REDUCTION OF HG2- AND I-( BY CHLORELLA CELLS IN T HE PRESENCE OF BR)

Hg2+ adsorbed to Chlorella cells in the presence of halide ions were n ot desorbed by the addition of EDTA or thiol compounds such as cystein e or glutathione. Rapid reduction of Hg2+ to metallic mercury (Hg-0) t ook place in the cells when the ion species [HgX(2)](0) (X=Br- Or I-) was dominant, and this was the reason why adsorbed Hg2+ was not desorb ed from the cells by the addition of extractants. Adsorption and reduc tion of Hg2+ decreased with increasing halide ion concentration, when the ion species [HgX(3)](-) and [HgX(4)](2-) became dominant. In the p resence of [HgBr2](0) complex, the amount of Hg-0 volatilized increase d with increasing Hg2+ added to the medium. A maximum amount of 125 mu mol.g-cells(-1) was recovered as volatilized Hg-0 at [HgBr2](0) compl ex concentrations of 170 similar to 250 mu mol.g-cells(-1). At 500 mu mol [HgBr2].g-cells(-1), no volatilization of Hg-0 was observed. In th e presence of [HgI2](0) complex, only 60 mu mol.g-cells(-1) was recove red as volatilized Hg-0 at 100 mu mol [HgI2].g-cells(-1). Reduction of Hg2+ was inhibited at a complex concentration of more than 150 mu mol [HgI2].g-cells(-1). Suppression of Hg-0 volatilization may be due to inhibition of the oxidation-reduction enzyme system in the cell, and t he [HgI2](0) complex seems to be more toxic to the cell.