Pollution Characteristics And Risk Assessment Of Heavy Metals And Polycyclic Aromatic Hydrocarbons In Surface Dust In The Main Urban Area Of ??Shijiazhuang City

Urban surface dust is an important part of the ecosystem,and plays an important role in the circulation of air,water and other environmental media.The destruction of the ecosystem by urban surface dust is hidden,potentially long-term.The surface dust in the city contains heavy metals,organic pollutants and other pollutants,which have a certain impact on the regional environment and human health.In this study,the surface dust in Shijiazhuang City was taken as the research object,and the composition of particle size of 64 dust samples,the content,distribution characteristics and pollution sources of heavy metals and PAHs of major pollutants,and the environmental risks of heavy metals and PAHs were analyzed.Health risks are evaluated.The main conclusions of this paper are as follows:(1)The first mode diameter of surface dust in Shijiazhuang City is 100?250 ?m,accounting for 26.25%of the total particles,followed by 500?1000 ?m(22.25%)and 250?500 ?m(accounting for 17.66%)particle diameter,63?100 ?m(14.13%)particle size and 45?63 pm(11.22%)particle size accounted for relatively even,and finallyless than 45 ?m(6.77%).When grain size is less than 100 ?m,the contents of the western and northeastern parts of Shijiazhuang Second Ring are relatively high,while those larger than 100 ?m are mainly distributed in the southern and central parts of the Second Ring of Shijiazhuang.(2)The average amounts of the heavy metals As,Co,Cr,Cu,Hg,Mn,Ni,Pb and Zn in the surface dust of the main urban area of Shijiazhuang are 14.24,36.04,60.18,33.25,0.14,498.16,20.97,38.28 and 150.16 mg/kg,respectively.Among them,the six heavy metals As,Co,Cu,Hg,Pb and Zn exceeded the soil background values and national background values of Hebei Province.Except for Pb,other heavy metals showed the trend of increasing heavy metal contents as the particle size decreased.The distribution ratio is the highest in particle sizes of 250?500 ?m and 500?1000 ?m respectively except for Pb and Co,and the other elements are the highest in particle size of 100?250 ?m.(3)The sources of different heavy metal elements in the surface dust of the main urban area of Shijiazhuang City are different.Among them,Pb,Zn,and Cu are mostly derived from traffic pollution;Mn and Cr are mainly affected by natural factors such as parent material;Asfor Hg,Ni,and Co,they are affected by industrial activities and coal-fired,among which Hg is also affected by traffic to a certain extent.(4)Based on the analysis of geoaccumulation index method,it was concluded that Co was moderately polluted,Hg and Zn were mildly polluted,and others were not contaminated by heavy metals.The analysis of the pollution load index method shows that the pollution of heavy metals in surface dust in the main urban area of Shijiazhuang(80%)is partiallymoderate pollution,and the pollution of individual samples is more serious.The ranking of the potential risk intensity of the nine heavy metal elements is roughly:Hg>As>Pb>Cu>Co>Cr>Ni>Zn>Mn,where Hg is above the strong potential risk level,and others have slight potential risk levels.The comprehensive potential ecological risk index RI = 195.25 indicates that the surface dust in the main urban area of Shijiazhuang is of moderate risk.(5)The population health risk assessment results showed that the total non-carcinogenic risk doses of the nine heavy metals were Mn>Zn>Cr>Pb>Co>Cu>Ni>As>Hg under the three exposure pathways.Of the three routes of exposure,hand-feeding pathways are dominated.The overall non-carcinogenic risk for children is higher than that for adults,but the HI of all heavy metal elements is less than 1,suggesting there is no non-carcinogenic risk.The exposure doses of the four heavy metals As,Cr,Co,and Ni are very low,and their orders are Cr>Co>Ni>As.The exposure risk of these four carcinogenic heavy metals was Cr>Co>As>Ni.The carcinogenic risk and the total carcinogenic risk of the four heavy metals were all lower than the carcinogenic risk range 10-6?104.Therefore,it is believed that the main urban area of Shijiazhuang Heavy metals in surface dust did not cause harm to the health of urban residents.(6)The total amount of 16 priority PAHs(?16PAHs)in surface dust in Shijiazhuang ranged from 0.897 to 81.458 mg/kg with an average of 8.138 mg/kg,and the highest content of Fla was 1.136 mg/kg,Flu.The lowest was 0.129 mg/kg,and the strong carcinogen Bap was 0.567 mg/kg.The content of seven carcinogenic polycyclic aromatic hydrocarbons(?7CPAHs)ranged from 0.213 to 43.690 mg/kg,with an average of 3.402 mg/kg,accounting for 41.80%of the ?16PAHs.Compared with other cities at home and abroad,the content of PAHs in surface dust of Shijiazhuang city is at a relatively high level,and is dominated by the 4th ring PAHs.(7)PAHs in surface dust of Shijiazhuang city mainly come from the combustion of fossil fuels,largely based on petroleum combustion.From the analysis of the spatial distribution of PAHs in Shijiazhuang dust,it is concluded that the traffic source contributes significantly to PAHs in dust in the second ring of Shijiazhuang.The single factor index and the evaluation of the Nemerow comprehensive pollution index showed that the surface dust in Shijiazhuang has been seriously polluted by PAHs.ERL and ERM analysis showed that the potential ecological risk of PAHs pollution is high.Analysis of life-long cancer risk increments(ILCRs)showed that CR was greater than 10-6,indicating that PAHs in surface dust have potential carcinogenic risk for both adults and children.(8)The correlation analysis between PAHs and heavy metals showed that the interaction between PAHs and heavy metals As,Co,Pb and Ni is relatively large.The ERM average quality benchmark(mERM-Q)evaluation results indicated that the surface dust in the main urban area of Shijiazhuang has potential biological risks.