Mercury

MERCURY

Mercury (Hg) is a naturally occurring silvery metal that has been associated with adverse health effects throughout history. Elemental mercury is a liquid at room temperature, and, because of this, Aristotle named mercury "quicksilver." There are three forms of mercury: elemental mercury (Hg⁰), organic mercury (e.g., methylmercury), and inorganic mercury (e.g., Hg⁺, Hg²⁺). Many different organic and inorganic mercury compounds are found in nature because of mercury's ability to form covalent or ionic bonds with other chemicals. Mercury has numerous commercial uses—including its use in the extraction of gold from ores—and is an ingredient in alkaline batteries (approximately 0.025% of battery content), mercury vapor lamps, thermostats, and mercury amalgam fillings (in the United States, 50% of a dental filling is made of mercury). Humans can be exposed to mercury compounds via the oral, inhalation, and dermal routes. The primary source of exposure to mercury compounds is attributed to the ingestion of fish and other seafood (marine mammals, crustaceans) that have bioaccumulated mercury compounds. Dental amalgams, which leach mercury, are another source.

Adverse health effects from elemental and inorganic mercury compounds have been observed, particularly in occupational settings. Health consequences commonly observed from exposure to compounds such as elemental mercury vapor and mercuric chloride include tremors, bleeding gums, abdominal pain, vomiting, and kidney damage.

Health effects from organic mercury compounds have also been well-documented, primarily because of the tragic mass poisonings from organic mercurials in locations such as Minamata, Japan, and in Iraq. These mass poisonings were primarily associated with central nervous system toxicity and death. Adverse health effects observed in poisoned individuals and their offspring included ataxia, dysarthria, impaired vision and hearing, and death. Methylmercury is particularly toxic because 95 percent of an ingested dose is absorbed into the bloodstream and can cross the blood-brain and placental barriers, causing adult and fetal neurotoxicity. One of the reasons that offspring are particularly susceptible is that methylmercury can accumulate at 30 percent higher levels in fetal red blood cells than in maternal red blood cells. Besides damaging the brain and peripheral nervous system, methylmercury may also adversely affect the adult and fetal cardiovascular systems.

Research continues to be performed on the potential neurodevelopment effects of ingesting low levels of mercury in seafood. Three particularly important, ongoing studies involve residents of New Zealand and the Seychelles and Faroe Islands who consume significant portions of seafood as part of their normal diets. Analyses performed to date on mother-offspring pairs from the Seychelles identified adverse neurodevelopmental impact in offspring attributable to maternal methylmercury exposure from seafood. Mild developmental effects were also reported among offspring of New Zealand and Faroe Island residents who ingested seafood containing relatively high levels of methylmercury. These studies are particularly pertinent to assessing potential health effects among Native Arctic populations who consume marine mammals (beluga whales, ringed seals) as part of their normal diet. An increased level of mercury has been noted in the Arctic environment since the 1970s, possibly due to anthropogenic sources such as fossil fuel combustion, or possibly from increased natural releases of mercury from geologic sources. It is hypothesized that the cold Arctic climate acts as a sink for mercury; a particularly troublesome prospect for Native Arctic populations who continue to consume mercury-laden mammals and seafood.

Margaret H. Whitaker

Bruce A. Fowler

(see also: Environmental Determinants of Health; Foods and Diets; Heavy Metals; Minamata Disease; Occupational Safety and Health )

Bibliography

Agency for Toxic Substances and Disease Registry (1999). Toxicological Profile for Mercury (Update). Washington, DC: U.S. Department of Health and Human Services.

Arctic Monitoring and Assessment Programme (1999). Arctic Pollution Issues: A State of the Arctic Environment Report. Available at http://www.amap.no.

National Research Council (2000). Toxicological Effects of Methyl Mercury. Washington, DC: Committee on the Toxicological Effects of Mercury. Board on Environmental Studies and Toxicology. Commission on Life Sciences.

Tenenbaum, D. J. (1998). "Northern Overexposure." Environmental Health Perspective 106(2): A64–A69.

U.S. Environmental Protection Agency (1997). Report to Congress on Mercury. Available at http://www.epa.gov/oar/mercury.html.

World Health Organization (1990). Methyl Mercury, Vol. 101. Geneva: International Programme on Chemical Safety, WHO.

—— (1990). Inorganic Mercury, Vol. 118. Geneva: International Programme on Chemical Safety, WHO.