Present State, Problem And Countermeasure Of Urban Environmental Geochemistry

Urbanization is the result of the development of industry and is a symbol of the improvement of civilization degree of the society. At present, the rapid development of city is the common global trend. While 30 percent of the global population, 2.5 billion people, lived in the city in 1950, the city population increased rapidly and has been up to 50 percent of the global population by the end of 20 century. It is estimated that the city population would account 60 percent of the global population in 2025. The environmental pollution is caused by the increase of the city number and population and a series of complex environmental problems that affect the human health and urban environment are brought. Urban environmental geochemistry is a new sub-discipline of geochemistry which emerges as the times require and its definition can be described as following according to the definition of geochemistry, i.e., urban environmental geochemistry is used to study the source, concentration, form, transference and recycle of the elements or compounds in the urban environmental factors, including rock, soil, atmosphere and biology. The environmental problems are studied, the geochemical method and techniques are probed into and the approaches how to sustain the urban environment are sought. 1 Present state of urban environmental geochemistry The primary coverage of urban environment geochemistry should include the distribution, evolvement, function and its influence on health of the elements and isotopes in the urban atmosphere, water and stream sediment, soil, biology, etc. At present, the aerosol is the emphases of the urban environmental geochemistry and is also an important index of air quality valuation. Through the study on the chemical component and the isotopic characteristics, the sources of the urban aerosol and its affection on the environment and human bodies could be disclosed and environmental behavior of aerosol could be understood, which provides important bases for the measurement established for the control of the urban air quality and the prevention and control of pollution. Water is the material basis of the existing and development of the city and the deficit of water resource and the water pollution have arose the attention of all countries. The quality of urban water environment is indicated by water chemistry, but some poisonous elements, especially some metallic elements, do not migrate in the form of solution while they combine with the particulate matter. The environmental characteristics of the stream sediment in city are the problem that needs to be paid attention to and is also a hot question of urban environmental geochemistry. The term urban soil can be understood to encompass all types of non-paved land within the city limits. Urban soil rather acts as a pollutant sink and, if undisturbed, preserves the cumulative history of trace elements inputs into it. The main sources of trace elements in the urban soil are the atmospheric deposition of particles generated by automotive traffic, heating systems and resuspended street dust, the uncontrolled disposal of urban and commercial wastes, and the addition of fertilizers and composted sewage sludge to the soil. Urban soil does not only act as a net accumulator of trace elements but also provides a significant amount of them to the atmospheric aerosol and, particularly, to street dust. Plant and human being are the main objects of urban environmental geochemistry. The study of tree ring data indicates that the width and the content of trace elements of tree ring variated obviously in the city. The degree of the air pollution can be designated by the content of some elements or compounds and the studies of the content of trace elements in bark and leaf have drawn many researchers' attention. The trace elements content of human body, especially blood, hair and urine, is of great value to indicate the urban environment. The basal stability of a city can be studied by detected the content of Rn, Hg, He, CO2, SO2, O2, CH4 and other hydrocarbons in soil gas and some gas isotopes, such as 13C, 3He/4He. The importance of urban environmental geochemistry in stone carves and cultural relic is indicted by the studies about the damage of marble carves in the open air caused by the air pollution and acid rain and the destroying of stone carves caused by the crystal process of all kinds of salts. The urban environmental radioactivity is also among the investigations of the urban environmental geochemistry, especially the indoorradon in cities. 2 Main problems of urban environmental geochemistry As a new sub-discipline of environmental geochemistry, urban environmental geochemistry involves many aspects about urban environment and is important to the sustainable development of the urban environment. But according to the research state and characteristics of urban environment, there are still some problems of research contents and methods. The problems about research contents can be concluded as followings: (1) The research area not only includes the city zone, but also includes the producing area of the main material needed by the city that is always ignored; (2) Most studies on urban environmental geochemistry aim at the outdoor environment, While few are about indoor environment; (3) Air, soil, water, organism and geology in city are the main objects studied by urban environmental geochemistry and they are usually considered isolated, while there are few comprehensive studies based on geochemistry about urban environment; (4) At present, most projects are launched to study the distribution, translation of element in all environmental factors and their effects on health, while the study about treatment and restoration of the polluted environment is often ignored. Furthermore, there are still some problems in the study of about urban environmental geochemistry, including sampling and disposal of geochemical samples, analyzing, geochemical valuation of urban environmental quality and expression of research result. 3 Future trends of urban environmental geochemistry Urban geochemistry will have to keep growing in pace with the increase in urban population around the world. It has already proved to have the capacity to bring about fundamental changes in urban life, as demonstrated by the gradual phase out of leaded petrol after decades of geochemical research on urban lead. However, a large number of questions about the urban environment have not been adequately or completely addressed yet. The modelling of the urban environment in terms of geochemical cycles, for example, is difficult due to the complex mixtures of materials constantly undergoing change. The challenge of this "multicomponent, multiphase" environment is likely to keep geochemists busy for some time to come. Urban geochemistry has been characterized from the beginning by the high social impact of its research, an ingenious ability to modify, combine and improve tools borrowed from other disciplines, and a wide spectrum of interests and challenges. Taking all these considerations into account, it is fair to assume that urban geochemistry will continue to generate exciting scientific...