Hydrogeochemical Evolution of Arsenic Concentrations and Speciation Along Groundwater Flow Paths: Linking Aqueous and Solid Phase Arsenic Speciation in Sedimentary Aquifers

[510697]约翰内松造成人类砷中毒的主要媒介是饮用饮用水，主要来自地下水。这种中毒目前影响着恒河三角洲和东南亚其他地区的数百万人。由于地下水也是美国饮用水的主要来源，因此了解导致地下水在含水层中流动的因素至关重要。在构建预测模型之前，首先有必要量化地下水流动路径上的As行为，因为条件（即pH值、氧化还原条件、溶液组成、含水层矿物表面位置）在时空尺度上发生了变化和演变。以前的许多研究，包括对恒河三角洲的研究，在试图确定造成动员的过程时都受到了影响。这类研究的失败部分反映了缺乏沿流动路径收集的地下水和含水层固相的砷形态数据。此外，由于氧化还原反应和As循环受到微生物的强烈影响，微生物过程可能在As迁移中发挥重要作用。核心假设是，地下水流动路径的变化伴随着化学风化和微生物促进的氧化还原反应，通过吸附/解吸、共沉淀和/或矿物溶解反应，催化了砷从含水层基质中动员和捕获。为了验证这一假设，我们将：(1)量化两个已得到充分研究的含水层（德克萨斯州Carrizo Sand和马里兰州Aquia含水层）沿流动路径的As浓度和形态[即As（III）、As(V)、有机砷、硫砷酸盐种类]和辅助地球化学参数（如pH、温度、主要溶质、碱度、磷酸盐、溶解二氧化硅、Fe浓度/形态、溶解O2、Eh、H2S、DOC、DIC和DOC的d34S、d13C）；(2)确定含水层固相As的形态[As(III), As(V)]，强调固相As的不稳定库和不稳定库；(3)在实地和实验室研究的基础上，构建As流动和物种形成的概念/半定量模型。微生物代谢对As动员的重要性将通过一系列批量培养研究间接检验。此外，计划与一位国际公认的微生物学家合作，他对砷的微生物循环进行了开创性的研究，并对含水层沉积物进行了光谱调查。该项目将极大地提高我们对地下水流动系统中砷生物地球化学的理解，并将建立含水层中砷动员和生物地球化学循环的概念模型。预计项目结果将为未来的研究提供基础信息（例如，更详细的微生物研究，表面络合模型，反应性输运模型）。

0510697Johannesson The principal vector responsible for arsenic (As) poisoning in human populations is consumption of drinking water, chiefly from groundwater sources. Such poisoning currently affects millions of people in the Ganges delta and other regions of Southeast Asia. Because groundwater is also the chief source of drinking water in the United States, understanding the factors responsible for As mobilization in aquifers is critical. Before predictive models can be assembled, it is first necessary to quantify As behavior along groundwater flow paths as conditions (i.e., pH, redox conditions, solution compositions, aquifer mineral surface sites) change and evolve over spatial and temporal scales. Many previous studies, including those for the Ganges delta, have suffered in their attempts to identify processes responsible for As mobilization. The failure of such studies reflects, in part, the lack of As speciation data for groundwater and aquifer solid phases collected along flow paths. Furthermore, because redox reactions, and hence As cycling, are strongly influenced by microbes, microbial processes likely play an important role in As mobility. The central hypothesis is that changes occurring along groundwater flow paths that accompany chemical weathering and microbial facilitated oxidation-reduction reactions catalyze As mobilization from, and capture by, the aquifer substrate via adsorption/desorption, co-precipitation, and/or mineral dissolution reactions. To investigate the hypothesis, we will: (1) quantify As concentrations and speciation [i.e., As(III), As(V), organoarsenicals, thioarsenite species] and ancillary geochemical parameters (e.g., pH, temperature, major solutes, alkalinity, phosphate, dissolved silica, Fe concentration/speciation, dissolved O2, Eh, H2S, DOC, d34S, d13C of DIC and DOC) along flow paths in two well studied aquifers (Carrizo Sand, Texas; Aquia aquifer, Maryland); (2) determine As speciation [As(III), As(V)] of aquifer solid phases, emphasizing the labile and nonlabile pools of solid phase As; and (3) assemble a conceptual/semi-quantitative model of As mobility and speciation along flow paths based on the field and laboratory studies. The importance of microbial metabolism on As mobilization will be indirectly examined via a series of batch incubation studies. In addition, collaboration with an internationally recognized microbiologist who has conducted seminal studies on microbial cycling of As is planned, as are spectroscopic investigations of aquifer sediments. The project will significantly improve our understanding of As biogeochemistry in groundwater flow systems, and will lead to a conceptual model of As mobilization and biogeochemical cycling in aquifers. It is expected that project results will provide fundamental information that will seed future research (e.g., more detailed microbial studies, surface complexation models, reactive transport modeling).