Frightening Mercury Levels in Minnesota: Is the Historic Fur Trade to Blame?

Minnesota's Grand Portage National Monument (GPNM) is a homage to the state's rich fur-trading past. However, researchers are now finding that this history does not come without consequence, as the monument and areas around it now boast a stunningly high rate of toxic mercury contamination.

Mercury can be naturally found at low concentrations in both water and air. However, elemental mercury and its toxic form, methylmercury, can approach dangerous levels with the addition of human industry. As things stand, coal burning and industrial smelting are two of the leading causes of mercury contamination in an environment, poisoning insects, fish, and the animals that eat them.

That's why 120 countries are members of the UN General Assembly's "Minamata Convention on Mercury," pledging to prevent mercury poisonings - which can result in crippling neural damage or death - by controlling how and when industrial waste is disposed of.

Still, the GPNM is far from an industrial area, and with its out-of-the-way pristine wilderness and well-tended trails, it's a wonder why anyone would suspect the region to be suffering from contamination. (Scroll to read on...)

However, according to Brandon Seitz, a biological science technician with the National Park Service, the monument has a unique history linked to dangerous mercury loads.

Initial assessments, as detailed in a study recently published in the journal Science of the Total Environment, show that the region's soil has about three times more mercury per organic carbon (which it binds to) than five other parks in the western Great Lakes region. Additionally, toxic methylmercury was found to make up a stunning 90 percent of all mercury levels found in dragonfly larvae. In other regions, even those that boast naturally high concentrations of elemental mercury, this concentration would be far less intense.

So what's going on here?

"We know it's a very sensitive ecosystem," Seitz recently explained to Environmental Health News, going on to add that the region's fur trading past, stretching back to the 18th century, may have left a lasting impact.

Serving as an important gateway between Canada and the wilds around the Great Lakes, the Ojibwe people and the North West Company frequently exchanged goods and gifts along the trails that the monument maintains. One of the major trade items at the time - in exchange for quality pelts - was a brilliant red synthetic pigment called vermilion. Unfortunately, the pigment contained high levels of mercury, and US Geological Survey (USGS) researchers have found elevated levels of mercury along the trails even today.(Scroll to read on...)

Another factor is a bit more natural. The monument's forest happens to consist primarily of needle trees, called conifers. These types of trees are known to "scour" mercury from the air itself, trapping emissions and keeping them in the soil. If mercury levels were elevated even centuries ago, they've really had no place to go since then.

So what does this mean for the area? According to the study, bait fish found in the region had adequately low mercury concentration levels, but the large fish that eat them were found to be approaching dangerous levels. Specifically, 61 percent of the fish from Grand Portage Creek, 97 percent from Poplar Creek, and 84 percent from Snow Creek had mercury levels higher than what is considered safe to eat for kingfisher birds, which are highly sensitive to mercury. And 23 percent of those same fish had levels that could cripple newborn minks.

Humans, too, may be seeing these impacts. The study authors bring up past work that highlights how residents of Minnesota's North Shore area, right by the monument, have seen heightened mercury exposure. A 2013 survey even found that among 1,400 newborn babies in the region, about 10 percent had potentially detrimental levels of mercury in their bodies.

Pat McCann, a research scientist with the state's Department of Health, who led the research, said that it remains unclear if these levels are higher, compared to levels in newborns elsewhere in the state.

However, she did add that "people definitely seem to be eating a lot of fish" in the North Shore area. And while recent research has made the argument that the benefits of eating fish during pregnancy outweigh the risks, it may be best that mothers in risky areas like near the GPNM stick to safer meals or fish-oil supplements.

Produced with material from Environmental Health News (CC0) - B. Bienkowski.

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