Lithological controls on the groundwater fluoride enrichment in central India

Petrographic and mineralogical observations are corroborated with the hydrochemistry data to identify the exact lithological source of fluoride contamination in the central part of India. Groundwater samples ( n = 57) representing both shallow and deep aquifers and lithological formations ranging from Archean to Late Cretaceous from central part of India were studied, where fluoride contamination in drinking water is causing a serious environmental health hazard. About 90% samples show high fluoride content than the maximum permissible limit of 1.5 mg/L. Fluoride concentrations in different rock formations such as granite gneisses, limestones, sandstones, and basalts were studied which shows maximum fluoride values of up to 4.9 mg/L. Several parameters (including Saturation Index and Gibbs’s plots) were evaluated to understand the factors which controlled the groundwater quality in the area. All signifies water–rock interaction as a major factor influencing composition of groundwater in both the seasons as well as support geogenic enrichment of fluoride. Low-temperature hydrothermal mineralization of fluorite in the limestone aquifers is responsible for the dissolution of fluorine in groundwaters with highest concentration. Moderate concentrations of fluoride up to 2.7 mg/L are observed in the basement granite gneisses. Our mineralogical studies recognized abundant fluor-apatite in granite gneiss aquifers, with high F − content ranging from 2.5 to 4.2 wt%, as a major contributor of fluoride in groundwaters. Rock-water interactions amplified in alkaline environments played an important role in the dissolution of fluorine in both the aquifers. Identification of main geogenic source of fluoride will be helpful for proper management of drinking water sources in the highly affected areas.