Leaching of dinoseb and metribuzin from potato fields in New Brunswick P. MILBURN1, H. O'NEILL2, C. GARTLEY3, T. POLLOCK2, J.E. RICHARDS1 and H. BAILEY2 1Agriculture Canada Research Station, P.O. Box 20280, Fredericton, NB, Canada E3B 4Z7; Environment Canada, Inland Waters Directorate, P.O. Box 861, Moneton, NB, Canada E1C 8N6; and JSoil and Water Section, New Brunswick Department ofAgriculture, P.O. Box 6000, Fredericton, NB, Canada E3B 5H1. Received 12 February 1990; accepted 7March 1991

Milbum, P.,O'Neill, H., Gartley, C, Pollock, T., Richards, J.E. and in Iowa and Minnesota alone. He furthernoted that pesticides Bailey, H. 1991. Leaching of dinoseb andmetribuzin from potato havebeen detected in winterand spring water samples, prior fields in New Brunswick. Can.Agric.Eng.33:197-204. Tiledrainage to new application, indicating that several pesticides are per waters from five systematically tiled, commercial potato fields in sisting in groundwater year-round. northwestern New Brunswick were analyzed for the herbicides Approximately 36 000 metric tonnes of pesticide active metribuzin and dinoseb from April 1987 to April 1989. Tile drain ingredient were sold in Canada in 1985 (Pierce and Wong outflowrate and volume were also recorded. Dinoseb and metribuzin 1988). Frank et al. (1987b) reported on sampling 359 rural were detected in tile outflow both during the year of application and during the subsequent spring melt period, butat concentrations sub wells in Ontario for suspectedpesticide contamination where stantially less than maximum acceptable concentrations (MAC) for the cited causes were spills, spray drift, or surface runoff drinking water published by Health and Welfare Canada. Average carrying pesticides into wells; 134 wells were contaminated. concentrationsof dinoseb twelve months after application ranged from In another Ontario study, Frank et al. (1987a) analyzed well less than the detection limit to 0.21 Jig-L"1 (five site-years), and the water samples from 91 farms onmineral soils where pesticides concentration of metribuzin ten months after application averaged were used but contamination was not suspected. Pesticide 0.22 M-g'L"1 (one site-year). Persistence ofdinoseb inthe tile outflow residues were detected in 12 wells; of the 45 pesticides ana did notappear tobe affected bythehistory of dinoseb use other than lyzed for, atrazine was detected with the greatest frequency. those applications occurring within thepast12months. Azinphosmethyl, diazinon, dinoseb, endosulfan, and D'avril 1987 a avril 1989, on a effectue une analyse des herbicides, fensulfothion residues were detected in farm ditch water «metribuzin»et «dinoseb», contenus dans les eaux de drainage de cinq champs de pommes de terre commerciales, drainees de maniere and/or sediments leading to rivers in the lower mainland of systematique par des tuyaux, dans le nord-ouest duNouveau-Bruns- British Columbia (Wan 1989). In pesticide leaching studies in wick. On a aussi enregistre le debitet le volume des ecoulements. Le Ontario and Quebec, respectively, Von Stryk and Bolton dinoseb et le metribuzin ont ete detectes dans les ecoulements de (1976) detected atrazine and Muir and Baker (1976) detected tuyaux durant Tannee d'application et pendant la periode de fonte atrazine, cyanazine, cyprazine, andmetribuzin (triazine herbi printaniere subsequente, mais a des concentrations bien infcrieures cides) in tile drainage waters. Priddle et al. (1989) reported auxconcentrations maximales acceptables dansTeaupotable,etablies alidcarb and NO3-N contamination of a sandstone aquifer be par Sante etBien-etre social Canada. Les concentrations moyennes de neathtwo potato fields in PrinceEdward Island. dinoseb, douze mois apres Implication, variaient d'une valeur moindre que la limite de detection a unevaleur de 0,21 \Lg.L~ (cinq In north western New Brunswick (NB) approximately 20 annees-sites). Celles de metribuzin, dix mois apres Fapplication, 000 ha of landareused for potato production annually; pesti etaient de 0,22 \ig.L~1 (une annee-site). La persistance du dinoseb dans cides are routinely employed in the production of potatoes recoupment des tuyaux ne semble etre reliee qu'aux applications (Advisory Committee on Potatoes 1986; Asiedu et al. 1987). faites dans les douze mois anterieurs. Nopublished information existsonpesticide leaching from the crop root zone under NB soil and climate conditions. Pesti INTRODUCTION cides have been detected in rural wells in the potato growing Contamination of groundwater by agricultural chemicalsand areas ofnorthwestern New Brunswick, but the cause has been the attendant concerns for human health have been the subject principally attributed to improper location of wells and/or of several recent studies and reviews (Hallberg 1986, 1987; improper casing of the well head to prevent entry of surface Pimentel and Levitan 1986; Ritter 1986; Lee and Nielsen runoff (Ecobichon et al. 1988). 1987; Fairchild 1988; White et al. 1988; and references cited The objective of our study was to determine if two herbi therein). Although groundwater contamination has many cides commonly used in NB potato production, namely sources, Lee and Nielsen (1987) suggested that agriculture's dinoseb and metribuzin, were leaching from the crop root relativecontribution may be significant as incidents ofground zone. This was achieved through analysis of tile drainage water contamination from pesticides and fertilizer have been waters from five on-farm sites where both the history ofpesti documented in many parts of the United States. Cohen et al. cide use and layout of the tile drainage system were known. (1986), as reported by Hallberg (1987), noted that at least 17 Field data were collected from April 1987 to April 1989. A pesticides have been found in 23 states of the US, as a result summary of the 1987 dinosebresultswas providedby O'Neill of routine agricultural practices. Hallberg (1987) indicated et al. (1989). Milburn et al. (1990) also reported on nitrate that 19 different pesticides have been detected in groundwater leaching from these sites.

