Speciation of heavy metals in the surface sediments from northern Beibu Gulf

The four species of heavy metals (Cu, Zn, Pb, Cr, Cd) were analyzed using BCR (the Bureau Communautaire de Reference) sequential extraction method. Results showed that, about the contents the four species (exchangeable and carbonate state, Fe-Mn oxides state, organic and sulfide state and residual state) in surface sediment, the average contents of Cu were 0.94 mu g/g, 2.17 mu g/g, 1.18 mu g/g and 13.19 mu g/g, respectively, the average contents of Pb were1.51 mu g/g, 12.90 mu g/g, 4.51 mu g/g and 16.42 mu g/g, respectively; the average contents of Zn were 1.82 mu g/g, 13.00 mu g/g, 4.20 mu g/g and 48.97 mu g/g, respectively; the average contents of Cd were 0.010 mu g/g, 0.012 mu g/g, 0.005 mu g/g and 0.063 mu g/g, respectively; the average contents of Cr were 0.32 mu g/g, 2.98 mu g/g, 4.22 mu g/g and 13.19 mu g/g, respectively. The predominant species of Cu, Zn, Pb, Cr, Cd is residual state. The relative abundance in residual state for these elements followed the order: Cr>Cu>Zn>Cd>Pb. The pollution degree was assessed with ratio of secondary phase to primary phase. Results showed that the sediments in the northern Beibu Gulf were uncontaminated with Cu, Zn and Cr. 12 % of the sites was slightly polluted with Cd. 47 % of the sites were polluted with Pb.