The poison chain for mercury in the environment

Abstract

The toxic effects of mercury in specific population groups, for example following occupational exposure or therapeutic application, has long been known, but mercury as a general environmental hazard has followed comparitively recent technological development. Contamination with both inorganic mercury and organic mercury compounds has resulted from industrial waste and from the use of the latter compounds as fungicides. Deposited eventually in rivers and lakes, this has led to raised levels of mercury in fish. Under appropriate conditions, methylation of mercury may occur in the natural environment, converting less toxic inorganic and aryl mercury compounds into the more toxic alkyl mercury form. In certain predominantly fish eating populations this has led to an increase in the body burden for organic mercury, resulting in localized outbreaks of methyl mercury poisoning. Raised levels of mercury in eggs and bird tissues have resulted from feeding on mercury contaminated fish and on organomercury treated seed. This has contributed to a reduction in some species of birds in certain areas. In addition to the direct toxic action of mercury, limited evidence suggests that methyl mercury compounds may possibly exert mutagenic and teratogenic effects, at levels below those usually associated with poisoning. Methyl mercury concentration should be monitored in exposed groups and where this is raised, epidemiological studies performed to evaluate a possible hazard.