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USGS Fact Sheet 067-97:
Pesticides in Selected Small Streams
in the Puget Sound Basin, 1987-1995

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Pesticides Detected in Streambed Sediments

Of the total number of compounds detected in streambed sediments, most were insecticides or insecticide degradation products. Six of the nine pesticides detected in streambed sediments were insecticides (or their degradation products), two were herbicides, and one a fungicide. The most frequently detected compounds in sediments, found in both urban and agricultural streams, were PCP, detected in five streams, and DDT and/or its degradation products DDD and DDE, detected in three streams. Chlordane was also detected in sediments. DDT, PCP, and chlordane are currently banned from use in the U. S., but were heavily used in the past. Because of their slow degradation rates, these pesticides are likely to be present in sediments for many years. DDT was used as an insecticide; PCP was used primarily as a fungicide, but also as an insecticide and herbicide. Other pesticides found in bed sediments from at least two streams were the herbicides dichlobenil and dicamba. The insecticides chlordane, diazinon, and endosulfan were identified in one stream each. The graph below shows that nine compounds were detected at concentrations either as estimated or quantifiable values. Pesticides in bed sediments do not have any State freshwater sediment-quality criteria, but USEPA guidelines to protect benthic organisms are proposed for DDT, chlordane, and endosulfan in bed sediments (Nowell and Resek, 1994). These guidelines, which are based on the amount of organic carbon in the sediments, do not apply to concentrations shown in the graph.

[Graph of concentrations of pesticides detected inbed sediment]
Click here for a graph of concentrations
of pesticides detected in bed sediment

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