Abstract

Arsenic pollution is pervasive at shallow depth in low-land organic rich Holocene (~10,000 year BP) alluvium in southern parts of the Bengal Delta. The upland terraces, mainly made up of Pleistocene (~10,000yr to ~1.8 my BP) sediments and capped by an oxidised zone, are free of arsenic problem [1,2]. Arsenic is sourced mainly from the Himalaya. Damodar fan delta, although entirely drained through Peninsular India, is also marginally affected. No arsenic mineral is present in contaminated alluvial aquifers; instead it occurs adsorbed on Hydrated Ferric Oxide (HFO), which generally coats sediment grains. Arsenic is released to groundwater mainly by bio-mediated reductive dissolution of HFO with corresponding oxidation of organic matter. Arsenic concentration in alluvium is broadly uniform, thus release process rather than source is important factor in arsenic pollution. Dug-well because of their oxygenated nature is useful low cost source of arsenic-safe water even in contaminated areas. This is particularly relevant in areas located away from surface water sources.