Great Lakes Environmental Assessment and Mapping Project

Mercury in Great Lakes Sediments

Mercury is a potentially toxic metal that is widespread in the Great Lakes. It is an important toxic substance affecting human and ecosystem health in the Great Lakes.1,2 While there are natural sources of mercury, most mercury loading in the Great Lakes comes from anthropogenic discharges. Scientists estimate more than 50% of the mercury in the environment today is from non-natural sources.

  • Natural sources of mercury include volcanic eruptions, weathering of rock and sediment, and forest fires.
  • Atmospheric deposition from coal-powered power plant and municipal waste incinerator emissions is the largest source of mercury pollution to the Great Lakes. In 2005, coal-fired power plants emitted 57% of the mercury pollution.3


The Mercury Cycle

  • Mercury is typically emitted in its inorganic form.
  • Through a series of complex processes, inorganic mercury is converted to organic methylmercury, which is the form associated with health risks for fish, wildlife, and humans.
  • Bacteria that thrive in low oxygen environments, such as lake sediments, play a key role in the conversion to methylmercury.
  • Mercury in the environment does not break down over time, and due to its bioaccumulative nature, even small concentrations of mercury in water can have large impacts on food webs. Mercury concentrations can be magnified by 1 million to 10 million times in fish and fish-eating birds like loons, reducing their growth and reproductive success.3


Effects of exposure to mercury

  • Human exposure to methylmercury in the Great Lakes basin is primarily through freshwater fish consumption.4 Exposure to methylmercury can cause serious impacts to the cardiovascular and nervous systems, including increased blood pressure, memory loss, nerve damage, difficulty concentrating, tremors, slurred speech, loss of color vision, paralysis, and even death. 
  • Top predators in the Great Lakes basin, such as sports fish, may bioaccumulate mercury concentrations exceeding human health guidelines.
  • Fish advisories limit the consumption of Great Lakes fish by vulnerable populations including women of child-bearing age, pregnant women, and children.


Mapping mercury as a Great Lakes stressor

We mapped surficial sediment mercury concentration using near-shore values obtained from a collection of monitoring projects compiled by the NOAA Assessment and Restoration division and in-lake values collected by EC’s sediment monitoring program.5,6 Data were kriged using ArcGIS algorithms with a 5-point neighborhood.
Spatial distribution of mercury as a stressor in the Laurentian Great Lakes. (Inset: Western Lake Ontario)
Additional Resources:
Mercury in the Environment (Environment Canada)
Contaminated Sediments Program (US EPA)
Great Lakes Mercury Connections: The Extent and Effects of Mercury Pollution in the Great Lakes Region (pdf) (Biodiversity Research Institute, Great Lakes Commission, and University of Wisconsin-LaCrosse)


Data Sources: 

1. Mohapatra, S.P., I. Nikolova, and A. Mitchell. 2007. Managing mercury in the great lakes: An analytical review of abatement policies. Journal of Environmental Management 83(1):80-92.
2. Evers D.C., J.G. Wiener, N. Basu, R.A. Bodaly, H.A. Morrison, K.A. Williams. 2011. Mercury in the Great Lakes region: bioaccumulation, spatiotemporal patterns, ecological risks, and policy. Ecotoxicology 20(7):1487-1499.
3. Evers, D.C., Wiener, J.G., Driscoll, C.T., Gay, D.A., Basu, N., Monson, B.A., Lambert, K.F., Morrison, H.A., Morgan, J.T., Williams, K.A., Soehl, A.G. 2011. Great Lakes Mercury Connections: The Extent and Effects of Mercury Pollution in the Great Lakes Region. Biodiversity Research Institute. Gorham, Maine. Report BRI 2011-18. 44 pages.
4. Turyk M.E., S.P. Bhavsar, W. Bowerman, E. Boysen, M. Clark, M. Diamond, D. Mergler, P. Pantazopoulos, S. Schantz, and D.O. Carpenter. 2012. Risks and Benefits of Consumption of Great Lakes Fish. Environmental Health Perspectives 120(1):11-18.
5. NOAA Assessment and Restoration Division. 2011. National Sediment Inventory – Great Lakes watershed. Online: Accessed 29 May 2011.
6. Marvin C., S. Painter, and R. Rossmann. 2004. Spatial and temporal patterns in mercury contamination in sediments of the Laurentian Great Lakes. Environmental Research 5(3):351-362.