Distribution Characteristics And Risk Assessment Of Heavy Metals In Sediments Of Ningxia Section Of The Yellow River B

Ningxia is located in the upper reaches of the Yellow River.Due to social and economic activities,a large amount of domestic sewage,agricultural backwater,industrial wastewater,and backwater are discharged into the Yellow River without being fully treated,causing certain pollution to the water environment of the Yellow River.The pollutants deposited in the sediment still continue to cause internal pollution to the water body.Therefore,studying the pollution status of the Yellow River sediment has important practical significance for the protection of the Yellow River ecological environment.In order to investigate the distribution characteristics and pollution status of heavy metals in sediment of the Ningxia section of the Yellow River Basin,the content of five heavy metals,namely lead(Pb),mercury(Hg),arsenic(As),chromium(Cr),and cadmium(Cd),in 118 sample points of sediment in the Ningxia section of the Yellow River Basin were measured in April,July,and October 2021.Research was conducted on the level and distribution characteristics of heavy metal content in sediment;Applying three multivariate statistical methods,namely correlation analysis,principal component analysis,and systematic clustering,to conduct traceability analysis of heavy metals in the sediment of the Ningxia section of the Yellow River Basin,identifying key influencing factors and heavy metal risk areas that affect the spatial differentiation of heavy metals in the sediment;The application of pollution load method,land accumulation index method,and potential ecological risk index method to ecological risk assessment of heavy metals in sediment of the Ningxia section of the Yellow River Basin aims to provide a basis for the control of heavy metal pollution in sediment of the Ningxia section of the Yellow River Basin.The main research results are as follows:(1)In 2021,the content values of heavy metals in the sediment of five water bodies in the Ningxia section of the Yellow River Basin were basically consistent in April,July,and October,with the highest to lowest values being Pb>As>Cd>Cr>Hg.The average annual concentrations of Pb(19.889mg/kg),As(10.451mg/kg),and Cr(0.095mg/kg)were all lower than the soil background values(20.600mg/kg,12.2mg/kg,62.7mg/kg),while the average annual concentrations of Hg(0.070mg/kg)and Cd(0.21 1mg/kg)exceeded the soil background values(0.02mg/kg,0.1 10mg/kg);From the sampling month perspective,the heavy metal content of water sediment shows as follows:October>April>July.(2)Use multiple statistical methods(correlation analysis,principal component analysis,and systematic cluster analysis)to analyze the source of heavy metals in sediment from the Nigxia section of the Yellow River Basin The correlation analysis results indicate that except for Cd,the other four heavy metals in the sediment of the Ningxia section of the Yellow River Basin are more or less correlated,and the heavy metals with correlation may have the same source The results of principal component analysis indicate that in April 2021,a total of four principal components were extracted from the sediment of the Ningxia section of the Yellow River Basin,with the first principal component being Pb and Hg,with a contribution rate of 42.19%;As contributes 20.49%to the second principal component,Cr 19.26%to the third principal component,and Cd 13.48%to the fourth principal component;In July 2021,four principal components were extracted from the sediment of the Ningxia section of the Yellow River Basin.The first principal component was Pb and As,with a contribution rate of 45.11%.Cd contributed 21.23%to the second principal component,Cr contributed 17.60%to the third principal component,and Hg contributed 9.93%to the fourth principal component;In October 2021,four main components of heavy metals were extracted from the sediment of the Ningxia section of the Yellow River Basin.The first main component was Pb and As,with a contribution rate of 41.51%.Cd contributed 22.52%to the second main component,Hg contributed 17.28%to the third main component,and Cr contributed 11.54%to the fourth main component.The results of principal component analysis can display information on heavy metals in sediment from the Ningxia section of the Yellow River Basin in April,July,and October 2021 The results of systematic clustering analysis indicate that heavy metals in the sediment of the Ningxia section of the Yellow River Basin were clustered into four categories in April 2021:I(Pb,Hg),Ⅱ(As),Ⅲ(Cr),Ⅳ(Cd).In July 2021,they were clustered into four categories:I(Pb,As),Ⅱ(Hg),Ⅲ(Cr),Ⅳ(Cd).In August 2021,they were clustered into four categories:I(Pb,As),Ⅱ(Hg),Ⅲ(Cr),Ⅳ(Cd).Based on the above results,it can be seen that the results obtained by correlation analysis,principal component analysis,and systematic clustering analysis are basically consistent.Among them,Pb metal,As metal,and Cd metal have low coefficient of variation due to their lower content than the background value,which is believed to be mainly due to natural reasons;The content of Hg and Cd metals is higher than the soil background value,with a high coefficient of variation.It is believed that the source is relatively complex and may be caused by multiple reasons.(3)The pollution load index method,land accumulation index method,and potential ecological risk index method were used to evaluate five heavy metals in the sediment of the Ningxia section of the Yellow River Basin.The results obtained by the three evaluation methods were basically consistent,and they all believed that Hg and Cd had certain ecological risks.The other three heavy metals did not have ecological risks.From the perspective of three evaluation index methods,the pollution load index evaluation results indicate that heavy metals in the sediment of Ningxia section of the Yellow River Basin are pollution-free;The evaluation results of the land accumulation index indicate that the sediment of the Ningxia section of the Yellow River Basin has no pollution of heavy metals;The evaluation results of the potential ecological risk index indicate that there is a moderate pollution risk of heavy metals in the sediment of the Ningxia section of the Yellow River Basin.From the sampling months,the degree of heavy metal pollution in the sediment of the Ningxia section of the Yellow River Basin is October>April>July.The potential biological toxicity analysis of heavy metals in the sediment of Ningxia section of the Yellow River Basin was conducted using the sediment heavy metal quality reference coefficient method.It was found that except for the possibility of occasional potential biological toxicity effects of Hg,the other four heavy metals did not have potential biological toxicity effects.The analysis results of the heavy metal quality benchmark coefficient method are basically consistent with the analysis results of the three heavy metal pollution evaluation methods mentioned above.