Pollution Characteristics,Content Prediction And Health Risk Assessment Of Polycyclic Aromatic Hydrocarbons In Soil Near Gas Stations In Beijing

With the rapid development of urbanization in China,the number of gas stations in cities is increasing.The oil composition of the gas station is complex,and a series of pollutants will be produced during the escape process.The pollution of PAHs emitted from gas stations is becoming more and more serious,and it will pose a potential threat to the surrounding environmental quality and human health.In view of the above problems,117 gas stations in 11 administrative regions of Beijing were selected as the research objects in this study.The surface soil samples of gas stations were collected to evaluate the concentration level of PAHs.The content level,composition characteristics,spatial distribution,sources and key influencing factors of PAHs in soil around gas stations in Beijing were analyzed by means of descriptive statistics,geostatistical methods,PMF model,BP neural network,XGBoost model and Monte Carlo simulation.At the same time,the content level prediction and risk assessment of PAHs in gas stations are carried out.The main results are as follows:（1）The content of∑₁₆PAHs in the surface soil of gas stations in Beijing ranged from 0.031 to 6.038mg/kg,with an average concentration of 0.034mg/kg.Based on the"Soil environmental quality Risk control standard for soil contamination of development land"（GB36600-2018）,the concentrations of 16 monomer PAHs were lower than the soil pollution risk screening values.The average concentration of 7carcinogenic PAHs was 0.039mg/kg,which was 49%of∑₁₆PAHs.The percentage of polycyclic aromatic hydrocarbons in the surface soil of the gas station was 4 ring,5ring,3 ring,6 ring and 2 ring.（2）The content characteristics of PAHs in different gas stations are closely related to the geographical location and existence time of gas stations,as well as the long-term impact of transportation load and human activities.The characteristic ratios showed that PAHs in the soil of Beijing gas stations were mainly derived from the combustion process,and a small part of them may be oil pollution sources.The results of PMF showed that the sources of PAHs in the surface soil of the study area were as follows:petroleum pollution source（38.77%）>traffic emission source（31.12%）>coal and biomass combustion source（30.11%）.（3）BP neural network was constructed to predict the content of PAHs in soil near gas stations in Beijing in 2030,and the goodness of fit was 0.922.The results showed that the content of PAHs in the soil of Beijing gas station in 2030 was all lower than the soil pollution risk screening value,but it increased with time,and the growth rate was faster in Chaoyang,Fengtai and Haidian areas.The root mean square error（RMSE）of the XGBoost model was less than 0.8,indicating that it could achieve better prediction effect in predicting PAHs content in soil around Beijing gas stations.（4）The results of probabilistic risk assessment showed that both adults and children were at a low carcinogenic risk.Children were sensitive receptors,and the health risk to children was higher than that to adults.The risk of soil PAHs exposure was in the following order:oral intake>inhalation>skin contact.The TEQ of 7carcinogenic PAHs ranged from 0.005 to 0.623mg/kg,with an average of 0.089mg/kg,accounting for 99.05%of∑₁₆PAHs,and the TEQ of the remaining PAHs was only0.95%.The contribution of different monomer PAHs to total TEQ was:Ba P>Bb F>Ba A>Dah A>Bk F>In P>Chr.The root cause of this phenomenon is the high level of pollution of toxic substances such as Ba P,and it is necessary to reduce the pollution of soil by controlling the emission of PAHs.Through the analysis of the current situation of PAHs pollution in Beijing,we can see the impact of urban development on PAHs pollution in soil.Although PAHs were at a low level and did not pose a risk to human health,they showed an increasing trend and should be paid full attention.The research results clearly clarify the pollution status and human health risks of PAHs in the soil of gas stations in Beijing,and have certain value for the scientific management of urban construction land in Beijing.