Anaerobic microbe mediated arsenic reduction and redistribution in coastal wetland soil

Arsenic (As) pollution in coastal wetland soil has attracted attention. However, how anaerobic microbes impact the fate of As in coastal wetland environments remains poorly understood. To elucidate underlying mechanisms of anaerobic microbes mediated As mobilization, incubation experiments were performed in this study. The results demonstrate that the concentrations of total dissolved As and As(III) were higher in biotic incubations compared with abiotic controls. The dissolved As(III) concentrations increased and reached maximum values of 11.0 ± 1.2 and 12.0 ± 1.1 μg/L for biotic incubations with and without additional sulfate, respectively. Sulfate and Fe reduction induced by anaerobic microbes were evidenced by the detection of sulfide and Fe(II) in biotic incubations. The sequential extraction results indicated that the content of crystalline Fe mineral fraction of As (As_cry) increased and that of amorphous Fe mineral fraction of As (As_amo) decreased in the solid phase. Therefore, the released As was attributed to microbially mediated reductive dissolution of amorphous Fe mineral matter and, after 40 days of incubation, the decreased As might be immobilized via re-adsorption onto, or co-precipitation with, the newly formed crystalline Fe minerals. The 16S rRNA results indicated that Proteobacteria, Chloroflexi, Actinobacteria, and Firmicutes constituted the majority of the bacterial community in biotic incubations. The sulfate-reducing bacterium Desulfocapsa induced sulfate reduction and further promoted the reduction and release of As in soils. This study provides insights into the mechanism for As mobilization and redistribution in coastal wetland soils.