Mercury in the Environment

Mercury in the Environment

Mercury is a naturally occurring element that is found in air, water and soil. Mercury exists in several forms: elemental (metallic); inorganic; and organic. Mercury cannot be created or destroyed.

Some forms of mercury are more dangerous than others, but all are toxic. Exposure to mercury - even small amounts - may cause serious health problems.

Mercury is released into the environment from many sources. Mercury becomes airborne when rocks erode, volcanoes erupt and soil decomposes. It then circulates in the atmosphere and is redistributed throughout the environment.

Human activities, such as burning coal, oil and natural gas, burning household trash and mining, add mercury to the environment. Once in the air, mercury falls to the ground with rain and snow, landing on soil or water bodies and causing contamination.

Many common products that we use every day contain mercury and may contaminate the environment when they are disposed of in trash, burned or poured down a drain. Mercury also may enter water bodies through a direct release of industrial waste or municipal sewage. Mercury may enter the air when products containing mercury break and release vapors.

Coal-burning power plants are the largest human-caused source of mercury emissions to the air in the United States. Nationwide, they account for more than 40 percent of human-caused emissions according to the U.S. Environmental Protection Agency. There are 5 coal-burning power plants in South Carolina that emit mercury. Another 219 Title V (major source) facilities also emit mercury.

Mercury also can be released into the environment when older vehicles are crushed, shredded or melted in steel furnaces. The mercury is from hood and trunk light switches. Vehicles manufactured after 2003 do not contain mercury switches. Mercury emissions from steel furnaces, thought to result primarily from these mercury switches, are more than 10 percent of the total mercury emissions in the nation.

How Does Mercury End Up In Fish?

Mercury in the air eventually settles into rivers, lakes, streams and oceans or onto land where it washes into water bodies. It is important to know that mercury can settle locally or be carried across continents by the wind. In water bodies, mercury can be transformed by natural processes into a more toxic form of mercury called methylmercury, a type of organic mercury.

Methylmercury is absorbed by small organisms that are, in turn, eaten by fish (and animals that eat fish). Methylmercury builds up or accumulates in fish - some more than others. The levels of methylmercury in fish depend on what they eat, how long they live and how high they are in the food chain. Sharks and swordfish, for example, have much higher methylmercury concentrations than fish that are lower on the food chain. This is true for both saltwater and freshwater fish.

The most common way people are exposed to mercury is by eating fish containing methylmercury. Methylmercury cannot be removed by cooking or cleaning the fish. Mercury cannot be detected in fish by its smell or appearance.

Pregnant women who eat contaminated fish can pass mercury to their unborn children, who are very sensitive to its toxic effects. South Carolina issues fish consumption advisories on many water bodies due to mercury. All 50 states issue some sort of fish advisory because of mercury. It is important to be aware of and follow fish consumption advisories.

What is South Carolina Doing to Limit Risks From Mercury?

  • Fish - The S.C. Department of Health and Environmental Control (DHEC) collects about 1,800 fish samples annually to test for mercury. Higher amounts of mercury in fish tissue tend to occur in the Coastal Plain rather than in the Piedmont. Once fish tissue is tested and advisories are reviewed, DHEC distributes the information across the state. Advisory booklets are sent to obstetrician/gynecologist offices, federal rural health clinics, DHEC regional offices, county public health departments and clinics, nurse midwives, state parks, the S.C. Department of Natural Resources and a mailing list of individuals who have requested the advisories. The information also is available online at
  • Water - Mercury is part of the monitoring requirements of numerous National Pollutant Discharge Elimination System (NPDES) permits, with some containing upper limits to the amount of mercury that can be in a facility's effluent discharge. For facilities serving municipalities that receive waste from multiple sources, DHEC may require the permit holder to work with industries within their service area to reduce mercury at its source. Facilities with stormwater discharges associated with industrial activity where mercury may be expected to be present, such as metal mining, hazardous waste treatment storage or disposal facilities, automobile salvage yards, scrap recycling and waste recycling facilities, are required to implement best management practices in their pollution prevention plans to specifically address, and to monitor for, the presence of this constituent in their stormwater discharges. Lastly, as part of DHEC's ambient monitoring program, surface water from lakes, rivers, and streams is collected and tested for mercury.
  • Air - DHEC implements federal regulations that limit mercury emissions from coal power plants and industrial boilers. Major facilities (e.g., coal-burning power plants) are required to inventory their mercury emissions. The state's open burning regulations make it illegal to burn household garbage, paper and cardboard, motor and waste oil, roofing materials such as shingles and tar, tires and other rubber products, plastic, paint, household cleaners, farm chemicals, electrical wire and insulation, and ductwork.
  • Toxics Release Inventory Program (TRI) - TRI reports information on toxic chemical releases including data on mercury and mercury compounds released in the state. Visit for more information.
  • Land - DHEC has assessed possible mercury contamination at inactive gold mine sites through surface water monitoring and has seen no areas of concern.
  • Healthcare - DHEC has removed and properly disposed of mercury thermometers from its lab and from local public health clinics.