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analysis identified the heavy metal accumulation layers of sediment profiles and showed the various sources of metals in the estuary. AbstractThe concentrations and chemical partitioning of heavy metals in the sediment cores of the Pearl River Estuary were studied. Based on Pearson correlation coefficients and principal component analysis results, Al was selected as the concentration normalizer for Pb, while Fe was used as the normalizing element for Co, Cu, Ni and Zn. In each profile, sections with metal concentrations exceeding the upper 95% prediction interval of the linear regression model were regarded as metal enrichment layers. The heavy metal accumulation mainly occurred at sites in the western shallow water areas and east channel, which reflected the hydraulic conditions and influence from riparian anthropogenic activities. Heavy metals in the enrichment sections were evaluated by a sequential extraction method for possible chemical forms in sediments. Since the residual, Fe/Mn oxides and organic/sulfide fractions were dominant geochemical phases in the enriched sections, the bioavailability of heavy metals in sediments was generally low. The 206 Pb/ 207 Pb ratios in the metal-enriched sediment sections also revealed the influence of anthropogenic sources. The spatial distribution of cumulative heavy metals in the sediments suggested that the Zn and Cu mainly originated from point sources, while the Pb probably came from non-point sources in the estuary. #

In the present study, surface sediments and sediment cores were collected at the Pearl River Estuary (PRE) and its surrounding coastal area. The samples were analysed for total metal concentrations, metal concentrations in the five operationally defined chemical fractions, and Pb isotopic compositions. The concentrations of Co, Cr, Pb, and Zn of the sediments in the PRE were about twice of those at the adjacent coastal area, while the Cu concentrations of the PRE sediments were four times higher than the sediments at the coastal area. The distribution of Cu, Cr, Pb, and Zn demonstrated a typical diffusion pattern from the land to the direction of the sea. Two hotspots of trace metal contamination were located at the mixed zone between freshwater and marine waters. The distribution of trace metals in sediments showed that the major sources of metal contaminants were probably from the discharges of sewage and other outlets in the west bank of the estuary. The enrichment of metal in the sediments could be attributed to the deposition of the dissolved and particulate trace metals in the water column at the estuarine area. The similar Pb isotopic signatures of the sediments at the PRE and its surrounding coastal area offered strong evidence that the This is the Pre-Published Version.

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The rapid economic development in the Pearl River Delta (PRD) region in south China in the last three decades has had a significant impact on the local environment.Estuarine sediment is a major sink for contaminants and nutrients in the surrounding ecosystem. The accumulation of trace metals in sediments may cause serious environmental problems in the aquatic system. Thirty sediment cores were collected in the Pearl River Estuary (PRE) in 2000 for a study on trace metal pollution in this region. Heavy metal concentrations and Pb isotopic compositions in the four 210 Pb-dated sediment cores were determined to assess the fluxes in metal deposits over the last one hundred years. The concentrations of Cu, Pb and Zn in the surface sediment layers were generally elevated when compared with the sub-surface layers. There has been a significant increase in inputs of Cu, Pb and Zn in the PRE since the 1970s. The results also showed that different sampling locations in the estuary received slightly different types of inputs. Pb isotopic composition data indicated that the increased Pb in the recent sediments was of anthropogenic origin. The * Corresponding author (X.D. Li), email: cexdli@polyu.edu.hk; fax: (852) 2334 6389; tel: (852) 2766 6041 This is the Pre-Published Version.2 results of trace metal influxes showed that about 30% of total Pb and 15% of total Zn in the sediments in the 1990s were from anthropogenic sources. The combination of trace metal analysis, Pb isotopic composition and 210 Pb dating in an estuary can provide vital information on the long-term accumulation of metals in sediments.

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