Pesticides in the Red River and its Tributaries in Southern Manitoba ...

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188 RAWN ET AL. mined at the Emerson sampling station and at two additional stations; Ste. Agathe, which is in the centre of the agricultural area, and Selkirk, which is downstream of the City of Winnipeg (Fig. 1). Sample Collection Materials and Methods River water samples were collected from seven tributaries of the Red River and three sites along the Red River (Fig. 1). Water (18 L) was collected by lowering a submersible pump into the centre of channel flow and pumping into stainless steel soft drink cans. Rivers were sampled every three weeks during the first year of the study, which began in June 1993. Samples were collected on a biweekly schedule from spring through freeze-up during 1994 and 1995. Samples were sealed and transported to the lab where they were stored at 4OC until processed. Prior to extraction, water samples were filtered under pressure using precleaned GFA filters (1 pm). One-litre water samples were collected for water chemistry para- meters, including total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP) and pH, by lowering a weighted sample bottle into the centre of stream flow. Sample Extraction and Cleanup Dissolved pesticides were extracted using a broad spectrum approach for both acidic and neutral compounds (e.g., 2,4-D and atrazine). Water samples were adjusted to pH 2 using sulphuric acid and mixed with dichloromethane (DCM) to extract acid herbicides, followed by adjustment to pH 10 using 10 M NaOH, to extract the hydrophobic organics (e.g., polychlorinated biphenyls [PCBs]). Sample extracts were evaporated to a small volume and methylated using freshly prepared dia- zomethane. Extracts were cleaned up using 5% deactivated Florisil, elut- ing with 20 mL hexane to remove PCBs, followed by 85 mL, 18% ethyl acetate (EtAc) in hexane to elute the acid and phenolic herbicides (methyl derivatives). Sample Analysis Sample extracts were analyzed by gas chromatography-mass spec- trometry (selected ion monitoring) (Hewlett Packard 5971 MSD) using a 60 m x 0.25 pm DB-5 column with helium as the carrier gas. Detection cri- teria were the correct ratios of two characteristic ions and retention times. Herbicides were quantified using external standard solutions and corrected for volume changes with PCB-104. Blanks of "Super Q" water were analyzed with each batch of samples. Average spike recoveries of tripli- cate analyses at both 10 ng/L and 100 ng/L for 18-L volumes and detection limits are reported in Table 2. All pesticides with
PESTICIDES IN THE RED RIVER 189 lated using instrument detection limits plus three times the standard deviation of the lowest concentration analysis (Keith 1991). TOC, TN and TP loadings in each river system were measured following standard col- orimetric techniques for nutrient analysis (Environment Canada 1997). Pesticide Use Estimates Pesticide application data were provided by Manitoba Agriculture for each year of the study for all municipalities in the six smaller watersheds (Manitoba Agriculture unpublished data). Landuse data were available for southern Manitoba through the Canadian census (Statistics Canada 1996). The area treated with each pesticide on a municipality basis was overlaid on watershed boundaries (Manitoba Natural Resources 1967) to estimate the pesticide-treated area within each watershed. Based on this area, an estimate of the amount of pesticides used (kg) was calculated using products commonly applied to regional crops and assuming recommended application rates. A pesticide use estimate was not performed for the Assiniboine River watershed because the watershed basin extends into Saskatchewan and pesticide use data for the entire watershed were not available (Fig. 1). Loading Estimates Loadings of six major chemicals from the watersheds under investigation were calculated for both the 1994 and 1995 field years. For purpos- es of loading calculation, MCPA, 2,4-D and bromoxynil concentrations were corrected for recovery efficiency. Loading was calculated as the product of herbicide concentration and discharge for each day (Larson et al. 1995). Herbicide concentrations were estimated by linear interpolation for days when sampling was not performed and concentrations below detection limits were assigned a value of zero (Larson et al. 1995) in all loading calculations. The daily loading values were summed for the sam- pliig season (March to end of October) to give the total seasonal loading values. Results Pesticide and Nutrient Concentrations Sixteen pesticides were frequently detected in waters of the Red River and its tributaries in southern Manitoba (Table 3). Pesticide concentrations were not correlated to discharge in any of the rivers under investigation in this study. Significant correlations between MCPA and bromoxynil (r2=0.25-0.93; p-values 0.01-
Page 1 and 2: Water Qual. Res. 1. Canada, 1999 Vo
Page 3 and 4: PESTICIDES IN THE RED RIVER 185 lon
Page 5: PFSTICIDES IN THE RED RIVER 187 Tab
Page 9 and 10: 0 ~ m o + h m ~ o m + o m m a m + m
Page 11 and 12: Table 3. (continued) Triallate Tric
Page 13 and 14: Table 3. (continued) 2,4-D Dichlorp
Page 15 and 16: Red River at Selkirk N=33 Alachlor
Page 17 and 18: PESTICIDES IN THE RED RIVER 199 Wit
Page 19 and 20: 2001 Red at Ste. Agathe PESTICIDES
Page 21 and 22: 20 1994 - GAtrazine l4 -- 0 Chlorpy
Page 23 and 24: PE~~ICIDES IN THE RED RIVER 205 Tab
Page 25 and 26: PESTICIDES N THE RED RIVER 207 area
Page 27 and 28: &blc 7. Seasonal discharge (m3) of
Page 29 and 30: Dakota and Minnesota, in the southe
Page 31 and 32: atrazine's greater persistence in s
Page 33 and 34: PESTICIDES IN THE RED RIVER 215 chl
Page 35 and 36: PESTICIDES IN THE RED RIVER 217 Win
Page 37: PFSTICIDES IN THE RED RIVER 219 Env

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