[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 (Igeo) 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 Ph 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.