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

孟加拉国的饮用水被砷严重污染。中国的饮用水供应大约有400万口水井，其中一半以上的天然砷含量超过了世界卫生组织0.01毫克/L的标准，使多达5000万人的饮用水中砷含量达到危险水平。浓度高达0.5毫克/L的情况很常见。大众媒体曾暗示，这可能是历史上最大的大规模中毒事件。我们的主要研究问题是：孟加拉国地下水中砷含量高的原因是什么？如果环境中砷的来源、去向和运输得不到了解，未来的水管理计划就有可能使问题复杂化。我们将检验一套关于砷污染原因(S)的工作假说，其中包括：(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；以及(C)砷迁移的人为原因。根据对高水平溶解砷的原因的理解，我们将考虑砷浓度可能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)我们能否开发更好的方法，通过插入采样地点的砷浓度来确定水井的位置？(C)砷水平是否因抽水或渗入化肥而上升？(D)深井能否提供长期解决办法？已经在临时基础上开始安装深井。我们将进行现场和实验室实验，配合建模练习，重点是安装在Munshiganj区的15口井，深度在3米到200米之间。我们还从大气中提取了200米长的固体含水层材料，以保持氧化还原状态，这可能是控制砷活动的关键。我们将通过分析沉积物和孔隙水的X射线吸收光谱(XAS)、微探针分析和细菌培养生长以及保存下来的沉积物样品的顺序提取等方法来研究砷的结合机理。然后，我们将通过从我们安装的井中进行注入-提取试验，使用经过化学改变的水来测试假想的砷结合机制，来研究地球化学扰动对砷的就地动员的影响。对砷结合机制的了解将支持有关砷迁移和运输的预测。反应运移模型将用于考虑季节性地下水通量的抽水和再分配引起的动员。受沉积特征变化知识的制约，将用地质统计学方法估计砷浓度的区域地图。学生和教职员工将积极参与现场、实验室和建模工作。为了为长期水资源管理奠定坚实的科学基础，我们将把我们的研究成果传达给决策者，帮助为孟加拉国提供安全饮用水。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.