Hydrogeochemical modelling and the probabilistic health risk assessment of nitrate and fluoride in the groundwater of Kota stone mine regions

Groundwater serves as the main source of drinking water, especially in rural India. The primary threats to human health and water quality are pollutants like nitrate and fluoride. To determine the concentration of fluoride and nitrate, as well as their geographical distribution and possible sources, the current study examined the hydrogeochemical properties of groundwater in the stone-mining regions of Kota, Rajasthan, India. In this study, multivariate statistics, health hazard assessment, and entropy water quality index (EWQI) determinations were also carried out. Around 84% of the samples had fluoride content above the threshold limit for drinking water (1.5 mg L⁻¹). Similarly, nitrate contents were 25.5% and 33.3% higher in pre-monsoon and post-monsoon, respectively, than the permissible limit for drinking water quality (45 mg L⁻¹). Considering the EWQI values, nearly 19.6% and 21.6% of the groundwater samples were poor and very poor, respectively; hence, they were unfit for drinking in the pre-monsoon season. In the post-monsoon period, rainfall-induced dilution exerted a significant positive influence on groundwater quality by reducing the concentration of dissolved contaminants. The average value of the hazard quotient (HQ) of fluoride through groundwater ingestion for adults (children) in the seasons before and after monsoon was 2.29 ± 0.31 (3.03 ± 0.41) and 2.19 ± 0.30 (2.89 ± 0.39), respectively; hence, they posed the risk of non-carcinogenic risk to people, which is a severe concern. In this study, elevated fluoride levels were found in the groundwater, likely due to the dissolution of fluoride-bearing minerals at higher temperatures and extended residence times, which encourages fluoride weathering in semi-arid regions. The findings of this study would be useful for managing groundwater resources strategically while preserving groundwater quality and reducing health hazards.