DOES A HIGH CONCENTRATION OF ARSENIC IN GROUNDWATER CAUSE BLACKFOOT DISEASE? AN ANSWER FROM INDIA, BANGLADESH AND TAIWAN

Major ion and trace element analyses have been performed on simultaneously collected (November and December 2006) groundwater samples from Indian, Bangladeshi and Taiwanese aquifer to examine geochemical differences to identify whether Blackfoot disease (BFD) in southwestern Taiwan is caused due to high concentration of As in groundwater. The result shows that the concentrations of Na, K, Mg, Cl, and SO₄ are generally high in groundwaters from southwestern Taiwan, while high Ca is observed in both Indian and Bangladeshi groundwater. The ratios of Na/Cl and SO₄/Cl demonstrate the effect of seawater in Taiwanese groundwater. Seawater could provide required electron acceptors (i.e., SO₄) for bacterial sulfate reduction and promote anoxia that is favorable for As mobilization. The Fe-reduction mechanism is supposedly the dominant geochemical process in Indian and Bangladeshi groundwater, while a combination of geochemical processes might have influenced the release of As in Taiwanese groundwater. Geochemical modeling and field data demonstrate that As(III) is the dominant As species in Indian and Taiwanese groundwater, while As(V) is dominant in Bangladeshi groundwater, which are consistent with the Eh values. The positive saturation index for Fe-bearing carbonates, and oxide phases act as a potential sink for As, while As bearing mineral phases tend to be in the solution. The geochemical comparison demonstrates that high As in groundwater alone is not causing BFD in southwestern Taiwan, however association of As with humic substances and their synergistic effects might have caused Blackfoot disease.