| Objective To understand the pollution and distribution of polycyclic aromatic hydrocarbons?PAHs?in the soil of Yinchuan City,and analyze the major sources and ecological and health risk assessments of PAHs in the soil.Methods Mathematical statistics and geostatistical analysis were used in this study.A total of 69 surface soil samples were collected from cities and towns in Yinchuan City from March to April 2019.Gas chromatography-mass spectrometry?GC-MS?was used to detect the content of 16 EPA-PAHs.First,according to different land use types,schemes of extraction and quality control were determined,and descriptive statistics of testing data in surface soils were utilized to understand the degree of PAH pollution and its spatial distribution,respectively.Then the composition characteristics of each PAH monomer and PAHs with different ring numbers were explained.Source analysis used molecular diagnostic ratio?MDR?for preliminary qualitative analysis,and a quantitative source analysis method combining principal component analysis?PCA?and positive matrix factorization?PMF?determined the main sources with contribution rates of PAHs pollution in the study area.Finally,comprehensive applications of traditional and probability risk assessment were used to analyze risk degree and influencing factors.Ecological risk assessment was based on ERL,ERM,toxicity equivalence?TEQ?and risk quotient?RQ?.Health risk assessment used carcinogenic risk?CR?and hazard quotient?HQ?and Monte Carlo model to deeply explore risk and underlying reasons of human health caused by PAHs contaminated soil.Results 1.The total content of 16PAHs in soils in Yinchuan City ranged between 70.0and 3876.6ng·g-11 with an average of 618.7ng·g-1,which varied greatly in different land use types and obtained as industrial area(255.73876.6,1529.5 ng·g-1)>traffic area(86.5811.2,330.3 ng·g-1)>farmland(70.0637.1,265.9 ng·g-1)>green park(121.6372.9,230.5 ng·g-1).7 carcinogenic PAHs accounted for 6.17%79.05%of?16PAHs.Compared with the pollution status of PAHs in soils of other cities,the pollution status of PAHs in Yinchuan was at a moderate pollution level.Spatial distribution map of Nemerow Pollution Index in Yinchuan City shows that PAHs in the soil of the industrial area were in medium and heavy pollution,especially in the energy base of Ningdong.PAHs in traffic area behaved differently based on traffic density,and samples of farmlands and parks were basically in mild to moderate pollution.The NPI value of farmland soils ranged from 0.54 to 5.38.Except for individual sampling points of green parks,mostly were in the light and medium pollution level.2.Composition patterns of PAHs in the surface soil were analyzed in this study.The proportion of Phe in soils of different land use types reached the highest,accounted for industrial area?57.85%?,farmland?50.70%?,green park?46.07%?and traffic area?33.43%?.Among the 16 priority PAHs,NaP was detected in extraordinary low proportion of sampling sites in farmland and parks,while accounted for 22.15%and 8.65%of industrial and traffic areas.Besides,Ant and BaA also had a higher proportion in farmland and parks.Except for specific sites,most of the sites were detected with higher proportions of 23 rings PAH homologous?7.74%89.62%,average 58.98%?,much owing to the high content of Phe detection and the origin of Phe should be concerned in this region.In the industrial area,the high ring of individual sampling points rose.3.The cross plot for molecular indices of Fla/?Fla+Pyr?and InP/?InP+BghiP?in different soils indicated that the major PAHs sources in Yinchuan were significantly combustion sources,and some sampling points may existed oil sources.PCA results revealed that the first three principal components accounted for 72.8%of the total variances.Factor1indicated of coal/biomass combustion?35.1%?,factor2 indicated of mixed pyrogenic sources,such as combustion of coal/biomass and refined petroleum production?28.6%?,and factor3indicated of combustion of crude oil and raw coal?9.1%?;The source compositions of four extracted factors from PMF,factor 1 represented a small-scale coke oven combustion?4.5%?,factor 2 represented a biomass combustion?6.8%?,factor 3 represented a vehicular emission source?19.1%?,and factor 4 represented a coal combustion?69.6%?.PCA and PMF models revealed that emissions from coal combustion,vehicles and burnt biomass acted as the most important factors.4.The individual PAH concentrations at mostly sites were below effects range median?ERM?,and the concentrations of some sampling points were also higher than effects range low?ERL?in different land use types of soils.Toxic equivalency quantity?TEQ?calculated as toxic equivalency factor TEFBaP.It showed that TEQBaP10aP10 ranged from 10.64 to 150.22ng.g-1,with a point over standard rate of 63.16%in industrial area.And risk quotient?RQ?has been shown to be useful for the characterization of the risk of PAHs to organisms and ecosystems.NaP and Phe in industrial area were>1,besides,the monomers of Phe,Ant,Pyr,BaA,BbF and DBA were at medium risk in farmland and park soils.Most of the monomers in traffic area at medium risk.RQ?PAHs?NCs?and RQ?PAHs?MPCs?of 16 PAHs evaluated of the total PAHs in the four types of land use types indicated that the soil in industrial areas and roads were at medium risk level 2,and PAHs in farmland and parks may caused medium risk level 1.5.Based on the site exposure,the health risks of PAHs carcinogenic and non-carcinogenic in different land use types were evaluated.All sampling points were divided into non-sensitive lands?sampling points in industrial and traffic areas?and sensitive land s?sampling points in farmlands and parks?.Traditional risk assessment show that the total carcinogenic risk under the two land use methods were 1.28E-03 and 3.84E-04,both exceed the upper limit of carcinogenic risk?10E-04?,and the total non-carcinogenic risks were 4.28and 1.59,respectively.The results revealed that the 95th percentiles cancer risks for non-sensitive lands and sensitive lands were 2.66E-02 and 3.47E-03,respectively.And the values were 4.29E+01 and 2.51E+01 for hazard quotient,consistented with traditional risk assessment results.The analysis of the contribution rate of each PAH monomer and three exposure pathways suggested that the main exposure pathways of PAHs pollution in soil were skin contact and oral intake,and the monomers of DBA,BaA and BbF were the main carcinogens,and Phe and Fla were stakeholders that cause non-carcinogenic effects.At the same time,NaP also had a higher contribution to THQ in non-sensitive land soils and Ant in sensitive land soils.Sensitivity analysis showed that exposure status and PAHs concentration were the key factors affecting the health risks of PAHs in the soil.Soil exposure parameters,such as exposure frequency?ED?,daily oral ingestion rate?OSIR?,and skin contacting soil?SAE?,had the greatest impact on health risks.Body weight has negative sensitivity,but the sensitivity is less than-1%.Conclusion 1.Polycyclic aromatic hydrocarbon pollution existed in the soils of different land use types in Yinchuan,with a moderate level of pollution in general,and the composition detected with higher proportions of 23 rings PAH,much owing to the high content of Phe.2.PAH pollutants originated mainly from coal combustion and vehicular emission,but coke oven,petroleum production and biomass combustion as sources were not negligible.3.There are no obvious ecological risks in the study area,but a small amount of PAHs have medium risks,individual PAHs show a higher level of risk,and pollution of PAHs in surface soil may cause certain degree of health risks.It is suggested that controlling population exposure and sensitive PAHs is important for health protection. |
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