FORMATION, DISTRIBUTION, AND ECOTOXICITY OF METHYLMETALS OF TIN, MERCURY, AND ARSENIC IN THE ENVIRONMENT

Findings on methylation of tin, mercury, and arsenic in the environment are reviewed. The development of separation and detection systems in trace analysis has made it possible to determine the concentration of these methylated forms in the environment. Abiological methylation mechanisms are similar for these three metals, and methylcobalamin and methyl iodide are thought to be the major methyl donors in the environment. Photochemical reaction and transalkylation produce methylmetals. Humic and fulvic acids are the factors affecting methylation. The research on biological methylation started from incubation with polluted water and sediments, and some exceptional reports cast doubt as to whether it was really biomethylation. Some organisms that can form methyl metals from their metal forms have been separated, and the mechanism has been investigated using the pure culture. Methylation of tin and mercury increases the toxicity of their original metal forms, while methylation of arsenic lowers its toxicity. Methyl metals also have an important role in the geochemical cycle with its higher volatility or lipophilicities. The distribution and ecotoxicities of these methylated compounds in the environment are also discussed.