose dwit hpol y

Table 16.Chemica lcharacteristic so fwate rfro mu tedoutdoo rtan kII I (Chapter 7), usedfo rth econversio n testswit ha z nphos-methyli nth elaboratory . Analysesb yth eEaster nLaborator yfo rWate rTestin g ,Doetinchem .Samplin gdate : 15Augus t 1977.Dat ao fanalyses :1 9Octobe r 1977

Characteristics Massconcentratio n (gm

COD 110

N03 <1 NH£ < 0.05 Total N 2.5 Orthophosphate (as PO,,) 5.2 Total phosphate (asPOi, ) 5.5 CI 345 Ca2+ 212

HC03 77

C02 3 C02- 0 2 so " 12

Hardness (as CaO) 301 „ 2+ Cu < 5m g m

Conductivity 113.4m S

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

39 ethylene caps.Fo reac h combinationo fcompoun dan dconcentration , 18jar swer e incubated. Inoutdoo r trials (Chapter 7), copper sulphatewa suse dt osuppres sa nalga l bloom inth ewate ro fth e tanks.Th eeffec to fcoppe r sulphateo nth e conversion rateo fazin - phos-methyli nwate rwa smeasure di na nincubatio n study. Copper sulphatewa s addedt o water fromuntreate d TankII It oa mas s concentrationo f3. 2g m ~. I ntha t test, the aqueous solutionwa s spikedwit h azinphos-methylw.p .a t1 6g m .Th eglas s jarswer e placedi nth edar ki ntw otemperature-controlle d cabinetsa t1 0an d2 0C . Triplicate sampleswer e extracted ina separator y funnelwit h consecutively 100,5 0 and5 0c m ofdichloromethan ea sdescribe d inSectio n 5.3.Analysi swa sb yGLC ,usin g Col umnI I(Tabl e 14)fo r all compounds.Th erecoverie so fazinphos-methy l andit s oxygen analogue were almost 100%,wit h lowcoefficient 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 l grade, inbuffere d aqueous solutionsa tdifferen t temperatures isshow ni nFigur e 7.Th edeclin e patterns were approximated witha first-orde r reaction rate equation.Th ehydrolysi s rate coefficientsan dhalf-lif e valuesar etabulate d inTabl e17 . The rate coefficients forhydrolysi san dth e coefficientso fdeterminatio n [r ;squar e ofcorrelatio n coefficient)wer e calculated witha standar d regression programo na Hewlet t Packard desk calculator. Table 17show s lowercoefficient so fdeterminatio na tlowe rpH ; this could have been improvedb ymeasurin g concentrations over longerperiods .Durin gth e hydrolysis tests,th edifference s between duplicate sampleso nth e sampling dateswer e less than 2%o fthei r average concentrations. The rate coefficients werehighl y dependento np Han dtemperature .Th eaverag e rate ofhydrolysi sa tp H8. 7t o8. 9wa s about four timesa sfas ta stha ta tp H7. 6t o7.7 . Increasingth etemperatur e inbot hbuffere d solutions resultedi na considerabl e increase inth e rate coefficients forhydrolysi s (k ).Th eeffec to ftemperatur eo n k inth e o c,w o c,w range 15-20 Cwa s smaller thani nth e range 20-25 C.Thi s effect couldno tb edescribe d bya nArrheniu s relationship,sinc ea plo to fl g k against 1/T didno tyiel da straigh t c,w line. Changei nth eaqueou s solutions (for examplea decreas ei nredo xpotentia l with time)migh t havedisturbe d theArrheniu s relationship. mass of azinphos-methyl (ug) 100 -

Figure 7.Effec to fp Ho nrat eo fhydrolysi so fazinphos - -methyl, analytical grade,i nbuffere d aqueous solutions atdifferen t temperatures,o = p H7.7 ,1 5°C ; G=p H 7.6,2 0°C ;A = p H7.6 ,2 5°C ;• = p H8.9 , 15°C ; •= pH 8.8,2 0°C ;A = p H8.7 ,2 5°C .

40 Table 17.First-orde rrat ecoefficient san dhalf- 1.ve sfo rth e hydrolysiso fazinphos-methyl ,analytica lgrade ,i pbuffere d aqueoussolutions .

Temperature PH Ratecoeff . Half-life Coef:: . of (°C) (d"1) (d) detettn

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 su.*faoe 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 )ar epresente di nTabl e1 8 {k c,w Althoughth esample so fsurfac ewate rwer eno tbuffered ,th evariatio ni np Hdi dno t disturbth eapproximat efirst-orde rconversio npatuern 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 si nth ethre esample so neac ho fth esam -

masso f substance (ug) 1000

"time(d ) Figure8 .Mas so fsubstanc ei nsurfac ewate r againsttim edurin g laboratoryincubation sa t 10(above )an d2 0° C (under).• - azinphos-me thyl(analytica l grade);x = th esame ,wit h half theinitia lmass ;o = azinphos-methy l (25%w.p.) ; A= azinphos-methy loxyge nanalogue ; +- azinphos-methy l (25%w.p. )an dcoppe r sulphateadded .

41 Table 18.First-orde r ratecoefficient san dhalf-live s for theconversio no fazinphos - -methylan d itsoxyge nanalogu e insurfac ewate rdurin g incubationi nth edar ka t 10an d 20°C .

Compound Temperature pH, average Rate Half Coeff. Averaged (°C) (and range) coeff. life of difference3 (d"l) (d) determ. (%)

Azinphos-methyl 101 7.5 (6.7-8.1) 0.0011 624 0.87 4 (analytical grade) 102 7.4 (6.4-7.9) 0.0011 613 0.89 3 20l 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 oxygen analogue 20 7.7 (7.4-8.3) 0.045 16 1.0 0 21

1.Dos e 0.5 mg. 2. Dose 0.25 mg. 3. See text.

plingdate swer eexpresse da sa percentag eo fth eaverag econcentration so ntha tsamplin g date.Afte rthat ,thes epercentage swer eaverage dfo ral lsamplin gtime sfo reac hincuba tiontes t (Table 18).Th eaverage ddifference swer erelativel ysmall ,wit ha nexceptio n forth eoxyge nanalogu eo fazinphos-methy la t2 0 C,wher edifferenc eaverage d 21%. Therat ecoefficient sfo rconversio no fth ecompound swer ehighl ydependen to ntem perature.A t 10 C,thes ecoefficient swer eonl yabou ta thir dt oa sixt ho fthos ea t2 0 C.Halvin gth edos eo fazinphos-methyl ,analytica lgrade ,hardl yaffecte dhalf-live s (Table18) .Wit ha w.p .formulation ,azinphos-methy l showeda somewha tfaste rconversio n thanwhe napplie da spur ecompoun d (Table18) . Theconversio nrat eo fth eoxyge nanalogu eo fazinphos-methy l insurfac ewate rwa s considerablyhighe rtha ntha to fazinphos-methy litself .Durin gincubatio no fazinphos - -methyli nsurfac ewater ,th eoxyge nanalogu ecoul dno tb edetected ,perhap sbecaus eo f therapi dconversio no fth eoxyge nanalogue . Addingcoppe rsulphat et oth esurfac ewate r (20°C )resulte di nrapi dconversio no f azinphos-methylshortl yafte rth estar to fth etest ,followe db ya perio dwit hslo wcon version (Figure 8). Thisdeclin epatter ncoul dno tb edescribe da sa first-orde rreaction . Anexplanatio n forthi sdeclin epatter ncoul dpossibl yb efoun di fcoppe rio nconcentra tionsha dbee nfollowe dwit htime . Acompariso no fth eresult so fth eincubation so fazinphos-methy l insurfac ewate ra t 20 C (Table18 )wit hthos eobtaine d inbuffere daqueou ssolution s (Table17 )wa srathe r difficulti nvie wo fth elo wcoefficien to fdeterminatio ni nth ebuffere dtest san di n viewo fth evariation si np Hi nth etest swit hsurfac ewater .Conversio no fazinphos-me thyli naqueou ssolution si nth edar ki sa rathe rslo wproces sa ttemperature sprevailin g outo fdoors .

42 6.3CONVERSIO NRAT E OFDIMETHOAT EI NAQUEOU SSOLUTJION 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 eexamine db yGriime re tal . (1968).Thei rresult sa 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 eincrease sb ya factoro falmos t10 0whe np Hincrease sfro m7. 0 tolo.O .Dimethoat ewa sfoun dt ob ede gradedmor eslowl ytha nomethoate .Dimethoat ei sdegrade dslowl yi naci daqueou ssolutions . Eichelberger& Lichtenber g (1971b)incubate dd :.methoat ei nrive rwate rplace d inth e laboratoryunde rsunligh tan dfluorescen tlight .Th op Hwa s7. 3a ttim ezer oan dincrease d to8. 0afte reigh tweeks .I ntha ttime ,hal fo fth e initialamoun twa sconverte d (onaver - -1, age, k 0.012d ).Brad y &Arthu r (1963)measui-e dth erat ecoefficien to fhydrolysi s ofdimethoat ei na sodiu mcarbonat esolution ,substimc econcentratio n0.0 5kmo lm (adjustedt op H 11),i nflask so na shaker .The ymeasure da k of2 8d ~ Unfortunately, temperatureswer eno tspecifie di nthes epapers .Wagre r& Frehs e (1976)referre d toindus trialdat aindicatin gtha thydrolysi srate so fdimethoat ean domethoat ea t2 1° Can dp H 9wer e0.1 2an d2. 3d " ,respectively .Thes evalue s agreefairl ywel lwit hth eresult si n Figure9 . Conversionrate so fdimethoat ei nsurfac ewate r atlowe rwate rtemperature swer eno t foundi nth eliterature .Furthe rtest swer edon et omeasur econversio nrate so fdimethoat e insurfac ewate ra tlowe rwate rtemperatures ,an dw it hadditio no fcoppe rsulphat ean dcal ciumchlorid et oth eaqueou ssolution .

rate coefficient for hydrolysis (d-1) 100*3

101

0.1 -

0.01 -

Figure9 .Effec to fp Hc therat ecoefficien tfo rhydrolysi s 0.001 ofdimethoat e (•-•) and methoate (x-x),i nbuffere daqueou s 5 10 pH solutionsa t2 5°C .(Af t Grimmere tal. , 1968).

43 Procedures for measuring the conversion of dimethoate in surface water

Theconversio nrat eo fdimethoat edissolve d inuntreate dwate rfro mTan k Iwa sstudied . Thewate rwa s filtered (Section6.2 )an dno tbuffered .Th echemica lcompositio no fthi s aqueoussolutio ni sshow ni nTabl e 19.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 (981purity) . Initiallyth econcentratio n inth eaqueou ssolutio nwa s2 0gm " .Detail so fincubatio nwer esimila rt othos efo r azinphos-methyl (Section6.2) .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 i " .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 s96'« ,wit ha coefficien to fvariatio no f 2%.

Table 19. Chemicalcharacteristic s ofth ewate rfro muntreate d outdoorTan kI (Chapte r 7)use dfo r theconversio ntest swit h dimethoatei nth elaboratory .Analyse sb y theEaster nLaborator y forWate rTesting ,Doetinchem .Samplin gdata :1 5Marc h1978 . Dateo fanalysis : 11Apri l1978 .

-3 Characteristics Massconcentratio n (gm )

COD 15 NC-i < 1.0 NHJ 0.19 Total N 0.19 Orthophos phate 0.20 Total phc sphate 0.30 CI" 11 Ca2+ 33 HCOi 59

C02 2 CO2- 0 so2- 57 Hardness (as CaO) kl Cu2+ < 5m g m Conductivity 19m S m~'

44 Measured conversion rates of dimethoate in surface later

Theeffec to ftemperatur eo nrat eo fconversio no fdimethoate ,analytica l grade,i n surfacewate ri sshow ni nFigur e 10.Th e declinepattern sa t2 0° Ccoul dno tb echaracter izedfo rth ewhol eperio do fincubatio nb ya first-orde rreactio nequation .Initiall y thedeclin ewa srelativel yslow ,late rconversio nmte s increased (Figure 10).Th ein creasei nconversio nrate sma yb edu et ochang ei nih echemica lo rmicrobia l conditions inth esurfac ewate rdurin g incubation.Ther ei sa napparen tinconsistenc yi nth eeffec t oftemperature . Thedifference sbetwee nconcentration si nth etriplicat esample sa tth e starto f incubationswer erathe rsmal l (Table 20). Howevert les edifference sbecam erathe rlarg e atth een do fth etests .Thi sphenomeno ncoul db epsrtl yrelate dt ochange si np Hi nth e unbufferedsurfac ewater .I nsom esample s incubateda t2 0 C,relativel yhig hp Hvalue s weremeasured ,whic hcorresponde dt 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 s fordimethoat ei nsurfac ewate r (Figure 10)wa s approximatedwit ha first-orde rrat eequation .Th elat ecoefficient s arepresente di n Table20 .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 rrat e coefficientsfo rth esecon dpar to fth edeclin ea t2 D° Cwer eomitte di nvie wo fth elarg e deviationsi nconcentration sfo rtriplicat esample sa tth een do fth etest s (Table20) . Thedeclin ecurv eo fdimethoat ei nsurfac ewate rwit hcalciu mchlorid ei sshow ni n Figure 11.Th econversio nrate sfo rth efirs tperio do fincubatio na t2 0 Cwit han d withoutadditio no fcalciu mchlorid ewer enearl y thesame .Th ewid escatte ro fpoint si n thesecon dperio dmad ean ycompariso nbetwee nconversio nrate si neithe rmediu mimpossible . Addingcoppe rsulphat et oth e aqueoussolutio n resultedi na grea t increasei nth e conversionrat eo fdimethoate .Th elimite dnumbe ro f samplesdi dno tallo wassessmen to f theshap eo fth edeclin ecurve .Assumin ga first-ord s r conversionrat eequatio nfo rth e firstfou rpoints ,a naverag erat ecoefficien to f0. I 12d" 1(* . =5. 9d )wa scalculate d (Figure11) .

mass ofdimethoat e(jjg ) 1000

100

Figure 10.Mas so fdimethoat e insurfac ewate ragain : timeo fincubatio na t 10(o) ,1 5(x )an d2 0° C(•) ,

45 Table 20.First-orde r rate coefficients and half-lives for conversion of dimethoate in surface water in the dark at 10, 15 and 20 C.

Additive Temp. Period1 pH, average Rate Half Coeff. Averaged (°C) (and range) coeff. life of difference2 (d-1) (d) determ. (%)

None 10 1,11 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

CaCl2 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 j 20 1,11 7.1 (6.7-7.7) 0.12 5.9 0.98 19

1.1= first period; II = second period (see text). 2. See Section 6.2. 3. Omitted values (see text).

The conversion rate of dimethoate incubated in surface water in the dark at pH around 7wa s rather slow, especially at low temperatures. In general,thes e rates were somewhat higher than those of azinphos-methyl (Tables 20 and18) . During incubation of dimethoate in surface water, the formation of the oxygen ana logue of dimethoate (omethoate) couldno t be detected. This might be related to the fast conversion of omethoate inhydrolysi s tests,a s reported in literature (Figure9) .

6.4 CONVERSION RATE OF AZINPHOS-METHYL IN SYSTEMS OF BOTTOM MATERIAL AND SURFACE WATER

Data on the conversion rateo f azinphos-methyl and its oxygen analogue under anaero bic conditions inbotto m material could not be found in the literature. More research was thus needed on decomposition rates in suchmedia . To simulate natural conditions, it was decided to investigate the conversion rate in a system ofbotto m material in contact with surface water. masso fdimethoat eCug ) 1000--

100

10-

Figure 11. Mass of dimethoate in surface water against time of incubation at 20 C. A = calcium chloride added; o = calcium 150 time(d) chloride plus copper sulphate added.

46 Procedures for measuring the conversion of azinphos -methyl in systems with bottom material

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 lcompositio no fthi saqueou s solutioni spresente di nTabl e16 . Thep Ha tth e starto fth e testwa s adjustedt o7. 0a sdescribe di nSectio n 6.2.Th ebot tommateria lwa s collected fromuntreate d TankII Iin dthoroughl y mixed beforeth estar t of thetest . 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 o: surfacewate r spikedwit hazinphos - -methyl (analytical grade,0. 5o r0.2 5 mg),it soxyj;e nanalogu e (1mg )o razinphos-methy l w.p. (0.5mg )wa sadded .Fo reac hcombinatio no fcoipoun dan dconcentration ,1 8centrifug e tubeswer eincubated . These tubeswer eplace di na controlled-temperatur ecabine ta t2 0 C +1 C.A t1 0°C ,onl y oneserie swa s setu pwit ha dos eo f0. 5m go fazinphos-methyl , analytical grade.Durin g incubation,th etube swer e placed twicea week o na shake rfo r5 min. Redoxpotential s inth ebotto mmateria lwer emeasure da tinterval so f2 weeks . At appropriate timeintervals ,thre e tubeso feac hserie swer ecentrifuge dfo r5 mi n at3 3H z(200 0mi n ).Th esupernatan t liquidwa sm easure dan dextracte da sdescribe di n Section 6.2.Th ebotto mmateria lwa squantitativel y transferred intoa glas s jaran dex tracteda sdescribe di nSectio n 5.6.Afte r extractien,th edr ymas so fth ebotto mmate rialwa sdetermine db ydryin gt oconstan tmas sa t10 5°C . Theextract so fth ebotto mmateria lwer e cleanedu pb ycolum n chromatography using the improvedpumpin g systemfo rth eelutio nsolven ta sdescribe di nSectio n 5.11.Th e 3 3 firsteluat e fraction (60cm ) couldb ediscarded ; tiesecon d eluate fraction (28c m) contained azinphos-methyl.Nex t2 0c m ofa mixtur ep fdichloromethan ean daceton e(2:1 , v/v)wa spumpe d through thecolum nan dwa sdiscarded ,Afte rtha tth eoxyge nanalogu eo f azinphos-methyl couldb ecollecte di nth efollowin g 20c m. The extractso fth eaqueou s solutionsan dth ecLeane dextract so fbotto m material wereanalyse db ygas—liqui d chromatographyo nColum iI I(Tabl e 14).Th erecoverie so f azinphos-methylan dit soxyge nanalogu e fromth eaquKxi ssolution swer e almost 100% (Ta ble 12).Th e recoverieso fthes ecompound s fromspik; dbotto mmateria lwer e 103% (coeffi ciento fvariatio n 3%)an d59 % (coefficiento fvariatio nals o 3%), respectively.Th erel ativelylo wrecover yo fth eoxyge nanalogu ewa sprobabl y duet olo wefficienc yo fextrac tionbecaus e the recovery forth eclean-u pprocedur ealon ewa s 96%,wit ha coefficien to f variationo f6% .N ocorrection swer emad efo r recoveoy. Measured conversion rates of azinphos-methyl in sysUms with bottom material

Theconcentration so fazinphos-methy l insystem s withbotto mmateria la tvariou s times during incubationa t1 0an d2 0° Car eshow ni nFigure s 12an d13 ,respectively .Th ecalcu - lated first-order ratecoefficient s forth econversiq n ofazinphos-methy l inthi s system arepresente di nTabl e21 . Theaverag eredo xpotentia li nth ebotto m layer ofth esyste mwa sabou t -0.12V .

47 mass of substance (ug) 1000

100-

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 (Table 21).Raisin gth etemperatur efro m1 0t o2 0° Cincrease d theconversio nrat eo fazinphos-methy lb ya facto r3.4 .Halvin gth eamoun to fazinphos - -methylresulte d innearl yth esam econversio nrate s (Figure13 ;Tabl e21) . Theconversio nrat eo fth eoxyge nanalogu eo fazinphos-methy li nbotto mmateria lwa s slightlyhighe rtha nth econversio nrat eo fazinphos-methy l itself.Durin gincubatio no f azinphos-methyl inthi 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 y 10t o2 0time sa sfas t (Tables 18an d 21).Howeve rth e

masso fsubstance(ug ) 10OO-

100

Figure 13.Mas so fsubstanc e insystem swit hbotto m material against timeo fincubatio na t2 0°C .• = azinphos-methyl (analytical grade);x = th esam e compoundwit hhal f theinitia ldose ;o » azinphos - -methyl (25%w.p.) ; A= azinphos-methy loxyge n analogue.

48 Table21 .Rat ecoefficient san dhalf-live sfo rth e inversiono fazinphos-methy lan d itsoxyge nanalogu eincubate d insystem swit hanaerobi cbotto mmateria la t 10an d 20"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 (analyticalgrade ) 20l 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 Azinphos-m ethy 1 20 6.8 (6.6-7.1) 0.079 8.8 0.99 (25%w.p. ) 14 Azinphos-methyl 20 6.8 (6.6-7.1) 0.10 7.0 0.98 oxygenanalogu e 13

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 CONVERSIONRAT EO FDIMETHOAT EI NSYSTEM SO FBOTITO MMATERIA LAN DSURFAC EWATE R

Nodat ao nth econversio nrat eo fdimethoat ei n anaerobicbotto mmateria lwer efoun d inth eliterature .

Procedures for measuring conversion of dimethoate in systems with bottom material

Theincubation swer ecarrie dou ti ncentrifug e rubeswit hground-glas sstopper s (Section6.4) .Abou t2 5go ffres hbotto mmateria l f-o muntreate dTan kI wa sintroduce d intoth etubes .T otha twa sadde d5 0c m ofsurfac ewate r (fromTan kI ;fo rchemica l characteristicsse eTabl e19 )spike dwit h1 m go fdinethoat e (analyticalgrade) .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 etim eintervals ,thre etube swer ecentrifuge dan dth esupernatan t liquidwa sextracte di nth esam ewa ya sdescribe d forazinphos-methy li nSectio n6.4 .Th e extractiono fdimethoat efro mth ebotto mmateria ldescribe di nSectio n5. 7wa smodified . 3 3 Afterremovin gth esupernatan t liquid,5 c m ofde-icnize dwate ran d4 0a n ofethy lace tatewer eadde dt oth ebotto mmateria li nth ecentrifug etube .Th etube swer eplace do na shakerfo r1 h ,thereafte rth etube swer ecentrifugé e andth 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 si n a rotaryevaporator . Theextract so fth ebotto mmateria lwer ecleane du pa sdescribe dfo rextract so fwa ter(Sectio n5.10) .Th eonl ydifferenc ewa stha tth eElutio nliqui d (ethylacetate )wa shalf - 3 -saturatedwit hwate r (massfractio no fwate r 1.64). [hefirs teluat e fractiono f1 0c mwa s discarded.Th enex t1 0c m ofeluat econtaine d thedinethoate .Th efraction swer eanalyse d

49 by GLCwit h Column III(Tabl e 15).Th eaverag e recovery ofdimethoat e from2 5spike d sam pleso fbotto m materialwa s901 ,wit ha coefficien to fvariatio n of41 . Nocorrection sfo r recoverywer e made.

Measured conversion rates of dimethoate in systems with bottom material

The results ofincubatio no fdimethoat e insystem s with anaerobic bottom materiala t 10, 15an d2 5 Car epresente d inFigur e 14.Initiall y theconversio n rates ofdimethoat e were slow,becomin g considerably higher later.Th edeclin e patterns were approximated with a first-order rate equation foreac ho fthes e twotim eperiods . The averagep Han drange so fp Hi nth esystem swit hbotto m material were nearlyth e same fordifferen t temperatures.Th eaverage d differences between theconcentratio no f dimethoate intriplicat e bottom samples were relatively small (Table 22).Th eincreas ei n conversion rate foreac ho fth eincubation s inth esecon d period couldb erelate d toa change inchemica l ormicrobia l conditions.Th eredo x potential inth ebotto m material dropped from -0.03V a tth estar to fth etes tt o-0.1 2V a tth eend . As temperature increased, theduratio no fth efirs t periodwit h comparatively slow conversion decreased.A sth etemperatur e increased conversion rates considerably increased in systemswit h bottom material. The conversion ofdimethoat e inth eanaerobi c bottom material systemwa sconsiderabl y faster than inaqueou s solutions (Tables 20an d22) .Th econversio n rateso fdimethoat ei n the firstperio do fincubatio nwer e slower than thoseo fazinphos-methyl . Inth esecon d periodo fincubation ,th erate so fdeclin e ofdimethoat e (Table 22)seeme d tob econsi derably faster than those forazinphos-methy l (Table21) .

masso fdimethoat e(u g) 1000

Figure 14.Mas s ofdimethoat e (analytical grade) in systems with bottom material against time during incubation testsa t1 0(o) ,1 5(x ) and 20° C(•) .

50 Table22 .First-orde rrat ecoefficient san dhalf- 1 ive sfo rconversio n ofdimethoat eincubate d insystem swit hanaerobi c lottommateria l at 10,1 5an d2 0°C .

Temp. Period1 pH,averag e Rate Half (joeff. Averaged (°C) (andranges ) coeff. life f difference2 (d"1) (d) determ.(% )

10 I 7.0 (6.9-7.0) 0.0044 157 .99 2 II 6.9 (6.8-6.9) 0.055 13 .97 14 15 I 7.0 (6.9-7.1) 0.010 68 01.99 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 0 6 II 7.0 (6.9-7.1) 0.23 3.0 86 5

I= firs tperiod ,I I= secon dperio d (seetext) . Seetext .

6.6 ADSORPTIONO FAZINPHOS-METHY LO NBOTTO MMATERIAL S

Adsorptiono fpesticide so nagricultura lsoil sunde rvariou scondition sha sbee n studiedb yman yworkers .Thes estudie ssho wtha tpesticid eadsorptio ni sa comple xphe nomenon,dependen to nth echemica lan dphysica lpropertie so fth epesticide sa swel la s ofth esoil .I nth efield ,adsorptio ni ninflucence ib yman yenvironmenta lfactor san d especiallyb ysoi lpropertie slik eorgani cmatte rcontent ,cla ycontent ,cation-exchang e capacity,surfac eare aan dpH .O fthes epartl yinterrelate dproperties ,organi cmatte r contentan dcla yconten tar eusuall yconsidere dth e mostimportant .Th ecompositio no f soilsan dbotto mmaterial sshoul dtherefor eb especified . Datao nadsorptio no fazinphos-methy lont obo t:o mmaterial sric hi norgani cmatte r andcla ywer eno tfoun di nliteratur e (Table9) .

Procedures in adsorption tests with azinphos-methyl

Adsorptiono fazinphos-methy lwa sstudie db yth ebatch-equilibratio ntechniqu efo r bottommaterial sfro mth etank san dfro mth ewatercourse so nfrui tfarms .Fo rcharacteris ticso fth ebotto mmaterial sse eTabl e23 . Solutionso fazinphos-methy l (analyticalgrade ] inde-ionize dwate rwer eprepare d withCaC la t55 5g m -3 Theconcentration so fazinpllos-methy lwer e 1,3 ,5 ,7 ,9 an d13. 5 -3 gm ,respectively .O feac ho fthes esolutions ,1 0 cm wereequilibrate di nquadruplicat e with2 g o fbotto mmateria l (airdry )i n13-c m centrifugetube swit hground-glas sstopper s Thetube swer eturne dovernigh t (15h )o na nincline dturntabl ea ta frequenc yo f0.2 2H z —1 o (13mi n )a troo mtemperatur e (18t o2 1 C). Aftercentrifuging ,5 c m ofth esupernatan taiueou sphas ewa sanalyse dfo r concentrations.I n1 4tubes ,th eremainin gbotto mmateria lwa sals oextracted ,afte r whichth eextrac twa scleane du paccordin gt oth ei iprove dprocedur supplieedescribe dt owate di rnan Sectio dbotto n mmateria l 6.4.Th erecover yo fth eamount so fazinphos-methy l Correctionsfo rrecover yo rdecom - wasabou t100 %wit ha coefficien to fvariatio no f7> . positionwer eno tmade .

51 r") <*0 m ro ro I I I I I OOOOO

u~l \£> r-. -4" \£>

O CN O en —

m m m m m Öft u ort G OOOOO o ms 4-1 t/i -u c +j C1J en H 0 er* CT\ — m r^ VI to (ij N -3- o — m r-* 0) v-i H m n1 - ~J CM

er« en — — o 3 ö ^D ^D n* r-* 1—

rn Fi C/) eu >, M Tl 0 M' *-> rÜ cri s-i >-l c c •i-l 4-1 n 0 al a <-> Ö »4-1 •H .a ai 0 •r-l Tl •U 0 a g r-^ m o o m c CTl X a) g 00 cN r-*. m — Tl m >,u U eu o w V •—&-«'

m -d- co r^ — en

— m cN m CM co

cri in — -j- 10

• CN m -j- in S o w >•> O PM CO vO v.O 0 r^ en TJ 4J CN CN a) et) -H ~ 4-> 4-> "-• X 0 C to bO ci) n a Ö •H •iH 0 C) fi0 c b0.fi tu •H C) C -fi O 4J 4-1 4J •H •>-(>, 4J Cl) t) C) f) 4-> r-i ,—1 CO ai Q) 0) f) a 0 to nj «H m 01 I-J Ö .ai •s î 4J co u-a 04 0 0 0 cti eu e tu >-l en fiC) ^C) M H m Ui •V -C en M-l X 42ffl U ai O Cl) n] r-l 4-) si 4-1 ,0 Pu tó PQ .Û •0 n .-1 l-l U e c w c/> t/1 y, FÎ « H m eu ffl >-)•-1 r-< CM m

52 Checkswer emad eo nth epossibl e effecto f dryingo fbotto mmateria lbefor eth e experiment.Adsorptio n testsfo razinphos-methy l vtereals odon ewit ha suspensio no f freshbotto mmaterial ,a suse dfo rth econversio n tests (Section 6.4).Thes e suspensions were alsoequilibrate di nth elarg etube s (70c m] for 15h .Th e extractionprocedur ewa s thesam ea sdescribe di nSectio n6.4 .

Measured adsorption coefficients of azinphos-methi, I

Themas s fractiono fazinphos-methy l adsorbed ontoth ebotto mmateria l (expressedo n drymatte rbasis )wa s plottedi nFigur e1 5agains t theconcentratio nremainin gi nth eso lution. Linearadsorptio n isothermswer ecalculate dwit ha regressio nprogra m fromth e pointsfo rth efiv e lowestconcentrations .Th eadsorptio ncoefficient s(- K /•.), whichre presentth eslop eo fth eisotherms ,ar egive ni nTabl e 23.A tth ehighes tconcentration , a smalldeviatio n fromth elinea radsorptio n isothermwa ssometime sobserved ,especiall y whenadsorptio nwa scomparativel ylow . Theadsorptio ncoefficient so fazinphos-methyt Lfo rth evariou sbotto mmaterial swer e muchhighe r thanth ecoefficient s reported forsilt-loa msoil s (Section3.4 ,Tabl e9) . Theadsorptio ncoefficient so fazinphos-methy lfo r pondwel lwit hth eorgani cmatte rcontent so fthes sbotto mmaterial s (Table23) . Theaverage ddifference sbetwee nth efina l concentrationso fazinphos-methy li nqua druplicate sampleswer e less than 5%o fth eaverag 3value sfo ral lconcentrations .

massfractio n adsorbed(m gkg" 1) 80-I

T 05 U> 15 mass concentrationi nsolutio n (g m~3)

Figure 15.Adsorptio n ofazinphos-methy lo n various bottom materials.Th elinea r adsorption isotherms were derived from thepoint s forth e lowest five concentrations.• = Benschop , siphon- -linked ditch, back section;o = Benschop , siphon-linked ditch, front section;x - Botto m material used intan k trial;A = Jaarsveld, middle ditch, front section.

53 Adsorptiono fazinphos-methy lont ofres hbotto mmateria lfro mth eoutdoo rtank sre - 3 -1 suitedi na nadsorptio ncoefficien to f0.07 3( m kg ),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

Valuesfo rth eadsorptio no fdimethoat eo nbotto mmateria lwer elackin gi nth elit erature.

Procedures in adsorption tests with dimethoate

Fourbotto mmaterial swer euse da scharacterize d inTabl e23 .Solution so fdimetho ate (analyticalgrade )i nde-ionize dwate rwit hCaCl ?a t555 0g m wereprepared .Th e L -3 initialconcentration so fdimethoat ewer e1.06 ,2.25 ,5.0 ,10.1 ,an d 19.5g m .Ofeac h ofthes esolutions ,1 0c m wereadde di ntriplicat et o2 g o fbotto mmateria l (airdry ) incentrifug etubes ,whic hwer e thenrotate dovernigh ta si nSectio n6.6 . Aftercentrifuging ,5 c m ofth esupernatan tliqui dwa sextracte dwit hconsecutivel y 10,5 an d5 c m ofdichloromethan e (Section5.4) .Again ,th emateria lbalanc ewa schecke d byextractin gth ebotto mmateria l (Section6.5) .Th erecover yo fdimethoat eapplie dt o1 1 adsorptionsystem swit hwate ran dbotto mmateria lwa s9H ,wit ha coefficien to fvariatio n of 2%.Correction sfo rrecover yo rdecompositio nwer eno tmade . Theeffec to fai rdryin go fbotto mmateria lo nth eadsorptio nisother mwa schecke di n thewa ydescribe d inSectio n6.6 .

Measured adsorption coefficients of dimethoate

Theadsorptio no fdimethoat eont oth ebotto mmaterial sa tvariou sconcentration si n solutioni sshow ni nFigur e 16.Linea risotherm swer ecalculate dwit ha regressio nprogra m usingal lth epoints .Th eadsorptio ncoefficient so fdimethoat eont oth evariou sbotto m

mass fraction adsorbed (mg kg-1) 25-1

10- Figure 16.Adsorptio no fdimethoat eo n variousbotto mmaterials .Linea radsorptio n isothermscalculate d usingth epoint sfo ral l concentrations.• = Benschop ,siphon-linke d ditch,bac ksection ;o = Benschop ,siphon - -linkedditch ,fron tsection ;A = Benschop , -i—i—i—i—i—i—i—1 O 10 20 supplementallydraine dditch ,bac ksection ; mass concentration insolutio n( gm" 3) 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 .s23) .Th edifference sbetwee nth econ - centrationso fdimethoat ei ntriplicat esample swi t thth esmal lcentrifug etube swer eles s than< Ho fthei raverages .Wit hth elarg ecentrifug etube s (70c m ), thedifference sbe tweentriplicat esample swer eles stha n 2%o fth e iverageconcentrations . Theadsorptio no fdimethoat ea trelativel y lowconcentration so nfres h (notdried ) bottommateria lan do npreviousl ydrie dbotto mmateria li spresente di nFigur e17 .Th e adsorptioncoefficien to fdimethoat eont ofres hb o:to 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 e ofth emos tessentia lcharacteristic s ofthes ecompound si nsurfac ewate ran dca nb esee r asconfirmatio no fearlie rinvestiga - tions. Conversionrate sca nb estudie dwit hvariou stiype so fwater ,includin gdistille dw a ter,de-ionize dwater ,ta pwater ,groun dwate ran d surfacewater .Clos ecompariso no fth e resultso fincubatio no fazinphos-methy li nsurfac ewate rwit hthos eobtaine di nbuffere d aqueoussolution swa srathe rdifficul ti nvie wo fvariation si np Hi nth esurfac ewate r tests. Remarkablei sth ecatalyti ceffec to fC u onconversio nrate so fazinphos-methy lan d dimethoatei nsurfac ewater .S oi nconversio nstudios ,coppe rconcentration s insurfac e

mass fractionadsorbe d (mgkg ")

15-

U>-

0.5-

Figure 17.Adsorptio no fdimethoat eo nbotto m materialo foutdoo rtanks .Isotherm swer ecal culatedwit h linearregressio nprogra mfo ral l relatively lowconcentrations .• « fres h(un - T 0 03 dried)botto nmaterial ,x « starte dfro mair - mass concentration insolutio n( g nrT*) -drybotto mnaterial .

55 watermus tb emeasured .Possibl yothe rion stha tma yb ypresen ti nsurfac ewate rca nals o catalyseconversio nreaction so fbot hcompounds . Highertemperatur eaccelerate dconversio no fbot hcompounds .Th eArrheniu srelation shipsometime sgav ea poo rdiscriptio no fth erelationshi pbetwee nth efirst-orde rrat e coefficientsan dtemperature .Mor eresearc hi sneede dt oclarif ythi srelationship . Manyothe rfactor sma y influenceth econversio nrate so fpesticide s insurfac ewaters , butstud yo fthe mha sonl yjus tstarted .Ligh tappear st ob ea nimportan tfacto ri ncon version.Laborator y testsb yLian g& Lichtenstei n (1972)showe dtha tonl yultraviole t lightwa seffectiv ei nth ephoto-chemica lconversio no fazinphos-methy li nwate r (k = 8.7 d ;i ,= 0.0 8 d),wherea syello wo rre dligh tyielde dconversio nrate sa slo wa si n 2 thedar k .I nth elaboratory ,th einfluenc eo fligh to nconversio nrate so fpesticide si n surfacewate rshoul dthu sb estudie dunde rligh tcondition srepresentativ efo rth efield . Photosensitizersaffec tth ephoto-chemica lconversio nrate so fpesticides ;therefor eex trapolationo frate sfro mth elaborator yt oth efiel di sextremel ydifficul t (Howarde t al., 1978). Aftera firs tperio do fslo wconversion ,a stron gincreas ewa susuall yobserve di n therat eo fconversio no fdimethoate .Thi sma yb erelate dt ochange s inth esystems ,bu t furtherresearc hwil lb eneede dt oclarif ythes echanges .Technique s forincubatio nunde r aerobiccondition sals onee dfurthe rattention .Th erelativel yfas tconversio no fbot h compoundsi nsystem swit hanaerobi cbotto mmateria li sremarkable .Literatur edat ao ncon versionrate so forganophosphoru spesticide si nanaerobi cbotto mmaterial sar estil lscarce , butconversio nrate so fvariou schlorinate dhydrocarbo npesticide si nbiologicall yactiv e sludgewer emor erapi dunde ranaerobi ctha nunde raerobi ccondition s (Hill& McCarty , 1967). Therei sa nobviou snee dt opredic tth econversio nrat eo fpesticide si nth efiel d fromstandardize d laboratorytests .Howeve ron eo fth edifficultie s ist otak erepresen tativewate rsample sfo rincubatio ntests ,a sth evariatio ni ntim ean dspac ei nbacte rialspecie san dnumber s isa seriou sproblem .Attempt sar emad et ous estandardize dwa tersystem sb yinoculatin gwit ha filtrat eo fbotto mmateria lan dsoil .Unfortunately , comparativedat ao nsuc hsystem sar eno tye tavailable .Anothe rpossibl eincubatio nsyste m isa nactive-sludg esyste mobtaine dfro ma sewag eplant . Becauseman yfactor sinfluenc eth econversio nrate so fazinphos-methy lan ddimethoat e insurfac ewater ,thes elaborator yresult sshoul dno tb euse ddirectl yt opredic tconver sionrate sunde rfiel dconditions .Th ebehaviou ro fth emode lcompound si noutdoo rtan k systems isdiscusse d inChapte r7 an dtha ti nditche si nth efiel di sdiscusse di nChapte r 9.

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

7.1 INTRODUCTION

Ratecoefficient sfo r thedeclin 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 rtria lwit h azinphos-methyli na wadin g pool filled withpon dwate ran dabotto m layero fsil t hasbee nstudie d (BayerA.G. , 1978). They foundtha ta ta wate r temperatureo fabou t2 9 °Can da tp H7 th erat eo fdeclin eo f azinphos-methyli npon dwate rwa s0.S 8d •1 .2d). Thehig hwate r temperaturean d CV1 near-neutralp Har eno t representative forsurfac e watersi nth eNetherlands .Rat ecoeffi cientsfo r thedeclin eo fdimethoat ei noutdoo rwatjer scoul dno tb efoun di nth elitera ture. To gainmor e insight intoth edeclin eo fazinphos-methy lan ddimethoat ei nsurfac e water,outdoo r trialswer ese tu pi ntanks .Th eimportanc eo fa laye ro fbotto mmateria l inth etank so nth ephysico-chemica l behaviouro ftti emode l compoundswa s also investiga ted. Theexten to fpenetratio no fazinphos-methy l afiddimethoat e into thebotto mmateria l inth etank swa s studiedo na limite dscale . Someattentio nwa spai dt odifference si nrat e ofdeclin ewhe n thecompound swer e applieda sanalytica l gradeo ra sformulate dproduct s

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 dapproxi mately5 c mabov eth esoi lsurfac et oavoi dcontaminatio nfro msurroundin g soil.Stainless - steelwire-netting s (meshsiz e 11mm )wer eplace do nth etank st oreduc edisturbance . The sideswer eo fenamel . Infou r tanks,a botto m layer0. 1m thic kwa s introduced; theothe rtw otank sdi dno t containbotto mmaterial .Al lsi xtank swer e filledvit h tapwater ,originatin g fromdee p groundwater.Th etank swit hbotto mmateria lwer e filledi nAugus t 1975;thos ewithou t bot tommateria lwer e installedi nsprin g1976 . Aftereac hadditio no fwate rwit ha bucke t(1 0 dm ), theris e inwate r levelwa s measuredwit ha stainless-stee l rule.Fro mth ecalibratio ncurve ,th evolum ei neac ho fth e tankscoul db einferre da tan ytim efro mth ewate r lsvel. Thebotto mmateria lwa scollecte d froma comparativel yclea nwatercours ewithou t sig nificanturba n influences,calle dth e'Tutenburgs eWatering' ,situate dnea rGiesbee k

57 (Provenceo fGuelderland) .Th ewatercours ewa senlarge dthre eyear sbefor esamplin gdurin g landconsolidatio nwork .Th euppe r 10c mo fth ebotto mmateria lfro mth ewatercours ewa s collectedwit ha basket-typ ecutte rhavin ga fine-meshe dwire-nettin g insideth ebasket . Thismateria lwa spartiall ydrie di nai ran dthe nsterilize ddurin gon eda yb ysteamin g undera sheet . Toobtai na simila rdevelopmen to fbiologica lactivit yi nth efou rtank swit hbotto m material,the ywer einoculate dwit h2 d m wellmixe dfres hbotto mmaterial ,fo rinstanc e withcyclops ,daphnias ,snail san dtubifex .Furthermore ,thes etank swer epartl yplante d witha fe wsmal lplant so fCanadia npondwee d {Elodea canadensis) collected fromth esam plingditch .

Application of pesticides

Tanks Ian d IIIwer ekep tuntreate ddurin gal ltrials .Th etank swithou ta laye ro f bottommateria lwer edesignate dTank sV an dVI .Fo rquic kreferenc eth evariou streatment s areindicate dwit habbreviation sconsistin go fth echaracter sA fo razinphos-methyl ,D fo r dimethoatean dF fo rformulate dproduct .Arabi cnumeral s indicateth evariou strial s( 1 to5 )an dT plu sRoma nnumera lrefer st oth etank s (It oVI ) (Table 24).Afte rapplication , theinsecticid edos ewa smanuall ymixe dwit hth ewate rusin ga skimmer .Th einitia lwa tervolum ei nth etank si nth efirs ttria lwa sabou t0. 1 m andwa s0.1 5m inal lothe r trials. Thefirs ttan ktria lstarte di nSeptembe r 1975wit hdimethoat eapplie dt oTank sI I and TVa sanalytica lgrad e (98%purity )a ta concentratio no f1 0m gm . Inal lothe rtan ktrials ,bot hazinphos-methy lan ddimethoat ewer eapplie dsimulta neouslya ta concentratio no fabou t 100m gm ~ .I nJun e 1976,th esecon dtria lstarte d withazinphos-methy lan ddimethoate ,bot hanalytica lgrade .Th ethir dtria lstarte di n July 1976wit ha wettabl epowde ro fazinphos-methy l (Gusathion,25 1 (w/w)w.p. )an da liq uidformulatio no fdimethoat e (Rogor,40° s w/v).

