Entropy-based groundwater quality evaluation with multivariate analysis and Sobol sensitivity for non-carcinogenic health risks in mid-Gangetic plains, India

This study assessed the quality and pollution status of the groundwater in an agricultural and densely populated area of Mid-Gangetic Plain Utilizing Principal Component Analysis (PCA), Spearman's correlation analysis, and Entropy water quality index (EWQI) and evaluated the public health hazard resulting due to nitrate and fluoride exposure using USEPA-based Health risk model and Sobol sensitivity analysis (SSA) on the basis of collected groundwater samples. The analysis revealed that several water quality parameters surpassed the permissible levels established by the Bureau of Indian Standards (BIS). Based on the third quartile values the sequence of ionic dominance in the groundwater was observed as: HCO₃^- > Ca²⁺ > Mg²⁺ > Cl^- > SO₄^2- > NO₃^- > PO₄^3- > F^-. Approximately 10% of groundwater samples exceeded the desirable fluoride level of 1 mg/l, and 12% of samples surpassed the BIS permissible nitrate limit of 45 mg/l. Correlation analysis suggested key factors driving groundwater chemistry, including agricultural runoff, wastewater discharge, and geological activities. PCA reduced 12 variables to 4 significant components, explaining 68.074% of the variation, identifying both geogenic and anthropogenic interventions on the groundwater quality, and highlighting the complex interplay of these factors in the study area. Groundwater quality, measured by EWQI, ranged from 36.30 to 234 revealing about 85% of samples falling in excellent to fair quality, suitable for drinking. Notedly, there was some overlap in the distribution pattern of poor water quality samples and those with high nitrate, phosphate, and magnesium levels. Health risk assessment revealed that nitrate and fluoride pollution pose a significant non-carcinogenic threat. The total hazard index ranging 0.328-2.77 for children, 0.26-2.23 for females, and 0.22-1.89 for males, with 56.10% of samples exceeding the safe threshold for children, signifying a potential health risk for children than adults. SSA revealed that concentration and intake rate are the most influential variables of nitrate and fluoride exposure, which causes health risks to residents. To ensure public health and safety, the study advises residents to rely on treated water from underground sources. Additionally, it stresses the need for ongoing monitoring of groundwater resources to guide the development of effective pollution mitigation strategies and maintain a safe and reliable water supply.