【作者】 秦松；

【导师】 南忠仁；

【作者基本信息】 兰州大学 ， 环境科学， 2008， 硕士

【摘要】 城市街道灰尘(Urban Street Dust)是城市环境学的研究对象之一。与城市土壤和大气颗粒物相比,城市街道灰尘是一种物质组成和来源更为复杂的环境介质,在交通运输、工业生产和城市建设等人类活动的强烈干扰影响下,包含了特定的环境信息和污染指示作用,成为城市环境污染的重要来源。兰州市西固城区是一个重工业河谷型城市,具有半个多世纪的工业发展史,重金属在街道灰尘中的不断累积不但对当地生态环境造成面源污染,而且对人体健康也会构成潜在威胁。因此,开展兰州市西固城区街道灰尘重金属含量及相关基础研究,具有较为深远的科学意义和现实意义。本论文以兰州市西固城区街道灰尘为研究对象,测定了街道灰尘的粒径组成、有机质含量和Cu、Zn、Pb、Ni、Cr、Cd等六种重金属元素的含量,研究了各重金属在西固城区街道灰尘中的含量统计与分布特征、来源、污染现状及潜在生态危害。研究结果表明:(1)研究区街道灰尘颗粒物中,粗砂(1-0.25mm)仅占7.79%,细砂(0.25-0.05mm)占47.05%,粉粘粒(＜0.05mm)占45.16%,自然降尘和人为活动对城区街道灰尘粉粘粒的贡献率分别为37.67%和62.33%。西固城区街道灰尘有机质含量均值为7.10%,大大高于兰州城区表土和灰钙土中有机质含量,服从对数正态分布特征。(2)统计分析结果表明:①、西固城区街道灰尘中Cu、Zn、Pb、Ni、Cr、Cd含量算术平均值分别为75.70mg/kg、350.03mg/kg、110.77mg/kg、167.38mg/kg、144.24mg/kg、2.87mg/kg,依次为城郊对照点街道灰尘中相应重金属含量的2.99倍、3.38倍、2.38倍、3.70倍、1.37倍和1.74倍,Cr受当地城区与城郊人类活动强度差别的影响相对较小。②、Ni、Cr含量在国内外均处于较高水平,而Cu含量处于较低水平;Zn、Pb、Cd在国内处于中等含量水平,而在国外处于较低含量水平。③、六种重金属元素的含量都高于相应地壳丰度值,也远高于我国土壤的自然背景水平;Ni、Cd及Zn的累积已非常明显,不利于维护人体健康,可能对城区街道两旁植物正常生长产生相对更大的威胁。(3)重金属含量分布规律如下:①、人类活动强度对于街道灰尘重金属含量的累积产生正效应,各重金属含量在不同功能区的分布表现出一致性:北部工业片区＞中部缓冲过渡区＞南部生活片区＞南部城郊对照点,具有从北向南递减的大致趋势,尤以Zn、Pb、Ni、Cr四种元素最为明显;②、Cu、Cd二元素含量分布受土地利用方式差异的影响相对较小,工业活动对西固城区街道灰尘中Zn、Pb、Ni三元素的含量分布有重要的影响,Cr元素的累积受工业活动的影响较小;③、本文划分的灰尘粒径对西固城区街道灰尘中Cu、Zn二元素的含量累积都无显著性影响。Pb、Cr两元素更易在0.25～0.074mm粒径街道灰尘中累积,Ni元素更易在0.074～0.050mm粒径街道灰尘中累积,Cd元素则更易在＜0.050mm粒径街道灰尘(粉粘粒)中累积。(4)相关分析和主成分分析结果表明:Cu、Zn、Pb、Cd四种重金属元素含量两两之间呈显著正相关,主要来自于工业和交通运输活动排放,其中Zn、Pb、Ni三元素部分工业来源来自钢材的磨损;Cr元素含量与其他5种重金属元素以及有机质含量之间都不具有显著相关性,主要来自土壤的风化。工业和交通活动来源占61.54%,自然来源占18.57%,其他来源占19.89%。各重金属元素之间的含量关系与元素表生地球化学特征有关。(5)地质累积指数和潜在生态风险评价结果表明,西固城区街道灰尘Cd属于偏重污染,Ni处于中污染水平,Cu、Zn、Pb三种元素均处于偏中污染水平,Cr仅受到轻污染;研究区街道灰尘重金属Cd含量的潜在生态危害极强,达Ⅴ级水平,而重金属Cu、Zn、Pb、Ni、Cr含量的潜在生态危害均轻微,为Ⅰ级水平。城区街道灰尘重金属潜在生态危害指数为698.29,总的潜在生态风险很强,达Ⅳ级水平。更多还原

