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本研究于湘江共采集了29个典型重金属污染断面底泥样品,测定了底泥中重金属Cd、Pb、Cr、Cu、Mn和Zn的含量及其有效态含量,并采用改进潜在生态风险指数法评价了底泥重金属的潜在生态风险.研究结果表明,湘江底泥存在主要由重金属Cd、Pb、Cr、Cu、Mn和Zn构成的复合污染,其含量范围依次为2.83—29.15 mg·kg-1、8—1784 mg·kg-1、10. 00—4884. 28 mg·kg-1、9—674 mg·kg-1、744. 83—16246. 22 mg·kg-1和61.50—3771.11 mg·kg-1;参考土壤环境质量Ⅲ级标准的断面超标率依次为100%、10. 34%、6. 90%、3. 54%、100%和24.14%;有效态百分含量范围依次为25. 04%—66. 63%、8.75%—50. 00%、1. 14%—35. 08%、3. 70%—39.00%、1.99%—65.79%和7.48%—47.96%;生态风险评价结果表明, Cd的潜在生态风险最高,其次是Pb和Mn,潜在生态风险指数贡献率(MRI)依次为90.37%、4.17%、3.03%,干流的潜在生态风险高于支流的生态风险,达到极强危害水平的采样断面占72.41%,主要集中于永州、衡阳、株洲、湘潭、长沙和郴州.

This study investigated the pollution characteristics and ecological risk of heavy metals in the sediments from the Xiangjiang River. Twenty nine sediment samples were collected from the typical monitoring sections of the Xiangjiang River. The contents and bioavailability of six heavy metals ( Cd、Pb、Cr、Cu、Mn、Zn) in these sediment samples were analyzed. And the ecological risk of the heavy metals was further assessed by the modified potential ecological risk index ( MRI) method. Results showed that heavy metal combined pollution existed in the sediments of the Xiangjiang River, in which the content of Cd、Pb、Cr、Cu、Mn and Zn were 2. 83—29. 15 mg·kg-1, 8—1784 mg·kg-1 , 10.00—4884.28 mg·kg-1 , 9—674 mg·kg-1 , 744.83—16246.22 mg·kg-1 , 61.50—3771. 11 mg·kg-1, respectively. According to the environmental quality standards for soils, approximately 100%, 10. 34%, 6. 90%, 3. 54%, 100%, and 24. 14% of the heavy metal concentrations in sediment samples exceed the third grade standard for Cd, for Pb, Cr, Cu, Mn,and Zn, respectively. The corresponding range of bioavailability fractions were 25. 04%—66.63%, 8.75%—50. 00%, 1. 14%—35. 08%, 3. 70%—39. 00%, 1. 99%—65. 79%, 7. 48%—47.96%, respectively. The results of ecological risk assessment indicated that the ecological risk was dominantly caused by Cd with the contribution to MRI counting for 90.37%, followed by 4.17% for Pb and 3.03% for Mn. Meanwhile, compared with tributary, the ecological risk of sediments in main stream was more serious. About 72. 41% of sampling sections in main stream reached extremely strong risk level, and the high-risk sections were mainly located in Yongzhou, Zhuzhou, Xiangtan, Changsha and Chenzhou district.