Mechanisms of Natural Arsenic-Pollution of Groundwater

河流沉积的沉积物（称为冲积沉积物）在世界范围内形成了重要的含水层。来自世界各地这些冲积含水层的地下水提供了世界上大部分的水供应。自1995年以来，在全球约30个三角洲和沿海含水层以及世界上许多其他内陆冲积盆地中发现了地下水砷污染。这个问题在东南亚尤其严重，尤其是西孟加拉邦和孟加拉国。这对人类健康的影响是巨大的。砷污染的地下水中砷的浓度高于世界卫生组织对饮用水的指导值，即每升砷10微克。砷无臭、无味、有毒，是一种潜伏期长（几十年）的致癌物。这一漫长的潜伏期使人们多年没有认识到地下水中砷对人体健康的不利影响。这种影响现在被认为是严重的和全球性的：仅在孟加拉国消耗富含砷的地下水的影响就被加州大学伯克利分校的流行病学家Allan Smith称为“历史上最严重的人口大规模中毒”，他预测，到2010年，该国十分之一的死亡可能与砷有关，除非迅速采取有效的补救措施。要有效治理砷污染，必须详细揭示污染的机理。在我们了解这一过程之前，含水层修复和开发的战略将不会以可靠的科学为基础。由于地下水中的过程是一般的，而不是特定地点的，许多意识到并试图理解地下水中砷污染过程的科学家都承认，砷是作为该地区沉积物中腐烂植物物质的微生物代谢的副产品释放到地下水中的。除了这个普遍的共识之外，关于砷是如何释放到地下水中的看法也存在分歧。特别是，可能负责推动这一过程的微生物的身份，以及它们如何做到这一点的细节，几乎是未知的。该项目旨在确定导致砷污染过程的细菌，发现该过程的细节，并显示含水层沉积物中砷动员相关细菌标记物的分布与砷污染分布的关系。无论什么被证明是驱动孟加拉盆地砷污染的精确机制或机制，都可能在世界范围内得到应用，因此我们的工作将提供一个框架，在这个框架内，我们可以了解世界上大多数冲积含水层污染的原因。对这一机制的理解将为决策者在全球范围内对这类含水层的开发和避免战略作出选择提供依据。这些资料对所有参与水质监测和健康调查的人都很有价值。我们获得的知识可能会改变未来砷研究、含水层开发和含水层修复的方法。

Sediments laid down by rivers (termed alluvial sediments) form important aquifers worldwide. Groundwater from such alluvial aquifers across the World provides much of the world's water supply. Since 1995, As-pollution of groundwater has been discovered in around 30 deltaic and coastal aquifers worldwide and in many other inland alluvial basins of the World. The problem is particularly severe in SE Asia, especially West Bengal and Bangladesh. The consequence for human health has been immense. Arsenic-polluted groundwater contains As in concentrations greater than the World Health Organization's Guideline Value for drinking water of 10 microgrammes per litre As. Arsenic is odourless, tasteless, poisonous, and a carcinogen with a long period of latency (tens of years). This long latency period for many years postponed recognition of the adverse affects of As in groundwater on human health. That impact is now known to be severe and global in extent: the effects of the consumption of As-rich groundwater in Bangladesh alone was termed 'the worst mass poisoning of a population in history' by Allan Smith, an epidemiologist at the University of California, Berkley, who predicted that, by 2010, one in ten deaths in that country might be As-related unless effective remediation was rapidly undertaken. If As-pollution is to be dealt with effectively, the mechanism of pollution must be revealed in detail. Until we understand that process, strategies for aquifer remediation and development will not be based on sound science. Because process in groundwater are generic, and not site specific, many of the scientists who are aware of, and seek to understand, the process of arsenic pollution in groundwater accept that arsenic is released into groundwater as a by-product of the microbial metabolism of decaying plant material in the sediments of the region. Beyond that general agreement, opinions differ as to how the arsenic is released into the groundwater. In particular, the identities of the microbes that may be responsible for driving the process, and the details of how they do so, are all but unknown. This project seeks to identify the bacteria responsible for the process of As-pollution, discover the details of that process or processes, and show how the distribution of relevant bacterial markers for As-mobilization in aquifer sediments are related to the distribution of arsenic pollution. Whatever proves to be the precise mechanism or mechanisms driving As-pollution in the Bengal Basin is likely to have a worldwide application, so our work will provide a framework within which to understand the cause(s) of pollution in most alluvial aquifers worldwide. The understanding of mechanism will underpin the choice made by policy makers regarding development and avoidance strategies for such aquifers across the world. Such information will be valuable to all those involved in water-quality monitoring and health surveys. The knowledge we gain may change future approaches to As research, aquifer development, and aquifer remediation.