Study On The Bioavailability Of Heavy Metals In The Sediments Of The Tributary Fluctuation Zone Of The Three Gorges

The Three Gorges Reservoir Area,as a key area of national water environmental protection,has important strategic significance for China’s freshwater storage.Its water quality directly affects social and economic development.Must fully grasp the current status of heavy metal pollution in the reservoir area,take effective measures to control and prevent heavy metal pollution.The object of this study is the Yulin River,a main tributary of the Three Gorges Reservoir Area.With the characteristics of alternating wet and dry in the fading area of the reservoir area,the diffusive gradients in thin-films technique（DGT）was used to detect the effective states of Pb and Zn in the sediment of the fading area.Combined with aerobic and anaerobic conversion experiments to explore the bioavailability changes of sediment Pb and Zn,and finally,according to the plant indicator method,the bioavailability test of the plant indicator heavy metal is carried out in the form of adding heavy metals exogenously,so as to obtain the best method for evaluating the bioavailability of the heavy metal in the soil.The research results and conclusions include the following aspects:（1）Evaluate the bioavailability of heavy metals in the sediments of five sampling sites of Yulin River by DGT technology.It was found that the ecological environment of Yulin River was good,and the risk of heavy metal pollution was lower.It was detected that the bioavailability of Pb and Zn in sediment is at a low level.Among them,the range of C_DGT-Pb is 0.0015～0.009μg/L,the range of C_DGT-Zn is 0.097～0.15μg/L,the effective state content of Pb is much lower than that of Zn.（2）The bioavailability of heavy metals in sediments varies from place to place and time to time.In terms of location,C_DGT-Pb is significantly higher in the upstream of Yulin River than downstream,indicating that the upstream may be subject to greater threats of Pb pollution.As for trace metal Zn,the C_DGT-Zn in the upstream of Yulin River is lower than that in the downstream,which may be due to the influence of external Zn pollution in the downstream of the river.In terms of time,the bioavailability of Pb and Zn is low from February to March,and the bioavailability is high from May to June,indicating that its bioavailability is suppressed in winter,but remains relatively active in summer.（3）The aerobic and anaerobic conversion experiments found that changes in redox conditions is an important cause of changes in the bioavailability of heavy metals.According to the correlation analysis,C_DGT-Pb,C_DGT-Zn and C_DGT-Fe and C_DGT-Mn detected in the sediments were significantly positively correlated.The presence of Fe-Mn oxides will affect the bioavailability of Pb and Zn.Under the oxidation conditions,the formed Fe-Mn oxide adsorbs and fixes Pb and Zn,reducing the effective state content of Pb and Zn,and under anaerobic conditions,Fe-Mn oxide can be reduced,and the fixed Pb and Zn can be released,improving the effectiveness of Pb and Zn State content,so the effective states of Pb,Zn,Fe,Mn showed the same trend during the test.（4）The Pb content in the soil has a great influence on the Chinese cabbage.In the pot experiment of Chinese cabbage,it was found that when the concentration of exogenous Pb was less than 100mg/kg,the fresh weight of Chinese cabbage was hardly affected.Correlation analysis showed that the concentration of exogenous Pb had a significant correlation with the fresh weight of Chinese cabbage.In addition,the increase in the concentration of exogenous Pb will also increase the concentration of Pb in pakchoi.Correlation analysis shows that the concentration of exogenous Pb and Pb in pakchoi have a significant correlation.（5）Compared with traditional methods,DGT method is more effective in detecting the bioavailability of heavy metals.Using DGT and traditional methods to detect soil Pb content,and correlation analysis with Pb content of pakchoi,it was found that the correlation coefficient from high to low is DGT method>Soil Solution method>EDTA method>Ca Cl₂ method>Total Heavy Metals method,showing that the DGT method can be widely used as an effective method.