CANADIAN AGRICULTURAL ENGINEERING 197 BACKGROUND Ivany et al. (1983) reported an average metribuzin half-life of 33 days on Prince Edward Island soils based on a 3-year Dinoseb field study and 3 metribuzin application rates (0.5, 1.0, 1.5 The following description is summarized from the Herbicide kg«ha"). They also measured average metribuzin concentra Handbook (WSSA 1989). Dinoseb is a dinitrophenol com tions in the top ten centimetres of soil 300 days after pound used as a selective, pre- and postemergence herbicide; application of23,36, and 34 |ig«kg_1 for application rates 0.5, it is also used in potatoes as a preharvest dessicant (topkiller). 1.0, and 1.5 kg-ha" , respectively. These residues did not affect Some important properties of the chemical include: oral yieldsof subsequentwinterrye andred clover crops,but yields LD5o(rat), 58 mg«kg"r; solubility in water (25°C), 52 mg-L"1; of barley and timothy were significantly reduced in one of the average persistence of phytotoxicity, two to four weeks. three crop years. Dinoseb is not tightly adsorbed on most agricultural soils. It The MAC of metribuzin in drinking water is 80 ^g«L_1 can leach in porous, sandy soils; but experiments have shown (Health and Welfare Canada 1987). Metribuzin concentrations that for normal temperate zone rainfall and infiltration rates, it detected in tile drainage water or well water in Quebec, Iowa, shouldnot be leachedfrom the top 300 mm of soil by rainfall and Minnesota ranged from 0.1 to 6.8 Jig-L"1 (Muir and Baker in the first year after application, during which time it is 1976; Hallberg 1986,1987). Frank et al. (1987 a, b) reported subjected to soil microbial degradation. concentrations of about 1 Jig-L'1 200 days after initial sam Dinoseb has been registered for use in Canada since 1947. pling of two highly contaminated rural wells (42 and 187 Recent assessments led Health and Welfare Canada to advise |ig«L~ ) that had incurred metribuzin spills at or near the well users that they are subject to appreciable health risks when head. Under normal use conditions in a field with no previous handling dinoseb (teratogenic effects, cataract formation, and history of metribuzin application, Muir and Baker (1976) re male reproductive effects). Similar conclusions regarding ported maximum concentrations in tile discharge of 1.65 dinoseb toxicology led the USEPA to suspend all dinoseb use ILig-L'1, reducing to less than detection levels (0.01 M^g-L"1) by in 1987, though extensions were granted up to two years for late November of the year ofapplication. certain critical uses (CAPCO 1989; USEPA 1988). In 1982, dinoseb was the 13th most widely used pesticide in the USA MATERIALS AND METHODS (Ritter 1986). The maximum acceptable concentration (MAC) of dinoseb Tile drain discharge rate, pesticide concentration of the tile in drinking water is under review (Health and Welfare Canada drain discharge, crop rotation, and pesticide use were moni 1987). Health and Welfare Canada has provided a guidance tored during the study. The five study sites, ranging in area value of 10 \igmUl (Personal communication: N. McTiernan, from 3 to 10 ha, were located within a 50 km radius in north Regional Pesticide Officer, Food Production and Inspection western New Brunswick (Fig. 1). Tile drain discharge rate was Branch, Agriculture Canada, Moncton, NB). measured during the non-freezing period of approximately April 1 to December 1 in 1987 and 1988. Pesticide samples Dinosebwasconsistently foundin ditch waterfor one year were collected during the same period, and also in April 1989. after the spray season in the lower mainland ofBritish Colum bia, at concentrations varying from 0.3 to 18.6 Hg«L-1 (Wan Precipitation was not measured at each study site. However, data from EnvironmentCanada weather stations atGrandFalls 1989). Cohen et al. (1986), as cited by Hallberg (1987), re and Centreville (Fig. 1) indicated that April 1 to December 1 ported that dinoseb had been detected in groundwater in the USA in only one state, and that typical concentrations ranged cumulative rainfall was within 4% of normal for 1987 and 1988 (Personalcommunication: G. Read, Climatologist, New from 1.0 to 5.0 ^g-L" . Frank et al. (1987b),reporting on well Brunswick Department of Agriculture, Fredericton, NB). contamination by dinoseb as a result of a spill, noted that four Monthlyprecipitationtotals at Grand Falls from April 1,1987 nearby wells on the same coarse textured soil were checked to December 1,1988 are shown in Fig. 2. Precipitation totals periodically for dinoseb contamination, and on day 382 after at Centreville for the same time period followed the same the spill, traces of dinoseb were detected in two of the four general trend of Fig. 2, including the above normal rainfall in wells (0.1, 0.3 M^L"1). In June 1988, Agriculture Canada August 1988. Details ofthe study sites, drainage systems, soil sampled 262 farm wells across Canada for pesticides. and climate conditions, and tile drainage discharge measure Dinoseb was detected in 8 of45 samples and 3 of 9 samples ment technique were provided by Milburn et al. (1990). collected in New Brunswick and British Columbia, respec tively. Concentrations ranged from 0.4 to 12.4 \x% L"1 Selected soil characteristics and total drainage system dis charges are given in Table I. Runoff and subsequent soil (Personal communication: N. McTiernan). erosion by water is a common problem associated with potato Metribuzin production on the rolling topography of this area (Chow et al. Accordingto the HerbicideHandbook(WSSA 1989),metribuzin 1990). However, in this study, attention was focused on the is a triazine compound used as a selective, pre- and postemerg quantity and quality of water passing through the root zone ence herbicide. Oral LD50 (male rat) is2200 mg-kg"1; solubility rather than surface runoff. in water (20°C) is 1220 mg«L_1. Metribuzin isreadily leached Water sample collection and analysis in sandy soils low in organic matter content, but leaching Water samples were collected manually in 1.14 L pre-washed potential is reduced on finer textured soils. Half-life at normal green glass bottles, according to procedures established by use rates is about 30 to 60 days during the growing season. Environment Canada, Water Quality Branch, Moncton, NB. Minimum half-life under field conditions is 7 to 28 days. Samples were collected in the spring prior to pesticide appli Persistence is increased by cool temperatures and/or low soil cation, after pesticide application, and after crop removal. moisture conditions. Samples were analyzed by the Environment Canada Water

