Mercury in the Great Lakes

February 19, 2013, 11:18 am
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Image Source: NASA


The five lakes, Lake Superior, Lake Huron, Lake Michigan, Lake Erie, and Lake Ontario, known as the Great Lakes contain about one fifth of the world’s total fresh water supply. While Lake Michigan is entirely within the United States, the other four lakes share the international border between U.S. and Canada.


caption © U.S. Army Corps of Engineers, Detroit District. {{PD-USGov-Military}} User: Zaphod

During the last few decades, there have been serious pollution problems in the Great Lakes due to agricultural and industrial development as well as the growth in human population. Major contaminants in the Great Lakes are pesticides, persistent organic pollutants (POPs), and heavy metals, such as mercury. Although mercury is a useful metal, it is highly toxic affecting the nervous and cardiovascular system. Exposure to mercury could lead to nausea, vomiting, diarrhea, severe kidney damage, hallucinations, memory loss, nerve damage, inability to concentrate, increase in blood pressure level, loss of color vision, tremors, loss of dermal sensitivity, slurred speech and even paralysis and death.

Mercury is found in natural deposits of cinnabar (HgS). Natural sources, such as volcanic eruptions, forest fires, erosion of mercury-bearing soils and rocks, evaporation of mercury-containing water, and animal secretions may contribute mercury to the atmosphere; however, human-related mercury emissions result in higher levels of mercury. Important sources of mercury emissions include electric power plants and general heating plants burning coal and oil, primary and secondary non-ferrous metal smelters, iron and steel production plants, cement plants, and municipal/hospital waste incinerators. The use of mercury in amalgam fillings in dentistry causes mercury emissions both to air during cremation and to water systems as a result of dental practices as well as from human feces from people with amalgam fillings. Human feces is also a source of mercury from ingested foods and tobacco smoke. The use of mercury in gold and silver mining in northwestern U.S.A. and in Canada before more efficient methods were developed also emitted mercury.

Industries, such as chlor-alkali plants and paper pulp factories have been major industrial sources discharging mercury as waste into water bodies. This disrupts the wastewater treatment processes and results in the release of large quantities of untreated or partially treated sewage containing mercury to the environment as well. Emissions from municipal landfill operations, consumer products such as batteries and fluorescent light bulbs, emissions from soil and plant surfaces, and mine wastes are other sources of mercury pollution. Once mercury is released to the atmosphere, it can transport to long distances. Ultimately, mercury is removed from atmosphere through deposition on soil, water and vegetation.

Mercury exists in many forms in the environment and some forms are more toxic than others. Elemental mercury accumulates in lakes and other water bodies where chemical and microbial activities convert a part of it to highly toxic methyl mercury. Methyl mercury may accumulate in living organisms and is passed along biological food chains. Thus, aquatic fish species and fish-consuming animals in the Great Lakes accumulate toxic levels of mercury in their tissues, although mercury may be initially present in water in very low concentrations. Elevated mercury concentrations in different species of fish have been observed in the Great Lakes. In addition, there are numerous reports of mercury contamination in the waters, sediments and biota other than fish.

Persons consuming Great Lakes fish have greater exposure to toxic substances resulting in adverse effects on their health. Elevated mercury concentration has been detected in the blood and/or body tissues of fish consumers of the Great Lakes. Persons consuming large amounts of some Great Lakes sport fish are found to have higher levels of mercury in blood. In addition, developmental defects and neurological problems in children of some fish-consuming parents, nervous system dysfunction in adults, and disturbances in reproductive parameters have also been detected. Children of women exposed to mercury during pregnancy by consumption of mercury-contaminated fish are worst affected. Again, blood mercury levels of the fish eaters of the Areas of Concern (AOCs) have been higher than in many other Great Lakes populations. At present, mercury levels in the Great Lakes remain high enough to cause developmental defects in infants. Cerebral palsy hospitalization has been attributed to methyl mercury exposure in the Great Lakes communities.

