Comparison of pesticides in eight US urban streams

Little is known of the occurrence of pesticides in urban streams compared t o streams draining agricultural areas. Water samples from eight urban strea ms from across the United States were analyzed for 75 pesticides and seven transformation products. For six of the eight urban streams, paired agricul tural streams were used for comparisons. The herbicides detected most frequ ently in the urban streams were prometon, simazine, atrazine, tebuthiuron, and metolachlor, and the insecticides detected most frequently were diazino n, carbaryl, chlorpyrifos, and malathion. In contrast to similar-sized agri cultural streams, total insecticide concentrations commonly exceeded total herbicide concentrations in these urban streams. In general, the temporal c oncentration patterns in the urban streams were consistent with the charact eristics of the local growing season. The insecticides carbaryl and diazino n exceeded criteria for the protection of aquatic life in many of the urban streams in the spring and summer. When the country as a whole is considere d, the estimated mass of herbicides contributed by urban areas to streams i s dwarfed by the estimated contribution from agricultural areas, but for in secticides, contributions from urban and agricultural areas may be similar. The results of this study suggest that urban areas should not be overlooke d when assessing sources and monitoring the occurrence of pesticides in sur face waters.