Prevalence of fluorosis in the fluoride enriched groundwater in semi-arid parts of eastern India: Geochemistry and health implications

Abstract

Fluorosis is becoming a global environmental toxicological problem and is most commonly found in water-stressed regions. In order to evaluate the geochemical mechanism of fluoride enrichment in groundwater and health implications in the Padwakodari environs of eastern part of India, a total of twenty two samples were collected and analysed for physico-chemical parameters spreading across the study area. Geologically, the area mainly comprises of phyllites, granite gneiss, mica schist and sandstone. High fluoride concentrations found mainly in the granite gneisses which are situated central to northwestern parts of the study area. The concentration of fluoride in the groundwater samples ranges from 0.3 to 11 mg/l with an average of 2 mg/l. 64% of the groundwater samples containing fluoride concentration that exceed the WHO drinking water guidelines value of 1.5 mg/l. Chronic ingestion of high doses has been linked to the development of dental fluorosis, and in extreme cases, skeletal fluorosis. The dominant geochemical facies present in water are Na–Ca–Mg–HCO3 (11 samples), Na–Mg–Ca–HCO3 (5 samples), Ca–Na–Mg–HCO3 (5 samples) and Ca–Mg–Na–HCO3 (1 sample). Sodium and bicarbonate ions being major component in majority of the water types (located mostly in the granite gneiss formation) has a tendency to increase fluoride concentration in groundwater by dissolving the fluoride from fluoride bearing minerals. The oversaturation of half of the samples with respect to calcite and majority of samples undersaturation with respect to fluorite makes it feasible for fluoride to get released in to the groundwater. Decreasing Ca activity downgradient (recharge to discharge) leads to a dominance of fluorite-unsaturated conditions and consequently to mobilization of fluoride in groundwater. The results indicate that the fluoride concentration in groundwater is mainly governed by high weathering of fluoride bearing minerals (i.e. apatite and biotite) in granite gneiss contains abundant fluoride, alkaline hydrogeological environment, high temperature, low rainfall, evapotranspiration and ion exchange.