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Characteristics and Potential Ecological Risk Assessment of Heavy Metal Pollution in the Sediments of Middle Reaches of Xiangjiang River

LIU Jun;ZHU Yun-hua;HU Jing-song;PENG Guo-wen;XIE Hong-yan;LI Zhi-liang;PENG Cui-ying;College of Pharmacy and Life Science,University of South China;College of Chemistry and Chemical Engineering,University of South China;  
In order to study characteristics and ecological risk of heavy metal pollution in the sediments of the middle reaches of Xiangjiang River,18 sediment samples were collected from 6 cross-sections of the Zhuzhou and Hengyang Sections of the river(3 samples per cross section) during the dry season for analysis of heavy metals and their total contents,chemical forms and bioavailabilities.Heavy metals pollution was analyzed by degree and graded with the geoaccumulation index method and single-factor index method,and effect of governance of the Xiangjiang River was evaluated.Results show as follows:(1) The contents of four typical heavy metals(Cd,Pb,Zn and Cu) were much higher than their respective background values in the soil of Hunan Province,being 83.1-1 178.7,4.46-15.9,2.88-16.1 and 3.35-6.22 times as high,respectively.On the whole,contents of the heavy metals rose gradually from the upper reaches to lower reaches;(2) Of the heavy metals in the sediment samples,the fraction of exchangeable form was rather low in proportion and the fraction of amorphous Fe-Mn oxides was in dominance,posing a high risk of secondary pollution;(3) The heavy metals in the sediments differed sharply in bioavailability.In the cross-sections at Xiawan Town and Songbai Town,the element the highest in bioavailability was Cu and in the other cross-sections,it was Cd;(4) According to Grade II criteria ofthe China Environmental Quality Standard for Soils(GB 15618-1995),Cd,Pb,Zn and Cu all exceeded the threshold values,with Cd in particular,which reached the severe-extremely severe level;and(5) After years of comprehensive pollution control,heavy metal pollution in the sediment of the river has been lowered by a certain degree and hence their ecological risks.
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