methylmercury

Methylmercury (MeHg) is an organomercury compound formed when certain microorganisms methylate inorganic mercury (Hg2+). This process occurs mainly in anoxic sediments, wetlands, and some marine environments. MeHg is highly lipophilic, readily crosses membranes, and bioaccumulates in aquatic organisms, biomagnifying up the food chain to highest levels in predatory fish. It is persistent in ecosystems; in humans, MeHg's biological half-life is about 70 days.

Exposure is primarily via contaminated seafood. Occupational exposure can occur in industries handling mercury. MeHg is a potent neurotoxin, especially for developing fetuses and young children, causing cognitive and motor deficits; in adults, higher exposures may affect sensation, coordination, and memory. High exposures can impair kidney function and immune responses.

MeHg crosses the placental and blood–brain barriers and binds to sulfhydryl groups in proteins, disrupting cellular processes. It is routinely monitored in seafood; U.S. guidance cites an EPA reference dose around 0.1 µg/kg/day, and various agencies set seafood safety limits (commonly 1 mg/kg for methylmercury in fish). To reduce risk, many advisories recommend choosing lower-mercury species.

Historical outbreaks, notably Minamata disease in Japan, highlighted methylmercury risks from industrial discharge. Environmental management seeks to lower mercury emissions and limit methylation in key ecosystems. Ongoing research covers exposure assessment, public health guidance, and remediation strategies.