USGS Study Finds Some Insecticides Widespread in Midwest Rivers

Location of neonicotinoid sampling sites in Iowa in 2013. Image by USGS

Location of neonicotinoid sampling sites in Iowa in 2013. Image by USGS

A recent U.S. Geological Survey (USGS) study showed that neonicotinoids, insecticides similar to nicotine, can be found commonly in streams throughout the Midwest. The study represents the first broad-scale investigation of neonicotinoid insecticides in the Midwest and one of the first conducted in the U.S.

Neonicotinoid insecticides dissolve easily in water, but do not break down quickly in the environment. This means they likely are transported in runoff from farm fields, where they were first applied, to nearby surface water and groundwater.

USGS found neonicotinoids in all nine rivers and streams studied, including the Mississippi and Missouri rivers. The waterways studied drain most of Iowa, and parts of Minnesota, Montana, Nebraska, North Dakota, South Dakota, and Wisconsin. These states have the highest use of neonicotinoid insecticides via both seed treatments and other forms of application.

Neonicotinoid insecticides, which kill a broad range of pests, have increased in use dramatically during the last decade. The use of clothianidin, one of the chemicals studied, on corn in Iowa alone almost doubled between 2011 and 2013.

Of the three most often found neonicotinoid insecticides, clothianidin was the most commonly detected. It showed up at 75% of the sites and at the highest concentration. Thiamethoxam was found at 47% of the sites, and imidacloprid was found at 23%. Both acetamiprid and dinotefuran were found only once. Thiacloprid was never detected.

“We noticed higher levels of these insecticides after rain storms during crop planting, which is similar to the spring flushing of herbicides that has been documented in midwestern U.S. rivers and streams,” said USGS scientist Michelle Hladik, the report’s lead author. “In fact, the insecticides also were detected prior to their first use during the growing season, which indicates that they can persist from applications in prior years.”

Imidacloprid is toxic to aquatic organisms at 10 to 100 ng/L if aquatic organisms are exposed to it for an extended period. Clothianidin and thiamethoxam behave similarly to imidacloprid and, therefore, are anticipated to have similar effects. Maximum concentrations of clothianidin, thiamethoxam and imidacloprid measured in this study were 257, 185, and 42.7 ng/L, respectively.

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