Other Metal-alkyl Complexes in the Environment

Tellurium biomethylation also occurs via the Challenger mechanism. However, it is not yet clear whether or not the same enzymes are used as in the case of sele- 

The formation of methyl antimony compounds by biomethylation has been confirmed only recently [25], despite the fact that methyl antimony compounds have been found in natural waters before [3a], The research on alkylated antimony compounds in biological environments got an initial impetus from the examinations on the possible role of trimethylstibine as contributor to the sudden infant death syndrome [26], 

Trimethyl bismuth occurring in the environment was detected in several environmental sources [27]. Biomethylation of bismuth very likely involves non oxidative methyl transfer, suggesting that 2 c is the most likely methyl source. 

Organic lead compounds have been introduced into the environment as pollutants, e.g. the fuel additive (anti knocking agent) tetraethyl lead, making it difficult to establish a biogenic origin of related compounds. However, methyl lead compounds, e.g. (CH3)4Pb have been discovered under environmental conditions, which are in accord with the biomethylation of lead [30]. In a comparative study, bioactive sediments methylated mercury, tin and lead substrates. Mercury underwent methylation ca. 10000 times faster than tin and lead, but lead was methylated more readily than tin [31]. 

Methyl thallium species have been discovered in natural water quite recently but thallium was reported to undergo biomethylation in vitro already more than two decades ago [32]. While the total thallium levels in oceans and lakes vary between 1.6 and 20.1 ng/L, levels exceeding 1000 ng/L have been found in industrial waste waters [33]. The proportion of [(CH3)2T1]+ to total thallium ranged up to 48%. The stability of the monomethyl derivatives varies in the order mercury(II) thallium(III) 2 lead(IV) bismuth(V) [3b]. 

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