Investigating spatial distribution of fluoride in groundwater with respect to hydro-geochemical characteristics and associated probabilistic health risk in Baruipur block of West Bengal, India

Fluoride (F-) enrichment in groundwater of the lower Gangetic plain in West Bengal, India is a major concern. Fluoride contamination and its toxicity were reported earlier in this region; however, limited evidence was available on the precise site of contamination, hydro-geochemical attributions of F- mobilization and probabilistic health risk caused by fluoridated groundwater. The present study addresses the research gap by exploring the spatial distribution and physico-chemical parameters of fluoridated groundwater along with the depth-wise sedimental distribution of F-. Approximately, 10 % of the groundwater samples (n = 824) exhibited high F- ≥ 1.5 mg/l from 5, out of 19 gram-panchayats and Baruipur municipality area and the maximum F- was observed in Dhapdhapi-II gram-panchayat with 43.7 % of samples showed ≥1.5 mg/l (n = 167). The distribution patterns of cations and anions in fluoridated groundwater were Na+ > Ca2+ > Mg2+ > Fe > K+ and Cl- > HCO3- > SO42- > CO32- > NO3- > F-. Different statistical models like Piper and Gibbs diagram, Chloro Alkaline plot, Saturation index were applied to better understand the hydro-geochemical characteristics for F- leaching in groundwater. Fluoridated groundwater is of Na-Cl type which implies strong saline character. The intermediate zone between evaporation and rock dominance area controls F- mobilization along with ion-exchange process occurring between groundwater and host silicate mineral. Furthermore, saturation index proves geogenic activities related to groundwater F- mobilization. All cations present in sediment samples are closely interlinked with F- in the depth range of 0-18.3 m. Mineralogical analyses revealed that muscovite is the most responsible mineral for F- mobilization. The probabilistic health risk assessment disclosed severe health hazard in the order of infants > adults > children > teenagers through F- tainted groundwater. At P95 percentile dose, all the studied age groups showed THQ >1 from Dhapdhapi-II gram-panchayat. Supply of F- safe drinking water is required through reliable water supply strategies in the studied area.