Groundwater arsenic in the Holocene Brahmaputra floodplains of Assam, Northeastern India: Distribution and trends of hydrogeochemical variations

摘要

Arsenic (As) enrichment of shallow groundwater sources in the northeastern state of Assam in India (Fig. 1) is a more recent but significant discovery (Singh, 2004) posing threat to a large exposed population. Concentration is often higher than the drinking water guideline values of World Health Organization (WHO) and the Bureau of Indian Standards (BIS). Studies conducted by Chakraborti et al. (2004) also found that nearly 43% and 26% of 137 hand tubewells analyzed in different parts of the state had As concentrations above 10 μg/L and 50 μg/L respectively. In a recent study, concentrations beyond 50 μg/L have been confirmed in 72 blocks out of 192 blocks in 22 districts of Assam (Mahanta et al., 2009).