| Great increases in population and industrial production in big cities have been accompanied by a rapid increase in contamination. Big cities produce more and more of pollutants than other regions in pollutant sorts and quantities. These contaminations are potentially harmful to the environment and human health. Soil is polluted by some of those contaminations as a result of both natural environent and human activities. Then, the contaminated soil is come to be a pollution source again to water resources and atmosphere. Among those contaminations, more attentions are paid to the heavy metals. In this dissertation, based on the investigation of the concentrations of soil heavy metals in the suburbs of Beijing, the spatial distributions of soil heavy metals were analyzed, and the pollution levels were assessed. Given the characteristics of the spatial distribution we obtained from the analysis, the effects on vegetable production are discussed: the strategies for decelerating the pollution are also presented. There are there main parts of this dissertation. The first is the description of concentrations and pollution levels of heavy metals in the soils of the suburbs of Beijing: the second is the research of the sptial distribution of soil heavy metal: the third is the description of concentrations and pollution levels of heavy metals in the vegetables of the suburbs of Beijing. Soil and vegetable samples were collected in the 13 districts and counties except for mountainous area, sampling distance between points is about 1-2km. 351 soil samples, 157 vegetable samples with 20 species including leaf, root and fruit types were collected Six heavy metals including Cu, Zn, Cd, Cr, Ni and Pb were selected to heanalyzed. Concentrations of soil heavy metals were analized using Method 3030B issued by USEPA . State criteria issued by Chinese government are followed in the analysis of vegetable Standard reference materials. For Cu, the criteria are GB/T5009. 13-1996, for Zn, GB/T5009. 14-1996; Pb, GB/T5009. 12-1996: Cd, GB/T5009. 15-1996; Ni, GB/T6343-1996 and Cr, GB/T14962-94. Except for Cr, soil concentrations of Ni, Cu, Zn, Pb and Cd in Beijing were now higher than the background values of natural soil. The values for Cu, Zn, Pb, and Cd were even beyond the criteria of the 2nd Standard of Soil Environmental Quality. As is said to the percentage between the samples overrunning the background, the highest for Cd is 24.3%, then the order is Pb> Cu> Ni>Zn. For the percentage between the samples overrunning the criteria of the 2nd Standard of Soil Environmental Quality, the highest was alsofound for Cd, 6.86%, then Cu>Zn>Pb Soil concentrations in Beijing are very high compared with that of the other countries. All concentrations of those 6 heavy metals are higher than the average in the United States of America. They are also higher than the average of the world except for Cd and Cr. Compared with the results of the survey conducted between 1976-1979, the concentrations are increasing except for Cr. the highest increasing rate is, tbr Cd, 3 times of the values obtained in the former investigation. It indicates that soil pollution caused by heavy metal in Beijing has been becoming more and more serious over the last 20 years. The correlationships between soil concentrations of different heavy metals are also statisted. The results show that the relationship between Cu and Zn, Zn and Cd are significant (a=0.0 1), and between Ni and Cr, Cu and Cd. the significant level is...
|
PDF Full Text Request