Mercury is a toxic pollutant that accumulates in fish and affects humans and animals that eat fish. Two-thirds of the mercury in the world is released into the environment by human activities, such as electricity production and waste incineration. Much of this mercury is released into the air; once it falls to earth, it cycles through soils and surface waters, entering streams, lakes, and estuaries.
Even small levels of mercury can pose serious health and environmental risks. In 2003, 44 states and American Samoa issued fish consumption advisories because of mercury contamination. From 2002 to 2003, the number of river miles with advisories increased by 60%. According to the U.S. Environmental Protection Agency (EPA), warnings not to eat fish have been issued for nearly one out of every four American rivers and one out of every three lakes.
Mercury in the Environment
Mercury is emitted in a combination of different chemical forms, each of which behaves differently once emitted. Elemental mercury, for example, which comprises 95%-99% of mercury in the atmosphere, can circulate in the air for up to a year before being deposited on land or in water. It is therefore the most likely species of mercury to travel long distances from its original source. In this sense elemental mercury is considered a "global pollutant." However, mercury can also exist in other forms that are deposited locally; scientists have identified many means by which it can be converted into a "local pollutant."
In addition to undergoing changes in the atmosphere, mercury can also undergo chemical transformations once it is deposited to the landscape. Of greatest concern to fish, wildlife, and humans is mercury's conversion to methylmercury. This conversion is most common in wetlands that are periodically flooded, where the bacteria that facilitate the process are abundant.
Globally, approximately 6,500 metric tons (1 metric ton = 1,000 kg or 2,200 lbs) of mercury are emitted each year. Of that amount, one-third is emitted by natural processes, such as volcanic eruptions and undersea vents. The other two-thirds come from industrial pollution. Currently, the largest single source of human mercury emissions in the U.S. is the electric utility industry. In this category, coal-fired power plants are the highest emitters at approximately 34% of the total. In addition to direct emissions into the air, power plants also produce 33 tons of mercury as coal waste. Mercury emissions from the utility industry are not regulated at the federal level or in New York State.
Research has found that mercury deposited in three study areas of the Northeast (the Adirondacks, Finger Lakes, and Catskills) primarily originates outside New York State. Thus, reducing emissions in other regions of the U.S. is important for decreasing mercury pollution in New York State.
The Effects of Mercury on Human Health and Ecosystems
Humans are primarily exposed to mercury through eating contaminated fish. In July 2000, the National Academy of Sciences estimated that more than 60,000 children born in the U.S. each year are at risk for nervous system effects resulting from methylmercury exposure in the womb. A study in 2003 by the Centers for Disease Control and Prevention found that 8% of American women of childbearing age had blood mercury levels exceeding those deemed safe by the U.S. EPA. Seventy-five bodies of water in New York State have fish consumption advisories due to elevated mercury levels. The NYS Department of Health (DOH) recommends that people eat no more than one meal (i.e., a half-pound) per week of fish from the state's fresh waters and certain marine waters at the mouth of the Hudson River. Coastal waters are also affected. The U.S. EPA has issued warnings against eating shark, swordfish, king mackerel, or tilefish and advises limiting the intake of other ocean fish. Children and women of childbearing age should not eat any fish from contaminated fresh or coastal waters of New York State. This now includes all waters in the Adirondack and Catskill parks.
Mercury has severe impacts on aquatic ecosystems, especially those with large wetland areas. Two properties of methylmercury, its ability to bioaccumulate and to bioconcentrate, contribute to its toxicity. Bioaccumulation refers to the build-up of a pollutant within the body of an organism over time. Bioconcentration (or biomagnification) refers to how mercury concentrations increase going up the food chain, becoming concentrated in higher-level predators such as fish, birds, minks, and otters. Mercury levels increase by 100-1,000 times or more through bioconcentration. For this reason, even relatively low concentrations of mercury in water can contaminate an entire food chain and make fish unsafe for human consumption.