Arsenic in the groundwater of Majuli – The largest river island of the Brahmaputra: Magnitude of occurrence and human exposure

•Arsenic contamination of groundwater in the largest riverine island Majuli, India.•37% and 16% of 380 tube-well water samples had As greater than 10 and 50μg/L.•90% of urine, 100% of hair and 97% of nail samples had As above the normal ranges.•Significant correlations between arsenic in water and As in hair, nail and urine.•Arsenic concentration in bore-hole sediment was 0.2–1.44mg/kg. Arsenic (As) concentrations in tube-well water, sediment, and biological samples, including hair, nail and urine were measured to determine the degree of contamination in groundwater and its impact on local inhabitants in the largest populated riverine island Majuli, Assam, India. Arsenic in the groundwater (n=380) ranged from