Table24 .Dat ao npesticide s inoutdoo r tanktrials .Abbreviations :A fo r azinphos-methyl,analytica lgrad e (98%purity) ;A Ffo razinphos-methyl , formulated product (Gusathion,25 %w.p.) ; Bfo rblan k (untreated)experiment ; Crefer s toa nadditio no fcoppe rsulphate ;D fo rdimethoate ,analytica lgrad e (98%purity) ;D Ffo rdimethoate ,formulate dproduc t (Rogor,40 %liquid) ; T plusRoma nnumera lrefer s toth etanks .

Trial Tank swit ha layero f bottommateria l Tanksw i thonl ywate r

TI Til Till TIV TV TVI

1 B DlTi l B DlTI V - - 2 B A2Ti l B A2TI V A2T V A2TV I D2Ti l D2TI V D2T V D2TV I 3 B AF3Ti l B AF3TI V AF3T V AF3TV I DF3Ti l DF3TI V DF3T V DF3TV I 4 B — B - AFC4T V AFC4TV I DFC4T V DFC4TV I 5 B AC5Ti l B AC5TI V AC5T V AC5TV I DC5Ti l DC5TI V DC5T V DC5TV I

58 Duringth efirs t three trials,alga lbloo mcause da dail y fluctuationi np Ho fth e watercompartmen to fal l tanks.Befor eth efourt hi:ria lstarte di nTank sV an dVI ,bot h tankswer ecarefull y cleanedan drefille dwit h freshdrinkin gwater .T oavoi dalga lbloo m inthes etanks ,th ealgicid ecoppe rsulphat ewa sacde dt omas s concentrationo fcoppe r 1.5g m ". I nthi sfourt h trial,th e sameproduct sa si nth ethir d trialwer e introduced intoTank sV an dVI . Inth elas t trial (No5 )i nth eautum no f1976 ,Tank s II,IV ,V an dV Iwer e replen ishedwit hdrinkin gwate ran dth esam econcentratio n (1.5g m )o fcoppe r sulphatewa s added.Afte r 11days ,a doubl eamoun to fcoppe r sulphatewa s introduced intothos etanks . Inth efift htrial ,azinphos-methy lan ddimethoat evrer eapplie da sanalytica l gradet o Tanks II,IV ,V an dV I(Tabl e24) .

Characteristics of the water

Somechemica l characteristicso fwate r samples fromth eoutdoo r tankswer emeasure d byth e EasternLaborator 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 e relatively highconcentration so fphosphate . Duet oth estron gsunshin edurin g 1976,a stron galga lbloo moccurre di nth eeutrophi c watero fal l tanks.Th ealga etak eu pCO ,durin gphotosynthesi si nth edaytim ean dreleas e

C02a tnight .Th eCO ,uptak edisturbe d equilibriumc fcarbo ndioxid ean dcalciu mbicarbo nate,causin ga ris ei np Hdurin gth eda y(Figur e M).

Table 25.Chemica l characteristicso fwate r samples fromoutdoo r tank trials,measure db yth e EasternLaborator yfo rWate rTesting ,Doetinchem . Sampling datefo rTria l2 ,1 5Jun e 1976;fo rTria l! ,2 1Septembe r 1976.

Characteristics Trial2 Trial5

TI I TI V TV TV I TI V TV

PH 9.7 9.6 8.7 9.1 7.6 8.1 COD (gm" 3) 110 125 95 65 180 125 NO3 (gm" 3) 1 1 <1 <1 <1 <1 NHj( gm -3) 0.29 <0.0 3 <0.0 3 <0.0 3 <0.5 2 <0.1 3 TotalN (gm -3) 3.1 3.2 1.9 1.4 0.68 1.4 Orthophosphate( gm -3) 0.60 2.4 <0.0 3 <0.0 3 0.25 0.08 Totalphosphat e( gm -3) 1.1 5.5 0.49 0.36 0.46 0.20 Cl" (gm" 3) 18 16 15 20 15 12 Ca2+ (gm" 3) 43 29 HCO3 (gm -3) 127 87 -3 9 2 C02 (gm ) C0§- (gm" 3) 0 0 Hardness(a sCaO )( gm -3) 68 49 Conductivity (mSm -1) 28.8 23.2 20.9 20.5 25.3 17.6

59 pH 11-1

Figure 18.p Hi nth ewate r compartment (averageo f r—i—'—'—i—'—'—i—I—'—'—"—1 . * . 4 8 12 16 slx water tanks) against timeo fday . Measurements timeo fth eda y(h ) on1 6Jul y1976 .

Thep Hi nth ewate r compartments were occasionally measured several times duringth e daywit ha digita l pHmeter .Th ep Hwa sals o mostly checked atinterval so f2 day sa t 08:30 and16:0 0h .A sth erelationship s betweenp Han dth ehydrolysi s rates ofth emode l compounds areno tlinear ,th eassessmen t ofa naverag ep Hi nth ewate r compartment is on lyo flimite d importance.

Characteristics of bottom material

InApri l 1977,th eyea r after thetrials ,wate rwa sslowl y removed fromTank s IIan d TVwithou t disturbing thesedimen t layer. Sampleso fbotto mmateria l were takenwit ha skimmer.Th ecompositio n ofth euppe r fewcentimetre s ofth emu dlaye ran dsom e physical and chemical characteristics ofth emu dlaye rwer e measuredb yth eLaborator y forSoi l andCro pTestin g inOosterbee k (Table 23).Th eminera l fractiono fth ebotto m material canb eclassifie d intoth e'clay ' textural class.Th eorgani c matter content israthe r high incompariso n with most agricultural claysoils . Formeasuremen to fth evolum e fraction ofliqui dan dbul k densityo fth ebotto mmate rial,mu dcore swer e taken intriplicat e fromTank s IIan dIV ,accordin g toprocedur e des cribed inSectio n 4.4.Th ecolumn s ofbotto mmateria l were frozena t-2 0 Can dsubse quently divided into sliceso fequa l thickness (0.01m )wit h amechanica l sawnormall y used forresearc ho nsoi l slides atth eSoi l Survey Institute inWageningen .Th eslice s wereweighe d (m,) an ddrie da t10 5 Ct oconstan t mass (u,),Th evolum eo fth eslice so f bottommateria l (7) wa scalculate d from Equation 11,assumin g complete saturationo f thebotto m material andconstan t density ofth esoli d phase inth euppe r fewcentimetre s ofth emu dlayer .

vb= K -m d)/pw+ m d/ps 01)

inwhic h

p =densit y ofwate r (kgm ) w -3 p =densit y ofsoli d phaseo fbotto mmateria l (kgm )

The density ofth esoli dphas eo fth ebotto mmateria lwa smeasure d as258 0k gm (at Laboratory forSoi lan dCro pTesting , Oosterbeek). The volume fraction ofliqui d (E.) andth edr ybul k density (p) wer e calculated

60 fromEquation s 12an d13 ,respectivel y

ei - K - "d^ViP (12) (13) Pb= md/pb

Theprofil eo fvolum e fractionso fliqui dan d cf bulkdensit yi nth ebotto mmateria l are showni nFigur e 19.Compare dwit h agricultural sjoils,th evolum e fractionso fliqui d arehig han ddr ybul k densitiesar elow ,especiall y inth euppe r layers.Dat aar esimila r tothos efo r ditchbottoms .

Sampling of water and GW analysis

Rainfallan devaporatio nresulte di na variati eao fth ewate rvolum ei nth etanks . Beforeeac hsampling ,th eheigh to fth ewate r surfac;wa smeasured ,afte rwhic hth evolum e couldb erea d fromth ecalibratio ncurve . Atth esamplin gdates ,th erang eo fwate r temperaturei nth eprecedin gperio dwa s read fromminimum—maximu mthermometer s immersedi nTank sI ,II Ian dV . Duringth efirs ttrials ,composit ewate r sample;totallin g 1d m werecollecte dwit h a stainlessstee l ladle.A tth ebeginnin go fal lothj rtrials ,composit ewate r samplesto talling0. 1d m were collectedwit ha pipett eo f1 0a n,an da ta late rstage ,whe ncon centrationsbecam elow ,composit e samples totalling Id m wereagai ntake nwit hth eladle . Allwate r sampleswer e extractedwit hdichloro msthan ei nseparator y funnelsa sdes cribedi nSectio n5. 3an d5.4 .Azinphos-methy li nth oextract so fth ewate rsample s from Trials3 an d4wa smeasure db yGL Co nColum nI ;th eiattract sfro mTrial s2 ,3 an d5 wer e analysedwit hColum nI I(Tabl e 14).Th e concentrationso fdimethoat ei nth eextract so fwa tersample s fromTrial s 1,3 an d4wer emeasure do n(lolum nI ;thos efro mTrial s3 an d5 wereanalyse do nColum nI Ian dthos efro mTria l2 wer emeasure do nColum nII I(Tabl e15) . Some serieswer e thusmeasure do ntw odifferen tcolum sa tdifferen t times,whic h sometimes gavesligh tdifference si nth econcentration sbu ton!. ysmal ldifference si nth eslop eo f

3 —3 bulk densi ty (k g m~ ) volume fraction of liquid( m m ) Q V400 800 \\

0.05- Ü depth in bottom (m) Figure 19.Volum e fractiono fliqui d andbul k density against depth inbotto mmateria lo f outdoor Tanks II(o )an dI V (x).

61 decline.N ointerferin g substanceswer e foundwhe nextract s fromth euntreate d TanksI an d IIIwer emeasure do nal lcolumns .S oclean-u po fth eextract so fwate r samples fromoutdoo r tankswa sno tnecessary .

Correction for sampling of water

Since thevolum eo fwate ri noutdoo r tanksvarie dwit hrai nan devaporation ,tota l masso fth e compoundsa tth esamplin g dateswer euse d forplottin gth e declineo fth ecom poundswit htime . Because thewate r sampleswithdraw n fromth e tankswer e sometimes rather large (espe cially duringTria l 1wit hdimethoate) ,a correctio n forvolum eremove dwa s necessarybe forecontinuou sdeclin eplot s couldb emade . The discontinuitiesdu et owate r samplingi nth erelationshi pbetwee n themas so fpes ticidei nth ewate r compartmento na logarithmi c scale against time couldb eeliminate d withth efollowin g equations:

m = o x V n w,n w,n t= 0 ,n = 1 : m= m.

tx "=2:^ = n2/(1-78il/yw>1) Vi n »3 : K = "v/<1 - VnVVn-P x v- V/ W (14) inwhic h

n =integer ,Samplin gN o(i ntim e series) (1) =measure dmas so fpesticid ei nwate r compartmentbefor e Sampling n (mg) n a - mass concentrationo fpesticid ei nwate r compartment (intim eseries)(m gm ) w, n -7 V =volum eo fwate r compartmentbefor e Samplingn (m) m' =mas so fpesticid ei nwate rcompartmen tcorrecte d forvolum eo f (mg) sampleswithdraw n V =volum eo fwate r sample(i ntim eseries ) (m) Thecorrectio n steps (Equation 14)wer e introduced intoa nadapte d linear regression programo na Hewlet tPackar d deskcalculator .Th efirst-orde r rate coefficients(/ ci n _i r d )fo rth edeclin eo fth esubstance s correspondt oth eabsolut evalu eo fth e regression coefficientso fth eregressio n linesfo rI n m' againsttime . The differencesbetwee n themeasure dmasse san dth ecorrecte d masseso fazinphos-me - thylan ddimethoat ei nth ewate r compartmento fth etanks ,du et owithdrawals ,coul db e neglectedi nTrial s2 ,3an d4 becaus e thevolume swithdraw nwer erelativel y small(0. 1 dm ). However,i nTrial s1 an d5 ,a correctio nwa snecessary ,becaus eth esampl evolum e was1 d m. Moreove ri nTria l 1,samplin gwa s rather frequentan di nTria l5 als owate r sampleso f2. 5d m were collectedfo rassessmen to fwate rquality .

62 Sampling of bottom ma.tem.al and GLC analysis

Thepenetratio no fdimethoat eint o thebotto mliy i erwa smeasure d duringTria l 1. Bot- tornsample swer e takenwit h tubesi ntriplicat eo n2 1 Septemberan d1 5Octobe r197 5 (Section4.4) . Thepenetratio no fazinphos-methy lwa s investigated during Trial2 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 sabou t 12.3c m. Themu dcore swer estore di na deep-freeze ra t 20 C.A sth edevelopmen to fa suita - ble clean-upmetho dfo r azinphos-methyl took several months,th estorag e timewa s nearly halfa year .Th e storage time forbotto m coreswit h iimethoatewa s less thanon emonth , The frozenmu d columnswer e divided intoslice s1- 2 anthic kwit ha carborundu mhandsaw , Theslice swer eweighe dbefor e extraction.Afte r extractionan ddryin ga t10 5°C ,th edr y masso fth ebotto mmateria lwa s estimated.Th evolume s ofth ewe tbotto mmateria l were calculated fromEquatio n 11.Th edept hbelo wth e sedLment --water interfacewa s calculated fromth evolum eo fth eslice ,an dth esurfac eo fth e bottom column.Th esaw-cu twa s2 m m for thehand-saw nmu dcolumns . Theprocedure sfo rextractio nan dclean-u po f tieextract sfo r azinphos-methylan d dimethoatear edescribe di nSection s 5.6,5.7 , 5.11 ind5.12 ,respectively .Th ecleane d extractswer e analysedb yGL Co nColum nI Ifo razinpfio s methylan do nColum n IIIfo rdime - thoate (Tables1 4an d15) . recoveryo fazinphos-methy l from Ina separat e testth eeffec to fstorag e time feparedfro m1 0g o fair-dr ybotto m frozenmu dcolumn swa s studied .Mi dsample swer ep r materialan d5 0c m ofwate ri na polyethylen ecup . Ihesesample swer e spikedwit hanalyti - cal-gradeazinphos-methy lan dstore da tabou t-2 0d , Theywer e extractedan danalyse daf - ter 1,10 5an d24 2day si nth esam ewa ya sth e slice; ofbotto mmateria l fromth e tank trials. Recovery from 16sample so fbotto mmateria l spijcedwit h azinphos-methyl was 9H, witha coefficien to fvariatio no f 1%(Sectio n5.11 ) After 105an d24 2days ,abou t 90% and 102%o fth e initial amountswer e recovered,wit h coefficientso fvariatio no fabou t 9% and 6%,respectively . These results showtha ta correctionfacto rfo r storage timewa sno t necessary.Als on ocorrection swer emad efo rth e recovery.Th eaverag erecover yo fdime - thoatefro mbotto mmateria lwa s 95%,s on ocorrectiofi s weremad e forrecover yo fdimetho - ateeither . Asa resul to fth eproblem s encounteredi n deveJ.opmento fsuitabl e clean-upprocedures , onlya fe wmeasurement s couldb edon eo npenetratio n ofth ecompound s intoth ebotto m layer ofth etanks .

7.3 MEASURED RATESO FDECLIN EI NWATE R

Theplot so fth ecorrecte dmasse so fazinphos-mëthy l inth ewate r compartment against time forTrial s2 t o5 ar eshow ni nFigur e 20.Plot s fordimethoat ei nTrial s 1t o5 ar e presentedi nFigur e 21. Differencesi ndeclin erat eo fth emode lcompound s inth etank swit hbotto mlaye r, (Tilan dTIV )i nth e firstthre e experiments (withou: additiono fcoppe rsulphate )wer e

63 massof ozinphos-methyl (mg) 20- mass of ozinphos-methyl (mg) 20-

AF3 TZ(»H&3-102)

AF3 TBC(pH7.6-10.3 )

AF3 Tn(pHae-Kie>

A2 TfftpHes-ia3) A2 TIE(0H9.1-110 )

I ' ' • • I 10 15 time(d)

mass of azinphos-methyl (mg) 20

AFC4 T3E(pH7.8-a3) AFC4 m AC5 Ttt{pH7.7-02)

3 TŒfpH73-ft1) .5 TX(pH7.M3)

ACS TK{pH7S-a2) 1 I ' ' ' ' I 15 20 25 time(d)

Figure20 .Mas so fazinphos-methy l inwate rcompartmen to foutdoo r tanks.A .Tria l 2:ana lyticalgrad eadde do n4 Jun e 1976.B .Tria l3 :formulate d product (Gusathion25 %w.p. ) addedo n 15Jul y 1976.C .Tria l4 :a sTria l3 adde d on5 Augus t 1976;coppe rsulphat eadde d tomas sconcentratio no fCu 2 1.5g m -3o n4August .D .Tria l5 :analytica lgrad eadde do n 20Septembe r 1976;coppe r sulphateadde d tomas sconcentratio no fCu 2+ 1.5g m -3 on1 9 Septemberan da furthe r 3g m -3 on 1October .I nTria l5 (Fig .D )th emas si scorrecte d forvolum eo fsample swithdrawn .Fo rcodin go fline sse eTabl e24 .

distinct.Th esam ehold sfo rrate so fdeclin ei nth etank swithou tbotto mmateria l (TVan d TVI)(Figure s20A ,B ;21A ,B,C) .Suc hdifference sca nprobabl ypartl yb eascribe d todif ferencesi nalga lbloom ,resultin gi ndifferen tp Han d lightpenetration .I nTrial s4 an d 5,wit hadditio no falgicide ,p Hfluctuation swer esmal l (Table 26). Consequentlyth edif ferencesi nth edeclin epatter no fth ecompound swer esmal l (Figures20C ,D ;21D , E). Ifth edeclin eca nb edescribe dwit ha first-orde rrat eequation ,th erelationshi p betweenth elogarith mo fth emas so fth epesticid ean dtim ei slinear .A sca nb esee n frommos tdeclin eplots ,th erelationshi pi salmos tlinea rfo ronl ypar to fth eperio do f investigation.Fo rthos epart so fth edeclin eplots ,linea rregressio nline swer ecalcula ted.Thes eline sar edraw ni nFigure s 20an d21 .Th ecorrespondin grat ecoefficient sfo r thedeclin eo fbot hcompound sar egive ni nTabl e26 . Therate so fdeclin eo fth emode lcompound s inth ewate rcompartmen twer emuc hfaste r thani nth elaborator ytest s (Chapter 6). Intank swithou tbotto mlayer ,th edeclin ewa s alsorathe rfast .I ntrial si nwhic hbot hcompound swer eapplie dsimultaneousl yt oth e sametank ,declin eo fazinphos-methy lwa sfaste rtha no fdimethoat e (Table26) . 64 Figure 21.Mas s ofdimethoat ei nwate r compartment (If outdoor tanks.A .Tria l I:analyti - cal grade added on2 3Septembe r 1975.B .Tria l2 : lytical grade addedo n4 Jun e1976 . C. Trial 3:formulate d product (Rogor 40%liquid ) added on 15Jul y 1976.D .Tria l 4:a s Trial 3adde d on5 Augus t 1976;coppe r sulphate add

Influenae of pH and temperature on the decline ratet

Therange so fp Hi nth ewate rcompartmen to f tie differenttanks ,measure di nperiod s withapproximatel y lineardecline ,ar epresente di n Table26 .Th erange so fp Hdurin geac h trialar eshow nagains tth eregressio nline si n Figtre s 20an d21 .Bot hfigure ssho wa n increasei nth edeclin erat ea tincreasin gp Hrang e This indicates thatth emaximu mp Hi n thewate rcompartmen ti sprobabl ya majo rfacto ri n therat eo fdeclin eo fbot hcompounds , For thisreason ,rat ecoefficient sfo rdeclin eo f cZ inphos-methylan ddimethoat ei nth e firstthre etan ktrial s (withoutcoppe rsulphate ) v eplotte dagains tth emaximu mp Hi n Figure22 .Th escatte ri nFigur e2 2result sfro mth e influenceo fothe rmajo rfactor slik e temperature,alga lbloo man dligh t (externalan di n thewate rcompartment) .

65 Table26 .First-orde r ratecoefficient sfo rdeclin eo fazinphos-methy lan ddimethoat ei n watercompartmen to foutdoo r tanks.Derive dfo rperiod swit happroximatel y linearrela tionshipsbetwee nmas so finsecticid e (logscale )an dtime .Abbreviations :A fo razinphos - -methyl,D fo rdimethoate ,F fo rformulate d compound,C fo rcoppe r sulphateadditio nan d Tfo rtank .

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 Cd"') (d) 8:30 h 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 D2TI I 0.22 3.2 06-04/ IV 9.3 10.6 21 10-28 A2 TIV 0.72 1.0 D2TI V 0.67 1.0 06-10 V 7.7 8.4 20 10-25 A2 TV 0.19 3.7 D2T V 0.013 53 VI 8.8 9.7 20 10-25 A2 TVI 0.26 2.7 D2TV I 0.12 5.6 II 9.0 10.3 20 13-27 A2 Til 0.49 1. 4 D2TI I 0.57 1.2 06-10/ IV 9.1 11.0 22 14-28 A2TI V 0.39 1.8 D2TI V 0.59 1. 2 06-30 V 8.1 9.5 20 14-26 A2T V 0.27 2.6 D2T V 0.20 3.5 VI 8.9 9.7 20 14-26 A2TV I 0.40 1.7 D2TV I 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 DF3TI V 0.25 2.8 07-30 V 8.2 10.2 21 15-30 AF3T V 0.17 4.0 DF3T V 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/ 1V 7.8 8.3 17 14-21 AFC4T V 0.25 2.8 DFC4T V 0.036 19 08-09 VI 7.7 8.1 17 14-21 AFC4TV I 0.21 3.3 DFC4TV I 0.010 67 08-09/ |V 8.2 8.3 20 17-24 AFC4T V 0.31 2.3 DFC4T V 0.14 5.0 08-16 VI 8.2 8.3 20 17-24 AFC4 TVI 0.36 1.9 DFC4 TVI 0.1 8 4.0 08-16/ V 8.2 8.3 19 11-24 AFC4T V 0.29 2.4 DFC4T V 0.078 8.9 08-30 VI 8.1 8.3 19 11-24 AFC4 TVI 0.28 2.5 DFC4 TVI 0.11 6.5 II 7.7 8.8 15 11-24 AC5TI I 0.1 6 4.4 DC5 TII 0.055 13 09-20/ IV 7.5 8.0 16 12-23 AC5TI V 0.13 5.5 DC5TI V 0.038 18 10-01 V 8.1 8.3 16 12-23 AC5 T V 0.17 4.0 DC5 T V 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 AC5 TII 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 DC5TI V 0.052 13 10-13 V 7.9 8.1 15 12-19 AC5 TV 0.17 4.1 DC5 T V 0.083 8.4 VI 7.9 8.1 15 12-19 AC5 TVI 0.18 3.8 DC5TV I 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 H7 ma yb eles stha n0. 1d " (i,> 7 d) . Therat ecoefficien to fdimethoat ei n 2 _1 surfacewate rwit hp H7 coul db eles stha n0.0 1d (t,> 7 0d )(Figur e 22). 2 Thetemperatur efluctuation s inth ewate rcompartment swer erathe rlarge ,rangin g from1 0t o3 0° Cdurin gth esumme ran dfro m3 t o2 4° Ci nth eautum n (Table 26).Averag e watertemperature swer ecalculate dfro mth ehighes tan dlowes twate rtemperature srea d

66 ratecoefficien t for decline (d ) 10-=

ai 10

Figure22 .F i it-orderrat ecoefficient sfo rdeclin e ofth emode l poundsi nth ewate rcompartmen to f outdoortank s igainstmaximu mp Hdurin gTria l 1t o 3.Averag e wat; r temperaturerange dfro m 16t o2 2°C . o= azinphos- m thyl,analytica lgrade ;• = azinphos - —1 -methyl25 %w . .;A = dimethoate ,analytica lgrade ; io 11 A= dimethoat e pH 40%liquid .

fromminimum—maximu mthermometers .Th eaverag ewate rtemperatur ei nsumme rrange dfro m 17t o2 2° Can dthos ei nth eautum nfro m 12t o1 7°Ç . -1 Thehighes trat eo fdeclin eo fazinphos-methy l (K 1.1d 0.63d )wa sfoun d ata combinatio no fth ehighes taverag ewate rtemperatur e2 1°C )an da hig hp Hrangin g 1 from9. 4 to10. 7(Tabl e 26).Th elowes trat eo fde c ineo fazinphos-methy l (k =0. 1d t,= 7. 3d )wa smeasure di nth eTria l5 (withcoppe rsulphate) ,a ta naverag ewate rtemper - o atureo f1 5 Can da p Hrang eo f7. 7t o9. 2 (Table f6).Th erat eo fdeclin eo fazinphos - -methylthu svarie db yabou ta facto rten . Therat eo fdeclin eo fdimethoat ei nth etrial ivarie db yabou ta facto r80 .Th elow estrat eo fdeclin e (k =0.01d •1 67d )wa sfoun da ta naverag ewate rtemperatur e of1 7 Can da ta p Hrang efro m7. 7 to8.1 ,i nth e"presenc I eo fcoppe rsulphat e (Table26) . -1 , Thedeclin ewa sfastes t (k =0.8 0d 0.87d ]fo rth ehighes taverag ewate rtemper - 'k ature(2 1°C )an dth ehig hp Hrang e (9.4-10.7)

Effect of formulation

Therate so fdeclin eo fth emode lcompound s applieda sanalytica lgrad eo ra sformula - tedproduct si nth ewate rcompartment ,durin gTrial s 1t o3 ma yb ecompare di nFigur e22 . Noclea rdifferenc ei nrat eo fdeclin ecoul db e obsehrvedbetwee nazinphos-methy la sanalyt - icalgrad ean d25 $w.p .Th esam ehold sfo rth e measurementso ndimethoate ,whethe ri twa s applieda sanalytica lgrad eo ra s40 $liquid .Fo r possibleeffect so fth eformulation si n additiont ocoppe rsulphat eo nth edelin erate so f bpthcompounds ,n oclea rtrend swer e found.

67 Effeat of copper sulphate

Additiono fcoppe rsulphat et oth ereplenishe dwate rcompartment sstrongl yretarde d growtho falgae ,s otha tp Hfluctuation swer estrongl ysuppresse d (Table26 ,Trial s4 an d 5). Howeverdurin gTria l5 i nTank sI Ian dI V(wit hbotto mlayer) ,thi ssuppressio nwa s onlytemporary ,probabl ydu et oadsorptio no fcoppe rsulphat eo nth ebotto mmaterial .I n Trial5 ,rate so fdeclin eo fbot hcompound s intank swit hbotto mmateria lwer eslowe rtha n thosei ntank swithou tbotto mmaterial ,despit eth econsiderabl yhighe rp Hi nth etank s withbotto mmateria l (Table 26).On eexplanatio nmigh tb ea decreas ei nth ecatalyti cac tivityo fcoppe rsulphate ,b yadsorptio no nbotto mmaterial .Anothe rexplanatio nmigh tb e thatth ecleane dan dreplenishe d tankswithou tbotto mmateria lallowe da greate rligh tpen etrationtha nth etank swit ha botto mlayer ,containin gals osom ealga ei nth ewate rcom partment.I nvie wo fth efaste rconversio nrat eo fbot hcompound si nsurfac ewate rafte r additiono fcoppe rsulphat ei nlaborator ytest s (Sections6. 2 and6.3) ,th eforme rexpla nationseem st ob emor elikely .

Effects of adsorption onto bottom material

Insituation swit ha fas tadsorptio no fth einsecticide sont oth ebotto mmaterial ,a fastdeclin ea tth ebeginnin go fth etrial sma yb eexpected .I nsuc hcases ,th eintercep t attim ezer oi slower .Th eplot sfo rth edeclin eo fdimethoat edi dno tsho wsuc hlo w intercepts.Som eo fth edeclin eplot sfo razinphos-methy lclearl yshowe da lowe rintercep t thanth eamoun tintroduce d (linesA 2TIV ,AF 3Ti lan dAF 3TI Vi nFigure s20A ,B) .Howeve r theregressio nline sfo rA 2Til ,AC 5Ti lan dAC 5TI Vdi dno tclearl y indicatea fas tad sorptiono fazinphos-methy lo nth ebotto mmaterial . Becauseo fth elarg efluctuation s inp Hi nth etan ktrials ,i ti sdifficul tt odra w conclusionso nth eeffec to fbotto mmateria lo nth erat eo fdeclin eo feithe rcompound . Therate so fdeclin eo fbot hmode lcompound sdurin gTrial s2 an d3 wer efaste ri ntank s witha botto mlaye rexcep tfo rAF 3TV Ian dDF 3TV I (Figures20 Ban d 21C).However ,th eex tremelyfas tdeclin eo fazinphos-methy lan ddimethoat ei nTan kV Idurin gTria l3 ca nb eex plainedb yth eextremel yhig hp Hrang eo f9. 4 to10. 7 (Table26) .

7.4 MEASUREDPENETRATIO NINT OBOTTO MMATERIA L

Masseso fazinphos-methy lmeasure di nextract so fslice so fbotto mmateria ldurin g Trial 2ar epresente di nTabl e27 . Themasse so fazinphos-methy l inth euppe rslice swer egenerall ymuc hhighe rtha ni n thelowe rslices .Ove rth edept hinvestigate d (0-6cm) ,a distinc tpenetratio no fazinphos - -methylwa sfound .Th edifference si nth emasse sfo rduplicat ecolumn swer elarge .Th edif ferencesbetwee nTank sI Ian d IVwer eals olarg e (Table 27).Th esmal lamount so fazinphos - -methyli nth ebotto mlaye ro fTan kI Vca npartl yb eascribe dt oth efas tdeclin erat eo f thattan k (Table26) . Thetota lmas so fazinphos-methy l inth ebotto mcompartmen to fth etank swa scalcula tedan dcompare dwit hmasse so fazinphos-methy li nth ewate rcompartmen t (Table 28).Afte r

68 Table27 .Measure d penetrationo fazinphos-methy l inth ebotto mlaye r duringoutdoo rtan kTria l2 starte do n4 Jun e197 6 Masseso fazinphos - -methylpe rcolum nslice .

Date Tank Slice1 Layeri nbotto m Mass oE azinphos- No No (m) -me thyL (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 TI V la 0 0.017 _2 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 -0.01 7 820 lb 0 -0.01 9 300 2a 0.019 -0.03 5 160 2b 0.021 -0.03 5 36 3a 0.037 -0.05 1 10 3b 0.037 -0.05 1 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 ,2 an d3 ar efirst ,secon dan dthir d slice;a an db refert oduplicat esamples . 2.Failur ei nanalysis .

5.5days ,th emas s fractionso fazinphos-methy li n thebotto mcompartmen to fTank sI Ian d IVwer e1 7an d27% ,respectivel yi nth etota lmassej s recoveredi nth etank .Afte r 11days , thesevalue swer e5 5an d72% ,respectively .The yi indicatetha tth erat eo fdeclin eo f azinphos-methyli nth ewate rcompartmen twa spro l obatly fastertha nth erat eo fdeclin ei n thebotto mmaterial .

Table28 .Mas so fazinphos-methy li nth ewate rcompartmen t(m J) 4 r A,w andbotto mcompartmen t (mAj, ) ofTank sI Ian dI Vdirin gth e second tankexperimen tstarte do n4 Jun e 1976.

Date Tank Azinphos-methyl No m m., /(m . + .) A,w mA,b A,b A,w m.A,b (ug) (Pg) (%)

10Jun e TI I 3530 740 17 TI V 250 94 27 15Jun e TI I 300 360 55 TI V 30 77 72

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 gfo 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 s 18%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 GENERAL DISCUSSION ON OUTDOOR TANKS TRIALS

Outdoortrial si nwate rtank sma ysho wth erat eo fdeclin eunde rfiel dcondition s andit svariation .However ,wel ldefine dan dmor eeasil ycontrollabl etest sunde 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 d penetrationo fdimethoat ei nth ebotto mlaye r duringoutdoo r tankTria l 1starte do n2 3Septembe r 1975.Masse so f dimethoatepe rcolum nslice .

Date Tank Slice1 Layer in Mass of No No bottom dimethoate (m) (ng)

15 October T II la 0 - 0.011 81 lb 0 - 0.010 79 lc 0 - 0.010 _2 2a 0.013 - 0.024 41 2b 0.012 - 0.023 50 2c 0.012 - 0.023 42 T IV la 0 - 0.011 43 lb 0 - 0.012 61 lc 0 - 0.013 52 2a 0.013 - 0.025 31 2b 0.014 - 0.025 28 2c 0.015 - 0.026 18 1.Slic eN o1 an d2 ar efirs tan dsecon d slice;a ,b an dc refert otriplicat ecolumns . 2.Failur ei nanalysis .

70 Tank trialsar eusefu l instudie s onth edecllin eo fpesticide s inth efield .However , even tank trialsar e rathercomplex .Alga lbloo mca neasil yoccu ran dcauses ,fo r instance fluctuation inp Hand ,variatio n inligh tpenetration .Tan ksystem swit h almostth e same initial situationma ydevelo pdifferently . Thep Ho fth ewate rwa sa majo r factori ndedlin eo fbot hmode l compounds.Th ep H in many surfacewater swil lno tb ea shig ha s inthes strials ,an d ingenera l thedeclin e willprobabl yb e slower. Inshallow ,relativel y smallditches ,however ,th esam ekin d of developmentma y occur.Mor e detailedmeasurement s D£p Han d temperature (preferablycon - tinuous)ar eneede d infutur etan ktrials . Abotto m layer inth e tankdi dno tdetermin e thedeclin eo fcompound s inth ewate r compartment. A cleareffec to f formulations ofbot hcompound so nth erate so fdeclin ecoul dno t be found. Coppersulphat e suppressed algalbloo man dprevente dp H fluctuation.However ,th e influenceo fC u on thedeclin erat eo fbot hcompound s inligh tcoul dno tye tb eanalysed . Witha botto m layer,C u seemed tob e inactivated rapidly. A distinctpenetratio no fth ecompound s into ihebotto m layerwa sdetected .Th econ centrationpattern smeasure dwoul d resultfro mdiffusio ni ncombinatio nwit hadsorption , withunknow ncontribution s frommixin gb yorganism s anddisturbanc eo fth ebotto m layer during sampling.Anothe rmechanis m forth etransfe i ofpesticide s toth ebotto mma yb e the depositionwit hphytoplankto nan dsuspende dsolids . Themeasurement s onazinphos-methy l indicated that thedeclin e inth ebotto mcompart mentwa sprobabl yslowe r than inth ewate rcomparurent .B yusin g computer simulations on thebehaviou ro fpesticide s inaquati c systemswit h a bottom layer,th econtributio no fa bottom layero nth erat eo fdeclin eca nb ebette re iraluate d (Chapter8) . Theresult so fthes eoutdoo rtan ktrial swil l jecompare dwit h those frommeasure - ments inth efield ,especiall y inditche swit hstanlin gwate r (Chapter9) .

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 tt odescrib e thebehaviou ro fpesticide si na wate r tankwit ha botto m layer. Sucha mode l canb ehelpfu l inevaluatin g theresult so fth e tank trials (Chapter 7)i nmor e detail.Besides , thismode l canb ea goo d starting point for thecomputation so nditc h sections. Inth e computationmodel ,som e simplifying assumptionswer emade . Introductiono fth e pesticideswa s assumedt ob einitiall y mixed evenly throughout thewate r compartmento fa tank.Pesticide s movementb ydiffusio n from thewater-sedimen t interface into the bottom layerwa sdescribe d ina one-dimensiona l system.Adsorptio n equilibrium was assumedt ob e established instantaneously.Th erate s fordecompositio no fth e insecticides inwate ran d inbotto m material were different.Th emos t reliable data availablewer e introduced into themodels . By comparingth eresult so fcomputation s with thoseo fmeasurement s inth e outdoor tanks, themos t important shortcomings inth ecomputatio n modelan di nth edat a canb e traced. Finally,th ecomputatio n modeli suse dfo rafe wsimulatio n experimentso nth e behav iouro fpesticide s ina naquati c systemwit ha botto m layer.Pesticid e characteristics liketh ediffusio n coefficienti nth e liquid phaseo fth ebottom ,th eadsorptio n coeffi cient, therat eo fconversio ni nbotto mmateria lan dth erat eo fconversio ni nwate rwer e varied. These computationsma yb ehelpfu li nevaluatin g therelativ e importanceo fpara metersi nth ebehaviou ro fpesticide s inwate r systems.

8.2 DERIVATIONO FTH E EQUATIONS

The fluxo fth esubstanc e through bottommateria lb ydiffusio ni nth e liquid phase was computed with Fick'slaw :

Jdif,lb= " Ddif,lb9o n/3a °5) inwhic h -2 -1 Ji-f ,L =arei cmas s fluxb ydiffusio ni nbotto mmateria l (mgm d ) D.-f ,.= diffusio n coefficiento fsubstanc ei nliqui d phaseo f (m d ) bottom material a,, =mas s concentrationo fsubstanc ei nliqui d phaseo fbotto m (mgm ) material z =dept hi nbotto m (m)

72 Thediffusio ncoefficien to fsubstanc e inliqui dphas e (Graham-Bryce,1969 ;Frisse l

etal. , 1970)D,. f, ,wa scalculate d from

(16) Ddif,lb" h el°dif, w

inwhic h labyrintho r tortuosity factor:raticj io fsurfac eare ao fbotto m CD material toliqui dphas e volume fractiono fliquid :volum e of liquiddivide db yvolum e of (1) bottommateria l 2 1 Dj-rair, w" diffusio ncoefficien to fsubstanc e ifcwate r (m d" )

Forth econversio no fth esubstanc e inwate r tynd inbotto m layer,first-orde r rate equationswer eused :

(17) ffc,w fec,w %

inwhic h -3 1 R c,w =rat eo fconversio n inwate r (mgm d" ) 1 k c,w =rat ecoefficien t forconversio no fsubstanc ei nwate r (d-_ ) a =mas sconcentratio no fsubstanc e inwati r (mgm " )

A similarequatio ni suse d forth ebotto mlayo r

(18) c,b "k c,b %

inwhic h 3 1 R„c,. =b rat eo fconversio n inbotto mmateria l (mgm" d" ) 1 k„c,* =b rat ecoefficien tfo rconversio no fsubstanc ei nbotto mmateria l «I" ) a =mas sconcentratio n ofsubstanc e inbotto mmateria l (mgm " )

Therelevan tconservatio nequatio n forth epesticid e inth ewate rcompartmen twit h volume v.,wwa s

3 7 K (19) < w M =-V^ dif>lb)3=o - w*c, w

inwhic h A, =surfac eare ao fbotto m compartment (m2)

For thebotto mmaterial ,th econservatio nequatio no fth epesticid ewa s

(20) 3ob/3t = -3t7dif,lb/3z- 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 sthen :

cib = V(£i+ pbv } (21)

inwhic h p, = (dry)bul kdensit yo fbotto mmateria l (kgm ) 3-1 K ., =distributio nquotien tsolid/liqui d (oradsorptio ncoefficient ) (m kg )

8.3 DESIGNO FTH ECOMPUTATION S

These to fequation s (15t o21 )wa ssolve dnumericall yafte rprogrammin g inth ecom puterlanguag eCSM P III (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 fazinphos-methy lan ddimethoat ei ntank swit hwate ran dbotto mmateria li sshow n inAppendi xA . Inth erun ssimulatin gTan kTria l2 i nJun e 1976,th einitia lmas swa s 13.2m go f azinphos-methyl inTan k IIan d 13.1m gi nTan kIV .Th einitia lmas so f1 m go fdimethoat e corresponded toth edos eapplie d toTank s IIan d IVdurin gTria l 1i 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 tzero . Sincevolatilizatio no fth emode lcompound sfro mth ewate rsurfac ewa sver yslow ,thi s processwa sno tintroduce dint oth ecomputatio nmode l (Section3.5) . Thevolum eo fwate ri nth etank swa s introduceda sa functio no ftim eaccordin gt o 2 themeasurement sdurin gth etan ktrials .Th esurfac eare ao fth ebotto mwa s0.6m . The bottomlaye r (0.1m thick )wa sdivide dint o1 0computatio ncompartments ,wit hgraduall y increasing thicknessfro mto pt obotto m (multiplicationfactor , rrir, 1.5).Th ethicknes s ofth etopmos tbotto mcompartmen twa s0.00 1 m.Th eeffect so fdifferen tthicknes so fth e topmostbotto mcompartmen tan ddifferen tmultiplicatio nfactor so nth eaccurac yo fth e numericalsolution swer echecked .Th ebul kdensit yan dth evolum efractio no fliqui do f thebottom so fTank s IIan d IVwer ebot hintroduce da sa functio no fdept h (Figure19) . Thediffusio ncoefficien to fazinphos-methy l inwate ra t2 0° Cwa sestimate d tob e 0.41 x 10~ m d ,accordin gt ocalculatio nmethod sgive nb yRei d& Sherwoo d (1966).Th e samevalu ewa scalculate d fordimethoat ea ta wate rtemperatur eo f1 5 C. Thetortuosit yfacto rƒ .fo rdiffusio nthroug hth eliqui dphas ei nth ebotto mwa s introduceda sa functio no fE . I twa s0.03 ,0.10 ,0.20 ,0.3 4an d0.5 0m 2 m~2 fore ,0.10 , 3 -3 0.20,0.30 ,0.4 0 and0.5 0m m ,respectively ,accordin gt oa literatur ecompilatio nb y Leistra (1978).Fo rhighe r E,n odat ao nth etortuosit y factorwer efoun di nth elitera

ture.Th etortuosit y factorsi nth erang eabov e£ =0.50wer eobtaine db ylinea rinterpo lationwit hth emaximu mvalu eƒ ,= 1. 0a te ,= 1.0 .Th ediffusio ncoefficien to fth esub stancei nth eliqui dphas ebetwee ntw obotto mcompartment swa scompute db ylinea rinterpo -

74 lation. Themeasure dadsorptio ncoefficien t K ,, ofaiinphos-methy l ontobotto mmateria li n 3 -1 ' -1 fordimethoat ewa s0.003 2m k*g a3-s 1 thetank swa s0.07 3m kg. Thecoefficien t K s/1 measured forfreshl ysample dbotto mmateria l (Chapter6 ) Therat ecoefficient s k . forconversio no flot hcompound s inth ebotto mo fTank s IIan d IVwer e derived fromth evalue smeasure di n incubationtest swit h systemso f fresh bottommateria l inwate r inth elaborator y (Chapter 6). Thecoefficien t k . ofazinpho s -methy_-.u..nl a .t. 2 o0n COnwa ._. s0.07 _ n „,3d, j- 1 ,,.„. ,^ *. ,. r__ ^.„.u-..fo- .rdimethoat. ,rS i._ - „e „ a,j-t 1I5 ° Cwa s 0.01d (Table 21). The k •c,t (Table 22) Therat ecoefficient sfe forconversio no fbot h compounds inth ewate r compartments c,w ofTank s IIan d IVwer e inth efirs tinstanc ese tequa lt o themeasure drat e coefficients fordeclin eo fbot hcompound s astabulate d inTabl e 26.Bu tth elatte rcoefficient s include theprocesse s ofadsorptio nont oan ddiffusio nint o thebotto m layer,s otha t theactua l ratecoefficien t forconversio n inth ewate rcompaitmen twoul dhav ebee nlowe rtha nth e ratecoefficient s fordecline ,especiall y during the firstperio do f theoutdoo rtrials . Therefore,als o lowerrat ecoefficient s forconversio n inth ewate rcompartmen twer ein troducedwhic hwer e0. 9 times themeasure d ratecoefficient s fordeclin e (Table 26). These lowerrat ecoefficient swer e introduced toestimat e therelativ econtributio no fconver sion,penetratio nan dadsorptio nt oth edecline . Thecomputation swer ecarrie dou twit hRunge-Kitta' s (RKS)integratio nmetho dove ra periodo f 27days .Th eintegratio nprocedur euse da variabl e time-step tominimiz e the integrationerror .A t regular intervalsdurin gcomputations ,th esimulate dmateria l bal anceo f thepesticid e inth etan ksyste mwa s checked.

