Shanghai Soil Heavy Metal Spatial Distribution Characteristics And Its Causes

In this paper, the Shanghai area was used as the studying case, the representative of the industry, roads, suburban agricultural soils was selected as the research object. Based on the data that had been collected from various sources as well as the soil samples that had been collected on the spot and analyzed, the methods of combining the multivariate statistics and geo-statistical together are put into use to give a systematic analysis on the spatial distribution regularities, source characteristics, the contamination of the heavy metal and the connection of urbanization of the heavy metal which are belong to the three different type of soils mentioned above. Expect to provide scientific grounds for the Shanghai Urban Land Use Planning and the comprehensive improvement of suburban soil environment. The main conclusions are as follows:1. The results of the research in three kinds of soil-use types of Shanghai shows that the soils used for industrial, transportation and suburban agricultural all have emerged a net cumulative trend respectively, and showing a obvious trend of combined pollution. Since different Land-use types have different impact from human activities, there is a big difference in the accumulation levels, element type and the spatial distribution of heavy metals in soils.2. The results of research in the industrial soils show that except As, the heavy metals of Cr, Cu, Pb, Zn,Ni in Shanghai industrial soil has emerged a dramatic cumulative trend, pollution levels were as follows:printing and dyeing>chemical industry>machine building. By compare with the heavy metal cumulation condition of different type of industry soils as well as analysis we have found that Cr, Ni are mainly related with the discharge of pollutants, such as chemical and mechanical manufacturing enterprises; Pollutants in the production process of printing and dyeing enterprises may be the main sources of Pb, Cu, Zn; The content of As is consistent with the context value, and the main source is relevant with soil parent material.3. The results of research in the heavy metals in traffic soils shows that there have been combined pollution of soils in the three roads of the studying area, pollution levels were as follows:Guilin Road>Hongcao Road>Fuminsha Road. Through comparative analysis of the traffic roads found that Pb, Zn, Cu was mainly affected by the traffic activity, the impact of heavy metals were as follows:Pb>Zn>Cu; Of these heavy metals, The pollution index of Zn, Pb which in the particular points was significantly higher than normal point; vehicle speed, braking and other factors have a greater impact on it; Transport have little to do with the accumulation of Cr and Ni, the source of Cr, Ni may be mainly concerned with the emissions of pollutants from everyday life of the residents live alongside the road; The content of As is consistent with the context value, and the exceeding rate of the samples were the lowest, so the main source of As is relevant with soil parent material.4. The results of research in the agricultural land of Baoshan District shows that there has been a net cumulative trend in the agricultural soils. The proportion of heavy metallic element that exceed average background values of soil in Shanghai were as follows:Zn>Cd>Hg>Cr>Pb\Cu>As; Combining multivariate statistics and spatial structure analysis shows that the distribution of Cd and Zn in the agricultural soils were mainly affected by the spatial distribution of industries and traffic factors; The spatial distribution of Cr, Cu were mainly affected by the industrial activities; The spatial distribution of Pb was mainly affected by the transport factors; There is a close relationship between the distribution of Hg and wastewater irrigation in agriculture; Through the probability distribution of contour lines of the critical value, it can be found that the Cd, Zn, Cr, Cu, Hg come mainly from the point sources of pollution, but the source of Pb is relatively dispersed.5. The results of research in the connection of urbanization level and the contamination of heavy metals in suburban soils show that the relativity of Zn single factor contamination index, Cu single factor contamination index and Comprehensive contamination index shows obvious positive correlation with the urbanization level,present typical features of EKC, the relevance among Pb and Cr in single factor contamination index with urbanization level is not obvious, But, research on EKC curve analysis shows that all suburban districts had not crossed the inflection point excepting Min-hang District, they are still in the left side of the EKC curve; Compared to the time of which industrial waste discharge volume, industrial COD discharge and SO₂ emissions crossed the inflection point, the time of soil heavy metal pollution indicators across the inflection point lags long behind.