| As the point pollution has been under control, non-point pollution source from urban surface runoff makes an obvious effect on urban water environment, and then it has become a main source of urban water pollution. Therefore, the study of heavy metals pollution on street dust and rainfall runoff system has become a hot issue In this thesis, Yubei and Jiangbei Districts in a rapid urbanization city of Chongqing were selected as study areas, which locate in the upstream of the Yangtze River, and rely on Pan-xi River which is a branch of Jialingjiang River. With monitoring urban rainfall runoff events between 2008 and 2009, we selected particle size and concentration of heavy metals as research objects, to analyze the output characteristics of particulate matter, output characteristics of heavy metals, and "source" and "converge" of heavy metals, and to assess the risk of heavy metals in street dust and runoff system. After all these works, we can understand the pollution process of heavy metals, recognize the control targets and key links of pollution control. The main research achievements were summarized as follows.1. During the precipitation process, distribution of particle sizes in rainfall runoff showed an obvious characteristic along with the rain event. The major mass of particle was<300μm, and particle with<45μm showed an increasing trend until kept a steady. The volume percent of particle size smaller than 45μm was the largest in the roof, the roads, the sewer and the river rainfall runoff, up to 52.54%,63.96%,47.65% and 51.81%, respectively. Comparison with various sample sites, we found that particle size was the finest in the roof, and the volume percent of particle size with 45～75μm, 75～150 um and 150～300μm hold small percent. The mass percent of particle size with small 45μm in the parking lot, the roads and the river exceeded 50%, and the mass percent in the river was the largest (up to 80%).2. During the whole precipitation event, the percent of particle heavy metal played a significant role, and different heavy metals showed different percent. Research showed that percent of particle heavy metal (Cr, Ni, Cu, Zn, Cd and Pb) were 80.11%, 90.89%,75.66%,84.63%,97.17% and 99.45%, respectively. The concentrations of heavy metals became larger with smaller particle size. Correlation research indicated that heavy metal showed a significant correlation with<45μm (p<0.05, n=10); the concentration of Ni, Cu. Zn, Cd and Pb displayed a significant correlation with particle concentration with smaller 75μm (p<0.05, n=10).3. With decreasing of particle size, the concentration of heavy metals showed an increasing trend in street dust. However, the change of heavy metal concentration didn't have obvious trend in particle in rainfall runoff. The concentration of heavy metals (Cr, Zn, Cd and Pb) with diameter of 150～300μm coarse particle were higher than in the street dust respectively.4. Street dust in Chongqing was seriously contaminated by Cr, Cu and Zn, which may disturb the quality of city water body and aquatic ecosystem seriously. In industry area, commercial area and parking lot, the concentrations of Cr, Cu and Zn in street dust with<45μm and 45～75μm exceed SEL, which endanger environment seriously. In rainfall runoff, Zn and Pb in particles with diameter of 150～300μm have a serious affection on urban water environment. In industry area, Cr, Ni, Cu, Zn and Pb in particulates with diameter of 150-300μm may held serious impacts on the environment.5. During the transportation process, heavy metal combined with particulates (45μm) and transported. The load of particle heavy metals displayed a significant difference. The load of particle heavy metals (Cr, Ni, Cu, Zn, Cd and Pb) was 74.0%, 85.0%,73.3%,61.0%.63.5% and 67.5% in the river, respectively. The load of particle heavy metals (Cr, Ni, Cu, Zn, Cd and Pb) were 50.7%,58.7%,60.1%,45.1%,51.8% and 52.3% in rainfall runoff on the roads, respectively. The load of particle heavy metals (Cr, Ni, Cu, Zn, Cd and Pb) was 41.1%,46.1%,52.2%,38.6%,46.4% and 45.1% in rainfall runoff on the parking lot, respectively. 6. The risk of Zn and Cd in the street dust was high, and the risks of Cd on the roads and parking pot dust were higher than in the river. The percent of exchangeable and bound to carbonate of Cd was about 31.4% on the roads in rainfall runoff, so Cd might have a high risk toward the aquatic environment. Cd on parking pot in rainfall runoff also displayed a high risk for environment, and Ni and Zn showed a medium risk. Zn and Cd in the river during the rainfall event also had a medium risk. During the precipitation, the releasing risk of heavy metals for water environment didn't show an obviously changeable trend. |
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