8.4 RESULTS OFTH E SIMULATIONSO FTAN KTRIAL S

Amounts in water compartment and bottom compartmenta

Thecompute dan dmeasure dmasse so fazinphos-methy li nth ewate rcompartmen tan di n thebotto mcompartment so fTank s IIan d IVa sa functio no f timear egive ni nFigur e23 . Thesam ekin d ofplot s fordimethoat ear eshow ni nfigur e 24.Th e figures showtha tth e differencesbetwee n themeasure dan dcompute dmas so fbot hcompound s inth ewate rcompart mentwer eusuall y small.Whe nth erat e coefficients ofconversio no f thecompound swer e seta t90 $o f themeasure dcoefficient s ofdecline , onlyslightl yhighe rmasse s inth e wateran dbotto m compartmentwer e computed (Figure:;2 3an d 24). Thecontributio no fpene tration intoth ebotto mlaye r todeclin eo fbot hco ipound si nth ewate r layerwa sonl y lim ited.Fo rbot houtdoo rtrials ,th ecompute dmas so fsubstanc e inth ebotto mlaye rwa s nearlyalway s less than 10%o fth edose .Th ematerie lbalance so fbot hpesticide s inth e tanksyste mafte ra computatio ntim eo f 27d ar eshew ni nTabl e30 .Decreasin g therat e coefficiento fconversio nb y 10$resulte d innearl y -methyl.Howeve r fordimethoate ,i tresulte d insomewha thighe rmasse si nth ewate ran di n thebotto m (Table30) . The limitedmeasurement s onazinphos-methy lan c dimethoate inth ebotto m layerd o notallo wdetaile d comparisonbetwee nmeasure d andcalculate d results forth ebotto mlayer . Inal l trials,th ecalculate dmasse so fazinphos-methy lan ddimethoat e inth ebotto m 75 mass of substance in water mass of substance in bottom material 15-, (mg) ~\ (mg) • /f\ 1.0- ' I \\ ; } \ TH 0.5- fV. 1 1 1 1 1 1 I 1 1 1 1 I 0 10 20 30

1.0-

TIZ

i *=»• «l-r-r-r-i-p T-I-I-l i i i l | 20 30 10 20 30 time(d) Figure 23.Mas s ofazinphos-methy l inwate ran d inbotto m material ofTank s IIan dIV . = computed mass (fecw =0. 9 fer); = computed mass (kc w = kt); o= measure d datao fTan k Trial 2 inJun e 1976(Chapte r 7). Vertical barsar e range inmas s ofsubstanc e inth ewhol e bottom material estimated from duplicate bottom columns.

layerwer ehighe rtha nth emeasure dmasse s (Figures2 3an d24) .Thi smigh tb ecause db y anincomplet emixin gi nth ewate rdurin gth eoutdoo rtrials .Anothe rreaso ncoul db ea fasterrat eo fconversio ni nbotto mmateria lunde rth eoutdoo rsituation stha nunde rth e laboratoryconditions .Furthe rto ohig ha valu eo fth etortuosit yfacto ra thig h e,wil l resulti na noverestimat eo fth emasse spenetratin g thebotto mlayer . Comparisonsbetwee nth emeasure dan dcompute dconcentration so fazinphos-methy lan d dimethoatea tvariou sdepth si nth ebotto mlaye rar eshow ni nFigure s2 5an d 26,respec tively.Th ecompute ddept ho fpenetratio no fazinphos-methy lwa sver ysmall .Afte r1 1d nearlyal lth eremainin gazinphos-methy lwa scompute d tob estil li nth euppe r0.0 2m o f thebottom .Howeve ri nth etan ktrials ,smal lamount so fazinphos-methy lwer erecovere d frombotto mmateria lbelo w0.0 2m dept h (Figure 25).Thi sma yb ecause db ydisturbanc e ofth ebotto mlaye rb ysamplin go rb yorganisms . Thecalculate dpenetratio ndept ho fdimethoat ewa slarge rtha no fazinphos-methy l (Figures2 5an d 26),th emai nreaso nbein gth emuc hlowe radsorptio no fdimethoate . Thecalculate ddept ho fpenetratio nfo rdimethoat ewa ssignificantl ymor etha nsam pleddurin gth etrial .Fo rth ecompariso no fcompute dan dmeasure dmasse si nth ebotto m layer (Figure 24),a correctio nwa snecessar y forth emas so fdimethoat etha tpenetrate d belowth esample ddept ho fabou t0.02 5m .Thes emasse swer ecalculate dwit hth ecomputa tionmode lt ob eabou t 25\ ofth ecompute dmas si nth ebotto mlaye rfo rbot htank sI Ian d IV(Figur e24 ,crosses) .Thes ecorrecte dvalue ssho wa smalle rdeviatio nfro mth ecompu tedmasse spenetrate dtha nth emeasure dvalues .

76 masso fsubstanc ei nwatt r masso fsubstanc eI nbotto mmateria l tS-i

0.10-

005-

I i i i i I i i i i I 0| i i i i| i i i i| ' • i i 'I 10 20 30 0 10 20 30

15-i 0.15-1

0.10-

005-

•• • 111 1 • I 10 20 30 time(d ) Figure 24.Mas s of dimethoate inwate r andi n bottom material of Tanks IIan d IV. » com

puted mass (fe.w - 0.9 fer); - computed

mass (kc w • k'T); O » measured data of the Tank Trial 1i n September 1975 (Chapter 7);X - value corrected forpenetratio n losses below sampled depth (Section 8.4). Vertical bars arerang e in mass of substance in thewhol e bottom material estimated from triplicate bottom columns.

Comparisono fth efe wpenetratio nmeasurement s withth ecompute dresult sindicat e thati nfutur epenetratio ntrial sfo rCompound swit h relativelyhig hadsorptio ncoeffi - cients,thi nslice so fbotto mmateria lshoul db e anilyseda tappropriat etim eintervals , Withlo wadsorption ,penetratio nmus tb estudie dt o greaterdepth stha ni nthi sstudy .

Table 30.Compute d items of themateria l balance of azinphos-methylan d dimethoate ina simulated tank system after 27d .

Compound Tank Rate coeff. Fraction of initial amount (%) k l remaining ccnverte d

in in li in water bottom w*te r bottom

Azinphos- II k 0.0 0.8 9C.8 8.4 -methyl 0Ü9 k_ 0.1 0.9 9(. 1 8.9 IV 0.0 0.3 9(.3 3.4 0.0 0.3 9i. 9 3.8 Dimethoate II k 25.0 9.6 6:.2 2.2 0?9 27.2 10.3 6C. 2 2.3 IV 22.6 8.6 66 2.1 0Ü9 25.1 9.3 63 2.2

k (Table 26)o r k 0.9 k

77 mass concentration (mg m ) 100 200 300 400 -J 1—I 1 1 1 1—I i i i i I j___ *__j_ t I

TTZ afte r 11days

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 kx) ; = computedmas sconcentratio n (kc w = kr); o= meas ureddat ao fTan kTria l2 i nJun e 1976 (Chapter7) . 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 m ) c) 9 7,., • X - T

TI1 0.05- /

depthi nbotto m(m ) Figure26 .Mas sconcentration s ofdimethoat ei n thebotto mmateria lo fTank s IIan d IVafte r2 2 days. =compute dmas s concentration (kc w = 0.9 kr); =compute dmas sconcentratio n lkc w kr); o =measure ddat ao fTan kTria l2 i nJun e 1976 (Chapter 7). Horizontalbar sar erang ei n concentrationo fsubstanc ei nslice so fdupli catebotto mcores .Vertica lbar sar eaverag e thicknesso f thebotto mslices .

78 Thecompute dresults ,showe dtha ti nsituation s withhig hconversio nrate si nth e watercompartmen tonly ,comparativel ysmal lamount s penetratedth ebotto mlayer ,eve nfo r substanceslik eazinphos-methyl ,whic har estrongl y adsorbed.Furthe rtrial so npenetra - tionwil lb eneede dt overif yth evariou sassumption s andt oimprov eth eapproximation s ofth ecomputatio nmodel .

8.5 DESIGNO FTH ESIMULATIO NEXPERIMENT S

Simulationexperiment so nth econversio no fpesticide si nth ewate rcompartmen tan d thepenetratio nint oa botto mlaye rwer ecarrie doui : withth esam ecomputatio nmode la s describedi nSectio n8.3 .The ywer eintende dt otesi : thesensitivit yo fth emode lsyste m tochange si nvariou sparameters ,especiall yfo rthes ewhic hvar ystrongl yi npractic e andthos ewhic hwer equit euncertain .Th eparameter : thatwer evarie di nth edifferen t computerrun sar egive ni nTabl e 31. 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 ec 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 eamcun to fpesticid etha tpenetrate dth e bottomlaye rwa scomputed .Th ebotto mlaye rwa sdivide dint o1 0compartment swit hincrea s ingthickness .Th ethicknes so fth euppe rbotto mconpartmen twa s0.00 1m an dth emult i plicationfacto r (mf) was 1.5.I nsituation swit hhig hrat ecoefficien tfo rconversio no f thesubstanc ei nth ebotto mlaye ro rwit hhig hadsoiptio ncoefficients ,th ethicknes s ofth euppe rbotto mcompartmen twa sse ta t0.000 5m , Thebul kdensit yincrease dlinearl y from20 0k gm atth esediment—wate rinterfac et o 680k gm at0. 2m depth .Th evolum e

Table31 .Parameter sintroduce d intoth ecompute rr ui so fth esimulatio nexperiment s

RunWate r Diffusion Maximum Adsorption Bottonmateria l Water No depth coeff. tortuosity coeff. (m) inwate r factor (m3 kg-1) rate coeff. half ratecoeff . half (m*d" 1) (O ofc o rsion life ofconversio n life (d-i) (d) (d_1) (d)

X 0.0 1 0.4 0.2 10-* 1.0 0.0 0.0 2 0.4 0.3 X 1U- 1.0 0.0 0.0 0.0 3 0.4 0.4 X 10- 1.0 0.0 0.0 0.0 4 0.4 0.4 X lu- 0.75 0.0 0.0 0.0 b 0.4 0.4 X lü- 0.5 0.0 0.0 0.0 6 0.4 0.4 X lü- 1.0 0.001 0.0 0.0 / 0.4 0.4 X ,ü- 1.0 0.01 0.0 0.0 8 0.4 0.4 X lu- 1.0 0.1 0.0 0.0 9 0.4 0.4 X lü- 1.0 1.0 0.0 0.0 10 0.3 0.4 X lü- 1.0 0.1 0.0 0.0 II 0.2 0.4 X lu- 1.0 0.1 0.0 0.0 12 0.1 0.4 X 1U 1.0 0.1 0.0 0.0 X - 0.006913 00 0.0 13 0.4 0.4 1Ü-4 1.0 14 0.4 0.4 X 1.0 0.0693 10 0.0 lb 0.4 0.4 X ,0- 1.0 0.693 1 0.0 16 0.4 0.4 X 10- 1.0 0.0693 10 0.00693 100 1/ 0.4 0.4 X 10- 1.0 0.0693 10 0.0693 10 18 0.4 0.4 X 10 1.0 0.0693 10 0.693 1

79 fractiono fliqui ddecrease dlinearl yove rth esam edistanc e from0.9 2 to0.74 . InRun s 1t 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 s zero.I nRun s4 an d5 ,differen trelationship sfo rth etor tuosityfactor ,ƒ, ,wer eobtaine db yinterpolatin g linearlyt oth evalue sƒ , =0.75 (Run4 )an dƒ .=0. 5 (Run5 )a tvolum efractio no fliqui d E =1.0 .I nfou rrun s (No6 to 9), 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 s forconversio no fth esubstanc ei nth ebotto mlaye rwer evarie d fromlo wt ohig hi nRun s 13t o15 .Finall yth emos trealisti csituation swer esimulate di n Runs 16t o18 ,introducin gals ovariou srat ecoefficient s forconversio 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 mass o* substance in bottom material (mg) s ^= ^~ . -^ 92- fc 1 i i i i I i i i i I i i i' I I 1 I 1 1 1 20 •KD 20 30 c) X) 30

60- —--" *

40- - / _—-——S 20-

III

10 20 30 time(d) Figure27 ,Mas so fsubstanc ei nwate rcompartmen t andbotto mcompartment s computedwit h thetan k model.Number srefe r toth ecompute rrun sliste d inTabl e31 .

80 penetrationwa sonl yslightl y slowertha ncompute d inRu n3 (Figure s 27B).Thu sth euncer - taintiesi nth evalue sfo rth ediffusio ncoefficien t D... andfo rth etortuosit y factor ƒ,a thig he- ivalue ssee mt ob eo fmino rimportanc e Theresult so fRun s6 t o9 wit hdifferen t adsorptio ncoefficient s {K ,-,) onth ebot - tornmateria lar epresente di nFigur e 27C.The ysho w a considerable contributiono fadsorp - tiont oth edeclin eo fth esubstanc ei nth ewate r dompartment.Man ypesticide shav emoder - 3 -1 ateadsorptio nvalue so nsoil s( X, .< 0.0 1m kg ),bu tadsorptio no nditc hbotto m materialsma yb ehighe rb ya facto r1 0(Section s6 . •j.an d6.7) .Wit ha adsorptio ncoeffi - 3 -1 ciento f0. 1m kg ,29.6 %o fth einitia ldos ewa s computedt odiffus eint oth ebotto m ina 27-da yperio d (Run 8). Bydecreasin gth ewate rdepth ,th einitia lmasf e concentrationi nth ewate rcompart - mentincreased .Thi s inducedgreate rpenetratio no f thesubstanc e intoth ebotto mlaye r (Figure 28A,Run s1 0t o12) .A ta wate rdept ho f0 . 1m an dusin gth esam eadsorptio n coefficienta si nRu n8 ,66 %o fth edos eha d diffusî d intoth ebotto mlaye rafte r2 7day s (Run 12). Especiallyi nditche swit hsmal lwate r debths,adsorptio no fpesticide so nth e bottomlaye rca nthu sb eo fgrea timportance . Theresult sobtaine dwit hvariou s rate coefficientsfo rconversio ni nth ebotto m layerar eshow ni nFigur e28 B(Run s1 3t o 15) Convîrsiono fth esubstanc ei nth ebotto m

man of substancei nwate r masso fsubstanc ei nbotto mmateria l WO-i (m9> .(mg)

. K) 20 30 time(d ) Figure 28.Mas s ofsubstanc e inwate r compartment and bottom compartments computed with thetan kmod el. Forth eparameter s used inth edifferen t com puter runs seeTabl e31 .

81 layeraccelerate dsubstantiall y thedecreas ei nth ewate rcompartment ,especiall yafte r thefirs tfe wweeks .Wit ha fas tconversio nrat ei nth ebotto mlaye r (Run15 ,t ,, = 1 d), 2> 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 di nth ebot tomlaye rafte r2 7day swa s74.3 %o fth edose . Theresult so fth erun swit hvariou srat ecoefficient sfo rconversio ni nth ewate r compartmentar epresente d inFigur 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 , =1 d )penetratio n 2> W intoth ebotto mlaye rwil lno tb eimportant .Afte r4 day si nRu n18 ,90 1o fth edos ewa s converted inth ewate rcompartment .I nthi scompute rrun ,th earei cmas sflu xint oth e firstbotto mcompartmen teve nbecam enegativ eafte r 1.5days . Inal lruns ,halvin g thethicknes so fth euppe rbotto mcompartmen tha donl ya ver y smalleffec to nth ecompute dmas so fsubstanc e inth ebottom .

Depth of penetration into the bottom

Theconcentratio npattern si nth ebotto mlaye rafte r9 an d 27day scompute di ntw o ofth esimulatio nexperiment sar epresente di nFigur e29 .Withou tadsorptio nont oth ebot tommateria l (Run 3), 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 ina 27-da yperiod .

mass concentration (mg m ) 100 200 _i i i i L

c) 1000 2000 3000 4000 ( , . I , . 1 .

0.01- ,** Run8 0.02- /'

depth inbotto m (m)

Figure29 .Mas sconcentratio no fsubstanc ei n bottom layerafte r9 d ( )an d2 7d ( ).Fo r theparameter suse d inth esimulatio nexperiment s seeTabl e31 .

82 8.7 GENERAL DISCUSSION

Formode l computations onth ebehaviou r ofpesticide s inaquati c systemswit hbotto m material,severa lparameter s areneeded .Th emos t importantparameter s are therat ecoeffi cients forconversio n Lnth ewate rcompartmen tan d respectively).Diffusio n intobotto m layersi sa fairly slowphenomenon .Th e adsorption coefficient isals oneede d todescrib e therat eo fileclin eo fa substanc e inwater .Th e adsorption coefficienthighl y affects thepenetratio ndept ho fsubstance s inth ebotto m layer. Unfortunately, inalmos tan ypublicatio no fex ]>erimenta lwor ko nth ebehaviou r ofpes ticides inaquati c systems,on eo rmor eo fth eessentia lparameter s arelacking .Conse quently,i twa sno tpossibl e tochec k thedevelope d computationmode l indetai l against datafro mth eliterature .Hamelin k &Waybran t (1973istudie d thedistributio no fDD E (a conversionproduc to fDDT )an d lindane,whic hwer e added toth eepilimnio no fa thermally stratified flooded limestonequarr y (15m deep), fo:-on eyear .Afte r threemonths ,85° »o f therecovere dDD Ewa spresen t inbotto msediments ,ihil e 72?»o fth emeasure d lindanewa s still inth ewater .Thei rresult s indicate thatth edeclin eo fver yslowl y converted pes ticides inaqueou s systemsma yb eprimaril ydu e toadsorptio nont obotto mmaterial .Mos t ofth estrongl y adsorbedDD Ewa s found inth eto p0,01 5 m inal lbotto msamples .Lindan e was found toa dept ho f0.05 5m . Thecontributio no fth evariou smechanism s ofdeclin eo fherbicide s inwate rbodie s ofaqueou s systems ishighl ydependen tupo nth ephysico-chemica lpropertie s ofth eherbi cides.Organi ccation s likediqua tan dparaqua t are adsorbed on thebotto mmateria lwithi n a fewdays .Th eweakl y adsorbedcompoun d 2,4-D israpidl y converted inwate r (Frank, 1970). However,suc h information isonl yo fqualitativ enatur ean d thusno t suitablefo r testing computationmodels . Comparisono fth e limitednumbe ro fmeasure d daltao nth emasse s of azinphos-methyl and dimethoatei nslice so fbotto mmateria l duringoutdoo rtan k trialswit h thecompute d masseso fbot h compoundsyielde d encouraging results.Th ecalculate d deptho fpenetratio n was small;therefor e themetho do fsamplin g theuppe r centimetreo fth ebotto m layer in aquatic systems isextremel y important.Samplin go f jottommateria lwit hdredge-typ ebot tomsampler swil lmostl y giveerroneou s results (Chaste r4) . Furtherexperiment swit h improvedprocedure s arsneede d totes tth evalidit y of the various assumptions andapproximation s inth ecomputitio nmodel . Infutur eexperiment s on penetrationint obotto mmaterial ,ver y thinslice so fbotto mmateria l shouldb e analysed. More information isneede d onth eeffec to faersbi can danaerobi ccondition so n the rateo fconversio no fth esubstanc e inth euppe r few millimetresbelo w thesediment—wate r interface.Furthe rcomplication s like theexistenc e )fdifferen tperiod s indegradatio n in watero rbotto m layermigh toccu r (Chapter 6). Also :noreinformatio n isneede do n theef - feeto fligh to nth erat eo fconversio n ofpesticidef ei nshallo wwatercourse s Only a fewfirs tstep shav ebee nmad e indescribin gpesticid ebehaviou r inaquati c tank-like systemsquantitativel ywit hcomputatio nm oiels .Muc h experimental andcomputa ^ 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 tfarming ,concen trationso fazinphos-methy lwer emeasure db yPon s (1972),wh ofoun dtha tth econcentratio n ofthi scompoun dincrease ddownstrea man dascribe dthi stren 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 san dnatura l substances.Mor equantitativ edat ao nth eoccurrenc eo fazinphos-methy li nwatercourse 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 eselecte di n197 5i nditche s onfrui tfarm swit hth eai mt oinvestigat eth eoccurrenc ean dbehaviou ro fazinphos-methy l anddimethoat e infar mditches .Th eselecte d farmsha 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 e foundi n197 5i nth editche so ntw ofrui t farms,mor edetaile dmeasurement swer ese tu pi n197 6t 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 . In1977 ,spra ydrif tt oditche swa smeasure d indetai lo nth esam efarm st oestimat emor eaccuratel y theinpu to fpesticide sint othes e ditches. Theditc hsyste mwa scharacterize db yvariou smeasurements .Man yo fth edat aassesse d wereals ouse di nsimulatio nmodel sfo rpesticid ebehaviou ri nditches(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 n inFigur e 30.Thre eo fthe mwer e inlarg e watercourses inth eKronm eRhin earea .Th eKromm e Rhinei sa distributar y ofth eNethe r Rhine.Th eKromm e Rhine flows througha nare awit h fruit farming situatedmainl yo n thenatura l levees alongth eriver san dgrasslan d farmingmainl yo nth eheav ybackswam p clays.However ,frui tfarmin go nsom eo fth elattej r soils ispossibl eb ylowerin gth e groundwater levelb ypumpin gth editches ,especiall y duringth ewinte rseason .A nexampl e ofthi s situationi sSamplin gPoin t5 nea r Bunnik Pumped ditchesar eals o foundo nloam y soils,wher esom eseepag ewate r fromth eRive rLe k (thecontinuatio no fth eNethe r Rhine), flowinga ta highe r levelmus tb eremoved .Thes e conditionsoccurre da tSamplin g Point6 nearSchalkwyk .A tPoint s5 an d6 ,windbreak s stood rightnex tt oth editche so non eside , whileo nth eothe rsid ewer e inspectionpath sfo r iitchcleaning .A tthes ePoint s5 an d6 , thefrui t treeswer eno timmediatel y nextt oth e watercourse.Thi si squit ea usua lpat - terno fplanting .

Figure 30.Ma p of the sampling points in the Kromm^ Rhine area and in theLopikerwaar d Polder. Sampling points: 1= Kromme Rhine near the inlet from the Nether Rh|Lne near Wyk by Duurstede. 2- Langbroeke r Canal from thebridg e near Sterkenburg Castle. 3 - Kromme Rhine from thebridg e near Odyk. 4 -Lopike r Canal near the Biezendyk bend. 5 - Drainage ditch on fruit farm near Bunnik. 6 =Drainag e ditch on fruit farm near Schalkwyk. 7 »Drainag e ditches on fruit farm near Benschop. 8 »Drainag e ditches on fruit farm near Jaarsveld. 9 -Drainag e ditches on fruit farm near Lopikerkapil

85 Somemor eexceptiona lSamplin gPoint swer eselecte di nth eLopikerwaar dPolder .A t SamplingPoint s7 an d8 ,man yfrui ttree sgre wjus talongsid e theditches ,s otha tdurin g applicationso fpesticide sa par to fth espra yinevitabl ydescende dint oth ewater .Th e Lopikerwaardi sa nare awit hrelativel yhig hgroundwate rlevels .Th evariou ssoi ltype s aremainl yuse dfo rgrasslan d farming.Ditc hwate rlevel si ngrasslan darea sten dt ob e ratherhigh ,especiall y inarea swit hpeat ysoi lo rwit hloam yan dclaye ylayer so na peatysubsoil .I fsupplementar ypump-drainag e isavailable ,frui tfarmin gi spossibl eo n someloam yan dclaye ysoils ,a saroun dSamplin gPoin t7 nea rBenschop ,o nth enatura llev eesnea rJaarsvel d (SamplingPoin t8 )an dnea rLopikerkape l (SamplingPoin t9) .Aroun d allsamplin gpoint si nth eLopikerwaard ,som edee pseepag ema yb eexpecte d (Studiegroep Lopikerwaard, 1973).Moreove ra tPoint s8 an d9 ,shallo wseepag eoccur sdurin ghig hrive r waterlevels .Th eSamplin gPoin t4 i nth eLopike rdrainag ecana lwa sselecte da sa repre sentativewater-inle tpoint . Thepoint si nth ewatercourse san dth edrainag editche swer esample dbefor ean daf terspra yoperation so nth efrui tfarm saccordin gt oth eprocedur edescribe di nSectio n 4.2. In1975 ,sample swer etake n5 times .Th esample so fwate rwer eextracte da ssoo na s possible (Sections5. 3an d 5.4).Som esurfac ewate rextract swer ecleane du p formor e accuratemeasuremen to fazinphos-methy lan ddimethoat e (Sections5. 9an d 5.10). During themonitorin gactivitie s in1975 ,th econcentratio no fazinphos-methy li n allwate rsample swa smeasure do non eGL Ccolumn ,sinc ea ttha ttim eonl yon eappropriat e columnwa savailabl e (Table14 ,Colum n 1).Dimethoat econcentration swer emeasure do ntw o columns (Table15 ,Column s Ian dIII) .

9.2.2 Results and discussion

Theaverag eapparen tconcentration so fazinphos-methy lan ddimethoat ei nextract so f watersample sfro mth elarg ewatercourse san dth evariou sfar mditche so n5 samplin gdate s in197 5ar egive ni nTable s3 2an d33 ,respectively .Mos to fth econcentration sar e presentedwit h 'smallerthan 'marks .Thes emark sar enecessary ,sinc eth eapparen tcon centrationso fazinphos-methy lan ddimethoat ei nth eextract swer eusuall ymuc hlowe raf terclean-up ;especiall y forsample sfro mlarg ewatercourses .Th eextract so fwate rsam pleswer ecleane du pabou ttw omonth slater ,afte rstorag efo rsevera lday so na labora torybenc han di na refrigerato ra t5 C.Muc ho fth ereductio ni nconcentratio nafte r clean-upo fth esample sfro mDitche s6 ,7 an d8 (Table32 )ma yresul tfro mdecompositio n duringstorage .Evidently ,interferin gsubstance sha donl ya mino reffec ta tthes erela tivelyhig hconcentration so fazinphos-methyl . Smallamount so fazinphos-methy lan ddimethoat ewer efoun dafte ron esingl eclean-u p ofwate rsample sfro mth eKromm eRhin eo n2 9July .Thes edat ad ono tsho wa significan t increasei nconcentratio nfo reithe rcompoun ddurin gflo wthroug hth eKromm eRhin eare a (Tables3 2an d33 ,Samplin gPoint s 1an d3) .Fo rmeasuremen to fth eactua lamount so f bothcompound s inth elarg ewatercourses ,large rwate rsamples ,mor eextensiv eclean-u p andanalysi swit hmor eGL Ccolumn swoul dhav ebee nnecessary . Duringmonitorin gi n1975 ,apparen tconcentration so fdimethoat ei nwate rsample s fromth elarg ewatercourse so fth efar mditche swer eonl ysmal l (Table33) .Lo wconcen -

86 Table 32.Averag e apparent mass concentrations of azinphos-methyl measured in extracts of water samples from largewatercourse s (Points 1-4) and from farm ditches (Points 5-9) during 1975.Fo r position of sampling points see Fig;ur e30 . -3 Sampling point Number Average concentratii of azinphos-methyl (mgm ) of samples 14Marc h 6Ma y 2Jun e 29 July 19Augus t

be fare after before after cl clean- clean clean- -up -up up -up

1. Wyk by Duurstede 2 <0.5 - <0.3 <0.021 <0.5 <0.09 <0.9 2. Sterkenburg 2 <0.08 <0.2 <0.2 <0.1 <0.9 3. Odyk 2 <0.4 <0.4 <0.7 <0.6 <0.07 <1.1 4. Biezendyk 2 <0.1 <0.3 <0.3 <0.4 <0.05 <0.1 5. Bunnik 2 <0.02 <1.1 <0.Î <0.4 _2 6. Schalkwyk"* 4 <0.06 <0.2 1.J <0.4 <0.2 0.3 7. Benschop 4 <0.1 <0.2 18 93 <0.1 0.5 8. Jaarsveld6 4 <0.2 10.5 6 43 <0.2 0.3 9. Lopikerkapel 3 <0.5 <0.03 <0.i <0.2 <0.2 -3 1. The detection limit was about 0.01 mg m . 2. Nowate r in the drainage ditch. 3. Clean-up twomonth s later on one sample of wateK 't.Azinphos-methy l spray at the end of May and Junii. 5.Azinphos-methy l spray on 30Ma y and 25June . 6. Azinphos-methyl spray on 30April , 16May , 28M|y , 26 June, 7July . 7. Azinphos-methyl spray only at the end of June. trationo fdimethoat ei nth e farmditche s couldb eexpecte d sincei ntha tyea r thecom poundwa s notapplie do nth eneighbourin g fields. Thecomparativel y high concentrationso fazinpjhos-methy lca nb erelate dt oth e spraying dateso nth e fruitfarms .

Table 33.Averag e apparent mass concentrations of dimethoate measured in extracts of water samples from largewatercourse s (Points 1-4) an|dfro m farm ditches (Points 5-9) during 1975. For position of sampling points see Figure 30 -3 Sampling Number Average concentration of iimethoate inm g m Point of samples 14Marc h 6Ma y 2 June 29 July 19Augus t

before after before after before after clean- clean- clean- clean- clean- clean- -up -up -up -up -up -up

1. Wyk by 2 <0.4 <0.1 <1 <0.11 <0.5 <0.04 Duurstede 2. Sterkenburg 2 <0.6 <0.2 <0.2 <0.03 <0.5 3. Odyk 2 _1 <0.5 <0.3 <1.9 <0.09 <0.5 <0.2 4. Biezendyk 2 <0.1 <0.2 <0.4 <0.1 <1.5 <0.1 <0.5 <0.2 5. Bunnik 2 <0.3 <0.04 <0.05 <0.04 _2 6. Schalkwyk 4 <0.05 <0.06 <0.3 <0.1 <0.03 7. Benschop 4 <0.06 <0.07 <0.02 <0.02 <0.02 8. Jaarsveld 4 <0.1 <0.013 <0.3 <0.1 <0.2 <0.1 <0.3 <0.01 9. Lopikerkapel 3 <0.3 <0.02 <0.04 <0.3 <0.2

1.Highl y interfering substances. 2. No water indrainag e ditch. _, 3.Th e detection limitwa s about 0.01 mg m

87 Beforeth eflowerin go fth efrui ttrees ,th ecompoun dwa sonl yapplie di nJaarsveld . Afterflowering ,frui ttree swer espraye dwit hazinphos-methy lnea rSamplin gPoint s6 ,7 and8 .Th econcentration swer ehighes ti ndrainag editche snea rBenscho pan dJaarsveld , aswoul db eexpecte dfo rsituation si nwhic hfrui ttree sgro wjus talongsid eth editches . The•concentrationso fazinphos-methy li nwate rsample s takena tJaarsvel do n6 Ma yrange d from9. 5 to11. 4m gm ;thos ei nth esample sfro mBenscho p (2June )range dfro m 10.4t o 22.5m gm .Wit ha windbrea kan da ninspectio npat halongsid e theditche s (Schalkwyk, Point6 ,2 June )th econcentratio nwa smuc hlower . Atth een do fJuly ,comparativel y lowconcentration swer efoun di nth editche so fal l fruitfarms ,perhap sbecaus eo fth elarg erainfal l intha tmonth .Fo rexampl ea tPoint s6 , 7an d8 ,nearl y 100m mo frainfal lwa smeasure dwithi na fe wday si nJuly .Thre eday so f continuouspumpin gwer enecessar y todischarg ethi sextrem erainfall .

9.2.2 Preliminary conclusions

Fromth emonitorin gdurin g 1975o fazinphos-methy lan ddimethoat ei nwatercourse san d inditche so nfrui tfarms ,a fe wpreliminar yconclusion scoul db edrawn . -Measuremen to fsmal lamount si nlarg ewatercourse swithou tadequat eclean-u pprocedure s willmostl ygiv eto ohig ha value . -A t leasttw oGL Ccolum npacking swit hdifferen tpolarit yhav et ob eused . -Goo dGL Canalysi s israthe rdifficul tan dver ytime-consuming .Continuou sattentio nha d tob epai dt oth equalit ycontrol . -Furthe rmonitorin go fth elarge rwatercourse swoul dyiel donl y limitedinformation . Therei salway sa certai n 'background'o fpollution ,probabl yb yintak eo fpollute dwate r fromth emai nriver .Eve nwit hrathe rfrequen tsamplin ga tsevera lpoints ,i tma yb edif ficultt otrac eth esource so finstantaneou s contaminationan dconcentratio nwave sma yb e overlooked. -O nth ewhole ,th econcentration s inth elarge rwatercourse ssee mt ob equit elo wan d therear en oindication s fora nincreas edownstream .Thi si sprobabl ydu et ofactor slik e thehig hdilution ,th escatte ro fth eorchard sbetwee npastur ean darabl elands ,th edis tributiono fapplication si ntim eo rals oth erelativel y rapiddeclin erat ei nsurfac ewa ter. -Man yfar mditche sdr yu pi nth esummer ,especiall y inth eKromm eRhin earea .S odurin g summerther ei sgenerall yn odistinc tdischarg eo fsurfac ewate rfro mthes efar mditche s intoth elarge rwatercourses . -Whe nfrui ttree sar esituate djus talongsid eth editches ,greate rcontaminatio no fditc h waterca nb eexpected . -O nmos tmoder nfrui tfarms ,windbreak san dinspectio npath soccu ralongsid eth editche s andth eintroductio no fpesticide s intodrainag editche sdurin gsprayin gwil lb efa rless . -Th esystemati ctracin go fa pesticid e fromth esourc ewil lprovid eth ebes tchanc efo r reliablequantitativ eresults . -Attempt sar eneede dt oreduc eth enecessit yo ftime-consumin g analysesfo ra nenormou s numbero fwate rsample sfo reac hpesticid eo finterest .Thi scoul db edon eb ysimulta neousdevelopmen to fcomputatio nmodels . -Fo rmor edetaile d investigations,ditche sar e neiidedfo rwhic hwate rbalanc eca neasil y bemeasure dan dt oa certai nexten tcontrolled .

9.3 FIELDTRIAL SO NTH E FATEO FAZINPHOS-METHY LA(I DDIMETHOAT EI NDITCHE SAFTE R SPRAY DRIFT

9.3.1 Introduction

Invie wo fth erelativel yhig h concentrations ofazinphos-methy li nsample so fwate r fromth edrainag editche si nBenscho pan dJaarsvel ^ in197 5 (Table32 ,Point s7 an d 8), thesefar mditche swer e selectedfo rfurthe rinve s ligationi n1976 . Theconcentration si n197 5raise dth e following questions, - Isi tpossibl et omeasur eth einpu to fbot ho ompdundsint oditche sdu et ospra ydrif t duringapplication so nfrui tfarms ? -Ho wquickl ywil lth econcentratio nb emixe dove r thecross-sectio no fth ewate rbod yi n theditch ? -I si tpossibl et oestimat eth erate so fdeclin e cfth ecompound si nditche s forperiod s without-discharg eo rintak eo fwater ? -Wha twil lb eth eeffec to fadsorptio no nrat eo f decline? -Ho wfa ran dho wfas twil l thecompound spenetrat e theditc hbottom ? Beforeth epesticid ebalanc ei nth efiel d ditehe s canb esolved ,th ewate rbalanc e ofthes editche smus tb eassessed .Th e circumstance|s werefa rfro midea lfo rsolvin g this waterbalance ,sinc eth esoil swer eheterogeneou s and hydrologicalcondition swer erathe r complex(asi softe ns oi npractice) . Duringth eperio do fpesticid eapplicatio no n bothfarm si n1976 ,a nattemp twa smad e toapproximat e thevariou s itemso fth ewate ran d pesticidebalance sfo rth epumpe d ditches.Befor ean dafte rsprayin g azinphos-methyl anddimethoate ,concentration swer e measuredi nman ywate rsamples .Penetratio no fa z inphos-•methylint oth editc hbotto mma - terialwa s alsomeasured .Th e ditchbotto mmateria l wascharacterized ,t oallo wth eus eo f simulationmodels .Profile so fth evolum efractio n jfliqui dan dth ebul kdensit ywer e measureda tsevera lpoint si nth edrainag editches .

9.3.2 Data on the trial fields in the Lopikerwaard Polder

Theditc hsections ,whic hwer eselecte di n1 197) formeasurement so nth ewate rbalanc e ando npesticid ebehaviou rar eshow ni nFigure s3 1 aid32 .I nBenschop ,tw oditc hsection s wereselected ,a siphon-linke dditc h (designatedB S )an dth elas tsupplementall ydraine d ditchsectio nbefor eth ewate rpum p (designatedBSD | (Figure 31).Th eleve lo fth esoi l surfacei nBenscho pvarie dfro m0.6 0m belo wsea - leVel (StandardAmsterda mLevel , NAP) nearDitc hSectio n1 t oabou t1 m belo wNA Pi nth e Lmmediatesurrounding so fth epump . The lowestwate rleve lo fth epumpe dditche so nth e fa m inBenscho pwa sabou t 2.06m belo w NAP.A tthi swate r level,th eelectri cpum pwa s automaticallyswitche dof fb ya floa t switch. Hydrologicalcondition si nJaarsvel dwer equit t complex.Onl y threeo fth eman yditche s

89 10 f"'Il 0 © fW © 0ll

BSL BSD

(S) (g) IH bx) z ûs_ 6 7 9 9 4

•~*. ^;~ 3

A2 "•V-1I

Figure31 .Positio nan dflo wpatter no fditche so na frui tfar mi nBenschop .Section s 1t o 10ha dsupplementar ydrainage .Th edashe d linesrepresen tditche swhic hwer eno tpumped ; thesesection swer efille d tonorma lpolde r level.Section s8 an d 10wer estudie d inmor e detail.The yar eindicate d assiphon-linke d ditch (BSL)an dsupplementall ydraine dditc h (BSD),respectively .Abbreviations :b fo rbac kan df fo rfron tpar to fa ditc hsection . Key:^4?=siphon , =groundwate r tubes, • =wate rpump . onth efar mwer estudie d (Figure 32).Thes editc hsection sar eindicate dwit hth eab breviationsJB ,J Man dJ Ffo rback ,middl ean dfron tditc hsection ,respectively . InJaars - veld,th eelectri cwater-pum pwa ssituate do nth ehighes tpar to fth efar mabou t0.6 0m a - boveNAP .Nea rth ewindpump ,th esurfac eleve lwa sabou t0.1 0m abov eNAP .Th ewate rlevel , atwhic hth epum pwa snormall ystopped ,wa sabou t0.7 9m belo wNAP . Datao nth edimension so fth edifferen tditc hsection sar eshow ni nTabl e34 ,whic h includescalculate dstandar ddeviation so fth evariou sparameters .Th eaverag ecoefficien t ofvariatio nwa sabou t )2%fo rabou t2 0measurement so fth edept han dwidt hpe rditc hsec tion.Th evariatio ni nth eslop eo fth elowe rpar to fth editc hwall swa sgreater ,becaus e thisslop ewa sreshape dtwic ea yea rdurin gditc hcleaning . InBenscho pther ewa sa composit e tile-drainagesystem .T ocalculat eth ecatchmen t areao fth editches ,i twa sassume dtha tth ewatershed swer ehalfwa ybetwee nditche so r 2 betweenditche san ddrains .Th etota ldraine dare ai nBenscho pwa sabou t13 500 0m and 2 thatfo rJaarsvel dwa sabou t7 00 0m .

90 b

!! t °b4h -1 » Ü X 7 Ü2 2 II f X . Ate ft H

JM (n ®

f 711 !! 'b

JF ® f t 11 H M

Figure 32.Positio nan dflo wpatter no fditche so ni frui t farmi nJaarsveld .Al lsection s werepumped .Th elef tdashe d linerepresent sa ditc ia tpolde r level.Th erigh tdashe d linei sa ditc hpumpe db ya windpum po fa nadjoinin ;frui t farm.Dashed-dotte d linesar e former ditches,fille dwit hol dtree san dtop-soil .Section s9 ,1 0an d1 1wer e studiedi n moredetail .The yar eindicate d withabbreviation s isJB ,J Man dJ Ffo r back,middl ean d front sections,respectively .Abbreviations :b fo rhac kan df fo rfron t parto fth editc h sections. y v Key::^<£=siphon ,® = groundwater tubes, •= wate rpump , 'y,= windpump.

