Insecticides widely used on farms, lawns and gardens — known as neonicotinoids — are showing up in rivers across the Great Lakes region.
Michelle Hladik, a research chemist with the U.S. Geological Survey and the lead author of the new study in the journal Environmental Pollution, says they found the highest concentrations of neonicotinoids in the rivers they tested during the spring and summer months.
"This was expected," she says. "These higher concentrations happened after planting of mostly corn and soybeans and then [in] summer you can get other types of broadcast applications."
She says they found neonicotinoids in Great Lakes rivers throughout the year, typically at low levels. But she says there are concerns about aquatic creatures being continually exposed to these insecticides.
"If you want to compare them to acute and chronic toxicity levels, rarely were we ever above an acute toxicity level," she says. "But for one of the compounds, imidacloprid, we did exceed the chronic toxicity level multiple times."
Hladik says researchers are finding aquatic invertebrates such as water fleas appear to be the most sensitive to the insecticides.
"These small invertebrates are the basis for food for a lot of other species in an aquatic environment," she says. "So there is concern that if these lower level organisms are being affected, that can then affect the food source that other species need."
Hladik says they also found a correlation between land use and neonicotinoids in the rivers. For instance, rivers with a significant amount of agriculture or urban activity or both around them had more frequent detections and higher concentrations of neonicotinoids.