Spatial and Temporal Changes in Arsenic, Iron, and Sulfur Speciation in a Shallow Aquifer

浅层含水层中砷、铁和硫形态的时空变化

• 批准号: 0409203
• 负责人: Peggy O'Day
• 金额: $ 27万
• 依托单位: University of California - Merced
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-08-15 至 2008-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0409203&HistoricalAwards=false
• 关键词: Spatial; Temporal; Changes; Arsenic; Iron

0409203Peggy A. O'DayThe chemical speciation of arsenic in sediments and porewaters of aquifers is the criticalfactor that determines whether dissolved arsenic accumulates to potentially toxic levels.Although we have a general understanding of the biogeochemical cycle of arsenic, there remainsa large gap in our quantitative understanding of the mechanisms of transformations, the role ofiron and sulfur, and the dynamics of natural processes that mobilize arsenic in the environment.We lack detailed measurements that allow us to quantify seasonal impacts on subsurface arsenicspeciation, and the rates at which speciation changes in response to surface infiltration fromrainfall and vertical fluctuations in water table depth. Using a combination of field, laboratory,and modeling efforts that employ both molecular and macroscopic methods, we will studyarsenic mobility and natural attenuation at a site near San Francisco Bay as a model system.These studies will address the following: (i) How do seasonal variations and changes in watertable as a response to storm events influence subsurface arsenic geochemistry, and thus themechanisms and rates of arsenic uptake or release? (ii) Does the formation of metastable, mixedvalent iron phases, Fe(II,III) hydroxides (green rust) play an important role in controllingarsenic attenuation and release? How is the formation and stability of labile iron phasesinfluenced by storm events and tidal flooding? (iii) Through molecular and macroscopicmodeling based on field and laboratory observations and data, can we predict local changes indissolved arsenic and iron concentrations in response to seasonal changes in water table and tostorm events? We will employ X-ray absorption spectroscopic methods, complementary bulkand spatially resolved geochemical characterizations, hydrologic observations, and molecularand macroscopic modeling to address these questions at different scales.Intellectual Merit: Our work will address the mechanisms by which arsenic is attenuated ormobilized in the environment through identification and understanding of its chemicalspeciation. This study will also begin to address the more difficult question of the rates ofarsenic transformation and mobilization in the field, and link temporal changes to mechanismsidentified at molecular and microscopic scales. This comprehensive approach will advancefundamental understanding of arsenic speciation and mobility, particularly with respect to littleknown seasonal fluctuations and field rates of uptake and release.Broader Impacts: Worldwide, elevated concentrations of arsenic in groundwater, a knowncarcinogen and mutagen, has the potential to adversely impact on the order of 90 million people,including 13 million in the US. This study will seek mechanistic, thermodynamic, and kineticunderstanding of arsenic mobility in the environment. Our approach seeks to scale results frommolecular to macroscopic and thus, our observations at this model study site will be generallytransferable to other subsurface settings.The P.I. has recently moved to the University of California at Merced, the first UCcampus to be built in over 35 years. This research proposal will serve to advance both graduateand undergraduate education at our fledging campus, which seeks to serve underrepresentedgroups in the agricultural San Joaquin Valley. In addition, our collaborators for this projectcome from industry and a national laboratory, providing opportunities for undergraduate summerinternship programs and collaborative work with graduate students.

0409203Peggy A.沉积物和含水层孔隙水中砷的化学形态是决定溶解态砷是否累积到潜在毒性水平的关键因素。尽管我们对砷的地球化学循环有一个大致的了解，但在对转化机制、铁和硫的作用、以及自然过程中砷在环境中流动的动力学。我们缺乏详细的测量方法来量化季节性对地下砷形态的影响，以及物种变化对降雨和地下水位深度垂直波动的表面渗透的反应率。结合现场，实验室和模拟工作，采用分子和宏观的方法，我们将研究砷的流动性和自然衰减在一个网站附近的旧金山弗朗西斯科湾作为一个模型system.These研究将解决以下问题：（i）如何做季节性变化和地下水位的变化，作为对风暴事件的响应影响地下砷地球化学，从而themechanisms和砷的吸收或释放率？(ii)亚稳态、混合价铁相、Fe（II，III）氢氧化物（绿色锈）的形成是否在砷的衰减和释放过程中起重要作用？风暴事件和潮汐洪水如何影响不稳定铁相的形成和稳定性？(iii)通过基于野外和实验室观测和数据的分子和宏观建模，我们能否预测地下水位季节性变化和暴雨事件对溶解砷和铁浓度的影响？我们将采用X射线吸收光谱方法，补充bulkand空间分辨地球化学表征，水文观测，以及molecularand macroscopic modeling来解决这些问题在不同scales.Intellectual优点：我们的工作将解决砷被削弱或动员在环境中通过识别和理解其chemicalspeciation的机制。这项研究也将开始解决更困难的问题，即砷的转化率和在野外的活动率，并将时间变化与分子和微观尺度上的机制联系起来。这一全面的方法将推进对砷形态和流动性的基本理解，特别是关于鲜为人知的季节性波动和实地吸收和释放率。更广泛的影响：在世界范围内，地下水中砷浓度升高，已知的致癌物和诱变剂，有可能对9000万人产生不利影响，其中包括美国的1300万人。这项研究将寻求机制，热力学，和kineticunderstanding砷在环境中的流动性。我们的方法试图将结果从分子尺度扩展到宏观尺度，因此，我们在这个模型研究地点的观察结果通常可以转移到其他地下环境。最近搬到了加州大学默塞德分校，这是35年来建造的第一个加州大学校园。这项研究建议将有助于推进我们羽翼未丰的校园的研究生和本科生教育，该校园旨在为农业圣华金河谷中代表性不足的群体提供服务。此外，该项目的合作者来自行业和国家实验室，为本科生暑期实习计划和与研究生的合作提供了机会。