Collaborative Research: Arsenic Contaminated Groundwater in Bangladesh: Characterizing the Source Mobilization and Transport.

0001348伊斯兰孟加拉国的饮用水被砷严重污染。在构成该国饮用水供应的大约400万口井中，超过一半的天然砷含量超过世界卫生组织0.01毫克/升的标准，使多达5000万人的饮用水中的砷含量达到危险水平。浓度通常高达0.5毫克/升。大众媒体认为[纽约时报，1998年11月10日]这可能是历史上最大的集体中毒事件。我们的主要研究问题是：是什么导致孟加拉国地下水中砷含量高？如果不了解砷在环境中的来源、命运和运输，未来的水管理方案就有使问题复杂化的风险。我们将测试砷污染原因的一组有效假设，包括：(a)固体和溶解砷分布的沉积解释；(B)高溶解砷浓度的地球化学/水文原因；(C)砷迁移的人为原因。根据对高溶解砷含量原因的了解，我们将考虑砷浓度如何随时间变化以及砷在全国范围内的分布情况。具体问题包括：(A)砷浓度是否与特定的沉积特征或地表水文特征相关？(B)我们能否开发出更好的方法，通过插值采样地点的砷浓度来定位水井？(C)砷的含量会因肥料的泵送或渗透而上升吗？(D)深井能提供长期解决方案吗？深井的安装已经开始临时进行。我们将进行现场和实验室实验，并配合建模练习，重点是在Munshiganj地区安装的15口井，深度在3米到200米之间。我们还从大气中提取了一个200米长的固体含水层物质核心，以维持氧化还原状态，这可能是控制砷活性的关键。我们将通过x射线吸附光谱（XAS）、微探针分析和细菌培养以及保存沉积物样品的顺序提取等方法分析沉积物和孔隙水，研究砷的结合机制。然后，我们将研究地球化学扰动对砷原位动员的影响，通过从我们安装的井中使用经过化学改变的水进行注入-提取测试，以测试假设的砷结合机制。对砷结合机制的了解将有助于预测砷的迁移和运输。反应输运模型将用于考虑由于抽水和季节性地下水通量的再分配而引起的动员。砷浓度的区域图将由地质统计学方法估计，但受沉积特征变化知识的限制。学生和教师将积极参与实地、实验室和建模工作。为了获得长期水资源管理的可靠科学依据，我们将把我们的研究成果传达给决策者，以帮助孟加拉国提供安全的饮用水。这是一个与麻省理工学院、辛辛那提大学和孟加拉国工程技术大学合作的项目。

0001348Islam The drinking water of Bangladesh is severely contaminated with arsenic. Over one-half of the approximately four million wells that constitute the country's drinking water supply have levels of naturally occurring arsenic above the World Health Organization's standard of 0.01 mg/L, exposing as many as 50 million people to dangerous levels of arsenic in their drinking water. Concentrations as high as 0.5 mg/L are common. It has been suggested in the popular media [New York Times, November 10, 1998] that this may be the largest mass poisoning in history. Our primary research question is: What causes high levels of arsenic in the groundwater of Bangladesh? If the source, fate and transport of arsenic in the environment are not understood, future water management schemes run the risk of compounding the problem. We will test a set of working hypotheses for the cause(s) of arsenic contamination that include : (A) Depositional explanations for the distribution of solid and dissolved arsenic; (B) Geochemical/hydrologic reasons for high dissolved arsenic concentrations; and (C ) Anthropogenic causes of arsenic mobilization. From this understanding of the cause of high levels of dissolved arsenic, we will consider how arsenic concentrations may change in time and how arsenic is distributed throughout the country. Specific issues include: (A) Are arsenic concentrations correlated with particular sedimentary characteristics or surface hydrologic characteristics? (B) Can we develop better methods to site wells by interpolating arsenic concentrations from sampled locations? (C ) Do arsenic levels rise due to pumping or infiltration of fertilizers? (D) Can deep wells provide a long-term solution? The installation of deep wells has already begun on an ad hoc basis. We will conduct field and laboratory experiments, coordinated with modeling exercises, focusing on a cluster of 15 wells that range in depth between 3 m and 200 m installed in the Munshiganj district. We have also extracted a 200-meter core of solid aquifer material isolated from the atmosphere to maintain the redox state, perhaps the key control on arsenic activity. We will study the mechanisms that bind arsenic by analyzing the sediments and pore water with methods including X-ray adsorption spectroscopy (XAS), micro-probe analysis and growth of bacterial cultures, as well as sequential extraction of the preserved sediment samples. We will then study the effect of geochemical perturbations on arsenic mobilization in situ by injection-withdrawal tests from our installed wells using water that has been chemically altered to test hypothesized arsenic binding mechanisms. An understanding of arsenic binding mechanisms will support predictions regarding arsenic mobility and transport. Reactive-transport modeling will be used to consider mobilization due to pumping and redistribution by seasonal groundwater fluxes. Regional maps of arsenic concentration will be estimated by geostatistical methods constrained by knowledge of variations in sedimentary characteristics. Students and faculty will actively participate in the field, laboratory, and modeling work. To gain a sound scientific basis for long-term water management, we will convey our research to decision-makers to help provide safe drinking water for Bangladesh. This is a collaborative project with MIT, the University of Cincinnati, and Bangladesh University of Engineering and Technology.