School of Ecology and Environment, Inner Mongolia University, Hohhot, 010021, China.
School of Ecology and Environment, Inner Mongolia University, Hohhot, 010021, China; Institute of Environmental Geology, Inner Mongolia University, Hohhot, 010021, China.
Chemosphere. 2022 Sep;302:134860. doi: 10.1016/j.chemosphere.2022.134860. Epub 2022 May 9.
In soils, the speciation transformation of As were inherently related to the behaviors of iron (oxyhydr) oxides. It is poorly understood that the effects of the transformation of iron (oxyhydr) oxides coupled with As speciation transformation during dissimilatory Fe(III) reduction (DIR) involving with humic substances (HS) as electron donor or shuttle in soils with high arsenic geological background. In this study, the relationships between the transformation of iron (oxyhydr)oxides and As speciation transformation were investigated according to the response between continuously As speciation monitoring and iron (oxyhydr) oxides identification during DIR in the soils. The results showed that F4 (arsenic incorporated with amorphous iron (oxyhydr)oxides including ferrihydrite and schwertmannite) and F5 (arsenic incorporated with crystalline iron (oxyhydr)oxides including hematite and magnetite) were the main source and sink for As(III) during DIR. During the incubation period, Fe(II) was the dominant driving force for the reduction of As(V) in the water-soil system. The XRD analysis indicated the changes of iron oxides such as ferrihydrite, schwertmannite, hematite and magnetite were closely related to the release and reduction of As, and those iron oxides could play governing roles for As speciation transformation during DIR in soils. Different from the known mechanism in low As concentrations, a limiting effect of As concentration on iron oxides transformation was found in our incubation experiments using soils with high As geological background (∼1000 mg/kg). This work provides new insights for Fe as governing role in As speciation transformation in soils with high arsenic geological background by firstly identifying the corresponding iron (oxyhydr)oxides in operationally defined arsenic speciation incorporated with iron oxides.
在土壤中，砷的形态转化本质上与铁（氢）氧化物的行为有关。在涉及富里酸（HS）作为电子供体或穿梭体的高砷地质背景土壤中，异化铁（III）还原（DIR）过程中，铁（氢）氧化物的转化与砷形态转化的耦合对砷形态转化的影响还知之甚少。在这项研究中，根据 DIR 过程中连续砷形态监测与铁（氢）氧化物鉴定之间的响应，研究了铁（氢）氧化物转化与砷形态转化之间的关系。结果表明，F4（与无定形铁（氢）氧化物结合的砷，包括水铁矿和硫铁矿）和 F5（与结晶铁（氢）氧化物结合的砷，包括赤铁矿和磁铁矿）是 DIR 过程中 As(III)的主要源和汇。在孵育期内，Fe(II)是水-土系统中 As(V)还原的主要驱动力。XRD 分析表明，铁氧化物如水铁矿、硫铁矿、赤铁矿和磁铁矿的变化与砷的释放和还原密切相关，这些铁氧化物在土壤 DIR 过程中对砷形态转化起着控制作用。与低砷浓度下已知的机制不同，在使用高砷地质背景土壤（约 1000mg/kg）的孵育实验中，发现砷浓度对铁氧化物转化的限制作用。这项工作通过首次在操作定义的砷形态中鉴定与铁氧化物结合的相应铁（氢）氧化物，为高砷地质背景土壤中铁对砷形态转化的控制作用提供了新的见解。
