HYDROCHEMISTRY OF ARSENIC-ENRICHED AQUIFER FROM RURAL WEST BENGAL, INDIA: A STUDY OF THE ARSENIC EXPOSURE AND MITIGATION OPTION

The present study aims to understand the hydrochemistry vis-à-vis As-exposure from drinking groundwater in a traditional orchard area of rural Bengal. The characteristic hydrochemical features of the groundwaters are low Eh (range: -151 to -37 mV; mean: -68 mV) and nitrate (range: 0.001-1.7 mg/L; mean: 0.14 mg/L) followed by high alkalinity (range: 100-630 mg/L; mean: 301 mg/L), Fe (range: 0.99-38 mg/L; mean: 8.1 mg/L), phosphate (range: 0.002-15 mg/L; mean: 0.54 mg/L), hardness (range: 46-600 mg/L; mean: 245 mg/L) and sulphate (range: 0.19-88 mg/L; mean: 7.2 mg/L), indicating reducing condition of the aquifer. The land use pattern (sanitation, surface water bodies, sanitation coupled with surface water bodies and agricultural areas) demonstrates local enrichment factor for As and Fe in groundwater. Among these, sanitation is the most prevailing where groundwater is generally consisting of high As (mean: 269 µg/L) and Fe (mean: 9.8 mg/L). This is also observed through questionnaire survey, and shows that more than 70% of the villagers in the study area do not have proper sanitation. Thus demonstrating that local unsewered sanitation could also cause As toxicity in rural Bengal. In the agricultural areas, higher mean values of alkalinity, PO4, SO4, hardness and electrical conductivity was observed, and could be linked with the use of fertilizers. Bio-markers study indicates that the accumulation of As in hair and nail is related with the duration of exposure (age). The strength and weakness of the on-going drinking water supply and achievability are also evaluated.