ECOLOGICAL ASSESSMENT OF STREAMBED SEDIMENTS AND FRESHWATER FISH SPECIES OF EDE-ONYIMA LAKE, IN OKARKI-ENGENNI, RIVERS STATE, NIGERIA

Aquatic ecosystems are heavily polluted by potentially toxic substances deposited in the sediment as a result of anthropogenic activities. These substances have the potential to enter the food chain, posing significant risks to human health and the environment. Five trace metals such as chromium (Cr), nickel (Ni), cadmium (Cd), lead (Pb) and Polycyclic Aromatic hydrocarbons (PAHs) which are regarded as potentially toxic substances were determined in sediments and soft tissues of three commonly consumed fish species, Ageneiosus ucayalensis, Alestes baremoze, and Clarias gariepinus, collected at six sampling sites in Ede Onyima Creek, Okarki-Engenni, Rivers State, Nigeria. The results of trace metals in sediments showed the following range: Ni (1.25 – 11.90 mg/kg); Pb (0.23 – 20.21 mg/kg), Cd (0.09 – 0.72 mg/kg); Cr (0.25 – 11.96 mg/kg) and PAHs (1.25 – 11.90 mg/kg). The mean whole-body concentration of the analyte in three fish species followed the order: Pb > Ni > Cd > PAHs > Cr. The concentrations of the trace metals in sediment were below the quality guideline values; PAHs, had higher threshold and probable effect concentrations (LEL, TEL-HA28, PEL-HA28), indicating toxicity to benthic organisms. The biota-sediment accumulation factor (BSAF) for the fish species ranked in the following order Cd>Pb> Ni>PAHs> Cr. Trace metal concentrations in the fish species exceeded the international permissible limits, indicating that these species are not suitable for human consumption. The contamination level of analytes was determined using the metal pollution index (MPI), which revealed gross contamination of fish species by Cd and Pb in the order Clarias gariepinus (1.8) > Ageneiosus ucayalensis (1.5) > Alestes baremoze (1.4). Furthermore, the flood event had a significant effect on the sedimentary compartment, remobilizing PTSs availability for fish ingestion while washing away legacy contaminated streambed deposits during baseflow.