Keywords: 
• soil /
• arsenic /
• microbial reduction /
• speciation transformation /
• redistribution

Abstract: The influence of microbial mediated speciation transformation of arsenic and ratio of distribution on the environmental behavior and fate of arsenic in soil were investigated in this work. The soil was collected from the wastewater-irrigated farmland in Zhangshi, Shenyang and was loaded with low concentration of arsenic. Phosphate and hydrochloric acid was applied to extract As, Fe, S in order to evaluate the effect of transformation of arsenic binding forms and soil minerals on the environmental behavior of arsenic in the incubated soil. Results showed that arsenate was significantly reduced by microorganism,then released to aqueous phase. The concentration of As(T) (total As) reached 16.9 μmol·L^-1 within 24 hours of incubation. Among of As(T), more than 91% of arsenic was As(III). After 48 hours, the released arsenic was resequestered in solid phase. The residual As(III) in solution was only 1.5 μmol·L^-1 in the end of incubation. Although the microbial reduction caused the activation of iron oxyhydroxides in soil, the amounts of phosphate extracted As and HCl extracted As sharply decreased from 45.3% and 49.8% of total As to 22.0% and 0.2%, respectively, after 15 days of incubation. Significant negative correlation was observed between sulfide produced by reduction of sulfate and the released As, suggesting that arsenic was reduced, released and resequestered under the action of anaerobic microbial activities. The speciation of arsenic was gradually transformed from dissolved, adsorbed and iron oxyhydroxide-associated forms into more stable species like sulfide-associated forms. The findings may have important implications to the prediction of the behavior and fate of arsenic and remediation of arsenic polluted soils.