Abstract-Farm ponds or dugout waters were monitored for residues of seven major herbicides used in the Canadian prairies from fall of 1987 to spring of 1989. The frequencies of confirmed detection of herbicides in water samples, depending on the time of sampling, in decreasing order were: 2,4-dichlorophenoxyacetic acid (2,4-D; 93-100%), diclofop (46-95%), bromoxynil (50-85%), 4-chloro-2-methyl-phenoxyacetic acid (MCPA; 33-70%), triallate (28-63%), dicamba (17-55%), and trifluralin (0-18%). The corresponding frequencies of quantifiable residues (Ն0.05 g/L) were lower, ranging from 75 to 86% for 2,4-D to 0 to 7% for dicamba. Median residues in all water samples were near or below the quantification limits of 0.05 g/L. Maximum residues varied widely and were (g/L): trifluralin (not detectable [ND]-0.11), bromoxynil (0.27-0.33), dicamba (ND-11.2), triallate (0.05-0.87), MCPA (0.12-1.97), 2,4-D (0.64-2.67), and diclofop (0.27-3.47). Maximum residues were seasonal and declined to near or below detection limits by the following sampling time. Median values were two to three orders of magnitude less than the corresponding maximum allowable concentration and interim maximum allowable concentration guidelines for drinking water in Canada and the United States. Maximum values were also less than these guidelines. Only the maximum values for residues of MCPA and 2,4-D approached the guidelines for these herbicides in water used for irrigation.

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The movement of several pesticides was studied from 1985 to 1987 in a small, agricultural watershed The watershed contained a distinct, ephemeral stream bed and two permanent, small reservoirs The five herbicides measured −2,4 dichlorophenoxyacetic acid (2,4 D), dicamba, bromoxynil, diclofop‐methyl, and triallate – were those most commonly used in the watershed Of the 105 collected ground water samples 47% contained residues of one or more herbicides Residues in surface water samples were less frequent, and concentrations were lower than those in ground water All spring snowmelt runoff samples were collected in 1985 and 1987 and contained some pesticide residues The significance of these findings will be discussed and related to potential environmental toxicological effects Severe grasshopper infestations in 1985 and 1986 resulted in insecticide treatments in the study area Water samples were tested for the insecticides carbofuran, carbaryl, chlorpyrifos, dimethoate, and deltamethrin Three samples of spring runoff, collected from one site in 1987, contained approximately 1 ppb carbofuran All other samples were less than the detection levels

Herbicides are the most commonly used group of agricultural pesticides on the Canadian Prairies and, in 1990, more than 20000 Mg of herbicides were applied in the provinces of Alberta, Saskatchewan, and Manitoba. The present paper reports on environmental concentrations of five herbicides currently used in the prairie region. The herbicides bromoxynil [3,5-dibromo-4-hydroxy-benzonitrile], dicamba [3,6-dichloro-o-anisic acid], diclofop [(RS)-2-[4-(2,4-dichlorophenoxy)-phenoxy]propanoic acid], MCPA [(4-chloro-2-methylphenoxy)acetic acid], and trifluralin [alpha,alpha,alpha-trifluoro-2,6-dinitro-N,N-isopropyl-p-toluidine] were measured in the atmosphere, bulk atmospheric deposits, surface film, and dugout (pond) water at two sites near Regina, Saskatchewan, during 1989 and 1990. All five herbicides were detected in air and surface film and all but trifluralin were detected in the bulk atmospheric deposits and dugout water. Trifluralin was most frequently detected in air (79% of samples) whereas bromoxynil was present in maximum concentration (4.2 ng m(-3)). MCPA was present in maximum levels in bulk atmospheric (wet plus dry) deposits (2350 ng m(-2) d(-1)), surface film (390 ng m(-2)), and dugout water (330 ng L(-1)), whereas dicamba was most frequently detected in surface film (47%) and dugout water (97%). The highest quantities of the herbicides tended to be present during or immediately after the time of regional application.