198 MILBURN, O'NEILL, GARTLEY, POLLOCK, RICHARDS and BAILEY Fig, 1. Location of on-farm studysites in northwestern New Brunswick.

programming. Metribuzin was quantified using aninternally millimeters modified method that used an XAD-4 resin column for extrac 200 tion, with elution by ethyl acetate (Personal communication; -— Current -B_ Normal Values J. Doull, Organic Chemist, Water Quality Branch, Analytical

150 _ Services Division, Environment Canada, Moncton, NB). Quantification initially wason packed column gas chromatog raphy with nitrogen-phosphorus detection. This was 100 subsequently changed in mid-1987 to capillary column chro- matograph (Lee and Stokker 1986) with a resultant lowering 50 ofthe detection limit. Results from laboratory quality assurance/quality control

0 procedures indicated dinoseb and metribuzin recoveries from A M J J A S 0 N DJ F MA M JJ A S 0 N spiked samples of 73% (n=5; SD=14.5) and 110% (n=2, Current 50 75 115 99 89 115\04 I2G 85 114 41 46 73 55 I0S 97 I6£ 71 90ioe SD=10), respectively. Detection limits for dinoseb and Normal Values 69 74 88 111 11711087 83 91 79 71 73 69 74 88 111 117110 87 83 metribuzin were determined to be 0.02 and 0.01 jig«L* , re April 87 to November 88 spectively. Fig. 2. Monthly precipitation totals for the Environment Because pesticide analysis is both expensive andtime con Canada weather station at Grand Falls, April suming, there wasa limitin thenumber of samples that could 1987 to November 1988. (Normals taken from be processed. Samples were collected approximately every Environment Canada (1982), Table 3.) four hours during selected flow events rather than at a long, constant time interval throughout the data collection season. Quality Laboratory in Moncton, NB. Analysis was conducted Due to variations in precipitation patterns among sites, the for the parent compounds only. Dinoseb was extracted using manual sampling constraint, and other sampling difficulties an in situ acetylation (Stokker 1987) and quantified using (i.e. travel, site access) it was not possible to consistently capillary column gas chromatography and electron capture sample major flow eventsonly.Therefore amixture of lowand detection. The method is similar to die clorophenol method of high flow events were sampled. Lee et al. (1984). Dinoseb acetate was quantified using SPB- 5-30 m and SPB-608-30 m capillary columns and temperature

CANADIAN AGRICULTURAL ENGINEERING 199 Table I. Some soil characterisltics an<1 total drauiage system discharges at the\ study sites (adaptea trc>m MUDurn ei ai. 1990).

