Speciation and contamination assessment of metals in the sediments from the Lanzhou section of the Yellow River, China

Heavy metals such as Cu, Fe, Mn, Ni, Zn, Cd, Cr and Pb in surface sediments from the Lanzhou Section of the Yellow River were investigated to analyze chemical speciation by a sequential "extraction and to evaluate their pollution level. The metal contents in the sediments were found to be in the range of (mg/kg) Cu 15.52-57.50, Fe 19 600.33-48 350.00, Mn 493.50-698.93, Ni 9.34-53.20, Zn 64.86-168.57, Cd 1.09-4.25, Cr 70.00-139.33, Pb 5.66-19.13. The arrangement of metal contents from higher to lower was: Fe > Mn > Cr > Zn > Ni > Cu > Pb > Cd. Fe, Mn and Cu and could have the same source according to their correlations. The quantity of immobile speciation (residual) was observed to be higher when compared with mobile speciation (acid soluble, reducible, and oxidizable) of Fe, Cu, Cd and Cr. The highly enrichment factors of Ni and Cr created a high environmental risk. The order of contamination level for heavy metals in sediment was Cr > Cd > Pb > Cu > Mn > Ni > Fe > Zn on the basis of performance of the geoaccumulation index, enrichment factor and pollution load index.