Department of Health and Environmental Sciences, Xi'an Jiaotong-Liverpool University, 111 Ren'ai Road, Suzhou, Jiangsu, 215123, China; Department of Environmental Science, University of Liverpool, Brownlow Hill, Liverpool, L69 7ZX, UK.
Department of Health and Environmental Sciences, Xi'an Jiaotong-Liverpool University, 111 Ren'ai Road, Suzhou, Jiangsu, 215123, China; Department of Environmental Science, University of Liverpool, Brownlow Hill, Liverpool, L69 7ZX, UK; Chemistry, Environmental & Life Sciences, University of the Bahamas, New Providence, Nassau, Bahamas.
Chemosphere. 2021 Apr;269:128713. doi: 10.1016/j.chemosphere.2020.128713. Epub 2020 Oct 22.
The sharp redox gradient at soil-water interfaces (SWI) plays a key role in controlling arsenic (As) translocation and transformation in paddy soils. When Eh drops, As is released to porewater from solid iron (Fe) and manganese (Mn) minerals and reduced to arsenite. However, the coupling or decoupling processes operating within the redox gradient at the SWI in flooded paddy soils remain poorly constrained due to the lack of direct evidence. In this paper, we reported the mm-scale mapping of Fe, As and other associated elements across the redox gradient in the SWI of five different paddy soils. The results showed a strong positive linear relationship between dissolved Fe, Mn, As, and phosphorus (P) in 4 out of the 5 paddy soils, indicating the general coupling of these elements. However, decoupling of Fe, Mn and As was observed in one of the paddy soils. In this soil, distinct releasing profiles of Mn, As and Fe were observed, and the releasing order followed the redox ladder. Further investigation of As species showed the ratio of arsenite to total As dropped from 100% to 75.5% and then kept stable along depth of the soil profile, which indicates a dynamic equilibrium between arsenite oxidization and arsenate reduction. This study provides direct evidence of multi-elements' interaction along redox gradient of SWI in paddy soils.
土壤-水界面（SWI）处的剧烈氧化还原梯度在控制水稻土中砷（As）的迁移和转化方面起着关键作用。当 Eh 值下降时，As 从固相中释放到孔隙水中的铁（Fe）和锰（Mn）矿物，并被还原为亚砷酸盐。然而，由于缺乏直接证据，淹没稻田 SWI 氧化还原梯度内的耦合或解耦过程仍然受到很大限制。在本文中，我们报告了在五种不同稻田 SWI 中，Fe、As 和其他相关元素在毫米尺度上的分布情况。结果表明，在 5 种稻田中的 4 种稻田中，溶解的 Fe、Mn、As 和磷（P）之间存在强烈的正线性关系，这表明这些元素的一般耦合。然而，在其中一种稻田中观察到了 Fe、Mn 和 As 的解耦。在这种土壤中，观察到 Mn、As 和 Fe 的释放曲线明显不同，释放顺序遵循氧化还原阶梯。对 As 形态的进一步研究表明，亚砷酸盐与总 As 的比例从 100%下降到 75.5%，然后沿着土壤剖面的深度保持稳定，这表明亚砷酸盐的氧化和砷酸盐的还原之间存在动态平衡。本研究提供了直接证据，证明了稻田 SWI 氧化还原梯度中多种元素的相互作用。
