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By Dan Gunderson

New research shows a widely used insecticide is common in shallow groundwater across Minnesota.

Neonicotinoid insecticides are a class of neurotoxic chemicals commonly applied to seeds before they are planted. The chemical is taken up by the plant as it grows and kills insects that feed on the plant.

Numerous studies have found the chemicals harm bees and other pollinators.

Research has shown plants absorb only a small percentage of the chemical. The remaining insecticide moves through the soil with water.

University of Minnesota researchers worked with the Department of Natural Resources to test water in 13 counties across the state.

“We found the highest concentrations in the karst areas of Minnesota where you have high connectivity between the surface water and the groundwater,” said U of M professor Bill Arnold. “And this was typically in springs or shallow groundwater where we saw the highest levels, and in deep ground waters where we get most of the drinking water drawn from we saw the lowest levels.”

Arnold said the second highest groundwater levels were found in Hennepin and Ramsey counties.

Neonicotinoids are also widely used in urban landscapes and in flea and tick collars for pets.

Previous studies have found neonicotinoid insecticides to be ubiquitous in surface water.

The federal Environmental Protection Agency has not established safe drinking water levels for the chemical.

Arnold said individuals relying on shallow groundwater or springs for drinking water have a higher risk of contamination from neonicotinoids compared to those getting their drinking water from deep groundwater wells. He said high nitrate levels in a well can be considered an indicator that neonicotinoids are likely in the water as well.

Arnold said researchers are collaborating with county and state agencies to expand monitoring for neonicotinoids and to educate watershed districts about the risks of using the insecticides.

“We need to think more about how we’re applying these in areas where we know we have connectivity between the surface water and the shallow groundwater,” said Arnold, who plans more research on how storm water management might affect groundwater contamination.

“There’s a big push to do infiltration of storm water and put it through storm water treatment practices that actually send it into the ground, into the shallow groundwater, hoping that that will remove things like nitrogen, phosphorus, and nutrients,” Arnold said.

“But we have to realize that those practices also should be looking at removal of pesticides and insecticides and other contaminants.”