Evidence for the absence of biological methylation of lead in the environment

Abstract

Biological methylation of arsenic and mercury by pure cultures of microorganisms such as moulds1 and bacteria2, and by ‘mixed cultures of environmental systems’, such as sediments3, sludges or canal mud4, seem to be well known processes, although there is no unequivocal evidence of the proposed pathways5–7. In contrast, the biomethylation of inorganic or ionic organic lead compounds has been a topic of controversy, with no conclusive explanation of the mechanism of the reactions that might lead to the corresponding alkyl lead compounds8–13. We report here attempts to produce leadalkyls in anaerobic and aerobic conditions. Our study was greatly helped by our use of labelled and unlabelled substrates as methyl donors and labelled and unlabelled lead compounds as acceptors. In none of numerous experiments have we found leadalkyls to be the products of biomethylation. Experiments with organic lead salts resulted in lead tetraalkyls but only as the products of chemical reactions.