Environmental hydrogeochemistry and genesis of fluoride in groundwaters of Dindigul district, Tamilnadu (India)

Fluoride (F-) is an indispensable element for the human's skeletal and dental health at prescribed levels and becomes lethal at higher levels. Spatial-temporal variability of F- and its geochemical control/association with other dissolved ions in groundwater in the Dindigul district of Tamilnadu (India) were conducted to describe the geochemical dynamics of F- in response to seasonal variability. High concentrations of fluoride (a parts per thousand yen1.5 mg L-1) were observed in the northern region of the district. High levels of F- were observed in non-monsoon periods and low levels in monsoon, because of dilution by precipitation. Bicarbonate was well correlated with F- which explains that both ions were derived from the weathering. While F- has a very weak correlation with silica, this implies that the silicate weathering does not supply F- to the groundwater system. The F- pollution in Dindigul groundwaters is mainly driven by two factors: (1) the geogenic weathering inputs, the geology of this area mainly comprises fluoride bearing minerals (e.g. hornblende biotite gneiss and charnockite); (2) the anthropogenic inputs (agri-fertilizers and tannery waste). Further, F- in the study area is mainly attributed to geogenic sources during pre and postmonsoons and anthropogenic sources in monsoon periods.