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Distribution, Trends, and Governing Factors

Lisa H. Nowell, Paul D. Capel, and Peter D. Dileanis


More than 400 monitoring studies and 140 review articles published from 1960 to 1993 were reviewed to assess pesticide contamination in bed sediment and aquatic biota of United States rivers and streams. The studies reviewed included reports from five major national programs that monitored pesticides in river or estuarine sediment, fish, or mollusks. The individual studies reviewed differed substantially in objectives, study design, and analytical methods. Forty-one pesticides or their metabolites were detected in sediment and 68 in aquatic biota, representing 44 percent of those pesticides targeted in sediment and 64 percent of those targeted in biota. Most of the pesticides detected were organochlorine insecticides or their metabolites. This reflects the hydrophobicity and persistence of this class of pesticides, as well as bias in the target analyte list. The studies reviewed rarely analyzed for any pesticides other than organochlorine insecticides in bed sediment and aquatic biota. Of these other pesticides, a number of moderately hydrophobic, moderately persistent ones were detected, although at lower frequencies than the more persistent organochlorine insecticides. These moderate pesticides have water solubilities of 0.05 to 1 mg/L and estimated soil half-lives of 30 to 150 days. Examples of these moderate pesticides include the insecticides chlorpyrifos, carbofuran, and diazinon; and the herbicides 2,4-D, dacthal, oxadiazon, and trifluralin.

Pesticide detection frequencies and concentrations reflect a combination of historical agricultural use, water solubility, environmental persistence, and analytical detection limits. In some studies, a few compounds were associated with land uses other than agriculture. These compounds include chlordane (urban and industrial use), mirex (red fire ant control and manufacturing inputs), and lindane and a-HCH (Superfund and industrial sites).

Existing data are adequate to assess nationwide trends for a number of organochlorine insecticides in freshwater fish, but not in bed sediment. For example, residues of DDT, chlordane, dieldrin, endrin, lindane, and a-HCH in freshwater fish declined nationally during the 1970s, then appeared to level off during the early 1980s. High concentrations have persisted in some local areas. Toxaphene residues in fish declined nationally during the early 1980s. The available data on currently used pesticides are not sufficient for assessment of trends in either bed sediment or aquatic biota.

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