A review of metal accumulation and toxicity in wild mammals. I. Mercury.

Release of Hg compounds into the environment from point sources has largely been curtailed due to the known impacts of Hg on biological systems. Mercury continues to be released into the environment, however, from nonpoint sources such as combustion of fossil fuels and smelting operations. While the accumulation and toxicity of Hg in aquatic biota, domestic animals, and humans is well documented, relatively little is understood about these processes in wild terrestrial mammals. The purpose of this paper is to review the available literature on Hg levels and toxicity in wild mammals (excluding marine mammals). It is clear that Hg levels are biomagnified within terrestrial food chains, where carnivores greater than omnivores greater than herbivores. Among carnivorous species, Hg levels are generally highest in fish-eating animals. There is usually a high degree of correlation of Hg levels between different animal tissues. The age and sex of an animal appear to influence observed Hg levels, but field data are conflicting for both factors. Tissue Hg levels are affected by location, with significant differences attributable to both local contamination and natural background variability. Experimental studies have shown many mammal species to sensitive to Hg intoxication, but documented incidents of Hg poisoning in wild mammals are rare. Such rarity may be more a function of our inability to observe and demonstrate Hg poisoning in wild populations, rather than an absence of the disease.