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What Is This Indicator, and Why Is It Important? This indicator reports on pesticides found in farmland streams and groundwater. The graphs on the top show the average number of pesticides detected throughout the year in streams and shallow groundwater wells. The graphs on the bottom show the percentage of streams and shallow groundwater wells with pesticide concentrations that exceeded standards and guidelines (benchmarks) set for the protection of human health or aquatic life. These graphs report currently used agricultural pesticides and selected breakdown products of these pesticides, as well as selected organochlorine insecticides that were widely used in the past but whose use is no longer permitted in the United States. The number of pesticides detected is important, but the presence of pesticides does not necessarily mean that the levels are high enough to cause problems. Comparison with benchmarks provides a useful reference to help judge the significance of contamination. However, drinking water standards or guidelines do not exist for 33 of the 76 pesticides analyzed, and aquatic life guidelines do not exist for 48 of the 76 compounds. Current benchmarks do not account for mixtures of chemicals and seasonal events involving high concentrations. In addition, potential effects on the reproductive, nervous, and immune systems, as well as on particularly sensitive people, are not yet well understood. What Do the Data Show? All monitored streams in farmland areas had at least one pesticide at detectable levels throughout the year, and about 75% had an average of five or more. Eighty-three percent of streams had at least one pesticide whose concentration exceeded aquatic life guidelines; about 4% had one or more compounds that exceeded human health standards or guidelines. About 60% of groundwater wells in farmland areas had at least one pesticide at detectable levels, and less than 1% had any pesticides that exceeded human health standards or guidelines. |
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