ABSTRACT
ABSTRACT: Arsenic pollution in groundwater mainly affects major parts of the GangaBrahmaputra delta in West Bengal and Bangladesh, as well as, parts of narrow entrenched lowermiddle sections of the Gangetic floodplains. Arsenic adsorbed on hydrated ferric oxides (HFO) was preferentially entrapped in organic rich deltaic Holocene sediments and less frequently in its floodplains. Severe reducing condition that developed later mobilized arsenic to groundwater mainly in the deltaic domain. The sediment cover on the Pleistocene uplands in the Bengal Basin and the interfluve Ganga plain are free of arsenic problem. Arsenic is mobilized to groundwater by bio-mediated reductive dissolution of HFO. Strong reducing nature of groundwater in the Bengal Basin and parts of affected flood plains is shown by high concentration of iron ( 9-36 mg/L), which is generally low (1 mg/L) in the Ganga alluvial plain upstream of the Bengal Basin indicating that groundwater is not adequately reducing in nature to mobilize arsenic.
