Distribution Characteristic And Pollution Assessment In Street Dust Along Overhead Road In Shanghai

Urban dust is not only an important contributor to urban environment pollution, but also a carrier of all kinds of environmental pollutants, which has the functions of guidance, transfer, solicitation and so on. But at present urban dust pollution was given less attention in environmental studies, and some studies on source, distribution, transfer, transformation, pollution effect, human health risk and so on in urban dust was attached less importance to. In recent years, studies on urban dust are gradually becoming a hotspot. Compared with urban soil, urban dust is an environmental medium having complicated composition and complicated source. Under the influence of traffic transportation, industrial production and urban construction, urban dust accumulates a mass of heavy metals and becomes an important source of urban environmental heavy metal pollution.This dissertation is supported by bidding project of Shanghai Environmental Protection Bureau(No. 44031590). The physiochemical properties, content, distribution characteristic as well as pollution assessment in street dust along overhead road in Shanghai are mainly studied. Besides, Hg and As in street dust along Neihuan overhead road are tested and analysed and compared with reference area. It is the first time to study the "linear pollution" in street dust along the important traffic main stem in Shanghai.The main conclusions of this study can be summed up as follows.1. The average pH in street dust along overhead roads is high, alkaline characteristic is obvious; The average grain size of street dust is 114.81μm, and there is great difference among sampling sites; the average content of organic matter is 4.49%, coefficient of variance is 37%, great difference still exists among sampling sites.2. The average content of Pb, Cd, Cu, Zn, Ni, Cr in street dust along overhead road in Shanghai is 261.73mg/kg, 0.96 mg/kg, 247.87mg/kg, 737.44 mg/kg, 61.29 mg/kg, 247. 86 mg/kg respectively, which is 10.28,7.37,8.67,8.56,1.92 and 3.30 times of the soil background values of Shanghai. Except Ni and Cr, others have a higher accumulation. Due to variance of heavy metal source and difference of climatic condition, content of heavy metal in winter and spring season is higher than that in summer and autumn season nearby studied residence area.3. Average content of Hg along Neihuan overhead road is 0.14mg/kg, and exceeds the soil background value of Shanghai a little. Average content of As along Neihuan overhead road is 8.01mg/kg, which is a little lower than soil background value of Shanghai. As reference area, the average content of Hg and As in street dust around upriver water source site of Huangpu river is 0.23mg/kg and 10.38mg/kg respectively, which are all higher than that along Neihuan overhead road.4. Analysis of correlation and principal components are used to explore source of heavy metal in studied area. From the primary judgement, Pb and Zn are mainly resulted from traffic; Cu, Cd and Ni are mainly resulted from industrial production, combustion of garbage; In addition, because Cu have some load in the first principal component, that indicates that abrasion in traffic is also a source of heavy metal; Cr is possibly resulted from weathering of soil. Hg and As in street dust along Neihuan overhead road have a lower content, the reason why Hg and As in street dust in reference area have a higher content may be the use of pesticide and fertilizer, burning of coal and industrial pollution.5. By using the method of geoaccumulation index and potential ecological risk index to assess the heavy metal pollution in urban street dust of Shanghai, the results show: Pb, Cd, Cu and Zn are all at middle pollution lever, Cr is at low to middle pollution lever, and Ni is at light pollution lever.6. The potential ecological risk of Cd in street dust along overhead road is at heavy pollution lever, Pb and Cu are all at middle pollution lever, Zn, Ni and Cr are all at light pollution lever, the potential ecological risk of every overhead road has the same regularity as the whole.