Pesticides were found more frequently in streams than in ground water, but concentrations were generally very low in both. Pesticide degradation products were frequently detected as well. One or more of the herbicides atrazine, metolachlor, and simazine were detected in 9 out of 10 streams and 5 out of 10 wells. For many of the pesticides that were found, human-health criteria standards have not yet been set. The information derived from the USGS studies on the occurrence of individual pesticides and the occurrence of mixtures of pesticides and their breakdown products are important to managing pesticide use and understanding how these chemical compounds occur in the Bay watershed.
Fish can accumulate and concentrate contaminants that are very hard to detect in samples of water.
Selected species of fish were collected and analyzed to determine if contaminants were present, not to determine if the fish were safe to eat. USGS methods examined whole fish, not fillets that people eat. Nevertheless, the levels for total chlordane, total DDT, or total PCBs that must be exceeded in the edible portion before consumption advisories are issued were not exceeded in the whole-body tissues at any of the sampling locations. The VOCs detected are present in commonly used industrial solvents and degreasers or are components of gasoline. The good news is that none of the concentrations of the VOCs detected in samples from 129 wells used as drinking-water supplies exceeded the Maximum Contaminant Levels or Lifetime Health Advisory Levels established by the U.S. Environmental Protection Agency.