Total drainage Average Particle size Depth to system discharge§ surface distribution:): compact Ogranic Canadian Apr. 1 to Dec. 1 slope Soil Sand Silt Clay layer t carbon t classification 1987 1988 Site no. (%) series! - (g-kg"1) - (cm) (g-kg-1) systemf (mm)

A 2 Siegas 260 560 180 30-60 29 Podzolic Gray Luvisol 105 103 B 4 Holmesville 440 430 130 30-60 19 Orthic Humo-Ferric Podzol C 5 Holmesville 410 490 100 30-60 23 Orthic Humo-Ferric Podzol 68 145

D 5 Holmesville - - 30-60 - Orthic Humo-Ferric Podzol 103 212 E 3 Carleton 350 500 150 30-100 33 Orthic Humo-Ferric Podzol 33 45

fRefer Fahmy et. al. (1986). t0-15 cm depth; average ofeight field samples. Organic carbondetermined by method 84-013 of Sheldrick (1984). §Due to freezing temperatures and site access difficulties, durationofdraindischargemonitoring was not the same for all sites.

RESULTS AND DISCUSSION ple, site D had the greatest history of dinoseb use, both as a Dinoseb herbicideand topkiller for 5 consecutive years, 1982 to 1986 Fourofthe five study sites had a history ofdinoseb use, either (Table II). When pre-emergent herbicide only was applied to as a pre-emergent herbicide, a topkiller (desiccant), or both site D in 1987, dinoseb concentrations of the tile outflow 12 (TableII). Table III summarizesthe rangeofdinosebconcen months later were less than the detection limit. This was trations measuredin tile drainage outflows over the courseof similar totheresponses of site C in 1986 and 1987 when only the study (April 1987to April 1989). Dinoseb was not detected a herbicide and a topkiller, respectively, were applied each in thetile drainage outflowof sitesA orE (Table III); dinoseb year. The past intensity ofdinoseb use at site C was consider wasnot applied at siteE, andwas applied only once(1985) at ably less than at site D (Table II). site A during the seven years of record (TableII). For site-years in which both a herbicide and topkiller was The six site-years of the study during which dinoseb was applied(Table IV), dinoseb persisted in the tile outflow for 18 applied are grouped inTable IV according todinoseb use (e.g. months at site B (1986) compared to 12 months at site D herbicide only),together with observed persistence of dinoseb (1986). However, the averageconcentrationat site B after 12 in the drain outflow. Four of the six site-years had dinoseb months was still rather low, 0.21 \ig*L~l. Data collection did concentrations in the tile outflow less than the detection limit notcontinue longenough atsiteB (1988) to provide results 12 12 months after application, regardless of use (herbicide, months following application. The higher average concentra topkiller, orboth)orhistory of dinoseb application. For exam tionat siteB (1988) after8 monthscompared to theothertwo

Tablen. Crop rotationand recordof dinoseb application at field sites.

Dinoseb application^: Subdrained

area Crop rotation t Site (ha) 1982-^1988 1982 1983 1984 1985 1986 1987 1988

A 10.4 g, g-b, g-b, p-b, b, p, ps hb B 2.6 p, o, h, p, p, fr, fr-p hb hb hb hb(5.6)§ t t t t(5.6)H C 7.7 p, p, o, h, p, p, b hb hb hb t(H) D 7.3 P» P» P. P. P. P. b hb hb hb hb bh hb(4.5) t t t t t E 3.1 h, h, p, w, h, h, p

tb =barley; fr =fall rye; g=pasture; h=hay; o=oats; p=potatoes; ps =peas; w=wheat thb =pre-emergent herbicide; t=topkiller. Recommended application rates were reported for the period 1982-1986. These are: hb, 9.2-12.5 L-ha'1; t, 5.6-8.4 L-ha'1. Actual product application rates given in brackets for 1987,1988. Blank spaces indicate no dinoseb application thatyear. §Applied onlyto potato crop, which occupied approximately one-half the drained area. ^Applied 5.6 L»ha" oneach of three separate occassions: Aug. 18, 24,31.

200 MLBURN, O'NEILL, GARTLEY, POLLOCK,RICHARDS andBAILEY TableHI. Rangeof dinoseb concentrations measured in tile drain outflow.

