Assessment of fluoride contamination and distribution: a case study from a rural part of Andhra Pradesh, India

In total, 123 groundwater samples were collected to evaluate the suitability for drinking purpose in a rural part of Andhra Pradesh, India. The groundwater is alkaline in nature and pH varying from 7.18 to 9.32 with a mean value of 8.36. The hydrogeochemical analysis reveals that the fluoride concentration varies from 0.4 to 5.8 mg/L with a mean of 1.98 mg/L. Higher fluoride concentration is found in west-central parts of Markapur region. The villagers have been exposed to the intake of high fluoride-bearing groundwater for the prolonged period and suffering from the deadly disease fluorosis. However, with respect to groundwater chemistry, the fluoride concentration is high in Na+–HCO3−-type groundwater and low in Ca2+–HCO3−-type groundwater in the Markapur region. Data plotted in Gibbs diagram show that all groundwater samples fall under rock weathering dominance group with a trend toward the evaporation dominance category. Therefore, rock–water interaction is the primary cause of elevated fluoride in the groundwater of the study region. Furthermore, a significant positive correlation exists between F− and pH, HCO3- as well as negative correlation exists between F- and Ca2+ and NO3−, which supports that the alkaline nature of water is the main cause for dissolving fluoride-bearing minerals.