中文摘要：

分别采用Hakanson潜在生态风险指数法和效应区间低、中值法，分析了长江口南支表层沉积物5种重金属（Cu、Zn、Ph、Cd和Hg）的分布特征及生态风险。结果表明，南支表层沉积物中Cu的中值质量比已超过工业化前最高背景值（30mg·kg^-1），达到31．85mg·kg^-1，且Cu、Zn和Pb的中值质量比明显高于邻近区域同期调查数据；Hakanson潜在风险指数RI值范围为16．15～93．27，中值为58．56，生态风险评价属于低风险水平；除cu外，所有站位沉积物Zn、Ph、Cd和№的浓度均低于相应元素效应浓度低值（ERL），约有50％的站位沉积物中的cu会对生物产生毒性效应，不过其预期毒性概率仅为0．34，产生毒性效应的风险概率较低，毒性效应仅偶尔发生。

英文摘要：

Sediment samples were collected from south branch of Yangtze River estuary in May and October 2008, and their heavy metal concentrations were analyzed in order to study the distribution characteristic and ecological risk of heavy metals. The median concentration value of copper, zinc, lead, cadmium and mercury was 31.85 mg·kg^-1, 71.23 mg·kg^-1, 13.35 mg·kg^-1, 0.36 mg·kg^-1 , 0.073 mg·kg^-1 respectively. The contamination factor （Ci） of each element was calculated and the score of each site were used for MDS analysis. Results showed that copper has the highest Cfi score among the five elements, due to its larger median value if compared to the highest background value of Pre-industrial age （30 mg·kg^-1 ）. The sites with higher Cfi score were those near to Zuyuan waters, one of the ∑Cfisewage discharge outlet of shanghai city. We have also compared the score of south branch with Hangzhou Bay, out of the estuarine mouth and the Nature Reserve of Juvenile Chinese Sturgeon （ Acipenser sinensis）. South branch scored highest among four zones. In addition, the median value of copper, zinc and lead at south branch sites were significantly higher than the sites of other three zones. The ecological risks were assessed as well with Hakanson potential ecological hazard and mean effects range median quotient （ mERMq） method respectively. Hakanson method with RI grading value can be used to detect the integrated risk. The RI median value of Hakanson was 58.56 with the range of 16.15 -93.27 indicating that the integrated risk in south branch sediments was very low. The latter method with ERL and ERM grading value can be used to identify the element which is toxic to aquatic organisms. The mean effects range median quotient value of zinc, lead, cadmium and mercury were all smaller than ERL value except copper. However, the probability of copper to become hazardous for aquatic organisms was very. low because the highest probability recorded was only 0.34.