Mercury concentration in the Great Lakes can be ascribed to direct discharges into the waters, disturbances of mercury previously deposited in sediments, and atmospheric deposition. There are numerous anthropogenic sources of mercury to the Great Lakes area from local, regional, and global sources. While there have been significant contributions from incineration and metallurgical sources, coal combustion is the largest contributor to atmospheric mercury deposition to these lakes. While combustion of coal accounts for most of the mercury emissions in the U.S.A., smelting of nonferrous metals represents the largest source of mercury emissions in Canada. The second largest source category of mercury emissions in both the U.S.A. and Canada is the combined incineration of municipal and medical waste. In addition to North American anthropogenic emissions, global atmospheric emissions also significantly contribute to the deposition of mercury in various parts of the U.S.A. and Canada including the Great Lakes basin.

Efforts to Contain Mercury

The International Joint Commission (IJC) assists both the United States and Canadian governments in the implementation of the Great Lakes Water Quality Agreement (GLWQA). GLWQA was formulated in 1972 with an intention to rid the lakes of persistent toxic substances, including mercury, by introducing the concept of ‘virtual elimination’. In 1987, Canada and the U.S. signed the 1987 Protocol to the Great Lakes Water Quality Agreement that aimed to restore degraded areas identified around the lakes, to prevent and control pollution and to conserve and protect human and ecosystem health.

The Great Lakes Binational Toxics Strategy was developed jointly by Canada and the U.S. in 1996-97 with the goal of virtual elimination of persistent toxic substances including mercury in the Great Lakes basin. According to the strategy, U.S.A. would achieve a 50 percent reduction nationally in the deliberate use of mercury and a 50 percent reduction in the release of mercury from sources resulting from human activity by 2006. The release challenge will apply to the aggregate of releases to the air nationwide and of releases to the water within the Great Lakes basin. Similarly, Canada vowed to achieve, by 2006, a 90 percent reduction in the release of mercury, or where warranted the use of mercury, from polluting sources resulting from human activity in the Great Lakes basin.

In June 1998, New England Governors and Eastern Canadian Premiers (NEG/ECP) adopted a Mercury Action Plan, which specified actions to protect the region’s citizens and its environment from mercury by a coordinated and powerful set of tools to reduce anthropogenic releases of mercury in the region and remove mercury from the region’s waste streams. In addition to the long-term goal of virtual elimination of anthropogenic mercury emissions in the region, the Mercury Action Plan set an intermediate goal committing to actions to reduce regional mercury emissions by 50 percent by 2003. This intermediate goal provided an important benchmark to motivate and track progress towards virtual elimination. The NEG/ECP in August 2001 adopted a second interim goal calling for 75 percent reduction of regional mercury releases by 2010. The activities of the NEG/ECP include outreach and education as well as pollution prevention programs. Outreach and education activities include increasing public awareness of fish consumption advisories; working with the hospitals and dental offices in the healthcare sector to reduce mercury releases and use; increasing local efforts to divert mercury from the waste stream through source separation and recycling; and working with schools to eliminate mercury hazards in the classroom. Pollution prevention programs include efforts to address the mercury content of consumer and commercial products through implementation of state legislation and through development of standards. Mercury collection programs and thermometer exchanges have also contributed to successful efforts to reduce the mercury burden in the solid waste stream.

The U.S. Environmental Protection Agency (EPA) has developed, under the Clean Water Act, surface water quality criteria both for aquatic life and human health providing guidance to states in adopting water quality standards. All the Great Lakes States of the U.S.A. have developed numerical water quality standards on the basis of the EPA surface water quality criteria. EPA has also issued water quality criteria for methyl mercury to be used by states in determining methyl mercury levels in fish tissue.

