Water-quality assessment of the White River Basin, Indiana: Analysis of available information on pesticides, 1972-92

An analysis of historical pesticide data (1972-92) for the White River was conducted as part of the U.S. Geological Survey National Water-Quality Assessment Program. Data on the presence of pesticides in streams, bottom sediments, fish, and ground waters were examined. Results are interpreted with respect to spatial, seasonal, and streamflow effects. Concentrations of water-soluble pesticides reach a peak during the first storm following application and remain elevated for 1 to 2 months. The most herbicide loading to the White River occurs during this time, when about 1 percent of the applied herbicides are transported out of the White River Basin. Bottom sediments and fish were analyzed for lipophilic pesticides. Dieldrin, components of technical chlordane, and DDT-related compounds were the most frequently detected. In areas where pesticide concentrations in sediment were high, concentrations in fish were high, indicating that bottom sediments are probably the primary source of lipophilic pesticides in aquatic biota. Ground- water/surface-water interaction and the presence of pesticides in ground waters were examined. The bedrock karst region had the highest degree of ground-water/surface-water interaction, indicating that the shallow ground water is susceptible to contamination from surface sources. Atrazine was the most frequently detected pesticides in ground waters. All wells where pesticides were detected are in karst or alluvial outwash, indicating that these geomorphic units are highly susceptible to contamination.