The 18th Century Fur Trade Polluted Lake Superior’s Shore With Mercury That’s Never Gone Away

The area’s elevated mercury levels aren’t healthy for fish, birds or humans

fur trade display
Animal furs on display at Grand Portage National Monument Layne Kennedy/Corbis

Before we recognized that the allure of quicksilver—elemental mercury—was tainted by its toxic effects, we used it to decorate, to develop photos, to make mirrors reflect and to heal the sick. Mercury still shows up in food, in batteries and even in cosmetics. We may finally be phasing it out, but that doesn't mean we're rid of it. Thanks to the 18th century fur trade in the Great Lakes, toxic mercury still lingers, centuries later, on the northern shore of Lake Superior.

At the very northeastern tip of Minnesota, where an 8.5-mile footpath offered fur traders a way around waterfalls and rapids of the Pigeon River, they built a Grand Hall and Fort Charlotte on the shore of Lake Superior. The site is now marked by the Grand Portage National Monument. Here, traders from Montreal met and made their exchanges with those who had ventured deeper into the continent’s interior and with members of the Ojibwe people. Today, this site has another distinction: Soil surrounding the monument has elevated levels of methylmercury — an even more toxic form than elemental mercury, reports Brian Bienkowski for Environmental Health News (via Scientific American). 

Since one of the major gifts traded at Grand Portage was vermillion, a mercury-containing pigment, the researchers suspect the fur trade is to blame, at least in part. Researchers recently measured the methylmercury levels in the streams surrounding Grand Portage, and, Bienkowski writes, "the monument’s soil has an estimated 3 times more mercury per amount of organic carbon - which is what mercury binds to - than five other parks in the western Great Lakes region."

Although the mercury might have originated with the fur trade, aspects of the monument's location conspired to make the contamination worse. The surrounding conifers can "scour mercury from the air," says Brandon Seitz, of the National Park Service. And the tea-colored streams have a low pH, which apparently helps convert elemental mercury to methylmercury. 

As a result, fish in the creeks carry high levels of mercury — many at levels higher than is safe for kingfisher birds to eat. The effects may be rippling through the food chain. Bienkowski:

Two years ago, researchers at the state’s Department of Health reported more than 1,400 babies in the region and found 1 in 10 were born with potentially dangerous levels of mercury in their bodies. Pat McCann, a research scientist with the state’s Department of Health who led the research, said it’s unclear if the levels in the babies were higher than other populations in the Great Lakes region. However, “people definitely seem to be eating a lot of fish,” in the North Shore area, she said.

Mercury poisoning can lead to organ damage and neurological issues like lack of coordination. It’s the toxin responsible for "mad hatter disease" and the poisoning of the Japanese village of Minamata in the 1950s. More testing in the area should help researchers state conclusively whether people are getting too much mercury from local fish as well as which species they should avoid. “We want them to choose the fish lower in mercury,” McCann said. “For fish caught from Lake Superior … lake herring or cisco, whitefish, smaller salmon and lake trout, depending on how often they eat it.”

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