Health Risk Assessment And Characteristics Of Soil Heavy Metal Pollution In Central Area Of Guiyang City

The rapid development of urbanization had caused many environmental problems,among which the potential risk of heavy metal pollution of soil to urban environment and human health had been paid much attention.As the administrative center of Guizhou Province,Guiyang City was bound to cause heavy metal pollution in soil in the region during the rapid development of society economy.However,the pollution degree,occurrence form and potential risk to human health are still unclear.Based on this,150 surface soil samples were collected from the central area of Guiyang（Guanshanhu District,Yunyan District and Nanming District）,and the contents and forms of five heavy metals（Pb,Zn,Cd,Cu and Ni）in the soil samples were analyzed and determined.The enrichment characteristics of heavy metals in the soil of Guiyang were determined by ordinary Kriging method and inverse distance weight method.Spatial variability and pollution distribution law were analyzed by spatial interpolation;The single factor index（_iP）,Nemerow composite index（_NP）,ground accumulation index(I_geo),pollution load index（LPI）and potential ecological hazard index（HRI）were used to evaluate the status of heavy metal pollution.The human health risk assessment model was used to calculate the non-carcinogenic and carcinogenic risk indexes for three exposure paths,including oral direct ingestion,respiratory ingestion and skin contact,and further evaluate the impact of heavy metals on human health risks.The main results are as follows:（1）The total content of Pb and Zn elements in the surface soil of the central urban area of Guiyang is 2.17-4.47 times that of the background value of the soil in Guizhou province,and the excess rate is 100%.The mean values of Cd,Cu and Ni are 1.41～4.26 times of the background values in Guizhou Province,and the over standard rates of Cd and Cu are94.67%and the over standard rates of Ni are 96.00%,indicating that the surface soil in the study area is more seriously polluted by Pb and Zn,and most areas are polluted by five elements.The coefficient of variation of five heavy metal elements in the study area ranged from 18.27 to 83.84%,showing moderate variability.In the surface soil of the study area,Pb is mainly active state,accounting for 78.11%,while Zn and Cu are mainly residual state,accounting for 67.85%and 51.00%,respectively,which are very stable and difficult to transform and migrate.（2）The spatial distribution of Pb,Zn,Cd,Cu and Ni pollution in topsoil showed a massive distribution with obvious heterogeneity;The pollution degree of Pb in Guanshan Lake>Yunyan and Nanming District gradually increases from south to north,while the pollution degree of Zn and Cd in Guanshan Lake<Yunyan and Nanming District gradually decreases from east to west.The high value of Cu is mainly distributed in Yunyan,Nanming District and southwest Guanshanhu District.The high value of Ni is mainly distributed in Yunyan,the middle and northwest of Nanming District and the southwest of Guanshan Lake District.The five elements are affected by natural factors and human activities.The partial pollution of Yunyan and Nanming districts is higher,and the overall pollution level is higher than that of Guanshanhu District,which is due to the exhaust pollution of transportation vehicles,and the pollution of urban industrial,urban construction and other wastes as well as household waste pollution.The pollution levels of Pb,Cu and Ni in Guanshan Lake District are higher than those in Yunyan and Nanming District,which may be due to the influence of factors such as soil parent material,surrounding industrial layout（Baiyun Aluminum Plant）and wind direction.（3）The evaluation results of different pollution index methods showed that the single factor index method showed that the heavy metal pollution rate of soil in the study area is higher;Nemerow composite index method shows that the whole study area belongs to safety or warning pollution level.The mean values of Pb,Zn,Cd and Cu are all greater than 0 according to the classification standard,and there is a certain degree of pollution,while the mean values of Ni are less than 0.The pollution load index method shows that the average pollution load index（PLI）of the three regions are 2.45,2.41 and 2.32,respectively,and the pollution grade is medium intensity,ranking Guanshanhu district>Nanming District>Yunyan District,indicating that the geological background,soil source and surrounding industrial layout affected the soil pollution degree.The potential ecological hazard index method showed that the hazard degree of the three study areas is Nanming District>Yunyan District>Guanshanhu District,and the HRI values were 166.33,150.14 and 138.04,respectively,indicating that Yunyan District and Nanming District,as the administrative centers of Guizhou Province,had been affected by human activities such as industrial production and transportation for a long time.So the ecological risk of heavy metals in soil is more serious.（4）Human health risk assessment shows that all five elements have a certain degree of non-carcinogenic risk,and Cd and Ni elements has carcinogenic risk.Direct ingestion was the main exposure route that caused health risk.Both non-carcinogenic and carcinogenic health risks are higher in children than in adults,indicating that children are more susceptible to heavy metal pollution;The total non-carcinogenic health risks of adults and children under exposure conditions are 4.67E-05 and1.10E-04,respectively,both of which were less than 1,indicating that the non-carcinogenic risks of heavy metals in the central urban area of Guiyang had little effect on human health and were at an acceptable risk level.The total carcinogenic health of adults and children under exposure conditions are 1.51E-04 and 6.38E-05,respectively,ranging from 10-6 to10^-4,indicating that the carcinogenic risk of heavy metal pollution in the central urban area of Guiyang is at the acceptable risk level.