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

0001348伊斯兰教 孟加拉国的饮用水受到严重的砷污染。 在构成该国饮用水供应的大约400万口威尔斯井中，有一半以上的天然砷含量超过世界卫生组织规定的0.01毫克/升的标准，使多达5 000万人的饮用水中砷含量达到危险水平。 浓度高达0.5毫克/升是常见的。 大众媒体[纽约时报，1998年11月10日]认为，这可能是历史上最大规模的中毒事件。 我们的主要研究问题是：是什么原因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、归宿和迁移，未来的水管理计划就有可能使问题复杂化。 我们将测试一组工作假设的原因（S）砷污染，其中包括：（A）沉积的固体和溶解砷的分布解释;（B）地球化学/水文原因高溶解砷浓度;和（C）砷动员的人为原因。 从这一理解的原因，高水平的溶解砷，我们将考虑如何砷浓度可能会随着时间的推移而变化，以及砷是如何分布在全国各地。 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)我们能否通过从采样点内插砷浓度来开发更好的方法来定位威尔斯？ （C）砷含量是否因泵送或渗入肥料而上升？ (D)深井威尔斯能提供长期的解决方案吗？ 已经开始临时安装深威尔斯井。 我们将进行现场和实验室实验，并与建模练习相协调，重点是安装在Munshiganj地区的15口深度在3米到200米之间的威尔斯井。 我们还提取了一个200米的固体含水层材料的核心，与大气隔离，以保持氧化还原状态，也许是砷活动的关键控制。 我们将通过分析沉积物和孔隙水的方法，包括X射线吸收光谱（XAS），微探针分析和细菌培养物的生长，以及保存的沉积物样品的连续提取来研究砷的结合机制。 然后，我们将研究地球化学扰动对砷动员原位注入-取出测试从我们安装的威尔斯使用水，已被化学改变，以测试假设的砷结合机制。 了解砷的结合机制将支持有关砷的流动性和运输的预测。 反应迁移模型将被用来考虑动员由于抽水和季节性地下水通量的重新分配。 砷浓度的区域图将通过地质统计学方法进行估算，并受沉积特征变化知识的约束。 学生和教师将积极参与现场，实验室和建模工作。 为了获得长期水资源管理的良好科学基础，我们将把我们的研究成果传达给决策者，以帮助为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.