Hg

The chemical symbol for mercury, a heavy metal that contaminates food mainly as methylmercury, which accumulates in predatory fish such as tuna and swordfish through the marine food chain. Because methylmercury damages the nervous system — especially in developing children and the unborn — regulators set maximum levels in seafood and issue consumption advice for vulnerable groups. Laboratories test fish tissue routinely for total and methylmercury content, and monitoring programmes track levels across species and fishing areas. Controlling mercury exposure is therefore a shared task of environmental regulation, fisheries management, and food-safety surveillance.