Evaluation of the processes controlling arsenic contamination in parts of the Brahmaputra floodplains in Assam, India

The present study attempts to develop an understanding of the processes contributing to groundwater arsenic (As) enrichment in the shallow aquifers of parts of the Brahmaputra floodplains in Assam, India, adjoining the India-Bhutan international boundary in the vicinity of the eastern Himalayas. Fifty groundwater samples were analyzed for different physico-chemical parameters (pH, EC, Na+, K+, Ca2+, Mg2+, Cl-, , , , , Fe and Mn) to elucidate the hydrogeochemistry of the study area. Arsenic concentration of the groundwater samples ranged from bdl to 0.200 mg/L with a mean of 0.055 mg/L. The arsenic concentration of 34 % of the samples analyzed was above the BIS limit of 50 A mu g/l. The dominant groundwater type is Ca-HCO3 with high concentrations of Fe and Mn, but low levels of and . The results of a hydrogeochemical study revealed that the reductive dissolution of MnOOH and FeOOH represents an important mechanism of arsenic release in the study area along with major cations playing an important role in leaching of As into the groundwater.