Dinoseb concentration (WS-L-1)

No. 1987 1988 1989 Samples Site collected Springt Summer-Fall Springt Summer-Fall Springt

A 35 LD* LD B 42 0.83-1.10 0.14-0.23 LD-0.12 0.23-3.10 1.00-5.10 C 57 0.11-0.14 LD-44.00 LD-0.96 LD LD D 38 0.17-0.20 LD-0.57 LD-0.07 LD-0.20 LD E 21 LD LD LD tApriltoMay, prior toplanting. Concentrations in this column indicate dinoseb carry- over from theprevious year(s); refer Table II for record ofdinoseb use. tLess than rninimum detection limit (0.02 fig-L"1). sites was probably due to the high rate of topkiller applied, of tile outflow exiting the potato portion of the field only may which was about double the maximum recommended rate have been double that measured at the drainage system outlet. (Table II). Since dinoseb was applied to only approximately An example of dinoseb concentrations in relation to the one-half of the drained area (footnote, Table II), measured drainage system discharge hydrograph is shown in Fig. 3 dinoseb concentrations would have been diluted by drainage Dinoseb was applied as a topkiller at site C on day 246 (Fig. water from the untreated part ofthe field. Assuming that water la). The first drainage event following application began on movement to the tile lines is uniform over the entire area day 255. The first concentration datum point of44 WJ»L" on served by the drainage system, actual dinoseb concentrations day 256 was originally assumed to be in error because it was

(44)

10-, T •-• CONCENTRATION 2 DINOSEB APPLIED — DISCHARGE DAY 246 5- 1- M

0-1 0 i i i i 1 I 1 n[n l ' ' ' I ' ' ' 1 ' ' ' 1 88 92 96 255 259 % 263 267 271 (Sept16) (Mor.28) 1988 JULIAN DAY 1987 o)

10 10-, 3 E - 2-| Z DINOSEB APPLIED o DAY 158 LJ 5- O 5 H

O o-i i i | i i t^ O •4V z 178 . 182x 186 o 8 (July 1) 1987 b)

10-, DIN0SEB APPLIED 2- DAY 158

5- 1-

T^P 1 I ' 87 91 95 . 183 % 187 (Mor.31) (July 1) 1988 c) Fig. 3 Examples ofconcurrent tile outflow rate and dinoseb concentration: a) first drainage event following topkiller application at site C, and during spring melt period the following year, b) first drainage event following pre-emergent weed control application at site D, and later the same crop year; c) before and following pre-emergent weed control application at site B.

CANADIAN AGRICULTURAL ENGINEERING 201 Table IV. Average dinoseb concentrations oftile outflow at selected times following application.

t Average concentreition (jXg'L"1)

Site-year 8 months 10 months 12 months 18 months

herbicide onlyt C(86) 0.13 (2S) LD(4S) D(87) 0.04 (6m) LD(2m) herbicide + topkillers§ B(86) 0.95 (28) 0.21 (4S) LD(4s) D(86) 0.18 (8S) LD(8m) B(88) 3.06 (6S) topkiller only§ C(87) 0.37 (10m) LD(12m)

t Average arithmetic concentration ofsamples collected within 1 month ofthe elapsed time indicated. Quantity in brackets indicates the number of samples available for the calculation;the subcript indicates whether the samples were collected during a single (s) drainageevent or more (m) than one drainageevent. Li the case of LD (less than detection; 0.02 \igmL~ ), all of the samples had concentrations less than the detection limit t Elapsed time sinceapplication calculated from June 1,the approximate time of pre-emergentherbicideapplication, ± 1month. § Elapsed time calculated from September 1,the aproximate time of topkiller application, ± 1 month. substantially greaterthan any other measuredduringthe study time of application. (Table III). However, analysis of the original sample by the Figure 3b shows concentrations of dinoseb in drainage NationalWater Quality Laboratory (CCIW,Burlington, ON) water at site D for the first drainage event following herbicide indicated that the first analysis was correct. Because only application on day 158. All concentrations were less than 0.6 small volumes of water drained through the soil during this \ig-U . Figure 3c shows small concentrations of dinoseb in period, as evidenced by the hydrograph, and because subse drainage water at site B prior to dinoseb application on day quent measured concentrations to day 279 were between 0.5 158, and concentrations varying from 1.3 to 0.6 \ig*L~l ap and 2.0 ug»L" , we speculated that the high concentration of proximately one month following application. 44 ng«L" was probably the result of preferential or bypass No obvious relation between drain flow rate and dinoseb flow through large soil cracks and biopores directly to a tile concentration of thedrainsystem outflowwasobserved at any line(s). Thisphenomenon has beenobserved by otherinvesti of the sites. This was not surprising since many processes in gators,and usuallyoccurs whena soil is just beginning to wet addition to leaching contribute to the breakdown of pesticides up,priorto saturationand onsetof uniform porousmediaflow [i.e. adsorption, microbial decomposition, photodecomposi- within thesoil(Coles andTrudgill 1985; Hallberg 1986; Rich tion, volatilization, chemical degradation (Wagenet and Rao ard and Steenhuis 1988). Drainage had not occurred at site C 1985; Ritter 1986)]. since day 190 (data not shown). Alternatively, it is possible With the exception of the single high concentration mea that theParshall flume wascontaminated by spray driftat the sured at site C in 1987 (44 \ig*L\ dinoseb concentrations