9.3.3 Measurement and approximation of the items of the water balance

Measurementso nitem so fth ewate rbalanc ewer e setu pi n197 6fo ra perio do fabou t 2months ,fro m thebeginnin go fMa yt oth ebeginnin g ofJuly .Afte r that,uncontrolle da - mountso fwate rwer e takeni no nbot h farmsfo r spriikleran dfurro w irrigation,an di tbe cameimpossibl et omeasur eth ewate rbalance . For theapproximatio no fth evariou s rateso fwate r flowi nth editc hsections ,a sim plecomputatio nmode lwa suse d (Chapter 10). Thewate rbalanc eo fa ditc hwate rcompart menti si nwords :rat eo fchang ei nwate rvolum e= rat eo fprecipitatio n- rat eo fevapo ration- rat eo foutflo w+ rat eo finflo w+ rat eo fJ lo w through thewette dperimete ro f theditc h+ rat eo fflo wfro mth edrain s (Equation 2') . Therat eo fevaporatio n froma fre ewate rsurfac ewa sestimate db yaveragin g thedat a ofD eBil tan dNaaldwy kmeteorologica l stations (KNMI, 1976) (Figure 33). Inth edr yan d

91 rate of evaporation from the water surface (mm d ) 7- 6- 5- •4 3- 2 1

I I I I I l I I I I [ I I I I I I II I | I I I I I I I I I | I I M I I I I I [ I I I I I I I I I |l I I 0 10 20 30 40 50 |60 1 | time(d) 3May Uune uùly Figure33 .Rat eo fevaporatio nfro mope nwater . Averageddat ao f DeBil tan dNaaldwy kmete orologicalstation s (KNMI, 1976).

sunnyyea r 1976,th erat eo fevaporatio nwa shigh . Duringth eperio do fpesticid eapplication ,th editc hwater-leve lwa smeasure do n samplingdates .Th editc hwater-level s aboveth ereferenc elevel s (atwhic hth epump snor mallystopped ,Tabl e34 )ar eshow ni nFigur e34 Can d35C .I nvie wo fth erelativel ydr y period,th efarmer sha draise dth eswitch-of fleve lo fth epum pa fe wcentimetre sabov e thereferenc elevel .Th ewate rleve lbefor eth epumpin gperio do n2 1Jun ea tBenscho pwa s readfro ma high-wate rmark ,manifeste db ya duckwee drin garoun dth epumpin gtube .Th e waterlevel sdurin gth epumpin gperiod swer eestimate db yusin ga computatio nmode l(Chap ter 10).A tJaarsveld ,th efluctuation so fth ewate rleve lcoul donl yroughl yb eapproxi mated.Th eamount so frai nwer erea ddail yb yth efarmer sa t08:0 0h .Thi sdail yrainfal l onbot hfarm si sshow ni nFigure s34 Aan d35A .Th etota lrainfal li nMa ywa s3 7m mi n Benschopan d4 2m mi nJaarsveld .I nth eNetherlands ,th e30-yea raverag erainfal li nMa y is5 1m m (KNMI,1976) . InJune ,4 8m mo frai nwa smeasure do nbot hfarm s (30-yearaverag e is5 4mm) . Onbot hfarm sth eelectri cwater-pum pwa sequippe dwit ha pumping-tim emeter .Th edu rationo fpumpin gwa srea db yth efarmer sa t08:0 0h eac hday .Normall yth ewate rpump s wereequippe dwit ha floa tswitch ,whic hkep tth editc hwater-leve lwithi nnarro wlimits . Afterth esprayin gdate si nth etria lperiod ,th ewate rpump swer eno tuse dfo rsom etim e inorde rt ostud yth edeclin ei nth epesticide si nth ewatercourses .The ywer eswitche do n byhan dwhe nnecessary ,whic hresulte di na rathe rdiscontinuou spatter no fpumpin g(Fig ures34 Ban d35B) . Theapproximatio no fth erat eo fdischarg eo fth edifferen tditc hsection swil lb e discussedi nChapte r10 . Atth ebeginnin go fth etrial si nJaarsveld ,unknow namount so fwate rwer etake ni n froma large rwatercours eb ya sipho nnea rth ebac kditc h (Figure32) .Thi sintak eoccur redfro m7 t oabou t1 2Ma yan dals oa tth een do fJun ejus tbefor eth etw oday swit hver y heavyrainfal l (Figures35A ,C) .Th eamoun to fwate rtake ni ndurin gth efirs tintak epe riodi nJaarsvel dwa sno tdirectl ymeasured .I tcoul db eonl yroughl yestimate dfro mth e risei nwate rleve li nth editc han dth eris ei ngroundwater ,assumin ga naverag estorag e factor.Durin gth esecon dintak eperio di nJaarsveld ,jus tbefor eth eheav yrainfall ,n o accuratedat acoul db eobtaine do nth eris ei nsurfac ewate ran dgroundwater .Consequent lyi twa simpossibl et oapproximat eth eamoun to fwate rtake nin .

92 tl XI 4J — o o o o o + o

CO •-!

01 •O

•o pH > — o o o o CU •mJ c>a 51 «1 •a a u >> ai xi •-> 4J 01 -H a-Io a > 0 ki a-H XI o T) u •«o 4J CO a Q /-s ^\ /~\ * tn ai a al en \o N en m u u 4J ca * S m CA ys —• o• o• o• I->.--I ' — O O O O rH «O H XI h O +I+I+I+I+I S -H • O co 4J G TJ TJ XI » 4J 4J -H ^ \-^*_ ^^ >^/ O 01 eu u CM — CM CM SH 4J J 4J (U dcl -o Ol CM co sr co co o •pi o. to CO al ai CM— OOOCMOOOO H -H 41 rH B O O O O I pH kl CM f- O O O. N a co CM 00 ON •H ai ai co 9 u CM M co TJ _ o _ « a u J= CO •U -H CO î^> •e u 01 pH pH 00 TJ B -o •* n Nis XI CO CO o Ol CM O O O § e ki a •O 4H o. 01 ^-s • • • • pi o — O o o o 2 •83 &o co •pi en .e • x: kl a. I-H ca » TJ TJ ' o i ^^ «ooo £ I ai ai o o e -» CM -T st o o O I XI -3 4J 4J en XoI xOi -Cf— OOO— OOOOCM C P. 4J o in m i i u 4J CM r» O ai o 0 ai a) a p. 4-1 co co ki ai ai co M M i« -a ai o. o X! X! Ol co M M 4-1 U « X! » ai p" XI B -—' *—i *-s >-v 01 -ri -H a u & a » » s kl o o CM CM CM ai o 4J Ck •H kl - es So X! PH 9 co co « CO 4J ^ v 'w g 4-1 ai ai e ai O a) *—'r-* Ol ai c CU R) Rl t|) .—\ ai ki u CO XI wo O OJ OJ ai H s xi co co s •S « 01 CM Hm M J-i J-i 0) w' O U XI *-*s CO •—\ Q) CT) 4 > «H e 6 6 U co ^"N 4J -H 1 1 «J ^ Ol CO • M-l ^^•IH WO U il H 0) •» U •£B• 4J 3 0) IPH CO *—6' — o cN ety e e u CO & o, o o U 01 X! CO O u > ai u X! u a s § o .-I V PH O 4J 4J CO Ol rH -O 00 u pH co co S en -> pj « e C TJ a O -r-l 04J4J4J ^ S wou co co 01 -rl aiHVHctiQiat^g H I-I •J » Qcnscflucjucoh H « M J Ifl

93 Groundwaterlevel swer eneede dt oestimat eth ewate rflo wthroug hth editc hbottom . Somegroundwate rtube swer eplace d inth efrui ttre erow sa tvariou sdistance sfro mth e selectedditc hsection s (Figure3 1an d 32).Th elevel so fth etub ehead swer etake nwit h alevellin ginstrument .Durin gpesticid eapplication ,th egroundwate rlevel swer emeasure d

rainfall (mm d ) 20-1 15- 10- 5-

n |li 11 il I h|111 i il• h •!i 11I. •1 • I | 11 111 i i It 111 11 11 i l l |i 9 10 20 30 40 50 fO 3Ma y Uuly

cumulative pumping time (d) B 1.0- i 0.8' 0.6 0.4- 0.2- I I M I I I I I I I I I I I I l'| I I I I | I I I I l I l l I I I I I I I I I I I I I I I I | I I I (|) 16 20 30 40 50 60 3 May Uuly water level (m) 0.30-1

Q20-

^\ jV^ - / rq-n • • I • • • • • • • • | | • • "I1"1""!!" 10 20 30 40 50 pO 33 Ma May Uune Uuly

averaged groundwater level (m) 0.4-1

I o o °- —- "•~°~—— » V \ 0.2-L -~-A \ \ i \ V

-r "I 'i n|ii I M I | I I 111111 | |'l • 10 20 50 60 33MMa

94 rainfall (mm a* ) A 2S-| 20- 15- 10- 5- 1 .1 .1 1 1 II 1 • ll 111 M i 11 ir 11111 il il 1111 11 irr I 10 20 30 40 50 BO j ay Uune Uuly

cumulative pumping time (d) B 3-1

1- -

0 10 20 30 40 50 BO 3M oy Uune 1 July water level (m) C Q50n

O40- / ; 030- / / / ; ! r- \ 1 > 020- i i i N ' 0.10- i S 1 i S ƒ I x/ 3 10 20 30 40 50 60 3^4a y Uune Uuly

averaged groundwater level (m) 0.4-1

Q3 & \ 0.2-

0.1-. //

0- %=* i H111111111M11•|H1111111111111111111111111111111« 111M |n 9 10 20 30 40 50 ]S0 3Ma y Uune Uuly time(d)

Figure 35.Fiel d observationsp nth efrui t farmi n Jaarsveld, during thetria l in 1976. A. Rainfall against time. B. Cumulative pumping time against time. C. Ditchwater-leve l above lowest pump level against time;x = measure d levels, = approximated levels. D. Averaged groundwater levels above lowest pump level against time;o (around front ditch), • (around middle ditch)an dA (around back ditch) are measured levels, = approximated levels.

95 onsamplin gdates .Thos eo fTube s III,IV ,VI Ian dVII Ii nBenscho pwer euse dt ocalculat e anaverag egroundwate rleve laroun dth esiphon-linke dditch ;thos eo fTube sI ,II ,I Xan d Xwer euse dfo ra naverag egroundwate rleve laroun dth esupplementaril ydraine dditc h(Fig ure 34D).Average dgroundwate rlevel saroun dth editc hsection sa tJaarsvel dar eshow ni n Figure35D .I nbot hfiel dsituations ,th egroundwate rros estrongl yafte rth eheav yrain falla tth een do fJune .A tJaarsveld ,th egroundwate rlevel saroun dth emiddl ean dbac k ditchros esignificantl ywit h thewate rintak ea tth ebeginnin go fMay . Thewate rflu xthroug hth editc hbotto man dth erat eo fflo wfro mdrain swer ecalcu latedfro mth ewate rbalanc ea sa closin gentry .A detaile ddiscussio no 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 sditc hsection san dground watertubes ,som ewate rsample swer esucke du pwit ha vacuu msample r (Section4.2) .Thes e sampleswer eanalyse db yth eEaster nLaborator yfo rWate rTesting ,Doetinchem .Th eresult s aregive ni nTabl e35 . Therelativel yhig hchlorid econcentratio ni nth editche si nJaarsvel dca nb eex plainedb yth eintak eo fwate rfro ma large rwatercours ewit ha hig hchlorid econcentra 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 ssample dwit ha faun ashovel .Sample swer ecollecte di nBenscho pa tfou r placesi nth efron tan dbac ksection so fbot hditche san di nJaarsvel dfro mtw oplace si n thefron tan dbac ksectio no fth emiddl editc h (Figure3 1an d32) . Witha Perspe xbotto msampler ,provide dwit ha stainless-stee lclosin guni t (Section 4.4),mu dcore swer ecollecte da tabou tth esam eplace si nth editches .Th elowe rpart so f thecolumn s (from2 2t o3 0c mbelo wth esediment—wate rinterface )take nfro mth efron t andbac ksection so fth edifferen tditches ,wer epu ttogether .Thes esample swer euse dfo r thechemica lan dgranula rcharacterizatio no 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 dmethod sdescribe d byHofste e& Fie n (1971).Th epH(KCl )o fth ebotto mmateria li nth efron tan dbac k sectionso fth edifferen tditche swa snearl yequal .Th ep Ho fth esub-botto mwa sdistinct lylowe rtha ntha to fth euppe rlayer so fbotto mmaterial .Wit hth epeat ysubsoi la tBen schop,th eorgani cmatte rcontent so fth euppe rlayer so fbotto mmateria lther ewer emuc h highertha na tJaarsveld .Thi swa sals ofoun dfo rth esub-botto mo fth editche so nbot h farms.Th eorgani cmatte rconten twa smeasure db y 'losso nignition 'an db ytota lelemen tarycarbo nanalysis .Organi cmatte ri nto psoil si nth eNetherland scontain so nth eaver age58 1carbon .Th eorgani cmatte rconten twa scalculate dfro mth emeasure delementar y carbonconten tb ymultiplyin gb ya facto r 1.724.Th eorgani cmatte rconten ti nth ebotto m materialmeasure db yth e 'losso nignition 'metho dwa scorrecte d forcla yan dCaCO, ,ac -

96 i voO

r^O — O— OOCMvO •H S *0 CO V vO CM u M ai (U •n 4J i-l a o Ol •»w e •o 3 h O Ol M o) M (M g(U O JS •1-1 CO o. Ol o r-4 o VD en o •J a u •d Hto 4J

a ai •H J3 9 4J

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r^irt — O — OONO** u a ~ CO NO H ai | -^ —' 01 o > u m -H S S o « ai -i 9 n»>, ai S B5 .c a-o " OB O i-l 00 4J -c4 P. 'i4U cd ai a a *-'oJC«-lOf-iM9 97 .-H 9 h o m ja a) o -o A b o -i Qil gUUUH C 3 a) o -H H P«. > o.v a < H S H o u 1-4• inncN^!N

a - « a ou~ia>o-icococNo S o u u o> u M o •ri .o a I o ja ,-J 3 — N

L/")r-^vd-00-d--^-Cir<")

. u-l vo — r^ in co r~-

o^-^-ino —u-i^ r

>> * 60 +-fflJ U n m o ji R u

n) i-i W) o CM — CM iO

O>CN-J-v£)C0CO-J-00

M o -^ n co ai r- ^D CN o CO O

4-» S c 4J i « O i JJ 4-1 o e * n Ö nfflH 4-) (It 1 O 0 c •H e J3 00 T3 m 4J •0n1 4J >, -u ^ 3. e M ^ tn •U tJ 4J B 3 J>! o a 10 "J 3 3. o S -~s u-l O nH •• * « « e "s KN i m O » - - - •Ö /-s O fU fj *—- V CN A rn n-) OJ Cl U3 w -H e v^ O ö 0) ö m til tO ^ rt i-l « O >. 4J T3 M t_> BJ -^ b»H MU ^ H [3 ü 35 U V-l Ctf ^ T-< « H tfl tfl b0 P. O O o o o to w OSi ZUS

98 cordingt ofactor s describedb yHofste e &Fie n (1971).Th edifferenc e inorgani c matter contentbetwee n thetw omethod swa s small (Table36) . Theminera l fractiono fth ebotto mmateria l fromthe-ditche si nBenscho p canb eclas sified as clay,i nJaarsvel d assand y clay-loam to :lay-loam (SoilSurve y Staff, 1975). Thebotto mmateria lwa s classified according toth e organic fraction following theclassi - ficationsyste m givenb yd eBakke r &Schellin g (1965). InBenschop , itca nb e classified as peaty clay andclaye ypea t toric h inhumus ,i nJaarsvel d asver yhumou s toric h inhumus . The cation-exchange capacity (CEC)o f thebotta nmateria lwa shigh ,a scoul db eexpec ted invie wo f thehig horgani cmatte rcontent s and thehig h clay contents.I nal lsamples , calciumwa s themajo rexchangeabl e cation. The solidphas edensit y ofth ebotto mmateria lwa sdetermine d forcalculatio no f the volume of the solidphas e inslice so fbotto mmateria l inpenetratio n trials (Section 9.3. -3 forth e 'peatyclay ' to 2500k g m -3 12). This solidphas edensit yvarie d from218 0k gm Jr ""- -'—'— " """""' forth e 'loamybotto mmaterial' . — ''--'

Profiles ofvolum e fractiono fliqui d andbul k density

InApri l 1977,mu dcore swer e collected intriplicat e from thevariou sditc h sections formeasuremen to fvolum e fractiono f liquid andba. kdensity .Th ecore swer e takenwit h thebottom-materia l sampler,provide dwit ha closin guni to n top.Th efroze nmu d columns weredivide dmechanicall y intoslice s about 2c mthick ,a sdescribe d inSectio n 7.2. Thevolum e fractionso fliqui d inth eslice s aieshow ni nFigur e 36.Th eplot s show theaverage sobtaine d fromthre ecolumn spe rsamplin gsite .Th edifference s between the threecolumn swer e rathersmall .Nea r thesediment—wate r interface,th evolum e fraction of liquidwa snearl y the same inal lsamples .Wit h increasing depth,th evolum e fraction decreased gradually.A ton e samplingpoint ,i nth e frontsectio no f the supplementally drained ditch,ther ewa s only aver ysmal ldecrease .Fo r the lowest sliceso fbotto mma terial,sometime s relativelyhig hvolum e fractions ofliqui dwer e found,whic hma yb edu e todisturbanc e during sampling. Thebul kdensitie s ofth ebotto mmateria l arepresente d inFigur e 36.Th e differences between thetriplicat e valuespe rsamplin g sitewer e rather large.Th ebul kdensit y of the bottommateria l nearth esediment—wate rinterfac ewa sver y low.Th epatter no f increase of thebul kdensit ywit hdept hwa s rather irregular.Th edistinc tdifferenc ebetwee n the frontan dbac k sectiono f thesupplementaril y drainedditc h inBenscho p canb e explained by thepresenc eo fa pea t layeri nth esub-botto m of the frontsectio no fthi sditch .Thi s was confirmed during sampling,sinc ebrow npiece s of peatwer evisibl e through the clear Perspexwal lo f thesamplin g tube.

Elementary carbon

Theorgani cmatte r content isa n important characteristic because iti shighl ycor - relatedwit h theadsorptio no fpesticide s (Section6 6). Organicmatte r contents inth e mechanically sawnslice so f frozenbotto mmateria l shown inFigur e 37wer e calculated from measured contentso felementar y carbono fpoole d mat(Tia l fromtw obotto mcolumns .Fo rth e

99 volume fraction of liquid (m3 m 3) 0.7 0.8 0.9 1J0 0.7 0.8 0.9 ID 0.7 0.8 0.9 10 0-r^ ' I ' . ' -r-V ' ' 1

0.10-

0.20- BSDb/ BSDf JMbi JMf /

O30-

bulk density (kg m ) 0 200 400 0 200 400 600 0 200 400 _1 l i i i I J I L

0.10- k BSLfABSLb BSDf \BSDb

0.20-

Q30-1

elementary carbon (°/o) 5 10 15 20 O 5 10 15 20 25 30 35 O 5 10 15

0.10-

BSDbi BSDf JMb! JMf Q20-

0.30- depthinbottom(m)

Figure36 .Characterizatio no fditc hbottom s inth eLopiker - waardPolder .Volum efraction so fliquid ,bul kdensitie san d elementary carboncontents .Abbreviation s forsamplin gsite : B= Benschop ,J = Jaarsveld ,S D= siphon-linke d ditch,S D= supplementallydraine dditch ,M = middl editch ,b = bac k and f= fron tpar to fth edifferen tditc hsection s (Figures 31an d32) . deeperlayers ,mor eslice s (about2. 2c mthick )wer ecombined .Th epatter no fdecreas eo r increasewit hdept hwa sirregula ran drathe rvariable .Th epresenc eo fpea tlump si nth e sub-bottomo fth efron tsectio no fth esupplementaril ydraine dditc hcoul dexplai nth ewid e variability incarbon .Th eelementar ycarbo ncontent s forth eto playe r (sampledt oa dept h ofabou t1 0cm )o fth edifferen tditc hbottom sshow ni nTabl e3 6agre efairl ywel lwit hth e elementarycarbo nprofile sshow ni nFigur e36 . Twocolumn so fbot hth esiphon-linke d ditchbotto man dth esupplementaril ydraine d ditchbotto mwer edivide dint o2 c mslices .Larg evariation si ncarbo ncontent swer efoun d

100 elementary carbon (%)

Figure37 . Mass fraction ofelementar y carbon in2 cm bottom slices fortw oditche s inBenscho p (— « siphon- linee d ditch and • supplementally )botto m(m ) drainedd i :ch).

(Figure 37). This variability shows thati twil l bedifficul tt otak e representative sam- pieso fth editc hbottom .

9.3.6 Spraying dates and procedures in 1976

The siphon-linked ditchi nBenscho pwa s surnkinded bya full-grow n apple orchard (standard tree).Alon g one sideo fth esupplement!iril y drainedditc hwa sa nol dpea ror - chard (standard tree)an do nth eothe rsid ea youi^ g appleorchar d (spill trees).N opath s werepresen t along thoseditches .Th etree s along theditche swer e sprayed twice,onc ei n thenorma lway ,an donc ewit honl yon esid eo fth e sprayhead s (ofa Kinkelde r low-volume sprayer)operating ,sprayin gonl yi nth edirectioi . of the trees justalongsid e theditch . Azinphos-methyl wasapplie di nBenscho pi n a;p i ean dpea rorchard so n3 May ,2 1June , 2Jul yan d9 Augus t 1976.Th elas tapplicatio nwa s not investigated.O nth e firsttw o spraying dates,azinphos-methyl ,applie da sGusatiio n 254w.p. ,wa suse di ncombinatio nwit h dimathoate,applie da sRogo r40 4 liquid.Th espra ) concentrationso factiv e ingredientwer e about2. 7k gm for azinphos-methylan dabou t1 kgm fordimethoate .Th eamount so f 3 -2 wateruse d forsprayin gwer e1 5c m m and2 5cm ' -2 forth eyoun gan dol dorchards , respectively. A standard apple treeorchar dwa s situated near thefron tditc hi nJaarsveld .A ton e sideo fth emiddl e ditch,a youn g spilltre eplani[a t ionwa splante dan do nth eothe r side ofthi sditc h stood standard trees.Alongsid eth e frontan dmiddl editch ,ther ewa sa far m road.Th eappl e trees along theothe r sideo f the«e ditcheswer e sprayed fromth efar m roadb y'sprayin gover ' theditch .A tbot h sides cf theback ditch ,a nol dappl e orchard (standard tree)wa splanted ,ver yclos et oth edittc h In197 7o non esid eo fth editch , theol dplantatio nwa s replacedb ya ne wspil lp i antation. InJaarsveld ,azinphos-methy l was appliedt o apple treeso n5 May ,2 4May ,2 1June , 1July ,6 Augus tan d1 9Augus t (theeffect so fth e lasttw oapplication swer eno tinves - tigated).Azinphos-methy l 25%w.p .wa sspraye d with a concentrationo factiv e ingredienta - bout2. 5k gm ~ usinga Kinkelde r low-volume spra)er The amountso fwate rspraye d were about2 0t o3 0c m m fo3r th- 2e youn g andol d trees ,respectively . Asmentione dbefor esuc hsituation s areunusia l inmos t fruit-growing areas;the y

101 representcondition stha tgreatl yfavou rth epollutio no fope nwate rwit hpesticides .

9.3.7 Concentrations of the insecticides in ditch watev

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 d inSectio n4.2 .Shortl yafte ran dbe tweenapplication so fazinphos-methy lan ddimethoate ,wate rsample swer ecollected .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-methyl anddimethoat ewer eextracte dfro mth ewate rsample swit hdichloro - methanei na separator yfunnel .Som eo fth eextract so fwate rsample swer ecleane du po n silicage lcolumns ,a sdescribe d inSectio 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) .

Concentrations in197 6

Theconcentration so fazinphos-methy lan ddimethoat emeasure d inwate rsample stake n fromth edrainag editche si nBenscho par eshow ni nTable s3 7an d38 .Th econcentration s ofazinphos-methy li nth editc hsection si nJaarsvel dar epresente di nTabl e39 .Th ere sultssho wtha tconcentration swer egenerall yver ylo wbefor espraying .Afte rspraying , concentrationswer einitiall yhig han ddecrease dgradually . Theconcentration so fbot hcompound si nwate rsample stake nbefor esprayin gwer ebe - _3 low1 m gm (noclean-up) .A nexceptio nwa s thesupplementaril ydraine dditc hi nBenscho p on3 May .Sinc ea smal lpar to fth efar mwa sspraye do n1 Ma yan dth ewate rpum pwa sno t switchedof fbefor e3 May ,smal lamount so fth ecompound scoul dhav ebee ncarrie dint oth e supplementarilydraine dditch . Theconcentration so fazinphos-methy li n197 6wer emuc hhighe rtha nthos emeasure di n 1975 (Table 32). In1976 ,th editche swer esample dshortl yafte rspraying ,sometime swith in1 h .Beside sth epump swer eou to foperatio nan ddifferen tsamplin gtechnique swer e used.

Effecto fdifferen tGL Ccolumn san dclean-u p

Theconcentration so fth ecompound swer emeasure do ndifferen tGL Ccolumn st oreduc e theris ko ferror scause db yinterferin gsubstance san dt oincreas eth eaccurac yo fmeas urements.Th edifference sbetwee nconcentration so fazinphos-methy lmeasure d ondifferen t GLCcolumn swer erelativel ysmall .Th econcentration so fazinphos-methy lmeasure do nGL C ColumnI Iwer ei nmos tsample ssomewha thighe rtha no nColum nI .Fo rdimethoat en osyste maticdifference scoul db efoun dbetwee nth econcentration smeasure dwit hdifferen tGL C columns. Theclean-u pprocedures ,a sdescribe di nSection s5. 9an d5.1 0wer euse do n1 0sam -

102 Ol Ü1 f w M H K> — — ro er w rt •p- ^J IC (C 01 t-, Ci HS O" > o O Ul M O B I-H c, c, E : 0 » H r1 f-o 3 C B S o ic 1 rt 13 9 Bg B9 ni g Cr < o ri 1 g •*s ll I roi m 1» h- "< 9 rt O ui pi n n^ 1 H> ro ro 00 3*T3 ^J 10 o 0 Ml O (0 m t-* a (t> a, B (-B» m i-t »rt SDDionnUBUna« « E S =1 FI rt H' H- H. o o a a o w » n UT m< S 3 n> 9 rt nunaaü'O^niiinn l-i. H- H« H« M* rt H' 01 h-» oi 01 n m C EEEEEK- EBEB •O T3 13 "O *0 O IC 9 oi c » O o n o n n us oooo n> M M o o H» o 9 0 •n 01 — o Ml FI h- doUnoiiiDoi a ö tö rf Bi g B vo g o H »S ÜJ13 a o o H* TO h" M a. O 0ro1 0101010101010101 H- •a rti o> ro « S E ECEEEEEE X) » • g a 1» w lu 9 ooooonoo 0 rt M' a M>< a. ro a n Mi a. 01 — H- «1 Mi •o rt M VI ro • gotnow oaacnacnoa a » H- roi-l M IB » o (0 M IC 01 01 01 M 01 01 •UHSüioicotooioi a 9 9 LH E E E B E E E E E E E E p- H* 01 rt «• H E O O O O O O O O o O o o ro "O en 9 ro o CT IC •o » m a »1 H' ro(0 l- Ë rt (I) a SjNlNjNjNj^NJ^JSl^NlSjNlSjSJON^ ON ON vl *-J V| *-J Vl n H 9 (o 0 m a* a. vJMOONHOOOO-WJ>-WW-(»000000-toOOO 01 T3 N tr u> •o re g w h-» M 1-* ••• 13 (D O Mi to O ro g* roo d f n N 0 » o rt C o o H» 9 Ln 01 — 9 0 O to I o •<»- * •*j 4>- kD £- N O vl 0> OMjiO O rt T) n oi s S O 9" ro9 S S S M» 01 0 rt •O rt E IC Oi K-* g4 tr ro v< — a^ A A o h- • O — — Ui o o O O LO NJ < rt ro oi oi ÜlO I MsJ W Ui ?f 9 00 N> rt 10 & a* g ro e- tr H- O H- to ro B 0> üiO O •c* vl O o h-' a ro i^i ro E o. o, o ON ON 00 •p* H- l-i g- S o m g to rt o rt TS ro QN JS — - Ui J> — -o NJ —v l LO b ~ ic g to o o* ON o » IO •_• 4>- «ö — Ui O O O — — ON Ln s *• g » I-J «3 os ON o O I Ui ON — NJ un \0 rt S 10 nro -o to Ht o 01 1 Mi ON o ro N> u> O Nï — Ni OO--00NJ IC Ml s ». (C 01 M rt S n m H _ rt B O Mi LO LO Isï Ui — K) O — ON 01 N" Ln -J ON ON LO ro § Eu co Ou CD H« tO WN) fO *• W Ml H •tht- Mi •i-b* rorol- l o roM l rog |S3 *- — — ONCO- VO -P- g- t. M 01 u O Ui O «X» VO M M - f) rt IC 4>- E IC o (10 M ar H- o S o 01 O — —LO to lo Ui —0 0 B E g rt o n ON 00 Ni 00 vO LO •P- IC o g- Ou Mi •— NJ LO 4>- LO 4>- roB rt o •o g- VI M 0 ro CO C/3 co CO 1 " O — LO hJ IO VO •M IO CO 01 g- IC g- o ON -C- LO ON VI ON o 01 g — rt i H- (-M•1 h-1 o o- o o H» o ~J o » g M> O « & E ?r 0 01 IC Mi a rt Ou O»JMnM00O»O* g* 1M" H« IC it Ui Ln UI \0 M M .p" roO Ou tuJ g- H* o KI — O 41- o B g o- a* ON — VO a *• N *• y cN o r* rn o — m o o — CN — — —

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o M ,a C p">^ ^ u •TH CU r—1 R P. •r-R( H ta Tl Ol CO e n UH e o> - o o\ co « « o ü ,-H ?-> 4-1 m J= >, «u v_- 13 to * tu a r- O ai o> i o t—>i* m• cet T-l co e O o 3 U 4-1 0 en i-l .e N •ri CJ r^ ooocN — oooocNcoin^ocoooooooo-a-H H c CtJ 'H C M 01 MH TJ 3 S« a a a o. o. en• C) Tl M 01 U •ri •H •H eu p, m c M J3 O Q o a O a H 01 4J C»-) P. o a y U n M M un eu auoej cjcjcjejcjcjcjcj m o 3 3 3 3 3 33333333 to 01 en to en o 0. (X o. o. O. cncncnco&HOHcncncocncococncn c eu c C 4-1 0J •H •H •H •ri •H •H -H CU 4-1 R R M > m o o O O O cnacnaQac/îQtnQtnQcna 4-1 u 01 3 3 CD CD CU T) f-H rH Cu eu O un O (M •H u o r H CtJ a) ai f-( ai 0!1* rH ^ tu C 0 a. u U C_> U 0] 01 0) Ä ^ >N 01 B 3 3 3 aj rJ i-ct C/l U s :> r-( O 3 <-i <-> P o t/j < ,£1 4-) >-> CO tl] -d- — Q to — — CN j- un UÏ r» Table39 .Mas sconcentration so fazinphos-methy li n sampleso fwate rfro mth edifferen t ditches inJaarsvel d during 1976.Fo rcode sfo rwa y ofsamplin g seeTabl e37 .Abbre - viationsf an db refe r toth efron tan dbac kse c tious ofth edifferen tditches .

Dateo f Wayo fsamplin g pH3 Concentra:io no fazinphos-methy l (mgm 3 ) sampling front middle back frontdit: h middleditc h backditc h ditch ditch ditch II II II

5May 1 BDi p BDi p BDi p 7.0 <0.6 <Ô.8 <1. 4 <1. 0 <0.1 <0.3 Dip Dip Dip 7.0 153 15» 113 118 108 119 7Ma y Dip Dip Dip 7.2 15 li 61 74 18 18 12Ma y Dip Dip Dip 7.0 7.9 10 2.8 2.9 1.1 2.4 fD s 7.0 21 21 Dip Dip 7.2 7.8 .1.6 3.7 4.5 17Ma y fS suc fS suc 7.2 14 1I 1.4 2.1 fD suc fD suc 7.2 13 >? 1.8 2.4 Dip Dip Dip 7.2 56 36 48 1.6 2.2 24Ma y 7 fS suc fS su c 7.1 214 19 20 fD fD su c 7.2 309 264 40 36 suc 38! bS suc 7.2 55 bD su e 7.2 53 61 1Jun e fDi p Dip Dip 7.8 52 6! 7.1 7.8 1.2 1.6 bDi p 7.8 11 5i 14Jun e Dip Dip 7.5 3.3 ï.7 0.4 0.6 fM su c fM su c 7.5 17 1 0. 0.4 21Jun e S suc f Ssu c fS suc 7.0 315 21 329 406 58 59 D suc fD su c fD suc 7.0 12 1 72 57 48 50 23Jun e S suc fS su c fS suc 7.0 62 66 64 73 5.5 12 D suc fD su c fD suc 7.0 71 6> 98 79 5.0 8.1 S suc 7.0 80 6S D suc 7.0 58 6) 1Jul y S suc suc f Ssu c 7.1 94 10> 114 132 19 27 D suc suc fD su c 7.1 28 29 175 203 20 24 S suc 7.4 11 1 D suc 7.4 24 21 5Jul y S suc suc 7.2 8.8 $.6 2.6 D suc suc 7.2 8.0 1 1.9 Msu c fM su c 7.4 24 2> 2.9 2.8

1.Spra ydate so n5 May ,2 4May ,2 1Jun ean d 1Jul y 1976(Sectio n9.3.6) . 2.GL CColum nI an dII ,se eTabl e15 . 3.Averag evalu efo rdifferen tditc hsections . pieso fwate rfro mth efar mditches .Th eaverag e reLativ e differencesi nconcentratio no f azinphos-methylan ddimethoat ebefor ean dafte rclefcn - -upwer eonl yabou t 6%fo rbot hcom - _3 pounds.Thes edifference swer eeve nsmalle ra tconcentration s above1 m gm .Invie wo f therelativel yhig hconcentration si nth efar mditche s ,clean-u pwa somitte di n1976 .

Effecto fsamplin gan destimatio no fmixin gtim e

In1976 ,man yshallo wwate rsample swer esuckej i up,abou t0 t o6 c mbelo wth ewate r surface,an ddee psamples ,abou t0 t o6 c mabov e ths sediment-waterinterface .Thi sgive s anindicatio no nth edistributio no fth ecompound s sverth ecross-sectio no fth ewate rbod y inth editch .Th edifference si nconcentratio ni n shallowan ddee psample swer egreates t aftersprayin go n2 1Jun ei nBenscho pan dJaarsvel d (Tables37 ,3 8an d39 ,respectively) , Iti sdifficul tt oestimat eth etim eneede d for completemixin go fth ecompound s

105 throughth ewette dcross-sectio no fth editch .Transvers emixin gmainl yoccur sb ywate r circulationresultin gfro mtemperatur edifference si nth ewater ,b ywin dactio nan db y dispersiondurin glongitudina l flow.I nthes efiel dsituations ,som eothe rfactor slik e localgrowt ho fduckwee d andshar pvariatio ni nwate rdept hmad ei tdifficul tt oestimat e therat eo fmixing .I nth editche sa tJaarsveld ,mixin gwa salmos tcomplet eafte rtw odays , asca nb esee nfro mth econcentration s inshallo wan ddee pwater so n2 1Jun ean d2 3Jun e (Table 39). Duringtha tperiod ,considerabl emixin goccurre di nth editche sa tBenscho p although itseeme dt ob eincomplete . Anexceptio nwa safte rsprayin go fazinphos-methy lo n2 4Ma y 1976i nJaarsveld .I n thefron tsectio no fth efron tditch ,ver yhig hconcentration so fazinphos-methy lwer e foundbot hi ndee pan dshallo wsample so fwater .Thi sexceptio nwa sdu et oa defec ti nth e sprayera tth estar to fspraying .

Variationi nconcentration swit hplac e

Besidesa stron gvariatio ni nconcentratio no fth ecompound swit hdept han dtime , variationwit hplac eca nb esee ni nTable s3 7t o39 .A tBenschop ,th econcentration s inth e middlesectio no fth esiphon-linke dditc hwer ehighe rtha ni nit sfron tan dbac ksections . Thisca nb eexplaine db yth epresenc eo fcomparativel ysmal ltree salongsid epar to fth e middlesectio no fth editch .Durin gspraying ,i twa sclearl yvisibl etha ta large rpar t ofth espra ypasse dacros sth esmalle rtrees . InJaarsveld ,th econcentration so fazinphos-methy l inth efron tan dmiddl editc hwer e muchhighe rtha ni nth ebac kditch .Thi scoul db edu et oth ewa yo fsprayin gacros sth e firsttw oditc hsection s (Section9.3.6) .

9.3.8 Direct measurement of spray drift into ditohes

In1977 ,spra ydrif tt oth esam editche sa sstudie di n197 6wa smeasure ddirectly . 2 Beforespraying ,Tempe x (expandedplastic )float s (0.25m ) wer einstalle do nth ewate r surfacea tfixe ddistance si nth editches .O nthes efloats ,glas sPetr idishe s (diameter 0.09m )wer eplaced .Afte rspraying ,th ePetr idishe swer eremove dwithi n 1h fromth e floatsan dplace di ndar kcoole dboxes .I nth elaboratory ,th ePetr idishe swer erinse d threetime swit haceton e (about 15t o2 0c m ). Thisrinsin gwa sdon ea squickl ya spossi ble,usuall ywithi n3 h o fspraying .Th erecoverie so fazinphos-methy lan ddimethoat e(a s tested ina separat etest )fro mth ePetr idishe swer eabou t100° san dshowe da lo wcoeffi ciento fvariatio n (3%). Theeffec to fsunligh to nth erat eo fdeclin eo fazinphos-methy lan ddimethoat efro m thePetr idishe swa steste dseparatel yo n1 5Jun e 1977.Spike dwate rsample s (0.5c m) wereadde dwit ha pipett et oglas sPetr idishe san dplace d inth esu nou to fdoors .I n3 h , azinphos-methyl showeda declin eo fabou t20° san ddimethoat edecrease db yabou t 12%.I n viewo fth ebrie fexposur eo fth efiel dsample st osunligh tan dth ecoolin go fth esample s duringtransport ,n ocorrectio nfacto rwa sapplie dfo rdecline . Spraydrif twa smeasure d twicedurin gsprayin gwit hazinphos-methy li n1977 ,bot ha t Benschopan dJaarsveld .Spra ydrif to fdimethoat ewa sonl ymeasure d atBenschop .Thes e

106 simplemeasurement sca nreplac ecalculatio no fspr^ y driftint oditche sfro mconcentratio n inth ewater .Ther ewer en ointerferin gcompounds , extractionwa sver yfas tan dcontamina - tioncoul db emeasure daccurately .

Resultso fmeasurin gspra ydrif ti nBenscho p

Themethod so fsprayin gan dth eamount sspray« dwer eth esam ea si n197 6 (Section 9.3.6).Distance sbetwee nstandar dappl etree sarom d thesiphon-linke dditc hwer e3 t o4 m.Aroun dth esupplementaril ydraine dditch ,th edistance sbetwee nth estandar dpea rtree s were4.5 man dbetwee nth espil lappl etree swer e1.5m .Th edistanc ebetwee nfloat swa s 14.3m forbot hditches .Th eamount so fazinphos-m£thy lan ddimethoat edetecte di nth e Petridishe si nBenscho par eshow ni nTabl e40 .Difference sbetwee nth eduplicat esample s wereusuall ysmal lan daverage d S%(0-28% )o fth eobserve damounts .Th evariatio ni nth e longitudinaldirectio nwa smuc hlarge rtha ni nth e plingSite s3 ,4 an d5 i nth esiphon-linke dditc he n2 6August) .Th ecoefficien to fvaria tioni nth eaverag eamount si nth elongitudina ldirectio no fth edifferen tditche srange d from2 9t o45% . Theamount so fdimethoat ei nth edishe swer elawe rtha nthos efo razinphos-methyl , whichcorresponde dfairl ywel lt oth einitia lconcentratio ni nth espraye r (Section9.3.6) .

Table40 .Masse s (ug)o fazinphos-methy l (A)an ddiÉetho a te(D )measure dafte r spraydrif ti nPetr idishe s (diam.0.0 9m )place do i floatso nth ewater-surfac e inditche sa tBenscho pi n1977 .Mea nvalue so fdup l :.catesamples .Th efloat swer e 14.3m apart .

1 Sampling Siphon-linkedditc h Suppl emer tarily DitchSectio n5 site drainedc itch

31Ma y 26Augus t 31Ma y 26Augus t A D A A D A

1(front ) 78 49 17 21 13 1.7 2 58 35 41 27 16 1.6 3 29 17 27(30)(26)2 27 16 0.8 4 49 29 25(29)(35)2 35 15 0.9 5 34 23 26(26)(28)2 25 22 6 27 16 15 36 20 7 54 32 43 29 17 8 (middle) 42 27 47 32 21 9 57 34 57 27 17 10 46 28 59 19 13 11 25 16 59 24 31 12 36 22 43 46 29 13 33 19 30 15 10 14 35 22 68 32 21 15(back ) 28 17 15 25 15 Average 42 26 38 28 18 1.3 Coefficiento f (36) (35) (45) (29) (38 (38) variation (%)

1.Ditc hSectio n5 wa sbehin da windbrea ko nth efru: . tfar ma tBenscho p (Figure 31).:" V 2.Value so f thedistributio no fth ecompoun dove rtty e widtho fth e siphon-linked ditch.; i

107 Theaverag eamount so fbot hcompound si nth edishe so fth esupplementaril ydraine d ditchwer e lowertha nthos eo fth esiphon-linke dditch .A ton esid eo fth esupplementari lydraine dditch ,a spil lappl etre eorchar dreceive da 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 fo rstandar 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 d inPetr idishe si nJaarsvel dar epre sentedi nTabl e41 .Th eaverag edifferenc ebetwee nth eduplicat esample swa s 6%(0-49%) . 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 ured inth elongitudina ldirectio no fth editche si nJaarsvel drange dfro m2 3t o55% .

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 in1977 .Mea nvalue so fduplicat esamples .

Sampling Frontd 3 tch Middle ditch1 Backditch 1

25Ma y 6Jul y 25Ma y 6Jul y 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 11 7 183C180)2 75 81 9 85 220(149)(214)2 92 110 10 51 169 95 65 11(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 fth editc hwa scleare d inJune . 2.Value so fth edistributio no fth ecompoun d over thewidt ho fth efron t ditch.

