EXPOSURE OF ARSENIC FROM GROUNDWATER AND RICE: A CASE STUDY FROM WEST BENGAL, INDIA

Natural contamination of groundwater by geogenic As is now a global issue. The problem is most severe in Bengal Delta Plain (BDP) where identifiable health outcomes have been reported during last few decades. This study deals with groundwater hydrochemistry vis-à-vis assessment of As exposure among rural population in Chakdaha block, West Bengal, India. According to survey during the study, 96% of the wells exceeds WHO guideline value (0.01 mg/L of As). Groundwaters are generally anoxic in nature (Eh range: -283 to -22 mV) with circum-neutral pH (range: 6.3 to 7.8). The groundwater chemistry is dominated by HCO₃^- (range: 208 to 440 mg/L), Ca²⁺ (range: 79 to 148 mg/L) and Mg²⁺ (range: 17 to 45 mg/L) along with redox sensitive elements (As_T range: 0.001 to 0.285 mg/L, Fe_T range: 1.2 to 16 mg/L, and Fe-II range: 0.74 to 16 mg/L). The study suggests that Fe-cycling (Fe-II«Fe-III system) is the dominant process responsible for high As in groundwater. During the field survey variety of rice samples have been collected from household, market as well as field to understand the exposure of As from rice. Recently low As groundwater has been supplied to the As affected villages in the study area. It has been found that the combined exposure from groundwater as well as rice is the major challenge to protect human health from As exposure. The current policy (supply of low As / safe drinking water) has to be regulated to cope with the situation.