Hydrogeochemical characterization and potential geogenic source of fluoride contamination in Gariaband district of southern Chhattisgarh, India.

Fluoride contamination of groundwater exerts serious health concerns in developing countries like India, where surface water resources in general are not considered for domestic consumption. The present investigation attempts to evaluate the groundwater quality in terms of fluoride contamination in Deobhog and adjoining areas in Gariaband district, Chhattisgarh. A total of 68 groundwater samples were collected both in the pre- and post-monsoon period and analyzed for different physicochemical parameters like Temperature, pH, EC, TDS, Na⁺, K⁺, Ca²⁺, Mg²⁺, HCO₃^-, NO₃^-, Cl^-, SO₄^2-, and F^-. The results reveal that the cation abundance is in the order of Ca²⁺ > Na⁺ > Mg²⁺ > K⁺, and that for anions, it is HCO₃^- > Cl^- > SO₄^2- > NO₃^- > F^-. Hydrochemical characterization shows that the water is dominantly calcium bicarbonate type in general, irrespective of their fluoride concentration. The source of the dissolved constituents in water is identified to be due to rock-water interaction. Hydrochemical processes like ion exchange, along with carbonate and silicate weathering, are responsible for major cations and anions concentrations in fluoride-rich water. Changes in alkalinity of water accelerate the dissolution of fluoride from fluoride-bearing mineral phases, thus increasing the concentration in water. The highest concentration of fluoride is observed at Nangaldehi village (4.9 mg L^-1 post-and 3.83 mg L^-1 pre-monsoon), in the north-eastern part where dental fluorosis is noted in residents of the affected area. Lithounits like mafic granulite, Dongargarh granite, charnockite, etc. have a higher concentration of fluoride due to the presence of minerals such as apatite, biotite, hornblende, etc., confirmed through detailed petrographic studies. The fluoride from these sources also dispersed into the residual soil developed over the weathered rocks. The water in the area is observed to be undersaturated with fluoride, which signifies the area's proneness to more fluoride contamination in the near future. The contaminated aquifers are structurally controlled, and the shallow, unconfined aquifers are less contaminated with fluoride than those that are present at an elevation around 200 m above mean sea level. This study provides first-hand information about the fluoride contamination in the area and established its geogenic origin. It also emphasizes to explore the possibility of alternate surface water sources for the affected areas.