108 Estimateo fdrif to fth einsecticide s intoditche s

Theaverag emas so fazinphos-methy li na Petr i iisho fare a63. 6c m inth .2e,siphon . - -linkedditc hwa s4 2y go r6. 6m gm ofevaporatin g surfaceo fth editch .Th emas sdos e ofazinphos-methy l dividedb ygroun d surfaceapplie d onth estandar d treesaroun dth e siphon-linked ditchwa s6 8n gm ' (Section 9.6.3). Tarelat econtaminatio nt odose ,a n 'areicrati oo fcontamination 'm . couldb edefine d asth erati obetwee n themas so fin - r,/ i areaan dth emas sdos edivide db y secticide fallingo na nare ao fwate r dividedb ytha t August,afte rspra ydrif t intoth e ground areao fth espraye dorchard .O n3 1Ma yan d2 6 siphon-linked ditch thisrati owa sabou t0.1 . azinphos-methyl wascalculate dt o For thepumpe dditch ,th earei c ratio,m ,fo r f A bothditche swer enearl yth esam ea s be 0.08.Th ecorrespondin g ratios fordimethoat eint 3 forazinphos-methy l namely0. 1an d0.09 ,respectivel y Lnphos-methyl,wer eabou t0.2 6fo rth e On2 5Ma yi nJaarsveld , thearei c ratiosfo ra z thebac kditch .O n6 Jul y these ratios frontditch ,0.3 2fo rth emiddl e ditchan d0.1 8fo r 0.41,respectively , forth e frontan dmiddl e ditcheswer e about0.3 9an d therati o m .wa s only 0.003. Forth editc hsectio nprotecte db ya windbreak ,

9.3.9 Estimate of rate coefficients for decline

Themas so fth ecompound si nth ewate rcompartmen tafte rth e firstapplicatio ni n Benschopo n3Ma y197 6wer eobtaine d fromth eproduci :o faverage dconcentration si n'dip ' samples taken fromth efront ,middl e andbac ksection s (Tables3 7an d38 )an dwate rvol umeso nsamplin gdates .Sinc eth eamount s shortlyaf;e rsprayin gwer eno tye tmixe d over thecross-sectio no fth ewate rbody ,thes e initialmasse swer e considered too uncertain forestimatio no frat ecoefficients . A declineplo t (logconcentratio na tvariou s tiiies)wa smad efo ra perio d without infiltrationo rdischarg eb yth ewate rpum p from5 t c ditchesa tBenscho p (Figure 38).Linea rregressio n lineswer edraw n (Chapter 7).Th erat e coefficients fordeclin eo fazinphos-methy lan ddimethoat ei nditc hwate r arepresente di n Table4 2(Perio d I).Th erat ecoefficient s fordéclin so fdimethoat ewer e distinctly lower thanthos e forazinphos-methyl .

masso fpesticid e(g ) 10

Figure 38. Mais of pesticides inth ewate r compartment ofd tches atBenscho p atvariou s times after applica iono n3 Ma y1976 . A• azinphos- -methyl ins i]'hion-linke d ditch (BSL); •« dimethoate in si; pion - linked ditch (BSL); A= azinphos- -methyl insu ] Iplementaril y drained ditch (BSD); o =»dimethoat e in supplementally drained ditch (BSD).

109 Table 42.First-orde r rate coefficients for decline of azinphos-methyl and dimethoate indrai i age ditches at Benschop. Period I from 5 to 17May ,an dPerio d II from 21 June to 1Jul y 1976

Period pH1 Water temp. Azinpl ios-meth yi Dimetl oate °C, av.,s.d . and range rate half coeff.o f rate half coeff.o f coeff life determ. coeff. life determ. (d-1) (d) (d-1) (d)

Siphon-linked I 7.0 14+2(11-19) 0.25 2.8 1.0 0 0.056 12 0.95 ditch II 7.0 19+2(15-21) 0.25 2.8 0.99 0.052 13 0.97 Supplementärily I 7.1 14+2(11-19) 0.18 3.9 0.91 0.061 11 0.983 drained ditch II 7.0 19+2(15-21) 0.26 2.6 0.98 0.19 3.6 1.00

1. pHwa smeasure d in the field. 2. Calculated from daily minimum andmaximu m temperatures in thewate r compartment near the water pump. 3. Value on 5Ma y for dimethoate was rejected. ^_^

After thesecon d application ofbot h compounds atth eBenscho p farm on 21 June1976 , the average masses ofbot h pesticides on 23Jun e and 1Jul y were calculated from theaver age concentration inshallo w anddee p samples ofwate r and thewate r volume onbot hdates . Shortly after thesecon d spraying, shallow samples ofwate r were taken. During the spray- -drift experiments in 1977,th erelationshi p between shallow sampling andarei c ratio of contaminationwa smeasured . By taking into account thewate r surface area in 1976,th e initial masses could be estimated. Fora perio d without infiltration ordischarg e from2 1 June to 1July , thedeclin e patterns atBenscho p areshow n inFigur e 39.Th e rate coeffi cients fordeclin e ofbot h compounds arepresente d inTabl e 42 (PeriodII) . The rate coefficients obtained during both periods of investigation arecomparabl e to the rate coefficients found inth eoutdoo r tanks forperiod s with similar conditions (compare Tables 26an d42) .

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

Concentrations ofbot h compounds insurfac e water outside both farmswer e measured on a limited scale. Theresult s areshow n inTabl e 43.Thes e datawer e obtained on different

masso f pesticide (g) 10

Figure 39.Mas s ofpesticide s in thewate r compartment of ditches at Benschop atvariou s times after the2n d application on 21 June 1976.A = azinphos-methyl in siphon-linked ditch (BSL); • = dimethoate in siphon- -linked ditch (BSL); A= azinphos-methyl in supplemen tally drained ditch (BSD); o= dimethoate insupple mentally drained ditch (BSD).

110 Table43 .Mas sconcentration s ofazinphos-methy lan c dimethoatei nsample s ofsurfac ewate ri nth eLopikerwaar dPolder ,i n197 É

Dateo f Site pH Concentration (mgm~ 3) sampling azinphos-methj1 dimethoate

II II III

7Ma y Intake,Jaarsvel d 7.2 0.4 0.8 24Ma y Discharge,Benschop 1 7.6 1.6 1.8 17 16 tJun e Discharge,Benscho p 7.8 0.4 0.7 5.8 9.3 9.7 BenschopperCanal 2 7.6 0.6 1.1 0.2 8.2 0.1 14Jun e Discharge,Benscho p 7.0 0.3 0.4 6.2 5.6 7.4

1.Discharge ,Benschop :surfac ewate rreceivin gwa t fromth efrui tfar ma t Benschop.1 2.Benschoppe rCanal :nea rth ebridg ei nBenscho pv i liage. 3.GL CColumn s (seeTable s 14an d15) .

GLCcolumn swithou tclean-u pprocedures . Thedischarg editc ha tBenscho preceive dwate r fromth ewate rpump .Th ehig hconcen - trationso fdimethoat ei nthi sdischarg editc hwa spossibl ydu et ocleanin go fth espra y equipmentnea rth esamplin gpoint . Thedevian thig hvalu efo rdimethoat ei nsurfad ewate r ('BenschopperCanal' ,1 June ) measuredo nColum nI Ishowe dtha tusin gonl yon eGL C columnpackin ginvolve d- aris ko f overestimatingth econcentration .

9.3.11 Preliminary measurements of coneentrations in groundwater

Beforesprayin gi n1976 ,som egroundwate rtubes !(lengt h2m ;diam .0.0 6m )wer eplace d inbor ehole s (diam.0.0 8m ) (Figures3 1an d 32).Th elowe rpar to fth ePV Cgroundwate r tubewa sperforated ,wit hfilte rlengt ho f0. 5m .Th sto po fth etub eprotrude dabou t0.1 5 mabov eth esurface .O nto po fth etubes ,screw-cap s wereplaced . Somegroundwate rsample swer esucke du pfro mth î îsetube swit hth evacuum-typ ewate r sampler (Chapter4 )fo ranalysis .Concentration so f )othcompound si nsample so fgroundwa terar epresente d inTable s4 4an d45 .Wit hon eexception ,th econcentration swer ever y low.Withou tclean-up ,th eazinphos-methy lconcentration s ingroundwate rtube sa tBen schopwer eusuall ybelo w1 m gm ~ .Althoug hth etube ;wer eemptie da fe wday sbefor eth e sampling,contaminatio ncause db yleakag ealon gth e Groundwatertube smigh tb epossible , becauseth ediamete ro fth ebor ehol ewa sgreate rthi nth ediamete ro fth etube . Duringinvestigatio ni n197 6a tBenschop ,hardl ran ywate rflo woccurre d fromth e ditchesint oth esubsoil .Howeve ra tJaarsveld ,a considerabl einfiltratio nfro mth emiddl e andbac kditc hwa smeasure dafte rwate rintak e (risinggroundwate ri nFigur e35 Dan dhig h chlorideconcentration si nGroundwate rTub eV Io n1 7Ma yan d 14Jun e 1976i nTabl e 35).A t Jaarsveld,th eazinphos-methy lconcentration si nGromdwate rTube s Ian dI Iwer elowe rtha n theconcentration si nTube sV an dVI ,whic hshowe da muchstronge rrépons eo fth eground - waterleve lt oraisin go fth editc hwate rtha nTube s Ian dI I(Figur e35D) .S ocontamina - tiono fgroundwate rfro mcontaminate dsurfac ewate rprobabl ycanno tb eexclude di narea s

111 Table44 .Mas sconcentration s ofazinphos-methy lan ddimethoat ei nsample so f groundwater atBenscho p in1976 .

Dateo f Ground pH Concentration (mgm ) sampling water tube azinph os-m e thyl dime thoate

II 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 CColumn s (seeTable s 14an d15) .

whereinfiltratio ni scommo nan dwher eresidenc etime sar erelativel yshort . Theconcentratio no fdimethoat e inGroundwate rTub e IIIo n1 4Jun e 1976a tBenscho p washighe rtha no fothe rmeasurement s (Table44) . Formor edefinit econclusion so npossi blegroundwate rcontamination ,mor emeasurement sar enecessary .I nth 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 di nBenscho 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 di na 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 s ofazinphos-methy l insample so fground watera tJaarsvel d in1976 . -3 Dateo f Ground pH , Concentration (mgm ) sampling water tube I1 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 Thevolume so fth ewe tmu dslice swer e calcul:ite d withEquatio n 11,usin g thedat ao n thedensit yo fth esoli dphas e (Table 36). The dep h belowth esediment—wate r interface wasobtaine db ydividin gth evolum eo fth ewe tmu d sampleb yth e averagesurfac eare ao f thefroze nmu dcolum n(4 9c m) .Th esa„ 2 wcu twa s abcbut2 m mfo rbot hhand-saw nan dmechani - callysaw ncolumns . Theslice swer eextracte dwit ha mixtur eo f solventsan dth eextract swer ecleane do n silicage lcolumn si nth esam ewa ya sth eextract s fromth ebotto mmateria li nth eoutdoo r tanks (Sections5. 6an d5.11) .Th ecleane dextract; ; wereanalyse db yGL Co nColum nI I (Ta- ble 14). Asignifican tdecreas ei nconcentratio ndurin g storageo fth emu dcolumn swa sno t detected,an dn ocorrectio n factorwa s introduced Chapter7) .

Resultsfo rpenetratio n

Themasse so fazinphos-methy li nbotto m mater:al s fromBenscho pan dJaarsvel dar epre - sentedi nTable s4 6an d47 ,respectivel y Unfortunâtely,severa lmu dcolumns ,includin g thesample so fbotto mmateria l takenbefor eth e sprayingperio dwer e lostdurin gstorag e byfailur eo fon eo fth edeep-freezers .Therefor e inth enex tyea r (March 1977),ne wun -

Table46 .Penetratio no fazinphos-methy l intoth e bottomo fth esiphon-linke dditc h andth esupplementaril ydraine dditc hi nBenscho p curing 1976.f ,fron to fth editch ; b, backo fth editch .

Dateo f Siphon-linkedditc h iupplementarily drainedditc h sampling site depthi n masso f Site depth in masso f andslic e bottom(m ) azinphos- nd slice bottom (m) azinphos- number -methyli n lumber -methyli n slices (ug) slices(yg )

17Ma y fl 0 -0.010 0.67 1 0 -0.008 0.14 f2 0.012-0.023 0.44 f|2 0.010-0.023 <0.01 f3 0.025-0.036 0.16 f3 0.025-0.036 <0.01 bl 0 -0.012 0.34 bl 0 -0.011 0.54 b2 0.014-0.025 0.17 b2 0.013-0.024 0.24 b3 0.027-0.039 0.07 b3 0.026-0.037 0.15 24Ma y fl 0 -0.009 _1 f 1 0 -0.009 0.07 f2 0.011-0.021 0.05 f2 0.011-0.026 0.09 f3 0.023-0.033 0.09 f3 0.028-0.043 0.08 bl 0 -0.007 0.13 bl 0 -0.021 0.15 b2 0.009-0.028 0.24 b2 0.023-0.034 0.17 b3 0.030-0.049 0.01 b3 0.036-0.047 0.08 21Jun e bl 0 -0.010 0.29 bl 0 -0.011 0.04 b2 0.012-0.023 _1 b2 0.013-0.023 <0.01 b3 0.025-0.036 0.18 b3 0.025-0.036 <0.01 b6 0.063-0.073 0.04 b4 0.038-0.050 0.04' blO 0.112-0.123 0.01 23Jun e fl 0 -0.011 0.30 f 0 -0.011 0.86 f2 0.013-0.022 0.29 f2 0.013-0.024 0.09 f3 0.024-0.034 0.18 f3 0.026-0.037 0.05 bl 0 -0.010 1.84 b 0 -0.010 0.38 b2 0.012-0.022 0.22 b2 0.012-0.022 0.24 b3 0.024-0.034 0.14 b3 0.024-0.036 0.11

1.Interferin gsubstances ;clean-u pfailed .

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 werecollecte d 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 0.1 0 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 21 June 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 23 June 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 1 July 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;clear-u pfailed .

treatedbotto msample swer ecollected .Th emasse so fazinphos-methy l inth euppe rlaye r werebelo wth edetectio n limitfo 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 euppe rslice swer ehighe rtha ni nth elowe rslices . Thedifference sbetwee nth efron tan dbac ksection so fth editche si nBenscho pwer elarg e (Table 46). Thelarges tamount so fazinphos-methy lwer e foundi nbotto mslice sfro mth 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 d39) . Inspit eo fth esmal lnumbe ro fbotto mcores ,som eapproximation swer emad eo nth e totalmasse so fazinphos-methy l inth edifferen tditc 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-methyl inth ewate rcompartment so fbot hditche si nBenscho p (Figure39) . Thetota lmas so fazinphos-methy l inth ebotto mcompartmen to fth esiphon-linke dditc ho n 23Jun ewa sestimate da t131 ,o fit smas si nth ewate rcompartment .Th ecorrespondin gper centagei nth esupplementall ydraine dditc hwa sonl y 2%.

114 Thepenetratio no fazinphos-methy li nth e bottom layerwil lb ediscusse di nmor ede - tailunde rcompute rsimulatio n forthes e situations (Chapter10) .

9.3.13 General discussion and conclusions

Thehydrologica l circumstanceso nbot h farms iith eLopikerwaar dPolde rwer e highly complex.Moreove r thesoi lsurfac ewa s ratherunevei ,th esoi lwa sver yheterogeneou san d datao nth ewater-conductin g substratumwer e lacking.Consequently , theusua ldrainag e for mulaecoul dno tb euse dt oestimat ewate r flow throjghth editc hbottoms . Intakeo funcon trolledamount so fwate rmad eestimatio no fth e iteiiso fwate rbalanc edifficult .Fo rac curatemeasuremen to fwate rbalances ,simple r field situationsan dautomati cmeasurin ge - quipmentwil lb enecessary . Thecharacterizatio no fditc hbottom s showedhig horgani cmatte rcontents ,lo wbul k densities andcorrespondin ghig hvolum e fractionso: : "liquid .Dat ao fthi skin d arerathe r scarcean dnee dmor e attentioni nth efuture . Introductiono fth einsecticide s intosurfac eTJrate rb yspra y driftcoul db emeasure d quicklywit hPetr idishes .It sexten ti shighl y influencedb yloca lsituation s (windbreaks, positiono ftrees ,paths )an dway so fapplication .Windbreak s (andprobabl y alsopath sa - longside theditches )reduc e thearei crati oo fco nlamination ,bu tmor e researchi sneede d toasses s theireffec ti ndifferen t situations.I nsuc hmeasurement so fspra ydrift , the lossesb yphotochemica l conversionan dvolatilizatio n shouldb emeasured . Therema yb eothe rsource so fcontaminatio n inuowatercourses ,fo rexampl eth e clean ingo fspra y equipment afteruse . Theconcentratio no fth ecompound si nth e farmditche swer e fairlyhig han dothe r substances didno t interfere during theGL Canalysi :.Th e calculatedhalf-live so fazin phos-methyli nth editche si nBenscho pwer e about3 t o4 days ,an dthos e fordimethoat e4 to1 3days .Thes ehalf-live s correspondedt oth eha ]f-live smeasure di noutdoo r tank trials (Chapter7) . Mixingo fth ecompound s throughoutth ecross-sectio no fth editc hoccurre dwithi na fewdays .Th e rateo fadsorptio nan dpenetratio n into thebotto mmateria lma yb elowe ri n situationswit h slowmixing .Mor e researchi sneede c toinvestigat e themixin gproces si n moredetail . Thedat ao npenetratio no fazinphos-methy l intc thebotto m layerwer eto o limitedt o estimate accurately thefractio no fth esubstanc e introduced thatpenetrated .Th erat eo f conversioni nbotto mmateria lunde r fieldcondition s wasno tknown ,bu tlaborator ydat a indicate thati tma yb efairl yhig h (Chapter 6).Th econtribution so fconvectiv e transport, diffusion,an dbiologica lmixin gt openetratio no fth einsecticid e into thebotto mar eno t known.Thes easpect swil lb ediscusse di nmor edetai lunde rth ecompute rsimulatio nfo r thesesituations . Onth ebasi so fthes efiel d trialsalone ,i ti s difficultt oestimat e thecontribu - tiono fdifferen tdeclin eprocesses .I nChapter s1 0 and 11,attempt swil lb emad et osepa - rateth eeffect so fth evariou sprocesse sb ycompute tsimulatio no fth editc h system.Thes e furtherstudie sshoul denlarg eth e transferabilityt oothe rsituation san dothe rpesticide s withdifferen tphysico-chemica lproperties .

115 10 Computations on the behaviour of pesticides in a ditch compartment

10.1 INTRODUCTION

The contributiono fth evariou sprocesse st oth edeclin eo fazinphos-methy lan ddime - thoatei nditche swa sdifficul tt oassess ,especiall yi nperiod so fwate r intakeo rpump ing.Th e extento fpenetratio no fbot hpesticide s intoth editc hbotto mwa sals odiffi cultt oevaluat e fromth e fieldexperiment s (Chapter 9). Toovercom e theseproblem sat temptsar emad et odescrib e thebehaviou ro fazinphos-methy lan ddimethoat ei na ditc h systemmor equantitativel ywit h computationmodels . Firstlyth erelevan twate rflo wi nth e ditch systemswer e approximated. Secondly, pesticidemovemen tan dconversio nwer ebuil t intoa computatio nmodel .Th emode l includes flowo fth epesticid e through theboundar y surfaceso fth ewate ran dbotto mcompartments . Much attentionwa spai dt oth e effectso fadsorptio no nan dpenetratio no fth epesticide s intoth editc hbottom .I na simulatio nexperiment ,th esignificanc ewa s studiedo finfil trationthroug hth editc hbotto mo nexten to fpenetratio no fpesticides . Comparisonso fth e resultso fth ecomputation swit h thoseo ffiel dmeasurement swer e onlymad efo rth etw o ditchesi nBenschop .Th elarg evariatio 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 sfo rth e approximationo fth ewate r bal ance.

10.2 DITCH GEOMETRYAN DDERIVATIO NO FEQUATION S

Thecross-sectio no fth editc hwa s assumedt oconsis to fstacke d trapezia (Figure40) . The slopeso fth ewall si nth e lowerpar to fth editche swer e steep (Table 34). Thewet tedperimete ro fth editc h (P)wa scalculate d from

P,= b, + 2h As2 +1 (22) 11 w 1 v J inwhic h

b] =widt ha tbotto mo fditc h (m) h =averag ewate rdept h (m) Sjo rtg a= slop eo flowe rpar to fditc hwall swit h respectt overtica l (1) (tga= horiz./vert. ) (Figure40 ) Thepesticide swer e assumedt ob ecompletel ymixe d through theditc hwate rcompart ment.Th editc hbotto mwa sdivide d intotwent y computationcompartments . Thesurfac e areao fth efirs tbotto m compartmenta tth esediment-wate r interface wa s Uh)= 0 computed fromth eproduc to fth ewette dperimete r (Pj)an dth elengt ho fth e

116 Fijur e40 .Cross-sectio no fa ditc hwit h thäshap eo fstacke d trapezia.Fo rsymbol s sestext . ditchcompartmen t (Z- ).Th esurfa œ areao fth e secondbotto mcompartmen twa s obtained fromth eproduc to f'interface 'perimete rP .an d I Theperimete rP .wa s computed from Equation23 :

P2 =2» ,+ 2d2 tg(lB)+ 2 (S w+ d2) Ja\ +l ' (23) inwhic h g =arct g (1/s.)(Figur e40 ) (1) d,= dept ho fuppe rsurfac eo fsecon dbotto m compartment, (m)

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

Water flow

Water flowi nth ewate rcompartmen t (Figure4 )wa scombine d intoth efollowin gcon - servationequation :

+ + (24) dVw /it = <7p " u d 4

q. q.

Figure41 .Sketc ho fa ditc h compartment.Fo rth eitem so f thewate rbalanc eo fth editc hcompartment ,se eEquatio n24 .

117 inwhic h dv'/At =chang ei nstorag eo fwate r compartment (m3 d" ) q =rat eo fprecipitatio n intowate r compartment (m3d " ) q =rat eo fevaporatio n fromwate r compartment (m3d " ) q =rat eo fdischarg e fromwate r compartment (m3d " ) q =rat eo fdischarg e fromupstrea mditc h section (m3d " ) q . =rat eo fintak e intowate r compartment (m3d " ) q. , =rat eo fintak e intodow nstrea mditc h section r 3 A- ) (m d q =rat eo fflo w throughwette d perimetero fditc h (m3d " ) q , =flo wrat e through drains (m3 d" )

3 -2- 1 The filtrationvelocit y (7 inm m d) throug h thedifferen tbotto m compartments was calculated from

vlhU) =qJ\U) (25)

in which A, =surfac e areao fbotto m compartment ()m j =inde xnumbe ro fbotto mcompartmen t (1)

Pesticide movement and conversion

The total areicmas s fluxo fpesticid e intobotto mmateria l (J ,,i nm em d ) is -2 -1 s,l b composedo fcontribution sb yconvection ,convectiv e dispersionan ddiffusion :

^s.lb= ^conv.lb+ ^disp.lb+ ^dif.l b (26)

inwhic h -2- 1 j =arei cmas s fluxb yconvectio n intobotto mmateria l (mgm d) conv,lb _j i j . =arei cmas s fluxb yconvectiv e dispersion intobotto mmate - (mmg d) disp,lb rial dif,1b = areicmas s fluxb ydiffusio ni nbotto mmateria l (mgm d) The areicmas s fluxb yconvectio nwa sdescribe db yth eproduc to ffiltratio nveloci

ty(^ lh)an dmas sconcentratio no fth epesticid ei nth eliqui dphas eo fth ebotto m (c., inm gm ):

J ,. =7 „ e,, (27) conv.lb lbl b ^ J Thearei cmas s fluxb yconvectiv edispersio nwa s calculated with

jdisp,ib = -*d|Fibhib/3a w

in which

118 Z. =dispersio n distance (m) a (m) z =dept h inbotto m

Thearei cmas s fluxb ydiffusio ni nbotto m materia iall («Tj.flh )wa scompute d inth e samewa ya sdescribe d inChapte r8 (Equation s1 5 aid 16). Therat eo fconversio n inth editc hwate r (R )an dth erat eo fconversio ni nth e ditchbotto mmateria l (R .) werc, be calculate dwit h first-order rateEquation s 17an d18 , respectively. Theflo wrat eo fsubstanc e intoth ewate r compartmentdurin ga nintak eperio d (f -1 S,W1 inm gd )wa scalculate d from

F s,w•i - g^.i a w,i (29)

inwhic h = mas sconcentratio no fsubstanc ei nintak ewate r (mgm ") o w,•i ^

The flowrat eo fsubstanc e intodownstrea mditc hsectio n duringa nintak eperio d (F .i nm gd )wa s computed from

s,wd i,d w (30)

inwhic h massconcentratio no fsubstanc e inwate rcompartmen t (mgm ~)

Theflo wrat eo fsubstanc eou to fth ewate rcompartmen tdurin ga pumpin gperio d (.F inm gd )wa scalculate dfro m

F - q. o (31) s,wo ^d w Theflo wrat eo fsubstanc e intoa wate rcompaitmen tfro mupstrea mditc hsectio n dur inga pumpin gperio d (F inm gd )wa scomputet )fro m

F = a, a (32) 8,WU d,u w,u inwhic h c =mas sconcentratio no fsubstanc e inupstrea mditc hsectio n (mgm ") w,u ^ Theresultin gconservatio nequatio n forth epesticid e inth ewate rcompartmen twit h volume V (m) wa s

vw vJ' *• b s.lb-'z-O s.wi s.wu F . - F - V R (33) s,va s,wo w c,w Theconservatio nequatio nfo rth epesticid ei n thebotto mmateria lwa s

119 3e./3t= -3= 7 ,,/32- R , (34) b s,lb c,b v ' Therelationshi pbetwee nmas sconcentratio ni nth ebotto mmateria l (c) an dth econ centrationi nth eliqui dphas e (e )wa scompute dwit hEquatio n21 .Th eadsorption—desorp - tionwa sassume dt ooccu rinstantaneously ,whil e theisother mwa sassume dt ob elinea ri n therelevan tconcentratio nrange .

10.3 DESIGNO FTH ECOMPUTATION SAN DVALUE SO FPARAMETER S

Thedifferentia lequations ,boundar ycondition san dbasi crelationship swer eprogram med inth ecompute rlanguag eCSM PII I (IBM, 1975).Th eprogra mwa sru no nth eDECsystem-1 0 computero fth eAgricultura lUniversity ,Wageningen .Th elistin go fthi scomputatio nmode l isgive ni nAppendi xB . Theinitia lmasse so fth esubstanc ei nth ewate rcompartmen tan di nth ebotto mcom partmentswer eassume dt ob e zero.Th espray-drif twa sse ta ta constan trat edurin gth e dayo fspraying .Thi sinpu twa sassume dt ob ecompletel ymixe dthroug hth ewate rcompart ment.Th etota lmasse sa tBenscho po nth efirs tsprayin gdat ewer ederive db ybackwar d extrapolationo fth eregressio nline si nFigur e3 8t oth eordinat eo nth edat eo fth e spraying.Th emasse sapplie ddurin gth esecon dsprayin gwer eobtaine d fromth evalue sa t theintercep twit hth eordinat ei nFigur e39 . InBenschop ,n owate rwa stake ni ndurin gth einvestigation ,thu sth erat eo fintak e intoth ewate rcompartmen t (q.) andth erat eo fintak eint odownstrea mditc hsection s (q. )coul db ese tt ozero .Becaus eth esiphon-linke dditc hwa sa branc ho fth edischarg e l,d system (Figure 31),n odischarg efro mupstrea mditc hsection soccurre d (q =0) .Durin g periodswit hdischarge ,th econcentratio no fth esubstanc e inwate rflowin gfro mupstrea m ditchsection s intoth esupplementall ydraine dditc hi nBenscho pwa sassume dt oequa lth e concentrationdischarge d fromth esiphon-linke dditch . Thedimension so fth editc hsection swer eintroduce dfro mTabl e34 .Th enumbe ro f computationcompartment s inth ebotto mwa stwenty .Th ethicknes so fth efirs tbotto mcom partmentwa s0.00 1 m.Th emultiplicatio nfacto rfo rth ethicknes so fth ebotto mcompartment s (m,)wa s 1.1.Th etota lthicknes so fth ebotto mlaye rwa sthe ncompute da t0.0 6m .Th epara meterso fth editc hbotto mlik eth ebul kdensit y (p) an dth evolum efractio no fliqui d (E )a sshow ni nFigur e3 5wer eintroduce da sfunction so fdepth .

Description of the water flow

Theflo wrate so fevaporatio n {q )an drainfal l (q )wer ecalculate dfro mFigure s3 3 e -1 p and34 Ab ymultiplyin g thefluxe s (inm md )b yth ewate rsurfac earea .I nth ecomputa tionmodel ,th erat eo frainfal lwa sdistribute devenl yove rth eda yprecedin gth etim eo f observation. Therat eo fdischarg eo fth ewate rpum pwa smeasure ddurin gdispersio nexperiment s (Chapter 11).Th erat eo fdischarg efro mth ewate rcompartmen t (q.) duringa da ywit hpump ingwa sobtaine db ymultiplyin gth efollowin gquantities :a )dail ypumpin gtime s (Figure 34B);b )rat eo fdischarg eo fth ewate rpump ;c )rati obetwee nth ecatchemen tare ao fth e

120 ditchcompartmen tan dth etota lcatchmen tare ao f he waterpum p (Table 34).Thi s resulted 3 1 indischarg erate s inBenscho p of

v O) =P „ (Ä. (35) 'llhb g g V'y inwhic h p =densit y ofwate r (kgm " ) w 2 g =acceleratio n duet ogravit y (m d" ) h =heigh to fgroundwate r levelabov editc hbotto m (m) g h =heigh to fwate r levelabov editc hbotto m (m) w 2 1 Y =drainag e resistance (kgm" d" )

Valueso fdrainag eresistanc e (Y)wer e calculated fromvalu eo f y (1),h and h on lb g w the firstfou rsamplin g dates. (Inthi sperio d no witerwa spumpe d outo r letint oth e ditches;thu s K.(1 )wa s reasonably known). These drainage resistanceswer e used toestimat e thechang eii iwate r leveldurin g ada ywit hwate r pomping. First,th echang e inwate r leveldurin gpumpinj g wasroughl yestimated , so thatfiltra - tionvelocit y V,. (1) couldb e obtainedwit h q. in cJDnservationEquatio n 24.Thes e values lb O of P,.(1 )wer e introduced inth eresistanc eEquatio i 35,b yassumin g aconstan t drainage resistance andwit h h thepatter no f thegroundw i at;r leveldurin g the investigation could becalculated . Bycomparin g thecalculate d andmea s jredgroundwate r levels,i twa s possible toge tbette r approximations forth echang e inwate r leveldurin g thepumpin gperiods .

121 Diffusion, disversion, adsorption and conversion parameters

Theaverag ewate rtemperatur ei nth editche swa sabou t1 5 C.Th ediffusio ncoeffi - o -4 2 cient (p,.c )o fazinphos-methy li nwate ra t1 5 Cwa scalculate dt ob e0.3 5x 1 0 m -1 dit.w _4 2 - d andtha tfo rdimethoat ewa scalculate dt ob e0.4 1x 1 0 m d (Reid& Sherwood ,1966) . Thesam etortuosit yrelationshi pwa sintroduce da sdescribe di nSectio n8.3 . Thedispersio ndistanc e (Z.,)i nth ebotto mmateria lwa sunknown .Fo ragricultura l soils,rathe rwid erange so fdispersio ndistanc ehav ebee nfound ,fo rexample ,a rang efro m 0.01t o0.0 6m (Frissele tal. , 1970).Th edistanc e introducedi nthi sstud ywa s0.01 5m . Theadsorptio ncoefficient s (K ,.)o fazinphos-methy lo nth ebotto mmateria lo fth ediffer entditc hsection swer emeasure d (Table 23). Therat ecoefficient sfo rconversio no fazinphos-methy lan ddimethoat ei nth ewate r compartments (k )o fbot hditche sa tBenscho pwer eapproximate dt ob e0. 9time sth erat e coefficientsmeasure d forth edeclin e (k )o fbot hcompound sfo rtw operiod si nthos e ditches (Table42) .Thi sassumptio nwa sbase do nth eresult so fth ecomputation sfo rth e tanktrial s (Chapter8) ,whic hshowe dtha tconversio ni nwate rma yb eexpecte dt ob eth e dominantproces sou to fdoors .Th erat ecoefficient sfo rconversio no fth ecompound si nth e bottommateria l (k ,) wer ederive d fromrat ecoefficient sobtaine di nincubatio ntest s c>b _i (Chapter6) .A t1 5°C , forazinphos-methy lwa sestimate d tob e0.03 8d (Table21 ) k c,b _,. andfo rdimethoat et ob e0.0 1d (Table 22).

Details on the computation method Thecomputation sfo razinphos-methy li nbot hditche sa tBenscho pwer edon eb yEuler' s integrationmetho d (RECT)usin ga tim este pA to f0.00 5d ,ove ra perio do f5 9days .Fo rdi methoatei nbot hditche sth etim este pha dt ob ereduce dt o0.00 2d .Th ecomputation swer e checkedb yhalvin gth etim este pan db yusin gth eRunge-Kutt a (RKS)integratio nmethod , whichautomaticall yselect ssmal ltim einterval swhe nrate so fchang ear ehig h (IBM,1975) . Forth econvectiv e flowi nth ebotto m (Equation27) ,th econcentratio ni nadjacen t compartmentswer eaveraged ,whic hminimize dnumerica ldispersio n (Goudriaan,1973) . Insituation swit hupwar dwate rflo wthroug hth editc hbotto man dwit ha stee pcon centrationgradien t (decreasingi ndownwar ddirection )a nartificia ldownwar dmas sflux , duet odispersion ,wa ssimulated .Thi sartefac twa smainl ysuppresse db ysettin gth emas s fluxint oth ebotto mlaye r (Equation26 )smalle rtha no requa lt oth eflu xo fdiffusio ni n suchsituation s (limitedflu xequation ,Appendi xB) .Thi sworkin gmetho dstil lgive sa slightoverestimat eo fdownwar dtranspor ti nth editc hbotto mcompare dwit hwha twoul dhav e beencompute dunde rthes econdition swit ha correc tmodel .A secon dmetho dwa stested , wherebyfo rupwar dliqui dflo wth edispersio nter mwa sse tal lth etim ea tzero .Thi smeth odgive sa nunderestimatio no fth epenetratio nint oth ebotto mi nrelatio nt oa correc t modelfo rsuc hconditions . Atregula rinterval sdurin gcomputations ,th ewate rbalanc ean dth emateria lbalanc e ofth epesticid ei nth editc hsyste mwer echecked .

122 10.4 COMPUTED RESULTS FORTH EFIEL D TRIALS

Results of computation of the water balance

Theheight so fth ewate r levelabov eth editc hbotto mi nth esiphon-linke d ditchan d thesupplementall ydraine d ditcha tBenscho par eshow ni nFigure s42 Aan d43A ,respective ly.Th e changesi nwate r leveldurin gpumpin gwer eapproximate db ycomparin gth ecalcu latedgroundwate r levelswit hth egroundwate r levelsmeasure do nsamplin g dates (Figures 42Ban d43B) . Invie wo fpossibl evariatio ni nth edrainag eresistanc e duringth eperio d of investigation,a smal l differencebetwee nth ecalculate dan dmeasure dgroundwate r levels was consideredacceptable .Durin gth efirs ttw opu npin gperiod s (Day 17an dDa y 24),a sig nificant risei nth ecalculate d groundwater levelwa sobtained .I nthes eperiods ,n osig nificant increasei nth efiltratio nvelocit y throughth ewette dperimete ro fth editc h

(Klb(1))wa scompute d (Figures42 Can d 43C).

height ofth e ditch water(m ) 0.5- 0.4- 0.3- », 0.2-"^' 0.1-

ii11iiiii|111111Mi|i1111 11| 1111 II 1111 height of the groundwater (m) B 1.0-1

I I I I III! I11 I I III I I 1 | I I I I II I II|| I I I | I | II | I I || I I || I | filtration velocity through the ditch bottom (mîm,2dHI) c 0O2-

0.01-

11 II i II 1111 II 11111111IIII11111n111 II111ni I 11 IT I I 11 111 10 20 30 40 50 60 time(d) Figure 42.Result s ofth eapproximatin g water balance calculations forth esiphon-linke d ditch at Benschop in1976 . A. Height ofth ewate r level above theditc h bottom.x,wate r height atsamplin g dates;P , pumping period. B. Calculated height ofth egroundwate r level above theditc h bottom,o ,groundwate r level on sampling dates. C. Filtration velocity calculated from Equation 25.

123 height of the ditch water (m) 0.5-1

height of the groundwater (m) 1.0-

0.6-

I J I I I I I I I I I J I I I I I M I I J I I I I I I I I I I I I I I I I I I I filtration velocity through the ditch bottom (m3m2d~1) 0.02-

1111111111111111111111 30 40 50 60 time(d ) Figure43 .Result so fth eapproximatin gwate r balance calculationsfo rth esupplementall y drainedditc ha tBenscho p in1976 . 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 ylarge rtha nth ein creasei nth emeasure dgroundwate rlevel .Thi si sattributabl et oa reductio ni ndrainag e resistancedurin gth eheav yrainfall . Duringth einvestigation ,usuall ysmal lvariation si nth efiltratio nvelocit y (K,,(1)) werecalculated .However ,muc hfaste rflo wthroug hth editc hbotto moccurre ddurin gth e heavyrainfall .Th epositiv evalue so f V.,(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 d fromdee pan dshallo wgroundwate rlevel s(He y& 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 0I i d justbefor eth eheav y

124 rainfall.Thes e flowrate sar ei nth esam erang ea s theestimate so fth eupwar d seepage rateo f0.00 02 m d ~, mentione db yth eStudiegroe p Lopikerwaard (1973)fo rcomparabl esit - uations. The itemso fth ewate r conservationEquatio n2f t forbot hditches ,cumulate d overth e periodo finvestigatio n from3 Ma yt o2 Jul y1976 , ireshow ni nTabl e48 .Th edischarg e fromth esiphon-linke d ditchwa srelativel y small thedr yyea r 1976.Th etota l discharge fromth esupplementaril y drainedditc hwa sequa lt o thedischarg eo fth ewate rpump . The substantial discharge fromupstrea mditc hsection s Intoth esupplementaril y drainedditc h waso fgrea t importancefo rpesticid emovemen tdurih g theperio dwit hwate rpumping .Th e totaldischarg e fromthi ssectio nwa smor e thante n timesth e averagevolum eo fwate ri n theditc hcompartment . Thecomputation swit hth e Runge-Kutta integration method (RKS)produce d nearlyth e sameresult sa sthos ewit hEuler' sintegratio nmetho d (RECT).Th edifference si nth evalue s ofth ewate r fluxeswhe nhalvin gth e computationtifcie - stepwer e alsosmall .

Pesticide movement and conversion

Pesticidei nth ewate r compartment

Thecompute dan dmeasure dmasse so fazinpho s methyli nth ewate rcompartmen to fth e siphon-linked ditchan dth esupplementaril y drained ditcha sa functio no ftim ear egive n inFigure s4 4an d46 .Th evalue sfo rdimethoat ei n bothditche sar eshow ni nFigure s4 5 and47 .Th emeasure dmas so fsubstanc ei nth editc h watercompartment swa sderive d from theproduc to faverag econcentratio ni nth editc h sectionsan dth ewate rvolum ea tsamplin g dates.Th erange si nth emeasure dmas s showni n Figures4 4t o4 7indicat eth ehighes tan d lowestaverag econcentratio ni nth efront ,middl e or back sectiono fth editc h (Tables3 7 and38) . With k =0.9 k (Table 42),th edeclin e processesi nth ewate rcompartmen twer edes - cribed fairlywell .Th esam ehold sfo r setting k equalt o k .Thi sconfirm sth e assump- c,w tiontha tconversio ni nth ewate rcompartmen twa s the predominantproces si nth edeclin e underoutdoo rconditions . Thecompute d curvesfo rth edeclin ei nth ewatej rcompartmen t (logscale) wer esome -

Table 48. Items inth ewate r balance (m) o fth ed i tches inBenscho p integrated over theperio d ofinvestigatio n from 3Ma yt o2 Jul| y 1976. During theperiod , nowate rwa stake nin .

Siphon--linked Supp Lementarily ditch drai ned ditch

Change in storage 33 42 Total rainfall 29 36 Total evaporation 95 117 Total discharge 111 1407 Total discharge from upstream 0 1295 Total flow through the 53 59 ditch bottom Total flow through the drains 157 176

125 masso f azinphos-methyl (g)

10#

0.001 111n 11 1n 11 111 n 11111111111 1H 11111 1n 1 1111 1i ii n 111 1111111 1 50 60 time(d) Figure44 .Compute d andmeasure dmas so fazin phos-methyl inth ewate rcompartmen to fth e siphon-linked ditcha tBenscho p from3 Ma y1976 . =compute dmas s (kc w =0. 9 kr); =com putedmas s (kc w = kr); 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-J

0.1-

I 11 I I I I | I I I I M M I | I I I I M I I I I I I I I I I | I II I M M I M I I I I I I I I I 10 20 30 40 50 60 time(d) Figure45 .Compute d andmeasure dmas so fdime - thoatei nth ewate r compartmento fth esiphon - -linkedditc ha tBenscho p from3 Ma y1976 . =compute dmas s (kc w =0. 9 kr); = computedmas s (&cw =fe r);o = average dmeas uredmasses ;S = sprayin gdate s (Chapter9) ; P =pumpin gperio d (Chapter 9). Verticalbar s arerang eo f themeasure dmass .

126 masso fazinphos-methy l (g) 10-a

O01

OJOOI I II I I I I I I I I I I I I 0 10

Figure46 .Compute d andmeasure d mass ofazin phos-methyl inth ewate r compartment ofth e supplementarily drained ditch atBenscho p from 3Ma y1976 . = computed mass (fec,w=0. 9fe r); o» average d measured masses;S = sprayin g dates (Chapter 9);P = pumpin g period (Chapter9) . Vertical barsar erang e ofth emeasure d mass.

mass of dimethoate(g ) 10T

0.1-:

O01 11I I Mil IIII II 50 60 time(d) Figure 47.Compute d andmeasure d masso fdime thoate inth ewate r compartment ofth esupple mentarily drained ditch atBenscho p from 3Ma y 1976. computed mass(fe , .9fc r); averaged measured masses;S - sprayin c,wg dates (Chapter 9);P •pumpin g period (Chapter9) . Vertical bars arerang e ofth emeasure d mass.

127 whatconcave .Thi sca nb epartl yexplaine dfro ma sligh tadsorptio nan dpenetratio nint o thebotto mlayer ,whic hwil lb esimulate d tob efastes ta tth ebeginnin go fth eexperiment . Becauseo fth ecomparativel ysmal lconversio nrat eo fth ecompoun d inth ebotto mlayer ,th e massflu xa tth ebottom—wate rinterfac eeve nbecam enegativ e (upwardflux )afte ra fe w days.Thi scontribute dt oth econcav epatter no fdeclin ei nth ewate rcompartment . Duringth ethre epumpin gperiods ,a decreas ei nth emas so fth ecompound swa scompu tedfo rth esiphon-linke dditch .Shortl ybefor eth ethir dpumpin gperio da sligh tincreas e inth emas so fazinphos-methy li nth ewate rcompartmen twa scalculate d duet oupwar ddrain agefro mth editc hbotto mdurin ga da ywit hmuc hrainfal l (Figure44 ,Da y 48). Duringth e firstpumpin gperio d inth esupplementall ydraine dditch ,relativel ystron gincreas ei n themas so fbot hcompound s inth ewate rcompartmen twa scompute d (Figure46 ,Da y 17).Thi s resultedfro mth erelativel yhig hconcentratio ni nth ewate rdischarge dfro mupstrea m ditchsections .Th eassumptio ntha tth econcentratio ni nth esiphon-linke dditc hwa srep resentative forth econcentratio ni nth einflowin gwate rma yno thav ebee ncorrect .Th e spray-drift intoth eupstrea mditc hSectio n2 (Figur e31 )coul dhav ebee nlowe rdu et o thepat halongsid etha tditc hsection .I nditc hsection swit ha contaminate dwate rflo w fromupstrea msections ,i ti srathe rdifficul tt oasses sa pesticid ebalance . Theitem so fth esimulate dbalanc e forbot hcompound si nth editches ,cumulate dove r theperio do finvestigatio nfro m3 Ma yt o2 Jul y 1976ar epresente d inTabl e49 ,whic h showstha tconversio ni nth ewate rcompartmen twa sth emos timportan titem .Th edifferen t conversionrate si nth ewate rha donl ya smal leffect .Increasin gth econversio nrat eo f azinphos-methyl inwate rb y 111(t oth edeclin erat eitself ;Tabl e 42),resulte di nonl y anextr a 1.5%o fth emas sapplie dbein gconverte d inwater .Fo rdimethoat eth ecorrespond ingvalu ewa ssomewha thighe r (3%).Th emasse so fbot hcompound sdischarge d fromth e supplementallydraine dditc hwer ehighe rtha nthos edischarge d fromth esiphon-linke d ditch.Durin gth ethre epumpin gperiods ,a considerabl emas so fsubstanc ewa stransporte d fromupstrea mditc hsection sint oth esupplementaril ydraine dditc h (Table49) .

