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

The biomethylation of arsenic by the filamentous fungus Scopulariopsis brev icaulis is well documented, and the biomethylation of antimony by this fung us was recently established. However, in all the previous studies each meta lloid was studied in isolation. Arsenic and antimony are often associated i n the environment, and so an understanding of interactions between these el ements is necessary. To this end, S. brevicaulis was grown in media contain ing mixtures of arsenic and antimony compounds in various proportions, and the principle nonvolatile biomethylation products (trimethylantimony and tr imethylarsenic species) in the medium were quantified by using HG-GC-AAS. I t was found that the yield of trimethylantimony compounds, obtained from th e biomethylation of potassium antimony tartrate, was increased in the prese nce of sodium arsenite. The production of trimethylarsenic species from sod ium arsenite was significantly inhibited in the presence of antimony (eithe r as potassium antimony tartrate or antimony trioxide) at antimony concentr ations too low to inhibit growth. This is although arsenic(III), in the abs ence of antimony, is much more readily biomethylated. That is 1.2-5.3% of a dded arsenic is biomethylated by S. brevicaulis whereas only 0.0006-0.008% of added antimony(III) is biomethylated over 1 month. Potassium hexahydroxy antimonate had no effect on arsenic biomethylation. The addition of potassi um tartrate to cultures did not inhibit arsenic biomethylation. The biometh ylation 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.