Mercury in our environment is most commonly found in one of the following three main forms: elemental (metallic) mercury, methylmercury, and mercury salts. Mercury can harm the central nervous system.
Elemental (metallic) mercury is a heavy, silvery metal element that is a liquid at room temperature. Liquid mercury evaporates at room temperature and these vapors are invisible, odorless, and, at high levels, are very toxic. In the home, metallic mercury is often found in thermometers, barometers, electrical switches, and thermostats. Even small spills can, in some cases, cause high levels of mercury vapors that are unsafe to breathe. You should respond immediately to all mercury spills.
Methylmercury (organic mercury)
When mercury is released from industries into the air, it can travel long distances and be deposited on soil and in lakes. In lakes, small organisms change the mercury to a form of organic mercury (methylmercury) that builds up in the bodies of fish. Some lakes in North Dakota have health advisories that recommend against eating too much of certain types of fish containing high levels of methylmercury.
Mercury salts are used in fungicides and preservatives for seeds, wood products, fluorescent lights, and in the manufacture of batteries and paper. Mercury salts are quite corrosive and if eaten, can quickly damage tissues of the digestive tract and kidneys.
For more information
The major sources of mercury exposure to the general public are through fish consumption and from spills of small amounts of metallic mercury (such as might occur from breaking thermometers or from mercury stored in school laboratories). For more information on mercury, see the Toxic Chemical Fact Sheet on Mercury.