Pesticidei nth editc hbotto m

Thecompute dan dmeasure dmasse so fazinphos-methy l inth ebotto mlaye ro fth esiphon - -linkedditc han do fth esupplementaril ydraine dditc ha tBenscho par egive ni nFigur e48 . Inbot hditches ,th ecalculate damount sar econsiderabl yhighe rtha nmeasured . Inthes e computations,i twa sassume dtha tth ecompoun di scompletel ymixe dthroughou tth ewate r compartment.However ,i npractic ether ear econsiderabl edifference sbetwee nconcentra tionsa tvariou sdepth si nth ewate rbod yi nth efirs tfe wday safte rcontaminatio n(Ta bles3 6an d 37).Th eeffec to fpenetratio nint oth editc hbotto mi sthu slikel yt ob eover estimatedwit hth emodel .Th erat eo fconversio no fth epesticid e inth editc hbotto m ,) unde rfiel dcondition si squit euncertain .Th evalu eo f ,i nfiel dsituation s v(kc,t r n k c,b maydeviat e fromth evalu eo f k ,measure d inlaborator y incubationstudie san dintroduce d intoth ecomputations . Themeasure dan dcompute dconcentratio npattern so fazinphos-methy l inbot hditc h bottomsar epresente d inFigure s4 9an d50 .Th ecompute dconcentratio ni nth euppe rcen timetreo fth editc hbotto mwa smuc hhighe rtha nth emeasure dconcentratio ni nth euppe r

128 O O

CO J3 M 3 to •o o o o o o o oo oooooo oo

•O M oo u h ço a • o co co » js o) o*cy*r^r~o\co co CN o J3 « a co o CO o (3 u •H kl m -M co -a 13 CM •O S 01 o « 4J rH CH

r^. CM in CU 0) •* o e S O -H ON GO 00 —• "• vu o co 4J «^ h 0) •o •o CU o 01 u e- s U o) S T3 O O H U • S O M 01 CO UP. co — co CM CM CM CM r-» A: s o c VO MNOVO — m 11 co oo co ^o r» r^ ei S •rt a •o o B c n •ri 4J co CU .O o » 3 •y O CO f> CO ** N — CfN ^. C0 CC) CO rg B O csj — — — — — mo -3- O £ -• CO a o to j= — — — — — o m ** a. B o -H

O O CO M B 0) CU co 0) M e « co B I 60 H -Hrt CO CO CO 0) M A; A! O 4-> > 01 01 tu » JS a ß 4J 4J ON ON ON ON a « O CO B o o o o o •H u u u N a) 0» <-N I CO 00 O* N—' co co a oi B o 00 0) 3 o u o •ni o" U 4-1 -H — r-- CH U CW CO 4J

I 00 >N^

O r- o» >d- JZ I M u 0) co a, a> *r4 •^ m 0 -ri J3 •H -O l-l (0 3! 01 01 M-i a> CL, .fi O J3 f S •U H •O co co m o O O c3 J= JS J3 s* SU O a a u o o 4J \D c B c 0) ja —i •H r* R •H a M "g o\ N *F4 O •o — OS »H B 01 u >• 3 i-i e- 3 S T> ON & o 0) • O O CNI O r-t • o o\ u , a o J.s3 a 4-J a a co en •H a 3 U FH w O Ml -O 129 mass of azinphos-methyl (g) 4-1 . Js,

1 4^\ y ^*s^. 'p* ^>^ Il 0.1- 1 ^=f

0.01- TTT 1 " "1 I'" 1 " "1

0.1T

0.01 ! I I I M M I I ! I I I I I I I I I I 11 I 11 I I I I I I I 0 10 50 60 time(d)

Figure 48.Mas s of azinphos-methyl in the ditch bottom of A. the siphon-linked ditch B. the sup plementally drained ditch at Benschop, starting

from 3Ma y 1976. = computed mass (fecw =

0,9 fer); = computed mass (kc w =fe r);o = measured mass; S = spraying dates (Chapter9) ; P = pumping period (Chapter 9).Vertica l bars are range estimated from duplicate columns.

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 d toth ehighe razinphos-methy lconcentration s inth 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 100 iy> 200

004-1 depth in bottom im) Figure49 .Mas sconcentration so fazinphos-methy li n thebotto m (mgm -3)o fth esiphon-linke dditc ha t Benschop. =compute dmas sconcentratio n (kc w 0.9fe r);o = averag emeasure d concentrations.Hori : talbar sar erang eo fconcentration smeasure d indupli cate.Vertica lbar sar eaverag ethicknes so fth ebotto m slices.

depth: 0.0005=5'! 0.0016:302 004-' depth in bottom (m) Figure50 .Mas sconcentration so fazinphos-methy lit . thebotto mo fth esupplementall ydraine dditc ha t Benschop. =compute dmas sconcentratio n (fec>w 0.9 kr); o =averag emeasure d concentrations.Hori : talbar sar erang eo fconcentration smeasure d indup|l i cate.Vertica lbar sar eaverag ethicknes so fbotto m slices.

131 waterflow ,a 'plugflow 'situatio nwa ssimulated .Thi sresulte di nsomewha tsmalle rfluxe 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 ,th e fluxint oth ebotto mcompartment sbecam enegativ e (upwardflux )afte ra fe wdays .I nsuc h asituation ,th e 'plug-flowmodel 'wil ltranspor tth epenetrate dpesticid eto ofas tou to f thebotto mcompartments .Wit hplu gflow ,th ecompute dmas so fth ecompound sconverte di n thebotto mwa ssomewha tlowe 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 efo rbot hmode lsituation swer erelativel ysmal l (Table49) .Th emode la sshow ni nAppendi xB wa spresumabl y themos tacceptabl eon ebe causeth elimitatio no fth efluxe sworke donl ya tth ebeginnin go fth ecomputations .

10.5 DESIGNO FTH ESIMULATIO NEXPERIMENT S

Insimulatio nexperiments ,th eeffec twa sstudie do fdrainag ean dinfiltratio no n theamount so fazinphos-methy lan ddimethoat epenetratin gint oth editc hbottom .A sim plifiedditc hsyste mwa sderive dfro mth ebac kditc hi nJaarsveld . Inthes 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 szero .I nth edrainag e (7 >0 )an ddiffusio n (7 =0 ) situations,th ethicknes so fth euppe rbotto mcompartmen twa s0.00 1m an dth emultiplica tionfacto rfo rth edownwar dincreas ei nthicknes so fbotto mcompartment s (m) wa s1.1 . Forth einfiltratio nsituation s (V.,< 0), thethicknes so fth efirs tbotto mcompartmen t was0.00 2m ,an d m, =1.2 .Th ebul kdensitie san dvolum efraction so fliqui dwer etake n forth ebac kditc ha tJaarsvel d (Table36) . Therat ecoefficient sfo rconversio no fth epesticide si nth ewate rcompartmen twer e seta t0. 9 timesth eaverag erate so fdeclin ea smeasure di nfiel dtrial s (Table42) .Th e ratecoefficien tfo rth econversio ni nwate ro fazinphos-methy lwa s0.2 1 d ,tha tfo r dimethoatewa s0.0 8d .Th erat ecoefficient s forconversio no fth ecompound si nth e ditchbotto mwer e0.03 8d and0.0 1 d ,respectively .Th eadsorptio ncoefficien to f 3 -1 azinphos-methylwa s0.07 7m kg (Table 23),tha tfo rdimethoat ewa sassume dt ob e0.00 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 s fordimethoat ea smalle r timeste po f0.00 2d ha dt ob eused .Th emode lsystem swer esimulate d for2 7d .Th ecom putationswer echecke dwit ha Runge-Kutt aintegratio nprocudur ewhic hselect sa 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 fsubstanc ei n water masso fsubstanc ei nbotto m <9> 1.0-i (g)

10-1

Figkire 51.Mas s ofsubstanc e inwate ran d bottom layer computed inth esimulatio n experiments. Numbers refer toth ecomput - runs listed inTabl e 50.A ,azinphos - -methyl;D ,dimethoate ; Run1 ,drainage ; 4 8 12 1e 20 24 28 Ó 4 è 12 16 2D 24 28 Run 3,diffusio n (noflow) ; Run5 ,infil time(d) tration.

tionwithou t water flow (only diffusion, RunsA 3 and D3)wa sslowe r than insituation s with water flow (drainageo rinfiltration) . Durinj drainage,a certain amounto fth ecom - pounds istransporte d outo fth ewate r compartment (RunsA 1an dD1) .Durin g infiltration, a fraction istransporte d into thebotto m layer (Funs A5 andD5) . Ascoul db eexpected , the masso fsubstanc e inth ebotto m layerwa smuc h higher with downward water flow(in - filtration) thanwit h upward water flow (drainage) The declineo fazinphos-methy l inth ewate r compartmentwithou t water flowwa smuc h faster than thatfo rdimethoate . This difference caused primarily byth erelativel y fast conversion rateo fazinphos-methy l inwate r The adsorption coefficient ofazinphos - -methylwa smuc h higher than thatfo rdimethoat e and thus thepenetrate d mass ofazinphos - methyl inth ebotto m layerwa shighe r than that for dimethoate. However,th epenetrate d masso fbot h compounds inth ebotto mha donl ya limited influence onth edeclin e curves inth esituatio n withn owate r flow (Figure 51, A3 and D3).I na drainage situation,th e masso fazinphos-methy l inth ebotto m layerwa s much higher than thatfo rdimethoat e(Fig - ure 51,A 1an dD1) ,du et oit srelativel y high adsarptiion . However,durin g infiltration (A5an dD5) , themaximu m masso fdimethoat e inth e bottom layerwa scompute d tob ehighe r than that forazinphos-methyl . This differencewa s causedb yth erelativel y lowconversio n rateso fdimethoat e inwate r andbotto m material The material balances ofbot h pesticidesi n ttie ditch system aftera computatio n time of 27d ar eshow n inTabl e 50.I ndrainag e situations the effecto fpenetratio n and conversion inth ebotto m layero fbot h compoundso n ttie total material balancewa sver y limited. Considerable amounts ofth esubstanc e were dfLscharged fromth ewate r compartment (Table50) . The infiltration simulation experiments showejl that thebotto m layerma yb ea nim - portant sink forpesticide s inwatercourses . Only Lnth einfiltratio n simulation RunD 5 a considerable fractiono fth einitia l masso f dimsthoatewa scompute d tob e transported outo fth elowes t bottom compartment (atdept ho f 3.35 m).

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134 Penetration depth

Theconcentratio nprofile si nth ebotto mlaye rafte r9 ,1 8an d2 7d fo rSimulatio n Runs1 ,3an d5 ar epresente di nFigur e52 .Whe nvate rflo wwa supwar d (drainage), the 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 r situationswithou twate r flow (diffu sion),th econcentration si nth ebotto mwer econs iierabl yhighe r thani ndrainag esitua - tions.Bu twit hdownwar dwate r flow (infiltration) considerablepenetratio nwa scompute d downt o0. 4m fo rdimethoate .Th epenetratio nfo r izinphos-methyli nth einfiltratio ncorn - putationswa sabou t0.1 5m .Howeve rth esimulatio n experimentswer ewit ha rathe rlo wad sorptioncoefficien t {K ..) ofazinphos-methyl ,a s measuredfo rth editc hi nJaarsveld . Witha highe radsorptio ncoefficient ,a smeasure d::o rth esiphon-linke dditc hi nBenschop , thedifferenc ebetwee nth epenetratio ndepth so falinphos-methy lan ddimethoat ewoul dhav e beenmor epronounced . Thesesimulatio nexperiment s indicateth epossibl econtaminatio no fgroundwate rdur inga ninfiltratio nperiod .I nth einvestigate d ama,period so fdrainag ean dinfiltra tionoccu ralternatel ybu tove rth ewhol eyear ,drainag ei spredominant .Durin ginfiltra tionperiods ,th ebehaviou ro fpesticide si nth editc hbotto man dsubsoi l shouldthu sb e furtherstudied .

mass concentration(m gm " ) L^s 0 50 o- _l L- 1 ,. I • .1, I I t I

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0.04-

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Figure 52.Compute d mass concentrations ofth e sub' stances inth ebotto mmaterial .Number s refer toth e computer runs listed inTabl e 50.A ,azinphos-methy l D, dimethoate;Ru n1 ,drainage ;Ru n3 ,diffusio n (no flow); 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 si nditc hsys tems,th echang ei nditch-wate r levelsan 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 able forestimatio 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 y inperiod swithou tpumping . Ina norma lsituation ,i nwhic hwate rlevel sar ekep twithi nnarro wlimits ,consider ableamount so fsubstanc eca nb edischarge d fromth 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 si nditc hsystems ,on eo rmor eo f theessentia lparameter sar elacking . Inth efiel dsituatio na tBenschop ,th econtributio no fth ebotto mlaye rt 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 n'th edispersio ncoefficient s inth 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 ditlches 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 lconversion .I nflowin gwater ,dispers ; ofth evelocit ydistributio nove rth ecross-sectio no fth ewatersour ei sno tuniform . A shortrevie wo fsom eequation snormall yusee ,fo rdescriptio no fconvectiv e flow anddispersio ni nflowin gwate ri sgive ni nthi sQapter .U pt oabou t1 6empirica lequa tionshav ebee ndevelope d forcomputin gth e longitidinaldispersio ncoefficien t (Bansal, 1971).Howeve ri tremain s difficultt opredic t thedispersio ncoefficien ti nsurfac ewa ter.Th evariou sempirica lequation sgiv evalue stla tdiffe rwidel y fora particula rflo w system.Althoug hman yempirica l dispersioncoefficient sar egive ni nth eliterature ,hard lyan ydat ao nth edispersio no fsubstance si nsmal lwatercourse s canb efound .Fo rthi s reason,a fe wdispersio nexperiment swer e carriedcu t forth esupplementall y drained ditchi nBenscho pan dfo rth e frontditc hi nJaarsveld . Invie wo fth etoxicit yo fth estudie dpesticides ,the ycoul dno tb euse di ndisper sionmeasurements .Therefor etw ofluorescen t dyes, fluorescein-sodiuman dRhodamin e WT, wereuse da stracers .Th ebehaviou ro fbot hcompound swa s investigated duringa pumpin g periodafte rmomentar yplacin ga sa ban dacros sth elas tditc hsectio nbefor eth etw owa terpumps . Questionsi ndispersio nexperiment si nsmal lditche sar ea sfollows .Ho wquickl ywil la substance spread-bydispersion ?Wha tdispersio ncoefficien tapplie si nditche swit h flowing watera tvariou s timesdurin g theyea runde rdiffersn tcondition so fvegetatio ni nth editch ? Willsprea db esymmetrica lo rasymmetrical ?Ho wgrea tar eth edeviation s fromth esymmet ricalpatter nan dho wca nthe yb eexplained ?Wha twil lb eth einfluenc eo fothe rdeclin e processes?Wil l thereb ea considerabl edifferenc e jetweenth espreadin gproces so fcom pounds,tha tar eeithe rstrongl yo rweakl yadsorbe dont oth editc hbottom ? All thesequestion scanno tb esolve dwit honl ya fe wrelativel ysimpl edispersio nex periments.Therefor e thebehaviou ro fth edye si nflowin gwater ,wa sals osimulate di na computationmodel ,whic h includedconvectiv e flow,ilispersion ,adsorptio nan dconversio n of thecompounds .Th eresult so fth ecomputation swor e comparedwit h thoseo fth edy edis persionmeasurement s forth editc hsection si nfron :o fth ewate rpump si nBenscho pan d Jaarsveld.Th edispersio nbehaviou ro fazinphos-metliy lafte ra ninstantaneou s inputwa s simulatedwit h thedevelope d computationmodel .

137 11.2 DERIVATION OF EQUATIONS FOR ONE-DIMENSIONAL CONVECTION AND DISPERSION OF SUBSTANCES IN FLOWING WATER

The one-dimensional dispersion coefficient (n) i sdefine db ydescribin gth e convec tionan ddispersio no fa substanc ei na give nditc hb yth ebasi c differential equationfo r one-dimensional convectionan ddispersion .Th edispersio n coefficient dependso nth eve locity distribution overth ecross-sectio nan dhenc eo nth egeometr yo fth e ditch.Unde r steady flowcondition s andwithou t conversionan dadsorptio no fth ecompound ,th e differ ential equationma yb ewritte na s

= 3 2 32c — (36) dow /U D, I a I "Axw - u / dx w

inwhic h a =mas s concentrationo fsubstanc ei nwate r 3 w (mg nf ) 2 D =longitudina l dispersion coefficient (m u =averag e flowvelocit yo fwate r (m d"') x =downstrea m distance alongditc h axis (m) t =tim e (d)

The dispersion coefficient canb ecalculate d fromexperimenta l datao fdispersio ni n a givenditc husin g Equation36 .Thi s equationca nb esolve dfo rth econditio no fa nin stantaneouspoin t source;th esolutio ni sthe n

a = m/{AÄw,t) exp[-( >- ut)2 / [.AD.t)] (37) w 1 i inwhic h m= initia l injectedmas so fsubstanc e (mg) 2 A= averag ewette d cross-sectional areao fditc h (m)

Multiplying both sideso fEquatio n3 7wit h /Fan dtakin gth e decadic logarithmo f both sideso fth eequatio nyield s

2 lg(ew/t) = lg [ml{A Äw[)} - [O - üt) /(4D1t)] lg e (38)

Ifthi smode lholds ,a straigh t linewil lb eobtaine dwhe nplottin g lg(cw/î)agains t {x - ut) /t; theslop eo fwhic hi sequa lt o[1/(40.) J lge . For symmetrical concentra tionpattern s ('Gaussiandistribution') ,th elongitudina l dispersioncoefficien t (D) can beobtaine d fromth eslope .Fo rasymmetrica l concentration curves,differen t straight lines willb eobtaine dfo rth efron tan dth etai lo fth econcentration—tim e relationship.Thi s resultsi nrathe rdifferen tdispersio n coefficients forth efron tan dth etai lo fth e con centrationcurve . Equation3 8ca nals ob euse dt oestimat e D, inanothe rway .Whe nth emaximu mconcen trationo fth ecompoun dpasse sth esamplin g point x - ut =0an dafte r rearrangingth e termsi nEquatio n 38, D canb ecompute d fromth efollowin gequation :

138 2 2 2 D,1 = m /(Àv Cw.ma x4ir *max )' (39)

inwhic h themaximu mmas sconcentratio na ta amplingpoin t (mgm ") w.max timea twhic h themaximu mmas s conceltration isreache da ta Cd) a samplingpoint .

Thedispersio ncoefficien t (calculatedwit h Equation39 )lie sbetwee nth evalue sob - tained fromth eslope so fth efron tan dth etai l o::th e concentrationcurve .

Relationship between dispersion coefficient and wa L,er depth

Various investigators havetrie dt ofin drel a ;ionshipsfo rpredictin gth elongitudi - naldispersio n coefficienti nnatura l streams. The comparativelysimpl eequation s include terms likeaverag ewate rdept h (\,),shea rvelocit y u^finmd 1)o rth eaverag e flowvelo - cityo fwate r u (inid * ).Example so fsuc h equationsar e

(40) D\'a\ u* (41) and D,1 = k h w û inwhic h aan dk ar e dimensionlessdispersio nconstant ^ (1)

Theshea rvelocit y {uj canb erelate dt oth e average flowvelocit y (u) byth efol - lowingequations :

-1 "»= /TO/P„'= •£* Ä"1/6 * (42) m inwhic h TQ =shea rstres sa tditc hwall s (kgm" 1d" 2) p =densit yo fwate r (kgm" 3) g =acceleratio ndu et ogravit y (md" 2) R =hydrauli c radius (m) X„= Manning scoefficien t forbotto m roughness (m1/3d" 1)

The relationshipbetwee n ut andü i nEquatio n[4 2show s thatEquation s4 0an d4 1ar e analogous. Awid e rangeo fvalue si sreporte d forth edimbnsionles sdispersio n constants. The constant arange dfro m2 t o750 0 (Day, 1975).A syet ,onl ya fe wdispersio nexperiment s inriver si nth eNetherland shav ebee ndescribe d (Tible 51).Fo rthes erivers ,th edimen sionless dispersionconstan t krange d from1. 5t o6 . Ifth e one-dimensional descriptiono fth e convactionan ddispersio nEquatio n3 6 holds,th emaximu mconcentratio no fa substanc e (c )o na downstrea mdistanc e a after

139 Table 51.Result so fdispersio nexperiment sfo rriver si nth e Netherlands. (Afterva nd eBei d& va nStraten ,1976) .

River Average Average Dispersion Dispersion flow water coefficient constant k velocity depth (m2d" 1) (0 (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 dfro mth efollowin gequatio n (43),whic hwa sob tainedafte rrearrangin gEquation s3 9an d41 .

a = m/(2A2Â A Hk h x) (43) w,max ^ w Forsymmetrica ldispersio ncurves ,th emaximu mconcentratio nca neasil yb epredicte d withEquatio n43 ,assumin gtha tth erelationshi pbetwee nth edispersio ncoefficient , waterdept han daverag eflo wvelocit y (asuse di nEquatio n41 )i svalid .

11.3 DISPERSIONMEASUREMENT SWIT HDYE S

Inth editc hsection si nfron to fth ewate rpumps ,fou rdispersio nexperiment swer e carriedou twit hfluorescen ttracers .Thre eexperiment swer ecarrie dou ti nth esupplemen tallydraine dditc ha tBenscho pan d onei nth efron tditc ha tJaarsveld .Thre eexperi mentswer ewit hfluorescein-sodium .I nvie wo fth erapi dconversio no fthi scompoun di n sunlight,Rhodamin eW Twa suse di non eexperiment ;i ti sslowe rdecompose di nsurfac ewa terunde rsunn yconditions .Detail so fth evariou sdispersio nexperiment sar etabulate di n Table52 .Durin gth efirs tthre eexperiments ,i nwhic hfluorescein-sodiu mwa sused ,th e skywa scompletel ycloudy .Th elas texperimen t (withRhodamin eWT )wa si nbrigh tsunn y weather. Mosto fth ewate rsample swer esucke du pwit hth evacuu msample r (Section4.2) .How ever,durin gth ethir ddispersio nexperiment ,wate rwa scontinuousl ypumpe dthroug ha spectrophotometeran dth eresult swer erecorde dsimultaneously . Invie wo fa rathe rlo w maximumpumpin gspeed ,smal lsuctio ntube swer euse dt oreduc eth etravellin gtim et oth e spectrophotometer.A difficult yo fsmal lsuctio ntube swa sth echanc eo fth esuctio nmout h blocking.On eo fth etube ssituate da fe wcentimetre sabov eth esediment—wate rinterfac e becameblocke ddurin gth econtinuou smeasurements . Thesample so fth efirs ttw oexperiment swer emeasure dwit ha spectrophotomete r (Beck- man,Act aCV )a t50 4nm .I nth ethir dexperiment ,wate rwa scontinuousl ypumpe dthroug ha spectrophotometer (Bausch& Lomb ,Spectroni c88 )unde rcomparabl ecircumstances .Th esam pleso fth edispersio nexperimen twit hRhodamin eW Twer emeasure do na fluoromete r(Perki n Elmer,Mode l 204),excitatio na t48 4nm ,analysi sa t51 3nm .Th ewate rsample so fth e firstexperimen twer eals omeasure dwit hth efluorometer .Th eaverag edifferenc ebetwee n 22measurement swit hth efluoromete ran dwit hth espectrophotomete rwa sonl y31 .

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c J2 •H & -O CO 0) h h tl 0 3 3 IV, •H Oenl r-l Tl Ol — e» 1 Ol o — o o 4J CJ I I I I B •eH 00 00 CU 01 CcO I-* r- CJ u a\ er« CsU CO CO CU •H !-a) U T1 a O 3 3 00 co r-l IM •aH •-H n II P.

11 U o M r-t 01 J3 O. 01 X H u

141 Before thestar to fth edispersio n experiments,th edischarg e rateo fth ewate r pumps was measured with the'Purdu e trajectorymethod 'a sdescribe db yBo s (1976). With thismeth od,th ecurv eo fa je to fwate r froma horizonta l discharge pipe isrelate dt oth edis charge rate throughth epip e (analogous toth eprincipl eo fa projectile) . Bymeasurin g the drop inth eje to fwate r 0.15m fromth een do fth epipe ,th ecorrespondin g discharge rateca nb erea d froma nomograp h (Bos, 1976). Themeasure d discharged rateo fth ewate r 3-1 3 1 pump inBenscho pwa sabou t 1705m d andi nJaarsvel d about 1440m d . IXiringth edispersio n experiments,wate r depthswer e measured frequently nearth e injectionpoint ,nea rth esamplin gpoin tan dnea rth ewate r pumpt oasses sth eaverag ewa ter depth duringth eexperiments . Results of dispersion experiments

The concentration—time relationship inth efou r dispersion experimentsar eshow n in Figure 53.Durin g thesecon d experiment,th edifference s betweenth econcentration s meas ured inth emiddl e andnea rth esid eo fth editc hwer e very small.Fo rtha t experiment, the concentrations insample s takenwit h thedifferen t tubeswer e averaged. The curves obtainedi nth eExperiment s 1,3 an d4 wer e asymmetrical.Suc ha tailing phenomenonca nb eexplaine db yzone swit h littleo rn oflo wnea r theside so fth editch . Duringth edispersio n experiments,i twa sobserve d thatpar to fth etrace r became entrapped ina zoneo flo wflo w rates alongth editc h sides.Afte r themai npar to fth edistri butionpassed , therewa sa smal l gradual releaseo ftrace r intoth emai n stream.Th etail ingma yals ob epartl y causedb ya ris ei nbackgroun d level atth een do fth eexperiment .

massconcentratio nI nwate r(m gm ) «!UUO-| (I 1500- I

1000- \ Exp1 Exp3

500- I V 250-1

Exp4 100- Figure 53.Mas s concentrationo fth edye s measured during dispersion experiments inditche s inth e Lopikerwaard Polder. Samples inth efourt h exper iment were takeni nth emiddl e ofth editc han d iQ0 I 5l l near theside .Experiment s 1t o4 a sdefine di n timea ) Table52 .

142 Inth eliterature ,th ezon eo fflo wrate si susuall yreferre dt oa s'dea dzone ' or 'stagnantzone' .Th eproces so ftrappin gan dslovl yreleasin ga trace ri na dead-zon e modelwa sdescribed ,fo rinstance ,b yHaye se tal . byCoat s& Smit h (1964)fo rion-exchang ei nsoil swit ha dispersiv esyste mwit hflui dmov ingthroug hlarg epore san dstagnan tflui di nblin dpores .Howeve rdifficultie si nth e modelo fHaye se tal . (1966)ar eestimatio no fth e fractiono fth edead zon ei nth etota l cross-sectionan dth emas s transfercoefficien tbetwee nth edea dzon ean dth emai nstream . Forthes ereasons ,th erelativel ysimpl edifferentia l equationfo rone-dimensiona lconvec tionan ddispersio n (Equation36 )wa sused . The longitudinaldispersio ncoefficient swer ecalculate db yEquatio n 39.Th e coeffi cientswer e calculated forExperiment s 1t o4 (Tabl e 53). Thedispersio n coefficients (PJ inth esupplementall ydraine dditc hwer e large:• thanthos efo rth efron tditc h(Ex periment 2). Thevariatio ni n D. forth esupplement s-il ydraine d 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,mor etha nSO Io fth ewate rsurfac eva s coveredwit ha duckwee d layer. Ex periment2 wa si na recentl y cleanedditch .Durin gEjpérimen t3 ,th esupplementaril ydraine d ditchwa s ratherclean .Howeve ri nExperimen t4 ,aboi tthre eweek s later,ther ewa sa dens e layero fduckwee di nfron to fa gratin gnea rth ewate rpump .

Theaverag eflo wvelocitie swer eobtaine d fromth eequation : x -"* max" 0 »whic h isvali dwhe nth emaximu mconcentratio ni sreache da tth e samplingpoint .Th eaverag e flow velocitieswer eshow ni nTabl eS3 .Th eaverag edischarg erat eo fth ewate rpum pwa scalcu latedfro mth eaverag ewette dcross-sectiona lare ao fth editc han dth eaverag eflo wvelo city (Table 53). DuringExperimen t4 ,th eaverag edischarg erat ewa sconsiderabl y lower thani nth eExperiment s1 an d3 .Thi swa scause db yti epresenc eo fa duckwee dbarrie ri n fronto fth epump .Durin gExperimen t 4,th ewate r levîlaroun d thepum pwa s temporarily loweredb y0.2 7m afte r8 0mi no fwate rpumping .I nEcperimen t3 ,th ewate r levelnea r thepum pwa s loweredonl y0.1 1m i nth esam epumpin g :ime.Th elowe rwate rleve l during Experiment4 gav eris et oa substantiall y lowerpumpin gcapacit y thani nth eearlie rex periments (Table 53).Th eaverag erat eo fdischarg eo :: thepump sobtaine d fromth edis persionexperiment s (Table53 )wer esomewha t lowerthi 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 f therat eo fdischarge .

Table53 .Longitudina ldispersio ncoefficient s (D\) measuredfo rditche si nth eLopiker - waardPolder .

Experiment Average Average Average Average Dispersion Dispersion water cross- flow rateo i coefficient constant k depth -sectional velocity dischal Re (m2d -') (1) (m) area (or) (md -1) (m3d- 1 ) 1 0.18 0.36 4640 1650 18600 22.3 2 0.21 0.33 4190 1380 5100 5.8 3 0.15 0.30 5640 1660 6280 7.4 4 0.16 0.32 3950 1250 16000 25

143 Thedimensionles sdispersio n constant k (Equation41 )measure d forditche si nth eLo - pikerwaard Polder ranged from5. 9t o25. 3 (Table 53). These constantswer ehighe r thanth e dispersionconstant smeasure d forriver si nth eNetherland s (Tables5 1an d 53).

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 s assumedt ohav eth eshap eo fa trapezium .Th ewet tedperimete ro fth editc h (P)wa scalculate d fromEquatio n22 . -2- 1 The totalarei cmas s fluxo fsubstanc ei nth ewate r (j inm gm d )wa scompose d s,w ofcontribution sb yconvection ,convectiv e dispersionan d diffusion:

J = J + J,. + J,.ç (44) s,w conv,w disp,w dir.w Thearei cmas s fluxb yconvectio n inm gm d )wa sdescribe -2- 1 db yth eaverag e ' (J conv.w ° JO flowvelocit yi nth editc han dth emas s concentrationo fth esubstanc ei nth ewater :

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

J.. =-Ö ,3 c hx (46) disp.w 1 w The areicmas s fluxb ydiffusio ni nwate rwa s calculatedwit h

J,.f =-D, do/3a : (47) dif,w dif.w w

wa s The areicmas s fluxb ydiffusio ni nth e liquidphas eo fth ebotto m {JA-f lh) obtained fromEquation s 15an d16 . Asi nth e earliermodels ,th erat eo fconversio ni nth editchwate r (R )an dtha ti n c,w theditc hbotto m (R )wer e computedwit h first-order relationships (Equations1 7an d 18). C, D The resultingconservatio nequatio nfo r thesubstanc ei nawate rcompartmen twit hvol ume V was: w

3(7 o)/3 t=-3( V J )/Sx - AAJ..t ,,) ,, - V R (48) w v w s,w^' b^dif,11/3= 0 w c,w ^ The conservationequatio nfo rth esubstanc ei nth ebotto mmateria lwa sth esam ea s describedi nEquatio n 20.Th erelationshi pbetwee nth econcentratio ni nth e liquidphas e and thati nth ebotto mmateria lwa s calculatedwit h Equation 21.A si nth epreviou smodels , theadsorptio n equilibriumwa s assumedt oestablis h instantaneouslyan dth eisother mwa s assumedt ob 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 programmedi nth ecompute r language CSMPII I(IBM , 1975).Th elistin go fth ethir dcompu tationmode li sgive ni nAppendi xC . Themas so fdy eo rpesticid e thatarrive di nti ewate ra ttim e zerowa sassume dt o bemixe d throughoutth efirs twate r compartment.Th sapplie dmasse swer eequa lt oth emas ses showni nTabl e 52.Th e concentrationo fsubstan p :ei nth ewate r flowing intoth efirs t water compartmentwa stake nt ob ezero . Thedimension so fth esupplementaril ydraine d litcha tBenscho pan dth efron tditc h atJaarsvel dwer eintroduce d fromTabl e34 .Th eaverag ewate rheight si nbot h ditchsec tionswer e introduced intoth emode la sgive ni nTabl e 52.Th editche swer e divided into ahundre d computationcompartments .Eac hditc hcompartmen t (2m long )wa scompose do fa ditchwateran da singl ebotto mcompartment .Th ethiiJoies so fth ebotto mcompartmen twa s 0.005m .Th editc hbotto mparameter s likebul kdensit yan dvolum e fractiono fliqui dwer e obtained fromFigur e 36.Chec krun swer emad eb yhalvin gth elengt ho fth editc hcompart mentsan dals ob yhalvin gth ethicknes so fth ebotto mcompartments . Whenth econcentration—tim erelationshi pwa sapproximatel y symmetrical (Experiment2) , theaverag evelocit yo fwate r flowcoul db eobtaine dfro mth etim ea twhic hth eto po fth e curvepasse d themeasurin gpositio n x:

•clt (49)

Forth eu obtaine dwit hEquatio n49 ,se eTabl e 53.Fo rth easymmetrica l curvefoun d inth efirs tdispersio nexperiment ,th eflo wve ] y ofwate rwa scalculate d alsoi nan - otherway .Fo rthi scurve ,th e average flowvelocitj y ofwate rwa sapproximate d formth e firstmomen t (M) (whichcorrespond st oth eaverag e residence timei nth editc hwate rcom - partment):

u - x/M (50)

inwhic hth efirs tmomen t M.wa sdefine das :

M,= So t At/fa dt (51) l ow ow

Theaverag e flowvelocit y ufo rth efirs tdispsrsio nexperimen tcalculate dwit h Equation5 0wa sabou t 2970m d .Sinc eth -1e flo wv e Locitiesi nth editc hwer e high relativet ofiltratio nvelocitie si nth editc h bottpm (Figure 43),th elatte rwer e assumedt ob ezer odurin gth edispersio nexperiment ^ The diffusioncoefficien to ffluorescei ni nbuL k watera t1 5° Cwa scalculate dt ob e -4 2- 1 0.35x 1 0 m d, accordingt oprocedure so fRei d & Sherwood (1966).Th eadsorptio n coefficient {K ..,)fo rfluorescei nont oth ebotto m Materialo fth esupplementaril y drained ditchwa smeasure di na slurr yexperimen tt ob eaboi|i t 0.007m 3kg -1.Th e. K „ forth e 3-1 s/1 same traceri nth efron tditc ha tJaarsvel dwa se : xt:-apolateda s0.00 3m kg .

145 Therat ecoefficien tfo rth econversio no ffluorescei ni nth ewate rcompartment s forbot hditche swa sestimate d tob e0.5 5 d (t1 =1. 3d )fro mdat ao fFeuerstei n& Sel - 2 lick (1963).Th erat ecoefficien tfo rth econversio no ffluorescei ni nth editc hbotto m (k ,) wasreporte dt ob ever ylo w (vand eOever ,1972) .Therefor e k , wasse ta tzero . c,b c,b Allcomputation swer ecarrie dou twit hEuler' s integrationmethod .Th ecomputation s werechecke db yhalvin gth etim este pan db yusin gth eCSM PRunge-Kutt a (RKS)integratio n procedure (IBM,1975) . Asi nth emode ldescribe dbefor e (seeAppendi x B),th econvectiv eflu xi nth ewate r compartmentswa scalculate db yaveragin gth econcentratio ni nadjacen tcompartments ,i n ordert ominimiz enumerica ldispersion .Th enumerica ldispersio ndu et otakin gsimpl efi nitedifference si ntim ewit hth erectilinea rintegratio nmetho dwa ssuppresse db yaddin g acorrectio nter mequa lt o(u ) At/2i nth edispersio ncoefficien to fEquatio n4 6(Bell a &Dobbins ,1968) . Thetim este p (At) usedwit hth erectilinea rintegratio nmetho dwa sselecte dfro m thestabilit yconditio n (Bella& Dobbins ,1968) :

At< I 2/(2 n) (52) com 1 inwhic h 1 =th elengt ho fth editc hcompartmen t (m)

Themateria lbalance so fth etracer si nth editc hsyste mwer echecke da tregula rin tervalsdurin gth ecomputations .

11.4.3 Results of simulations for the tracer experiments

Themeasure d andcompute dconcentratio npattern so fth edye swer ecompare donl yfo r DispersionExperiment s 1an d2 .A compute rsimulatio no fDispersio nExperimen t3 wa somit tedi nvie wo fth esever etailin g (Figure53) .Durin gth eDispersio nExperimen t4 ,a grat ingnea rth ewate rpum pbecam eclogge dwit hduckweed ,s oth eexperimen twa scurtaile dan d couldno tb echecke di ndetai lwit hth ecomputatio nmodel . Thedifferenc ebetwee nth ecompute dan dmeasure dconcentratio npatter no ffluorescei n inExperimen t 1wa srathe rlarg e (Figure54) ;fo rExperimen t2 ,th ecorrespondenc ewa s rathergoo d (Figure54) .Th ecomputatio nmode lgav ebes tresult sfo ra rathe rclea nditc h (Experiment 2).Wit ha dens educkwee dcove ro nto po fa ditc h (Experiment 1),th emeasure d tailingwa smuc hlarge rtha npredicte dwit hth ecomputatio nmodel .Th edifferenc ebe tweenth ecompute dan dmeasure dconcentratio npatter ni nth efirs texperimen tcoul db ere ducedb yintroducin ga somewha tlowe rflo wvelocit yi nth editc hsyste m (Figure54) .Thi s reducedvelocit ywa sobtaine d fromth erelationshi pbetwee nth efirs tmomen to fth econ centrationcurv ean dth eaverag eflo wvelocit yo fwate r (Equations5 0an d 51).Mos tprob ably,th etailin gphenomeno ni nditche swit ha duckwee dcove rca nb edescribe dbette rb y dead-zonemodels .Bu ti nvie wo fth echang ei nwate rleve ldurin gth eexperiment san dth e uncertaintiesi nth ereductio no frat eo fdischarg eafte rabou t1 h o fwate rpumping ,th e elaborateproces so ffittin gparameter si nth edead-zon emodel swa somitted .

146 mossconcentratio n in water (mg m ) 2000-1

1000- Exp1

»-, , ^-=* -i 1 r^ 1 r I O05 ai 500

300

Figure54 .Measure d andcompute d concentration patternfc rth eis tan d2 nddispersio nexper imenti nth editche s inth eLopikerwaar dPolder , measuredmas sconcentration s (Figure 53); — computedmas sconcentration s(Appen - dixC) ;- =compute dwit hreduce daverag eflo w velocity.

Thecompute ditem so fth emateria lbalanc efo rfluorescei 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: ;o fdy efro mth editc hwa sth emajo r itemo fth emateria lbalanc e (Table54) . Halvingth elengt ho fth editc hcompartmen tt o 1m 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 yincreased .Th eresult so fcomputation s withEuler' sintegratio nmetho d (RECT)wer enearl yih esam ea sthos eobtaine dwit hth e moresophisticate dRunge-Kutt aintegratio nmetho d (IKS) . Halvingth ethicknes so fth ebotto mcompartmen l resultedtemporaril yi nhighe rcon - centrationsi nth ebottom ,whic hca neasil yb eexpl £: inedb yth esteepe rdiffusio ngradient . Althoughth etota lmas so fth edy ei nth ebotto mcorpartment sincreased ,th eeffec to fthi s

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

Experiment Mass Fractiono fmas ssupplie d (a) supplied —~-~~~~~~~~~~^~~~~~~ (g) in in converted converted discharged water bottom inwate r inbotto m fromditc h

50 0.0 0.3 2.3 0.0 97.4 7.5 0.0 0.3 2.6 0.0 97.1

147 diffusiono nth econcentration s inth editc hwate rremaine dsmall .Fo rtha treaso nn orun s weremad ewit ha nextende dmodel ,includin gsevera lbotto mcompartment spe rditc hcompart ment.

11.4.4 Design of the simulation experiments with pesticides

Underflo wcondition sa sshow ni nTabl e5 3fo rDispersio nExperiment s 1an d2 ,a fe w simulationexperiment swer ecarrie dou twit hazinphos-methy lan ddimethoate .Th ebehaviou r ofbot hpesticide safte ra sudde ninpu t (forexampl edu et oinsufficien tcar edurin gtan k cleaning)int oth etw oditc hsection si nth eLopikerwaar dPolde rwa ssimulated . Thesam ediffusio nan dadsorptio nparameter so fazinphos-methy lan ddimethoat ewer e introduceda sdescribe di nSectio n10.3 .Th erat ecoefficient s forth 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 eimportanc eo fth elongitudina ldispersio ncoefficien to nth emaximu m concentrationo fth epesticide si nwatercourse swa steste db ydoublin gth ecoefficient .

