我国城市土壤重金属污染研究现状和展望

随着我国城市化和工业化的高速发展,城市土壤重金属污染越来越受到关注,本文在文献调研的基础上,比较国内主要城市土壤重金属污染的含量水平,综述了我国城市土壤重金属污染来源、化学形态、分布特点、生态效应等,并提出了研究展望,以期为相关研究、环境决策和环境管理提供参考。     

城市污泥及其堆肥对土壤重金属积累的影响

与对照相比,在城市污泥及其堆肥的作用下,土壤耕层的重金属含量在一定程度上增加。耕层土壤在试验0的处理(3)、(4),即施城市污泥30 t hm-2和60 t hm-2和试验1的处理(4)即施污泥堆肥60 t hm-2的情况下,根据污染等级,土壤处于重度污染等级,其他处理的土壤耕层处于中等污染等级。在作用后效方面,两个试验中,对于土壤中全量和可吸收态的重金属元素得到下面递减排列:CdZnCuNiPb。比较试验各处理的Zc和土壤污染等级,试验0和试验1的处理4使土壤产生重度污染,其他处理导致试验土壤产生中度污染。     

水分及干燥过程对土壤重金属有效性的影响

土壤水分变化可显著改变土壤性质进而影响土壤重金属有效性。本试验通过测定土壤溶液和采用薄层凝胶梯度法(DGT)表征的Zn、Cd、Cu、Ni浓度,研究土壤含水量变化对重金属有效性的影响。结果表明,不同水分处理显著影响土壤溶液中可溶性有机碳(DOC)含量和土壤中重金属的有效性;随土壤水分降低DGT表征的Zn、Cd、Cu和Ni浓度和土壤溶液中Cu和Ni浓度呈下降趋势,且随干湿交替次数增加而降低;与长期风干土壤相比,经干湿交替后风干土壤重金属有效性降低或显著降低;与土壤溶液法相比,DGT法能反映水分变化对土壤固相金属缓冲补给能力的影响,能更好地表征土壤金属有效性的变化。在农业生产中可通过适当水分管理措施降低重金属的有效性,从而缓解重金属的毒害作用。     

重金属对土壤微生物酶活性的影响

本文通过含有不同浓度的铜、铅、砷、镉 4种重金属的大豆、小麦盆栽试验 ,采用气相色谱方法测定土壤微生物酶活性 .结果表明 :低浓度的重金属能够提高固氮酶和反硝化酶的活性 ,而高浓度的重金属对上述二种酶有强烈的抑制作用     

城市土壤重金属污染特征分析

目前越来越多的大城市的土壤受到不同程度的重金属污染,这将深刻影响到城市环境质量和人体健康。因受人类活动的强烈扰动,城市土壤重金属污染特征与传统意义上的土壤重金属污染特征差别很大,文章就城市土壤重金属污染特征做了详细的分析,并提出了一些相应的管理对策。     

黄粉虫幼虫对城市污泥重金属的积累作用

室内采用正交试验设计进行4 因素多水平试验, 研究了温度、城市污泥和麦麸配比、饲养密度、幼虫体重对黄粉虫幼虫生长速度、死亡率以及幼虫重金属含量变化的影响, 探讨黄粉虫幼虫在城市污泥中的生长状况和对城市污泥重金属的积累作用。结果表明: 随着温度的升高, 幼虫生长率和死亡率都呈上升趋势, 饲养密度、污泥和麦麸配比对黄粉虫幼虫生长率、死亡率无显著影响; 15 ℃、密度为0.2 g·cm^-2、污泥/麸皮为1∶2、幼虫体重为85.4±5.9 mg 时, 幼虫对Cu、Se、Hg 的积累作用较显著; 15 ℃、密度为0.4 g·cm^-2、污泥/麸皮为1∶0、幼虫体重为85.4±5.9 mg 时, 黄粉虫幼虫对Cd 的积累能力显著; 20 ℃、密度为0.4 g·cm^-2、污泥/麸皮为1∶0、幼虫体重为34.9±4.9 mg 时, Zn 的积累系数较大; 黄粉虫幼虫对Cu、Cd、Se、Hg 和Zn 等重金属元素有很强的积累作用。     

冲刷时间对土壤分离速率定量影响的实验模拟

土壤分离过程为侵蚀产沙提供了物质准备 ,对它发生、发展的过程进行准确模拟 ,具有重要的实践和理论意义。利用变坡实验水槽 ,在较大流量 (0 .5～ 1 .5 L / s)和坡度 (5°～ 1 5°)范围内 ,系统研究了冲刷时间对土壤分离速率的定量影响。研究结果表明 :不同流量和坡度条件下 ,土壤分离速率均随着冲刷时间的延长而呈良好的幂函数形式下降 (Dr=At B) ,系数 A随着流量和坡度的增大而增大 ;土壤分离速率与坡度和流量间的关系随着冲刷时间的不同而不同 ,当冲刷时间在 1 0 s以内时 ,随着冲刷时间的增加土壤分离速率与流量和坡度间的相关性增大 ,当冲刷时间大于 1 0 s后 ,随着冲刷时间的增大其相关性反而减小 ;以土样下切 2 cm为条件 ,建立了最佳冲刷时间与流量和坡度间的幂函数关系 ,为相关实验径流冲刷时间的设计提供了思路     

