The Characteristics Research Of Heavy Metals Pollution In Sediments Of The Xiangjiang River

The Xiangjiang River, which is one of the seven major tributaries of Yangtze River, and which is the largest water system of Dongting Lake, acting as the major drinking water source and water body of containing pollutants in Hunan Province, the water quality has a great effect on Hunan’s economic and social development. The Xiangjiang River once was the most contaminated river by heavy metals in China. After treating the heavy metals pollution for many years, the water quality of the Xiangjiang River has been improved obviously. The heavy metals in water usually deposit in the sediment, which act as the "source and sink" of metals, threatening the safety of water body. Although many studies about heavy metal pollutions in the Xiangjiang River have been conducted, there were lacking a comprehensive and in-depth study about the pollution characteristic of heavy metals in the sediment. According to the need of the Water Project of the 12th Five-Year Plan, studying the pollution characteristic of heavy metals in sediments was meaningful to build the management system of the prevention of heavy metal pollution.Sediments of 29 typical sections with heavy metals pollution in the Xiangjiang River were collected, and the speciations of Cr, Mn, Cu, As, Zn, Cd, Pb and Hg were extracted by the Tessier’s sequential extraction procedure. Then, the total contents and speciations contents of the metals in sediments were analyzed by the methods of atomic absorption spectrophotometry and atomic fluorescence spectrometric. Eventually, the pollution levels and ecological risks of heavy metals in sediments were assessed by the methods of Index of Geoaccumulation and Index of Potential ecological risk.The research results of total contents characterics of heavy metals showed that the total contents of heavy metals were 240.97 mg·kg-1 for Cr、3472.90 mg·kg-1 for Mn、72 mg·kg-1 for Cu、68.31 mg·kg-1 for As、600.22 mg·kg-1 for Zn、13.29 mg·kg-1 for Cd、213 mg·kg-1 for Pb and 0.667 mg·kg-1 for Hg, respectively. Comparing with the Environmental Quality Standards for Soils of China, there were combined heavy metals pollution that mainly consist of Cd, Mn, As, Zn and Hg in sediments, and the exceeding times of Cd, Mn, As, Zn and Hg were 44.29,3.88,2.73,2.40,1.33, respectively. And the exceeding rate of Cd, Mn, As, Zn and Hg were 100%,96.55%, 55.2%,27.9%,41.3%. The seceitons with higher levels of metals pollution were mainly concentrated on regions of Chenzhou, Loudi, Hengyang and Zhuzhou.The research results of speciations characterics of heavy metals pollution showed that pollutions of Cd, Pb, Cr, As in sediments were influenced by Bound to Iron and Manganese Oxides (T3) fractions, and that of Cu, Zn, Mn, Hg were influenced by Bound to Organic Matter (T4) and Residual (T5) fractions, and the metal pollution with the strongest bio-availability was Cd. then are Zn, Pb, Mn, Hg, Cu, As and Cr, with the contents rage of available are 66.93%,33.80%,30.81%,18.38%,17.58%, 10.20%,9.81% and 7.65%.The assessment results of ecological risks ofheavy metals showed that Cd and Hg were the very factors that caused highest ecological risk in all selected sections of the Xiangjiang River, contributing to the index of potential ecological risk with 74.05% and 21.82%, respectively. And that of Mn, Cr, Cu, As, Zn and Pb were mainly focused on tributaries. The sections with very high ecological risks were ZZ-3, XT-3, XT-4, CZ-1, CZ-2, CZ-3, LD-2 and LD-3.