METRIBUZIN APPLIED 15-, l-6-i DAY 150 •-• CONCENTRATION — DISCHARGE I -o E 1

o UJ O z o o o-J 0.0 M i i |—i—i—r |T^i i | i i i' |—i ~i r I ' » « I 219 223 291 295 299 303 307 311 315 (Aug.6) (Nov.2) JULIAN DAY 1988 a) b) Fig. 4. Example of concurrent tileoutflowrateandmetribuzin concentration at site E: a) first drainage event following pre-emergent weed control application; b) later the same crop year.

202 MELBURN, O'NEILL, GARTLEY, POLLOCK, RICHARDS and BAILEY reported in our study were less than the guidance value for 1. Dinoseb and metribuzin concentrations were detected in drinking water provided by Health and Welfare Canada (10 tile outflow both during the yearofapplication andagain the jig-L"), and were of similarmagnitudeto dinoseb concentra following spring. tions ingroundwater oragricultural drainage reported by other 2. Only one sample had a concentration greater than 10 investigators (Wan 1989; Hallberg 1987; Frank et al. 1987b; |ig«L" . Thisconcentration occurred soon afterdinoseb appli N. McTiernan, personal communication). cation during a very low drain outflow condition ( 0.1 Metribuzin mm»d"). One week later, during continued low flow condi tions, concentrations were approximately 1jig'L"1. Metribuzin wasapplied only at site E;once in 1984 andagain 3. Ninety-five percent of the positive dinoseb and in 1988, the same years that the site was planted to potatoes metribuzin samples (minimum detection level) had concentra (Table II). Metribuzin residue from 1984 was not detected in tions less than 2 jig'L"1. the drainage waters at site E during the first yearof the study (1987; 11 samples analyzed). Concentrations in the drainage 4. For the five site-years where sufficient time had elapsed since application to observe the persistence of dinoseb in the water following metribuzin application in 1988 are shown in Fig. 4. Concentrations ranged from 0.06 to 1.53 |ig-L"\ and tile outflow, dinoseb concentrations were less than detection level after 12 months and 18 months for four and one site- were highest during the first drainage event following applica year(s), respectively. In the latter case, average concentration tion on day 150 (Fig. 4a). When data collection ceased in April at 12 months was 0.21 (Xg-L"1 or 2 percent of the maximum 1989, metribuzin concentrations averaged 0.22 Mg*L" (n=4; acceptable limit (MAC) for drinking water. Persistence did not range0.14 to 0.31), which is 0.28% of the MAC published by appear to be affected by use (weed control or topkiller) or Health and Welfare Canada (1987). Our measured metribuzin previous dinoseb application history ofthe site. concentrations are similar to those ofother studies reported in 5. The average metribuzin concentrations in tile outflow ten the literature (Muir and Baker 1976; Hallberg 1986, 1987; Frank et al. 1987a, b). Our result and corresponding months after application was 0.22 ^g-L"1 or 0.28 percent ofthe metribuzin history for site E closely parallel that of Muir and MAC for drinking water. Baker (1976). Background concentrations prior to pesticide 6. There was no obvious relation between tile outflow rate application werelessthan detection limitsin bothstudies, and andpesticideconcentration ofthe tile outflow. peak concentrations were alsoabout thesame(1.6|ig#L").We detected some metribuzin in November ofthe year ofapplica We conclude that dinoseb and metribuzin, when applied at tion, unlikeMuir and Baker, but concentrations were low (Fig. recommended rates, can leach from the crop root zone under 4b). In our study, the metribuzin application rate was greater soil and climate conditions common to potato production in (0.75 compared to 0.56 kg-ha"1) which may partly explain the New Brunswick, and that the concentrations of dinoseb and higher concentrations measured in November. metribuzin measuredin this study are of similar magnitude to those reported in groundwater ortiledrainage studies inother Total losses areas of Canada and the USA. Future studies under more Theaverage April-to-November cumulative drainage outflow controlled conditions are required to determine the fate of of the five study sites during the two years of outflow rate pesticides leaching from the plantroot zone. measurement wasapproximately 100mm (Table I). Assuming this average outflow, anaverage dinoseb and metribuzin out ACKNOWLEDGEMENTS flow concentration of2\ig*L~l, and amaximum recommended Partial funding for this project was provided by theTechnol application rate for each pesticide, estimated total losses intile ogy Subprogram of the Canada-New Brunswick Agri-Food drainage for theApril-to-November period were 0.06 and 0.3 Development Agreement (1984-1989). Appreciation is ex percent of the dinoseb and metribuzin applied, respectively. pressed to Mr. Gordon Walker and Mr. George Read of the Year round measurement of concurrent tile outflow rate and New Brunswick Department of Agriculture, Fredericton, for outflow pesticide concentration are required to determine pre theirassistancein graphicalpresentation. ciselyannual pesticide lossesin tile drainage. REFERENCES SUMMARY AND CONCLUSIONS ADVISORY COMMITTEE on POTATOES. 1986. Potato To determine if dinoseb and metribuzin were leaching from crop variety, weed, and pestcontrol recommendations for the thecrop rootzone under soilandclimate conditions common Atlantic Provinces. Publication 300A. Published by authority to New Brunswick's"potatobelt", we collectedandanalyzed of the Atlantic Provinces Agricultural ServicesCo-ordinating 232 tilewater samples overatwo year period from five3 to 10 Committee. 8 p. Available from the New Brunswick Depart hatile-drained potato fields. Collectively, these sitescovered ment of Agriculture, P.O. Box 6000, Fredericton, NB. approximately 30 haandencompassed variations in soiltype, topography, crop management, and climate conditions. Four ASIEDU, S., S.E. COLEMAN, T. HALIBURTON and M.C. sites had a history of dinoseb application; more dinoseb was HAMPSON(eds.). 1987.Atlantic Canada Potato Guide.Pub applied to three of theseduring the study.Metribuzin hadbeen lication 1300/87. Published by authority of the Atlantic previously applied to the fifth site, and more was applied Provinces Agricultural Services Co-ordinating Committee. 47 during the study. Of the 232 samples collected, 126 had con p.Available from theNew Brunswick Department of Agricul centrations greater than the minimum detection limit (102 and ture, P.O. Box 6000, Fredericton, NB. 24 samples for dinoseb and metribuzin, respectively). CAPCO. 1989. Dinoseb-update. CAPCO Note 89-06. Cana We observed that: dian Association of Pesticide Control Officials. Published by

