Institute of Biogeochemistry and Pollutant Dynamics, ETH Zurich, CHN, 8092 Zurich, Switzerland.
Environ Sci Technol. 2010 Jan 1;44(1):116-22. doi: 10.1021/es902100h.
Arsenic (As) in soils and sediments is commonly mobilized when anoxic conditions promote microbial iron (Fe) and As reduction. Recent laboratory studies and field observations have suggested a decoupling between Fe and As reduction and release, but the links between these processes are still not well understood. In microcosm experiments, we monitored the formation of Fe(II) and As(III) in the porewater and in the soil solid-phase during flooding of a contaminated floodplain soil at temperatures of 23, 14, and 5 degrees C. At all temperatures, flooding induced the development of anoxic conditions and caused increasing concentrations of dissolved Fe(II) and As(III). Decreasing the temperature from 23 to 14 and 5 degrees C strongly slowed down soil reduction and Fe and As release. Speciation of As in the soil solid-phase by X-ray absorption spectroscopy (XAS) and extraction of the Fe(II) that has formed by reductive Fe(III) (hydr)oxide dissolution revealed that less than 3.9% of all As(III) and less than 3.2% of all Fe(II) formed during 52 days of flooding at 23 degrees C were released into the porewater, although 91% of the initially ascorbate-extractable Fe and 66% of the total As were reduced. The amount of total As(III) formed during soil reduction was linearly correlated to the amount of total Fe(II) formed, indicating that the rate of As(V) reduction was controlled by the rate of microbial Fe(III) (hydr)oxide reduction.
土壤和沉积物中的砷通常在缺氧条件下促进微生物铁（Fe）和砷还原时被迁移。最近的实验室研究和野外观察表明，Fe 和 As 还原和释放之间存在解耦，但这些过程之间的联系仍不清楚。在微宇宙实验中，我们监测了受污染洪泛区土壤在 23、14 和 5°C 时淹没过程中孔隙水中和土壤固相中铁（II）和砷（III）的形成。在所有温度下，洪水都会导致缺氧条件的发展，并导致溶解的 Fe（II）和 As（III）浓度增加。将温度从 23°C 降低到 14°C 和 5°C 会强烈减缓土壤还原和 Fe 和 As 的释放。X 射线吸收光谱（XAS）对土壤固相中 As 的形态分析以及通过还原 Fe（III）（氢）氧化物溶解提取形成的 Fe（II）表明，在 23°C 下 52 天的洪水期间，只有不到 3.9%的所有 As（III）和不到 3.2%的所有 Fe（II）释放到孔隙水中，尽管最初的抗坏血酸可提取的 Fe 中有 91%和总 As 的 66%被还原。土壤还原过程中形成的总 As（III）的量与形成的总 Fe（II）的量呈线性相关，表明 As(V)还原的速率受微生物 Fe（III）（氢）氧化物还原的速率控制。
