Study shows cause and effect on mercury in the Saint Louis River

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Matt Doll, Minnesota Environmental Partnership

The Minnesota Environmental Partnership recently commissioned an eye-opening report on one of the greatest ongoing environmental hazards in Northern Minnesota – the mercury contamination of the Saint Louis River estuary, which empties into Lake Superior at Duluth. The report, put together by contractors at Trains, Planes & Automobiles LLC, details why this problem exists, the harms it is doing to communities in Northern Minnesota and Lake Superior, and how experts think we should best move forward to address this serious issue. 

This report will be released on MEP’s website soon, but the facts the researchers found are no secret. Mercury, especially in the compound methylmercury, is a potent toxin that can damage nerves and brain function and cause birth defects when ingested. From small microorganisms, it works its way up the food chain through fish and shellfish and into humans, which is why fishing in the St. Louis River carries a health hazard. There is emerging evidence that fish further out into Lake Superior are also contaminated by the pollution in the lake’s largest tributary.

Mercury, which is used in a number of technological applications, most frequently makes its way into aquatic ecosystems like the St. Louis River via industrial processes. Mining and coal combustion are the largest of these sources, and fortunately, direct mercury deposits into the environment are becoming rarer.

The good news is that Minnesota has been cutting down on our mercury emissions for decades, and while we can’t necessarily control sources out of state, the decline of coal power has also helped prevent new mercury deposits. The bad news? There’s already a tremendous amount of mercury deposited in the riverbed of the St. Louis, just waiting for something to come along and spread it into the food chain.

That something is a dangerous level of sulfates, another industrial pollutant. When sulfate levels in the river exceed one milligram per liter of water, they cause a frenzy of bacterial activity that turns mercury into methylmercury, which then ends up being consumed and accumulated by progressively larger organisms, all the way up to humans. 

Because of the process of “biomagnification,” large fish, birds, and humans suffer the most health problems from this process. In a state that prides itself on a diverse fishing culture, where Ojibwe tribes are guaranteed the right to fish, and which is the third most popular fishing destination in the country, the mix of sulfates and mercury in fishing waters is not a problem we can continue to avoid. Its health impacts on Duluth, the Fond du Lac Reservation, and nearby communities are growing.

The St. Louis River’s high sulfate levels largely come from mining activities in Northern Minnesota that unearth sulfur compounds, allowing them to form sulfates and wash downstream. While efforts have been made to adequately address sulfates (which are also devastating to wild rice) in Minnesota, no real solution has materialized. For example, the Minnesota Pollution Control Agency (PCA) proposed a sulfate standard in wild rice waters that would limit discharges, but the standard was simultaneously not strong enough to help wild rice and too strong for industry’s liking. The PCA also dropped out of efforts to establish a Total Maximum Daily Load plan for the St. Louis River Watershed, despite partners in Wisconsin, the Fond du Lac Band, and the federal government still being willing to proceed.

This problem could get worse before it gets better, as climate change causes extreme weather events that could exacerbate methylmercury production through droughts and runoff from heavy rains. Even worse would be if new sulfide mining operations like PolyMet were permitted to build, as they would result in even greater sulfate pollution. Under the Lake Superior Zero Discharge Demonstration Program, Canada and the United States were charged with virtually eliminating a group of toxic pollutants including mercury from the Lake Superior basin by this year. At the very least, we can’t jeopardize the reductions that have already been achieved by letting mercury spread around the lake’s ecosystem.

There isn’t a silver bullet that will heal the St. Louis River, and some continued research is needed. But continuing to wait around and let sulfate pollution spread mercury into people just isn’t good enough for Minnesotans. We need state leaders, especially the Pollution Control Agency, to make the critical choices that will provide safe water and safe food for all the people of Northern Minnesota.

The full report, Mercury in the St. Louis River Watershed, will be released soon on The report was authored by Robin Washington, Bob Hirshon, and David Schafroth. Robin Washington is the former editor of the Duluth News Tribune and the former editor/publisher of the Lake County News Chronicle. Bob Hirshon is a veteran science journalist working in print, broadcast and digital media. David Schafroth is a writer and community organizer in Duluth.

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