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Neonicotinoids widespread in Minnesota deer

Sixty-one percent of the spleens of deer submitted by Minnesota hunters contained residuals of neonicotinoid pesticides. The widespread distribution among deer harvested in farm country, urban and forest areas surprised researchers.

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Hunters in west central Minnesota are in the field with optimism on the opening of the 2021 firearm season. DNR photo

ST. PAUL — We now know that neonicotinoid pesticides are far more widespread in Minnesota’s deer population than many had suspected.

We are still to learn what harm they may represent to the state’s deer.

More than 800 hunters submitted spleens from the deer they harvested to the Minnesota Department of Natural Resources as part of a citizen science research project. Sixty-one percent of the spleens had evidence of neonicotinoids.

The chemicals showed up in the spleens of deer from all over the state, “which was a surprise,” said Dave Olfelt, director of the division of fish and wildlife. He was among DNR and Department of Health officials hosting a conference call with reporters on March 1 to announce the results of the project.

Neonicotinoids showed up in deer found in farm country, urban areas and the great north woods.


Neonicotinoids are under scrutiny for the harm they cause pollinators. Virtually all of the corn and the majority of soybeans planted in Minnesota are treated with the pesticides, as are many lawns. They reach the environment by leaching into groundwater, as runoff into waterways and lakes, and by being transported with soil carried by the wind.

A study in South Dakota identified the potential harm they could cause deer, and led the DNR to conduct this study to determine how widespread they might be and the risk they may represent.

The study of captive deer in South Dakota, released in early 2019, found that white-tailed deer with “high levels of neonicotinoid pesticide in their spleens developed defects such as smaller reproductive organs, pronounced overbites and declined thyroid function. Fawns with elevated levels of the pesticide in their spleens were found to be generally smaller and less healthy than deer with less of the chemical in their organs,” according to published findings of the study.

Michelle Carstensen, supervisor for the DNR’s wildlife health program, said the results received at this point are preliminary. The DNR will be receiving better information on the levels of the neonicotinoids found in the spleens in a month or so. She noted that some of the preliminary levels were above the thresholds that were impacting fawns in the study that triggered the concern.

The DNR launched its project as part of ongoing work to protect the deer population. If neonicotinoids are impacting fawn survivability, the DNR needs to take that into account in its deer population modeling, she explained.

The levels found in these deer do not indicate any danger for the hunters consuming the venison , according to Jim Kelly with the Minnesota Department of Health. Based on the preliminary results, the levels of neonicotinoids found in the deer were very low, with 10 parts per billion on the high end of the results, he said. The limits for residuals of these chemicals in food products is in the 300 to 500 ppb range, he said.

He also told reporters that the low levels found in the spleens of these deer suggest that the neonicotinoids likely did not become distributed in the muscle tissue of the animals. He said the chemicals are broken down relatively quickly in the animals.

Researchers initially believed the project would help them identify areas of the state where they should focus their attention. With detections of the chemicals in deer from all the different habitats in the state, “it’s hard to say where to take a closer look,” said Carstensen.


The Minnesota deer spleens were submitted to the South Dakota laboratory which had performed the analysis for the earlier South Dakota research. A number of the Minnesota spleens were also submitted for a mass spectrometry analysis to verify the laboratory results. The spectrometry results have not yet been received.

The final results will help researchers better understand the impact these pesticides may have on the deer population. There is still much to learn. At this point, we don’t know for sure how deer are being exposed, and whether the exposure in this study was recent or represented some accumulation of the chemicals over time in these deer, according to Carstensen.

The permit areas where hunter submitted spleens of deer contained neonicotinoids are shown in the shaded areas of the map. DNR map

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