| By the end of this decade, more than half of the world's population will live in cities. It is clear that the development of urban areas hold the key of many of the challenges we face in our interactions with the environment. Urban areas are complex and dynamic systems that reproduce within their territory the interactions, among geographical and environmental processes on a local, regional, and global scale. This is one of the reasons why urban areas have become an increasing focus for the IGBP and IHDP.Aiming to discuss the research framework and methods of Urban Physical Geography, this paper presents the main findings of a study carried out in Shanghai (China), during June 2005 to July 2006 with two main purposes: to discuss the pollutants transport processes and mechanisms in rrban surface environmental system; and to evaluate, by means of risk assessment strategies, the potential adverse health effects of the exposure of children living in Shanghai to surface dust.(1) Particles play a role in virtually every process of pollutant behaviors in urban environment by ①deliveringthe contaminants to roadway surfaces as dust and dirt, ②affecting howreadily the contaminants are mobilized during storms, and ③influencing thephysical, chemical and biological transformations that contaminants undergo as they aretransported to receiving waters through sanitary and roadway runoff sewer systems. ④In receiving waters, particles modulate the biological impact that contaminants haveon aquatic and benthic organisms.(2) An understanding of pollutant characteristics on impervious surfaces is essential to estimate pollutant wash off characteristics and to design methods to minimize the impacts of pollutants on the environment. This paper presents data on surface pollutant characteristics on different urban road surfaces in Shanghai city, from samples collected over one year period at weekly interval. Result shows that particle size distribution has the important influence on pollutant concentrations. The <75μm fraction dominates throughout the cascade since it contains the highest levels of all of the heavy metals, and the order refers to Cr>Pb>Cd>Zn>Ni>Cu.(3) A five-step sequential extraction of roadside sediments showed that Zn, Cd and to a lesser degree Ni occur predominantly in the carbonate bound fraction, while Pb is highest in the reducible fraction, Cu in the organic fraction, and Cr in the residual fraction. It was found that the concentrations in the readily available exchangeable fraction were generally low for most metals examined, except for Ni whose exchangeable fraction was appreciable. Considering the proportion of metals bound to the exchangeable and carbonate fractions, the comparative mobility of metals probably decreases in the order of Zn>Pb>Ni>Cd>Cr>Cu.(4) The surface pollutant load data collected in this experimental study on an urban road surface indicate that pollutant buildup occurs over the dry days. The surface pollutant also becomes coarser over the dry days as it is disintegrated by traffic and other factors. The washoff of surface pollutant is dependent on the rainfall and runoff characteristics, but the results here show that common storms only remove a small proportion of the total surface pollutant load. The results also suggest that the rainfall and runoff disintegrates and dissolves more surface pollutant that they can actually remove.(5) Particulate emissions occur whenever vehicles travel over a paved surface such as a road or parking lot. Dust emissions from paved roads have been found to vary with what istermed the "silt loading" present on the road surface as well as the average weight of vehicles traveling the road. The term silt loading (sL) refers to the mass of silt-size material (equal to or less than 75 micrometers [μm] in physical diameter) per unit area of the travel surface. Emission factors of Shanghai surface dust of PM2.5,PM10 and TSP refer to 0.99, 7.64 and 9.17 g/VKT, emission quantities are 1.7,13.1 and 696 thousand t/a. High traffic volμmes in urban areas are responsible for increased Particulate contents within the breathing zone, due to the turbulence in the near-surface atmosphere and suspension of particles from the road surface.(6) Increased stormwater flow and the companying runoff pollution are a direct result of urbanization and the consequent increase in the proportion of land area under impervious surface. Runoff from urban areas is often presumed to be a significant contributor to nonpoint source (NPS) water pollution and has been identified as one of the major causes of the deterioration of the quality of receiving waters. And so, the objectives of this study were to investigate the characteristics of pollutants in storm events, and the relationships between pollutant load and flow-runoff patterns, and to analyze EMCs loadings of pollutants, then revealed "First Flush effect" of road runoff in different functions in Shanghai City.(7) Stormwater quality and quantity were investigated in urbanized catchments in the Central Shanghai city in order to characterize Temporal-spatial distribution and First Flush Effect of stormwater runoff pollution. Sampling locations selected can be grouped into at four sites with different land use categories (traffic, commercial and residential areas). The result indicates that concentration of contaminants decrease with the increasing of rainfall time. A single index known as event mean concentrations (EMC) can be used to characterize runoff constituents. Several heavy metals such as Pb-Zn-Cu and Cd, Cr-Ni groups show similar environmental behaviors during the runoff process, which reflect their sources in urban environment.(8) Dimensionless cumulative curves of First Flush Effect from four watershed sampling sites for selected storm events, and the magnitude of the first flush phenomenon is calculated using a method of M (V) fitting power curves, parameter b and MFF30 depending M (V) curves are used to illuminate strength of FFE. Result indicates that the magnitude of the first flush phenomenon was found to be greater for high intensity rainfall events and less for low-intensity ones, and strength of FF refers to Ni>Pb>Zn>Cd>Cu>Cr. Compared with total heavy metals, Dissolved heave metals show a less distinctive first flush phenomena(9) The maximum rainfall intensity, Imax, and the time between the start of the event and the occurrence of Imax, Tmax, have the most important influence on FFE. The association between MFF30 of heavy metals and Tmax is negative and strongly linear. If rainfall intensity maximum appears earlier (Tmax is smaller) it would cause a more distinctive first flush phonomina and therefore a negative correlation between MFF30 of pollutants and Tmax is found.(10) The examination of the movement of sediment in the urban environment in terms of the four compartments has proven an effective tool in establishing some trends in the contamination of the urban environment by heavy metals. The overall trend is for the deposits to contain the highest concentrations of Ni, Cu, Cr and Pb, whilst the highest concentrations of Zn and Cd and are found in the transported sediments. Different trends in concentrations are shown by some of the heavy metals such that Cu increases in concentration from source to deposit, Cd decreases in concentration, whilst Ni peaks in value in the transported material. This may reflect the growth of antigenic material such as organic matter diluting the concentration or addition of contaminated material, which would increase it.(11) The use of risk assessment strategies has proved helpful in identifying the routes of exposure to urban surface dust and the trace elements therein of most concern in terms of potential adverse health effects. In Shanghai city, the highest levels of risk seem to be associated with route of ingestion of dust particles, for all the elements included in the study presents a slightly higher risk than ingestion. It appears that the exposure pathway which results in the highest levels of risk for children exposed to street dust is ingestion of this material, and that three elements — Pb, Cr and Ni—are of most concern regarding the potential occurrence of health effects. However, given the large uncertainties associated with the estimates of toxicity values and exposure factors, and the absence of site-specific biometric factors, these results should be regarded as preliminary and further research should be undertaken before any definite conclusions regarding potential health effects are drawn.
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