CANADIAN AGRICULTURAL ENGINEERING 203 Pesticides Directorate, Agriculture Canada, Ottawa, ON. LEE, L.K. andE.G. NIELSEN. 1987. The extent andcost of groundwater contamination by agriculture. J. Soil Water Con- CHOW, T.L., J.L. DAIGLE, I. GHANEM andH. CORMIER. 1990. Effectsof potato cropping practices onwater runoffand serv. 42(4):243-248. soil erosion. Can. J. Soil Sci. 70:137-148. MILBURN, P., J.E. RICHARDS, C. GARTLEY, T. POL LACK, H. O'NEILL and H. BAILEY. 1990.Nitrateleaching COHEN, S.Z., C. EIDEN, and M.N. LORBER. 1986. Moni toring groundwater for pesticides. In: Garner, W.Y. et al. from systematically tiled potato fields in New Brunswick, (eds.), Evaluation of pesticidesin groundwater, 170-196. Am. Canada. J. Environ. Qual. 19(3):448-454. Chem. Soc. Symposium Ser. 315. MUIR, D.C. and B.E. BAKER. 1976. Detection of triazine COLES, N. and S. TRUDGILL. 1985. The movement of ni herbicides and their degradation products in tile-drain water trate fertilizer from the soil surface to drainage waters by from fields under intensive corn (maize) production. J. Agric. preferential flow in weakly structuredsoils, Slapton, S. Devon. Food Chem. 24:122-125. Agric. Ecosyst. Environ. 13: 241-259. O'NEILL, H.J., T.L. POLLOCK, H.S. BAILEY, P. ECOBICHON, D.J., R. HICKS, M.C. ALLEN and R. AL MILBURN, J.E. RICHARDS and C. GARTLEY. 1989. BERT. 1988. Groundwater contamination in rural New Dinoseb presence in agricultural subsurface drainage from Brunswick. Unpublished report. New Brunswick Department potato fields in north western New Brunswick. Bull. Environ. of Health and Community Services, P.O. Box 5100, Frederic Contam. Toxicol. 43:935-940. ton, NB. 14 p. PIERCE, R.C. and M.P. WONG. 1988. Pesticides in agricul ENVIRONMENT CANADA. 1982. Canadian climate nor tural waters: The role of water quality guidelines. Can. Wat. mals 1951-1980. Atmospheric Environment Service, 4905 Res.J. 13(3):33-49. Dufferin St., Downsview, ON. 602 pp. PIMENTEL, D. and L. LEVITAN. 1986. Pesticides: Amounts FAHMY, S.H., H.W. REES, and J.K. MACMBLLAN. 1986. applied and amounts reaching pests. Bioscience 36(2):86-91. Soils of New Brunswick: A first approximation. New Bruns PRIDDLE, M.W., R.E. JACKSON and J.P. MUTCH. 1989. wick Departmentof Agriculture,Fredericton, NB. 105 p. Contamination of the sandstone aquifer of Prince Edward FAIRCHILD, D.M. (ed.). 1988. Groundwater quality andag Island, Canada by aldicarb and nitrogen residues. Ground ricultural practices. Lewis Publishers, Chelsea, MI.402 p. Water Monit. Rev. 9:134-140. FRANK, R., B.S. CLEGG, B.D. RIPLEY and H.E. BRAUN. RICHARD, T.L. and T.S. STEENHUIS. 1988. Tile drain sam 1987a. Investigations of pesticide contaminations in rural pling of preferential flow on a field scale. J. Contam. Hydrol. wells, 1979-1984, Ontario, Canada. Arch. Environ. Contam. 