CH3Hg

CH3Hg, commonly known as methylmercury, is an organomercury compound with the formula CH3Hg. In most contexts it exists as the methylmercury cation CH3Hg+ and forms complexes such as CH3HgCl in solution. Methylmercury is produced in the environment primarily by microbial methylation of inorganic mercury (Hg2+) in sediments and aquatic systems. Human activities that release mercury can increase the pool of inorganic mercury available for conversion.

Methylmercury is highly lipophilic and binds strongly to sulfhydryl groups in proteins, enabling rapid distribution to tissues. Its lipophilicity allows it to cross the blood–brain barrier and the placenta. In aquatic ecosystems, it bioaccumulates in organisms and biomagnifies up the food chain, leading to elevated concentrations in predatory fish. Humans are exposed mainly through consumption of contaminated seafood.

It is a potent neurotoxin and teratogen. Symptoms include sensory disturbances, impaired coordination, and cognitive deficits; fetal exposure is particularly dangerous. The biological half-life in humans is about 70 days, and elimination occurs slowly. Environmental demethylation by bacteria and photodegradation can reduce methylmercury levels.

Regulation and history: The Minamata disease outbreak highlighted the hazards of methylmercury discharge. Health agencies maintain guidelines to limit exposure; for example, the U.S. Environmental Protection Agency sets a reference dose of about 0.1 μg/kg/day, and the U.S. Food and Drug Administration has an action level of 1 ppm for methylmercury in fish and shellfish.