| In this study,the method of extracting and adsorbing heavy metal forms in sediments combined with particle size separation was used to explore the release mechanism of heavy metals with different particle size particles under suspension disturbance.According to DGT desorption experiments,the release risk of different forms of heavy metals was verified,which provided a basis for further evaluation of the ecological risk of sediments in Chaohu Lake.This study is located in Chaohu,a shallow lake,with 5 sampling points in East Chaohu,Zhongchaohu,and West Chaohu Lake.The surface sediments of Chaohu Lake are used as the research object.The collected surface sediments are wet-settling according to the Stokes sedimentation formula to facilitate To separate the required particle size components(<1 μm,1-2.5 μm,2.5-5 μm,5-10 μm,10-30 μm).Then the Tessier method was used to analyze the morphology of the five groups of particle size particles and raw mud,and the physical and chemical properties of each particle size were determined(organic matter,free iron and alμminμm,amorphous iron and alμminμm).Secondly,the adsorption characteristics of typical metals Cu and Pb by particles of various sizes were studied,and the behavior of plant roots to absorb heavy metals from sediments was simulated by DGT.Finally,various common ecological risk assessment methods are used to evaluate the potential ecological risks of each group of particulate matter.The relevant research results are as follows:(1)The physical and chemical index concentrations of particles with different particle sizes at the 5 sampling points all increase with the decrease of particle size.The variation range of organic matter with particle size is 0.50%～3.96%,and the amorphous iron oxide is 7.10～34.65 g/kg,free iron oxide is 50.39～134.36 g/kg,amorphous alμmina is 0.675～6.79 g/kg,and free alμmina is 2.01～11.95 g/kg.(2)The concentration of the metal on the particles of different sizes increases with the decrease of the particle size.The concentration of As on the particles of different sizes ranges from 14.15 to 51.51 mg/kg,and the concentration range of Cd is 0.130～0.830 mg/kg,the concentration range of Cr is 59.70～212.0 mg/kg,the concentration range of Cu is 11.57～58.02 mg/kg,the concentration range of Ni is 16.31～75.27 mg/kg,and the concentration range of Pb is 19.63～82.18 mg/kg,the concentration range of Zn is 54.78～426.8 mg/kg.The effective state concentration of several heavy metals such as Cu,Ni,Pb,Zn,etc.,accounts for 30%to 60%of the total concentration.The risk is relatively high,and the combined state of iron and manganese oxide and the combined state of organic matter are dominant.The effective state concentration of Cd accounts for more than 90%of the total concentration.Among the effective states,the first ion exchange state is the dominant state,accounting for about 70%.In addition,the residual state of Cr and As has a larger proportion,accounting for approximately 90%of the total concentration.(3)In this study,quasi-second-order kinetics and Freundlich model had better fitting effect on Cu and Pb.The adsorption capacity of the original mud of each sampling point on Cu and Pb was 5#>1#>3#.The adsorption capacity of Cu and Pb ranged from 4616.7 to 5611.4 mg/kg and 15102.6 to 16684.1 mg/kg,respectively.The adsorption capacity of Cu and Pb by particles with different particle sizes at each sampling point is the smaller the particle size is,the larger the adsorption capacity is.The adsorption capacity of Cu with different particle sizes ranged from 3,170.6 to 8,494.2 mg/kg,and that of Pb ranged from 11,811.7 to 19489.3 mg/kg.(4)The results of ecological risk assessment showed that the smaller the particle size was,the greater the ecological risk was,which was<1 μm The ecological risk of particle size is 3～8 times that of coarse particle size 10～30 m.The results show that Cu has a relatively small release risk,while Cd and Fe have a relatively large release risk. |
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