【Abstract】 Urban street dust is an important research object in urban environics.Compared with urban soil and atmospheric particles,urban street dust is an environmental medium with complicated composition and multi-sources.Influenced by the human activities including traffic transportation,industrial production and urban construction,etc.,urban street dust itself accumulates a component of pollutants such as heavy metals,contains important indicator information for environment pollution,and becomes a significant source of urban environment pollution.As a valley and a heavy industrial city,Xigu region of Lanzhou city has more than a half century’s history of industrial development.Heavy metals accumulated in the street dust of this city may be not only a non-point pollution source of ecological environment,such as urban soil and rivers,but also a potential threat to urban human health.And so,it significantly has realistic and scientific meaning to study on heavy metal pollution in urban street dust at the study region.The particle size composition,organic matter content and concentrations of six heavy metals(Cu,Zn,Pb,Ni,Cr,Cd)in urban street dust of Xigu region were determinated.On this basis,this dissertation studies content levels,accumulation characteristics,source, pollution status and potential ecological risk of heavy metals.The main conclusions of this study can be summed up as follows:(1)Rough sand particle(1-0.25mm)content(w/w)accounted for only 7.79 percent, fine sand particle(0.25-0.05mm)content(w/w)47.05 percent,and powder clay particle (＜0.05mm)content(w/w)45.16 percent.The contribution ratio of natural dustfall and human activities are 37.67 and 62.33 percent,respectively.The average organic matter content is 7.10 percent,higher than those of topsoil and gray calcium soil of Lanzhou city.(2)The results of statistical analysis indicate that:①The average contents of Cu,Zn, Pb,Ni,Cr,Cd in urban street dust of study region are 75.70mg/kg,350.03mg/kg, 110.77mg/kg,167.38mg/kg,144.24mg/kg and 2.87mg/kg respectively,which are 2.99, 3.38,2.38,3.70,1.37,1.74 times as high as those of heavy metals in suburb street dust of control points.②The contents of Ni and Cr have higher levels in the world,and Cu is at a lower level.However,the contents of Zn,Pb,Cd are at medium levels in domestic and lower levels in abroad street dust.③The contents of six heavy metals are higher than crustal abundance and natural background in alkaline soil of China.Moreover,Cd,Zn,Ni are significantly cumulative and may threat to human health and roadside plant.(3)The distributions of heavy metals in street dust:①The impact of anthropogenic activities’ intensity on the accumulation of heavy metal contents is positive,and the content distribution from high to low is following northern industrial area,central buffer zone,Southern residential area and suburb control point.What is,from north to south,the concentrations of heavy metals gradually reduce,especially for Zn,Pb,Ni and Cr.②The distributions of Cu and Cd are less influenced by land use types.Industrial activities play a more important role in the contents of Zn,Pb and Ni in street dust of Xigu region,but not the same to the content of Cr.③The difference of three dust particle sizes have no obvious impact on the contents of Cu and Zn.However,Pb and Cr are more easily accumulated in street dust particles of 0.25-0.074mm,Ni those of 0.074-0.050mm,and Cd those of＜0.050mm(powder clay).(4)The results of pearson correlation analysis(CA)and principal component analysis (PCA)showed that there are significantly positive correlations among the contents of Cu, Zn,Pb and Cd,which may mostly come from traffic transporation and industrial production emissions.Furthermore,the contents of Zn,Pb and Ni also have significantly positive correlations,and the source maybe fretted steel products.However,there is no significantly correlation between Cr and any other heavy metal or organic matter content, which may indicate that Cr mainly comes from weathering soil.Totally speaking,the source of industrial and traffic activities occupies 61.54 percent when the nature source occupy 18.57 percent and the other source 19.89 percent.(5)The queue of geoaccumulation indexes of six heavy metals in street dust is:Cd＞Ni＞Pb＞Zn＞Cu＞Cr,and that of potential ecological risk indexes is:Cd＞Ni＞Pb＞Cu＞Zn＞Cr.The potential ecological risk of Cd is the highest element whose content is LevelⅤ,and all the other five element contents are LevelⅠ.However,total potential ecological risk index of six heavy metals is 698.29,LevelⅣ.更多还原