三峡水库蓄水期长江口多氯联苯的污染特征

为揭示三峡水库蓄水期长江口多氯联苯的污染水平与空间分布特征,于2010年11月份采集长江口河道及邻近海域24个采样点表层沉积物和一个沉积物柱芯,对其中多氯联苯(PCBs)进行测定,结果表明本区PCBs污染处于较低水平,潜在生态风险较小.由于11月份处于枯季前期以及三峡水库蓄水期,外源PCBs输入变化以及三峡水库蓄水使得上游来沙减少,导致11月长江口PCBs含量较洪、枯季典型时段低.由于受海水倒灌和颗粒物盐析的共同作用,长江口北支的PCBs污染重于南支.在口外海域,受河口过滤器效应的影响,PCBs被潮流拦截在20m等深线区域.沉积物PCBs含量与沉积物TOC、粒径均无明显相关性.表层沉积物中PCBs组成以低氯取代PCBs为主.柱芯沉积物中PCBs组成与含量有明显分段特征.主成分分析发现南北支来源差异明显,较深柱芯与较浅柱芯差异明显.

Pollution levels and spatial distributions of polychlorinated biphenyls in sediments of Yangtze Estuary during water impoundment of Three Gorges Reservoir

The surface sediment and core sediment samples taken from the Yangtze Estuary during the water impoundment of the Three Gorges Reservoir were analyzed to reveal the pollution levels and spatial distributions of polychlorinated biphenyls (PCBs). The PCB levels of the Yangtze Estuary were relatively low compared to other industrial/urban coastal environments worldwide. Generally, the samples taken in November were less polluted by PCBs than those taken in August and February because of the changes of PCB input and the water impoundment of the Three Gorges Reservoir. Samples collected in the north branch showed higher PCB concentrations. In the adjacent sea area, PCB values along the –20m isobath were higher than those along the –10m isobath due to the “marginal filter” phenomenon formed by different water currents. The effects of the physicochemical characteristics (TOC and grain size) of surface sediments on the distributions of PCBs were also investigated. Masked by various other factors, the TOC contents and sediment grain sizes did not exhibit a strong influence on the distributions of PCBs. Analysis of the PCB congener distribution patterns revealed the predominant proportion of light PCBs with 2~3chlorines. According to the principal component analysis (PCA) of source contributions, the PCB sources of the north and south branch were quite different, and the PCB sources have changed from the past.