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题名: 水体沉积物中的酸挥发性硫化物及其在沉积物重金属质量基准中的应用
作者: 方涛
答辩日期: 2000
导师: 徐小清
专业: 水生生物学
授予单位: 中国科学院水生生物研究所
授予地点: 中国科学院水生生物研究所
学位: 博士
关键词: 重金属 ; 沉积物 ; 酸挥发性硫化物 ; 平衡分配法 ; 沉积物金属质量基准
摘要: 通过对沉积物质量基准(SQC)进行研究,才能科学、客观地进行沉积物和水环境质量评价,从而为最终制定具有行政管理和强制执行能力的沉积物质量控制标准奠定技术基础。酸挥发性硫化物(AVS)因能与多种重金属元素生成难溶的金属硫化物,从而控制间隙水中重金属元素的浓度,因此它对沉积物质量基准的影响不容忽视。本文采用形态分析试验、金属加标试验、吸附释放试验对具代表性的长江典型江段沉积物及东湖沉积物的特征进行了研究,并应用非均相平衡理论、离子分级交换平衡理论、对流一扩散模型对所得结果进行了理论分析。研究内容包括:不同性质和污染状况的沉积物中的重金属化学形态及控制重金属活性的主导化学因子;AVS及同时提取金属(SEM)的时空分布规律;AVS对上覆水中重金属元素的影响作用;并采用相平衡分配法初步提出了长江水系的区域性的沉积物重金属相对质量基准。主要研究内容及结果如下:1、通过对沉积物基本化学特征的分析,结果表明东湖沉积物是一还原型沉积物,长江沉积物是一氧化型沉积物,由于区域地球化学背景相似,因而铁锰水合氧化物的含量及性质相近,但东湖沉积物的有机质、硫化物含量均高于长江沉积物。通过与长江背景值的比较,发现两种沉积物均不同程度的受到了重金属污染。2、形态分析结果表明,不同重金属元素在同一种沉积物中有不同的形态分布:Cu与有机物及硫化物结合相的亲和力最高,尤其是有机物,Zn和Pb易与铁锰氧化物结合,Cd则更易与碳酸盐结合,但东湖沉积物中Pb与有机物/硫化物结合的比例较高。同一种重金属元素在不同的沉积物中的形态分布也不尽相同:在东湖沉积物中重金属的有机物/硫化物结合态要高于长江沉积物中的。3、通过研究间隙水中重金属浓度对重金属元素加标量响应关系,发现间隙水中的浓度与加标量之间并无简单的线性响应关系。当加入的重金属与沉积物中AVS的摩尔浓度相当时,出现间隙水中重金属浓度显著上升的直线响应。因此,AVS是控制沉积物中重金属分配的关键要素。当[SEM]/[AVS]<1时,有过量的AVS存在,此时间隙水中重金属离子溶解态活度{M~(2+)}由式:{M~(2+)}/[M]_A 1时,因没有足够的AVS固定重金属,该沉积物间隙水中重金属元素则会以较高浓度的自由离子或其他具较强化学活性和生物有效性的化学形态存在,即:{Me~(2+)} = γM~(2+)a M~(2+)([M]_A-[AVS])。因此AVS归一化法可作为预测和评价二价有毒金属化学分配行为有效的方法。4、首次将沉积物中固液两相作为一个整体,成功的建立了AVS垂直分布的对流一扩散模型。这一方法在国内外研究中尚未见报道。研究结果表明,AVS在沉积物中的分布可用方程:C_s = A_0 + A_1e~(-B\h) + A_2e~(-B2h)表示;对模型参数的计算结果显示沉积物中的AVS的平均含量与含硫有机质的含量有关,它是含硫有机质的氧化、AVS的沉淀及溶解反应的综合结果。沉积物中的AVS及SEM随季节及深度而呈现出不同的分布特征,尽管沉积物性质的差异和污染程度的不同使AVS的时空分布特征各异,但总体趋势是:AVS的含量夏季较高,冬季较低,并随深度的加深而先升高后降低;SEM的的垂直分布变化不明显:从而使SEM/AVS在沉积物表层及深层较高,中层较低。因此,在运用SEM/AVS来判定沉积物中重金属的毒性时,若采用了均一化的样品或在单一时间采样,都可能导致不正确的结论。一般情况下,AVS的含量低时,重金属的生物有效性较高,因此采样应在AVS含量最低的时候进行,并对沉积物样品进行分层测定,才不致过低或过高的预测重金属元素活性。5.目前对重金属元素在沉积物或颗粒物上的吸附特征多用Langmuir或 Freundlish等温线方程进行描述,在我们研究中发现这两种方程对酸化沉积物这一特殊体系不适用,而采用了兼具上述两种方程的Sips表达式效果较好,该表达式为:ε= (NaC~b)/(1 + aC~b) 。同时,用分级离子交换理论研究重金属元素的释放也获得较满意的结果。研究表明,存在于水溶液中的重金属可以不断地与沉积物结合,从而使水溶液中的重金属浓度维持在一很低的水平上;并且,一旦与沉积物结合,重金属就很难再释放出来。AVS的存在增加了沉积物的吸附容量,但AVS经过酸化被除去后,与沉积物结合的重金属元素就会释放出来。曝气试验则表明了氧化作用会加剧沉积物结合的重金属的释放。6、在还原型沉积物中,AVS是主要的重金属结合相;而在氧化型沉积物中,由于AVS的含量很低,当其含量低到不足以约束所有的重金属时,其它的重金属结合相将成为控制重金属活性的主要因素。7、应用平衡分配法建立沉积物重金属质量基准被认为是最有前途及实际意义的方法。SQC可由方程:SQC=K_PWQC + [AVS] + [Me]_R求得。本文在前面研究的基础上,结合长江水系的相关数据,提出了区域性的长江水系相对沉积物重金属质量基准,分析了影响SQC的因素,评价了该区域的沉积物污染情况,为该区域的沉积物环境质量控制提供了依据,具有一定的理论意义。这一研究成果在国内当属首次,具有一定的实际意义及应用价值。
英文摘要: Acting as repository or source of various contaminants under different conditions, problem sediments may pose the immediate or potential risk to aquatic organisms. Proper sediments quality criteria (SQC), therefore, are required to indicate the contamination situation, to assist managers and regulators in making decision on treatment and remediation. Among various proposals for deriving SQC, equilibrium-partitioning approach (EqP) received extensive attention. Due to their widespread release and persistent nature, metals such as silver, cadmium, copper, mercury, nickel, lead and zinc are commonly evaluated in aquatic sediments. In developing sediment quality criteria for metals, it is essential that bioavailability