Mechanisms for the biomethylation of metals and metalloids

The case of methylmercury pollution has demonstrated the profound importance of understanding biologically mediated transformation reactions that yield organometallic compounds with a high potential for bioaccumulation and toxicity. Toxic elements that form organometallic compounds, especially the metal-alkyls (e.g., methylmercury), deserve special concern. Most metal-alkyls are poisonous to the central nervous systems of higher organisms, and these compounds do accumulate in cells. Metal-alkyls that are stable in water, and that have been reported to be synthesized biologically, can be formed from the following toxic elements: Hg, Sn, As, Se, Te, Pd, Au, Tl and Pb. In this report we present details of the mechanisms for biological methylation of certain metals and metalloids with special emphasis on those elements that are widely dispersed in the biosphere. In addition we present preliminary results on the use of flourescence quenching techniques to determine cellular diffusion rates and partition coefficients for methylmercuric chloride.