Microbial and geochemical processes controlling the oxidation and reduction of arsenic in soils

Abstract

Arsenic (As) is a common contaminant in soil-water systems, where it exists predominately as arsenate (AsV) or arsenite (AsIII), the latter of which is considered to be the more mobile and toxic form. The amount of arsenite or arsenate in natural water systems is influenced by geochemical conditions and the presence of As transforming microorganisms. Consequently, the goals of this study were to evaluate the effects of: (i) arsenic concentration on microbial populations responsible for As oxidation-reduction in a previously uncontaminated soil, and (ii) phosphate:arsenic ratio on the oxidation or reduction of arsenic. Laboratory column experiments were conducted to evaluate the influence of soil arsenic concentration on microbial community composition and to identify microorganisms and mechanisms responsible for As transformations occurring under aerobic conditions. Indigenous microorganisms within a previously uncontaminated agricultural soil were exposed to arsenite or arsenate at three concentrations (2, 20 and 200 mg As L-1) for approximately 30 days.