be a prime consideration. Various studies have shown that while dry weight metal concentration in sediments are not predictive of bioavailability, metal concentrations in interstitial water (IW) are correlated with observed biological effects. A key partitioning phase controlling cationic metal activity and toxicity in the sediment-interstitial water system is acid volatile sulfides (AVS), which is defined as that fraction that can be extracted by 1M cold ECl. Several metals, such as Cu, Cd, Pb, Ni, Zn and Ag, form highly insoluble sulfides, thereby reducing biological availability. However, the AVS research are concentrated on marine sediments, only a few of them studied on freshwater. Furthermore, these AVS studies on freshwater did not take the oxic sediments into account. Besides, although there is few examples established SQC for metals on the basis of EqP, some uncertainty still remains. In particular, the research of AVS and SQC is rarely conducted in our country. Aiming at those problems above, this thesis deals with acid volatile sulfides in sediments and with the application of AVS to sediment quality criteria for metals. In the first two chapters, a review of acid volatile sulfides and sediment quality criteria for metals is described. The next four chapters deal with characteristics of AVS and SEM of sediments from lakes and rivers. Chapter 3 focuses on methods for research of AVS and SEM. Chapter 4 describes the main factors controlling the heavy metals (Zn, Cu, Cd, Pb and Ni) activity in the Changjiang River and Donghu Lake sediments. Chapter 5 analyzes the vertical and seasonal distribution of AVS. Chapter 6 presents influence of AVS on aquatic environmental quality. In chapter 7, the relative SQC for metals (Cu, Zn, Cd, Pb, Ni, Fe, Hg and As) of the Changjiang River water system are reported, and the factors of effects on relative SQC are discussed. The main results are as following: 1. The FeOOH and MnOOH contents of sediments from the Changjiang River (Yichang city) and the Lake Donghu are similar because they have the same geochemistry area background, but TOC and AVS contents in the lake sediments are higher than those in the river, showing the sediment from the lake is an anoxic one while the sediment from the river is an oxic one. As a result, the org-C and AVS fraction of trace metals is higher in lake sediments than in those of river. In addition, compared with the background values of heavy metals, both of the sediments have been contaminated. 2. During the metal spiked experiment, the concentrations of heavy metals m IW didn't correlate with total metals spiked, but increased linearly as soon as the molar concentrations of total metals spiked approach or equal to the molar concentrations of AVS in the sediments.
语种: 中文
内容类型: 学位论文
URI标识: http://ir.ihb.ac.cn/handle/342005/12542
Appears in Collections:中科院水生所知识产出(2009年前)_学位论文

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水体沉积物中的酸挥发性硫化物及其在沉积物重金属质量基准中的应用.方涛[d].中国科学院水生生物研究所,2000.20-25
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