Mercury is a naturally occurring element that is toxic to humans and animals. At room temperature, mercury is a silvery, liquid metal, but it can also evaporate and become airborne. Mercury does not break down into less toxic substances like some pollutants. It used to be common in products such as switches, thermometers, and fluorescent lights.
Products that still contain mercury are less common but still pose a risk to human health. When these items are broken or thrown away, mercury can escape into the environment. Activities such as burning coal and processing taconite also release mercury into the air.
Mercury emitted into the atmosphere moves with wind and weather and may deposit on land or water. Mercury pollution from outside the state affects Minnesota, and mercury concentrations in fish have not significantly declined despite emissions reductions in North America. However, while we're seeing global increases in mercury emissions, ambient air mercury concentrations across the United States have fallen due to federal and state regulatory actions and market forces, indicating that local mercury reductions are still important.
Human health and environmental concerns
When deposited mercury ends up in lakes or oceans, it can accumulate in fish. Eating contaminated fish is a primary way people are exposed to mercury. As fish eat plankton and smaller fish that are contaminated, mercury concentrations increase. Large fish such as bass, walleye, and northern pike tend to be the most contaminated.
Mercury affects nervous systems, particularly in young children and fetuses. Animals that eat lots of fish, such as loons, eagles, otters, mink, kingfishers, and osprey, are also at risk of neurological damage. See the Minnesota Department of Health web site for guidance on fish consumption:
If mercury is exposed to the air – for instance, when a mercury thermometer breaks – it can evaporate and create dangerous vapors. Learn more:
Monitoring, reporting, and regulations
The federal government has enacted standards for mercury emissions from coal-fired power plants and banned the use of mercury in latex paints and as an agricultural fungicide.
Minnesota laws cover the sale, use, labeling, and disposal of all forms of mercury:
- Elemental mercury and compounds may be sold only for specified uses.
- All products must be labeled in a manner that informs users of mercury prior to sale and at time of disposal/recycling.
- The manufacture and sale of nearly all mercury-containing products has been phased out.
- Disposal of mercury in solid waste or wastewater is prohibited for households and businesses
- All mercury must be recycled.
Mercury and water quality
A body of water is listed as impaired when more than 10% of a fish species in a lake or river has a mercury concentration in fillets that exceeds 0.2 parts per million. If the mercury level is below 0.57 ppm, the impaired waters are included under the Statewide mercury total maximum daily load. Lakes and rivers with mercury levels in fish above 0.57 ppm require additional reductions. See the Minnesota impaired waters list for information about bodies of water that do not meet water quality standards for mercury.
For larger fish such as bass and walleye to be safe to eat, MPCA scientists say that we must reduce mercury emissions to 789 pounds per year, a 76% reduction from 2005 levels. Working with stakeholders, the MPCA has developed a plan to meet this goal by 2025.