Characteristics and ecological risk assessment of heavy metals contamination in sediments of the Xiangjiang River

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.