Occurrence, source identification, and human health risk assessment of potentially toxic elements in freshwater sources used for aquaculture in the Senegal, Gambia, and Casamance river basins

Freshwater resources in Senegal play a crucial role in drinking water (DW) supply, agriculture, and the rapidly expanding aquaculture sector promoted under the National Sustainable Aquaculture Development Strategy. However, no nationwide assessment has previously investigated potentially toxic elements (PTEs) in freshwater resources supporting aquaculture. This study provides the first integrated evaluation of dissolved arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) in surface water and groundwater collected from 17 aquaculture farms distributed across the Senegal, Gambia, and Casamance river basins. Median PTE concentrations followed the order Cu > Zn > Ni > Cr > Pb ≈ As > Cd, and all measured concentrations remained below the corresponding World Health Organization DW guideline values. Human health risk assessment indicated that ingestion was the dominant exposure pathway, producing substantially higher chronic daily intake than dermal exposure for both adults and children. Nevertheless, hazard quotient, hazard index, and carcinogenic risk values remained below the United States Environmental Protection Agency acceptable thresholds, indicating no significant non-carcinogenic or carcinogenic health risks associated with the investigated PTEs. Principal component analysis identified distinct river-specific contamination signatures, with Zn, Cu, and Cd predominantly associated with the Casamance basin, whereas Cr and Pb were more strongly related to the Senegal River, while the Gambia River exhibited consistently low PTE concentrations. Overall, these findings indicate that freshwater resources supporting aquaculture in Senegal are currently of good chemical quality with respect to the investigated PTEs. This study provides the first national baseline for environmental monitoring and supports sustainable aquaculture development and water-resource management in Senegal.