Spatial Distribution,source And Ecological Risk Assessment Of Polycyclic Aromatic Hydrocarbons In Soil Of Northern Songnen Plain

Polycyclic aromatic hydrocarbons（PAHs）is a kind of semi volatile and persistent organic pollutants,because of its persistence,cumulative,long distance migration,carcinogenicity,teratogenicity,mutagenicity,highly toxicity,causing potential ecological safety problem and influencingpeople’s daily life,so it has been paid extensive attention from the international community.Surface soil is the most important sink of terrestrial ecosystems PAHs and if PAHs goes into the soil it will have a series of physical and chemical reactions.Part of it is affected by the natural environment to degradate and convert into other small molecular substances.Another partwill retain in the soil for a long timeand have a negative effect on soil,plants and animals there.Songnen Plain is the important commodity grain base.The research selects Songnen Plain as the research area and studiesthe PAHs in the surface soil of Songnen plain.because Persistent organic pollutants concentration in soil directly related to food security.Firstly,study the methods of analyzing 16 PAHs in the soil with accelerated solvent extraction and high performance liquid chromatography（HPLC）.Secondly,explore thespatial distribution characteristics of PAHs in the surface soil in northern Songnen Plain,and try to analyze the influence that organic carbon（TOC）and pH impact on distribution of the content of PAHs in the soil.Thirdly,analyze the source of PAHs in the surface of the soil by using the characteristic ratio and principal component analysis（pca）.Finally,use a variety of methods to analyze ecological risk assessment of the PAHs to protect the farmland environment of northernSongnen Plain and providethe basis for controlling PAHs environmental pollution.The analysis of PAHsin the surface of northern Songnen Plain soil samples shows that most of the 16 PAHs detection rate are 100%,the other detection ratesare over 90%.It means that PAHs widely exists in the surface soil of the study area.The 16 PAHs concentration range is between 131.93¹699.14 ug/kg,the average value is 675.99ug/kg,the median is 668.84 ug/kg,the standard deviation is 336.25 ug/kg.PAHs spatial distribution in the northeastern study area is high,while southwestern area is low.Studies have found that 2³ ring PAHs accounts for 24.81%²4.81%of the total PAHs,with the average is 50.39%;4 ringPAHs accounts for 8.19%⁸.19%of the total PAHs,with the average is 23.15%;5⁶ ringPAHs accounts for 1.66%¹.66%of the total PAHs,with the average is 26.45%.In general,low rings PAHs include 2³ rings in Songnen Plain farmland surface soil accounts for 50.39%,central and epipodium aromatics include 4⁶ rings accounts for 49.71%of the whole PAHs.Using a variety of characteristic ratios to do a qualitative judgment of PAHs sources,it can be found that the results are relatively consistent;the source of PAHs in the study area is extensive-coal and biomass burning,also petroleum source burning and petroleum source pollution.Their contributions to PAHs:coal,biomass burning>petroleum source burning>petroleum source pollution.Combustion source is the main pollution source;the petroleum source burning is the second.To judge the source in quantitative,the author uses principal component analysis（pca）,extracts five main factors.The five main factors of the cumulative contribution rate reached 72.163%,more than 70%.Therefore,the five main factors can explain the source of PAHs in the study area.Among them,the principal component 1,2,3,mainly reflect the PAHs in soil comes from 3⁵ rings,sothe components are the combustion sources and they account for 54.612%.The source contains the incomplete combustion of wood and other biomass,emission of the coal and coking industry and the burning of coal industry and biomass,etc.Principal component 4 means traffic pollution sources,9.456%of the total contribution rate.Principal component 5 means oil source,8.095%of the total contribution ratio.The results are approximatewith characteristic ratio.Evaluating the ecological risk of northern Songnen Plain surface soil,the author usesThe Soil Environment Quality Standard（GB15618-2008）to judge the pollution levels of PAHs from 59 sampling points in the north of Songnen.The results show that by analyzing the compontents of PAHs,most of the northern Songnen Plain soils are relatively pure.The government should work hard to prevent the pollution.Individual monomers PAHscompontentsare more than the secondary pollutants standard limit,so they belong to the mild pollution,including:Nap（5 points）,Chry（2 points）,DahA（5points）.It is potentially harmful,so it should been given full attention.Evaluating biological toxicity in the study area,among all 12 PAHs that haveERL and ERM,the DahA content is greater than the value of ERM only in two sample points.The detection rates of the remaining four PAHs（as long as there are BbF,BkF,InP and BghiP,they will have a negative effect on biology）are higher than 90%.The PAHs contents of the remaining samples are lower than ERL.This shows that in all sampling points,most PAHs occasionally has negative ecological effects,while BbF,BkF,InP,BghiP and DahA should be paid great attention,because they can always produce negative ecological effects.Studying the potential risk of carcinogenicity,the author finds that the TEQ_Baprange of the 16 PAHs is 4.606³55.075 ug/kg,the average value is 95.001ug/kg,the TEQ_Bap range of 7 carcinogenic PAHs is 86.800⁹9.813%.It shows that 7carcinogenic PAHs are major contributors for the 16 PAHs TEQ_Bap.Compared with other regions,the total TEQ_Bap content in the surface soil of northern Songnen Plain is low,potentially carcinogenic risk is smaller.