Bringing the Complex Picture of Mercury Pollution in the Great Lakes into Focus

By on February 28, 2018

The winter waters of Lake Superior make geometric art around the Keweenaw Bay where local Ojibwe families have fished for generations. (Credit: Sarah Bird/Michigan Tech)

In 1968, a Life Magazine photographer documented what seemed to many to be fatal levels of pollution in the Great Lakes, including voluminous structures of soap suds, oil slicks, dead fish, runoff from chemical plants and farms, and just plain dumping from all kinds of sources. This was before the Clean Water Act and the Environmental Protection Agency. Since that time, the Great Lakes have, in many ways, made a miraculous comeback.

However, they are not entirely out of danger. New research into mercury pollution in the Great Lakes reveals both a complex range of problems and a series of points for improvement in the way we deal with pollutants in the Great Lakes.

Mercury threatening local communities

Mercury is a toxic pollutant that is widespread in the environment. It is classified as an atmosphere-surface exchangeable pollutant (ASEP), a substance which is invisible and capable of traveling long distances along with its ASEP cousins, such as polychlorinated biphenyl compounds (PCBs). This classification describes the qualities that make mercury so dangerous: its ability to linger undetected throughout each step within the food chain, persisting until people unwittingly consume it in food and beverages.

Although exposure to mercury is a public health problem that affects people all over the world, mercury regulations vary from place to place. On the Upper Peninsula in Michigan, almost 80 percent of inland lakes are impaired by levels of mercury pollution. And while there are plenty of technical questions to follow up with, for most people, including members of the Keweenaw Bay Indian Community (KBIC), the overarching question is fairly basic, yet very important: can we fish and eat what we catch?

Unfortunately, it’s far more difficult for experts to answer that question. The research team in this case sought to respond to the query by using an interdisciplinary team of social scientists, environmental engineers, and biogeochemical modelers to determine how mercury was affecting the food chain on the Upper Peninsula. Team member Noel Urban, a professor of environmental engineering who focuses on the biogeochemistry of the pollutants, spoke with EM about the research.

“Several of the project investigators located at Michigan Tech have long standing research interests in local environmental degradation as does the local tribe of Ojibwe,” Urban explains. “We have collaborated with them in a variety of ways over the years. The funding from NSF is through their coupled human and natural systems program. This program seemed like an ideal venue to meld our interests in improving our scientific understanding of certain contaminants (ASEPs), in working with the tribe to address some of their environmental concerns, and in improving the linkages between science and policy.”

One of the team’s challenges was to answer this question that is of great importance to the community, because this makes the science and stewardship of the area more relevant to local residents as stakeholders. Hence, the interdisciplinary effort, involving a team that encompassed 36 researchers from six institutions and 11 partnering organizations.


The Keweenaw Bay Indian Community’s Natural Resources Department runs a fishery where they raise whitefish fry. The staff tag the fins and release the young fish into the bay. (Credit: Sarah Bird/Michigan Tech)

Digging into the problem

One of the tools the team employed was GEOS-Chem, a global 3D tropospheric chemistry model. The team used GEOS-Chem to parse out sources of emissions, exchange rates, migration routes, and resting places of pollutants.

“GEOS-Chem is the right tool because it accounts for all known human emissions of mercury from local to global, and it makes predictions of air concentrations and atmospheric deposition on spatial scales ranging from local to global,” details Urban. “A key part of our project was identifying on what level regulations must be imposed to have an effect on local (upper peninsula of Michigan) and regional (Great Lakes region) mercury concentrations and deposition. The output from GEOS-Chem must be used in models of mercury cycling in watersheds and lakes to fully answer the question. Those models, however, are always locale-specific.”

In their paper, the team projected mercury levels under three different public policy scenarios through 2050: the elimination of all anthropogenic sources of mercury emissions; a moderate reduction of these emissions based on policy-in-action; and a no policy action, minimal-regulation scenario. They found that it will take more than our lifetime to achieve mercury levels that are safe, and that past models have miscalculated the effects of mercury, given the different rates of deposition in lakes and forests.

Furthermore, the Upper Peninsula landscape is particularly sensitive to mercury.

“It is primarily the abundance of wetlands that makes the Upper Peninsula so sensitive to mercury deposition,” Urban remarks. “Mercury falling on wetlands is methylated in the wetlands and subsequently exported to lakes. The organic matter exported from wetlands lowers the pH, the dissolved oxygen, and the availability of nutrients in lakes—all factors that make the lakes more vulnerable to mercury inputs.”

A variety of local sources of mercury are causing this problem, including power plants—primarily those that are coal-fired—taconite roasting iron ore and other mining operations, solid waste disposal concerns—including those that employ incineration—and cement manufacturers.

“In addition, there were large local mercury emissions from copper mining in the past, from 1860 to 1995,” states Urban. “We still do not know how active these ‘legacy’ emissions are in the environment.”

Compounding the nuances that make this work so challenging is the persistence of mercury in bodies of water itself, which differs depending on the size of the waterway.

“There are many interacting factors that result in mercury behaving differently in lakes of different sizes,” Urban explains. “The flushing rates of lakes tend to decrease with increasing lake size; this means large lakes retain mercury inputs longer. Large lakes tend to have lower nutrient concentrations which results in their having longer food webs that cause more biomagnification in the food chain. Large lakes tend to have larger watersheds; this provides a larger surface area for collecting mercury and funneling it into the lakes. Those factors just mentioned all act to make mercury more of a problem in large lakes.”

Of course, this doesn’t mean that smaller lakes are in the safety zone when it comes to mercury.

“Small lakes are affected more by wetlands than are large lakes because there is less water to dilute the wetland inputs; therefore, all of the wetland impacts on mercury mentioned above are more accentuated in small lakes,” asserts Urban. “In the Upper Peninsula, the wetland effects outweigh the other factors, and hence small lakes are more prone to have high fish mercury concentrations.”

The future of fishing the Great Lakes


Fishing on Keweenaw Bay is an all-seasons endeavor and is an important source for food the local indigenous community. However, because of the landscape’s sensitivity, mercury levels remain higher than the tribe considers safe in key species like lake trout and whitefish. (Credit: Sarah Bird/Michigan Tech)

Ideally, the team will continue sampling in the lakes of the Upper Peninsula, assuming they can secure funding to support this important work—designed not just to produce technical answers, but also to bridge some of the gap between the scientific community and the public.

“While government agencies now fund more of this type of work than they used to do, it still is not a major fraction of the work funded,” states Urban. “On the other hand, scientists in the circles in which we revolve are definitely more aware of the need to make research accessible to the public, and also want to do socially relevant research more now than they did in the past. I’m not too confident about predicting the future, especially for next three years.”

This may be the beginning of what could be a long process for these researchers, even if funding doesn’t become an issue.

“As always in science, this project made some first steps in understanding the issues and raised new questions,” remarks Urban. “Our priorities are to understand the threat from the combination of pollutants present in fish, to determine the extent to which legacy mining is still contributing mercury to the environment, and to further clarify the intersection between human activities, environmental conditions, and external forcing factors that will determine the distribution of pollutants in the environment, the exposure of people and wildlife to those pollutants, and the effects of that exposure. By continuing to work with social scientists and local communities, we hope to provide inputs useful to policy makers and rural inhabitants.”


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