Chemical pollution and bioaccumulation of trace elements in aquatic ecosystems in the Cavally River basin (Ity–Floleu area, Côte d’Ivoire): case of the fish Coptodon walteri and Chrysichthys teugelsi

This study assessed chemical pollution in the aquatic ecosystems of the Cavally River watershed in the Ity-Floleu area (Côte d'Ivoire), focusing on the bioaccumulation of trace elements (As, Cd, Cu, Hg, Ni, Pb, and Zn) in two fish species: Coptodon walteri and Chrysichthys teugelsi. Surface water, sediment, and fish samples were collected over two consecutive years and analysed by atomic absorption spectrometry after acid digestion. The results showed that surface waters generally complied with FAO standards for irrigation, while sediments were heavily polluted in all seasons, with sediment pollution indices ranging from 80.91 to 53,775.17, well above ecotoxicological thresholds (IPS ≥ 20). Transmission factors revealed transfers of trace elements between compartments, notably arsenic and copper from water to sediments in the Cavally, and lead from sediments to the waters of the Floleu River during the rainy season. Biological analyses showed that concentrations of As (up to 1.60 mg/kg), Cu (221.01 mg/kg), and Pb (28.90 mg/kg) in fish tissue sometimes exceeded FAO/WHO limits. Bioconcentration factors revealed a more marked accumulation in Coptodon walteri, especially during the rainy season, with values reaching 290.00 for As, 15.99 for Cd, and 161.34 for Cu. These results reveal a worrying level of contamination in the aquatic biotope, with ecotoxicological risks for biodiversity and health implications for populations that consume fish.