Study On The Pollution Of Heavy Metals And Polycyclic Aromatic Hydrocarbons In Soil In Different Functional Areas In Xi'an

In this study,geochemical characteristics of nine heavy metals(Cr,Mn,Co,Ni,Cu,Zn,As,Pb and V)and polycyclic aromatic hydrocarbons(PAHs)in soil environmental media from different functional areas in Xi'an were as the main research objects.The pollution level,composition characteristics,source identification,ecological and health risk assessment of the total of 55 surface soil samples were studied in detail.X-Ray fluorescence spectrometer was used to for determine the concentration of 16 kinds of heavy metal elements in soil samples.The concentration of 16 priority PAHs were detected by high performance liquid chromatography.The pollution current situation,sources and risk in soils were assessed by different methods,such as multivariate statistical method.The main research conclusions are as follows:(1)The content of nine heavy metals in urban soil from Xi'an city were higher than soil background values of Shaanxi Province.The total concentrations of sixteen PAHs,specific combustion compounds and seven carcinogenic PAHs ranged from 0.310 to 288.237mg kg-1,0.084 to 234.765 mg·kg-1 and 0.051 to 146.821mg·kg-1,respectively.The concentration of LMW and HMW range is from 0.110 to 32.463 mg·kg-1 and 0.092 to 255.775 mg·kg-1 respectively.The Bap of strong carcinogens content is from ND to 25.984 mg·kg-1.The changing ruler from high to low level of?PAHs in different functional areas is residential area(31.191mg·kg-1),industrial zone(5.532 mg·kg-1),transport area(1.565 mg·kg-1),educational area(1.432 mg·kg-1),park(0.638mg·kg-1).(2)Mn,Cr,Ni,As and V these five heavy metals were less affected by human activities,all samples exhibited negligible comtamination by these five elements.Co,Cu,Zn and Pb elements in soils present certain relative pollution level.Comprehensive pollution indexes and PIL results showed that all samples was polluted,the serious pollution is industrial area.According to the PAHs pollution classification standard of Maliszewska,the PAHs achieved serious and moderate pollution level' s sample number of all soil samples in Xi'an are 54.55%and 23.64%.Among them,PAHs in the industrial area,educational area,traffic area and residential area surface soil were dominated by from 3 to 5 rings PAHs.PAHs in the park soil were dominated by low molecular weight PAHs with 2 and 3 rings.(3)The method of principal component analysis results show that extract the two factors of eigenvalues greater than 1,the cumulative total variance is 74.498%.Cr,Co,Ni,Cu,Zn and Pb on the first factor of the load is bigger,explained 44.705%of the total variance,regard as traffic pollution sources,coal combustion,residents activities and industrial "three wastes" emissions and so on of the artificial emission source.Mn,As and V of load is bigger on the second factor,28.794%of the total variance were explained,is seen as characteristic elements of natural source.The ratio method results of source analysis showed that the PAHs in the soils from different functional area derived from the mixture of oil,coal and other fossil fuel combustion source,not a single source as the leading factor.The PAHs source in some point is complicated,for the oil spill,oil burning,incomplete combustion of coal and biomass mixed sources.(4)There are slight potential ecological harm of Cr,Mn,V and Zn element.Co,Cu and As is mild and moderate potential ecological harm degree.Ni and Pb have mild,moderate as well as serious degree of potential ecological harm.The average value of comprehensive index of potential ecological harm of nine heavy metals is 53.35.This value show that topsoil of Xi'an exists moderate potential ecological harm on the whole samples.The ecology risk assessment result of PAHs showed that total PAHs in the park,education area and traffic area are not over ERL value,showed that three functional areas PAHs ecological risk is light less than 10%.The concentration of total PAHs in industrial area and residential areas is more than ERL value,residential area more than the ERM value in several sample sites.Some single PAHs exceed ERL value does not exceed ERM value,have occasionally on ecological harm.Individual single PAHs exceed REM value,ecological harm is bigger.The ecological risk in residential and industrial area is greater than educational area,traffic area and park.(5)The carcinogenic risk of four heavy metals and non-carcinogenic risk of nine heavy metals total value are sensitive land greater than nonsensitive land.The cancer risk is,As>Cr>Co>Ni.The change ruler from high to low of total cancer risk and non-cancer risk value of nine kinds of heavy metal elements in different functional areas are park,educational area,residential area,industrial area and traffic area.Ingestion is the main exposure pathways for Cr in sensitive land.Breath is the main exposure pathways for Cr in nonsensitive land.The main exposure pathway of Mn and Co elements is breath inhaling soil particles.The main exposure pathway of Ni,Cu,Zn,As,Pb and V elements is hand-intake exposure way.The incremental life cancer risk assessment indicated that the PAHs risks for children exposed to the soil were considerably higher than for adults,PAHs carcinogenic risk present from high to low is residential area,industrial zone,educational area,traffic area and park.Among the three kinds of exposed ways,dermal contact was the main exposure pathway that resulted in the relatively higher risk,followed by ingestion.The exposure pathway of inhaling soil PAHs of minimum for less than 0.01%is negligible.Three kinds of exposure pathways for children and adults,the skin contact pathway for children's risk is greater than adults.Ingestion and breath inhaling soil PAHs exposure pathway for adult's risk are higher than children.(6)The results of correlation analysis shows that the TOC and pH are not influence factors of PAHs residues in urban soils from Xi'an city.However,pH and onbehalf of the natural source of heavy metal elements in soil exist positive correlation.TOC and on behalf of the natural source of heavy metals exist negative correlation,exist positive correlation and delegate to the anthropogenic source of heavy metal elements.And the content of PAHs in soil and delegate to the anthropogenic source of heavy metals has significant correlation.PAHs and the heavy metal elements have similar sources and environmental geochemical behavior.