Mechanisms of Natural Arsenic-Pollution of Groundwater

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.