Toxicology and immunotoxicology of mercury: a comparative review in fish and humans.

This review addresses an important area of environmental and mammalian toxicology by evaluating and comparing mercury-induced effects upon the immune responses of two evolutionarily divergent yet immunologically-related species. The mechanisms of mercury toxicology and immunotoxicology are described herein, including supporting data from the following: sources of exposure; bioavailability and biodistribution; metabolism; and laboratory and field investigations. Based upon the studies presented, the relative sensitivities of fish and human immune cells to mercury exposure are compared and contrasted with regard to mercury's ability to stimulate and/or suppress host immunocompetence. In addition, results from immune assays are compared to mercury tissue burdens, as well as to toxicological threshold level estimates. Such comparisons may help to resolve gaps in our knowledge regarding sensitivity of immunological assays, standardization of immunotoxicological techniques between species, and the extent to which the vertebrate immune system possesses functional reserve and redundancy in response to xenobiotics. A review of this type begins to provide support for the potential usefulness of fish immune cells to serve as indicators for human immunotoxicology risk assessment. Analysis of the reviewed studies supports the following conclusions in both lower and higher vertebrates: a threshold for mercury-induced immunotoxicological effects is likely; multiple exposure scenarios involving high and/or chronic exposures leading to increased body burdens are linked to increased risk of immunomodulation; and highly exposed and/or susceptible subpopulations are at greater risk of toxicological impact.