Speciation and Mobility of Selected Heavy Metals in Sediments of the Nun River System, Bayelsa State, Nigeria

The speciated fractions of some selected environmentally toxic heavy metals (Pb, Cu, Cr, Cd, Zn, Fe and Ni) were assessed in the bottom sediments of the Nun river system. The concentrations (mg/kg) of the selected heavy metals per fraction were analysed using the GBC AVANTA PM A6600 FAAS. Chemical speciation study applying the five-stage sequential extraction scheme revealed the prevalent fractions where the selected heavy metals were bound: Pb, Cu, Cr, Cd, Zn and Fe were prevalent in the residual fractions while Ni was mainly bound to the Fe-Mn oxide fraction. The mobility factor indices of the metals depicted the following trends: Pb>Cr>Zn>Cd>Ni>Cu>Fe and Pb>Cr>Cd>Ni>Zn>Fe>Cu for the samples and control points respectively. Mobility factor indices showed highest lability for Pb and Cr across the sample and control points, while the least lability and mobility was observed for Fe and Cu across all sampling points of the river. The sediments of the Nun river system revealed a high mobility and bioavailability for Pb and Cr. The two-way ANOVA statistical analysis of data showed significant variation (P<0.05) between metal fractions and the spatial distribution of sediment samples across the river system except for Pb which revealed the highest mobility and tendency for bioavailability.