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Rare Earth Elements Geochemistry and Provenance Discrimination of Sediments in Tolo Harbour, Hong Kong

Rare earth elements (REE) concentrations have been analyzed in 13 sediment samples from Tolo Harbour. The highest concentrations of ∑REE, ∑LREE (light rare earth elements) and ∑HREE (heavy rare earth elements) are all at site G as the enrichment of Mn–Fe oxyhydroxides and the highest pH of site G relative to its nearby areas. The relatively higher ∑LREE/∑HREE ratio at site G is probably due to the stronger REE fractionation. During the fractionation process, LREE are preferentially scavenged on particle surfaces such as Mn–Fe oxyhydroxides and clay minerals. Concentrations of ∑REE, ∑LREE and ∑HREE at sites Y and Z are much lower than those at other sites as calcareous biological debris dilute the REE abundances of the sediments in Tolo Harbour. REE are released from sediments into waters due to the high salinity in Tolo Harbour and REE fractionation occurs in this release process. The provenance of sediments in Tolo Harbour is terrigenous and the North American shale composite (NASC)-normalized REE patterns of the 13 samples in Tolo Harbour all display strongly negative Eu anomalies. ∑REE is poorly correlated with Zr and Hf, which suggests that Tolo Harbour is heavily polluted by human activities.