Midwestern streams were found to contain 52 pesticides on average

More than 180 pesticides and their by-products were detected in small streams throughout 11 Midwestern states, some at concentrations likely to harm aquatic insects, according to a new study by the U.S. Geological Survey. The mixtures of pesticides are more complex than previously reported by the USGS—94 pesticides and 89 pesticide byproducts were detected. On average, 52 pesticide compounds were identified 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, ranging from acute effects—like death after a short-term exposure—to chronic effects—like longer-term impairments to reproduction and development. Two to four pesticides exceeded that threshold in more than a quarter of the streams. Aquatic insects, like mayfly and stonefly larvae, are critical to stream health because they are an essential link in the aquatic food web.

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. Numbers of streams tested in each state include: Illinois (19 sites), Indiana (15), Iowa (17), Kansas (3), Kentucky (3), Minnesota (7), Missouri (14), Nebraska (8), Ohio (7), South Dakota (1), and Wisconsin (6).

Source: USGS, August 9, 2017