New study investigates insecticide contamination in Minnesota's water

Individuals relying on shallow groundwater or natural springs for drinking water have a higher risk of contamination from these insecticides compared to those getting their drinking water from deep groundwater wells. They also found that these insecticides could affect organisms in the streams that are fed by those springs.

The research was recently published in Science of the Total Environment, a peer-reviewed scientific journal.

With the increased use of insecticides for agriculture and insect control in the past few decades, research has shown that consistent application of them can lead to contamination in water. This can have a negative impact on human health and pollinator insect species, such as bees and butterflies.

A large portion of Minnesota's drinking water comes from groundwater. Looking at the levels of these specific insecticides can help water treatment plants determine what to monitor and filter.

In this study, researchers looked at the levels of neonicotinoids in surface and groundwater across Minnesota, identifying factors that may affect the extent of contamination. The DNR was able to collect water samples from 15 springs and 75 unique wells from 13 counties in Minnesota over four years (2019-2022) allowing comparisons between urban and rural areas.

The researchers not only collected an extensive amount of geographic locations, they also looked at the chemical levels at various depths. In testing the water samples, they found that natural springs are very susceptible to contamination from neonicotinoid insecticides.

"Oftentimes people think a natural spring has water that is safe to drink," said Bill Arnold, Distinguished McKnight University Professor & Joseph T. and Rose S. Ling Professor in the University of Minnesota's Department of Civil, Environmental, and Geo- Engineering. "That's not necessarily true, it depends on how deep that water is sourced."

There are multiple ways these types of chemicals can get into the environment. In addition to direct application, stormwater runoff and snow melt can contribute to these chemicals in ground and surface water. The researchers were able to map different classes of the insecticides across the state.

"This study is a key first step in identifying pollutants in the water, even in some unexpected places like natural springs," said Arnold. "We use so many of these insecticides in Minnesota -- basically every corn and soybean seed is treated before planting -- and many of these chemicals can be purchased at a local hardware store for spraying fruit trees, flea and tick control for your pets, and eliminating bedbugs."

While the researchers knew they would find traces of the insecticide in water, some of their study results were unexpected.

"We were surprised by the high levels of the chemical detected in the natural springs and in some cases the chemicals were observed at much deeper levels in wells than we expected going into this project," Arnold added.

As a follow-up to the study, researchers are collaborating with county and state agencies to include these chemicals on water treatment monitoring lists and want to continue to educate watershed districts about these insecticides. The researchers will also work with the University of Minnesota's St. Anthony Falls Laboratory to improve stormwater treatment methods for urban environments, including the use of biofiltration to remove pollutants.

In addition to Arnold, the team included University of Minnesota Department of Civil, Environmental, and Geo- Engineering retired adjunct associate professor Paul Capel, former research assistant Grant Goedjen, and John Barry from the DNR's Division of Ecological and Water Resources.

This work was funded by the Minnesota Environment and Natural Resources Trust Fund (ENTRF) as recommended by the Legislative Citizen Commission on Minnesota Resources (LCCMR). The ENRTF is a permanent fund in Minnesota that provides funding for the protection and conservation of Minnesota's natural resources.