11.4.5 Results of the simulation experiments with pesticides

Thecalculate dconcentration—tim erelationship so fazinphos-methy lan ddimethoat e passingth esam esamplin gpoint sa suse di nDispersio nExperiment s 1an d2 wer enearl yth e samea sth ecalculate dconcentratio npattern so fth etrace r (Figure 54). Inth etw oditc h sectionsa tBenscho pan dJaarsveld ,th edifferenc ebetwee npesticid econcentratio nan dtrac erconcentration ,a tth etim etha tth emaximu mconcentratio npasse dth esamplin gpoints , wasabou tH forbot hpesticides .Th ecalculate dconcentration so fth epesticid ewer e slightlyhighe rtha nth etrace rconcentrations ,whic hwa scause db yth erelativel ysmal l conversionrat eo fth epesticide si nth editc hwater . Thecompute d itemso fth emateria lbalanc eo fazinphos-methy lan ddimethoat efo r bothsimulatio nexperiment sar eshow ni nTabl e55 .Fo rshor tperiod so ftim e (2h )th e influenceo fadsorptio nan dconversio nwa sonl yslight .I nal lsimulatio nexperiment smor e than98° io fmas ssupplie dwa sdischarge d fromth editc hsyste m (200m length).Comparin g theresult so fth eitem so fth emateria lbalanc eo ffluorescei n inbot hdispersio nexperi mentswit hbot hpesticide sonl yshowe drelativel y smalldifference s (Tables5 4an d55) . Somesimulate dconcentration—tim erelationship so fazinphos-methy la tdownstrea m

Table55 .Compute ditem so fmateria lbalanc eo fazinphos-methy l (A) anddimethoat e (D)i nsimulatio nexperiment so nthei rbehaviou ri n ditcheswit h flowingwater ,cumulate d over0.08 3d (2 h).

Experiment Mass Fractiono fmas ssupplie d (%) supplied (g) in in converted converted discharged water bottom inwate r inbotto m fromditc h A 50 0.0 0.3 0.9 0.0 98.7 D 50 0.0 0.3 0.3 0.0 99.3 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 h system s areshow ni nFigur e 55.Th eeffec t ofdoublin gth elongitudina l dispersioncoefficien t isals opresente di nFigur e 55.B y increasingth edispersio ncoefficien tb ya facto r 2,th emaximu m concentrations thatpasse d thesamplin gpoints ,wer econsiderabl y lower,a s vJouldb eexpecte d fromEquatio n43 .Th e maximumconcentration sa tth esamplin gpoint s computedwit hth esimulatio nmode lwer e nearlyth esam ea sth emaximu m concentrations calculatedwit hth esimpl eEquatio n43 .Fo r timeperiod si nwhic hth econversio ni nwate ran d bottommateria lca nb eignored ,th eef - feeto fa sudde ninpu to fazinphos-methy lan d dimethoateint oa ditc hsyste mca nb eesti - mated fromEquatio n43 .Fo rtim eperiod si nwhic h theconversio no fpesticide sma yno tb e ignored inrelatio nt odischarg e ratei nth editc h system,th econcentration—tim e rela- tionshipca nb ebette rpredicte db yusin gth e compütationmodel .

11.5 GENERAL DISCUSSION

Thedispersio nexperimen ti na clea nditc hshbwe d a rathersymmetrica l concentration- -time relationship.Suc hconcentratio npattern s could bepredicte d ratherwel lwit hth e computationmodel .I nditche swit ha cove ro fduckwee d a differentconcentration—tim e relationshipwa sobserved .Th ecurve sshowe da rattie r steep frontan da relativel y long tail.Th ecorrespondenc ebetwee nth ecompute dan d themeasure d concentrationcurve swa s

massconcentratio ni nwate r(mg m ) 3000-

2000

1000-

T I r I | I I 1 I

600- JF JF x:58 x=1>8 400-

200

T-r-C O05 0.05

Figure 55.Simulate d concentration—time rela tionships of azinphos-methyl at different downstream distances( x inm ) in the supplementally drained ditch at Benschop (USD) and the front ditch at Jaarsveld (JF). «computie d with dispersion coefficients (Table 52); • commuted with doubled values of thedispersio n coefficient

149 onlyreasonabl ea tth eto po fth econcentratio ncurves ;a tth efron tan despeciall ya t thetai lo fth ecurves ,ther ewer elarg edeviation sbetwee nth esimulate dan dmeasure d concentrations.Th etailin gca nprobabl ybette rb edescribe dwit hdead-zon emodels . Thewate rflo wwa srelativel y fast.Withi n2 h o fwate rpumping ,nearl yal lsupplie d masso fdy eo rpesticide swa stransporte dou to fth editc hsyste m (200m length). Invie w ofth eshor tresidenc etim ei nbot hditc hsections ,th eothe rprocesse slik econversio n andpenetratio nint oth editc hbotto mwer ecompute d tob eo fmino rimportance . Thephysico-chemica lbehaviou ro fdye s (fluoresceinan dals oo fRhodamin eWT )ca nb e comparedwit hth ephysico-chemica lbehaviou ro fdimethoate .Dy eexperiments ,therefore , canb euse d tosimulat eth ebehaviou ro fcertai npesticides .I nvie wo fth efa reasie r analyticalmethod san dth elowe rtoxicit yo fdyes ,suc ha procedur eha sadvantages .How ever,fo rpesticide swit hlo wsolubilit y inwater ,th econcentratio nove rth ecross-sec tiono fa watercours ema yb edifferent .Fo rthem ,dispersio nexperiment swit hmor eapola r tracersma yb enecessary . Themajo rfacto ri nth emaximu mdownstrea mconcentration safte ra sudde ninpu twa s undoubtlyth edispersio ncoefficient .Fo rman yditc hsystems ,n odat ao nth edispersio n coefficientsar eavailable .Therefor epredictio no fth emaximu mconcentratio ni nditc h systemsremain sdifficult .Mor edispersio nexperiment sar enecessar y invariou sditc hsys temsunde rvariou sconditions .Base do nthes eexperiments ,a classificatio no fdispersiv e behaviourfo rdifferen ttype so fditc hsyste mma yb epossible . Insituation swit hlo wvelocit yi nth editc hwater ,th eadsorptio no fpesticide son toth editc hbotto mca nprobabl yno tb eignored .Fo rsuc hsituation sth edescriptio no f theditc hsyste mwit honl yon ebotto mcompartmen tpe rditc hcompartmen ti sto oroug han d thenumbe ro fditc hbotto mcompartment sshoul dthe nb eincreased . Increasingth enumbe ro f compartments,however ,considerabl y increasecomputatio ntime . Thecomputatio nmode lhold sonl yfo rrathe rsymmetrica lconcentration—tim erelation ships.I ndispersio nexperiment swit hsever etailing ,th edispersio nproces scanno teasi lyb edescribe dwit hth eone-dimensiona lcomputatio nmodel .Mor eexperimenta lan dcomputa tionalresearc hremain st ob edon et opredic tsuc hconcentration—tim erelationships . Iti shope dtha tth ecomputatio nmodel s (Appendixes)ca nb efurthe relaborate dt o makethe msuitabl efo rpredictio no fth ebehaviou ro fpesticide si na naquati cenvironment , givena se to fphysico-chemica l datao na pesticid ean do fhydrologica ldat afo rth efiel d situation.

150 Summary

Theus eo fpesticide s inagricultur e andhorticultur ema y resultunde rspecia lcir cumstances inunintentiona lpollutio no fsurfac ewater .Som esituation s inwhic hsuc hpol lutionca noccu rar edescribe d inChapte r 1.I nth e tento fthes e immissions is impededb y theoccurrerc eo fpesticide s inth eRive rRhin e (Tables 1,2 an d 3). Inth epresen tstudy ,on eo fth esource so fagricultura l pollution wasstudie d inmor edetail ,i.e .spra ydrif tdurin g farming.Th emotivatio n forth edesig no fth epresen t study isdescribe d inChapte r2 . Thestud ywa srestricte d toth ebehaviou ro f twoimportan torganophosphoru s insecti cidesazinphos-methy lan ddimethoat e insurfac ewater .Th egenera l characteristicso fbot h insecticideswit h respectt o theirbehaviou ran deifect si nwatercourse s are giveni nChap ter3 .Bot h compoundshav ea relatively lowsaturate dvapou rpressur e (Tables 5an d 6). The rateo fvolatilizatio n fromsurfac ewate rwa scalculate d tob ever y lowan d tob enegligi blewit h respectt oth econversio ni nsurfac ewate r (Section 3.5).Th esolubilit yo fdime thoate inwate r isconsiderabl e greater thantha to Fazinphos-methyl .A nassociate dprope r ty is theconsiderabl y loweradsorptio ncoefficien to fdimethoat eo nsoi l thano fazinphos - -methyl.Azinphos-methy l israthe r toxic forcrusta:ean s and some fishes (Table 10). Dime thoatei shardl y toxicfo rfis h (Table 11). Ina norientatio nstag eo fth einvestigatio nvariou ssurfac ewater swer e sampled in theKromm eRhin eare aan d inth eLopikerwaar dPold e:(Sectio n9.2) . Forsamplin g ofwate r andditc hbottoms ,specia l techniqueswer edevelope d forth einvestigatio n (Chapter4) . Littledisturbe d sampleso fbotto mmateria l couldb otake nwit ha corin gdevic e (Figures 3 and 4). Afterfreezin g thebotto mmaterial ,sample s wereslice dan danalysed , Theanalytica lprocedure s forazinphos-methy l anddimethoat e insurfac ewate ran d in bottommateria l aredescribe d inChapte r 5.Wate r sampleswer e extractedwit hdichlorome - thane,sometime s followedb y clean-upwit hcolum nchromatography .Th e insecticideswer e measuredwit ha gas—liqui d Chromatographequippe dvdt ha flame-photomete r detector.Th e recoverypercentage swer ehig h (Tables 12an d 13). Oftensevera l columnswit h stationary phaseso fdifferen tpolarit ywer euse d forga schro ilatograph y (Tables 14an d 15). Large amountso f interfering substances inal lextract s oi:botto mmateria lcoul db e removedwit h silicage lcolumns . Somebasi cdat afo rbot h insecticideswer eneece d tostud y theirquantitativ ebehav - ;iou ri nsurfac ewater .Dat ao nrate so fconversio nc fthes ecompound s insurfac ewate r '•wer e still toolimited .Conversio nrate so fazinphos-methy l anddimethoat e insurfac ewate r and inbotto mmateria lwer emeasure dunde rcontrolle d conditions inth elaborator y (Chap ter 6). Therat eo fhydrolysi so fazinphos-methy l strongl y increasedwit hp H (Figure7) . Thisbehaviou rcorresponde dwit hsom edat ai nth e literature.Th econversio no fazinphos - -methyli nsurfac ewate ran dbotto mmateria lcoul db edescribe dwit h afirst-orde r rate

151 equation (Figures8 ,1 2an d 13).Th econversio nplot s fordimethoat e inbot hmedi afollowe d a first-orderconversio npatter nonl y fora limite dtim e (Figures 10,1 1an d 14).Th erat e ofconversio no fdimethoat e increaseddistinctl ywit htim e (Table22) . Copperion swer ecatalyti ci nth econversio no fbot hmode lcompound si nsurfac ewater . Theincreas eo fth econversio nrate sa tincreasin gtemperatur ewa sstudied . Theconversio nrate so fbot hcompound s inanaerobi cbotto mmaterial ,measure di nin cubationtest si nth edark ,wer econsiderabl egreate rtha ni nsurfac ewate r (Tables18 , 20,2 1an d 22).Muc hwor kremain st ob edon eo nth edevelopmen to flaborator ytests ,th e resultso fwhic hca nb euse dfo rpredictio no fth ebehaviou ro fpesticide s insurfac ewa ter. Theconversio nrate so fth eoxyge nanalogu eo fazinphos-methy l (Table7 )i nsurfac e wateran dbotto mmateria lwer egreate rtha nthos eo fazinphos-methy l (Tables 18an d20) . Theadsorptio no fazinphos-methy lan ddimethoat eo ndifferen tbotto mmaterial scoul d bedescribe dreasonabl ywel lwit hlinea radsorptio nisotherm s (Figures 15,1 6an d 17).Th e adsorptioncoefficient so fazinphos-methy lwer eabou t 100time stha to fdimethoate .Th e adsorptioncoefficient so fbot hsubstance scorrelate dclosel ywit hth eorgani cmatte rcon tento fth edifferen tbotto mmaterial s (Table 23).Th eadsorptio ncoefficient so fbot hcom poundso nbotto mmaterial swer emuc hlarge rtha nthos eo nagricultura lsoils . Ina nearl ystag eo fth einvestigation ,i tbecam eclea rtha ttrial si nditche sca nb e complicated.Therefor erelativel ysimpl etrial swer eals ose tu pi noutdoo rtanks .Th e rateso fdeclin eo fbot hmode lcompound si nwate ran dth epenetratio ni na laye ro fbotto m materialwer emeasure d (Chapter 7). Thedeclin eo fbot hcompound si nth ewate rcompartmen t ofth etank scoul db edescribe dreasonabl ywit ha first-orde rrat eequatio n (Figures2 0 and21) . Thedeclin eo fazinphos-methy lan ddimethoat ei nth ewate rcompartmen to fth etank s wasmuc hfaste rtha nth edeclin emeasure di nincubatio ntest swit hsurfac ewate ri ndark ness (Tables 18,2 0an d 26).Alga lbloo mcause dconsiderabl edail yfluctuatio ni np Ho f thewate r (Figure 18).Th eapproximativ evalue sfo rth efirst-orde rrat ecoefficient sfo r thedeclin eo fbot hcompound swer eclosel ydependen to nth emaximu mp H (Figure 22).A sig nificanteffec to fformulatio no fbot hmode lcompound so nrate so fdeclin ei nth ewate r compartmentcoul dno tb eassessed .Th epresenc eo fa botto mlaye ri nth etank swa sno ta dominantfacto ri ndeclin eo fth emode lcompound si nth ewate rcompartment . Laboratorytest si nth edar kha donl ylimite dvalu efo rpredictio no fth erat eo fde clineo fbot hcompound si nsurfac ewater .Ther ei sa nobviou snee dfo rlaborator ytest st o assessth eeffec to fligh to nth erat eo fdeclin eo fpesticide si nsurfac ewate ri na rep resentativeway . Theevaluatio no fth ebehaviou ro fman ypesticide si nsurfac ewate runde rdifferen t conditionsrequire sa nenormou sresearc hcapacity .Sinc eth ephysico-chemica lprocesse s forman ypesticide si sth esame ,computatio nmodel sca nb euse dfo rquantitativ edescrip tiono fbehaviour .Th efirs tcompute rsimulatio nmode l (AppendixA )describe sth ebehavi ouro fpesticide si na tan ksyste mwit ha botto mlaye r (Chapter 8).Movemen to fpesticide s bydiffusio nfro mth ewater—sedimen tinterfac eint oth ebotto mlaye rwa sdescribe d ina one-dimensionalsystem .Adsorptio nequilibri awer eassume dt ob eestablishe dinstantaneous ly.Rate so fdecompositio ni nwate ran dbotto mmateria lwer eintroduce da sfirst-orde r

152 ratecoefficients . Therelativ e significanceo fdifferen tdeclin e processeso fpesticide s insurfac ewa terca nb edescribe d betterb y thedevelope d conçutationmodel .Simulation s ofth etan k trials showed thatconversio no fbot hmode lcompourd swa s themajo r factor inmateria l bal ance (Table 30).Th ecompute dmas so fbot hinsecticide si nth ebotto mlaye rwa s always lesstha n 10$o fth eapplie d dose.Th ecompute dmasse swer ehighe r thanth emeasure d mas ses (Figures 23an d24) . Thecompute d deptho fpenetratio no fdimethoat ewa s larger thantha to fazinphos-me - thyl,mainl ybecaus eo fth erelativel y lowadsorptio no fdimethoate . Insimulatio nexperiments ,th esensitivit ywa s testedo f themode lo fth e tank system tochange s inparameter s (Table 31). Diffusioni nt h ebotto mlaye rwa srelativel yslow . Uncertainties inth ediffusio ncoefficien t through theliqui dphas e inth ebotto mmate rialappeare d tob e less important (Figure 27A).Th 3gradua ladsorptio no fpesticide s onto bottommateria l canb e ofgrea timportanc e inshal la wditches ,especiall ywhe nth econver sionrat e inwate r is low.Penetratio n intoth ebotto mlaye r iso fmino r importance insit uationswit hrelativel yhig hconversio nrate s (half-liveso fsom e days). Measurements ofazinphos-methy l anddimethoat e inwatercourse s and farmditche s inth e Kromme Rhineare aan d inth eLopikerwaar d Polderar ädescribe d inChapte r9 . Ina norien tationstage ,fou rsamplin gpoint s inlarg ewatercoarse san d five infar mditche swer e sampled in 1975 (Figure 30). Interfering substances inth eextract so fwate r fromlarg e watercourses couldb e reducedb y clean-upo nsilic a gelcolumns .N odistinc tevidenc ewa s found fora nincreas e of themode l compounds inth e watero fth e KrommeRhine ,durin g transport through thearea .Relativel yhig hconcentration swer e found inwate ro f farm ditcheso nfrui tfarm s inth eLopikerwaar d Polder. These farmditche swer e selected forfurthe rstud yi n 1976an d 1977.The yalway s con tainedwate r during thegrowin gseaso nan do nbot h farmsther ewa s a supplementarydrain agesystem ,s otha ta wate rbalanc e ofthes editch e; couldb e approximated (Section9.3.3) . Allkind so fcomplication s came to light,suc ha s tiestrongl yheterogeneou s soils,th e complexhydrologica l situationan d thenecessit y totak ei nwate r inth edr yyea r 1976 (Figures 31 to 35). Theditc h systemswer ewel lcharacterize db ymeasurement s toallo w simulation fora mode lsyste m (Tables3 4an d 36). Tiehig horgani cmatte rcontents ,th e lowbul kdensitie s and thecorrespondin g highvolum ;fraction so f liquid inth ebotto mmate rialwer e remarkable (Figure36) . In 1976,afte rapplicatio no fbot hmode lcompound so nth etw o fruit farmsi nth eLo pikerwaard Polder,th econcentration s inth efar md.tche s weremor eclosel y studied (Ta bles 37,3 8an d 39). Thesewer e ratherhigh ,especiall y shortlyafte rapplication . Inter feringsubstance s didno t interfere during 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-order rateequatio n fora pnrio dwithou t intakeo rdischarg e of water (Figures 38an d 39). Thecalculate dhalf-live s ofazinphos-methy l inthes e ditches wereabou t 3t o4 days ,thos e fordimethoat evarie d from4 to 13day s (Table 42). These half-lives agreedwit h thehalf-live smeasure d intiin ktrial s (Table 26).Th epenetratio n ofazinphos-methy l inth ebotto mmateria l ofth ediuche swa s small (Tables4 6an d47) . Introductiono fth e insecticides intoth e farmditche s in 1977wa smeasure d inmor e

153 detailwit hPetr idishe splace do nfloat si nth editche s (Section9.3.8) .Th eexten to f introductiondepende dclosel yo nloca lsituation sa tth efrui tfarm s (windbreaks,distanc e fromfruit-tree st oth ewatercourses ,paths )an dth ewa yo fapplicatio n (Tables4 0an d 41).Th erati obetwee nmas so finsecticid eintroduce dpe runi tsurfac eare ao fwate ran d massdos epe runi tsurfac eare ao forchar dsoi l (=arei cmas srati oo fcontamination )wa s highestb ysprayin gacros sth editc h (0.4),th elowes tratio swer emeasure dfo rditche s protectedb ya windbrea k (0.003). Estimationo fth evariou s itemsi nth ewate rbalanc ei nth editc hwa sno teas y (Fig ures41 ,4 2an d 43).Th eflu xo fwate rthroug hth editc hbotto mwa sderive dfro mth ewa terbalanc ea sa closin gentry .Thi sflu xwa srelativel y lowan dmostl yth edirectio no f theflu xwa s intoth editc h (positive) (Section 10.4).Th edistributio no fth edischarg e rateo fth ewate rpum pove rth evariou sditc hsection scoul db eestimate donl yroughl y (Tables3 4an d 48). Infutur eexperiment si nditc hsystems ,th echang ei nlevel so fditc h wateran dgroun dwate rshoul db erecorde dcontinuousl yt oimprov eth edescriptio no fwa terflow . Acomputatio nmode lfo rth ebehaviou ro fpesticide si na ditc hcompartmen twit hcom pletelymixe dwate ri sdescribe d inChapte r 10.Thi scomputatio nmode l (AppendixB )des cribesfluxe so fwate ran dpesticid ei nth editc hsyste man dals oinclude sfluxe sthroug h theboundar ysurface so fth ewate rcompartmen tan do fth ebotto mcompartments .Th eintro ducedrat ecoefficien tfo rconversio ni nth editc hcompartmen twa sse ta t0. 9 timesth e measuredrat ecoefficien tfo rth edeclin e (Table 42).Thi sresulte di na reasonabl eagree mentbetwee nth emeasure dan dcalculate dconcentration—tim erelationship s inth ewate r (Figures4 4t o47) .Fo rth esiphon-linke dditc hi nBenschop ,th econversio no fth emode l compoundsi nth editc hwate rcompartmen twa sth emai ndeclin eprocess .I na perio do f5 9d with lowwate rdischarge ,6 9t o 88%o fth eintroduce dmode lcompound swa scalculate dt o beconverte d inth ewate r (Table 49). Forth esupplementaril ydraine dditc hi nBenscho p (lastditc hsectio nbefor eth epump) ,calculation ssuggeste d thatdischarg efro mth ewa tercompartmen t inth esam eperio dmigh tb esevera ltenth so fth eintroduce damoun t(Ta ble 49).Th ecompute d totalmasse so fazinphos-methy li nth editc hbottom swer elarge r thanth emeasure dmasses ,jus ta sfo rsimulatio no fth etank s (Figure48) . Insimulatio nexperiments ,th eeffec to fpenetratio nint oth ebotto mwa sver ylimite d inditche swit ha flo wo fwate rfro mgroundwate r (drainagesituation )(Figure s5 1an d52) . Withinfiltratio nfro mth editch ,th editc hbotto mca nb econsidere d asa nimportan t'sink ' (Table 50).Mor eresearc ho nth edispersio nbehaviou ri nbotto mmateria li ninfiltratio n situationsi sneede dt oallo waccurat edescriptio no fconcentratio nprofiles .Th epene trationdept hwit hth epresen tcomputatio nmode li ndrainag esituation si ssomewha tover - -estimated.A technicalproble mi nth emodel ,artificia l 'backward'dispersion ,canno tye t beremove dcompletely . Measurementan dcomputatio no nth ebehaviou ro fsubstance si nditche sdurin gwate r flow (forexampl eb ywate rpumping )ar edescribe d inChapte r 11.Althoug hman yempirica l dispersionequation sar edescribe di nth eliterature ,dat ao nth edispersiv ebehaviou ro f substancesi nsmal lwatercourse sar escarc e (Table 51).A fewdispersio nexperiment swer e carriedou twit hdye si nditche so nbot hfrui tfarm si nth eLopikerwaar d (Table 52).A relatively lowdispersio ncoefficien twa smeasure d ina dispersio nexperimen ti na recent -

154 lycleane d ditch.Th edispersio n coefficient ina ditchsituatio nwit ha layero fduck - weedwa s four timesa s large (Table 53). Insuc ha situation,ther ewa sa strong tailing inth econcentration—tim e relationship atth es ; amblingpoint s (Figure 53). The dispersion constants (Equation41 )fo rthes esmal lwatercourse s were larger thanthos e forstream san d rivers inth eNetherland s (Tables5 1 and53) . A computationmode lwa sbuil t todescrib e the behaviouro fsubstance s inditche sdur - ingwate r flow (Appendix C). Themode l included mary processes like convective flow,dis - persion,diffusion ,adsorptio nan d conversion of tie substances.Goo dagreemen tbetwee n measurements andcomputation swa s onlyobtaine dfo i thecondition s ina clea nwatercours e (Figure 54). Thetailin gphenomeno n inconcentratio n timerelationship s canprobabl ybet - terb edescribe dwit hstagnant-phas emodels , Simulatio n experimentswit hbot hdye san d k model compounds inditche swit ha highe rflo w velocit y showed thatconversio nan dpenetra - tionint o theditc hbotto mar enegligibl e inth e short period (Tables5 4an d 55). Spread- ingb ydispersio nwa sb y farth emos t important process insuc h fieldsituation s (Figure 55). Forsituation swit h lowflo wvelocitie s inth e ditcho rfo rditche swit hperiod so f , nowate rflow ,a mode lma yperhap sb ecompile db y combinationo fth esecon dmode l (Appen- dixB )an d the thirdmode l (Appendix C). The preserc e ofvariou sprocesse swit h fardif - ferent rateshoweve rgive scomplication s inth e require d computationtime , Thecomputatio nmodel swer euse d firsto fal l asresearc htool st otrac ean ddefin e areaso fto o limitedknowledge .Th e resultso fmodej l computations andcompariso nwit hrefe- suitso fmeasurement sprovid e goodstartin gpoint s forfutur e investigations.Afte r further elaboration,th ecomputatio nmodel s couldperhap s be used inpredictin g thebehaviou ro fpes - ticides inth eaquati cenvironment ,startin g froma limitedse to fphysico-chemica l data ona pesticid e ando fth ehydrologica ldat a from thî fieldsituation .

155 Samenvatting

Hetgebrui kva nbestrijdingsmiddele n inland -e ntuinbou wka nonde rbepaald eomstan dighedenee nniet-gewenst everontreinigin gva nhe toppervlaktewate ropleveren .Ee naanta l situatieswaari nzulk everontreiniginge nkunne noptreden ,worde nbeschreve ni nhoofdstu k 1.He tvaststelle nva nd egroott eva ndez everontreinigin gword ti nNederlan dnoga lbe moeilijktdoo rd eaanwezighei dva nbestrijdingsmiddele n ind eRij n (Tabellen1 ,2 e n3) . Indez estudi ei séé nva nd eagrarisch eemissiebronne nmee ri ndetai lbestudeerd ,n.1 .he t overwaaienva nspuitvloeisto ftijden stoepassin gva nbestrijdingsmiddele n ind efruitteelt . Demotivati eva nd eopze tva ndi tonderzoe ki sbeschreve ni nhoofdstu k2 . Hetonderzoe kbepaal tzic hto the tgedra gva ntwe ebelangrijk eorgano-fosfo rinsekti - ciden (azinfos-methyle ndimethoaat )i noppervlaktewater .Ee nalgemen ekarakteriserin gva n beideinsekticide nme the too go phu ngedra ge neffekte ni nwaterlope ni sgegeve ni nhoofd stuk3 .Beid estoffe nbezitte nee ntamelij klag everzadigd edampdru k (Tabellen5 e n 6).Be rekeningenove rd esnelhei dva nvervluchtigin gva ndez everbindinge nvanui toppervlaktewa terleverde nzee rlag ewaarde nop ,zoda tdi tproce sverwaarloosbaa r lijktt.o.v .d eomzet tingi noppervlaktewate r (Sectie3.5) .D eoplosbaarhei dva ndimethoaa ti nwate ri saanzien lijkgrote rda n"di eva 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 ltoxisc hvoo rcrustaceeë ne nsommig evissoorte n (Tabel 10).Dimethoaa t isrelatie fweini gtoxisc hvoo rvi s (Tabel 11). Inee noriënterend e faseva nhe tonderzoe kwerde nverschillend eoppervlaktewatere n inhe tKromm eRij ngebie de ni nd eLopikerwaar dbemonster d (Sectie9.2) .Bemonsterin gva n watere nslootbodemmateriaa lvereist especial etechnieke ndi evoo rdi tonderzoe kverde r werdenontwikkel d (Hoofdstuk 4).Wéinig-verstoord eslibmonster swerde ngestoke nme tee n kolomsteekapparaat (Figuren3 e n 4). Deslibmonster swerde nn ainvrieze nlaagsgewij sop gedeeld engeanalyseerd . Dewerkwijze nbi jd echemisch eanalys eva nazinfos-methy le ndimethoaa ti noppervlak tewatere nslootbodemmateriaa l zijnbeschreve ni nhoofdstu k5 .D ewatermonster swerde nge ëxtraheerdme tdichloromethaan ,som sgevolg ddoo ree nzuiverin gd.m.v .kolomchromatografie . Deconcentratie sva nd einsekticide nwerde nbepaal dme tee ngaschromatograaf ,uitgerus t metee nvlamfotometerdetektor .D e 'recovery'-percentagesware nhoo g (Tabellen1 2e n13) . Debeid emodelstoffe nwerde nvaa kgescheide no pverscheiden egaschromatografisch ekolomme n metstationair efase nva nverschillend epolaritei t (Tabellen1 4e n 15).Grot ehoeveelhede n storendestoffe ni nall ebodemmateriaalextracte nkonde nworde nverwijder dme tbehul pva n silicagelkolommen . Voord ekwantitatiev ebeschrijvin gva nhe tgedra gva nbeid einsekticide ni nopper vlaktewaterwa see naanta lbasisgegeven snodig .D egegeven sove rd eomzettingssnelhede n vandez everbindinge ni noppervlaktewate rware nno gt ebeperkt .Omzettingssnelhede nva n

156 azinfos-methyl endimethoaa t inoppervlaktewate re n inslootbodeimiateriaa lwerde no.a . bepaald inhe t laboratoriumonde rbeheerst eom s tandjigheden (Hoofdstuk 6). Dehydrolyse - snelheidva nazinfos-methy lna mster k toeme t toene«end e pH (Figuur 7). Ditgedra gwa s in overeenstemmingme tenkel e literatuurgegevens.D e ajfbraakva nazinfos-methy l inoppervlak tewatere nbodemmateriaa l konbeschreve nworde nme t eeneerste-ord e snelheidsvergelijking (Figuren8 , 12e n 13). De afbraakcurves voor dimethbaati nbeid emedi avolgde nvoo ree n beperkte tijdee neerste-ord e afbraakpatroon (Figurai 10,1 1e n 14). De afbraaksnelheid vandimethoaa tna mduidelij k toeme td e tijd (Tabel 22). Koperionenbleke nster kkatalytisc ht ewerke n ypd eomzettin gva nbeid emodelstoffe n inoppervlaktewater .Nagegaa nwer d hoeveeld e omzettingssnellhede nva nbeid estoffe ntoene - menbi jstijgin gva nd etemperatuur . Deomzettingssnelhede nva nbeid e stoffen in anaëroob slootbodemmateriaal,bepaal d in incubatieproeven inhe tdonker ,ware naanzienlij k groterda ndi ei noppervlaktewate r (Ta- bellen 18,20 ,2 1e n 22). Aanhe tontwikkele nva n 1iboratoriumexperimentenwaarva nd ere - sultatenkunne nworde ngebruik tvoo rd evoorspellin g vanhe tgedra gva nbestrijdingsmid - delen inoppervlaktewate rmoe tno gvee lwer kworde n gedaan. Deomzettingssnelhede nva nhe t zuurstofanaloog vanazinfos-methy l (Tabel7 )i nopper - vlaktewatere nslootbodemmateriaa lware ngrote rda n dieva nazinfos-methy l (Tabellen 18e n 20). De adsorptieva n azinfos-methyle ndimethoaa t ianverschillend ebodemmateriale nko n redelijkbeschreve nworde nme t lineaireadsorpti e isothermen (Figuren 15,1 6e n 17). De adsorptiecoëfficiëntenva nazinfos-methy lware n ong3vee r 100maa ld ecoëfficiënte ngemete n voordimethoaat .D eadsorptiecoëfficiënte n vanbeidj s stoffencorrespondeerde n goedme the t organischestofgehalt eva nd everschillend e bodemmateriale n (Tabel 23). De coëfficiënten vooradsorpti eaa nslootbodemmateriale nware nvee l logerda nd e coëfficiëntenvoo radsorp - tieva ndezelfd everbindinge naa nlandbouwgronden . Inee nvroe gstadiu mva nhe tonderzoe kwer d hetduidelij kda texperimente n inslote n zeergecompliceer d kunnen zijn.Daaro mwerde noo k rîlatiefeenvoudig eexperimente nuitge - voerdme tbassin s ind eope nlucht .D eafnamesnelhejle n vand emodelstoffe ni nwate re nd e penetratie inee n laagbodemmateriaa lwerde ngemete i (Hoofdstuk 7). Deafnam eva nbeid e stoffen inhe twatercompartimen tva nd ebassin sko n redelijkgoe dbeschreve nworde nme t eeneerste-ord e snelheidsvergelijking (Figuren2 0 i 21). Deafnam eva nazinfos-methy l endimethoaa t in ietwatercompartimen tva nd ebassin s wasvee l snellerda nd eafnam egemete nbi j incubati^ inoppervlaktewate r inhe tdonke r (Tabellen 18,2 0e n 26). Tengevolgeva nalgenbloe i :rade ree naanzienlijk e dagelijkse schommelingo p ind ep Hva nhe twate r (Figuur 18). )ebenaderend ewaarde nvoo rd eeerste - -ordesnelheidscoëfficiënte nvoo rd eafnam eva nbeiii e stoffenblee kster kafhankelij kva n demaximu mp H (Figuur 22). Eenduidelij keffec tva n verschillende formuleringenva nbeid e modelstoffeno pd eafnamesnelhei d inhe t watercompartimentko nnie tworde nvastgesteld .D e aanwezigheidva nee nbodemlaa g ind ebassin swa s geai dominerende faktorbi jd eafnam eva n demodelstoffe n inhe twatercompartiment . Laboratoriumexperimentenuitgevoer d inhe tdonke r hebbenslecht see nbeperkt ewaard e voorhe tvoorspelle nva nd eafnamesnelhei dva nbei ds stoffeni noppervlaktewater .E ri s duidelijkbehoeft eaa nlaboratoriumnethodieke nwaarjie e oprepresentatiev ewijz ehe teffek t

157 vanlich to pd eafnamesnelhei dva nbestrijdingsmiddele ni noppervlaktewate rka nworde n vastgesteld. Deevaluati eva nhe tgedra gva nvel ebestrijdingsmiddele nonde rverschillend eomstan dighedeni noppervlaktewate rvereis tee nenorm eonderzoekscapaciteit .Aangezie nd eaar d vand efysich-chemisch eprocesse nvoo rvee lverbindinge ndezelfd ei skunne nrekenmodelle n goedbenu tworde nvoo rd ekwantitatiev ebeschrijvin gva nhe tgedra gva ndez emiddelen .He t eerstecomputersimulatiemode l (AppendixA )beschrijf the tgedra gva nbestrijdingsmiddele n inee nwaterbassinsystee mme tee nbodemlaa g (Hoofdstuk 8). Bewegingva nbestrijdingsmid delent.g.v .diffusi evana fhe twater-sedimen tgrensvla ki nd ebodemlaa gwer dbeschreve n inee néén-dimensionaa l systeem.Adsorptie-evenwichte nwerde nveronderstel d zichonmiddel lijki nt estellen .D eafbraaksnelhede n inwate re nbodemmateriaa lwerde ningevoer dal s eerste-ordereactiecoëfficiënten . Hetrelatiev ebelan gva nverschillend eafnameprocesse nva nbestrijdingsmiddele ni n oppervlaktewaterka nme tbehul pva nhe tontwikkeld erekenmode lbete rgekwantificeer dwor den.Ui td emateriaalbalan sva nbeid emodelstoffe ni nsimulatie sva nd ebassinexperimente n bleekda tomzettin gva nd estoffe ni nwate rd ebelangrijkst e faktorwa s (Tabel 30).D ebe rekendemass ava nd ebeid einsekticide ni nd ebodemlaa gwa sbijn aaltij dlage rda n10 1va n detoegepast edosering .Dez eberekend emassa' sware nhoge rda nd egemete nhoeveelhede n(Fi guren2 3e n24) . Deberekend epenetratiediept eva ndimethoaa twa sgrote rda ndi eva nazinfos-methyl . Dehoofdoorzaa kvoo rdi tverschi li sd erelatie flag eadsorpti eva ndimethoaat . Simulatie-experimentenwerde nuitgevoer do md egevoelighei dva nhe tmode lva nhe t bassinsysteemvoo rveranderinge ni nparameter st eteste n (Tabel 31). Diffusiei nd ebodem laagblee kee nrelatie flangzaa mproce st ezijn .Onzekerhede ni nd ecoëfficiën tvoo rdif fusieva nd estoffe ndoo rd ewaterfas ei nhe tbodemmateriaa lbleke nminde rbelangrij kt e zijn(Figuu r27A) . Inslote nme trelatie fgering ewaterdiept eka nd egeleidelijk eadsorp tieva nbestrijdingsmiddele n aanbodemmateriaa lva ngroo tbelan g zijn,voora lal sd eaf braaksnelheid inwate rgerin gis .I nsituatie sme tee nrelatie fhog eafbraaksnelhei d (hal veringstijdva nenkel edagen )i spenetrati ei nd ebodemlaa gva nondergeschik tbelang . Demetinge nva nazinfos-methy le ndimethoaa ti nwaterlope ne nbedrijfsslote ni nhe t KrommeRij ngebie de ni nd eLopikerwaar dzij nbeschreve ni nhoofdstu k9 . Inee noriënte rendefas eva nhe tonderzoe k in197 5werde nvie rbemonsteringspunte ni ngroter ewaterlope n envij fbedrijfsslote nbemonster d (Figuur30) .D einterferenti edoo rstorend everbindinge n inextracte nva nwate rui tgroter ewaterlope nko nme tbehul pva nsilicagelkolomme naanzien lijkverminder dworde n (Tabellen3 2e n 33). Erwerde ngee nduidelij kindikatie sgevonde n vooree ntoenam eva nd emodelstoffe ni nhe twate rtijden sdoorstromin gva nhe tKromm eRij n gebied.Relatie fhog econcentratie swerde naangetroffe ni nwate rva nbedrijfsslote no p fruitteeltbedrijven ind eLopikerwaard . Dezebedrijfsslote nwerde nuitgekoze nvoo rverder eonderzoekinge ni n197 6e n1977 . Dezeslote nbevatte nsteed swate rtijden she tgroeiseizoe ne no pbeid ebedrijve nwa see n onderbemalingaanwezig ,zoda tee nwaterbalan sva ndez eslote nko nworde ngescha t (Sectie 9.3.3).Tijden sd eduu rva nhe tonderzoe kkwame nallerle i complicatiesaa nhe tlicht ,zo alsd esterk eheterogenitei tva nd egronden ,d ecomplex ehydrologisch esituatie se nd enood zaakto the tinlate nva nwate ri nhe trelatie fdrog ejaa r 1976 (Figuren3 1t/ m 35).D e

158 slootsystemenwerde ngoe dgekarakteriseer d doormetinge no msimulatieberekeninge n vooree n modelsysteemmogelij k temake n (Tabellen3 4e n 36). Opvallendware nd ehog eorganisch e j stofgehaltes,d e lagevolumiek emassa' s end ehienre eovereenkomend e hogevolumefracties ! bodemvochti nhe tslootbodemmateriaa l (Figuur36) . In 1976werden ,n ad etoepassin gva nbeid emodslstoffe no pd e tweefruitteeltbedrij - ven ind eLopikerwaard ,d econcentratie s ind ebedrijfsslote nnauwkeuri gbepaal d (Tabellen 37, 38e n 39). Dezeware n tamelijkhoog ,voora lkor tn a detoepassing .E rwer d geen last ondervondenva nstorend estoffe nbi j degaschromatografisch eanalyses .D eafnam eva nbei demodelstoffe ni nd ebedrijfsslote no phe tfruittesltbedrij fi nBenscho pko n (vooree n periode zonderwaterinlaa te nwaterafvoer )redelij kbeschreve nworde nme tee neerste-ord e snelheidsvergelijking (Figuren3 8e n 39). Deberekeid ehalfwaardetijde nva n azinfos-methyl indez eslote nware nongevee r3 tot4 dagen ,di eva idimethoaa tvarieerde nva n4 tot 13 dagen (Tabel 42). Dezehalfwaardetijde n stemdenoveree nme td ehalfwaardetijde n gemeten in L bassinexperimenten (Tabel 26).D epenetrati eva na zLnfos-methy li nd eslootbodem sbleej c J^*t* relatiefgerin g te zijn (Tabellen4 6e n47) . De immissieva nd e insekticidennaa rd ebedri jrsslote nwer d in 1977meèg :i ndetai l gemetenme tbehul pva nPetrischale n geplaatst opdr.jver s ind e sloten (Sectie 9.3.8).D e mateva n immissieblee k sterkafhankelij kva nloka l; situatieso pd e fruitteeltbedrijven (windsingels,afstan dva nd evruchtbome n totd ewaterlopen ,schouwpaden )e nd ewijz eva n toepassing (Tabellen4 0e n 41). Deverhoudin g tusse:id ehoeveelhei d insekticidedi ete rechtkwa mpe roppervlakte-eenhei d watere nd edoserin gpe roppervlakte-eenhei d boomgaard- grond (=immissieverhouding)wa she thoogs tbi j zgn.ove rd e slootspuite n (0.4),d e laagste immissieverhoudingenwerde ngemete nvoo rslote nach:e rwindsingel s (0.003). Het schattenva nd everschillend eposte n ind ewaterbalan s vand esloo twa snie teen voudig (Figuren41 ,4 2e n 43). Dewaterflu xdoo rd eslootbodem ,al ssluitpos t afgeleidui t dewaterbalans ,wa s relatieflaa g (Sectie 10.4)e nva smeesta lnaa rd esloo tgerich t (po sitief). D everdelin gva nd eafvoersnelhei d vand ei om pove rd everschillend e slootsecties konslecht s globaal geschatworde n (Tabellen3 4e n <•8) . Inverder e experimenten insloot - systemen zoudend everanderinge n insloot -e ngrondwaterpeile ncontin ugeregistreer d moe tenworde no md ekarakteriserin g vand ewaterstromir g teverbeteren . Eenrekenmode lvoo rhe tgedra gva nbestrijdingsmiddele ni nee nslootcompartimen tme t vollediggemeng dwate rword tbeschreve n inhoofdstu l 10.Di trekenmode l (AppendixB )be schrijftnaas td e relevantewater -e npesticidefluxe ni nhe tslootsystee moo kd e fluxe n doord egrensvlakke nva nhe twatercompartimen t envs nd ebodemcompartimenten .D e ingevoer desnelheidscoëfficiën t voorafbraa k inhe tslootwatercompartimen twer dgelij kgestel d aan 0.9 keerd e snelheidscoëfficiënt voord egemete nafnam e (Tabel 42). Dit leverdeee nrede lijkeovereenstemmin g op tussend egemete ne nd ebeiekend econcentratie-tij d relaties in hetwate r (Figuren4 4 t/m 47).Voo rd e 'duiker'sloo t inBenscho pwa s omzettingva nd emo delstoffen inhe tslootwatercompartimen t hetbelangrijkst eafnameproces . Inee n 59-daagse periodeme tgering ewaterafvoe rwer dbereken d dat6 9 tot88 1va nd egeïntroduceerd emodel - stoffenwer domgeze t inhe twate r (Tabel 49). Voord ? 'onderbemalen'sloo ti nBenscho p (laat ste leidingvakvoo rd epomp )wer d indez eperiod ebereken d datafvoe rvanui the tslootwa tercompartiment enkele tientallenprocente nva nd eg^introduceerd ehoeveelhei d kanbedra gen (Tabel 49). Evenals ind ebassinsimulatie-experiiiente nware nd e totalemassa' sva na -

159 zinfos-methyli nd eslootbodem sgrote rda nd egemete nwaarde n (Figuur48) . Uitsimulatie-experimente nblee kda ti nslote nme tee nafvoe rva nwate rvanui tgrond water (drainagesituatie)he teffek tva npenetrati ei nd ebode mzee rbeperk twa s (Figuren 51e n 52). Insituatie sme tinfiltrati evanui td esloo tko nd eslootbode mal see nbelang rijke 'sink'worde nbeschouw d (Tabel 50).Voo ree nnauwkeurig ebeschrijvin gva nd econcen tratiepatronenme td ediept ei ninfiltratiesituatie s ismee ronderzoe knodi gove rhe tdis persiegedrag inslootbodemmateriaal .I ndrainagesituatie sword td epenetratiediept eme t hethuidig erekenmode l (AppendixB )iet soverschat .Ee nmodeltechnisc hproblee mbetreffen dekunstmatig e 'achterwaartse'dispersi eka nno gnie tgehee lworde nopgelost . Metingene nberekeninge nove rhe tgedra gva nstoffe ni nslote ntijden swaterstromin g (bijv.tengevolg eva npompen )staa nbeschreve ni nhoofdstu k 11.Hoewe le ri nd eliteratuu r veleempririsch edispersieformule sstaa nbeschreve nware ne rbijn agee ngegeven sove rhe t dispersiegedragva nstoffe ni nkleiner ewaterlope n (Tabel 51).Enkel edispersie-experimen tenwerde nuitgevoer dme tkleurstoffe ni nslote no pd ebeid efruitteeltbedrijve ni nd eLo - pikerwaard (Tabel 52). Inee nexperimen ti nee npa s 'opgeschoonde'waterloo pwer dee nre latieflag edispersiecoëfficiën tgevonden .I nee nsituati eme tee nkroosde kwa sd edisper siecoëfficiëntee nfakto rvie rgrote r (Tabel 53). Inzo' nsituati etra de ree nflink e staartvormingo pi nd econcentratie-tij d relatieo pd emeetpunte n (Figuur 53).D edisper sieconstanten (Vergelijking41 )voo rdez eklein ewaterlope nware ngrote rda ndi evoo rbeke n enriviere ni nNederlan d (Tabellen5 1e n53) . Erwer dee nrekenmode lontwikkel do mhe tgedra gva nstoffe ni nslote ntijden swater stromingt ebeschrijve n (Appendix C). Hetmode lomvatt evel eprocesse n zoalsconvectiev e stroming,dispersie ,diffusie ,adsorpti ee nomzettin gva nd estoffen .E rwa sallee nee n goedeovereenstemmin gme tmeetresultaten ,di everkrege nware ni nee nschon ewaterloo p(Fi guur 54). Hetverschijnse lva nstaartvormin gi nconcentratie-tij drelatie ska nwaarschijn lijkbete rbeschreve nworde nme tzgn .'stagnant efase 'modellen .Ui tsimulatie-experimen tenme td ebeid ekleur -e nmodelstoffe ni nslote nme tee nrelatie fgrot estroomsnelhei d bleekda td eomzettin ge npenetrati ei nd eslootbode mverwaarloosbaa r zijni nd ebetref fendekort eperiod e (Tabellen5 4e n 55).Afvlakkin gva nd econcentratieverdelin gdoo rdis persiewa sverrewe ghe tbelangrijkst eproce s indez esituatie s (Figuur55) . Insituatie sme tlag estroomsnelhede ni nhe tslootwate ro fvoo rslote nme tperiode s vanwaterstilstan dka ne rwellich tee nmode lsamengestel dworde ndoo rcombinati eva nhe t tweederekenmode l (AppendixB )e nhe tderd erekenmode l (Appendix C). Hetvóórkome nva ndi verseprocesse nme tster kverschillend esnelhede nlever techte renig ecomplicatie ste n aanzienva nd ebenodigd erekentijd . Derekenmodelle nwerde nallereers tgebruik tal shulpmidde lbi jhe tonderzoek ,waar doorgebiede nme tt eweini gkenni sduidelijke rkonde nworde nopgespoord .D eresultate nva n modelberekeningene nd evergelijkin gme tmeetresultate nverschaffe ngoed estartpunte nvoo r verderonderzoek .N averder etoetsin gkunne nd erekenmodelle nwellich tworde ningeze tvoo r hetdoe nva nvoorspellinge nomtren the tgedra gva nbestrijdingsmiddele n inoppervlaktewa ter,uitgaand eva nee nbeperk taanta lfysisch-chemisch egegeven sove ree nbestrijdingsmid dele ngegeven sove rd ehydrologisch esituati ei nhe tveld .

