Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Key Laboratory of Drinking Water Science and Technology, Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China.
J Environ Sci (China). 2021 Dec;110:21-27. doi: 10.1016/j.jes.2021.03.011. Epub 2021 Mar 26.
The redox state of arsenic controls its toxicity and mobility in the subsurface environment. Understanding the redox reactions of arsenic is particularly important for addressing its environmental behavior. Clay minerals are commonly found in soils and sediments, which are an important host for arsenic. However, limited information is known about the redox reactions between arsenic and structural Fe in clay minerals. In this study, the redox reactions between As(III)/As(V) and structural Fe in nontronite NAu-2 were investigated in anaerobic batch experiments. No oxidation of As(III) was observed by the native Fe(III)-NAu-2. Interestingly, anaerobic oxidation of As(III) to As(V) occurred after Fe(III)-NAu-2 was bioreduced. Furthermore, anaerobic oxidization of As(III) by bioreduced NAu-2 was significantly promoted by increasing Fe(III)-NAu-2 reduction extent and initial As(III) concentrations. Bioreduction of Fe(III)-NAu-2 generated reactive Fe(III)-O-Fe(II) moieties at clay mineral edge sites. Anaerobic oxidation of As(III) was attributed to the strong oxidation activity of the structural Fe(III) within the Fe(III)-O-Fe(II) moieties. Our results provide a potential explanation for the presence of As(V) in the anaerobic subsurface environment. Our findings also highlight that clay minerals can play an important role in controlling the redox state of arsenic in the natural environment.
砷的氧化还原状态控制其在地下环境中的毒性和迁移性。了解砷的氧化还原反应对于解决其环境行为尤为重要。粘土矿物通常存在于土壤和沉积物中，是砷的重要宿主。然而，关于砷与粘土矿物结构铁之间的氧化还原反应的信息有限。在这项研究中，我们在厌氧批量实验中研究了非绿脱石 NAu-2 中砷（III）/砷（V）与结构铁之间的氧化还原反应。天然铁（III）-NAu-2 未观察到砷（III）的氧化。有趣的是，铁（III）-NAu-2 被生物还原后，发生了砷（III）厌氧氧化为砷（V）。此外，随着铁（III）-NAu-2 还原程度和初始砷（III）浓度的增加，生物还原的 NAu-2 对砷（III）的厌氧氧化作用显著增强。铁（III）-NAu-2 的生物还原在粘土矿物边缘位置生成了反应性铁（III）-O-Fe(II) 配位。砷（III）的厌氧氧化归因于铁（III）-O-Fe(II)配位内结构铁（III）的强氧化活性。我们的结果为厌氧地下环境中存在砷（V）提供了一个潜在的解释。我们的发现还强调了粘土矿物在控制自然环境中砷的氧化还原状态方面可以发挥重要作用。
