Microbial reduction of arsenate in the presence of ferrihydrite

Increased mobilization of As under anaerobic conditions is of great concern in As contaminated soils and sediments. The identification of important re lease mechanisms may assist in designing safe and effective remediation str ategies, In this study we investigated the effect of microbial reduction of aqueous arsenate (As(V)) on the solubilization of As(V) sorbed to ferrihyd rite, in the absence of reductive dissolution of the Fe(III)-oxide solid ph ase. The addition of 0.1, 1.0, and 5.0 mM As(V) to serum bottles containing 10 mmol L-1 Fe(III) as ferrihydrite resulted in the sorption of 98, 75, an d 20% of the applied As(V), respectively. inoculation with an As(V) reducin g, glucose fermenting microorganism (CN8) was followed by complete reductio n of aqueous As(V) to As(III) at nontoxic As concentrations (up to 1.0 mM), but no reduction or dissolution of the Fe(III) solid phase was observed, D espite rapid reduction of aqueous As(V) to As(III), sorbed phase As remaine d primarily as As(V), and desorption of As(V) was too slow to cause a signi ficant increase in aqueous As concentration over the 24-day experiment, Our study suggests that the reduction of aqueous As(V) may play a relatively m inor role in the solubilization of As(V) sorbed to Fe (hydr)oxide. Arsenic release from contaminated soils and sediments may proceed considerably fast er under conditions favoring dissimilatory Fe(III) reduction leading to the dissolution of sorbing phases.