Bacterial Reduction of Arsenate in Sea Water

Abstract

ARSENIC in the ocean exists primarily as arsenite and arsenate and thermodynamic calculations¹ indicate that in oxygenated sea water at pH 8.1, the equilibrium ratio of the activity of arsenate to arsenite should be about 10²⁶. But observations^2–4 suggest that the ratio is, in fact, in the range 10⁻¹ to 10¹, far from the equilibrum value. My experiments with the inorganic oxidation of added sodium arsenite in surface Sargasso Sea water (in preparation) suggest that, at natural concentrations, all arsenite should be oxidized to arsenate in a matter of weeks or months. The fact that significant quantities of arsenite have been found in all oceanic regions examined is therefore puzzling unless some steady state mechanism can be discovered to account for it.