CRUCIAL FACTORS IN THE ENVIRONMENTAL IMPACTS OF MERCURY

As with other potentially-toxic trace elements, the environmental impact of mercury depends in part on the availability of the element, and its chemical form, in addition to its concentration in the environment. Unlike most other heavy metals, mercury exhibits a substantial vapor pressure and can develop significant gaseous concentrations. In addition, mercury can be subject to processing by microorganisms, and its methylation to organic forms is particularly important with respect to its environmental toxicity. The cycling of mercury through the various environmental compartments is particularly active and complicates the understanding of source, transport, fate, and environmental impact of this heavy metal.

The primary pathway of mercury from the environment to humans is through the consumption of fish. The mercury in fish is thought to be >95% organic mercury which is essentially 100% absorbed by humans during consumption. Little mercury is currently being released to the environment in its organic form, but certain environmental conditions promote the conversion of inorganic forms to the more toxic organo-mercurials. In fact, modern studies show that there is little relationship between total mercury in the environment and its accumulation in fish and subsequently in humans. More important is the biogeochemical cycling that results in availability of organic mercury. Conversely, natural and human-induced environmental conditions or modifications can suppress the solubility, availability, and chemical form of mercury. An understanding of these factors is critical to assessing the environmental danger of mercury in discrete areas and in guiding environmental manipulations that can suppress its environmental impacts.

This paper will discuss details of the geochemistry and environmental cycling of mercury that impact its environmental danger to humans, using examples from global sites contaminated with mercury.