渭河咸阳段沉积物重金属污染研究

【作者】 翟雨翔；

【导师】 卢新卫；

【作者基本信息】 陕西师范大学 ， 环境科学， 2009， 硕士

【摘要】 随着我国经济的快速发展和城市化进程加速,我国城市区域内的河流污染愈来愈严重。在污染河流的众多污染物当中,重金属由于其毒性和持久性而成为影响河流较严重的一类。沉积物作为水环境中重金属的主要蓄积库,反映了水体受重金属的污染状况。研究沉积物中重金属的含量及水平分布可以判断研究区受污染的程度及污染来源,了解重金属的扩散范围;研究重金属在沉积物柱状样不同层位的含量分布,则可了解所研究区域重金属的污染历史;把重金属含量与未污染区背景值进行对照,可反映出不同历史阶段人类活动对所研究区域重金属输送量的变化情况。本研究以渭河咸阳段为研究区域,经过详细调查、采样和实验分析,首次系统地研究了渭河咸阳段沉积物的理化性质（pH值、电导率、CaCO₃、磁化率、粒径、烧失量）。用X-Ray荧光光谱仪测量了沉积物中Cu、Cr、Pb、Zn、Mn和Ni元素的全量;采用BCR四步连续提取法提取了沉积物中重金属Cu、Cr、Pb、Zn、Mn和Ni的四种形态,并用原子吸收分光光度计火焰法分析测定了渭河咸阳段表层和柱状沉积物样品中这六种重金属元素的赋存形态;通过相关分析研究了重金属之间、重金属全量与形态之间以及重金属与各理化指标间的相互关系,以期为渭河流域资源合理开发与防治重金属污染提供参考依据。本研究的主要结论如下:1.理化指标分析结果显示:渭河咸阳段沉积物为碱性沉积物,质地类型主要为沙粒。各项理化指标的均值分别为:pH值8.041,电导率416μs/cm,烧失量为4.160%,低频磁化率(x_LF)为83.22×10^-8m³/kg,高频磁化率(x_HF)为82.18×10^-8m³/kg,频率磁化率(x_fd)为1.31%,黏粒为4.67%,粉沙粒为39.81%,沙粒为55.53%,CaCO₃为91.40g/kg。2.从整个研究河段来看,渭河咸阳段表层沉积物中Cr、Cu、Pb和Zn四种元素重金属含量的平均值均高于研究区环境背景值,其中Cr和Pb平均含量较高,分别高出环境背景值32.9%和34.3%,Cu高出环境背景值16.7%,Zn略高于环境背景值,超出6.2%。Mn和Ni的平均含量低于环境背景值,说明整体上这两种元素的人为累计量相对较小,但在某些断面仍表现出高富集现象,所以也需引起注意。渭河咸阳段表层沉积物重金属元素的平均含量从大到小依次为:Mn＞Cr＞Zn＞Cu＞Ni＞Pb。在空间分布上,各表层沉积物中重金属元素含量上总体均呈先升高再降低的趋势,各重金属元素的高值区均位于渭河咸阳段中游至下游段,渭河咸阳段各采样断面的重金属累积叠加值由高到低依次为:断面2＞断面3＞断面4＞断面5＞断面1。渭河咸阳段柱状沉积物的垂向分布上,总体上各个断面的大部分重金属元素平均含量呈波折多峰型分布,总量自上而下呈现逐渐变小的趋势,这表明研究河段的重金属污染在近些年有加剧的趋势。Cr在各断面上明显地呈不规则的锯齿状多峰分布特征,即随深度出现一至多个含量明显偏高的峰值,这可能与Cr的沉积后再迁移过程有关。Cu、Ni和Zn在每一个断面中有相似的垂向变化特征,这表明它们很可能相同来源。各段面Mn和Pb的垂向变化规律不明显。3.渭河咸阳段表层沉积物中重金属形态分析结果显示:总体上各重金属元素的主要赋存形式均是残渣态。各重金属元素的不同形态在不同条件下迁移转换的顺序分别是:在乙酸的弱酸性环境中:Mn（38.49%）＞Pb（27.66%）＞Ni（13.3%）＞Zn（9.09%）＞Cu（7.93%）＞Cr（0.00%）;在还原环境中:Cu（26.36%）＞Pb（12.81%）＞Zn（11.81%）＞Mn（11.71%）＞Ni（7.23%）＞Cr（0.00%）;在氧化性的环境中:Ni（13.09%）＞Cu（7.47%）＞Zn（5.42%）＞Pb（5.14%）＞Mn（3.96%）＞Cr（2.61%）。在整个环境介质中,整体发生迁移转化的顺序是:Mn（54.16%）＞Pb（45.61%）＞Cu（41.76%）＞Ni（33.62%）＞Zn（26.32%）＞Cr（2.61%）。柱状沉积物重金属形态分析结果显示:总体上各柱样中Cu、Cr、Pb、Zn、Mn和Ni的四种形态含量随深度均呈波折型分布,大多数重金属在乙酸提取态中表现出浅层含量高于深层,而在残渣态中则深层含量明显高于浅层,可还原态和可氧化态随深度变化趋势不明显。各断面大多数重金属的“非稳态”含量所占总量的比率也表现出上浅层高于深层,这与上述结论基本一致。4.重金属各元素之间的相关分析表明:Cr仅与Pb呈显著性相关,与其它4种重金属的相关性不显著,Cu、Zn、Pb、Mn、Ni五种重金属两两之间呈极显著性相关关系。重金属的“非稳态”与总量之间的相关分析表明:六种重金属这两项指标之间均呈显著的正相关关系。重金属的全量、赋存形态、“非稳态”分别与理化指标之间的相关分析表明:理化指标中Ec值、LOI、低频磁化率(x_LF)、高频磁化率(X_HF)、CaCO₃、黏粒和粉粒与各种金属的多数形态之间均显示出很好的相关性,表明这7种理化指标是影响渭河咸阳段沉积物中重金属赋存形态的主要因素;重金属中Pb、Cu、Ni、Mn和Zn与上述7种理化指标之间均呈极显著性正相关关系,也表明这7种理化指标是影响渭河咸阳段沉积物中重金属富集的主要因素;同时,“非稳态”也与这7种理化指标显示出很好的相关性,相关性结果基本一致。5.利用次生相与原生相的分布比值评价研究区域的结果显示:渭河咸阳段表层沉积物中Mn、Pb、Cu分别存在着轻度污染,其它元素不存在污染。Mn在四个断面（断面2、断面3、断面4和断面5）都存在污染,其中在断面2的次生相与原生相分布比值显示最高,达140%;Pb在两个断面（断面3和断面4）都存在污染,其中在断面4的次生相与原生相分布比值显示最高,达116%;Cu仅在断面3存在污染,次生相与原生相分布比值为116%。断面3的污染元素最多（Mn、Pb和Cu）,断面4有两种污染元素（Mn和Pb）,断面2和断面5的均存在Mn污染。6.从研究区域重金属分布位置看,重金属富集在断面2和断面3比较高,这说明这一段渭河沉积物重金属受污染源影响较大,其它断面变化不大,这表明主要受沉积物成土母质特点等自然因素影响,而Cr、Pb、Cu、Zn、Mn和Ni这六种重金属之间的相关性都很好,因此,可以得出结论:总体看渭河咸阳段沉积物中重金属含量是受沉积物母质及污染源的综合影响。更多还原

