赤水河流域表层沉积物重金属的污染特征及生态风险评价

赤水河是长江水系唯一一条主河道没有筑坝的一级支流,对长江流域珍稀鱼类繁殖具有重要的生态意义.为了解赤水河流域沉积物中重金属的污染特征,采集32个样品,并对7种重金属(Cu、Zn、Cd、Mn、Ni、Hg、As)含量分别进行测定.结果表明,赤水河沉积物中7种重金属含量全部高于赤水河沉积物背景值,但与我国其他河流相比,赤水河重金属含量较低,污染较少.地累积指数评估结果表明,7种重金属的平均Igeo值由高到低依次为CdMnNiAsCuZnHg,其中90.62%的采样点存在不同程度的Cd污染.污染负荷指数计算表明,上、中、下游的污染负荷指数分别为1.49、1.14、1.03,均属中等污染.Hakanson潜在生态风险指数法评价结果表明,各重金属单因子生态危害程度由强至弱依次为CdHgAsNiCuMnZn,各采样点7种重金属的潜在生态风险指数(RI)介于32.34~930.07之间,总体潜在生态风险较低.

Pollution characteristics and ecological risk assessment of heavy metals in the sediments of Chishui River

As a natural protection area of great significance for rare fish breeding, Chishui river is the only tributary of Yangtze River without dam. In order to understand the pollution signatures and the potential ecological risks of Chishui River, the concentrations of 7 heavy metals (Cu, Zn, Cd, Mn, Ni, Hg and As) in 32 sediment samples were analyzed. The results indicated that the concentrations were higher than background values while lower than those of other rivers in China. The heavy metal contamination in sediments estimated by geo-accumulation index (I_geo) followed the order: Cd> Mn> Ni> As> Cu> Zn> Hg, and 90.62% of the samples revealed different Cd pollution levels. The pollution load indexes (PLI) of upstream, midstream, downstream and the whole basin were 1.49, 1.14, 1.03 and 1.18 respectively, which suggested moderate pollution. The E_rⁱ potential ecological risk was characterized by the order of Cd> Hg> As> Ni> Cu> Mn> Zn. The potential ecological risk indexs (RI) of heavy metals ranged between 32.34 and 930.07, which demonstrated that the whole basin was in low ecological risk.