土壤是地下水和农产品中砷的主要来源。硫酸盐的输入能够促进还原条件下固相砷的活化释放，但目前对硫酸盐影响土壤砷形态和行为的分子机制尚不清楚。本项目拟以我国典型砷污染土壤为研究对象，通过野外调研和室内实验研究不同条件下硫酸盐输入对污染土壤中砷、铁、硫等元素形态转化、活化迁移的影响；通过精确控制物理化学条件确定导致土壤砷活化释放的硫酸盐含量、pH、Eh临界值。同时研究典型土壤矿物对不同形态砷的吸附动力学和吸附容量，采用红外光谱、同步辐射XAFS、多重散射从头计算（ab initio）等手段表征解析砷在矿物表面的分子结构，从分子层面揭示砷在矿物表面的吸附解吸对其在固液两相分配的影响。根据野外和室内实验的结果，结合光谱表征和热力学计算，最终揭示不同环境条件下硫酸盐输入对土壤砷活化迁移的影响，确定其分子机制，为预测污染土壤砷释放对地下水和食品安全的影响提供科学依据。

Soil is a dominant As source of ground water and food. The addition of sulfate can significantly accelerate As mobilization under anoxic conditions. However, presently, the effect of dissimilatory sulfate reduction on geochemical occurrence and behavior of As in soils remains unclear. This project is attempting to discover the effect of sulfate addition on the transformation and mobilization of As, Fe and S under anoxic conditions, and to determine the critical value of sulfate concentration inducing As mobilization in contaminated soils through field survey and laboratory experiments. At the same time, we will investigate the sorption kinetics and capability of typical soil minerals for different species of As and use FTIR, synchrotron XAFS and multiple scattering ab initio calculation technology to discover the molecular structure of As on the surface of minerals and its effect on As distribution between solid and aqueous phases. Based on the results of field survey, laboratory experiments, spectrometrical characterization and thermodynamic calculation, the effect of sulfate addition on As transformation and mobilization in soils and its mechanism could be more comprehensively understood. In turn, the achievements of this project can provide solid scientific basis for predicting the potential risks of As contaminated soils for ground water and foods safety.