【Abstract】 With the rapid development of economy and acceleration of urbanization process,the pollution of China’s urban areas’ river is becoming more and more serious.Among the various contaminates, heavy metals have become more serious due to their toxicity and persistence.As the main accumulation of heavy metals in the water environment,sediments reflect the heavy-metal contamination of the water.We can determine the level of contamination and pollution sources in the research areas and know the spread of heavy metals according to studying contents and horizontal distribution of heavy metals in the sediment.Of course,we may know the history of heavy metals pollution in the research areas by way of studying their contents of core sediments in different vertical positions.Compared heavy metals contents of the core sediments with the background in non-contaminated areas,it reflects the change condition of human activities on the transportation amounts of heavy metals in different historical periods.Xianyang section of Wei River is regarded as the research-area in this thesis.According to full investigation,collecting samples and experimental analysis,it systematically studies the physical-chemical characteristics（pH value,conductivity,CaCO₃,susceptibility,particle size,loss on ignition） of this area for the first time.Total contents of Cu,Cr,Pb,Zn,Mn and Ni are determined by X-Ray fluorescence spectrograph.Chemical extractions of Cu,Cr,Pb,Zn,Mn and Ni in all of the sediments are studied by BCR four-step sequential extraction method.Also determined the fractionations of the six heavy metals in the area’s samples by flame atomic absorption spectrometry （AAS）.Through analyzing the interconnection between the heavy metals,heavy metals contents and their fractionation,as well as physical-chemical indicators of heavy metals,we want to provide a scientific reference for rational development of resources and prevention of heavy metals pollution in the Wei River.The main conclusions of this study are as follows:1.The results of analyzing physic-chemical indicators show that:the sediments of Xianyang section of Wei River are of alkaline.The sediments texture type is mainly the sand particle.The average value of various physic-chemical indexes is respectively:the pH value is 8.041,conductivity is 416μs/cm,loss on ignition is 4.160%,the low-frequency magnetic susceptibility(x_LF) is 83.22×10-8m3/kg,the high-frequency magnetic susceptibility(x_HF) is 82.18×10-8m3/kg,the frequency magnetic susceptibility(x_fd) is 1.31%,the clay content is 4.67%,the silty sand content is 39.81%,and the sand particle content is 55.53%,CaCO₃ is 91.40g/kg.2.Through the entire research river,the average contents of four heavy metals（Cr,Cu,Pb and Zn） in surface sediment from Xianyang section of Wei River are higher than environmental background value of the research area.The average contents Cr and Pb are higher than environmental background being worth 32.9%and 34.3%,The average content of Cu is higher than environmental background being worth 16.7%,The average content of Zn is a little higher than environmental background being worth 6.2%.The average contents of Mn and Ni are lower than environmental background,which shows that accumulated amounts of this two elements from man-made is relatively less on the entirety,however,some sections also show high concentration. Therefore,we also need some attention.The average contents of heavy metals in surface sediment from Xianyang section of Wei River are in the following order:Mn＞Cr＞Zn＞Cu＞Ni＞Pb.On the space distribution,the average contents of heavy metals in surface sediment assume that the trend rising first to reduce again,most of high value areas are located in the middle to lower sections of research area.The cumulative values of research sections are in the following order:section 2＞section 3＞section 4＞section 5＞section 1.The average contents of most heavy metals in each section are of twists and turns on the vertical distribution of core sediment from Xianyang section of Wei River.The total contents display the gradually changeable small trend from above to below,which indicates that heavy metals pollution in research area are aggravated in recent years.Cr assumes the jagged and irregular multi-peak distribution characteristic obviously in all sections,one or more significantly high peaks emerge with depth,which may be related to the deposition of Cr after the migration