Groundwater chemistry and health hazard risk valuation of fluoride and nitrate enhanced groundwater from a semi-urban region of South India

Abstract

Evaluation of groundwater chemistry and its related health hazard risk for humans is a prerequisite remedial measure. The semi-urban region in southern India was selected to measure the groundwater quality to know the human health risk valuation for different age groups of adults and children through oral intake and skin contact with elevated concentrations of fluoride (${\mathrm{F}}^{-}$) and nitrate (${\mathrm{NO}}_{3}^{-}$) groundwater. Groundwater samples were collected from the semi-urban region for pre- and post-rainfall periods and resolute its major ion chemistry. The pH values showed the water is alkaline to neutral in nature. Total dissolved solid (TDS) ranged from 201 to 3612 mg/l and 154 to 3457 mg/l. However, ${\mathrm{F}}^{-}$ concentration ranges from 0.28 to 5.48 mg/l and 0.21 to 4.43 mg/l; and NO₃⁻ ranges from 0.09 to 897.28 mg/l and 0.0 to 606.10 mg/l elevating the drinking water standards of ${\mathrm{F}}^{-}$ in 32% and 38% samples and for ${\mathrm{NO}}_{3}^{-}$ about 62% and 38% during pre- and post-rainfall seasons, respectively. The fluoride-bearing minerals are the main sources of elevated concentrations of ${\mathrm{F}}^{-}$ and excessive use of chemical fertilizers as the chief source of NO₃⁻ concentration in the aquifer regime. Water quality index (WQI) ranged from 18.3 to 233 and 12.97 to 219.14; 20% and 22% showed poor water quality for pre- and post-rainfall seasons with WQI ≥ 200. Piper plot suggests that 46% and 51% of samples signify carbonate water type (${\mathrm{Ca}}^{2+}-{\mathrm{HCO}}_{3}^{-}$), and 32% and 28% of groundwater samples show (${{\mathrm{Ca}}^{2+}+{\mathrm{Na}}^{+}+\mathrm{HCO}}_{3}^{-}$) type water for pre- and post-rainfall seasons respectively. Gibbs’ plot suggests the dominance of water–rock interaction in the aquifer system. Further, the principal component analysis (PCA) revealed three and four components which explain 74.85% and 79.30% of the variance in pre- and post-rainfall seasons with positive loading of EC, TDS, Ca²⁺, Na⁺, Mg²⁺, K⁺, ${\mathrm{SO}}_{4}^{2-}$, Cl⁻, and ${\mathrm{HCO}}_{3}^{-}$ due to mineral weathering and water–rock interactions altering the chemistry for an elevated concentration of ${\mathrm{F}}^{-}$ and ${\mathrm{NO}}_{3}^{-}$ in groundwater. Cluster analyses of chemical variables observed four clusters with a linkage distance of 5 to 25 with a linkage between different variables displaying predominant ion exchange, weathering of silicate and fluoride-rich minerals, salinization of the water, and a high value of ${\mathrm{NO}}_{3}^{-}$ concentration, resulting from fertilizers. The hazard quotient (HQ) through ingestion (HQ_ing) and dermal (HQ_der) pathways of F⁻ and NO₃⁻ was observed higher than its acceptable limit of 1.0 for different age groups indicating the non-carcinogenic effect on human health. Effective strategic measures like defluoridation, denitrification, safe drinking water supply, sanitary facilities, and rainwater harvesting structures are to be implemented in the area for improvement of human health conditions and also bring awareness to the local community about the health hazard effects of using high concentrated ${\mathrm{F}}^{-}$ and ${\mathrm{NO}}_{3}^{-}$ water for daily uses.