There are two types of pretreatment standards for toxic substances release from industries in the U.S.A., namely, categorical standards, and local limits. The categorical standards are technology based standards applicable to specific industrial categories and are uniform throughout the nation. The local limits are developed by the local authorities and are applicable to all industrial units in that area. In cases where there is both a local and categorical limit, the more stringent would prevail. Publicly Owned Treatment Works (POTWs) are responsible for implementing both types of standards.

Many states in the U.S.A. including four Great Lakes States (Illinois, Indiana, Michigan, and Minnesota) have banned the sale of mercury thermometers. In addition, there are several regulations in the U.S.A. designed to curb mercury emissions, the Battery Act of 1996 and the Chlor-alkali Plants Act of 2003 being specifically meant to regulate the release of mercury. The most important and recent mercury rule of 2004 aims at permanently capping and reducing mercury emissions from coal-fired power plants. However, some critics say that the recent mercury rule sets a much more leisurely pace for mercury reduction. The recent mercury rule also includes an emissions trading system for mercury. This rule will allow poorly performing power plants to buy credits from plants with lower mercury emission levels instead of cleaning up. Such a scheme may result in the creation of so-called mercury hotspots in areas downwind of plants that rely on buying credits.

In Canada, some regulations like chlor-alkali mercury release regulation under the Canadian Environmental Protection Act aim at direct reduction of mercury release. The Hazardous Products Act prohibits the use of mercury or its compounds as paint on children’s toys. The use of mercury in thermometers remains one of the largest sources of mercury in Canada. About 1.7 tonnes of mercury associated with fever thermometers is discarded each year in Canada. In addition, another 5 tonnes of mercury are found in fever thermometers in medicine cabinets around the country. Canada’s lack of action has resulted in Canada becoming the dumping ground for North American mercury thermometers that are rapidly being phased-out of use in the United States. Although some major pharmaceutical companies in Canada have stopped selling mercury thermometers, there is no provincial/federal ban yet.

The National Pollutant Release Inventory (NPRI), established in 1992, requires companies to report information on releases and transfers of pollutants to the Government of Canada on an annual basis. The information is available as an annual public report that can be accessed and searched through an on-line database. NPRI lowered the reporting threshold for mercury and its compounds from 10 tonnes to 5kg for the 2000 reporting year.

In Canadian Great Lakes provinces, namely, Ontario and Québec, primary responsibility for controlling industrial discharges into sewers is delegated to local and regional municipalities. Many municipalities have by-laws specifying the maximum concentration of mercury that can be released by industrial units to the sewer system and have been successful in regulating the release of mercury. For example, the Toronto by-law specifies the requirement for dental practices and operators to install, operate and maintain dental waste amalgam separators. Installation of the separators is one of the process changes expected as a result of pollution prevention planning. Within the first eight months of Toronto’s sewer use by-law coming into effect, mercury levels flowing in the city’s sewers fell by between 40 percent and 68 percent. However, there is pronounced variation in the limits for discharge of mercury within municipalities.

The Canada-Ontario Agreement 2002 envisages a 90 percent reduction in mercury releases by 2010 compared to releases in 1988. The strategies outlined in the agreement involve developing standards for mercury emissions from coal-fired plants, developing technical information to guide municipalities in identifying and reducing sources of mercury discharges to sewer systems, developing and implementing life cycle management programs to divert mercury-containing products from the waste stream, in addition to a public education program on mercury.

There is a need to reduce human exposure to mercury in the Great Lakes basin and thus reduce the risks of adverse effects. Though releases from point sources have been significantly curtailed during the past 30 years, very little has been done to remove the historic pools of mercury in sediments. The mercury residues remaining within the various environmental compartments and due to past practices may be significant contributors to the continuing mercury pollution in the Great Lakes. There is a lack of commitment by both the countries to the policy for virtual elimination of persistent toxic substances like mercury as articulated in the Great Lakes Water Quality Agreement.

