Project 4: Arsenic and Manganese Mobility: Land Use, Redox Shifts

恒河三角洲数千万人继续饮用危险的地下水 被砷和锰污染。我们估计，在孟加拉国，如果食用受污染的 如果继续饮水，砷中毒和皮肤癌的患病率将约为200万和10万 每年的死亡率分别为，由砷引起的癌症死亡率将约为 每年3,000箱尽管对锰的关注较少，但锰的危险水平 在孟加拉国的地下水中也很常见。在他们里程碑式的地下水化学调查中，英国 地质勘测发现，锰和砷是两种经常超过安全标准的污染物。 最近的流行病学研究表明，锰可能会损害 班加尔德西儿童的神经功能5。 孟加拉国是研究将有毒金属转移到环境中的过程的理想场地。 在地球化学还原条件下。孟加拉国的低氧地下水条件与Ta的对比 项目2的小溪遗址，采矿使大量矿物暴露在快速氧化之下。在……里面 孟加拉国，灌溉稻田和池塘的建设引入了大量缺氧的有机水稻 水。这种转变发生在过去的40年里，随着灌溉抽水的出现， 地下水的停留时间现在也在几十年到一个世纪的数量级。因此，其影响 在这些化学变化中，补给水现在正在穿过地下水系统并驱动 可以观察到的既能动员又能隔离有毒金属的生物地球化学过程。 在这项拟议的超级基金基础研究计划(SBRP)中，我们的研究将解决土地利用和 地下水运输控制饮用水中砷和锰的浓度。这些问题存在于z 水文学和生物地球化学的交叉是理解金属的关键未解决的问题 环境中的动员。在过去的十年里，我们对静电有了细微的了解 砷污染含水层的地球化学特征及其微生物快速介导性 沉积物孵化实验中对化学扰动的响应。然而，令人惊讶的是， 了解对了解地下水演化至关重要的水文地质学的基本方面 流动路径上的化学作用。虽然水平衡数据是从农业的角度存在的，但我们没有 了解推动锰和砷流动的溶质通量是如何进入含水层的，是什么模式？ 随之而来的是地下水流动，或者说溶质如何在不同的流动路径中混合。人们对更深层次的东西知之甚少 地下水流动，甚至是基本问题，如区域流动的重要性7“9和地下水 抽水10~12分钟仍然是有争议的。在我们的野外区域，我们最近对季节性水文进行了量化 含水层补给和排出的周期。在这个项目中，我们将建立在这种水平衡的基础上 描述砷和锰在人体内流动的位置和生物地球化学条件 当这些毒素随后通过复杂的瞬时三维模式传输时 流水线将它们输送到饮用水水井。 作为我们努力的一部分，我们将努力推进两项有可能广泛应用的技术 申请。我们将开发使用传感器监测变化的生物地球化学条件的新方法， 我们将试验就地修复砷和锰的新方法。一个网络 将建造探测器，以高时间分辨率监测数小时内土壤条件的变化， 季节和年份。我们将专注于限制漂移和生物污损的实际问题，并将整合 地化探头与我们成功的包气带水力传感器网络。我们的就地修复 实验将重点放在推拉式注井方法上，这种方法使用氧化剂在周围制造“过滤器”。 井通过用沉淀的锰氧化物和铁氧化物包裹含水层沉积物来吸附砷。

Tens of millions of people in the Ganges Delta continue to drink groundwater that is dangerously contaminated with arsenic and manganese. We estimate that in Bangladesh, if consumption of contaminated water continues, the prevalence of arsenicosis and skin cancer will be approximately 2 million and 100,000 cases per year, respectively, and the incidence of death from cancer induced by arsenic will be approximately 3,000 cases per year4. Although less attention has been given to manganese, dangerous levels of manganes are also common in Bangladesh's groundwater. In their landmark survey of groundwater chemistry, the BritisH Geological Survey2 found that manganese and arsenic are the two contaminants that routinely exceed safe concentrations in Bangladesh, and recent epidemiological work has shown that manganese may damage the neurological function of Bangaldeshi children5. Bangladesh is an ideal field site for studying processes that mobilize toxic metals into the environment under geochemical reducing conditions. The anoxic groundwater conditions of Bangladesh contrast to the Ta Creek site of Project 2, where mining has exposed large quantities of minerals to rapid oxidation. In Bangladesh, construction of irrigated rice fields and ponds has introducing large inflows of anoxic, organic-ric water. This shift has occurred over the last forty years and, with the advent of irrigation pumping, the residence time of groundwater is now also on the order of decades to a century. Consequentially, the effects of these chemical alterations to recharge water are now moving through the groundwater system and driving biogeochemical process that can be observed to both mobilize and sequester toxic metals. In this proposed Superfund Basic Research Program (SBRP), our research will address how land use and groundwater transport control arsenic and manganese concentrations in drinking water. These questions lie z the intersection of hydrology and biogeochemistry and are key unresolved questions for understanding metal mobilization in the environment. Over the last decade, we have gained a nuanced understanding of the static geochemical characteristics of arsenic-contaminated aquifers and have characterized the rapid microbialmediated response to chemical perturbations in sediment incubation experiments. However, remarkably little known about basic aspects of hydrogeology that are vital for understanding the evolution of groundwater chemistry along flow paths. Although water-balance data exist from an agricultural perspective6, we do not know how the solute fluxes that drive manganese and arsenic mobility enter the aquifer, what patterns groundwater flow follows, or how solutes mix across different flow paths. Little is known about deeper groundwater flow, and indeed, basic issues such as the significance of regional flow7"9 and groundwater pumping 10~12 are still controversial. At our field area, we have recently quantified the seasonal hydrologic cycle by which aquifers are recharged and discharge. In this project, we will build on this water balance to characterize the locations and biogeochemical conditions where arsenic and manganese are mobilized as we as the subsequent transport of these toxins through the complex transient three-dimensional pattern of streamlines that deliver them to drinking-water wells. As part of our effort, we will work to advance two technologies that have the potential for widespread application. We will develop new methods for using sensors to monitor shifting biogeochemical conditions, and we will experiment with new methods for in-situ remediation of arsenic and manganese. A network of probes will be constructed to monitor, at high temporal resolution, changing soil conditions over hours, seasons and years. We will focus on practical issues of limiting drift and biofouling and will integrate the geochemical probes with our successful network of vadose-zone hydraulic sensors. Our in situ remediation experiments will focus on push-pull well-injection methods that use oxidizing agents to create "filters" around well screens to adsorb arsenic by coating aquifer sediments with precipitated manganese and iron oxides.