New USGS Study on Pesticides in Midwestern Streams

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A new study by the U.S. Geologic Survey (USGS) on the prevalence of pesticides (including mixtures) in the Midwest, and potential impacts on aquatic insects was recently published.  More than 180 pesticides and their byproducts were detected in small streams throughout 11 Midwestern states, some at concentrations likely to harm aquatic insects, according to the new study.

On average, 52 pesticide compounds were detected in each stream.  At least one pesticide in at least half of the 100 streams sampled exceeded a threshold predicted to cause harm to aquatic insects and other stream organisms.  Pesticides were not measured at levels predicted to be toxic to fish in most streams.  While numerous pesticides were detected at low levels, only a few—atrazine, acetochlor, metolachlor, imidacloprid, fipronil, and organophosphate insecticides—were predicted to be major contributors to toxicity.  The first three are widely used agricultural herbicides, and the latter three are insecticides used in both residential and agricultural settings.

This is one of the most extensive assessments of pesticides in streams to date: 1,200 samples were collected at 100 Midwest streams over a 12-week period during the 2013 growing season and analyzed for 228 pesticide compounds.  This study is one component in the first in a series of five USGS regional stream quality assessments.