Dimethylarsinoylacetate from microbial demethylation of arsenobetaine in seawater

The fate of 11 arsenic compounds in microbially enriched seawater was monitored for up to 10 days by HPLC–ICPMS. Most of the arsenicals underwent little or no change in this medium, whereas two of the compounds, arsenobetaine and arsenocholine, were completely degraded. Arsenobetaine (Me3As+CH2COO−), the predominant form of arsenic in marine animals, was transformed within hours, initially to dimethylarsinoylacetate (Me2As(O)CH2COO−) and then to dimethylarsinate (Me2As(O)O−). Arsenocholine behaved similarly but degraded at a slower rate. The identity of the new metabolite, dimethylarsinoylacetate, was confirmed by LC electrospray MS. A repeat experiment with arsenobetaine and dimethylarsinoylacetate, and employing LC electrospray MS to monitor the metabolites, produced results qualitatively identical with those from the first experiment. The rapidity of the degradation processes offers an explanation for the apparent absence of arsenobetaine in natural waters. Copyright © 2001 John Wiley & Sons, Ltd.