Methylmercury

Methylmercury (CH₃Hg⁺) is a neurotoxin, and the form of mercury that is most easily bioaccumulated in organisms. Methylmercury consists of a methyl group bonded to a single mercury atom, and is formed in the environment primarily by a process called biomethylation. Mercury biomethylation is the transformation of divalent inorganic mercury (Hg(II)) to CH₃Hg⁺, and is primarily carried out by sulfate-reducing bacteria that live in anoxic (low dissolved oxygen) environments, such as estuarine and lake-bottom sediments. Methylmercury can also be degraded in the environment, either by photodegradation reactions that take place without the help of bacteria or other organisms, or by bacteria through a variety of pathways.

Several forms of mercury occur in the environment. Elemental mercury (Hg⁰) is a shiny, silver-white, odorless liquid that was commonly used in thermometers. Elemental mercury contamination can be found at abandoned gold mine sites where it was used to extract gold from gold-bearing ores.

Divalent mercury (Hg(II)) can combine with sulfur, oxygen, and chlorine to form mercury salts. Mercuric chloride (HgCl₂), which has been used as a preservative for water-quality samples for nutrient analysis, can cause gastrointestinal and kidney problems. Mercury sulfide (HgS) is the mineral cinnabar, which is mined as a source for mercury.

Organic mercury is mercury that has formed compounds with carbon. Methylmercury is the most common example of this form of mercury. Phenylmercury and dimethylmercury are other examples of organic mercury that had medical and commercial uses. They are rarely found in the environment. Methylmercury and ethylmercury compounds were once used as fungicides; however, their use was banned in the 1970s due to their adverse health effects.

Mercury Headlines

• A New Source of Methylmercury Entering the Pacific Ocean
• USGS Mobile Atmospheric Mercury Laboratory Makes an Impact
• National Fish Mercury Model Available On-Line
• OSTP Report on Methylmercury in the Gulf of Mexico
• Glacial Ice Cores Reveal the History of Global Mercury Contamination
• Mercury-Contaminated Fish--Is it Old or New Mercury?
• New Method for Assessing Bed Sediment Contamination

Information on Assessing Mercury Contamination

• Mercury Transport in the Carson River Basin
• Assessing Bottom Sediments as a Source of Mercury Contamination, Far West Reservoir, California
• Yolo Bypass Studies, Yolo Bypass, Sacramento, CA; Cache Creek, CA
• Evaluation of the Effectiveness of Remediation Dredging--The Fox River Deposit N Demonstration Project, Lower Fox River, near Kimberly, Wisconsin (pdf)
• Mercury Cycling in the Everglades

Fact Sheets on Mercury in the Environment

• Mercury Contamination of Aquatic Ecosystems: U.S. Geological Survey Fact Sheet FS-216-95
• Mercury in the Environment: U.S. Geological Survey Fact Sheet 146-00
• Mercury Contamination from Historic Gold Mining in California: U.S. Geological Survey Fact Sheet FS-061-00
• Are Walleye from Lake Roosevelt Contaminated with Mercury?: U.S. Geological Survey Fact Sheet FS-102-97
• Mercury Studies in the Florida Everglades: U.S. Geological Survey Fact Sheet FS-166-96
• Mercury and Selenium Poisoning: U.S. Geological Survey Fact Sheet 1999-15
• Environmental Geochemistry of Mercury Mines in Alaska: U.S. Geological Survey Fact Sheet FS-072-94

More USGS Information on Mercury in the Environment

• Effect Of Mercury on Aquatic Ecosystems
• USGS Mercury Research Laboratory
• Other USGS Mercury Activities
• Mercury Research in the USGS

Other Mercury Information

• Mercury, Information from the U.S. Environmental Protection Agency
• Mercury and the Environment, Information from Environment Canada
• METAALICUS (Mercury Experiment To Assess Atmospheric Loading In Canada and the United)

Mercury Toxicity Information

• ToxFAQs™ for Mercury, Frequently asked health questions about mercury from the Agency for Toxic Substances and Disease Registry (ATSDR)
• Toxicological Profile for Mercury, Agency for Toxic Substances and Disease Registry (ATSDR)
• Methylmercury (MeHg) (CASRN 22967-92-6), Integrated Risk Information System, U.S. Environmental Protection Agency
• Toxicological Effects of Methylmercury, National Academy Press

References

• Agency for Toxic Substances and Disease Registry (ATSDR), 1999, Toxicological profile for mercury: Atlanta, GA, U.S. Department of Health and Human Services, Public Health Service.
• Alpers, C.N., and Hunerlach, M.P., 2000, Mercury Contamination from Historic Gold Mining in California: U.S. Geological Survey Fact Sheet FS-061-00, 6 p.
• Compeau, G.C., and Bartha, R., 1985, Sulfate-reducing bacteria: Principal methylators of mercury in anoxic estuarine sediment: Applied and Environmental Microbiology, v. 50, no. 2, p. 498-502.
• Gerould, S., 2000, Mercury in the Environment: U.S. Geological Survey Fact Sheet 146-00,4 p.
• Gilmour, C.C., Henry, E.A., and Mitchell, R., 1992, Sulfate stimulation of mercury methylation in freshwater sediments: Environmental Science and Technology, v. 26, p. 2281-2287.
• Krabbenhoft, D.P., and Rickert, D.A., 1996, Mercury Contamination of Aquatic Ecosystems: U.S. Geological Survey Fact Sheet FS-216-95, 4 p.
• Marvin-DiPasquale, M., Agee, J., McGowan, C., Oremland, R.S., Thomas, M., Krabbenhoft, D., and Gilmour, C., 2000, Methyl-mercury degradation pathways: A comparison among three mercury-impacted ecosystems: Environmental Science and Technology, v. 34, no. 23, p. 4908-4916.
• Robinson, J.B., and Tuovinen, O.H., 1984, Mechanisms of microbial resistance and detoxification of mercury and organomercury compounds: Physiological, biochemical, and genetic analyses: Microbiology Reviews, v. 48, no. 2, p. 95-124.
• Sellers, P., Kelly, C.A., Rudd, J.W.M., and MacHutchon, A.R., 1996, Photodegradation of methylmercury in lakes: Nature, v. 380, p. 694-696.

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