Genesis and mobilization of fluoride in groundwater of India: Statistical evaluation, health impacts, and potential remedies

Groundwater contamination by fluoride (F- >1.5 mg/L) is pervasive and typically confined to arid and semi-arid regions. Therefore, several parts of India are contaminated with F-. However, genesis, sources, and mobilization of F- in groundwater are unclear or so far evaluated based often on studies conducted at a local scale. To understand the severity of F- contamination at the national scale and to devise remedial strategies, we performed a statistical evaluation between F- and its influencing factors, including geology, hydro-meteorology, and potential hydro-chemical parameters based on a large dataset (n = similar to 2000) published in the last two decades throughout India. Results revealed that (a) alkalinity plays a pivotal role in the mobilization of F- into groundwater from the sediments/rocks, (b) high F- in groundwater is more pronounced in the arid and semi-arid areas of alluvial plains than hard rock regions, and (c) positive correlation of elevated F- with SiO2 and K+ indicates the dominance of geogenic sources linked to the weathering of fluorine bearing silicates. Investigations show that one-third of the Indian drinking water wells are contaminated with F-, thereby risking the health of over millions of people through the drinking water pathway. Findings from this study have addressed the most possible sources, pathways, and regional prevalence of F- contamination in the groundwater of India, and suggested the suitable remedial measures based on prevailing surface and sub-surface conditions. Lastly, this review also addresses challenges and propose future research directions to tackle high F- groundwater and ensure safe drinking water supply in India.