Environmental Controls on Bioavailability of Arsenic and Toxic Metals

摘要(项目4：乔恩·乔尔弗和马克·布鲁索) 遗留尾矿是砷和有毒金属暴露于邻近社区的主要来源 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(Loid)S立即将其沉积。风化反应，这是由陨石推动的 水和气体的输入，表现为“反应锋”，或从高度风化到 地表以下深度不断增加的未风化尾矿。反应前沿的传播速度和 反应产物的类型取决于气候和尾矿矿物组成。风化作用- 砷、铅和锌的诱导转化改变了它们的生物有效性，产生的颗粒物可能比 或者在摄入或吸入时毒性低于主要尾矿颗粒。尽管气候和尾矿岩性 控制风化速度，风化过程本身发生在颗粒尺度上，在那里充斥着流体的孔隙， 有时彼此很接近，可能在化学成分上表现出急剧的梯度 集中精神。必须了解在这种孔到芯的尺度上发生的传输和反应。 从力学上更好地预测尾矿的成岩蚀变和污染物的生物有效性 气候的作用，并加强我们进行准确风险评估和有效补救的能力 接近了。我们将评估10个联邦超级基金地点正在进行的风化过程 气候变化范围大，人类健康风险主要与 硫化矿源尾矿介质。将根据深度和深度从每个地点收集岩芯 运输到实验室进行详细的物理、矿物学、微生物和 地球化学成分。将确定随深度变化的风化趋势和反应前沿。这些 整体反应前沿和转变将与砷、铅和锌分子的变化相关。 物种形成和生物可获得性。提取的岩心的子集，表示不同的金属路径(Loid) 改造，将用于在实验室进行的仪表柱实验 受控制的条件。专栏将受到详细研究在过程中的演变 孔结构、金属(Loid)形态和相关生物可及性的实验。这些实验，即 将包括溶液取样器作为沿柱的长度的函数，将使得能够收集反应性 TRANSPORT数据集识别不同条件下控制金属(Loid)转变的生物地球化学反应 条件。生成的数据将用于实现尾矿的反应性运输和命运模型 成岩作用将作为评估与尾矿堆积相关的健康风险的预测工具 在不同的气候情景下。

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.