Heavy metal pollution in tidal zones of Bohai Bay using the dated sediment cores

Three sediment cores were collected in November 2003 from Dagu estuary to Qikou estuary. The main polluted heavy metals in the sediment of tidal zones for the Bohai Bay have been found by analyzing the relationship among the conte nts of heavy metals, the contents of geochemical elements(Fe, Al and Mn) and the size of grain. The dominating contaminative elements in tidal sediments of Boha i Bay are Pb, Zn and Cd. Their contents are higher than the corresponding upper limit of environmental background values and they have very faint correlation wi th the corresponding contents of geochemical elements and the size of grain, ind icating the anthropogenic enrichment. Especially, the preliminary study on the p ollution sources and the history of heavy metals in the Dagu estuary has been do ne using the dated results. The contamination by Zn and Cd also started in the m iddle 1950s, while the contamination by Pb appeared in the early 1940s. The poll ution by Zn and Cd mainly originate from sewage discharge, while the pollution b y Pb has many sources, like atmosphere deposition and industrial discharge.