Spatial and temporal variation of metal trace elements (MTE) and health risk assessment in the waters of the upper Bandama (northern Côte d'Ivoire)

Abstract

The Bandama Basin hosts one of the country's major river systems. Due to overexploitation and the expansion of human activities in the Upper Bandama Basin, the river's water quality has severely deteriorated due to trace metal elements. This study aimed to assess water quality and the health risks associated with consuming this water. The study was conducted at three stations across the Upper Bandama Basin during two hydrological seasons: low-flow (April 2024) and high-flow (September 2024). Six trace metal elements (Fe, Cu, Zn, Pb, Hg, Cd) were analysed using an atomic absorption spectrometer (AAS); subsequently, contamination factors (CF), the Heavy Metal Pollution Index (HPI), the Heavy Metal Evaluation Index (HEI), and non-carcinogenic risks were evaluated. The results indicate that concentrations of Hg, Cd, Cu, and Fe were significantly higher during the low-flow period than during the high-flow period (p < 0.05). During the low-flow period, Hg levels ranged from 0.001 to 0.006 mg/L, Cd levels from 0.002 to 0.025 mg/L, and Fe levels from 2.0 to 3.8 mg/L. Cu and Zn concentrations remained below World Health Organization guideline values, whereas Cd, Pb, and Fe levels occasionally exceeded these limits. Contamination factors indicated low contamination for Cu and Zn (CF < 1), moderate to high contamination for Cd (1.67 ≤ CF ≤ 8.33) and Pb (1 ≤ CF ≤ 9), and high contamination for Fe (CF > 6) during the low-flow period. The HPI value reached 185.80 during the low-flow period, whereas it remained below 100 during the high-flow period. Children were the population most vulnerable to non-carcinogenic risks, primarily associated with Hg, Cd, and Pb. The analysis confirmed a common origin for Fe, Hg, Cd, and Cu, while anthropogenic activities appeared to have a stronger influence on Pb. Hierarchical agglomerative clustering revealed a primarily seasonal differentiation among the samples, highlighting the role of the season in the distribution of trace metal elements.