Mercury is an element that is found in air, water and soil. It has several forms. Metallic mercury is a shiny, silver-white, odorless liquid. If heated, it is a colorless, odorless gas. It also combines with other elements to form powders or crystals.
Mercury is in many products. Metallic mercury is used in thermometers, dental fillings and batteries. Mercury salts may be used in skin creams and ointments. It's also used in many industries. Mercury in the air settles into water. It can pass through the food chain and build up in fish, shellfish and animals that eat fish.
The nervous system is sensitive to all forms of mercury. Exposure to high levels can damage the brain and kidneys. Pregnant women can pass the mercury in their bodies to their babies.
Agency for Toxic Substances and Disease Registry: http://www.nlm.nih.gov/medlineplus/mercury.html