Chemical forms of Pb, Zn and Cu in the sediment profiles of the Pearl River Estuary

The chemical forms of heavy metals (Pb, Zn and Cu) in sediment cores of the Pearl River Estuary were studied using a sequential chemical extraction me thod. The isotope ratios of (206)pb/Pb-207 in various chemical fractions we re also measured to assess the potential Pb sources. Zinc and Cu were mainl y associated with the residual fraction, The Fe-Mn oxide and organic/sulphi de fractions were the next important phases for Zn and Cu, respectively. Fo r Pb, different chemical partitioning patterns were found among different s ediment cores. Most Ph was associated with the residual fraction in the sed iments. In some sediment profiles, the major phase of Pb in the top layers was the Fe-Mn oxide fraction. The proportion of Pb in the Fe-Mn oxide fract ion decreased significantly with increasing depth. Among the different dept hs, the (206)pb/(207)pb isotope ratios in the residual fraction remained fa irly stable, with a mean value of 1.202, which may represent the natural ba ckground value, The (206)pb/Pb-207 ratios in the exchangeable fraction were the lowest among the five fractions, particularly in top sediments, showin g the anthropogenic inputs of heavy metals from recent rapid industrial dev elopment in the surrounding region. For the other three non-residual fracti ons, there was a similar trend of increasing (206)pb/(207)pb ratios down th e profile. Results from this study are useful in assessing both the chemica l changes for heavy metals in marine sediments and the potential of heavy m etal release into the water environment of an estuary area. (C) 2001 Elsevi er Science Ltd. All rights reserved.