Research On Distribution Characteristic Of The Soil Heavy Metals And Assessment Of The Soil Environmental Quality In Changchun

With the development of the urbanization and the increase of urban population density, the human activity imports a large amount of heavy metal to the urban soil, which causes the pollution of heavy metal in urban soil more and more serious. The urban soil heavy metal which is transported through ground dust, surface runoff, and food chain destroys the urban entironment seriously, and endangers human health. This paper makes a comparatively systematic summary in characteristics, sources, and harmfulness of the soil heavy metal and the current domestic and international situation in the soil heavy metal. The soil of Changchun city is regarded as the research object in the paper. 352 surface soil samples are collected. And using the statistical software SPSS, analyze pH, mineral element, the content of As,Hg,Zn,Cd,Cu,Pb,Cr in the soil, and study the variety of content of urban soil element, distribution law and geographic spatial division. With the single pollution index method and the Nemero comprehensive pollution index method, estimate the soil heavy metals pollution of Changchun, and draw the contaminate degree chart of each assessment factor and the soil general quality chart of Changchun based on the interpolated result of Surfer and software ArcGIS and count different pollution grade or level area. Then, the model that appraisal for the soil environmental quality in Changchun is set up with application of software MATLAB7.0, according to Soil Environment Quality Standard (GB15618-1995), it appraises whether the soil of Changchun can reach and ensure agricultural production and safeguard the quality level of the human health. In order to explain the accuracy of the result, compared the result of Artificial Neural Networks with the result of Discriminant Analysis and Fuzzy Comprehensive Evaluation, the two results have good agreement. According to the result above and the spatial analysis function of GIS, choose 46 seriously polluted points in 352 sampling points in Changchun, then probe into mainly pollution source and distribution law and put forward the corresponding prevention method by Factor Analysis Method. The result of the study shows:1. As the promotion of the urbanization, there is trend which is rising gradually in the soil PH value of top layer of the research area, rely mainly on neutrality and alkalescence, which relates to the fact that the content of carbonate rises gradually in the soil. PH value of agricultural land in suburb is small and the soil assumes acidity, while the soil in industrial area possesses big pH value and assumes alkalescence. The main reason is that the soil in the industrial area often mixes with building offal, cement, fragment of brick and other alkaline mixture, etc., so Ca releasing into the soil causes PH value of the soil being difference to natural soil obviously.2. Soil mineral element Ca and P have biggish changes in the research area, the coefficient of variation is 44.4% and 41.7%. The maximum value and the minimum value of Ca can differ by 5.9 times, the maximum value and the minimum value of P can differ by 13.4 times. The content of K, Na, Mg, Al, Fe is comparatively identical among the soil of Changchun. The distribution law of the seven kind of mineral elements is: K, Na, Mg, Al, Fe are normal distributions, Ca, P are lean normal distribution, the space whose distribution frequency is the most is: K :0.0252~0.0268;Na:0.0167~0.0184;Mg:0.0117~0.0138;Al:0.1325~0.1475;Fe:0.04~0.05;Ca:0.012~0.025;P: 4~9.3. Using the locating function for space position of Arcgis, according to different regions, carve up 352 pieces of soil sampling point of Changchun. According to the distribution characteristics of soil heavy metallic element in different regions, the content of seven kinds of heavy metal is lower than the environmental background value of soil in Economic and Technological Development Zone and New Technology Development Zone; the content of heavy metal exceeds the environmental background value of soil of Changchun, in Erdao Department, Kuancheng Department and Nanguan Department, mainly because the main factory of Changchun is mostly distributed in Tiebei-Erdao industrial areas, influenced by human factor, makes soil environmental quality worsen. 4. Relevant relations exist among the content of heavy metallic element, pH, total Fe and total Mn. The correlation coefficient of arsenic with total Fe and pH value is 0.306, 0.131; the correlation coefficient of Cr with total Fe and total Mn is 0.561 and 0.348; three kinds of elements Cu, Pb, Zn present prominent and extremely prominent relevance with total Mn and pH value; some metallic elements also have a certain relevance between, among them, Cu, Pb, Zn are close and distant elements, so have prominent relevance.5. The topsoil has already been polluted by the heavy metal in various degree in Changchun. Cr has slight pollution only in the small area near Volkswagen of the First Automobile Factory, the pollution area is rounded in shape; the content of Pb is relatively high in the main streets and near the square; Cu obviously pollutes in a few factory districts; As is mainly distributed in Tiebei-Erdao industrial area, sulfuric acid factory, Cu smeltery and fur factory, these locations relatively concentrate distributing area for the industry and the old city zone of Changchun, pollution range takes the form as a island, there is a severe contaminated area of small area in the eastern gear wheel factory; the contaminated area of Cd is mainly distributed in the area to the north of the Jilin road, only localization for NO.1 and NO.5 chemical plants, diesel engine manufactory, there is fragmentary slight pollution in other places; the area where Hg is high-load is distributed in Changchun urban area and surrounding area, the sulfuric acid factory, smeltery, meteorological instrument plant, printing factory, rubber plant are in order to mainly pollution area; The contaminated area of Zn is irregular in shape or the alone island form is distributed in the Tiebei-Erdao industrial area.6. According to the degree of pollution of seven kinds of heavy metal of topsoil in Changchun, As is the most serious in pollution, the regional area of serious pollution reaches 4.02km2, secondly it is Hg, though the regional area of serious pollution is 1.63 km2, the regional area of slight pollution is the largest, have already reached 10.16 km2. The pollution of soil heavy metal in Changchun is in order: As>Hg>Zn>Cd>Cu>Pb>Cr; from the polluting area, the pollution of Tiebei-Erdao industrial area is the most serious especially near sulfuric acid factory, smeltery, chemical plant, fur factory, form the severe contaminated area which is in irregular; from the administrative area, seriously polluted in proper order: Erdao Department>Kuancheng Department> Nanguan Department>Luyuan Department>Chaoyang Department> Economic and Technological Development Zone>New Technology Development Zone; from geographical distribution, urban area> suburb, north > south of urban area.7. According to Environmental Quality Standards in Soils, the Changchun soil environment quality is appraised. Generally speaking, the research area has good the environmental quality, basically keeps the natural level, and does not threaten agricultural production and human health. In 352 soil sampling points, 321 belong to primary quality standard, 31 belong to secondary quality standard. The results of Artificial Neural Networks, Discriminant Analysis and Fuzzy Comprehensive Evaluation have been compared, there are 90%-93.75% of the sampling points whose results are thought accordant, have made better appraisal result.8. There are four main sources of soil heavy metal pollution in Changchun, I.e.: the pollution sources of traffic, the area whose factor scores in the high value, including the sampling points CCT191, CCT192 and CCT340; the pollution sources from coal, household coal, industrial coal and the lag of burning way are the main reasons for the pollution of the top layer soil of Changchun; the industrial pollution sources, the area whose factor scores the high value is distributed in Tiebei-Erdao industrial area, mainly from the discharge of the industrial sewage; the Metallurgical pollution sources, the contaminated area is mainly distributed in Tianlin Smeltery which is in the north in urban area of Changchun (CCT138), Lanzhou Smeltery (CCT214) and near Huoshaoli in the west and near the steel mill in center(CCT343). So the key of preventing and curing the pollution of the topsoil heavy metal in Changchun is the administration of industrial pollution and adjustment of energy structure.