Arsenic and antimony biomethylation by Scopulariopsis brevicaulis: Interaction of arsenic and antimony compounds

The biomethylation of arsenic by the filamentous fungus Scopulariopsis brevicaulis is well documented, and the biomethylation of antimony by this fungus was recently established. However, in all the previous studies each metalloid was studied in isolation. Arsenic and antimony are often associated in the environment, and so an understanding of interactions between these elements is necessary. To this end, S. brevicaulis was grown in media containing mixtures of arsenic and antimony compounds in various proportions, and the principle nonvolatile biomethylation products (trimethylantimony and trimethylarsenic species) in the medium were quantified by using HG-GC-AAS. It was found that the yield of trimethylantimony compounds, obtained from the biomethylation of potassium antimony tartrate, was increased in the presence of sodium arsenite. The production of trimethylarsenic species from sodium arsenite was significantly inhibited in the presence of antimony (either as potassium antimony tartrate or antimony trioxide) at antimony concentrations too low to inhibit growth. This is although arsenic(III), in the absence of antimony, is much more readily biomethylated. That is 1.2-5.3% of added arsenic is biomethylated by S. brevicaulis whereas only 0.0006-0.008% of added antimony(III) is biomethylated over 1 month. Potassium hexahydroxyantimonate had no effect on arsenic biomethylation. The addition of potassium tartrate to cultures did not inhibit arsenic biomethylation. The biomethylation of sodium arsenate was not inhibited as much by antimony compounds. The inhibitory effect of antimony was found to be a function of the ratio of antimony to arsenic rather than the absolute amount of antimony.