3:307-325. Toxicol. 16:9-22. RITTER,W.F. 1986. Pesticide contamination of groundwater FRANK, R., B.D. RIPLEY, H.E. BRAUN, B.S. CLEGG, R. - a review. Paper No. 86-2028. Am. Soc. Agr. Engrs., St. JOHNSTON andT.J. O'NEILL. 1987b. Survey of farm wells Joseph, MI. for pesticides residues, southern Ontario, Canada, 1981-1982, SHELDRICK, B.H. 1984. Analytical methods manual 1984. 1984. Arch. Environ. Contam. Toxicol. 16:1-8. Land Resource Research Institute contribution 84-30. Re HALLBERG, G.R. 1986. Overviewof agricultural chemicals search Branch, Agriculture Canada, Ottawa, ON. in groundwater, p. 1-63. In: Proceedings of the Agricultural STOKKER, Y.D. 1987. Method for theanalysis of dinoseb in Impacts on Groundwater: A Conference. August 1986, natural waters by in situ acetylation. NWRI Contribution 87- Omaha, NE. National Water Well Association, Dublin, OH. 61. Canada Centre for Inland Waters, Burlington, ON. HALLBERG, G.R. 1987. The impacts of agricultural chemi USEPA. 1988. Pesticide fact handbook. Noyes Data Corpora calson groundwater quality.Geo. J. 15:283-296. tion, Park Ridge, NJ. 827 p. HEALTH and WELFARE CANADA. 1987. Guidelines for VON STRYK, F.G. and E.F. BOLTON. 1977. Atrazine resi Canadian drinking water quality. Prepared bytheFederal-Pro dues intile drain water from corn plots as affected bycropping vincial Subcommittee on Drinking Water. Published by practices and fertility levels. Can. J. Soil Sci. 57:249-253. authority of the Minister of National Health and Welfare. Canadian Government Publishing Centre, Supply and Ser WAGENET, R.J. and P.S.C. RAO. 1985. Basic concepts of vicesCanada, Ottawa, ON. 20 p. modeling pesticide fate in the crop root zone. Weed Science 33 (Supplement 2):25-32. IVANY, J.A., J.M. SADLER, and E.R. KIMBALL. 1983. WAN, M.T. 1989. Levels of selectedpesticides in farm ditches Rate of metribuzin breakdown and residue effects on rotation crops. Can. J. Plant Sci. 63:481-487. leading to rivers in the lower mainland of British Columbia. J. Environ. Sci. Health B24(2): 183-203. LEE, H.-B., L.-D. WENG and A.S.Y. CHAU. 1984. Chemical derivatization analysis of pesticide residues. VIII. Analysis of WHITE, F.M.M., F.G. COHEN, G. SHERMAN, and R. 15 chlorophenols in natural water by in situ acetylation. J. MCCURDY. 1988. Chemicals, birth defects, and stillbirths in Assoc. Official Analytical Chemists 67(4):789-794. New Brunswick: Associations with agricultural activity. Can. Med. Assoc. J. 138:117-124. LEE, H.-B. and Y.D. STOKKER. 1986. Analysis of eleven triazines innatural waters. J.Assoc. Official Analytical Chem WSSA. 1989. Herbicidehandbook, sixth edition. Weed Science ists 69(4):568-572. Society of America, 309West Clark Street, Champaign, IL.

204 MILBURN, O'NEILL, GARTLEY, POLLOCK, RICHARDS and BAILEY