| This study investigated 5 heavy metals(ie., Cr, Cu, Ni, Pb and Zn) in urban dust. Firstly, this research focused on the build-up process and modelled it. Then heavy metals in different material surfaces dusts were analyzed and the ecological risk and health risk were assessed. Additionally, the wash-off characters of heavy metals in typical landuse districts and different urban surfaces were analyzed. Lastly the annual heavy metals loadings were accumulated and the ecological risks were assessed.It is found from the study of the build-up process that the distributions of heavy metals in different size fractions were relatively steady regardless of landuse. The highest percentages of heavy metals loadings were consistently found in the <75μm size range. It is also found from the model fitting results that exponential model can simulate the build-up of heavy metals in various landuse districts and the build-up process has basically completed while the dry period over 10 days.The dusts collected from 3 typical impervious surfaces(ie., wall, roof and road) were investigated and the concentrations of heavy metals decreased in the order of wall > roof > road, while the heavy metals loadings decreased in the opposite order. According to the analysis of heavy metal speciation, the mobility sequence percentages of Zn were much higher than other elements regardless of impervious surfaces materials. It is found that the potential ecological risk values of galvanized metal roof and asphalt road both have high risk for the ecology. According to the assessment of non-carcinogenic risk, there was no non-carcinogenic risk to adult while the risk of Pb, Cr in galvanized metal roof and Pb in asphalt road to children have already exceeded the safe value 1, which indicates that some effective measures must be taken to protect children’s health. It is also found from the assessment of carcinogenic risk that there was no carcinogenic risk regardless of impervious surfaces materials. The potential ecological risk model and health risk assessment model were both modified to evaluate the risks of whole demonstration region of Changzhou. The ecological risk of demonstration area was 401.2, which belongs to the relatively high category. Although risk non-carcinogenic risk of Pb was much higher than other elements, there was no threat to local residents. Additionally, the results of Cr and Ni carcinogenic risk assessment showed that there is no threat of cancer in this region.In the study of urban dust wash-off, it is observed that the heavy metals concentrations of runoff originated from different surfaces decreased in the order of road > lawn > roof > courtyard impervious surface while the runoff originated from different landuse area decreased in the order of commercial area > residential area > industrial area. It is found that impervious surfaces showed the transport-limited phenomenon while the pervious surface(lawn) showed the source-limited phenomenon. It is interesting that particles in runoff could dramatically adsorb the dissolved Cu and Zn originated from rainfall. In the correlation study, SS(Suspended Solid) showed the highly correlation with all the heavy metals in runoff, which means that SS is an effective index to estimate the concentration of heavy metals in runoff. Additionally, according to the character of wash-off, the initial rainfall of demonstration region could be defined as 4 m.A joint model based on build-up and wash-off process was built to accurate the annual heavy metals loadings. The annual loadings of Cr, Cu, Ni, Pb and Zn were 97.8 kg/a, 112.6 kg/a, 29.6 kg/a, 181.8 kg/a and 723.4 kg/a, respectively. It is obvious that most of the pollutants originated from road(58%), followed by courtyard impervious surface and roof, and the lawn contributed the lowest pollutants(only 4%). According to ecological risk assessment, annual runoff of demonstration region presented relatively high ecological risk. |
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