ST. PAUL — Minnesota wildlife officials said Monday, March 1, they will continue to analyze the levels of a popular insecticide and the effect on deer health after a preliminary study of white-tailed deer spleens showed a majority of samples collected across the state contained neonicotinoids.
Neonicotinoids, neonics for short, are found in more than 500 commercial and domestic products, used from crop to residential applications, including pets, the Minnesota DNR said.
The DNR collected 800 spleens from across the state during the 2019 hunting season and 61% of samples indicated exposure to neonicotinoids.
“They came from deer from all over the state which was a surprise to us,” Dave Olfelt, the director of the DNR wildlife health program, said in a conference call.
“With Minnesota’s landscape, it gave us a really unique opportunity because we have deer that inhabit all these different regions from the forests to the prairie to urban areas, and so having a representative sample of spleens from deer in all these different habitats gave us an interesting first look,” said Michelle Carstensen, DNR wildlife health program supervisor.
The DNR launched its research project following a 2019 South Dakota State University study on captive deer that raised concerns about neonicotinoid exposure potentially leading to several birth defects in deer, as well as reduced fawn survival.
Imidacloprid, a neonicotinoid pesticide, was found to concentrate more readily in deer spleens rather than in livers, which is likely causing lower metabolism and lethargy in affected animals, the study said.
The study also discovered a relationship between imidacloprid levels in deer reproductive tissue and the size of organs. Higher levels decreased the size of the spleen, genitals and liver.
The SDSU study found that imidacloprid was not found at dangerous levels in deer brains.
In North Dakota, harvested wild deer had an average of 3.5 times more imidacloprid in their spleens than the captive deer used in the SDSU study who were intentionally given the pesticide, researchers said.
Minnesota officials used the same methodology as the SDSU test to try to draw comparisons. While the levels are not yet exactly known, Eric Michel, a research scientist with the DNR who also worked on the SDSU study, said preliminary indications showed the levels were similar to the North Dakota deer.
Nearly 2,000 hunters requested sampling kits for the Minnesota project. Those who submitted samples will be emailed the test results from their deer, the DNR said.
“We wanted to know if wild deer in natural settings are being exposed to neonics and if certain habitat types had a higher risk,” Carstensen said. “Minnesota is a great place to ask this question, as deer are dispersed across the forest, farmland, prairies, and urban landscapes.”
Carstensen said 57 subsamples are currently being tested at Michigan State University to find out if there is more than one neonic compound in the samples or if there is interaction between neonics. Those results could be available in a few weeks, she said, and those results may help researchers find out if certain habitats are affecting levels.
“These impacts, potentially to deer health and particularly to fawn survival, caught our attention because it's such an important metric in our modeling.” Carstensen said.
For venison consumers, there appears to be little-to-no human health risk, the Minnesota Department of Health said. Early findings suggest concentration levels found in the deer spleens were far below the U.S. Environmental Protection Agency’s allowable levels for consumption.
“We know these neonicotinoid pesticides are broken down within the body of the deer. That happens relatively quickly so we don’t see them distributing within the muscle tissue of the deer,” said Jim Kelly, an environmental health manager with the Minnesota Department of Health. “They’re mostly focused in the spleen and liver so we don’t expect to see concentrations in the muscle tissues that hunters are typically eating.”
Kelly said the acceptable thresholds of neonic residuals in foods such as apples and cattle meat can range from 300 to 500 parts per billion.
“We are seeing less than 10 parts per billion in deer,” he said.
Neonicotinoids can also pose a problem for the bee population. A 2016 study published by the Xerces Society of Invertebrate Conservation said residue from the chemical in both crops and ornamental plants can cause bees to experience detrimental sublethal effects, such as changes in foraging behavior, reduced predator avoidance, delayed development or reduced reproduction rates.
The study also noted that residue levels in some ornamental plants far exceed the level of lethal concentration for honey bees and bumblebees, which suggests, according to researchers, that non-agricultural use of neonicotinoids is more harmful to bees than agricultural use.