The Study Of Heavy Metals In The Soil Of South-eastern Suburb Chemical Industry Zone In Beijing

Environmental geochemical mapping with high-density soil sampling was conducted to determine the spatial distribution,possible sources and potential ecological risk of heavy metals at a former chemical industry area in Beijing.Many surface soil samples were collected and the concentrations of heavy metals,such as Ni,Cr,V,As,Cu,Pb,Cd,Zn and Hg,were analyzed.The spatial distribution characteristics of these metals were demonstrated by environmental geochemical mapping.The principal component analysis and cluster analysis were used in the source identification of 9 heavy metals in the topsoil.And the potential ecological risk of 9 heavy metals was quantitatively estimated for each site and the risk map was plotted for assessment.The mean concentration of V,Ni,As,Cr,Pb,Cu,Cd,Zn,Hg were 64.8,23.3,8.55,60.3,33.7,31.3,0.174,83.8,0.316(mg/kg).Elements of V,Ni,As and Cr having lower coefficient of variation and the enrichment factor,while that of Pb,Cu,Cd,Zn and Hg with larger coefficient of variation and the enrichment factor.Histograms and box-plots can also reflect the distribution of various elements.The elements V,Ni,and As were normally distributed in the topsoil of the study area,so they are thought to be affected mainly by the soil parent materials.Cr showed an approximately normal distribution,while Pb,Cu,Cd,Zn,and Hg exhibited non-normal distributions,indicating that they may be affected strongly by exogenous substances.The box-plot shows that V,Ni,As and Cr have approximately symmetrical distributions with fewer outliers,while Pb,Cu,Cd,Zn and Hg exhibited a right-skewed distribution with more outliers and extreme outliers,which may be caused by pollution with exogenous substance.The distribution maps of heavy metals showed that the distribution of V,Ni,As and Cr have some similar features.The spatial distribution showed that the elements V,Ni,As and Cr had no large 'hot spots',their distributions showed no apparent regularity,and the high-value areas were distributed randomly in the main plant area.The spatial distribution patterns of Pb,Cu,Cd,Zn and Hg were distinctly different from those of V,Ni,As,and Cr.The former five elements had significantly larger high-value areas,and there were two large high concentration or hot spots of these elements:one in the Beijing Coking Plant and the surrounding areas,the other in the Second Chemical Plant and the surrounding areas.All of the studied heavy metal elements were characterized by higher concentrations in the heavily populated old plant areas or the closer surrounding areas and lower concentrations in the relatively distant areas with low industrial production activity density.Principal component analysis and cluster analysis results show that nine heavy metals in the surface soil can be divided into two categories:Cluster I contained Pb,Cu,Cd,Zn and Hg;all of these elements showed high mean concentrations compared with the background values in the studied area.This group of elements has previously been interpreted as anthropogenic metals.Cluster II consisted of V,Ni,As and Cr.This group of elements mainly originated from the soil parent materials.Potential ecological risk factors of different heavy metals in the topsoil in this study were calculated.Most heavy metals,such as Cr,Ni,V,Cu,Zn,Pb and As,posed low ecological risk in the topsoil of the study area.In contrast,Cd and Hg posed higher individual ecological risk than the other studied heavy metals.Thus,all of these heavy metals in the topsoil are of great concern in terms of the ecological hazard that they pose in the topsoil in southeastern suburban Beijing.The potential ecological risk indices(RI)were calculated to assess pollution by multiple heavy metals in the topsoil.It was found that the highest RI values were located in the main plant areas.