process.Cu,Ni and Zn in each section have the similar vertical distribution characteristic, which indicates them probably having the similar source.The vertical distribution characteristic of Mn and Pb in each section is not obvious.3.The results of analyzing fractionation of heavy metals in surface sediment from Xianyang section of Wei River shows that:In general the main fractionation of heavy metals is residual state. Each heavy metal in different forms under different relocation conditions are in the following order: in the acid extractable fractionations:Mn（38.49%）＞Pb（27.66%）＞Ni（13.3%）＞Zn（9.09%）＞Cu （7.93%）＞Cr（0.00%）;in the reducible fractionations:Cu（26.36%）＞Pb（12.81%）＞Zn（11.81%）＞Mn（11.71%）＞Ni（7.23%）＞Cr（0.00%）;in the oxidable fractionations:Ni（13.09%）＞Cu （7.47%）＞Zn（5.42%）＞Pb（5.14%）＞Mn（3.96%）＞Cr（2.61%）;In the environmental media, the overall migration and transformations is in the following order:Mn（54.16%）＞Pb（45.61%）＞Cu（41.76%）＞Ni（33.62%）＞Zn（26.32%）＞Cr（2.61%）.The result of analyzing fractionation of heavy metals in core sediment from Xianyang section of Wei River shows that:The vertical distribution of four fractionations of Cu,Cr,Pb,Zn,Mn and Ni are of twists and turns,most of heavy metals fractionations in shallower part are higher than deep part in the acid extractable fractionations, but it turns out just the opposite in the residual fractionation,the vertical distribution trend of oxidable and residual fractionations are not obvious.In most of sections,it shows that the proportion of "labile" fractionation in total contents in shallower part is higher than in deep part,which is basically the same as the above conclusions.4.The interconnection analysis among the heavy metals shows that:Cr has a positive relation to Pb,no relation to other four heavy metals.There are significantly positive correlations among five heavy metals（Cu,Zn,Pb,Mn and Ni）.The correlation analysis between "labile" fractionation and total contents displays:There are significantly positive correlations between every two indicators in six heavy metals.The correlation analysis between total contents of heavy metals,fractionation, "labile" fractionation with physic-chemical indexes displays:most of the heavy metals fractionation shows significantly correlation with conductivity,loss on ignition,low-frequency magnetic susceptibility(x_LF),high-frequency magnetic susceptibility(x_HF),CaCO₃,the clay and the silty sand.The above phenomenon reflects that seven physic-chemical indexes are the main factors of influencing fractionations for heavy metals in sediment from Xianyang section of Wei River;Pb, Cu,Ni,Mn and Zn have significantly positive relation to the seven physic-chemical indexes,which also shows that seven physic-chemical indexes are the main influencing factors for heavy metals in sediment from Xianyang section of Wei River;At the same time,"labile" fractionation also shows significantly correlation with seven physic-chemical indexes,which is basically the same as other conclusions.5.The result of evaluating research area by using Ratio of Secondary Phase in surface sediments of beavy mental displays:Apart from light pollution of Mn,Pb and Cu,other heavy metal elements have no pollution in surface sediments of Xianyang section of Wei River.The pollution of Mn exists in four sections（section 2,section 3,section 4 and section 5）.The RSP value of section 2 is the highest,amounting to 140%.The pollution of Pb exists in two sections（section 3 and section 4）.Tbe RSP value of section 4 is the highest,amounting to 116%.The pollution of Cu exists in section 3.The RSP value is 116%.There are three pollution elements（Mn,Pb and Cu） in section 3. There are two pollution elements（Mn and Pb） in section 4.The pollution of Mn exists section 2 and section 5.6.According to the distribution region of heavy metals in research area,there are high concentration in section 2 and section 3.It reflects that the content of heavy metals is affected significantly by pollution sources in the sediment from this section of Wei River.Others have little change,which indicates that the sediment is mainly affected by natural factors,such as soil parent material characteristics.Moreover,there are significantly positive correlation among six heavy metals（Cr,Pb,Cu,Zn,Mn and Ni）.So it can be concluded that:the content of heavy metals in sediment from XianYang section of Wei River is affected by parent material and pollution sources of the sediment.更多还原