GIS based evaluation of fluoride contamination and assessment of fluoride exposure dose in groundwater of a district in Uttar Pradesh, India

Groundwater is the main source of drinking water in both rural and urban areas of the Pratapgarh district in the eastern Uttar Pradesh. Fifty-five groundwater samples were collected from 17 blocks of the Pratapgarh district and analyzed for fluoride (F-) and other water quality parameters (pH, EC, TDS, turbidity, Cl-, HCO3-, SO42-, NO3-, Ca2+, Mg2+, Na+, K+, silica and total hardness) to assess its suitability for drinking uses. The fluoride concentration in the analyzed groundwater of the Pratapgarh district varied between 0.41 and 3.99mg/L. Fluoride concentration in about 78% of the groundwater samples exceeded the acceptable level of 1.0mg/L, while in 70% samples it exceeded the maximum permissible limit of 1.5mg/L. A geographic information system (GIS) tool was used to study the spatial variation of fluoride concentrations in the groundwater of the Pratapgarh district. Fluoride is positively correlated with pH (0.36) and HCO3- (0.22) and negatively with Ca2+ (-0.23) and Mg2+ (-0.08), suggesting dissolution of fluoride-bearing minerals with the precipitation of Ca/Mg carbonate in the alkaline environment. The maximum exposure dose to fluoride for adults in the study area was found to be 6.8times higher than the minimum risk level (MRL) of 0.05mg kg(-1) day(-1) estimated by the Agency for Toxic Substances and Disease Registry (ATSDR).