Mercury is a heavy metal that occurs naturally and can be toxic to humans. It exists in elemental, inorganic, and organic forms, with organic mercury posing the greatest risk. Sources of mercury exposure include mining, fossil fuel combustion, industrial manufacturing, and consumption of contaminated fish. Mercury poisoning can cause neurological, kidney, and developmental issues. Symptoms range from rashes and irritability to tremors, impaired vision and hearing, and Minamata disease.