Distribution And Concentrations Of Heavy Metals In Surface Dust In Different-scale-cities

Based on 145 samples of surface dust collecting in different-scale-cities, Zhengzhou, Zhongmou, Hansi and Guoxin, the concentrations, distribution and pollution assessment of heavy metals in the samples were studied, the sources of heavy metals on surface dust were also discussed in this paper.There are six main parts of this dissertation:Partâ… :In this part, the current situation and development tendency of the research about the urban surface dust were generally introduced. Then the author summarized the present situation of the study abroad on the urban surface dust.Partâ…¡:Background of study areas such as the history of different-scale-cities, the natural situations and the economies were also introduced.Partâ…¢: Mainly introduce the principles, methods, sample processing and preparation of urban surface dust, and the steps of experimental methods.Partâ…£:Mainly introduce the concentrations and their space distribution of heavy metals, and the relationship of the concentrations between the particle fractions.Partâ…¤:Mainly introduce the EF index, with this method to analyse the sources of the heavy metals.Partâ…¥:Mainly introduce two ways of the pollution assessment methods, to analyse the conditions of pollution in different-scale-citiesThe main conclusions of this study can be summed up as follows:(1) There are different levels of accumulation on the content of heavy metals in different-scale-cities. The average content of Cr, Ni, Zn, Pb and Cu on surface dust of the city in Zhengzhou area is 84.59, 37.60, 317.00, 227.01 and 22.66 mg/kg respectively, which is 2.3, 1.9, 7.3, 4.9 and 7.0 times of the dust background value. The average content of Cr, Ni, Zn, Pb and Cu on surface dust of the town in Zhongmou area is 47.36, 21.37, 179.05, 80.57 and 12.40 mg/kg respectively, which is 1.31, 1.05, 4.14, 1.76 and 3.84 times of the dust background value. The average content of Cr, Ni, Zn, Pb and Cu on surface dust of the town in Hansi area is 41.57, 15.50, 67.89, 46.91 and 2.11 mg/kg respectively, which is 1.15, 0.76, 1.57, 1.02 and 0.65 times of the dust background value. The order of the heavy metal content on surface dust is Zhengzhou > Zhongmou > Hansi > Guoxin.(2) There are differences between the spatial distributions of each heavy metal on urban surface dust in Zhengzhou. And the partial pollution is serious. Heavy metal pollution of Cu and Pb and Zn are serious in the urban areas especially within the industry districts and the heavy traffic areas of the South and West; the heavy metal pollution of Cr and Ni are relatively less serious, the Cr of the pollution centers situated mainly at the outer circle of the west and somewhere from south to north; the Ni of the pollution centers situated at the outer circle of the north and west. The lowest level content of the heavy metals situated at the northeast of Zhengzhou. Because that area is limited and not functional, the spatial distribution of each heavy metals on surface dust in Zhongmou and Hansi is obvious but without orderliness.(3)There are differences between the size of particles on urban surface dust of the different-scale-cities. The most of the particles is the small particles, and the least is the coarse particles. The different sizes of the surface dust of the contribution rate for heavy metals are: small particles> coarse particles > medium particles, except Cu. The reason is that the bigger specific surface area it is, the stronger absorbability it has. Some intensive study will be carried on.(4) With the concentration of heavy metals in the contrast areas as the background, we found that the EF index in the big scale city is higher than the small ones. The order of the average index of EF in Zhengzhou is: Pb>Cu>Zn>Cr>Ni. The highest EF index of the heavy metals is Pb which reaches high pollution level; the EF index of Cu and Zn reach middle level; and the index of Cr and Ni reach light. The order of the index of EF in Zhongmou is: Zn >Cu> Pb >Cr > Ni. The highest EF index of the heavy metals is Zn. The index of Zn and Cu reach middle pollution level; the others reach light pollution level. The order of the index of EF in Hansi is: Cr > Pb > Zn > Ni> Cu. The index of Cr, Pb and Zn reach the light pollution level and others reach the clean level. As result, The heavy metals of Cr and Ni on surface dust mainly originate from the erosion and weathering of the rock and soil, they are the lithopogenic heavy metals; the heavy metals of Zn, Cu and Pb mostly come from the sources of traffic-related and industrial, and they are the anthropogenic heavy metals.(5) By using the method of geoaccumulation index to assess the heavy metal pollution on surface dust of Zhengzhou, Zhongmou and Hansi, the order of the geoaccumulation index in different-scale-cities is: Zhengzhou > Zhongmou > Hansi > Guoxin, owing to the scale expansion, population explosion and intensive industries, there is a strong tendency on the pollution of the heavy metals. Pollution of Cu in dust is the most serious, then that of Zn and Pb, Cr is the lightest, and that of Ni is clean. The geoaccumulation index of five heavy metals in Hansi is below 0, which means that they are all at clean level.(6) By using the method of potential ecological risk index to assess the heavy metal pollutions on surface dust, the results show that: they are all at light pollution level. The order of potential ecological risk index in different-scale-cities is Zhengzhou >Zhongmou >Hansi> Guoxin.