160 Appendices

Appendix A

TITLEBEHAVI0U R 2FAZIHPH0S-METHY L IMTAN K 2 (DIFFUSI0N M0DEL1) fr************************************************************** » TANK WITH MIXED WATER C0MPARTMSMT AND C0$1PARTIMENTALIZATI0N 0F B0TT0M LAYER STeRAGEDPeRL(10)/KSL(10)/CAPL(10)/CABeTB(| l IO)/DEB0SU(11) ST0RAGE TB0T(1 0>/D IFD(10)/DE30C0(10)/BD(1 0I >/VFL(lO)/T0R?(lO> ST0RAGECLB(10)/FLRS3(11)/RDEC3(10)/CM(10 ) FIXED KBC0M/J/NBC0MP IKITIAL N0S0RT * A3BREVIATI0NS :C0MP.=C0MPARTMEMT(S ) * BASIC UtJITS sMILLIGRA M (MG)# METE R (II) DAY (D) *»* DEFINITIONTAN K SYSTEM GE0METRY *VWTT=V0LUME0 FVATE R C0MP. (M3)A SF(TIKE & FUHCTie»VWTT=(0./0.154)/(3.64/0.148)/(5.6(1/0-142)/(9.64/0.133)/ . (13.64/0.ISO)/(30./0.ISO) *305U=SU?.FAC EARE A eFTH EBeTT0 M C0MP.(Mfc ) PARAMB0SU=O. 6 * TB0T=THICKNESS 0FB0TT0 M C0MP. (M) * N3CeM=NUMBER 0F30TT0 MC0MP . *MFAC=MULTIPLICATI0 NFACT0 R FeRT30T/WFAC ' "WEIGHT FACT0R F0RTB0 T PARAM NBC0M=10/MFA C=1. 5 WFAC=1.0<'(MFAC+ 1.0 ) PARAM TB0T1=O.OO1 TB0T(1)=TB0T1 D0 10 J=2/NBC0M 10 TB0T(J)=UFAC*T30T(J-1) NBC0MP=HBC0M+1 *DEB0C0=DEPT H 0FCENTRE S eFTH E3eTT0 M CefcP.(M ) *DIFD=DIFFUSI0 NDISTANC EBETWEE N BCTT0HC l IIMP . (H) * DE30SU=DEPTH 0FUPPE R SURFACES 0FB0TT0 M C0MP. (M) DE30C0(1)=0.5*T3eT(1) DIFD(1)=O.5*TB0T(1) DEB0SU(1)=O.O D0 11 J*2/N3C0M DIFD(J)=O.5*(TB0T(J-1)+T30T(J)) DEB0C0(J)=DSB0C0(J-1)+DIFD(J> 11 DEB0SU(J)=DEB0C0(J-1)+O.5*TB0T(J-1) DE30SU(NBC0MP)=DEB0C0(NBC0M)+O.5*TB0' (NBC0M) WRITE(6/78)(T30T(J)/J=l/NBCeM) 78 F0RMAT(1KO/'TB0T=,/2X/1OE1O.3> WRITE(6/79)(DEB0C0(J>/J=1/HBC0M) 79 F0RMAT(1H /'DEB0C0=•/10E10.3) *** PHYSICAL CHARACTERISTICS 0F THE B0TT*M * BDT=BULK DENSITY 0F 30LID PHASE (KG/M3(Mi:DIUM>) AS F(DEPTH) FUHCTI0N BDT= (0./200.)/(0. 0 1/370.)/(0-02.. 54O.)/(0.03/660.)/ ... (0.04/650.)/(0.05/670.)/(0.20/680.) * VFLT=V0LUME FRACTI0N 0FLIQUI D (M3(LIQUI&)/M3(MEDIUM))A S F(DEPTH) FUKCTI0NVFLT<=(0./0.92)/(0.01/0.88)/(0.02/Q.79)/(0.03/0.74)/ . (0.04/0.75)/(0.05/0.75)/(0.20/0.74) * T0RTT=T0F.TU0SITY FACT0R (M2(MEDIUM)/M2(LlQUID)) AS F(VFL) FUNCTI0N T0RTT»(O./O.)/(0.1/0.03)/(0.2/O.i:/(0.3/0.2)/(0.4/0.34)j

161 (0.5,0.5),(1.9/ 1.0 ) D0 20 J=1,NBC0M BD(J)=AFGEN(BDT,DEBeC0(J)> VFL(J)=AFGEK(VFLT,DEB0C0(J)) 20 T0RT(J)=AFGEK(T0RTT,VFL(J)) ,* DIFV=DIFFUSI0N C0EFFICIENT 0F SUBSTANCE IN BULK VATER (!! 2( L IQU ID)/ D) "PARA M DIFV=0.41E- 4 * D?0RL=DIFF'J3I0 N C0EFFICIENT 0F SUBSTANCE IN LIQUID PHASE (M3CLICUID)/ DP0r.L*T0RT(l)*DIFV (M(KEDIUM)D)) D0 21 J=2,NBC0M 21 D?0P.L(J)=VFAC*(KFAC*VFL(J-1)*T0RT(J-1)+VFL(J)*T0RT(J))*DIFV *** PARTITI0N 0F SUBSTANCE 0VER B0TT0M PHASES,INSTANTANE0US EQUILIBRIUM * KSL=DISTRI3UTI0N RATI0 S0LID/LI2UID PHASE =ADS0P.PTI0N C0EFFICIEKT * (K3/KG(30LI D PHASE))/(M3/M3(LIÏUID PHASE)) * K3LT=i:SL AS FCDEPTH) FUNCTI0N KSLT=(0.,0.073),(0.2,0.073) * CAPL=SU3STANCE CAPACITY FACT0R RELATING T0 C0NCENTRATI0N IN LIQUID PHASE * (K3(LIGUID)/M3(MEDIUM) ) D0 30 J=l,N3C01i KSL(J)=AFGS:i(KSLT,DEB0C0(J)) CAPL(J)=VFL(J) +3D(J)*KSL(J ) 30 CA30TB(J)=CAPL(J)*30SU*TB0T(J) *** DEC0MP0SITI0N 0F THE SU35TANCE * RCDEVT=RATE C0EFFICIE1;T(l/D ) FOR DEC0MP0SITI0N IN VATER AS F(TIME«) FUNCTI0N RCDE'..'T=(0.,0.23) ,(5 .64 ,0.23) ,(5 .65 ,0.49) ,(30 .,0.49 ) * RCDEBT=RAT E C0EFFICIENT(1/D ) F0P.DEC0MP05ITI0 N IN B0TT0M AS F(TIME) FUNCTI0N RCDEBT=(0.,0.073),(30.,0.073) *** INITIAL AND B0UNDARY C0NDITI0NS * KSV=MAS5 0F SUBSTANCE IN WATER C0M?. (MG) * KSB=MASS 0F SU3STAMCE IN 30TT0M C0MP. (MG) * I REFERS T0 INITIAL C0NDITI0N INC0N IM S"J =13 .2 TABLE IMSB(1-10 3=10*0. 0 * FLRS3=FL0V RATE 0F SUBSTANCE INT0 30TT0M C0MP. (MG/D) FLR53(NBC0M?)=0. 0 DYNAMIC N0SeR T *** SUBSTANCE M0VEMEMT * RMSV=RATE 0F CHANGE IN MASS 0F SU3STANCE IN VATER C0MP. (MG/D) MSW=I NTGRL (IMSV,P.MSV ) * RMSB=RATE 0F CHANGE 11!MAS S 0F SUBSTANCE IN B0TT0M C0MP. (MG/D) MS3=INTGRL(IMSB,RMSB,10) * CW=C0NCENTRATI0N 0F SUBSTANCE IK WATER C0MP. (MG/M3) VWT=A F3EN(VWTT,T IME ) CW=M3W/VVT * CLB=C0NCENTRAT10N 0F SUBSTANCE IN LIQUID PHASE 0F B0TT0M C0MP. (MG/M3) * CM=C0NCENTRATI0N 0F SUBSTANCE IM B0TT0M C0MP. (MG/M3(MEDIUM)) D0 50 J=1,NBC0M CLB(J)=MS3(J)/CA30T3(J) 50 CM(J)=CLB(J)*CAPL(J) FLP.S3(1 )=-DP0RL (1 )*303U*(CLB (1)-CW)/DIFD (1 ) D0 51 J=2,N3C0M 51 FLRS3(J)=-DP0RL(J)*B03U*(CLB(J)-CLB(J-l))/DIFD(J) *** DEC0KP05ITI0N 0F THE SUBSTANCE * RDECV=RATE 0F DEC0MP0SITI 0N IN VATER C0MP. (MG/D) * P.DEC3=RATE 0F DEC0MP0SI TI 0H IN B0TT0K C0MP. (MG/D) * TRDECB= T0TA L RATE 0F DEC0MP0SIT 10N IN THE B0TT0M (MG/D) ROECV=AFGEt;(RCDEVT,TIME)*MSV TRDEC3=0.0 D0 55 J=I,N3C0M RDECB(J)=AF3EN(P.CDEBT,TIME)*MSB(J) 55 TRDECB=TRDECB+RDECB(J) * TDECW=T0TAL MASS 0F SUBSTANCE DEC0MPCSED IN VATER C0MP. (MG) * TDEC3=T0TAL MASS 0F SUBSTANCE DEC0MP0SED IN B0TT0M (MG) TDECW=INTGRL(0.0,RDECV)

162 TDECB=INTGRL(0.0.»TRDECB) *** 0VERALL RATE EQUATI0NS *RMSW=RAT E 0FCHANG E INMAS S 0F SUBSTANCE IN "JATER C0MP (MG/D) RMSW=-FLRS3<1 )-EDEC W * RMSB»RATS 0F CHANGE IN MASS 0F SU3STAÎ1CE IN B0TT0M C0MP. (MG/D) D0 60J=1,NBC0 M 60 RMSBCJ)=FLRSB,FLRSBC1-11 :,t:sa..MSW#.. . THSB,TDSCW#TDECB METH0D RKS 0UTPUT MSW(0.J15.)>TMS3<0.,1.5) TIMER PRDEL=0.5>0UTDEL=O.5,FI NTIM=2 7. END ST0P ENDJ0B

Appendix B

TITLE WATER AND PESTICIDE BALANCES F0RDRA I NAGEAN D INFILTRATI0N DITCH ******************************************* *************************** * DITCHWIT H MIXED WATER C0MP.AN D C0MPARTI MENTALIZATI0N 0FDITC HB0TTe K ST0RAGETB0T(2O).,DIFD<2O),DEB0C0<2O).»BD<2O ) ,VFL<2O)/T0RTC2O) ST0RA3EDP0RLC2O),KSL<2O).,CAPL<2O),CA30TBC2O>,DEB0SUC21>>CM<2O > ST0RAGEB0SU(21),CLB<2O),FLRSBC21),RDECB<2O ) ),VB0T<2O),DT07BC2O) ST0RAGE PUKPT<6O)..INTAKT<6O>,EVAP0T<6O>.»RAl|r NT<60)jSUPSTC63),FDIFLB(20) FIXEDNDAY,J,NBC0M.,NBC0M P INITIAL N0S0RT * ABBREVIATI0NS :C0MP.=C0MPARTMENT *** DEFINITI0N 0FDITCH-LAN D SYSTEM GE0KE|TRY * LC0M=LENGTH 0FTH EDITC H C0MPARTMENT * Wl-WIDTHA T THEB0TT0 M 0FTH EDITC H ASSIGNED T0 THEDITC H PARAM ISADB»2750.,ISADR=0- ISAD=ISADB+ISADR * P=WETTED PERIMETER 0FTH EDITC H CM).CALCULATED FReMAH V *AHW-AVERAG E HEIGHT 0FTH EWATE R LEVEL (M) PARAM AHW*0.30 P«WI+2.0*AHW*SQRTCS1**2+1.0 ) * N3C0M=NUMBER 0FB0TT0 M C0MP. * TB0T-THICKNESS 0FB0TT0 M C0MP.

163 PARAM NBC0M=2O*KFAC=1•1 WFAC=I.O/CMFAC+1.0) PARAMTB0T1=O.OO 1 TB0T(1)=TB0T1 D0 10J=2*NBC0 M 10 T30T(J)=MFAC*TB0T(J-1) N3C0MP=N3C0M+1 * DEB0C0=DEPTH 0FCENTRE S 0FTH EB0TT0 M C0MP. CM) * DIFD=DIFFUSI0N DISTANCEBETVEE N B0TT0M C0MP. CM) * DEB0SU=DEPTH 0FUPPE R SURFACES 0F30TT0 M C0MP.CM ) * B0SU=SUP.FACEARE A 0FTH E30TT0 M C0MP. =O.5*T30T(1 ) DIFDC1)=O.5*T30T(1) DEB0SU(1)=O.O 30SUCl)=LC0M*P BETA=ATAN(1.0/51) D0 11J=2*MBC0 M DIFD(J)=O.5*(T30T(J-1)+TB0T(J)) DE30C0(J)=DE30C0(J-1)+DIFD(J) DEB0SU(J)=DEB0C0(J-1)+O.5*TB0T(J-1) 11 B0SU(J)=LC0M*(Wl+2.O*DEB0SU(J)*SirKO.5*BETA)/C0S(O.5*3ETA)+.•. 2.O*(AHW+DE30SU(J))*SQRTCS1**2+1.0)) DEB0SU(NBC0MP)=DEB0 C0

164 *** DECOMPOSITION 0FTH E SUBSTANCE * RCDEVT-RATE COEFFICIENT1/D )FO RDEC0MP0 $ ITION INWATE R AS F(TIME) FUNCTION RCDEWT«(0./0.225)/(60./0.225) * RCDEBT-RATE COEFFICIENTC1/D> FORDEC0MP0 4 ITI0N INBOTTO M COMP.A S F(TIME) FUNCTION RCOEBT-CO.,0.038)/(60.,0-038) *** DEFINITION OFTH EITEM S OFTH EWATE R BALANCE * DISRAT«DISCHARGE RATE ASSIGNED TO DITCH SECTION +P0SSIBLEUPSTREA M * DITCH SECTION PARAM DISRAT-135. * PUMPT»PUMPIN3 TIME =60*0. * INTDOD«INTAKE RATE INTO DOWNSTREAM DITCH SECTION (M3/D) PARAM INTD0D=O.O * EVAP0T-RATE 0FEVAPORATIO N FROM OPEN WATfcR (M/D) TABLE EVAPOT(1-60>-18*0.0041/11*0.004/10*0 0047/10*0.0044/10*0.0065/... 0.0066 * RAINT=RAINFALL INTENSITY/(4.5/0.27),(9.5/0.30)/... (14.5/0.33>/(15.5/0.34)/(17./0.35)/( 8./0.29),(21.5,0.32),... (24./0.34)/(25./0.25)/(29.0/0>27)/(C3I I .0,0.28),(37.,0.30),..• (42.5/0.30)/(47./0.29)/(48./0.34)/(C4! > .,0.29)/... (49.5/0.31)/(51.5/0.34)/(53./0.34)/( !i9 ./0.30>/(60./0.30) *** SUPPLY/INITIAL ANDBOUNDAR Y C0NDITI to:i s * SUPST«RATE OFSUPPL Y TODITC H WATER DUE 0 SPRAY DRIFT (MG/D) TABLE SUPST(1-60)«10250./48*0.0/2100./10*0 0 * MSW-MASS OFSUBSTANC E INWATE R COMP.(M 3 * MSB-MASS OFSUBSTANC E INB0TT0 M C0MP.( CM(i) * IREFER S T0 INITIAL CONDITION INC0N IMSW«0.0 TABLE IMSB(1-20)«20*0.0 * CWINT«C0NCENTRATION 0FSUBSTANC E ININTAK E WATER (M3/M3)A S F(TIME) FUNCTIONCWINT«(0./0.)/(60./0 O * CWUPDT«C0NCENTRATI0N OFSUBSTANC E IN WATER FROM UPSTREAM DITCH SECTION (MG/M3) * AASS F(TIME Fi ) FUNCTION CWUPDT«(0./0.)/(60./0.) DYNAMIC NOSORT NDAY«TIME+1+0.05*DELT DAY-NDAY *** RATE 0FCHANG E INTH EDITC H WATER VOLUME * P REFERS TOTIM E PLUS DELT ,M REFERS T0 TIME MINUS DELT * CENTRAL DIFFERENCE SCHEME HWP«AFGEN(HWT/TIME+DELT) HW«AFGEN(HWT/TIME) IF(TIME .GT. 0.0)G OT e4 1 IFCHW .GT.HWS )G OT O4 2 VWD«HW*(W1+S1*HW)*LC0M VWDM-VWD G0 TO4 3 42 VWD"VWDL*(HW-HWS>*(W2+S2*(HW-HWS))*LÇ0M VWDM«VWD G0 TO4 4 41 HWM«AFGEN(HWT/TIME-DELT) IF(HW .GT.HWS )G OT O4 5 VWDM-HWM*(WI+S1*HWM)*LC0 M

165 VWD=HW*CW 1+S 1 *HV )*LC0 M A3 VWDP=HVP*(W1+S1*HWP)*LC0M G0T 04 6 45 VWDM=VVDL+(HWM-HWS)*(V2+S2*(HWM-HWS))*LC0M VWD=VWDL+(HW-HWS)*CW2+S2*(HW-HWS))*LC0M 44 VWDP=VVDL+(HWP-HWS)*(W2+S2*(HWP-HWS))*LC0M * RVWD=RATE 0FCHANG E INDITC HVATE R V0LUME (M3/D) 46 RVVD=(VVDP-yWDM)/<2.*DELT) *** EVAP0RATI0N ANDPRECIPITATI0 N EVAP0=EVAP0T(NDAY) RAIN=RAINT(NDAY) IF(HW .3T. HWS) 30 T0 47 * EVASU=EVAP0RATIN3 SURFACE 0FA DITCH WATER C0MPARTMENT (M2) EVASU=LC0M*(W 1+ 2•0*S1*HW ) G0T 04 8 47EVASU=LC0M*(W2+2.O*S2*(HW-HWS) ) 48 C0NTINUE * QEVAP=RATE 0FEVAP0RATI0 N CM3/D) QEVAP=EVAP0*EVASU * GPREC=RATE 0FRAINFAL L INT0TH EDITC HWATE R C0MP. (M3/D) QPREC=RAIN*EVASU *** INTAKEAN D DISCHARGE * QDISCH=RATE0 FDISCHARG E 0UT 0FTH EDITC H WATER C0MP.(M3/D ) QDISCH=PUMPT(NDAY)*DISRAT * ODUPDS=RATE 0FDISCHARG E FR0M THEUPSTREA M DITCH SECTI0N CM3/D) QDUP3S=PUMP TCNDAY )*DISUP D * QINT=RATS0 FWATE R INTAKE INT0TH EDITC H WATER C0MP. CM3/D) QINT=INTAKT(NDAY)*INTRAT * QID0DS=RATE0 FWATE R INTAKE INT0D0WNSTREA M DITCH SECTI0N CM/D) QID0DS=INTAKT(NDAY)*INTD0D *** FL0W THR0UGH DITCH B0TT0M AND DRAINS (CL0SING ENTRY=CLENT) CLENT=RVWD+O.EVAP-QPREC+QDISCH-QDUPDS-QINT+QID0DS * IFCLEN T ISP0SITIVE:DRAINA3 EAN D IFNEGATIVE:INFILTRATI0 N IF(CLENT .LT.0.0 ) 30T 04 9 * QWB0T=FL0W RATETHR0U3 H THEWETTE D PERIMETER 0FTH EDITC H (M3/D) QWB0T=DSADB/DSAD*CLENT * QVDR=FL0W RATETHR0UG HDRAIN S (M3/D) QWDR=DSADR/DSAD*CLENT G0T 05 0 49 QWB0T=ISAD3/ISAD*CLENT QWDR=ISADR/ISAD*CLENT 50 C0NTINUE * FL0DB=FL0W RATETHR0UG HTH EDITC H B0TT0M EXPRESSED INM/ D FL0DB=QWB0T/DSADB * VB0T=WATER FLUX THR0UGH THEWETTE D DITCH PERIMETER (M3(LIQUID)/(M2(MEDIUM)D); D0 51J=1,NBC0 M 51 V30T(J)=QWB0T/30SU(J) *** SUBSTANCE M0VEMENT * RMSW=RATE 0FCHANG E INMAS S 0F SUBSTANCE INWATE R CeMP. (MG/D) MSW=INT3RL(IMSW,RMSW) * RMSB=RATE 0F CHANGE INMAS S 0FSU3STAMC E INB0TT0 M C0MP.(K3/D ) MSB=INT3RL(IM3B>RMSB^20) * CW=C0NCENTRATI0N 0FSUBSTANC E INWATE R C0MP. (M3/M3) CV=MSV/VWD * CLB=C0NCENTRARI0N 0F SUBSTANCE INLIQUI D PHASE 0FB0TT0 M C0MP. CMG/M3) * CM=C0NCENTRATI0N 0FSUBSTANC E INB0TT0 M C0MP.(MG/M3(MEDIUM) ) D0 52J=I,NBC0 M CLB(J)=KSB(J)/CAB0TB(J) 52 CM(J)=CLB(J)*CAPLCJ) CWIN=AFGEN(CVINT,TIME) CWUPD=AF3EN(CWUPDT,TIME) * FLRSWD=FL0W RATE 0F SUBSTANCE INT0D0WNSTREA M DITCH SECTI0N (DURING INFIL- * TRATI0NPERI0D ) (MG/D) FLRSWD=CW*2IDeDS * FLRSWI=FL0W RATE 0F SUBSTANCE FR0K WATER INTAKE (DURING INFILTRATI0N * PERI0D) (MG/D)

166 FLRSWI=CWIN*GINT * FLRSW0=FL0W RATE 0FSUBSTANC E DISCHARGED GUT 0FTH EWATE R C0MP. * (DURING PUMPING PERI0D) (MG/D) FLRSW0=CW*QDISCH * FLR5WU=FL0W RATE 0FSUBSTANC E FR0M UPSTREAM DITCH S2CTI0N (DURING PUMPING * PERI0D) (M3/D) FLRSWU=CWUPD*QDUPDS DT0TB(1)=DISPD*A3S(VB0T(1) )+DP0RL(1 ) IF(VB0T(1) .LT.0.0 ) G0T 05 3 * FLRS3=FLeW RATE 0F SUBSTANCE INT0A B0TT0 M C0MP (MG/D) FLRSB(1)=-QWB0T*CLB(1>-DT0TB(1>*B0SU < 1)*(CLB(1)-CW)/DIFD(1) FDIFLB(I)=-DP0RL(1)*B0SU(J)*(CLB(1)-qW)/DIFD(I ) FLRSB(1)=AMIN1(FLRSB(1).,FDIFLB(1)) 30T 05 4 53 FLRSB(I)«-QWB0T*CW-DT0TB (1) *B0SU (1) * (|CLB (1 ) -CW )/DIFD <1) 54 C0NTINUE D0 55J«2,NBC0 M DT0TB(J)*DISPD*ABS(VB0T(J))*DP0RL(J) FLRSB(J)=-QWB0T*WFAC*(MFAC*CLB(J-1)+C|LB(J))-DT0TB(J)*... B0SU(J)*(CLB(J)-CLB(J-1))/DIFD(J) IF(VB0T(1) .LT.0.0 ) 30T 05 6 FDIFLB(J)=-DP0RL(J)*B0SU(J)*(CLB(J)-CLB(J-1))/DIFD(J) FLRSB(J)=AMIN1(FLRSB(J),FDIFLB(J)> IF(CLB(J) .LT.0.0001 )FLRSB(J)=AMAX 1 (FLRSB(J),0.0> G0T 05 5 56 IF(CLB(J-I> .LT.0.0001 )FLRSB(J)=AM I Nl(FLRSB(J),O.0> 55 C0NTINUE IF(QWB0T .LT.0. ) G0T 05 9 FLRSB(NBC0MP)=O«O G0T 06 0 59 FLRSB(NBC0MP)=-QWB0T*CLB(NBC0M) 60 C0NTINUE *** DEC0MP0SITI0N 0FTH E SUBSTANCE * RDECW=RATE 0FDEC0MP0SITI0 N INWATE R C0MP (MG/D) RDECW=AFGEN(RCDEWT,TIME)*MSW *RDECB=RAT E 0FDEC0MP0SIT0 N INB0TT0 M C0MP (MG/D) * TRDECB=T0TAL RATE 0FDEC0MP0SITI0 N INTH E B0TT0M (MG/D) TRDECB-0.0 D0 61J=1,NBC0 M RDECB(J)«AFGEN(RCDEBT,TIME)*MSB(J) 61 TRDECB*TRDECB+RDECB(J> * TDECV=T0TAL MASS 0FSUBSTANC EDEC0MP0SE D }NWATE R C0MP.(MG ) * TDECB»T0TALMAS S 0FSUBSTANC E DEC0MP0SED NB0TT0 M (MG) TDECW=INTGRL(0.0,RDECW) TDECB»INTGRL<0.0*TRDECB) *** 0VERALL RATEEQUATI0N S SUPS=SUPST(NDAY) * RMSW*RATE 0FCHANG E INMAS S 0FSUBSTANC E INWATE R C0MP (MG/D) RMSW=FLRSWI+FLRSWU+SUPS-FLRSB(1)-RDECîr-FLRSWD-FLRSW0 * RMSB-RATE 0FCHAN3 E INMAS S 0F SUBSTANCE NB0TT0 M C0MP. (MG/D) D06 2J=1,NBC0 M 62 RMSB(J)«FLRSB(J)-FLRSB(J+1)-RDECB(J> *** 0UTPUT SECTI0N * TEVAP=T0TAL V0LUME 0FWATE R EVAP0RATED (MJ) TEVAP=INTGRL(0.0*QEVAP> * TRAIN=T0TAL V0LUME 0FWATE R FR0M RAINFALL (M3) TRAIN=INTGRL(0.0,QPREC> * TINT=T0TALV0LUM E 0FWATE R TAKEN IN (M3) TINT»INT3RL(0.0#QINT> * TID0DS»T0TALV0LUM E 0FWATE R INTAKE INT0DOWNSTREA M DITCH SECTI0N (M3) TID0DS«INTGRL(O.O*QID0DS> M * TDISCH»T0TALV0LUM E 0FWATE R PUMPED 0UT0 F THEDITC H (M3) TDISCH«INTGRL(0.0>QDISCH) * TDUPDS«T0TALV0LUM E 0FWATE R DISCHARGED FR|0MTH EUPSTREA M DITCH SECTI0N (M3) TDUPDS»INT3RL(0.0*QDUPDS) * TWB0T-T0TAL V0LUME 0FWATE R TRANSP0RTED TtfR0UGHTH EDITC HB0TT0 M (M3)

167 TW30T=INTGRLCO.O,QWB0T) * TDRAIN=T0TAL V0LUME 0FWATE R FR0M THEDRAIN S (M3) TDRAIN=INTGRL(0.0>QWDR) * TST0R=T0TALV0LUM E 0FWATE R ST0RED INTH EDITC H (M3) TST0R=INT3RL(O.O#RVWD) * TMSINT=T0TAL MASS 0FSUSTANC E TRANSP0RTED INT0TH EWATE R C0MP. (VIA INTAKE)f TMSINT=INT3RL(0.0,FLRSWI) * TMSUPD=T0TAL MASS 0FSUBSTANC ETRANSP0RTE D INT0TH EWATE R C0MP.VI AU PSTREA M * DITCH SECTI0NS (MG) TMSUPD=INTGRL(0.0,FLRSWU) * TMSD0D=T0TAL MASS 0F SUBSTANCETRANSP0RTE D 0UT 0FTH EWATE R C0MP.INT 0 * D0WNSTREAM DITCH SECTI0NS CMG) TMSD0D=INTGRL(O.O>FLRSWD) * TMS0UT=T0TALMAS S 0F SUBSTANCE TRANSP0RTED 0UT 0FTH EWATE R C0MP.VIA PUMP (K TMS0UT=INTGRLCO.O,FLRSW0) * TMSINF=T0TALMAS S 0FSUBSTANC E INFILTRATED THR0UGH THEL0VES TB0TT0 M C0MP.(M TMSINF=INTGRL(O.O,FLRSB(NBC0MP)) * TMSSUP=T0TAL MASS 0FSUBSTANC E SUPPLIED T0TH EDITC H DUET 0 SPRAY DRIFT CMG) TMSSUP=INTGRL<0.0/SUPS) PRT=IMPULSC0. 0,PRDEL ) IF 100 C0NTINUE PRINT VWD.,TEVAP,TRAINJTINT,TID0DS,TDISCH,TDUPDS,TST0R,TDRAIN.»TWB0T,. • • FL0DB,V30T(1),FDIFLB(1-2),CW,CM(1-20),FLRSB(1-10)>TMSB,MSW ,.. . TDECW,TDEC3,TMSINT,TMSUPD,TMSD0D,TMS0UT.,TMSINF,TMSSUP METH0D RECT 0UTPUTCW,MSW,TMS B TIMER DELT=O.OO5/PRDEL=O.5*0UTDEL=O.5^FINTIM=59.O ..END

~~Appendix C~~

TITLEBEHAVI0U R 0F SUBSTANCES INDITCHE S WITH FL0WING WATER * WITH DIFFUSI0N INT0 0NEB0TT0 M C0MP•1VARIABL EWATE R LEVELAN D VARIA3LEFL0 W 5T0RAGEFLRSW(10l)*CWC100)*CLB(100)*FLRSB(100),RDECW(100>>RDECB(100 > FIXEDNDC0M/NDC0MP.. I INITIAL N0S0RT * BASIC UNITS :MILLIGRA M (MG) , METER (M) , DAY (D) » AB3REVIATI0NS :C0MP.=C0MPARTMENT(S ) *** DEFINITI0N 0FDITC H C0MPARTMENT GE0METRY * LC0M=LEMGHT 0FTH EDITC H C0MP. (M) * S1=SL0PE 0FTH EL0WE R PART 0FTH EDITC HWALL S CH0RZ./VERT•) (-) * W1=WIDTH AT THEB0TT0 M 0FTH EDITC H (M) * AHW=AVERAGE HEIGHT 0FTH EWATE R LEVEL INTH EDITC H (M) PARAMLC0M=2.,S1=O.32,W1=1.92,AHV=0.1 S * P=WETTED PERIMETER 0FTH EDITC H (M) P=W1+2.0*AHW*SQP.T(S1**2+ 1.0 ) * NDC0M=NUM3ER 0FDITC HWATE R C0MP. (-) PARAM NDC0M=1OO NDC0MP=NDC0M+1 * TB0T=THICKN'ESS 0FB0TT0 M C0MP. (M) PARAMTB0T=O.OO 5 * B0SU=3URFACEARE A 0FTH EB0TT0 M C0MP. (M2) B0SU=P*LC0M *** PHYSICAL CHARACTERISTICS 0FTH EB0TT0 M * BD=BULKDENSIT Y 0F S0LID PHASE (K3/M3(MEDIUM )) * VFL=V0LUMEFRACTI0 N 0F LIQUID (M3(LIQUID)/M3CMEDIUM)) * T0RT=T0RTU0SITY FACT0R (M2(MEDIUM)/M2(LIQUID))

168 * DIFW»DIFFUSI0N C0EFFICIENT 0FSUBSTANC E : NBUL K WATER (M2(LIQUID)/D) PARAM BD=13O.,VFL=O.95,T0RT=O.95,DIFW=O.3 îsi: 4 * DP0RL=DIFFUSI0N C0EFFICIENT 0F SUBSTANCE INLIQUI D PHASE (M3(LIQUID)/M(MED.)D> DP0RL»VFL*T0RT*DIFW *** PARTITI0N 0F SUBSTANCE 0VER B0TT0M PHASES ,INSTANTANE0US EQUILIBRIUM * KSL-DISTRIBUTI0N RATI0 S0LID/LIQUID PHASï =ADS0RPTI0N C0EFFICIENT * /(M3/M3(LIQUID PHAS E)) PARAM KSL-0.007 * CAPL*SUBSTANCE CAPACITY FACT0R RELATING 1 0C0NCENTRATI0 N INLIQUI D PHASE * (M3(LIQUID)/M3(MEDIUM)) CAPL=VFL+8D*KSL CAB0TB*CAPL*30SU*TB0T *** DESCRIPTI0N 0FWATE R FL0W THR0U3HT H DITCH C0MPARTMENTS * U=AVERAGE VEL0CITY 0FWATE R FL0W IN THE CI TCH (M/D) * UT-UA S F(TIME) FUNCTI0N UT»(0.,4640.),(L,4640«) * HW-HEIGHT 0FWATE R LEVEL INDITC H F0RDEC0MP0S| I TI0N INWATE R AS F(TIME) FUNCTI0N RCDEWT=(0.,0.55),(1.,0.55) * RCDEBT»RATE C0EFFICIENT(1/D> F0RDSC0MP0S| I TI0N INB0TT0 M C0MP.A SF(TIKE ) FUNCTI0N RCDEBT<=(0.,0»),(1.0,0.) *** INITIAL ANDB0UNOAR Y C0NDITI0NS * MSW=MASS 0F SUBSTANCE INWATE R C0MP.(M3 ) * MSB-MASS 0F SUBSTANCE INB0TT0 M C0MP. (MQ * I REFERS T0 INITIAL C0NDITI0N TABLE IMSW(1-100)=50000.,99*0. TABLE IMSBC1-100)=100*0.0 DYNAMIC N0S0RT *** C0MPUTATI0N 0FTH EWATE R FL0W CHARACTERISTICS U«AFGEN(UT,TIME) HV=AFGEN(HWT,TIME) * A-WETTED CR0SS-SECTI0NAL AREA 0FTH ED I tTCH (M2) A-HV* * VWD»V0LUME 0FWATE R INDITC H WATER C0MP. (M3) VWD-A*LC0M * Q-FL0W RATE 0FWATE R INT0 A DITCH C0MP. W3/D) Q»A*U * DLDISW-L0NQITUDINAL DISPERSI0N C0EFFICIE^T INWATE R C0MP. (M2/D> DLDISV=DISC0N*ABS(U)*HW * DT0TW-T0TAL SPREADING C0EFFICIENT IN WAT^R C0MP. (M2/D) DT0TW=DLDISW+DIFW*U**2*DELT/2.O *** SUBSTANCE M0VEMENT * RMSW=RATE 0FCHANG E INMAS S 0F SUBSTANCE INWATE R C0MP. (M3/D) * RMSB=RATE 0FCHANG E INMAS S 0F SUBSTANCE INB0TT0 M C0MP. (MG/D) MSW«INTGRL(IMSW,RMSV,100) MSB«INTGRL(IMSB,RMSB,100) * CW-C0NCENTRATI0N 0F SUBSTANCE INWATE R C BMP. (MG/M3) D0 30 I*1,NDC0M 30 CW(I)=MSW(I)/VWD * FLRSW=FL0W RATE 0FSUBSTANC E INT0 A WATEH C0MP. (MG/D) FLRSW(1)=INSW(Q,Q*CW(1>,0.0> FLRSW(NDC0MP)*INSW(Q,O.O,Q*CW(NDC0M)) D0 33 I»2,NDC0M 33 FLRSW(I) =a* 0• 5 *(CW (I - 1) +CW (I ) ) -DT0TW*(A * (CW(I)-CW(I-1))/LC0M * CLB-C0NCENTRATI0N 0F SUBSTANCE IN LIQUID PHASE 0FB0TT0 M C0MP. (M3/M3) D0 35 I=1,NDC0M 35 CLB(I)=MSB(I)/CAB0TB * FLRSB-FL0W RATE 0F SUBSTANCE INT0A B0T T 0M C0MP. (MG/D) D03 6I=1,NDC0 M

169 36 FLRSB(I)=-D?0RL*30SU*(CL3(I)-CW(I)>/(O.5*TB0T ) *** DEC0MP0SITI0N 0FTH E SUBSTANCE * RDECW=RATE 0FDEC0MP0SITI0 N INWATE R C0MP. (MG/D) * RDEC3=RATE 0FDEC0MP0SITI0 N INB0TT0 M C0MP.CMG/D) * TRDECW=T0TAL RATE 0FDEC0MP0SITI0 N INTH EWATE R (MG/D) * TRDECB=T0TAL RATE 0FDEC0MP0SITI0 N INTH EB0TT0 M (MG/D) RCDECW=AF3EN(RCDEWT,TIME) RCDECB=AFGEN(RCDEBT,TIME) TRDECW=0.0 TRDECB=0.0 D04 0 I=1,NDC0M RDECW(I)=RCDECW*MSW(I) RDECB(I)=RCDEC3*MSB(I) TRDECW=TRDECW+RDECW(I) 40 TRDECB=TRDECB+RDECB(I) * TDECW=T0TAL MASS 0F SUBSTANCE DEC0MP0SED INWATE R C0MP. (M3) * TDEC3=T0TALMAS S 0FSUBSTANC EDEC0MP0SE D INB0TT0 M (MG) TDECW=1NTGRL(0.0/TRDECW ) TDECB=INTGRL(0.0,TRDECB) *** 0VERALLRAT EEQUATI0N S 005 0 I=1,NDC0M RMSW(I)=FLRSW(I)-FLRSW(I+1)-FLRS3(I)-RDECW(I) 50 RMSB(I)=FLRSB(I)-RDECB(I) *** 0UTPUT SECTI0N * TMSW0F=T0TAL MASS 0F SUBSTANCE TRANSP0RTED 0UT 0FFIRS T WATER C0MP. (MG) * TMSW0L=T0TAL MASS 0F SUBSTANCE TRANSP0RTED 0UT 0FLAS TWATE R C0MP. (MG) TMSW0F=INTGRL(0.,-FLRSW(1)) TMSW0L=INTGRL(0.0*FLRSW(NDC0MP)) PRTIM=IMPULS(0•0,PRDEL ) IF(PRTIM*KEEP .LT.0-5 )3 0T 0 100 * TMSW=T0TAL MASS 0F SUBSTANCE INWATE R C0MP. (MG) * TMSB=T0TAL MASS 0F SUBSTANCE INB0TT0 M (MG) TMSW=0.0 TMSB=0.0 D0 60I=1,NDC0 M TMSW=TMSW+MSW(I) 60 TMS3=TMS3+MS3(I) CW51=CW(5I) MSW51=MSW(51) MSB51=MS3(51) 100C0NTINUE ' METH0D RECT PRINT Q*U,DT0TW,RCDECW,RCDEC3,TMSW,TMSB,TMSW0F,TMSW0L,TDECW,TDECB,.• • CW51,MSW51,MSB51 0UTPUTCW51(0.,2000.),MSW51(0.*1000.)>MSB51(0.>1000. ) TIMER DELT=0.000025*PRDEL=0.0025,0UTDEL=O.0025,FINTIM=0.1 END ST0P ENDJ0B

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