Arsenic Pollution of Groundwater in Bangladesh-Characteristic of Arsenic Concentration and Mechanism of Arsenic Elution to Groundwater in Samta.

We have surveyed water quality in Samta village in Bangladesh since March 1997, and analyzed the arsenic concentrations of groundwater in the area surrounding Samta. This paper shows the results of the survey, concerning the characteristics of arsenic contamination of groundwater and the nechanism of arsemic elution.1) The arsenic concentration of groundwater in Samta showed the tendency to increase with the passage of time.2) The arsenic contamination is observed widely in the area surrounding Samta, although not so high as in Samta.3) It is characteristic that concentration of HCO3- and Fe2+ in groundwater are high and their distribution is in accordance with that of arsenic contamination.4) The pentavalent arsenic concentration in groundwater was higher than that of trivalent in the north of Samta, but in the south trivalent arsenic concentration was higher than that of pentavalent.5) The distribution of HCO3-, Fe2+ and EC in groundwater explains that the mechanism of arsenic elution to groundwater is mainly caused via the reduced state of groundwater and partially via oxidation state.6) There is some correlation between thickness of upper muddy layer and distribution of arsenic concentration of groundwater in Samta.