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Herbicide Concentrations in Select Waterfowl Production Area Wetlands in West Central Minnesota, 1993

Twenty-eight emergent, seasonally to semipermanently flooded wetlands in an intensively farmed area of west central Minnesota were sampled before and during the 1993 crop growing season to determine surface water concentrations of widely used herbicides.

Specifically, water obtained from eight isolated Waterfowl Production Area (WPA) wetlands ("reference") and twenty co-owned WPA wetlands ("treatments") (bordering agricultural croplands which had high potential for exposure to chemical influences) was analyzed to determine whether, and to what extent, wetland basins both adjacent to, and isolated from, agricultural lands contained measurable concentrations of herbicides. Surface water samples were screened for alachlor and triazine class herbicide types using enzyme-linked immunosorbent (ELISA) assays. Identification of individual herbicides were determined by chemical analyses. Although alachlor and triazine concentrations are no longer used on Service lands, both were found by ELISA detection at concentrations in surface waters from WPA reference wetlands. Chemical analyses failed to detect (when measured) any individual common or acid herbicides in any of the eight reference wetlands. Herbicide occurrence in reference wetlands at the maximum observed concentrations is not known to significantly impact aquatic vegetation or invertebrates. However, while concentrations of these herbicides in reference WPA wetlands were found to be low, timing of increases in their respective concentrations tended to follow trends observed in the treatment WPA wetlands. Such results strongly suggest the existence of aerial drift and/or precipitation deposition of herbicides in "isolated" WPA wetlands. Based on a limited number of samples, it is apparent that some co-owned WPA wetlands can acquire herbicide concentrations which exceed concentrations typically detected in isolated WPA wetlands. Several herbicide concentrations (triazine and alachlor classes, dicamba, bentazon, imazethapyr, atrazine, cyanazine, alachlor) in some wetlands were up to several orders of magnitude higher in co-owned treatment WPA wetlands than concentrations found in isolated WPA reference wetlands. The FY 93 survey maximum alachlor and triazine concentrations derived by ELISA were similar to the FY 92 maximum concentrations found in privately owned wetlands (individual herbicides were not measured in FY 92 survey). Herbicide concentrations in some of the treatment WPA wetlands suggest that concentrations of those herbicides being introduced into WPA wetlands by way of direct runoff from adjacent croplands may be biologically significant. Also, apparent differences in herbicide concentrations occurred within the four WMDs and may reflect geographic climatic, cropping pattern differences, or local biases toward specific herbicides for given crop types or application rates across the district. Lastly, comparisons of ELISA and analytical chemistry determinations of triazine and alachlor-related compounds showed measurement differences at low and high concentrations in some wetlands. Dr. Jim Zajicek (Chemist, Immunochemistry Research Section) of the National Biological Survey reviewed the data and provided an important discussion to explain the discrepancies. His review (provided in Appendix I) will be extremely beneficial in future ELISA studies for the Environmental Contaminants Program of the Service.

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États-Unis d'Amérique
agINFRA The RING is part of the agINFRA project EC 7th framework program INFRA-2011-1.2.2 - Grant agr. no: 283770