Mercury. How does it occur, what are the sources, how does it affect health?

Main Category: Public Health
Article Date: 09 Aug 2004 - 0:00 PDT


How does mercury occur in the environment?

Mercury is a naturally occurring element that can be found throughout the environment. Human activities such as burning coal and using mercury to manufacture certain products, 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.

What are the biggest sources of mercury air emissions?

According to EPA's 1999 National Emissions Inventory, coal-fired electric power plants are the largest source of human-caused mercury air emissions in the U.S. Power plants account for about 40% of total U.S. manmade mercury emissions. Other large sources are industrial boilers (about 10% of U.S. mercury emissions), burning hazardous waste (about 5%), and chlorine production (also about 5%). Burning municipal waste and medical waste was once a large source of emissions but today, in response to EPA and State regulations and reductions in mercury use, these sources are much less important.

How do people and wildlife become exposed to mercury?

Mercury that is emitted to the air falls to the ground either very close to the source or many miles away. When mercury is deposited into the water, or runs off the ground into the water, microorganisms convert it to methylmercury, a highly toxic form of mercury.

Small organisms take this up as they feed. As animals higher up the food chain eat those small organisms, they also take in methylmercury. The process, known as bioaccumulation, continues with levels of mercury increasing as it moves up the food chain. Fish that are higher in the food chain, such as sharks and swordfish, have much higher mercury concentration than fish that are lower on the food chain. Humans become exposed when they eat fish that are contaminated with mercury.

How does mercury affect health?

Methylmercury is highly toxic. The developing fetus is the most sensitive to the effects of mercury, and so women of childbearing 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, reduced neurological test scores, and delays and deficits in learning ability.

Eight percent of the women of childbearing age have levels of mercury in their blood that exceeds the level EPA considers safe. In addition, there is growing evidence that methylmercury exposure can have adverse cardiovascular effects for adults, resulting in elevated blood pressure and incidence of heart attack.

Do some fish contain more mercury than others?

Yes. Predator fish - big fish that eat smaller fish - tend to have higher methylmercury concentrations than other fish. The Food and Drug Administration has issued advise to pregnant women regarding consumption of certain types of fish. States issue fish advisories that inform consumers of the extent to which they need to limit their consumption of locally caught fish. Certain species of commercially available saltwater fish, such as shark and swordfish, kingfish and tilefish also can contain high levels of mercury. National and regional information is available from our Fish Advisory page.

http://www.epa.gov/mercury/information1.htm

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