Mercury

Abstract

Mercury is a global pollutant that exists in three oxidation states: Hg 0 (metallic), Hg + (mercurous), and Hg 2+ (mercuric) mercury. In organometallic derivatives, such as methylmercury (CH 3 Hg + ), mercury is covalently bound to carbon. In its elemental form, mercury is a dense, silvery‐white, shiny metal, which is liquid at room temperature and boils at 357°C. At 20°C, the vapor pressure of the metal is 0.17 Pa (0.0013 mmHg), and a saturated atmosphere at this temperature contains a mercury concentration of 14 mg Hg/m 3 , which is more than 200 times the occupational exposure limit. Hg 0 residence in the atmosphere can be high (greater than a year). Mercury compounds differ greatly in their solubility, with metallic mercury being very sparingly soluble, and several salts, such as mercuric chloride, being soluble in water. Of relevance for its environmental fate, methylmercury interacts with nucleophilic groups (i.e. thiols) in aquatic organisms (mainly fish), being bioaccumulated and biomagnified in the aquatic food chain, which represents a major source of human exposure. Both Hg 2+ and methylmercury have strong affinity for thiol groups, in such a way that in the presence of living cells and dissolved organic matter, they will be found mainly bound to sulfide‐ or thiol‐containing molecules.