Study On The Quality Benchmark And Ecological Risk Threshold Of Typical Heavy Metals In Baiyangdian Sediments

Based on the Baiyangdian Baseline Survey Project in Xiongan New Area,Baoding City,Hebei Province,this study investigated the status quo of heavy metals in sediments of different land types in Baiyangdian,carried out research on the quality benchmarks and ecological thresholds of heavy metals in typical sediments of Baiyangdian,and conducted in-depth research on the impact of heavy metals in sediments on heavy metals.The potential risks and toxic effects of the water environment and aquatic organisms are expected to provide a scientific basic theoretical basis for the management and restoration of the benthic ecological environment of Baiyang Lake.This study selects different types of sediments in Baiyangdian as the research object,evaluates the content and morphological distribution characteristics of different heavy metals in Baiyangdian sediments,uses the phase equilibrium distribution method to deduce the typical quality standards of Baiyangdian sediments,and determines the Baiyangdian sediments while verifying the quality standards ecological risk threshold.（1）Four types of water bodies in Baiyangdian Lake,including water channels,trenches,lake surfaces and fish ponds were selected,and the morphological characteristics of Cd,Cr,Cu,Ni,Pb and Zn in sediments were analyzed by the improved BCR（European Communities Bureau of Reference）extraction method.The content of heavy metals in Baiyangdian sediments was systematically assessed for pollution and ecological risk by using potential ecological risk index,secondary phase and primary phase（RSP）and risk assessment code（RAC）.The results showed that:（1）The average contents of heavy metals Cd,Cu and Zn in the sediment were 0.37,28.49 and 83.08 mg/kg,respectively,and 94.91%,73.91% and 46.39% of the points exceeded the soil background value,respectively.（2）Cd is mainly in the non-residue state（F1+F2+F3）,with a mass fraction ranging from 54% to 97%,and Cr is mainly in a residual state（F4）,with a mass fraction of 87% to 99%.Cu,Ni,Pb and Zn mainly exist in the residual state,but in the non-residual state,Cu and Ni are mainly in the oxidizable state（F3）,and Pb and Zn are mainly in the reducible state（F2）.（3）Based on the RAC evaluation results: Cd has risks in 68.97%,39.89%,54.84% and 49.78%of points in waterways,trenches,open lakes and fish ponds,respectively,while the risks of heavy metals such as Cu,Ni and Pb are low.In general,the overall level of heavy metal pollution in Baiyangdian is low,but there are ecological risks and high biological mobility of Cd in some waterway areas such as Fuhe River and Baigouyin River estuary in Nanliuzhuang area.（2）In this study,the film diffusion gradient（DGT）technique was used to determine the bioavailable effective concentrations of heavy metals Cd,Cr,Cu,Ni,Pb and Zn in the pore water of Baiyangdian sediments.CDGT was lower than the centrifugation method.The recharge rate of the six heavy metals was in the order of Zn > Cd > Cu > Cr > Pb > Ni.The recharge rates of six heavy metals in baiyangdian sediments were all in a state of partial buffering.The diffusion flux of the six heavy metals is in the order of Zn > Pb > Cu > Ni > Cr > Cd.The release flux of Zn from solid phase to liquid phase is the highest,and Cd is easier to release from solid phase to liquid phase in the surface of sediment,which has potential harm to aquatic ecological environment.（3）Simultaneous extraction of five heavy metals in Baiyangdian surface sediments The contents of heavy metals（SEM）from high to low are arranged as follows: Zn>Pb>Cu>Ni>Cd.There was a high correlation between acid volatile sulfide（AVS）and SEM in sediments,indicating that AVS played a certain role in controlling the release of heavy metals.Generally speaking,the toxicity of heavy metals in Baiyangdian sediments to benthic organisms is low.（4）The mass reference values of heavy metals Cd,Cu,Pb and Zn in Baiyangdian sediments were preliminarily estimated to be 9.01,121.56,212.58 and182.78 mg/kg,respectively.Comparing the SQC value with the total amount of heavy metals in the sediment,it was found that the contents of the four heavy metals did not exceed the reference value,which may have less risk to the environment.Comparing the results of this study with the domestic and foreign watershed benchmark values,it is close to the SQC value established in some watersheds,which is more reasonable.（5）Toxic spiking experiments were carried out using A.dorsalis as the tested benthic organisms,and the concentrations of heavy metals in the sediments were set to different concentration gradients.The spiking concentrations were 1,5,10,15 and20 mg/ kg,the deduced quality benchmark was verified by 4 indicators of mussel survival rate,heavy metal content in the body,superoxide dismutase and carboxylesterase.)value basically conforms to the meaning it represents.At the same time,the ecological threshold of heavy metal Cd in Baiyangdian sediments is obtained through data analysis,that is,between 10 and 15 mg/kg,there may be ecological toxicity risks,and if it is greater than 20 mg/kg,it must be Toxic effects on the environment.