Appraisal of Heavy Metals Pollution in the Stream Sediments from Okemesi-Ijero Area, Southwestern Nigeria: Insight from Geochemical Fractionations and Multivariate Analysis Techniques

Abstract

The distribution and accumulation of heavy metals in the stream sediments of Okemesi-Ijero area, southwestern Nigeria was examined. Stream sediment samples from tensites were characterized for metals content such as Cadmium (Cd), Lead (Pb), Copper (Cu), Nickel (Ni), Iron (Fe), Manganese (Mn) and Zinc (Zn). The extractable heavy and macro metals such as, Cd, Pb, Cu, Zn, Ni, Fe and Mn in the stream sediment samples were analysed using Atomic Absorption Spectrometry (AAS). Apart from total concentration, the general distribution of these metals into five physico- chemical phases such as aqueous, exchangeable, bound to inorganic, bound to organic matter, and residual was explored using modified sequential chemical extraction scheme. The results showed higher vulnerability and bioavailability of Ni with non-lithogenous source. This was due to its higher percentage in the most mobile fraction. A significant amount of Cd, Cu, Mn and Fe in lithogenous fraction could be attributed to formation of stable complexes with Fe and Mn oxides. Considerable amount of Ni, Pb and Fe existed in the organic fraction due to their preference to the organic matters which often can form complex with humic substances. Principal Component Analysis (PCA) result reveals high concentration of Cd and Pb in study sites such as Odo-Owa-2, Ijero/Ipoti, Odo-Owa-5, Erigbe, Oke-Asa-1 and Arapate) which could be contributed by anthropogenic sources. This result pattern is consistent with clustering groups, which could provide more information about contributing sources. This study therefore suggests heavy metal contamination could be linked to the socio-economic activities.