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

Abstract

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^- > SO₄^2- > CO₃^2- > 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.

Keywords: Fluoridated groundwater; Hydro-geochemical attributions; Mineralogical analyses; Muscovite; Probabilistic health risk assessment; Statistical models.