Speciation and determination of priority metals in sediments of Oyun River, Ilorin, Kwara, Nigeria

This work was carried out to determine the concentrations, bioavailability and mobility of priority metals in sediments of Oyun River, Sango, Ilorin, Nigeria. The river sediments were sampled at six selected locations and the samples were analyzed for some certain priority metals to determine the concentration, speciation and distribution pattern of the metals. The sediments were obtained specifically at upstream, middle-stream and downstream of the river. In general, the total metal concentrations was in the order: Mn > Pb > Cu > Cd in sediment samples and for Tessier's sequential fractionation, manganese was found to be more in the exchangeable phase, while Pb was higher in the residual form and Cu was found to be more concentrated in the organic phase. Total priority metal bio-availability and mobility of Pb, Mn, Cu and Cd in the samples varied between 0-83.61 mg/kg, 93.01-96.65 mg/kg, 23.53-45.88 mg/kg and 0-100 mg/kg, respectively. This clearly indicates that with the exception of Cu, the metals are highly bioavailable leading to it having a higher impact on its target system, subsequently leading to contamination of the water. The high percent bioavailability is an indication of poor retention in the residual geochemical form partly due to saturation of the sediment (river). The pH value was found to be basic but within the WHO standards throughout all locations. The high percentage of Mn, Cd and Pb in the bioavailable forms suggested the need to keep close surveillance on these metals because of their high toxicity. KEY WORDS: Speciation, Mobility, Priority metals, Sediments, Bioavailability, Pearson correlation, Principal component analysis