Methylmercury

Methylmercury is the organic form of mercury produced when aquatic microbes convert inorganic mercury pollution into a compound that accumulates in fish, shellfish, and marine mammals. It is a potent neurotoxin that crosses the blood-brain barrier and the placenta, and the developing nervous system is especially vulnerable, which is why health agencies advise pregnant women and young children to limit consumption of high-mercury fish such as shark, swordfish, king mackerel, and large tuna. Regulators set maximum limits for methylmercury in seafood, and monitoring programs test commercial catches against them using cold-vapor and mass-spectrometric methods. It is routinely measured as the key indicator of mercury contamination of foods, especially seafood and water.