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

世界各地都报道了周期性淹水土壤中的砷(As)污染，如富营养化土壤。通常，Fe(111)(Hydr)氧化物(FHO)控制土壤溶液中As的浓度，从而控制其生物有效性。然而，氧化还原振荡会导致FHO与溶解的有机物(QM)共沉淀。除了As对纯FHO的吸附外，通过多价金属桥(三元As络合物)与OM的结合被认为是As的重要吸附机制。因此，FHO-OM共沉淀物是一种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显著不同。这些共沉淀物可能会在氧化还原振荡时发生变化，无论是从铁矿物学还是OM而言。氧化还原振荡对AS固定化的累积影响尚不清楚。同样，在FHO-OM共沉淀物中As的动员潜力尚不清楚。该项目的目标是阐明(I)As通过金属桥与OM的结合，(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，将进行间歇和生物反应器实验以及薄梯度扩散(DGT)实验。通过使用57Fe-Mössbauer和同步辐射X射线吸收光谱等分析工具，该项目将有助于从根本上了解受氧化还原振荡影响的富有机土壤中砷的非生物控制。

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.