Quaternary shoreline shifting and hydrogeologic influence on the distribution of groundwater arsenic in aquifers of the Bengal Basin

Naturally occurring high arsenic concentration in groundwater of most alluvial aquifers in the Bengal Basin has been causing serious health problems in millions of people. Elevated dissolved arsenic concentrations are mostly confined within a shallow depth (<150 m) of the Middle Holocene aquifers of the GBM delta and the rapidly subsided Sylhet trough. Arsenic-rich zones in the Bengal Basin are located in the south-central parts of Bangladesh and northeastern parts of West Bengal, India, bounded by Chittagong Hills in the east and the Indian Craton to the west. Holocene sea level rise and development of reducing conditions at organic-rich swampy lands are directly linked to epicenters of arsenic distributions. Surface elevation and topographic slope seem to control the distribution of arsenic because higher levels of dissolved arsenic occur mainly within the present-day topographically low areas. Delta lobes that have experienced tidal influx in the recent past do not appear to have high arsenic concentrations in groundwaters. Groundwater quality data suggest that the sulfate-reducing condition in the coastal aquifers may limit the dissolved arsenic and iron concentrations in aquifers.