Entropy-Based Water Quality Index and Human Health Risk Assessment in Eastern Gangetic Plains

Abstract

Groundwater (GW) is the primary water source in the Eastern Gangetic Plains and is increasingly threatened by geogenic and anthropogenic contamination, posing risks to dependent populations. This study assesses GW hydrogeochemistry and its suitability for drinking and irrigation in Bodh Gaya, Bihar, India, a major Buddhist pilgrimage center hosting the UNESCO-listed Mahabodhi Temple. Fifty GW samples were collected and analyzed using standard methods. Results show that concentrations of NO₃⁻, F⁻, Ca²⁺, Mg²⁺, and total dissolved solids (TDS) exceed Bureau of Indian Standards (BIS 10500:2012) limits in several samples. Ionic dominance follows Ca²⁺ > Na⁺ > Mg²⁺ > K⁺ and HCO₃⁻ > Cl⁻ > SO₄²⁻ > NO₃⁻ > F⁻, indicating control by alkaline earth metals and weak acids. About 26% of GW samples exceed the acceptable limit of nitrate. The entropy water quality index (EWQI) classifies 96% of samples as good to excellent for drinking. However, health risk assessment indicates noncarcinogenic risk, with hazard quotient (HQ) values exceeding safe limits in 16% of samples for adults and 24% for children. Principal component analysis reveals three dominant factors explaining 81.78% of total variance, reflecting combined geogenic and anthropogenic influences, mainly mineral dissolution and rock weathering. Irrigation indices (electrical conductivity [EC], sodium adsorption ratio [SAR], residual sodium carbonate [RSC], Na%, and magnesium hazard ratio [MHR]) suggest most GW is suitable for agricultural use. Overall, GW quality is largely acceptable, but elevated nitrate levels require targeted management to protect public health in this ungauged region.