Detail study of arsenic pollution mechanism in Gotra area, Nadia district,West Bengal, India

摘要

Arsenic contamination in groundwater of Bengal delta covering West Bengal and adjoining Bangladesh has become one of the worst environmental problems in the world. Arsenic in alluvial sediments is getting released into the groundwater, at places, crossing the permissible limit of drinking water standard and thus creating pollution. Gotra village in Chakdah block of West Bengal is one such arsenic-polluted area where majority of the tubewells are yielding high arsenic in groundwater. The village is situated over a curvilinear levee. The villages beyond this levee do not have much arsenic in groundwater.Groundwater in all 49 available tubewells of variable depths in Gotra village are analysed for elemental abundance. Four boreholes of 40m depth, two each from high and low arsenic-zones, are drilled for lithology and subsurface sediment analysis. Six additional boreholes, each of 30m depth are drilled for subsurface lithology. Porewater at two points from both high and low arsenic zones are collected through Waterloo profiler up to 40m depth. The geochemical interactions between sediment-porewater-groundwater are envisaged to propose the arsenic pollution mechanism.Sediment arsenic shows strong positive correlation with sediment iron, manganese and calcium. The porewater and groundwater arsenic show strong positive correlation with ammonia and alkalinity, weak positive correlation with iron, calcium and magnesium but weak inverse correlation with dissolve oxygen, manganese and sulfur. These relationships suggest that a reductive desorption process is acting as the principal mechanism for creating arsenic pollution in Gotra groundwater.