National Water-Quality Assessment (NAWQA) Program
Lisa H. Nowell and Peter D. Dileanis, U.S. Geological Survey, Sacramento, California and Paul D. Capel, U.S. Geological Survey, Minneapolis, Minnesota.
More than 400 monitoring studies and 140 review articles (1960's-1992) were reviewed to assess pesticide contamination in sediments and aquatic biota of United States rivers. These include five major national programs that monitored pesticides in river or estuarine sediments, fish, or mollusks. The studies differed substantially in objectives, study design, and analytical methods. Forty-one pesticides or their metabolites were detected in sediments (44% of those targeted) and 68 in aquatic biota (64%). Most of the pesticides detected were organochlorine insecticides or their metabolites. This reflects the hydrophobicity and persistence of these compounds as well as bias in the target analyte list. Relatively few pesticides other than organochlorine insecticides were analyzed; of these, several compounds of intermediate water solubility and hydrophobicity were detected. Examples 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 past agricultural use, water solubility, environmental persistence, and analytical detection limits. A few compounds were associated with land uses other than agriculture in some studies. Examples include chlordane and isopropalin (urban and industrial use), lindane, and aHCH Superfund and industrial sites). Existing data are adequate to assess nationwide trends for many pesticides in freshwater fish, but not in sediments. Nationally, residues of DDT, chlordane, dieldrin, endrin, lindane, and (a-HCH declined during the 1970s then leveled off during the early 1980s. Local areas of high concentrations have persisted. Toxaphene residues declined nationally during the early 1980s. The limited data available do not indicate a national decline in dacthal contamination.