Characteristics Of Soil Heavy Metal Pollution In Jinzhong Basin

The contents of Pb,Cr,Cd,As and Hg in soil of 12 counties and cities in jinzhong basin were determined.The ecological risk assessment of soil heavy metal hazards in the study area was carried out by using the single seed pollution index method,the potential ecological hazard index method and the Nemero comprehensive pollution index method combined with Arcgis Kriging interpolation method to understand the status of soil pollution in the study area.Geostatistical methods were used for semivariogram analysis,statistical method correlation analysis,PCA and cluster analysis,and machine learning method random forest regression model for source analysis of heavy metals in the study area.(1)The mean contents of five kinds of heavy metal are all higher than the corresponding background values for Shanxi.Specifically,As and Cr content averages are are close to background values.The content of Pb is slightly higher than that of soil background values in Shanxi.Cd and Hg contents are significantly above the standard,where 11.5% and60.0% of sample points of Hg and Cd,respectively,exceed the national second-level soil quality standard level.(2)The results of the single pollution index showed that the major heavy metals contributing to the pollution in the study area were Hg and Cd,followed by Pb,and Cr and As were the least.The results of the comprehensive pollution index evaluation and the potential ecologicalrisk evaluation showed that the basin pollution degree was relatively serious,and the proportion of sample points with moderate pollution and severe pollution reached more than 95%.The spatial analysis of pollution shows that the basin as a whole has a deep degree of pollution,and there are obvious prominent pollution areas in yangqu in the north of taiyuan,qingxu in the south of taiyuan and jiexiu.(3)The results of source analysis show that As and Cr are mainly from natural sources like soil parent materials,whereas Pb,Cd,and Hg are mainly from artificial sources including industrial and agricultural production.The random forest model results show that the importance of the main factors affecting the Cd content follow the order of soil organic matter content,industrial output per capita,and soil total nitrogen content.This indicates that the accumulation of Cd is affected by combined effects of industrial activities and chemical fertilizer application in agricultural activities.The most important factor affecting the Hg content is per capita industrial output value,followed by distance from polluting enterprises,indicating that Hg is mainly from industrial pollution activities.The main factors affecting Pb content are ranked in the order of road distance,per capita industrial output value,and distance from polluting enterprises,indicating that Pb is affected by both transportation and industrial activities.