Mercury exists in metallic, inorganic, and organic forms. Metallic mercury is used in thermometers and fluorescent lamps and can cause pollution when used for gold mining. Organic mercury, like methyl mercury, accumulates in fish and shellfish through the food chain. The highest levels of mercury are found in large predatory fish. Mercury is released from volcanoes and transformed by microorganisms into methyl mercury that fish ingest. Mercury distributes throughout the body, especially the liver and kidneys, and is slowly excreted, with half the amount remaining in the body after 70 days.