Fractal Characteristics Of Soil Heavy Metals And Health Risk Based On Industrial Enterprise Scale

With the rapid development of urban industry,a large number of heavy metal compounds enter the soil,causing heavy metal pollution.Shanghai is the core city with the largest economy and population in the Yangtze River Delta region.The discharge of three wastes in the process of urban development has caused adverse effects on the soil environment,and heavy metal pollution in soil has been widely concerned by the society.As the source of heavy metals in urban soil,the analysis of heavy metal pollution in industrial production sites is of great significance to improve the urban environmental management ability,prevent the potential risk of soil environmental pollution,and promote the healthy and sustainable development of the city.In this paper,the pollution distribution of heavy metals Co,Cu,Pb,Zn,Ni,Hg and As in the soil was studied on the enterprises by sampling and analyzing the content of heavy metals in the production sites of industrial enterprises.This study used multivariate statistical analysis to analyze the content,correlation and clustering of different heavy metals.Combining fractal and geostatistical methods to analyze the spatial differentiation characteristics of heavy metals in soil,the pollution degree of soil heavy metals in the study area was evaluated,and the human health risk assessment of soil heavy metals was carried out.In order to provide support for accurate diagnosis of soil pollution and taking targeted remediation measures.The conclusion is as follows:1、The statistical analysis of soil heavy metal content in the study area showed that part of the heavy metal content in the topsoil of the study area exceeded the background value of Shanghai soil,but it was generally safe.The average content of heavy metals in the soil in the study area is:Zn、Ni、Cu、Pb、Co、As、Hg.The degree of variation was respectively:Hg、Ni、Cu、Zn、Pb、Co、As.Except for soil Hg,the remaining six kinds of soil heavy metals showed moderate variation,and soil Hg showed strong spatial variation.2、The results of multivariate statistical analysis of soil heavy metals in the study area showed that,There were significant correlations between Cu,Ni,Pb,As,Hg,Zn and Co in the soil,and the seven heavy metals may come from the same source.According to the principal component analysis,the first four principal components can explain 81.41%of the soil heavy metals in the study area.Based on the analysis of four principal components,it was found that the accumulation of heavy metals in the soil was mainly caused by industrial production,the influence of transportation could also be one of the sources of soil heavy metal pollution in the study area,and the pollution of residents also had an impact.3、The spatial structure analysis of soil heavy metals showed that Cu,Zn and Co fit the exponential model,Ni and Pb fit the spherical model,As and Hg fit the linear model and Gaussian model,respectively.The nugget coefficient of the heavy metals in the soils ranged from 0.07%to 100%,and the descending order was As,Cu,Pb,Co,Zn,Ni and Hg.The nugget coefficients of Zn,Ni and Hg in soil are all less than 25%,and there is a strong spatial autocorrelation among the various points.The Cu,Pb and Co in soil are 36.79%,32.52%and 25.31%,respectively,which belong to the moderate spatial autocorrelation.The As in soil is 100%,which is pure nugget form,indicating that the spatial distribution of As in soil presents strong randomness and independence.4、The results of the spatial distribution of heavy metals in the study area showed that:The distribution of Cu,Ni and Co in soil was Island,and had similar spatial distribution characteristics.The high value points of soil Pb were relatively dispersed and showed obvious point-like distribution characteristics.The soil Zn has obvious point source pollution characteristics at the high value points,the maximum content was 1.87 times of the background value of Shanghai soil.The spatial distribution of soil As was generally moderate,and there was no obvious high value area.There was obvious spatial enrichment of Hg.The high value areas of soil heavy metals in the study area were basically distributed in the northern region.5、The curve of generalized dimension spectrum of heavy metals in different soils showed a decreasing function relationship,and the heavy metals in soils had multifractal characteristics.The capacity dimension of seven kinds of soil heavy metals in the region is close to each other,and the value of D₁ is also large,which indicates that the distribution range of soil heavy metals in the region is wide,and the higher the uneven degree of soil heavy metals,the wider the distribution range.The results show that the multifractal singular spectra of seven kinds of soil heavy metals are quadratic parabola with opening downward and show asymmetry,which indicates that there are local specificity and heterogeneity of soil heavy metals in the study area.The width of multifractal spectrum can show the singularity of heavy metal distribution.The multifractal spectrum of heavy metals in the soil of the study area is wide,and there are heterogeneity and singularity in the seven kinds of soil heavy metals in the study area.6、The results of non-carcinogenic risk assessment of heavy metals in soil showed that,The hazard quotient（HI）of seven kinds of soil heavy metals in adults ranged from large to small:As（2.91E-02）、Pb（1.01E-02）、Ni（3.30E-03）、Hg（2.87E-03）、Co（1.32E-03）、Cu（1.05E-03）and Zn（4.14E-04）,less than 1,which belonged to the acceptable risk level.The hazard quotients of Pb and As in soil for children were 5.23 and 1.1,respectively,and the risk quotients were all greater than 1,suggesting that it might pose a threat to children’s health.According to carcinogenic risk assessment,The cumulative carcinogenic risk of soil As and Ni to adults is acceptable,in the range of 10^-6～10^-4,soil Ni is 5.67E-05,soil As is 5.54E-06.For children,the cumulative carcinogenic risk of soil As is within the acceptable range,which is 2.00E-05.The cumulative carcinogenic risk of soil Ni is 1.30E-04,more than 10^-4,which is not acceptable.The areas with high carcinogenic risk and non-carcinogenic risk basically appeared near the production workshop,scrap metal yard,unloading yard and surfacing shed.So it is necessary to strengthen the treatment and repair of these contaminated soils.