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

0510697 Johannesson造成人类砷中毒的主要媒介是饮用水，主要是地下水源。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，因此了解含水层中As动员的因素至关重要。在可以组装预测模型之前，首先有必要将As沿沿着地下水流路径的行为量化为条件（即，pH值、氧化还原条件、溶液成分、含水层矿物表面位置）在空间和时间尺度上变化和演变。许多以前的研究，包括恒河三角洲，遭受了他们试图确定负责动员过程。这种研究的失败部分反映了缺乏沿着流动路径收集的地下水和含水层固相的As形态数据。此外，由于氧化还原反应，因此作为循环，强烈的微生物的影响，微生物的过程可能发挥重要作用，作为流动性。 中心的假设是，发生的变化沿着地下水流路径，伴随化学风化和微生物促进氧化还原反应催化作为动员，并捕获，含水层基质通过吸附/解吸，共沉淀，和/或矿物溶解反应。为了研究这一假设，我们将：（1）量化As浓度和形态[即，As（III）、As（V）、有机砷、硫代亚砷酸盐物种]和辅助地球化学参数（例如，pH值、温度、主要溶质、碱度、磷酸盐、溶解硅、铁浓度/形态、溶解O2、Eh、H2S、DOC、DIC和DOC的d34 S、d13 C）沿着两个研究良好的含水层中的流动路径（Carrizo Sand，Texas; Aquia aquifer，马里兰州）;（2）测定含水层固相As的形态[As（III），As（V）]，强调固相As的不稳定和不稳定库;（3）在野外和实验室研究的基础上，建立了砷沿沿着迁移和形态分布的概念/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次孵育研究间接检查。此外，还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。该项目将显着提高我们的理解，在地下水流系统中的砷地球化学，并将导致在含水层中的As动员和地球化学循环的概念模型。预计项目结果将提供基础信息，为未来的研究提供种子（例如，更详细的微生物研究、表面络合模型、反应性运输模型）。

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).