Toxicology of Mercury

MERCURY

Metallic mercury as “quicksilver”—the only metal that is liquid under ordinary conditions—has attracted scholarly and scientific interest from antiquity. The mining of mercury was early recog-nized as being hazardous to health. As industrial use of mercury became common during the last 200 years, new forms of toxicity were recognized that were found to be associated with various transformations of the metal. In the early 1950s, a mysterious epidemic of birth defects and neurologic disease occurred in the Japanese fishing village of Minamata. The causative agent was determined to be methylmercury in contaminated seafood, traced to industrial discharges into the bay from a nearby factory. In addition to elemental mercury and alkylmercury (including meth-ylmercury), other key mercurials include inorganic mercury salts and aryl mercury compounds, each of which exerts a relatively unique pattern of clinical toxicity.

Mercury is mined predominantly as HgS in cinnabar ore and is then converted commercially to a variety of chemical forms. Key industrial and commercial applications of mercury are found in the electrolytic production of chlorine and caustic soda; the manufacture of electrical equipment, thermometers, and other instruments; fluorescent lamps; and dental amalgam. The wide-spread use of elemental mercury in artisanal gold production is a growing problem in many developing countries. Mercury use in pharmaceuticals and in biocides has declined substantially in recent years, but occasional use in antiseptics and folk medicines is still encountered. Thimerosal, an organomercurial preservative that is metabolized in part to ethylmercury, has been removed from almost all the vaccines in which it was formerly present. Environmental exposure to mercury from the burning of fossil fuels, or the bioaccumulation of methylmercury in fish, remains a concern in some regions of the world. Low-level exposure to mer-cury released from dental amalgam fillings occurs, but systemic toxicity from this source has not been established.