CAREER: Role of Mn(III) in Limiting Oxidative Transformation of As(III) by Mn(III/IV) Oxides

水中的砷既是自然存在的，也是人类活动的结果，世界各地的饮用水中都有砷。该项目的总体目标是了解环境因素如何控制砷的存在形式，以及它是溶解在水中还是附着在土壤等固体上。当砷溶解在水中时，它更有可能移动并影响人类健康。这项工作很重要，因为全世界有超过1.5亿人暴露在饮用水中不安全的砷中。含有锰元素的矿物存在于许多天然沉积物中，它们是强有力的化学反应物。该项目将确定锰矿物如何以及以多快的速度与砷反应以改变其形态，从而确定其流动性。这个项目还将研究非常常见的元素铁如何改变锰矿物与砷的反应。将开展宣传活动，教育人们矿物质如何影响水质，并将开展工作，让K-12和本科生参与环境地球化学领域的工作。该项目将致力于增加来自不同背景的学生参加环境科学课程和研究的人数。砷是一种自然存在的和人为的污染物，存在于世界各地的饮用水供应中。砷在自然系统中的环境迁移性以及去除系统的效果和效率都受到其氧化状态的强烈影响。ASV很容易吸附土壤和沉积物中的许多矿物成分，或在含氧系统中吸附滤床介质和/或混凝剂絮体，而AsIII通常与这些材料形成不太稳定的键。在地下环境中，As III的氧化很大程度上是由与MnIII/IV氧化物的相互作用驱动的。尽管它们在控制As的地球化学形态方面发挥了作用，但除了其他氧化还原活性污染物外，许多确定氧化速率和机理的研究结果往往不一致。特别是，固体缔合的MnIII在限制污染物转化速率和程度方面的作用充其量也是知之甚少。本项目将系统地研究各种MnIV氧化物矿物对AsIII的氧化，重点是量化固相MnIII和FeIII对AsIII的氧化速度、程度和As表面络合物形成的影响。这项建议旨在将传统的实验室测量与现场快速扫描X射线吸收光谱和X射线光电子能谱(XPS)相结合，以确定MnIII在限制AsIII氧化中的作用。这项研究将(1)检验MnIII含量对早期时间段(例如1分钟)AsIII氧化动力学的影响，(2)寻求系统地定义MnIII/IV氧化物中FeIII替代对AsIII氧化和吸附的影响，以及(3)量化氧化动力学、机理和MnIII/IV氧化物表面变化之间的基本关系。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Arsenic in water occurs both naturally and as a result of human actions and arsenic is found in drinking water supplies throughout the world. The overall goal of this project is to understand how environmental factors control the form of arsenic that is present, and whether it is dissolved in water or attached to solids like soil. When arsenic is dissolved in water it is more likely to move and impact human health. This work is important because more than 150 million people worldwide are exposed to unsafe amounts of arsenic in drinking water. Minerals with the element manganese are found in many natural sediments and they are powerful chemical reactants. This project will determine how, and how fast, manganese minerals react with arsenic to change its form and therefore how mobile it is. This project also will look at how the very common element iron changes how manganese minerals react with arsenic. Outreach will be conducted to educate people about how minerals affect water quality and there will be work to engage K-12 and undergraduate college students in the field of environmental geochemistry will be. This project will work to increase the number of students from diverse backgrounds who take classes and do research in environmental science.Arsenic (As) is a naturally occurring and anthropogenic contaminant present in drinking water supplies around the world. The environmental mobility of arsenic in natural systems as well as the efficacy and efficiency of removal systems are strongly influenced by its oxidation state. AsV readily sorbs to many mineral components of soil and sediments or to filter bed media and/or coagulant flocs in oxic systems, while AsIII generally forms less stable bonds with these materials. In subsurface environments, oxidation of AsIII is largely driven by interaction with MnIII/IV oxides. Despite their role in controlling the geochemical speciation of As, in addition to other redox-active contaminants, the results of numerous studies to determine oxidation rates and mechanisms are often inconsistent. In particular, the role of solid associated MnIII in limiting contaminant transformation rates and extents is at best, poorly understood. This project will systematically investigate the oxidation of AsIII by various MnIV oxide minerals, with an emphasis on quantifying the effect of solid-phase MnIII and FeIII on AsIII oxidation rate, extent, and the formation of As surface complexes. This proposal aims to combine traditional lab-based measurements with in situ, quick scanning X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy (XPS) to determine the role of MnIII in limiting AsIII oxidation. The research will (1) examine the effect of MnIII content on the kinetics of AsIII oxidation during early time periods (e.g., 1 min), (2) seek to systematically define effects of FeIII substitution in MnIII/IV oxides on AsIII oxidation and sorption, and (3) quantify the fundamental relationship between oxidation kinetics, mechanism, and changes in the MnIII/IV oxide surface.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.