Environmental Controls on Bioavailability of Arsenic and Toxic Metals

摘要（项目4：乔恩·乔罗弗和马克·索索） 遗留的尾矿是邻近社区砷和有毒金属暴露的主要来源 在半干旱的西南部。因为它们在地球表面条件下是地球化学不稳定的， 尾矿开始经历风化转变，导致分子形式或“物种形成”的变化 有毒金属（类金属）的沉积。风化反应，由流星驱动 水和气的输入，表现为“反应前沿”，或从高度风化到 未风化的尾矿在地表以下深度增加。反应前沿的传播速率和 形成的反应产物的类型取决于气候和尾矿矿物组成。风化- 砷、铅和锌的诱导转化改变了它们的生物利用度，产生了更多的颗粒， 或当被摄入或吸入时比初级尾矿颗粒毒性更小。虽然气候和尾矿岩性 控制风化速率，风化过程本身发生在颗粒尺度上，其中流体填充孔隙， 有时彼此非常接近，可能在化学成分上表现出明显的梯度， 浓度.必须了解在这种孔隙到核心尺度上发生的运输和反应 从机械上更好地预测尾矿的成岩蚀变和污染物的生物利用度， 气候的功能，并加强我们准确评估风险和有效补救的能力 接近。我们将评估10个联邦超级基金场地的风化过程， 在气候范围内，人类健康风险主要与砷浓度升高有关， 硫化物矿石衍生的尾矿介质。将从每个地点收集岩芯，作为深度和 运送到实验室进行详细的物理，矿物学，微生物和 地球化学成分将确定与深度有关的风化趋势和反应前沿。这些 体反应前沿和转化将与砷、铅和锌分子的改变相关 物种形成和生物可及性。提取的岩心的子集，代表金属（类金属）的不同路径 转换，将用于在实验室中进行的仪器柱实验， 控制条件。将对柱子在整个过程中的演变进行详细的研究， 孔结构，金属（类）形态，和相关的生物可及性的实验。这些实验， 将包括作为沿柱沿着长度的函数的溶液取样器，将能够收集反应性的 运输数据集，以确定控制金属（loid）在不同条件下转化的地球化学反应 条件产生的数据将用于实施尾矿的反应性迁移和归宿模型 成岩作用，将作为一种预测工具，用于评估与尾矿沉积有关的健康风险 在不同的气候条件下。

ABSTRACT (Project 4: Jon Chorover and Mark Brusseau) Legacy mine tailings are a primary source of arsenic and toxic metal exposure to proximal communities throughout the semi-arid Southwest. Because they are geochemically unstable under Earth surface conditions, tailings begin to undergo weathering transformations that lead to changes in the molecular form or “speciation” of toxic metal(loid)s immediately upon their deposition. Weathering reactions, which are driven by meteoric inputs of water and gases, are manifest as a “reaction front”, or a transition zone from highly-weathered to unweathered tailings with increasing depth below the surface. The rate of the reaction front propagation and the types of reaction products formed depend on climate and tailings mineral composition. The weathering- induced transformations of arsenic, lead, and zinc alter their bioavailability, yielding particles that can be more or less toxic than the primary tailings particles when ingested or inhaled. Although climate and tailings lithology control the weathering rate, the weathering process itself occurs at the grain scale, where fluid filled pores, sometimes in close proximity to each other, may exhibit sharp gradients in chemical composition and concentration. The transport and reactions that occur at this pore- to core-scale must be understood mechanistically to better predict the diagenetic alteration of tailings and contaminant bioavailability as a function of climate, and to enhance our capacity for accurate risk assessments and effective remedial approaches. We will evaluate the weathering processes underway at 10 federal Superfund Sites spanning a wide range in climate, where human health risk is primarily associated with elevated arsenic concentrations in sulfide-ore derived tailings media. Cores will be collected from each of the sites as a function of depth and transported to the laboratory for detailed characterization of physical, mineralogical, microbial, and geochemical composition. Depth-dependent weathering trends and reaction fronts will be determined. These bulk reaction fronts and transformations will be correlated with alterations in arsenic, lead, and zinc molecular speciation and bioaccessibility. A subset of the extracted cores, representing distinct pathways of metal(loid) transformation, will be utilized in instrumented column experiments conducted in the laboratory under controlled conditions. Columns will be subjected to detailed studies of the evolution over the course of the experiment of pore-structure, metal(loid) speciation, and associated bioaccessibility. These experiments, which will comprise solution samplers as a function of length along the column, will enable the collection of a reactive transport dataset to identify the biogeochemical reactions controlling metal(loid) transformation under different conditions. The data generated will be used to implement a reactive transport and fate model of tailings diagenesis that will serve as a predictive tool for assessment of health risk associated with tailings deposition under differing climatic scenarios.