| With the rapid development of urbanization and industrialization,high degree of aggregation of the population,and mass use of transportation,urban environmental problems are increasingly serious.One of the major task is to reveal the urban environmental quality.In large cities,there are a lot of different types of education institutions especially the primary schools and kindergartens,which own the characteristics of wide coverage and distribution uniform.In this case,research on the quality of the campus environment condition has a very important significance on the knowledge to environment status and protection method.,This research regards campus dust of Xi’an as experimental subject,and we use magnetic susceptibility meter,laser size analyzer,pH meter,muffle furnace and XRF to analyze the calcium carbonate,magnetic susceptibility,particle-size composition,pH,organic matter and common element contents of campus dust.At the same time,XRF and AAS are applied to measure heavy metals concentrations in whole dust sample and different particle size fraction samples.Based on above study,the paper employs multivariate statistical and GIS to study the characteristics of heavy metals pollution in campus dust.Through the above research work,some valuable conclusions were revealed as follows:1.The arithmetic means of As,Ba,Co,Cr,Cu,Mn,Ni,Pb,V,and Zn in the studied dust samples are 11.5,958.9,39.6,154.2,62.1,546.2,32.2,151.6,68.7 and 390.7 mg kg-1,respectively,which are all higher than the corresponding background values of Shaanxi soil,except for Mn.The max values of Cu,Pb,Zn,Cr,Co and Ba are 2.9,7.1,5.6,2.5,3.7 and 1.9 times the background values of Shaanxi soil,respectively.All the heavy metal had the higher genetic variation except Mn and V,the variation coefficient of Zn and Pb was maximum.2.The heavy metals concentrate in PM2.5,PM2.5-PM10 and PM100 have different characteristics.The mean values of Co,Cr,Mn,Pb and Zn in different particle size fraction of dust decrease in the order of PM100>PM2.5-PM10>PM2.5.The mean values of Cu and Ni in different particle size fraction of dust decrease with the order of PM2.5-PM10>PM100>PM2.5.3.Chemical speciation analysis of heavy metals in PM2.5,PM2.5-PM10 and PM 100 showed that all the heavy metals exist as unstable status in PM2.5.All the heavy metals exist as unstable status in PM2.5-PM10,except Cr.At last,Co,Cr and Ni are stable in PM 10,while Cu,Mn,Pb and Zn are unstable.With increase of the particle size the acid soluble decrease and the residual enhance in campus dust.4.The heavy metals in urban dust show that As-Cu,Ba-V and Pb-Zn exhibit similar spatial distribution.The high value zone of As and Cu locate in the middle and southwest high-tech industrial area.The high value zones of Ba and V are near the east industrial area,southwest high-tech industrial area and south commercial area.The high value zones of Pb and Zn located around the south second ring road and most area within the city walls of Xi’an city.Because the concentration of Mn and Ni in the dust is close to the background value of Shaanxi soil,the distribution laws of Mn and Ni in the urban dust are mainly controlled by natural sources.The distribution laws of Co and Cr are different with other heavy metals,suggesting the different source of Co and Cr.The spatial distributions of heavy metals in PM2.5,PM2.5-PM10 and PM100 show that the spatial distribution of Co is similar in different particle size fraction.In addition,spatial distribution of Cr in PM2.5 and PM 100 and Ni in PM2.5 and PM2.5-PM10 are very close,respectively.For other heavy metals,this value in PM2.5,PM2.5-PM 10 and PM 100 were large differences.5.All the heavy metals in campus dust exist in different degrees of pollution and enrichment except As,Mn,Ni and V The PLI of heavy metals in dust ranges from 1.21 to 3.48 with an average of 2.06,which is a serious pollution.The PLI-calculated results of heavy metals in PM2.5,PM2.5-PM10and PM100 shown,and the PLI with an average of 0.98 for PM2.5,1.36 for PM2.5-PM10,and 1.66 for PM100.This result indicated that the heavy metal in PM2.5 is uncontaminated and the heavy metal in PM2.5-PM10 and PM 100 are moderately contaminated6.The results of ecological risk analysis showed that there was much higher potential ecological harm in Xi’an campus dust.The 29%of dust samples belonging to moderate ecological risk,the other 66%samples have reached higher ecological risk and 5%belongs to high ecological risk.For non-cancer risk to different students,ingestion of dust particles appears to be the main exposure route for metals,followed by dermal contact.The order of noncancer risks of metals to students is nursery children>pupil>middle school student>undergraduate.The maximum HIs levels correspond to Pb,Cr and As.For cancer risk,these levels are lower than the acceptable range.7.All elements were grouped into five categoriesl.The first set of elements(As-Ni-Cu-Mn)have mixed sources-nature and traffic.The second set of elements(Ba-V)were mainly derived from nature,but partly also from industry.The third group of elements(Pb,Zn)came from traffic.The fourth set of element(Cr)was mainly affected by the impact of the industry and traffic.The fifth set of element(Co),which was principally originated from industrial emissions and construction.The heavy metals in PM2.5 were classified into the third categories using multivariate statistical analysis.The first set of elements(Cr-Mn-Zn-Cu-Ni)have mixed sources-nature,traffic as well as industrial emissions.The second set of element(Pb)mainly derived from industrial.The third group element(Co),which was principally originate from industrial emissions and construction.The heavy metals in PM2.5-PM10 were also grouped into three categories.The first set of elements(Cr-Mn-Pb-Zn)have mixed sources-nature,traffic and industrial emissions.The second set of elements(Cu-Ni)mainly derived from nature and industrial.The third group element(Co),which was originate from industrial emissions and construction.The heavy metals in PM 100 were still grouped into three categories.The first set of elements(Cu-Ni)have mixed sources-nature and industrial emissions.The second set of elements(Co-Cr-Mn)mainly derived from industrial emissions,construction,traffic and nature.The third group elements(Pb-Zn),which was originate from traffic. |
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