Geochemical Investigation on Arsenic Contamination in the Alluvial Ground-water of Mankyeong River Watershed

As-rich alluvial groundwaters occurring in the agricultural area of Mankyeong River watershed were geochemically studied. 15 out of 29 investigated wells (52%) showed As levels exceeding the WHO drinking water standard (10 mu g/L). Their chemistry is characterized by low Eh levels, low NO3 and SO4 concentrations, and high pH, alkalinity, Fe, NH4, and PO4 levels. This suggests that arsenic is enriched by the reductive dissolution of As-bearing Fe-/Mn-(hydro) oxides, the commonest process in Bangladesh and West Bengal of India, of which groundwaters are severely contaminated by As. It was also revealed that As concentrations in the area are strongly regulated by the presence of agrochemicals such as NO3 and SO4.