西安市表层土壤重金属污染的环境地球化学研究

【作者】 陈秀端；

【导师】 卢新卫；

【作者基本信息】 陕西师范大学 ， 区域环境学， 2013， 博士

【摘要】 西安市地处关中平原,是中国西部地区的核心城市。随着西安城市化进程的不断推进,尤其是国际化大都市的建设,人类活动排放的大量污染物进入城市生态环境,造成城市环境污染,城市土壤成为污染物的主要承载介质之一。本文以西安市三环内的表层土壤为研究对象,通过多种实验手段测定土壤的理化性质、重金属全量和存在形态,运用SPSS、GIS、Excel、Matlab等软件,利用地统计学的空间变异函数和克里格插值方法,研究西安市表层土壤中重金属的空间分布特征,采用污染负荷指数、潜在生态危害指数等模型研究西安市表层土壤中重金属的污染特征、环境风险及综合污染的空间差异,探究土壤重金属来源研究的新方法,为西安城市土壤环境管理提供借鉴。通过以上的研究,得到以下研究结论：1.西安市表层土壤的理化性质具有一定的空间差异,与城市绿地类型以及城市化水平具有一定关系。西安市表层土壤中As、Ba、Co、Cr、Cs、Cu、Mn、Ni、 Pb、Sn、Sr、V、Zn等13种重金属元素的平均值分别是褐土背景值的0.99、1.20、1.46、1.35、1.08、1.67、1.05、1.10、2.12、2.28、1.48、1.00和1.71倍,As、Cu、 Pb、Zn、Cr、Ni的平均含量均远低于国家土壤环境质量三级标准(GB15618-1995)的含量值。在不同绿地类型土壤中,Pb、Zn、Cu、Sn、Cr的含量差异较大；而As、Co、Cs、V、Ni、Mn、Sr、Ba等元素在不同绿地类型土壤中的变化不大,且Mn、Ni、V的平均含量均略高于褐土背景值。2.形态分析表明,重金属的迁移顺序为Pb(60.79%)>Mn(60.12%)>Zn(46.64%)>Cr(44.55%)>Co(41.59%)>Ni(32.75%)>Cu(31.43%),其中60%以上的Pb、Mn可以迁移,危害较大,都应成为优先防控对象。3.由于不同城市区域中人类活动的密集程度和重金属元素的来源不同等原因,重金属在不同圈层的累积程度不同。城墙内区域和城墙至二环区域的土壤中Cr、Cu、Co较为稳定而Pb、Mn、Zn三种元素的活性较强,易被迁移转化；二环至三环的区域土壤中Cu、Ni、Zn较为稳定而Mn、Pb的稳定态含量较低。行政区功能特征的不同导致土壤重金属的累积和赋存形态也具有较大的差异。西安市三环内表层土壤中所研究13种元素的含量与采样点到市中心的距离呈非线性关系。基于GIS的分析表明,不同重金属元素在西安市的空间分布规律不同。As、Mn、 Ni、V具有相似的空间分布趋势,尤其是Mn、Ni、V的最高值和最低值出现的区域具有相同性。西安市表层土壤Cu、Pb的空间分布特征相近,高值区均分布在交通密集,且工业企业分布众多的城市中心区域和传统工业密集的城西区域；低值区主要分布在交通流量相对小、人口密度低、工业企业分布较少的东南曲江旅游度假区和东北浐灞生态新区；西安市表层土壤Sn含量的空间分布特征不明显。元素Ba则表现出城西较高、城中较低、城东北较高的空间分布特征；土壤Zn含量的高值区具有交通密度较大,城市道路与铁路混合分布的特征,且布局较多的工业企业,西安市传统工业区土壤Zn含量也较高,低值区主要分布在西安市东北的浐灞生态区和东南的曲江度假旅游区。土壤Co的空间分布表现为城西和城东北较高而东南较低的特征,两倍于褐土背景值的区域主要分布在城东北区域和城西车城附近；元素Cr含量的低值区分布在西安市东北的浐灞生态新区,高值区分布在西安市西郊工业区；西安市表层土壤Sr的含量的空间分布特征为自西北向东南递减,东南的曲江旅游度假区的土壤Sr含量较低。西安市三环内大多数地区的土壤Cs含量低于褐土背景值而城市北部和西南部的局部地区的Cs含量略高于褐土背景值。此外,同一元素的不同赋存形态的空间分布也存在差异。4.污染评价结果表明,西安市表层土壤重金属的PLI为1.27,属于中度污染水平,存在空间区域上的差异。西安市表层土壤中Mn、V受人类活动影响程度较轻,As、Ba、Co、Cr、Cs、Cu、Ni、Pb、Sn、Sr、Zn等11种重金属元素的污染的区域差异较大,西安市域内均存在不同范围和程度的累积,尤其是人类活动对重金属Cu、Pb、Sn等元素的累积影响较大,存在污染较严重的局部地区。西安市表层土壤总体上存在中等程度的潜在生态危害,272个样品中分别有95.58%、1.84%、1.84%、0.74%的样品存在中等程度、轻微程度、较高程度、高的潜在生态危害。西安市表层土壤中重金属的单项潜在生态危害指数的平均值按照以下顺序减小：As(9.90)>Cu(8.38)>Pb(7.37)>Co(7.29)>V(5.68)>Ni(5.51)>Zn(4.11)>Cr(2.71)>Mn(1.05),所有元素均存在轻微潜在生态危害。5.来源分析表明,多元统计分析方法将13种元素归为五类,基于最小生成树的分类模型与其分类结果相同,即As-Mn-Ni-V、Ba-Zn、Co-Cr-Sr、Cu-Pb-Sn、Cs,说明最小生成树分类模型在土壤来源分类领域具有一定应用价值。利用GIS将因子分析结果插值得到五个因子的空间分布图,与交通分布图和企业分布图相叠加,解析西安市表层土壤重金属的来源。第一组元素As-Mn-Ni-V主要受自然因素——成土母质的影响,为自然因子。第二组元素Cu、Pb、Sn在城市土壤中的累积主要来源于城市交通活动。第三组元素Ba-Zn被看作是交通活动、工业生产活动和居民活动综合作用的结果,为综合因子。第四组元素Co、Cr、Sr在城市土壤中的累积主要受工业生产活动的影响,为工业因子。第五组元素Cs的累积既受自然因素的影响也受多种人类活动的作用,为混合因子。更多还原

