Improving evaluation of groundwater heavy metal(loid)s pollution efficiencies: Insights from novel Shannon entropy-weight and one-way ANOVA analysis

Abstract

This study explores the hydrogeochemical behaviour of heavy metal(loid)s [HMs] in groundwater, their seasonal variations in enrichment and depletion, and adverse effects on human health in the Bahraich district of Uttar Pradesh, a part of the Ghaghara River basin, India. The Shannon's Entropy-Weighted Heavy Metal(loid)s Index (EW-HMI), a novel tool, has been applied to quantify cumulative groundwater pollution levels at each 42 monitoring sites, including critical evaluation of existing conventional pollution indices. Results from One-way ANOVA analysis indicate a significant seasonal difference in the mean concentrations of As, Fe, and Mn, demonstrating that monsoonal recharge is a governing factor for observed seasonal variation. The computation of EW-HMI reveals that >50% of sites are marked by ‘poor’ to ‘extremely poor’ water quality in Pre-monsoon 2022 (Pre-M). Distinctly, there is a notable improvement in 'excellent water quality', increasing from 9.5 to 57.1% in Post-monsoon 2022 (Post-M). This pattern of temporal change in EW-HMI, in contrast to HPI, is clearly depicted by the GIS-based spatial distribution maps. Thus, EW-HMI is a robust index and more effectively addresses apparent flaws in conventional indexing systems that could be used for wider applications. Health risk assessments (HRA) show that both children and adults in the Bahraich district are at risk of non-carcinogenic (NCR) and carcinogenic (CR) health effects from drinking contaminated groundwater. Children are anticipated to have a higher total CR mean value of 3.6 and 1.7 per 1000 children while adults estimated to have relatively low total CR mean values of 2.3 and 1.1 per 1000 adults in Pre-M and Post-M, respectively. This research offers valuable findings that can guide policymakers and stakeholders in identifying priority areas to facilitate the implementation of sustainable water resource management initiatives on both national and global scales.