Here’s the release from the USGS (Sarah Stackpoole):
A new USGS study of pesticides in U.S. rivers and streams reports that, on average, 17 pesticides were detected at least once at the 74 river and stream sites sampled 12 to 24 times per year during 2013–2017. Herbicides were detected much more frequently than insecticides and fungicides.
The number of pesticides detected at a site over the study mirrored the intensity of pesticide use in the region where the site was located. Pesticide use intensity was greatest in the Midwest (49 kg/km2), where 25 pesticides were detected, on average, at each site. Herbicides were heavily used in agricultural settings and were consistently detected in surface waters at concentrations >100 ng/L (nanograms per liter). In contrast, insecticides had lower agricultural-use intensities and surface-water detection frequencies at concentrations >100 ng/L were rare.
An Environmental Protection Agency (EPA) chronic aquatic-life benchmark—estimates of the concentrations below which pesticides are not expected to represent a risk to aquatic life—was exceeded at least once at more than half of the stream sites in every region—Midwest, South, Northeast, West, and Pacific. Such exceedances indicate the potential for harmful effects to aquatic life such as fish, algae, and invertebrates like aquatic insects. However, an EPA human-health benchmark was exceeded only four times (1.1% of samples).
Of the 221 pesticides measured, just 17 were responsible for the aquatic-life benchmark exceedances. Many of these 17 were herbicides, which frequently occurred at relatively high concentrations that exceeded benchmarks for fish, invertebrates, and plants. Others were insecticides, which occurred at lower concentrations, but which are much more toxic to aquatic invertebrates than herbicides.
Here’s the abstract from the study (Sarah M.Stackpoole, Megan E.Shodab, Laura Medalie, Wesley W.Stone):
Pesticides pose a threat to the environment, but because of the substantial number of compounds, a comprehensive assessment of pesticides and an evaluation of the risk that they pose to human and aquatic life is challenging. In this study, improved analytical methods were used to quantify 221 pesticide concentrations in surface waters over the time period from 2013 to 2017. Samples were collected from 74 river sites in the conterminous US (CONUS). Potential toxicity was assessed by comparing surface water pesticide concentrations to standard concentrations that are considered to have adverse effects on human health or aquatic organisms. The majority of pesticide use is related to agriculture, and agricultural production varies across the CONUS. Therefore, our results were summarized by region (Northeast, South, Midwest, West and Pacific), with the expectation that crop production differences would drive variability in pesticide use, detection frequency, and benchmark exceedance patterns. Although agricultural pesticide use was at least 2.5 times higher in the Midwest (49 kg km−2) than in any of the other four regions (Northeast, South, West, and Pacific, 3 to 21 kg km−2) and the average number of pesticides detected in the Midwest was at least 1.5 higher (n = 25) than the other four regions (n = 8 to n = 16), the potential toxicity results were more evenly distributed. At least 50% of the sites within each of the 5 regions had at least 1 chronic benchmark exceedance. Imidacloprid posed the greatest potential threat to aquatic life with a total of 245 benchmark exceedances at 60 of the 74 sites. These results show that pesticides persist in the environment beyond the site of application and expected period of use. Continued monitoring and research are needed to improve our understanding of pesticide effects on aquatic and human life.