【Abstract】 Xi’an city, located in the Guanzhong Plain, is the core city of western China. With the urbanization of Xi’an city, especially the construction of the international metropolis, the emissions of pollutants from human activities into the urban ecological environment caused some urban environment pollution, and urban soil was one of bearing medium. In this paper, the physical and chemical properties, concentrations and chemical speciation of heavy metals were measured with a variety of experimental methods. The contamination characteristics and environmental ecological risks of heavy metals in Xi’an topsoil were evaluated based on the pollution load index and potential ecological hazard index. The Kriging interpolation methods with GIS were used to studying the characteristics of the spatial distribution of heavy metals and integrated pollution level in Xi’an urban topsoil. Combined statistical and mathematical methods, the main source of heavy metal accumulation in the surface soil from Xi’an city were sorted out. And a new research method had been done to probe the sources of heavy metals in topsoil. The conclusions would provide some reference for the soil environment management of Xi’an city. Through the above research work, the following conclusions as follows:1) Some spatial differences with related to greenland types and the level of urbanization, were found in the physical and chemical properties of the topsoil from Xi’an city. The average concentrations of As, Ba, Co, Cr, Cs, Cu, Mn, Ni, Pb, Sn, Sr, V and Zn in Xi’an topsoil were0.99,1.20,1.46,1.35,1.08,1.67,1.05,1.10,2.12,2.28,1.48,1.00and1.71times soil background values of cinnamon soil, respectively. The average concentrations of As, Cu, Pb, Zn, Cr, Ni were below the three national soil environmental quality standard (GB15618-1995). Some significant difference were found in the concentrations of Pb, Zn, Cu, Sn, Cr in those soil from different types greenland, but that of As, Co, Cs, V, Ni, Mn, Sr and Ba were little difference. The concentrations of Mn, Ni, V were slightly higher than the background values of cinnamon soil.2) The results of chemical speciation analysis showed that the migration of heavy metals was in the order of Pb (60.79%)> Mn (60.12%)> Zn (46.64%)> Cr (44.55%)> Co (41.59%)> Ni (32.75%)> Cu (31.43%). And Pb and Mn should become a priority objects to be prevented and controlled, of which more than60%of the concentrations of Pb, Mn could be migrated and cause some harm for ecological environment.3) The study results of spatial distribution showed that the accumulation of heavy metals in different spheres were different due to varying intensive degrees of human activities and different sources of heavy metals. It should be paid attention that Cr, Cu and Co were relatively stable and Pb, Mn and Zn were converse and easy migration in those areas within the city walls and from the city wall to the Second Ringroad. It was more stable for Cu, Ni, Zn, but lower concentrations of stable states for Mn and Pb in the area from the Second Ringroad to the Third Ringroad. The different features of the different administrative area of Xi’an city resulted in the greater difference in the concentrations and chemical speciation of heavy metals. The concentrations of As, Ba, Co, Cr, Cs, Cu, Mn, Ni, Pb, Sn, Sr, V and Zn in topsoil inside Third Ringroad in Xi’an city showed the non-linear relationship with the distance from the center of the city.The characteristics of spatial distribution of every element were different based on the spatial analysis of GIS and geostatistical model. The spatial distribution characteristics of As, Mn, Ni and V content are similar, and the highest and lowest values of Mn, Ni and V appears to the same area. The spatial distribution characteristics of Cu and Pb in the topsoil in Xi’an are similar. Their high-value areas were distributed in those area of the city center and traditional industries intensive western region with heavily traffic and a large number of industrial enterprises, and low value areas were mainly distributed in Qujiang Resort District in southeast of city and Chanba ecological District in northeast of city with the low