Interaction of As with organic matter and Fe (III)-organic matter associations

世界各地都报道了周期性浸水土壤（如fluvisol）中砷污染的情况。一般来说，铁（ll）（氢）氧化物（FHOs）控制土壤溶液中砷的浓度，从而控制其生物利用度。然而，氧化还原振荡会导致FHOs与溶解有机物（QM）共沉淀。除了砷吸附到纯FHOs上外，砷通过多价金属桥（三元砷配合物）与OM的结合被认为是一种重要的吸附机制。因此，FHO-OM共沉淀物是复杂的吸附剂混合物，其固定As的能力可能与实验室研究中常用的纯fho有很大不同。这些共沉淀物可能在氧化还原振荡中发生了Fe矿物学和OM的改变。氧化还原振荡对砷固定化的累积效应尚不清楚。同样，FHO-OM共沉淀物中As的动员电位也不清楚。该项目的目标是阐明(i)通过金属桥将As与OM结合，（ii）氧化还原振荡时共沉淀物组成的变化及其对As吸附的影响，以及（iii）从FHO-OM共沉淀物中动员As。为了实现这些目标，将进行批处理和生物反应器实验以及薄梯度扩散（DGT）实验。通过使用57Fe-Mössbauer和同步加速器x射线吸收光谱等分析工具，该项目将有助于对富有机质土壤中受氧化还原振荡影响的砷迁移的非生物控制有一个基本的了解。

Arsenic (As) contaminations in periodically water-logged soils such as Fluvisols are reported throughout the world. Generally, Fe(lll) (hydr)oxides (FHOs) control the soil solution concentrations of As and hence its bioavailability. Redox oscillations, however, can cause coprecipitation of FHOs with dissolved organic matter (QM). Besides of Sorption of As to pure FHOs, binding of As to OM via multivalent metal bridges (ternary As complexes) has been suggested as an important sorption mechanism of As. Therefore, FHO-OM coprecipitates are complex adsorbent mixtures whose capability to immobilize As may significantly differ from that of pure FHOs commonly used in laboratory studies. These coprecipitates might be altered upon redox oscillations with respect to both Fe mineralogy and OM. The cumulative effects of redox oscillations on As immobilization are unknown. Likewise, the mobilization potential of As in FHO-OM coprecipitates is unclear. The objectives of the project are to elucidate (i) the binding of As to OM via metal bridges, (ii) changes in coprecipitate composition upon redox oscillations and its effect on As sorption, and (iii) the mobilization of As from FHO-OM coprecipitates. To achieve these goals, batch and bioreactor experiments as well as diffusion in thin gradients (DGT) experiments will be conducted. By using analytical tools such as 57Fe-Mössbauer and synchrotron X-ray absorption spectroscopy, this project will help to gain a fundamental understanding of the abiotic controls of As mobility in organic-rich soils subject to redox oscillations.