Evaluation of fluoride contamination in groundwater in a semi-arid region, Dausa District, Rajasthan, India

Groundwater is the major source of drinking water in semi-arid region of Rajasthan, India but its quality has been degraded by the addition of contaminants through natural and or anthropogenic reasons. Fluoride is one among these contaminants. The deterioration in the water quality may result in the health hazards. To ensure proper groundwater management in the area present study is carried out to understand the status of groundwater quality and possible causes for high fluoride concentrations. 34 groundwater samples were collected from Dausa district of Rajasthan. Analysed results show that the fluoride concentration ranged between 0.48 and 3.64 mg/l with an average of 1.66 mg/l in groundwater of study area. Fluoride concentrations in about 82% of the samples are more than the permissible limit (1.0 mg/l) set by the Bureau of Indian standards (BIS, 1991), whereas based on the WHO standards (F:1.5 mg/l) (WHO, 2009), about 41% of samples are exceeded the maximum permissible limit. The order of major cations and anions are Na+>Mg+2>Ca+2>K+ and HCO3- > Cl > SO4-2 >CO3-2 >NO3- > F, respectively. Weathering of rocks, evaporation and anthropogenic activities are found be responsible for high fluoride concentration. Since the geological unit in study area are alluvium, quartzite and granite gneisses containing fluoride bearing minerals like - Biotite, Muscovite, Fluorite and Albite, the major contribution comes from weathering of rocks. This finding is further supported by Scholler Chloro-alkaline indices and high Na+/Ca+2 ratio (>1.0) suggesting ion-exchange. The high fluoride content render the water unfit for agriculture and drinking purpose in the area thus to ensure sustainable uses corrosivity ratio (CR) is utilized to assess groundwater suitability for industrial uses.