Elevated fluoride levels in groundwater in the Himalayan aquifers of upper Indus basin, India: Sources, processes and health risk

Abstract

Groundwater plays an important role in socio-economics and ecosystem development in mountainous catchments of Himalaya. However, enriched geogenic pollutants in groundwater e.g. Fluoride (F−) and Arsenic (As) in many aquifer systems has deteriorated its suitability for drinking purpose. Although, F− enrichment in other Himalayan basins is well documented but its sources, fate and transport in groundwater of upper reaches of Indus Basin, western Himalaya is still unknown. In the present study, we collected groundwater samples (n = 334) across Upper Indus Basin, (UIB) India to assess the distribution, hydrogeological and geochemical processes controlling the origin, fate and transport of F− in the complex aquifer system. The groundwater is circum-neutral to alkaline with HCO3− -Na+, HCO3−- Ca2+- Na+ and HCO3−- Ca2+- Mg2+ type suggesting the dominance of silicate and carbonate weathering. The results showed that F− enriched groundwater is widespread in the basin with 70% samples having F− above the maximum permissible limit of 1.5 mg/L. High F− groundwater showed distinct hydrochemical evolution attributed to higher pH, HCO3−, Na+, low Ca2+ with Na+/Ca2+ ratio >1 exhibiting F− in groundwater is geogenic, facilitated by the release of Na+ and HCO ions via silicate and carbonate dissolution. F− release in groundwater is also assisted by the incessant dissolution of fluorinated minerals (fluoride) with active exchange between Na+ and Ca+. High HCO3− also facilitates exchange of hydroxides (OH−) and F− on sediment surfaces that contributes to F− enrichment in groundwater through desorption. Geochemical modelling indicated that the precipitation of calcite, dolomite and aragonite is conducive for F− release. F− risk assessment exhibited that people living in UIB are highly vulnerable to the potential risk of dental and skeletal fluorosis. Therefore, it is highly substantial to provide an alternative drinking water source or treat the contaminated water before consumption to mitigate human health hazards.