Toxic Substances Hydrology Program
MethylmercuryMethylmercury (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
Information on Assessing Mercury Contamination
Fact Sheets on Mercury in the Environment
More USGS Information on Mercury in the Environment
Other Mercury Information
Mercury Toxicity Information
References
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