Surface waters such as streams and lakes tend to have higher pesticide concentrations than groundwater -- in other studies, the USGS detected one or more pesticides in 90 percent of urban, agricultural or mixed-use streams tested -- but the amounts fluctuate more; pesticides get flushed off of croplands in rainfall and then are gone. "If it does get into groundwater, it's probably not going to go away for quite a while," Bexfield said. "The big deal is once the groundwater is contaminated, it's a long-term contamination," agreed Paul Capel of the USGS and the University of Minnesota, Twin Cities. "The occurrence of any of them is an indication that there is something going on and we should pay attention before we screw up the resource. Generally, in terms of immediate health concerns, it's not a big concern because the concentrations are so low." The vast majority of concentrations found by the scientists don't reach dangerous levels for drinking water, Bexfield added. A previous USGS survey found that about one percent of wells studied exceeded human health benchmarks for pesticides derived from Environmental Protection Agency guidelines. Related Links: National Water Quality Assessment Program "Pesticides in the Nation's Streams and Groundwater, 1992-2001 |
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