Arsenic Complexation with Reduced Organosulfur Moieties in Soil Organic Matter: Implications for Arsenic Oxidation via Biotic and Abiotic Pathways

在化学系环境化学科学项目的支持下，马修·里德教授和他的学生正在研究无机砷和溶解有机物（DOM）之间的相互作用。DOM是来源于植物残体和微生物的复杂生物分子混合物，是所有自然环境的重要组成部分。DOM与砷结合形成溶解的配合物，其性质与未结合的无机砷分子明显不同。这些反应影响水中砷的浓度和植物对砷的吸收，对人类接触砷（一种人类致癌物）具有重要意义。然而，DOM与砷反应的官能团却知之甚少。在本项目中，研究人员探索DOM的结构如何影响其与砷的反应性，并评估砷与DOM结合如何影响砷在土壤中的行为。在整个研究过程中，本科生和研究生接受实验方法和表征技术的培训，以解决环境化学中的基本问题。一名研究生正在与卡尤加自然中心的外联工作人员合作，开发使用便携式x射线荧光仪器的动手活动。这种拓展活动加强了学生的科学交流技能，并使高中教师和公众参与到具有社会重要性的土壤化学主题中来。本项目从不同硫浓度的湿地土壤中分离出标准腐殖质以及疏水和亲水DOM组分，与亚砷酸盐（as (III)）反应，探索as (III)-DOM配位反应。在研究的第一阶段，将湿化学分析和基于同步加速器的XAS与实验室透析平衡实验相结合，量化条件分布系数，表征DOM中硫的形态，确定DOM结合As的As配位环境。在研究的第二阶段，通过实验室批量研究评估了DOM结合As（III）对As（III）通过非生物和微生物途径氧化动力学的影响。这些研究活动旨在验证假设，即硫醇功能部分是As（III）的高亲和力结合位点，并且在氧化条件下，DOM中与硫醇功能结合的As（III）将稳定在其三价氧化状态。研究成果有望完善富dom环境中砷形态的地球化学模拟，并为氧化还原动态环境中砷氧化反应的研究提供新的思路。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Supported by the Environmental Chemical Sciences Program in the Division of Chemistry, Professor Matthew Reid and his students are studying interactions between inorganic arsenic and dissolved organic matter (DOM). DOM is a complex mixture of biomolecules derived from plant residues and microorganisms, and is an important component of all natural environments. DOM binds arsenic to form dissolved complexes with significantly different properties than unbound inorganic arsenic molecules. These reactions influence arsenic concentration in water and uptake into plants, with important implications for human exposure to arsenic, a human carcinogen. However, the functional groups of DOM that react with arsenic are poorly understood. In this project, researchers explore how the structure of DOM affects its reactivity with arsenic, and evaluate how arsenic-DOM binding influences arsenic behavior in soils. Throughout this research, undergraduate and graduate students are trained in experimental methods and characterization techniques to address fundamental problems in environmental chemistry. A graduate student is partnering with outreach staff from the Cayuga Nature Center to develop hands-on activities with a portable X-ray fluorescence instrument. This outreach strengthens the student's science communication skills and engages high school teachers and the public with soil chemistry topics of societal importance. In this project, standard humic substances as well as hydrophobic and hydrophilic DOM fractions isolated from wetland soils with a range of sulfur concentrations are reacted with arsenite (As(III)) in order to explore As(III)-DOM coordination reactions. In the first phase of the research, wet chemical analysis and synchrotron-based XAS are integrated with laboratory dialysis equilibrium experiments to quantify conditional distribution coefficients, characterize sulfur speciation in DOM, and determine the As coordination environment in DOM-bound As. In the second phase of the research, impacts of As(III) binding by DOM on As(III) oxidation kinetics via abiotic and microbial pathways are evaluated using laboratory batch studies. These research activities are designed to test the hypothesis that thiol functional moieties are high-affinity binding sites for As(III), and that As(III) bound with thiol functionalities in DOM will be stabilized in its trivalent oxidation state during oxidizing conditions. Research outcomes are expected to improve geochemical modeling of As speciation in DOM-rich environments and provide new insight into arsenic oxidation reactions in redox dynamic environments.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.