In an intensive synoptic study of Midwestern streams, pesticides were analyzed in water, sediment, and passive samplers from 100 wadeable streams by the U.S. Geological Survey National Water-Quality Assessment (NAWQA), in collaboration with the U.S. Environmental Protection Agency. During May–August, 2013, 227 pesticide compounds were analyzed in 12 weekly water samples and in extracts of Passive Polar Organic Chemical Integrative Samplers (POCIS) deployed over a 5-week period. At the end of the water-sampling period, bed sediment was collected and analyzed for 118 pesticide compounds, and invertebrate communities were surveyed. Pesticide mixtures in water were complex, with medians of 25 compounds detected in water and 62 detected in POCIS extracts. Herbicide concentrations were higher in agricultural watersheds, and fungicide and insecticide concentrations typically were higher in urban watersheds. At all sites, the Pesticide Toxicity Index (PTI), which reflects both concentrations and invertebrate toxicity of pesticides within a mixture, was dominated by insecticides—usually a single insecticide—most often by the neonicotinoid imidacloprid in water and by the pyrethroid bifenthrin in sediment. Pesticide occurrence in POCIS was consistent with mean concentrations in weekly water samples collected during POCIS deployment, with a few exceptions. For example, insecticides flubendiamide, methoxyfenozide, and two pyrethroid degradates (cis-cyhalothric acid and 3-phenoxybenzoic acid) were detected more often in POCIS than in water samples, and fungicides pyraclostrobin and trifloxystrobin were detected more often in water than in POCIS. Bifenthrin occurrence in bed sediment was only weakly correlated with occurrence of the two pyrethroid degradates in POCIS, suggesting that POCIS may provide an indicator of total pyrethroid occurrence that is not always captured by bed sediment or water sampling. In boosted-regression models, the pyrethroid degradates in POCIS were significant explanatory variables of invertebrate community metrics. Similarly, pyrethoids in sediment showed strong (significance level &lt;10%) multivariate correlations with invertebrate communities.

Use of complementary sampling methods to assess pesticides in Midwestern streams: water, bed sediment, and passive samplers

252nd National Meeting (2016)

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