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?