Study On The Migration And Transformation Mechanism Of Typical Heavy Metals In Sediment-Water Interface Process Of Baiyangdian Lake

The pollution of heavy metals in the water environment is one of the major problems,which was faced in the world.Baiyangdian Lake is the largest freshwater lake(or wetland)in northern China,one of the amounts of lakes in China.The environmental issues of which were received widespread attention with the construction of the Xiong'an New Area.The purpose of this study is to comprehensively and systematically understand the characteristics and source of typical heavy metals(As,Cd,Cr,Cu,Pb,Ni,Sb and Zn)in Baiyangdian Lake.And then,discuss and make sure the influencing factors,migration and release mechanism of the heavy metals in the sediments using the in-situ analysis technology.Meanwhile,the oxidation and migration mechanism of antimony in sediment-water interface was also analyzed in this study.According to the results of this study,the main conclusions are as follows:(1)The pollution characteristics of heavy metals in Baiyangdian LakeThe concentrations of the selected heavy metals in the water of Baiyangdian Lake were in the middle or low abundance level,meanwhile,the water quality of which is“excellent”according to the result of water quality index(WQI).The local residents should not suffer non-carcinogenic risk based on the result of health risk assessment.The heavy metal concentrations in the surface sediment of Baiyangdian Lake were similar to the local soil background value,except for cadmium(Cd).According to the results of geological accumulation index(I_geo)and potential ecological risk(RI),there were somewhat pollution risk of Cd in the sediments of Baiyangdian Lake,and the pollution risk in the north of which were higher than that in the south.The lead(Pb)isotope ratio analysis shows that the anthropogenic pollution source of heavy metals in Baiyangdian sediments were from coal burning,and atmospheric deposition was considered to be the main transmission route.Meanwhile,the local residents will not cause adverse health risks due to the consumption of fish in the lake during the sediment resuspend.(2)The migration and release characteristics of effective heavy metals in the sediment of Baiyangdian LakeThe ex-situ sequential extraction(the Community Bureau of Reference,BCR)analysis results showed that Cd,Pb and As in the surface sediment mainly existed in non-residue fraction;and Cu,Zn,Ni,Sb and Cr were mainly in residue fraction.The release risk of Cd,Pb and As in northern sediment were higher than that in southern sediment based on the results of risk assessment code(RAC)and bioavailable metal index(BMI).However,the in situ diffusive gradients in thin-films(DGT)analysis shows that different metal elements show different migration directions at different sampling sites,and there is no obvious regional difference.(3)Diffusion characteristics and migration factors of the effective heavy metals across sediment-water interfaceThe results showed that the average diffusive fluxes of Cu,Ni,Pb and Zn in the entire Baiyangdian sediment were:-1.78,0.09,18.25 and 0.55 pg·cm^-2·s^-1.The migration and release of Cu,Ni,Pb,and Zn were mainly related to the co-release of sulfides.Furthermore,a further analysis results found that the diffusive fluxes of As,Cd and Cr were-3.19,0.002 and-1.48 pg·cm^-2·s^-1 at the northern sediment.The migration and release of As,Cd and Cr were mainly related to changes of Fe/Mn(hydrogen)oxides.(4)The oxidation and migration mechanism of Sb across the sediment-water interfaceThe experiment of mechanism showed that the oxidative migration process of Sb(III)at the sediment-water interface is mainly completed by abiotic pathway.At first,Sb(III)was adsorbed when it entered the sediment-water interface,and then oxidized and released to the upper water.During the oxidation process,the transformation mechanism of Sb(III)oxidation was divided into two stages.The first stage was that the dissolved Mn is oxidized into heterogeneous Mn^III,IV(hydrogen)oxide by self-catalysis which caused the oxidation of Sb(III);the other was that the Sb(III)could form complex ligands with Fe(III)in the solution under(weak)alkaline conditions,and Sb(III)was oxidized by the process of ligand to metal charge transfer(LMCT).In this study,the migration characteristics and their potential influence factor of effective heavy metals was proved in the sediment of Baiyangdian Lake with the in-situ DGT analysis technology.Meanwhile,it also provided a new perspective for the research of heavy metals in Baiyangdian Lake.Furthermore,this study has effectively promoted antimony geochemical cognition in natural shallow lakes.