The Characteristics of Pollution and Ecological Risk Assessment of Heavy Metals in Sediments of Taihu Lake

Abstract: The studies of concentration and modality(status) of the heavy metals in sediments from Taihu Lake provide insights into the actuality and development trends of heavy metal pollution in sediments in Taihu Lake. It provides basis for the treatments of the heavy metal pollution in sediments from Taihu Lake and references for the research and treatment of heavy metal pollution of grassland.In this paper, the surficial sediments in Taihu Lake was selected as research object and typical ares was choosed such as the seriously polluted coastal zones, river estuary, central area of the lake, etc, and 40 research points was set. By using columnar dredge device for sampling, the research was turned to the total quantity and status of Hg, As, Pb, Cu, Cr, Cd, Ni,and Zn, and a evaluation was made for the status of heavy metal pollution in Taihu Lake. The results are as follows:1. ICP-MS which was based on this study for the total quantity and configuration of heavy metal can basically content the needs of accuracy and precision that experimental analysis and determination require. The sediment samples was pretreated by using HNO3 digestion system, and soil and sediment standard reference materials (GSBZ50012-88 and GBW-07307) was used as control samples. The recovery rate of sediment reference materials was between 85% to 115% and the relative standard deviation (RSD) was less than 5%, which indicated that the method could totally content the need of the total quantity determination of heavy metals in sediments.2. Cr, Cd, Ni, Cu, Pb, Zn, Hg and As in surficial sediments from Taihu Lake were all detected. The total quantity of heavy meatals in Zhushan Bay, Meiliang Bay and Gong Lake were higher than the average amount in Taihu Lake and the total quantity of Cr, Cu, Hg and Ni was 3-4 times more than the average of the whole lake. The speciations of the eight heavy metals were significantly different, Cr and Hg mainly presented in residual fraction, Ni, Zn, As and Cu in exchangeable and carbonate fractions, Cd in iron and manganese oxides and residual fraction, Pb in iron and manganese oxides, exchangeable and carbonate fractions. Generally speaking, Arsenic pollution in Taihu Lake was severe and only trivalent arsenic and pentavalent arsenic were detected in the surficial sediments from Taihu Lake, and less toxic pentavalent arsenic accounted for the main part. But the amounts of arsenite were significantly higher than the average level of the whole lake in the river estuary and the North Gong Lake, etc.3. The evaluation results of heavy metal pollution in surficial sediments from Taihu Lake by the two methods showed that Zhushan Bay, Meiliang Bay and Xu Lake in the nothern part of Taihu Lake and the western coast were severely polluted by heavy metals and the central areal was less polluted. The main heavy metals which endangered the ecological safety of Taihu Lake were As, Cr, and Hg, but Cu, Zn, Pb and Cd pollutions were relatively less. As the results evaluated in different methods of Ni were not consistent, further research should be conducted.
Key words: Taihu Lake; sediments; heavy metals; pollution characteristics; ecological risk assessment;

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