Introduction to 2nd Issue on Special Topic: Selenium and Mercury as Interactive Environmental Indicators

This is the second issue of Environmental Bioindicators presenting invited articles describing interactions between methylmercury (MeHg) and selenium (Se). The findings described in these articles confirm the importance of using Se as a bioindicator of environmental and physiological susceptibility to Hg exposure, since these and similar studies indicate the relationship between Hg toxicology and the Se-physiology pathways are important aspects of the environmental Hg issue. The results of these multi-disciplinary studies of Hg-Se interactions coincide and complement one another, and the status of the science on this issue appears to be making the transition from “converging research” to “confirmatory studies”. It is gratifying to note that progress in this research area is improving both understanding of both MeHg toxicity and Se physiology. Although sulfur (S) and Se are chemically similar, Hg’s affinity for Se is ∼10 6 greater than Hg’s affinity for sulfur; ([HgSe]/[Hg 2+ ][Se]=10 45 M) vs. ([HgS]/[Hg 2+ ][S]=10 39 M) (Dyrssen and Wedborg 1991). Although the affinities between the organic forms of Hg, S, and Se are known to be lower than those of the inorganic forms, the relative affinities remain similar. Therefore, it is increasingly clear that most if not all of the adverse impacts of high MeHg exposures occur as a result of pathological effects secondary to impaired