General Info:

Where does mercury come from? Are mercury levels increasing?
Mercury is a naturally occurring element that is present throughout the environment and in plants and animals. Human activity can release some of that mercury, increasing the amount available to accumulate in humans and other animals.
Human activities have increased the amount of mercury that is currently cycling in the atmosphere, in soils, and in lakes, streams and the oceans. Mercury in these locations increases risks to people and wildlife. Although the U.S. and many other industrialized countries have substantially reduced mercury uses and releases in recent decades, these reductions are not yet reflected in the air, soils, water or fish.

What is methylmercury?
There are three forms of mercury -- methyl, elemental, and inorganic. Releases of mercury to the environment are usually in the form of elemental or inorganic forms. Methylmercury is an organic form of mercury. Biological processes change the chemical form to methylmercury, which is the more toxic form found in fish. Methylmercury bioaccumulates through the food chain and, once in the body, can affect the fetal and adult nervous systems.
What are the biggest sources of mercury air emissions?
According to EPA's 1997 Mercury Study Report to Congress, coal-fired electric utilities are the largest source of human-caused mercury air emissions in the U.S. Utilities are followed by:
1. Municipal waste combustors (19 percent);
2. Medical waste incinerators (10 percent);
3. Hazardous waste combustors (4+ percent).

How does mercury move through the environment?
In the atmosphere, mercury is transported by wind either as a vapor or as particles. Mercury reaches waters either through direct deposition or as run-off from soil after rain. In the water, biological processes can transform mercury into methylmercury – a highly toxic form, which can accumulate in fish.

How does mercury from power plants wind up in fish?
When mercury is deposited into the water, microorganisms help convert it to methylmercury, a highly toxic form of mercury. Small organisms and plants take up the mercury as they feed. As animals higher up the food chain eat those plants and organisms, they, too, take in methylmercury. The process continues, with levels of mercury increasing, up the food chain. This process is known as bioaccumulation. Fish higher in the food chain, such as sharks and swordfish, have much higher mercury concentrations than fish lower on the food chain.

How much does the U.S. contribute to worldwide mercury emissions?
Although the amount of mercury the U.S. contributes globally is small (about 3 percent), it still contributes more than it receives. Approximately two-thirds of U.S. mercury emissions are transported outside our borders. However, approximately 60 percent of the mercury deposition that occurs in the U.S. comes from domestic, human-made sources of pollution. The highest deposition rates from U.S. sources occur in the southern Great Lakes, the Ohio Valley, the Northeast, and scattered areas in the Southeast.

How does mercury affect health?
At high doses, mercury exposure can cause tremors, inability to walk, convulsions, and even death. At levels more commonly seen in the United States, the mercury exposure effects documented include more subtle – yet still serious – damage to the senses and brain.
The developing fetus is the most sensitive to the effects of mercury, and so women of child-bearing age are the population of greatest concern. Children of women exposed to relatively high levels of methylmercury during pregnancy have exhibited a variety of abnormalities, including delayed onset of walking and talking, and reduced neurological test scores. Children exposed to far lower methylmercury exposures in the womb have exhibited delays and deficits in learning ability.

Do some fish contain more mercury than others?
Yes. Freshwater fish caught by recreational or subsistence fishermen (people who fish for their food) from contaminated waters have been shown to have particularly high levels of methylmercury. Certain species of commercially available saltwater fish, such as shark and swordfish, kingfish and tilefish also can contain high levels of mercury.