The effect of selenium on mercury assimilation by freshwater organisms

In this study, we showed that selenium (Se) deposition from metal smelters in Sudbury, Ontario, greatly re duces the bioassimilation of mercury (Hg) by aquatic biota throughout the food web. Concentrations of total and methyl mercury in tissues of zooplankton, mayflies (Stenonema femoratum), amphipods (Hyalella azteca), and young-of-the-year perch (Perca flavescens) were positively correlated with increasing distance from Sudbury smelters and inversely correlated with Se concentrations in lake water. Although concentrations of total Hg and total Se in tissues showed weak or no correlation in most of the studied aquatic species, methyl mercury and total Se showed much clearer inverse trends. Similar to the results of our previous study of muscle tissue from adult perch and walleye (Sander vitreus), these findings suggest that Se plays an important role in limiting the whole-body assimilation of Hg at lower levels of the aquatic food chain. High Se concentrations may force a preferential assimilation of the element over Hg through a competitive adsorption on binding sites. They may also restrict the solubility and availability of Hg to aquatic organisms or reduce the methylation of this metal in lakes.