Fluoride levels in the groundwater of the south-eastern part of Ranga Reddy district, Andhra Pradesh, India

The fluoride level in groundwater is controlled by the distribution of Ca2+ and SO42-, ionic strength and the presence of complex ions in its composition. In the study area, situated in the Ranga Reddy district, Andhra Pradesh, India, the concentrations of fluoride in the groundwater vary from 0.7 to 4.80 mg/l and from 0.4 to 4.20 mg/l during the pre- and post-monsoon seasons respectively. From the correlation coefficient studies, it is observed that fluoride is inversely related with Ca2+ and positively related with HCO3-, whereas the correlation coefficient between fluoride and other ions is very poor during both seasons. The difference in F- concentrations between pre- and post-monsoon seasons could be because the ionic concentrations in the groundwater during the post-monsoon period were generally less than their counterparts during the pre-monsoon period, because of dilution by rainwater. By contrast, the fluoride concentration in many places was relatively high during the post-monsoon period. This indicates contamination of groundwater from surface pollutants.