Mercury in the Environment

Mercury becomes a problem for the environment when it is released from rock and ends up in the atmosphere and in water. These releases can happen naturally. Both volcanoes and forest fires send mercury into the atmosphere.

Human activities, however, are responsible for much of the mercury that is released into the environment. The burning of coal, oil and wood as fuel can cause mercury to become airborne, as can burning wastes that contain mercury.

This airborne mercury can fall to the ground in raindrops, in dust, or simply due to gravity (known as “air deposition”). The amount of mercury deposited in a given area depends on how much mercury is released from local, regional, national, and international sources.

Emissions from Power Plants

Since mercury occurs naturally in coal and other fossil fuels, when people burn these fuels for energy, the mercury becomes airborne and goes into the atmosphere. In the United States, power plants that burn coal to create electricity account for about half of all manmade mercury emissions Learn more about mercury from power plants

Other Causes of Mercury Air Emissions

  • Burning oil that contains mercury
  • Burning wood that contains mercury
  • Burning mercury-containing wastes, including
  • wastes from the manufacture of Portland cement
  • consumer products that contain mercury, like electronic devices, batteries, light bulbs and thermometers, that are thrown into garbage that is incinerated
  • Using certain technologies to produce chlorine
  • Breaking products that contain mercury
  • Burning iron ore, coke and limestone in electric arc furnaces used to produce steel
  • Using coal-fired boilers in many industries to generate forms of thermal heat like steam

The burning of municipal and medical waste was once a major source of mercury emissions. A reduction in the use of mercury along with state and federal regulations, however, has led to a decrease in emissions from this source by over 95%.

Trends in Air Emissions

Every year, industrial and commercial facilities are required to report their releases of chemicals through EPA's Toxics Release Inventory (TRI) Program. You can view a chart showing the annual amount of mercury emissions into the air from facilities throughout the United States from 2003 to the present.

Mercury Emissions around the Globe

What happens to mercury after it is emitted depends on several factors: the form of mercury emitted, the location of the emission source, how high above the landscape the mercury is released (for example, the height of a power-plant stack), the surrounding terrain, and the weather.

Depending on these factors, mercury in the atmosphere can be transported over a range of distances -- anywhere from a few feet from its source, to halfway around the globe -- before it is deposited in soil or water. Mercury that remains in the air for prolonged periods of time and travels across continents is said to be in the "global cycle." One major source of mercury emissions outside of the U.S. is small-scale gold mining that occurs in many countries.

Additional Resources

• EPA’s Report on the Environment – Mercury Emissions • Mercury Study Report to Congress, Volume II: An Inventory of Anthropogenic [Human-Caused] Mercury Emissions in the United States • Mercury Emissions: The Global Context • Report: Children's Exposure to Elemental Mercury (Agency for Toxic Substances & Disease Registry) (2009)