Pollution Status and Potential Ecological Risk of Toxic Metals in Sediments of the Lower Calabar and Great Kwa Rivers, Nigeria

Contaminants present in sediments serve as vital indicators of environmental health in aquatic ecosystems. This study aimed to investigate the current heavy metals pollution status and potential biological effects of the surface sediments of Great Kwa and Calabar Rivers, Nigeria, from October 2021 to August 2022. The concentrations of lead (Pb), cadmium (Cd), mercury (Hg), and arsenic (As) were determined. The total metals concentrations in the sediment of both eivers ranged between: 4.457-11.341mg/ kg, 0.311-0.978mg/ kg, 0.034-0.096mg/ kg, and 0.134-0.755mg/ kg for lead, cadmium, mercury and arsenic, respectively. Metal concentrations in the sediment of Calabar River were significantly (P≤ 0.05) higher than the Great Kwa River, except for arsenic. Both rivers did not exhibit significant seasonal variations in metal concentrations. Assessment of metals using United States Environmental Protection Agency, and the Australian and New Zealand sediment quality guidelines indicated that neither river was polluted with respect to the metals under study. The contamination factor for the metals corresponded to a low contamination level, except for lead, which showed a moderate contamination factor during the dry season. The average contamination degree for each river corresponded to low contamination degree. The pollution load index (PLI) also supported the conclusion that both rivers were not polluted. However, the concentration of cadmium at Esuk Nsidung exceeded the Threshold Effect Level (TEL), indicating potential risks to organisms in this specific location. The ecological risk factor analysis revealed that Pb, Cd, Hg, and As posed a low potential ecological risk to other components of the environment. This study emphasizes the importance of periodic monitoring of water and sediment quality in the Great Kwa and Calabar Rivers to ensure sustainable management and to safeguard human and environmental health.