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 by F¯. However, the genesis, sources, and mobilization of F¯ in groundwater are unclear or 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 = ∼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 by 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 remediation measures suitable based on prevailing surface and sub-surface conditions. The review will also address challenges and propose future research directions to tackle high fluoride groundwater and ensure safe drinking water supply in India.