Characterization of Heavy Metal Contamination from their Spatial Distributions in Sediment of an Urban Lake of Hanoi, Vietnam

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Ho Tay (West Lake) in Hanoi, Vietnam receives wastewater from the city center and the surrounding residential areas, which can cause both eutrophication and enrichment of toxic heavy metals in the lake ecosystem. The aim of this study is to evaluate the recent trends of metal contamination in this lake from their spatial (horizontal and vertical) distributions in the lake sediments. Sediment cores with up to 70 cm in depth were sampled from four locations in the lake and analyzed for heavy metals (Cd, Cr, Cu, Mn, Ni, Pb and Zn) including a metalloid (As) and total organic carbon (TOC). High concentrations of the metals (except for Mn) and TOC have accumulated in sediment at the site where an inlet of sewage from the city center was located nearby. Increasing trends of the metal contents in the sediment profile toward the surface at the sites distant from the sewage inlets imply that the loads of these metals into this lake have been continuously increasing. In addition, Pb isotopic ratios in sediment profile could be used as an indicator of anthropogenic Pb pollution in the lake.