Concentrations and contamination trends of heavy metals in the sediment cores of Taihu Lake,East China,and their relationship with historical eutrophication

To assess the contamination trends and potential bio-availability of sediment-bound heavy metals,concentrations of heavy metals in acid-leaching fraction and in bulk sediments from the two typical bays(the Meiliang Bay and Xuhu Bay) of the Taihu Lake,East China,were studied.Pb and Zn showed elevated concentrations in the sediments from both areas,although sedimentation history and degree of pollution are different between the two bays.In the Meiliang Bay,both Pb and Zn pollutions started in the late 1970's,the same time as the beginning of eutrophication of the lake,while the in the Xuhu Bay the metal contamination started since recent 10 years.The concentrations of acid-leachable Pb in the sediments from the Meiliang Bay are correlated with the historical eutrophication process.Before the eutrophication and heavy metal pollution,the chemical properties of the lake sediments were the same as the source compositions of the Xiashu loess.Both Pb and Zn in the sediments mainly occur in leachable forms by nitric or hydrochloric acid,whilst most of Cu is in residual fraction.The results indicate that both Pb and Zn may have higher mobility and bioavailability in water and biology than Cu.