traffic, low population density and less distribution of industrial enterprises. The spatial distribution characteristic of the concentrations of Sn was not obvious, and the overall level was much higher than the background value of cinnamon soil. For Ba, the concentration was higher in the western region and northeast region, but the lower in middle region. The high value area of Zn had the characteristics of the high traffic density (mixing distribution of urban road and rail) and the intensive industrial enterprises. And the concentration of Zn in topsoil from Xi’an traditional industrial zone was also higher, but that from Chanba ecological District in the northeast and the Qujiang vacation area in the southeast of the city were lower. The spatial distribution characteristics of Co in topsoil manifested as higher in the western and northeastern regions and the lower in southeast of the city. Those areas of the concentrations twice the background value of cinnamon soil were mainly located in the northeast region and western car-city nearby. The low concentration areas of Cr was distributed Chanba Ecological District in the northeast of Xi’an city, and high-value areas were located in the western industrial district of Xi’an, surrounding the railway line distribution. The concentrations of Sr in topsoil within the Third Ringroad in Xi’an city decreased from northwest of the city to southeast of the city, and that was lower in topsoil from Qujiang tourist Resort in the southeast of city. The concentrations of Cs were lower than the background value of cinnamon soil in most parts of city, but slightly higher than the background value of cinnamon soil in the local area of the north and southwest of the city. And the characteristic of spatial distribution of different speciation of the same element were different.4) The pollution evaluation results showed that PLI was1.27, indicating moderately polluted level in Xi’an topsoil. The contaminations of Mn and V were affected to a lesser extent by human activities. There were large regional differences in the contaminations of As, Ba, Co, Cr, Cs, Cu, Ni, Pb, Sn, Sr, Zn in the surface soil of Xi’an city, and the extent of the accumulation of these elements were different. Some sever pollution area for Cu, Pb, Sn, which related to larger cumulative impact of human activities were found. The results of ecological risk analysis showed that there was moderate potential ecological harm in Xi’an topsoil generally. And there were moderate, slight degree, higher degree, high potential ecological risk in95.58%、1.84%、1.84%、0.74%of272samples, respectively. The average individual potential ecological risk index of heavy metals in the surface soil of Xi’an reduced in the following order:As (9.90)>Cu (8.38)>Pb (7.37)>Co (7.29)>V (5.68)>Ni (5.51)>Zn (4.11)>Cr (2.71)>Mn(1.05). And there was slight potential ecological harm for all elements.5) All elements were grouped into five categories using multivariate statistical analysis. There were the same classification results based on minimum spanning tree classification model, which were As-Mn-Ni-V, Ba, Zn, Co-Cr-Sr, Cu-Pb-Sn, Cs. Therefore the classification model based minimum spanning tree was a valuable research method for the field of soil source classification. The GIS interpolation maps with five factors from factors analysis, overlaying traffic maps and enterprises maps were used for analyzing the sources of heavy metals in Xi’an urban topsoil. The first set of elements (As-Mn-Ni-V) was natural factors, which were mainly affected by the soil parent material. The accumulation of second set of elements (Cu, Pb, Sn) in urban soils were mainly related with urban traffic, which was traffic factor. The third group of elements (Ba, Zn), as the result of the combined affects of the industrial production activities, traffic emission and the activities of citizens, was comprehensive factor. The fourth set of elements (Co, Cr, and Sr) in urban soils was mainly affected by the impact of the industrial production activities, which was industrial factor. The fifth group element, Cs, which was affected by natural factors and human activities, was the blending factor.更多还原