Naomi Nakagaki

Regression models for explaining and predicting concentrations of organochlorine pesticides in fish from streams in the United States

Empirical regression models were developed for estimating concentrations of dieldrin, total chlordane, and total DDT in whole fish from U.S. streams. Models were based on pesticide concentrations measured in whole fish at 648 stream sites nationwide (1992-2001) as part of the U.S. Geological Surveys National Water Quality Assessment Program. Explanatory variables included fish lipid content, estimates (or surrogates) representing historical agricultural and urban sources, watershed characteristics, and geographic location. Models were developed using Tobit regression methods appropriate for data with censoring. Typically, the models explain approximately 50 to 70% of the variability in pesticide concentrations measured in whole fish. The models were used to predict pesticide concentrations in whole fish for streams nationwide using the U.S. Environmental Protection Agencys River Reach File 1 and to estimate the probability that whole-fish concentrations exceed benchmarks for protection of fish-eating wildlife. Predicted concentrations were highest for dieldrin in the Corn Belt, Texas, and scattered urban areas; for total chlordane in the Corn Belt, Texas, the Southeast, and urbanized Northeast; and for total DDT in the Southeast, Texas, California, and urban areas nationwide. The probability of exceeding wildlife benchmarks for dieldrin and chlordane was predicted to be low for most U.S. streams. The probability of exceeding wildlife benchmarks for total DDT is higher but varies depending on the fish taxon and on the benchmark used. Because the models in the present study are based on fish data collected during the 1990s and organochlorine pesticide residues in the environment continue to decline decades after their uses were discontinued, these models may overestimate present-day pesticide concentrations in fish.

Design and methods of the Southeast Stream Quality Assessment (SESQA), 2014

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Mixtures of dissolved pesticides in 100 streams in the Midwestern U.S., 2013

Dissolved pesticides were measured in weekly water samples from 100 freshwater streams across eleven states in the Midwestern U.S. during May-August, 2013. A total of 182 pesticide compounds (94 pesticides and 88 degradates) were detected, with a median of 25 compounds detected per sample and 54 detected per site. Potential aquatic toxicity was evaluated using the Pesticide Toxicity Index and by comparison to U.S. Environmental Protection Agency aquatic-life benchmarks. In a screening-level assessment, about 5% of streams were predicted to have potential effects on fish and 58% potential effects on invertebrates. In 75% of streams, short-term effects on algal growth were predicted, with potential for longer-term effects on algal communities predicted in 9% of streams. A relatively small number of pesticides the herbicides atrazine, acetochlor, and metolachlor, the insecticides imidacloprid, fipronil, and organophosphate (OP) insecticides, and to a lesser extent, the fungicide/degradate carbendazim were predicted to be the largest contributors to potential toxicity of pesticide mixtures. This data release provides pesticide compound concentrations, watershed characteristics, and aquatic-life benchmarks used in the analysis presented in the journal article, Pesticide mixtures and potential aquatic toxicity in a synoptic study of Midwestern U.S. streams, May-August, 2013, by Nowell, L.H., Norman, J.E., Moran, P.W., Schmidt, T., Mahler, B., Nakagaki, N., Van Metre, P.C., Shoda, M.E., Stone, W.W.