[Microbial reduction and mobilization of adsorbed arsenate on ferric/aluminum hydroxides]

Although the mechanisms of arsenic release into groundwater remain poorly characterized, microbial reduction of As (V) adsorbed on the surface of iron oxides and the reductive dissolution of iron oxides are generally considered to play a key role in the mobilization of arsenic. We investigated the impact of bacterial reduction of adsorbed As (V) on a Al:Fe (1:0, 1:1, 0:1) hydroxides on arsenic mobilization using the mixed bacterial culture. After inoculation, the increase of dissolved As (III) concentration was observed, whereas As (V) was negligible in aqueous phase. Arenic release for the Al:Fe (1:0, 1:1, 0:1) hydroxides systems was 60 microg/L, 1.3 mg/L and 7.8 mg/L respectively. On the contrary, neither reduction nor release of arsenic was observed in the uninoculated groups. Furthermore, the introduction of aluminium may be responsible for the release of arsenic owing to its weaker affinity to As (III). In addition, our results showed that Fe reduction occurred far later than arsenic reduction and mobilization and obvious increase was not observed even after Fe reduction occurred. It suggested that in natural systems, the biotic reduction of As (V) adsorbed on ferric oxides or Fe (III) may not the major cause of arsenic release in sediment or groundwater system as previous works proposed. The reduction of As (V) bound to aluminum oxides or other minerals may play a key role.