The Status Assessment and Preliminary Risk Assessment of Total Mercury in Sediments from Middle and Lower Reaches of the Yarlung Zangbo River

摘要

The occurrence and accumulation of total mercury (T-Hg) in sediments collected from the Yarlung Zangbo River (YLZB),the Lhasa River,the Niyang River and the Palongzangbu River were analyzed and the soil samples simultaneously collected from the bank were employed as control.Meanwhile,pollution status and potential ecological risk of Hg were calculated and assessed using index of geoaccumulation ( I geo ) and potential ecological risk assessment method (Er) in this study.The results showed that the T-Hg concentrations in sediments at eight sections of YLZB ranged from 4.23 to 48.1 μg/kg with mean concentration of 25.1 μg/kg,which was higher than background Hg value of soils in Tibet.T-Hg concentrations in sediments at three typical segments of YLZB were all significantly higher than those in soils collected from its bank (P<0.05).The Igeo and E r indexes revealed that the T-Hg pollution levels were slight pollution in two sections and moderate ecological risk in six sections of YLZB.Hg pollution risks also existed in the sediments of partial sections of the Lhasa River and the Niyang River,and slightly moderate Hg contamination with high ecological risk was presented in Lhasa urban district.The level of Hg in sediments of YLZB showed a notable spatial distribution characteristic with a trend of increasing firstly and then declining.Human activities played an important role in increasing Hg content in sediments of the river.