厌氧微生物作用下土壤中砷的形态转化及其分配

厌氧微生物作用下土壤中砷的形态转化及分配比例对砷的环境行为与归趋具有重要影响。实验利用张士污灌区土壤负载低浓度砷,研究了厌氧微生物作用下砷的形态转化过程,并通过磷酸盐及盐酸提取土壤中的砷、铁和硫,探讨了砷在土壤中结合形态的变化及土壤矿物结构转化与砷环境行为的关联。实验结果表明,微生物作用下土壤负载的砷被迅速还原为As(III)并释放进入液相,培养24h后液相累积的As(T)量达到16.9μmol·L-1,其中As(III)占液相总砷含量的91%以上;48h后释放的砷被再次固持,液相残留的As(III)浓度仅为1.5μmol·L-1。尽管微生物还原作用造成土壤中铁氧化物的活化,但固相中磷酸盐提取态与盐酸提取态砷所占的比例分别从载砷量的45.3%和49.8%降低到22.0%与0.22%,而体系中硫酸盐还原产生的硫离子的量与砷的释放量保持负相关。可见微生物还原作用下砷发生了活化,释放和再固定的过程,土壤负载的砷从溶解态、吸附态及铁氧化物结合态逐渐被转化为更稳定的硫化物结合态。此研究对于预测土壤中砷的行为与归趋及污染土壤修复具有一定意义。

Speciation Transformation and Distribution of Arsenic in Soils under Action of Anaerobic Microbial Activities

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.