Antimony isotope fractionation through biomethylation
Fermenter cultures with anaerobe bacteria communities (sewage sludge medium) were analysed for volatile and non-volatile methylantimony species. Gas-samples were analysed by GC-ICP-MS, and fermenter sludge medium and cytosol by HG-GC-ICP-MS. Trimethylstibine was the sole volatile species, and non-volatile methylantimony species were found in the fermenter sludge medium, but higher levels were found in sludge cytosol. Antimony isotopic fractionation values were determined as high as d 123Sb + 150 in one fermenter experiment. Additionally, the species-specific isotope ratio ‘fingerprint’ from the methylantimony species confirmed the mechanism proposed by Challenger for the biomethylation process. It showed the formation of partially methylated antimony species as intermediates. However, other stimulated bacteria cultures did not show any antimony isotope fractionation through biomethylation. Further investigation into the biomethylation process was studied to determine whether antimonate, Sb(V), is methylated by anaerobe bacteria communities. For this purpose, isotopically enriched 123Sb(V) was used to monitor the antimony isotope ratio of the methylantimony metabolite species. The antimonate was stepwise methylated. Environmental gas samples from a landfill site and a digester plant, showed trimethylstibine as the prominent organometal(loid)-species. Moreover, the biovolatilisation species trimethylstibine was determined to have an antimony isotope fractionation value of d 123Sb + 10. Antimony-glutathione complexes were identified in both in vivo and in vitro studies of antimony interactions with biomolecules. The molecular structures of these Sb-GS complexes were determined using FI-ESI-MS. The glutathione influence was then further investigated in a non-enzymatic methylation of antimony with methylcobalamin. The prominent species produces in vivo was monomethylantimony, with small amount of dimethylantimony.