Pollution Characteristics,Source Apportionment And Risk Assessment Of PAHs In Topsoil In Main Urban Area Of Lanzhou

Soil is an important component of urban ecosystem and the basis for maintaining urban ecological security.With the rapid development of my country’s economy and society,polycyclic aromatic hydrocarbons(PAHs)continue to enter the soil through various channels and have potential impacts on the ecological environment and human health.Therefore,it is necessary to fully understand its status,sources and risks in the soil environment.In this study,62 topsoil samples were collected in the main urban area of Lanzhou,and 16 priority-controlled PAHs in the samples were analyzed by gas chromatography-mass spectrometer(GC-MS).Discuss its pollution characteristics,spatial distribution,potential sources and risk levels,in order to provide a scientific basis for the improvement of the soil environmental quality in Lanzhou.The results showed that:(1)The concentration of ∑16PAHs in surface soil was 1069～7377 μg·kg-1,with an average of 2423 μg·kg-1.The average concentration of 7 carcinogenic PAHs was 1126 μg·kg-1,accounted for 46.13%of ∑16PAHs.The PAHs in the topsoil of the main urban area of Lanzhou were dominated by high rings.The ring number percentage of soil PAHs was 4 rings>5 rings>3 rings>6 rings>2 rings.The areas with high PAHs content were mainly concentrated in the northwest of the study area.The region was dominated by heavy industries such as petrochemical industry.During the production process,a large amount of fossil fuels was consumed to form PAHs and finally settle through the atmospheric dry and wet to sink into the soil.(2)The diagnostic ratio showed that PAHs in the main urban area of Lanzhou were mainly derived from the combustion process,and a small part of PAHs might be the source of petroleum pollution.PCA analysis showed that fossil fuel combustion sources and traffic emission sources were the main sources of PAHs in the topsoil of the study area.PMF results showed that the main sources of PAHs in the topsoil of the study area were:traffic emission sources(31.58%)>biomass combustion sources(25.14%)>coal combustion sources(22.47%)>petroleum sources(20.8%).The spatial contribution ratio of major pollution sources showed that the sources of PAHs in the topsoil of the study area were complex and extensive,and human activities had a great impact.Feasible measures should be taken to ensure the environmental quality of the soil.(3)The risk entropy value indicated that the topsoil in the study area was medium ecological risk,except for Pyr was high ecological risk.The highest risk entropy was 116.2～1002.8,and the lowest risk entropy was 1.16～10.03.The overall pollution level was moderate,and the risky areas should be repaired in time.The toxic equivalent concentration of 7 carcinogenic PAHs in the topsoil of the study area was 0.616～675.8μg·kg-1,accounting for 98.5%of ∑16PAHs.The contribution from high to low was:BaP>DahA>BbF>BkF>BaA>InP>Chry.The main reason was its high toxicity equivalent factor,so measures should be taken to reduce the entry of these carcinogenic PAHs into the soil.(4)According to the US EPA method,the carcinogenic risks of topsoil PAHs in the study area to children and adults were 4.86×10-7 and 6.48×10-7,both within the acceptable limits.Among them,BaP and DahA had higher carcinogenic risk.Skin contact and oral ingestion were the main exposure routes of carcinogenic risk for children and adults.The level of non-carcinogenic risk for children and adults was within an acceptable range.The contribution of different exposure routes to the non-carcinogenic risk of children and adults from high to low was:oral ingestion>skin absorption>respiratory inhalation.