Spatial Distribution Characteristics And Layered Health Risk Assessment Of Organic Pollutants In Soil Of Petrochemical Enterprise Legacy Sites

With the continuous acceleration of urbanization in China,the reuse of industrial land in cities has become one of the key issues that people pay attention to.The closure or relocation of polluting enterprises leaves behind a large number of contaminated sites.Before re planning and utilizing these contaminated sites,it is necessary to understand the spatial distribution characteristics of pollutants and conduct a human health risk assessment.The research on human health risk assessment of contaminated sites in China is still in the development stage.Traditional health risk assessment considers all exposure pathways of pollutants,neglecting the impact of soil depth changes on pollutant exposure pathways,and the evaluation results are too conservative.The paper takes the organic pollutants in a petrochemical enterprise’s legacy site as the research object,and divides the site into 5 layers based on the geological characteristics.Firstly,three interpolation methods,namely ordinary Kriging method(OK),inverse distance weighting method(IDW),and radial basis function method(RBF),were selected for cross validation to analyze the spatial distribution characteristics of soil organic pollutants;Then conduct a layered health risk assessment of organic pollutants in the site;Finally,the evaluation results of stratified health risk assessment and traditional health risk assessment were compared and analyzed.The specific results are as follows:(1)Descriptive statistical analysis of organic pollutant concentrations found that the maximum concentrations of benzene,ethylbenzene,and petroleum hydrocarbons(C10-C40)exceeded the screening values,indicating the presence of pollution in the study area;The coefficient of variation of the three organic pollutants in different strata shows extremely high variability,indicating significant changes in the concentration of organic pollutants and uneven distribution in the soil.(2)The nugget values of the three organic pollutants are all positive,and the nugget coefficient is basically between 25%-75%,belonging to medium spatial correlation,indicating that they are influenced by both human and natural factors;Three spatial interpolation methods were used to interpolate the pollution data of different soil layers in polluted sites.The cross validation method was used to analyze the interpolation results based on the characteristics of each layer of pollutant data.It was found that in soil layers with pollutant concentrations exceeding the screening value,i.e.those with significant changes in pollutant concentrations,the ME and RMSE of the inverse distance weighting method were lower,indicating high interpolation accuracy and suitability for such organic pollution sites.(3)From the spatial distribution characteristics of organic pollutants in the research area,benzene pollution is concentrated in the first and second layers of soil in the diesel tank farm on the east side of the site;The scope of ethylbenzene pollution is concentrated in the soil of the catalytic cracking unit area on the west side of the site and the third,fourth,and fifth layers of the sewage treatment plant;The pollution range of petroleum hydrocarbons(C10-C40)is concentrated in the first layer of soil in the loading area,office building,and pump room on the east side of the site,as well as the second layer of soil near the raw oil tank area and loading area.(4)The results of the stratified health risk assessment show that the carcinogenic nsk of benzene in the second layer of soil,the carcinogenic risk of ethylbenzene in the third,fourth,and fifth layers of soil exceeds the acceptable carcinogenic risk of the human body by 10-6,and the carcinogenic risk of petroleum hydrocarbons(C10-C40)is not calculated due to the lack of toxicological parameters.The non carcinogenic risk of benzene,ethylbenzene,and petroleum hydrocarbons(C10-C40)is lower than the acceptable hazard quotient of the human body by 1.(5)Using the stratified health risk assessment method to calculate the amount of soil to be remediated,the volume of benzene pollution decreased by 404.83m3,and the volume of ethylbenzene pollution decreased by 4545.33m3.Compared with traditional health risk assessment,layered health risk assessment considers the impact of soil depth changes on the exposure pathways of pollutants in different strata,and the calculated soil remediation target values are more reasonable,reducing the amount of soil remediation and saving remediation costs.