长江水系表层沉积物重金属污染特征及生态风险性评价

对2007年采集的长江水系表层沉积物中的9种重金属(Cr、Co、Ni、Cu、Zn、Pb、Cd、As和Hg)含量进行了分析.结果表明,沉积物中除了重金属Cr、Co、Ni外,Cu、Zn、Pb、Cd、As和Hg的含量都明显高于20世纪90年代调查结果.主成分分析(PCA)结果表明,前3个主成分的累积贡献率达到86.75%,表明了重金属的3种主要来源,分别为采矿与工业排污、岩石的自然风化与侵蚀和城市电镀工业废水与自然源.地累积指数和富集因子评估结果同时显示,长江水系表层沉积物中未受Cr、Co和Ni的污染,Cu、Zn、As和Hg受轻度污染,而Cd和Pb的污染最大.Hakanson生态风险指数法对沉积物中重金属的生态风险评价表明,各重金属单因子生态危害程度为CdHgAsZnPbCuCoNiCr.综合潜在生态指数表明,在61个位点中,中等生态危害的样点占36%,有3个位点属于强生态危害范畴,即长江干流重庆段、支流资水洞庭湖入口和信江位点;而支流湘江衡阳段、湘江株洲段、湘江洞庭湖入口、洞庭湖和安徽顺安河位点为极强生态危害范畴.

Pollution Characteristics and Ecological Risk Assessment of Heavy Metals in the Surface Sediments of the Yangtze River

The concentrations of Cr, Co, Ni, Cu, Zn, Pb, Cd, As and Hg in surface sediment samples of Yangtze River collected in 2007 were analyzed and evaluated. The results indicated that the concentrations of Cu, Zn, Pb, Cd, As and Hg were significantly higher than those measured in 1990s.Principal Component Analysis showed that the cumulative proportion of the first three components accounted for 86.75% of the total variable, indicating the three major sources of heavy metals were industrial and mining wastewater, weathering and erosion of rocks, and urban electroplating industry wastewater and natural sources. Geoaccumulation index (I_geo) and enrichment factors (EF) also showed that the surface sediments of the Yangtze River were not contaminated with Cr, Co and Ni, lightly contaminated with Cu, Zn, As and Hg, and majorly contaminated with Pb and Cd. The ecological hazards for the heavy metals in the sediments were evaluated with the Hakanson ecological risk index. It was concluded the ecological hazards for each metal in a descending order were Cd>Hg>As>Zn>Pb>Cu>Co>Ni>Cr. The comprehensive index of potential ecological risks for metals indicated that 36% of the 61 sites had moderate potential ecological risks. Three sites had a high potential ecological risk, namely, Chongqing site of the main Yangtze River, Zishui Dongting Lake and Xinjiang site, whereas Xiangjiang Hengyang section, Xiangjiang Zhuzhou section, Xiangjiang Dongting Lake entrance, Dongting Lake and Shunan River belonged to the areas with extremely high potential ecological risk.