Chemical speciation of heavy metals in the Ase River sediment, Niger Delta, Nigeria

Abstract

The speciation patterns of heavy metals were assessed with a view to providing information on the bioavailability of metals in the sediment matrix. The results indicate that cadmium is speciated into residual and readily exchangeable forms, while copper speciated into organic bound, residual and Fe – Mn oxide fractions: lead into Fe – Mn oxide, organic and residual fractions; chromium into Fe – Mn oxide, organic and residual fractions; nickel into residual and organic bound fraction; zinc into residual Fe – Mn oxide and carbonate fractions; iron and manganese into Fe – Mn oxide, residual and easily exchangeable fractions. The speciation pattern gave a general picture that the majority of the metals exist either in the organic, or Fe – Mn oxide and residual fractions except for cadmium. It implies that metals that are predominantly in the Fe – Mn oxide and organic fractions can only be remobilised under conditions that change the redox potential of the sediment. There are significant spatial and temporal variations in the speciation patterns of heavy metals in river sediment.