Directions for Future Actions

There is a need to undertake prospective epidemiological research on cognitive, neurological, and neurobehavioral function in cohorts of infants and children of women who had high intakes of mercury from the consumption of fish prior to and during pregnancy. Although health advisories on fish consumption are issued both in Canada and the United States, the public awareness and concern for these are uncertain. People who eat fish from the Great Lakes should pay close attention to fish advisories in order to avoid high mercury levels in their body.

Direct and indirect discharge of mercury from industrial premises should be reduced and gradually brought to an end. There should be regular monitoring programs in place and the authorities should maintain a registry of mercury load to the municipal sewer system. Combustion of fossil fuels by the power generation sector is a major source of mercury in the Great Lakes basin. Gradual elimination of coal-fired power plants by both the U.S.A. and Canada with a concomitant increase in the use of alternate sources of energy is the ideal solution. The Ontario Government has set an example by deciding to close all existing coal-fired power plants in the province by 2007. However, the coal-fired power plants in the U.S.A. greatly affect the Canadian Great Lakes region as predominant wind patterns in the U.S. Midwest cause the migration of air pollutants towards Ontario and other downwind provinces. By eliminating the use of coal, the United States could avoid smog-filled skies, acid rain, polluted waterways, contaminated fish, and scarred landscapes, and could save each year about 25,000 lives, reduce respiratory and cardiovascular illnesses, avert potential neurological damage for 630,000 babies in addition to saving of over $160 billion in terms of health care bill. Until the time all coal-fired power plants are phased out, it is necessary to adopt stringent mercury emission limits for all coal-fired boilers and develop effective strategies for dealing with coal combustion waste. Emission control in North America would substantially reduce mercury input to the Great Lakes. Reducing mercury emissions in other parts of the world is, nonetheless, equally important, as long-range and regional transport has been found to be very significant sources of mercury deposition in the Great Lakes.

caption Image Source: NASA

Further Reading

  • Cohen, M., Artz, R., Draxler, R., Miller, P., Poissant, L., Niemi, D., Ratté, D., Deslauriers, M., Duval, R., Laurin, R., Slotnick, J., Nettesheim, T., McDonald, J., 2004. Modeling the atmospheric transport and deposition of mercury to the Great Lakes. Environmental Research 95, 247-265.
  • Cole, D.C., Kearney, J., Sanin, L.H., Leblanc, A., Weber, J., 2004. Blood mercury levels among Ontario anglers and sport-fish eaters. Environmental Research 95, 305-314.
  • Gilbertson, M., Carpenter, D.O., 2004. An ecosystem approach to the health effects of mercury in the Great Lakes basin ecosystem. Environmental Research 95, 240-246.
  • Mackay, D., Toose, L., 2004. Quantifying the fate of mercury in the Great Lakes basin: toward an ecosystem approach. Environmental Research 95, 298-304.
  • Mason, R.P., Sullivan, K.A., 1997, Mercury in Lake Michigan. Environmental Science and Technolology 31, 942-947.
  • Mohapatra S.P., Nikolova I and Mitchell A 2007 Managing mercury in the Great Lakes: an analytical review of abatement policies. Journal of Environmental Management, Elsevier, UK. 83:80-92
  • NEG/ECP, 1998. Mercury Action Plan 1998. New England Governors/Eastern Canada Premiers, June 1998.
  • Pilgrim, W., Poissant, L., Trip, L., 2000. The North-Eastern states and Eastern Canadian provinces mercury study: a framework for action: summary of the Canadian chapter. The Science of the Total Environment 261, 77-184.
  • Shannon, J., Voldner E., 1995. Modeling atmospheric concentrations of mercury and deposition to the Great Lakes. Atmospheric Environment 29, 1649-1661
  • Trip, L., Bender, T., Niemi, D., 2004. Assessing Canadian inventories to understand the environmental impacts of mercury releases to the Great Lakes region. Environmental Research 95, 266-271.


Mohapatra, S. (2013). Mercury in the Great Lakes. Retrieved from


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