mercury (Hg) /mur″kyərē/ [L, Mercurius, mythic messenger of the gods] , a metallic element. Its atomic number is 80; its atomic mass is 200.59. It is the only common metal that is liquid at room temperature, and it occurs in nature almost entirely in the form of its sulfide, cinnabar. Mercury is produced commercially and is used in dental amalgams, thermometers, barometers, and other measuring instruments. It forms many poisonous compounds. The air, soil, and water in many areas of the world have become contaminated by mercury because of the burning of fossil fuels that contain the element and because of the greater use of mercury in industry and agriculture. The major toxic forms of this metal are mercury vapor, mercuric salts, and organic mercurials. Elemental mercury is only mildly toxic when ingested because it is poorly absorbed. The vapor of elemental mercury, however, is readily absorbed through the lungs and enters the brain before it is oxidized. The kidneys retain mercury longer than any of the other body tissues.
