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PH16 Metals in the Environment: Chemistry and Fate Issues
(PH150) The effect of thioarsenite formation on As(III) toxicity.
Rader, K1, Dombrowski, P1, Farley, K1, Mahony, J1, DiToro, D2, 1 Manhattan College, Riverdale, New York, USA2 University of Delaware, Newark, Delaware, USA
ABSTRACT- Soluble arsenite-sulfide complexes (thioarsenites) play a significant role in the chemistry of arsenic in reducing, sulfidic environments at circumneutral pH. Chemical equilibrium calculations using thioarsenite thermodynamic data from the literature indicate that the formation of a dithioarsenite complex, AsS(OH)(SH)-1, reduces the concentration of all uncomplexed As(III) species present (defined as HxAsO3x-3), usually dominated by H3AsO30 at neutral pH. The Microtox® acute toxicity test was used to assess the effect of thioarsenite formation on As(III) toxicity. Tests performed on solutions with varying S:As ratios provide strong evidence that As(III) toxicity is primarily a function of the HxAsO3x-3 concentration rather than the total soluble arsenite concentration. This suggests that the formation of thioarsenites mitigates As(III) toxicity. The potential for thioarsenite formation to reduce As(III) toxicity in sediment is evaluated using chemical equilibrium calculations and sediment pore water field data from various sources.
Key words: Microtox, arsenic, thioarsenite, toxicity
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