GEOGENIC CONTAMINATION OF FLUORIDE IN GROUNDWATER OF URAVAKONDA, ANANTAPUR DISTRICT, ANDHRA PRADESH, INDIA

Although fluorine, which generally occurs in nature as fluoride, is beneficial to human health in trace amounts, it can be toxic in excess. This powerful calcium-seeking fluoride can interfere with the calcified structure of bones and teeth in the human body at concentrations above 1.5 mg/L causing dental or skeletal fluorosis. Fluoride-rich groundwater is well known in granite aquifers in India and the world. One of the main exposure routes of fluoride from minerals is via drinking water and hence hydro geochemical investigation has been carried out in the granitic terrain of Uravakonda area, Anantapur district, Andhra Pradesh State, India with an aim to understand the relationship of fluoride with other major ions, and also to identify the source of fluoride in groundwater. Fifty groundwater samples were analyzed in the study area for fluoride and other major ions like calcium, magnesium, chloride, carbonate, bicarbonate, sodium, potassium, sulfate, and nitrate in addition to pH and electrical conductivity. Fluoride concentration in groundwater of different aquifers varies from < 0. 50 to 7.2 mg/l. Most of the groundwater has fluoride exceeding the maximum permissible limit per the Bureau of Indian Standards (1.5 mg/L).Geochemical classification of groundwater shows that Na–HCO₃, Ca–Cl, and Ca–HCO₃–Na are the dominant hydrochemical facies. Preliminary scanning electron microscopy (SEM) investigations were conducted to assess the nature and distribution of minerals in granites and indicated deposition of minerals (fluorite) on the cleavages surfaces.Probable sources of fluoride are weathering and leaching of fluoride bearing minerals under the alkaline environment. The fracture network in disturbed and fragile contact zone has facilitated development of potential aquifers and enhancement in F^- concentration. Further the concentration of fluoride is aided by high rate of evaporation, longer residence time of waters in the aquifer zone, intensive and long term irrigation. Dental and skeletal fluorosis and deformation of bones in children as well as adults were observed in the study area indicating the health impact of fluoride in groundwater.