武汉市土壤重金属积累特征及其污染评价

通过在武汉市的城区和城郊进行现场调查采样与室内分析,研究了其0-20 cm表层土壤中6种典型重金属的积累状况,并采用污染指数法对土壤污染状况进行了评价.结果显示:土壤中Hg、As、Cd、Pb、Cr和Cu 6种重金属平均含量均是城区高于城郊.参照湖北省土壤背景值来看,城区土壤中Hg、Pb和Cd积累明显,分别超过其背景值186.1%,83.2%和76.6%,主要集中在交通区,工业区和公园区这3大功能区;城郊土壤中重金属Hg、Cd、Pb和Cu积累明显,其中最明显的是林地土壤Hg,比相应背景值高266.8%,除林地土壤As超过背景值13.8%外,蔬菜地、旱地和水田这3种利用方式下土壤中的As和所有城郊土壤中Cr,其含量均在湖北省土壤背景值之下.从单因子评价结果看,武汉市土壤中6种重金属的单项污染指数都小于0.7,其中Cd污染指数最大,其次为As、Hg、Cu、Cr和Pb;综合因子评价结果显示城区各功能区和城郊不同利用方式下土壤的综合污染指数均小于0.7,处于清洁无污染状态.     

影响城市土壤重金属污染因子的关联度分析

城市土壤深受人为活动的影响 ,具有明显的重金属人为富积的特点 ,认识这些土壤重金属丰度、形态与土壤理化性质及周围环境因子的关系 ,有助于更好地保护和修复城市土壤生态系统。本文对南京城市土壤中Pb、Zn、Cu、Cd四种重金属元素的含量和形态特征进行了研究 ,并用灰色系统理论方法对南京城市土壤重金属污染的影响因子进行了灰色关联度分析 ,认为最主要影响因子是距工业区远近 ,其次是土壤粘粒含量、pH值 ,而交通车流量、生产生活废弃物在土壤中堆埋的比例和土壤有机质对城市土壤重金属污染的影响相对较小     

开封市城市土壤磁化率空间分布及对重金属污染的指示意义

建立基于土壤磁化率的重金属污染等级标准可为土壤重金属污染评价提供更为简便的磁学方法。采集开封市城市土壤表层样品99个,测定As、Cd、Cr、Cu、Ni、Pb和Zn含量以及低频磁化率(χLF)和高频磁化率(χHF)。采用普通Kriging插值法探讨χLF的空间分布,污染负荷指数(PLI)评价土壤重金属污染程度,并在PLI与χLF相关分析的基础上建立了基于χLF的土壤重金属污染等级标准。结果表明,开封市城市土壤各样点7种重金属的平均PLI为2.53,呈中度污染,Cd是最主要的污染因子。土壤χLF平均值为125.7×10-8m3kg-1,总体上由东南向西北递减,高值区出现在东南部、老城区北部和陇海铁路沿线附近。各样点土壤重金属PLI与其χLF的回归方程为PLI=0.011χLF+0.320(r=0.663),呈极显著正相关(p0.01)。用土壤χLF可以评价开封市城市土壤重金属污染程度:当土壤χLF≤62×10-8m3kg-1时,为无污染;当62×10-8χLF≤153×10-8m3kg-1时,为轻度污染;当153×10-8χLF≤244×10-8m3kg-1时,为中度污染;当χLF244×10-8m3kg-1时,为强度污染。     

我国北方典型日光温室蔬菜生产系统土壤重金属积累趋势

本文以山东省寿光市日光温室蔬菜生产系统为例,研究了As、Cd、Cu、Hg、Pb和Zn等重金属元素在土壤中的积累趋势。结果表明：有机肥中Cu、Zn元素含量较高,而无机肥中Cd、Zn元素含量较高,但所有元素均未超过目前的相关标准。表层土壤中上述元素的平均含量均未超出《温室蔬菜产地环境质量评价标准》(HJ333-2006)相应的标准限值,但Cd平均含量已接近评价标准。除了As和Pb元素外,表层土壤中Cd、Cu、Hg和Zn的含量随着种植年限的增长而增加,出现积累。在目前的重金属积累状况下,主要蔬菜可食部分的重金属含量明显低于中国食品污染物限量标准,处于安全级别。由于蔬菜生产最初均是在底层土壤上开始的,加之封闭的生产环境,表明土壤中重金属主要来自各种农用投入品的输入,而各种肥料的高量输入是其积累的主要原因。今后对该地区设施蔬菜生产的环境管理,除了制定更严格的肥料重金属含量标准外,更重要的是要严格控制各种肥料的施用量,这样既可降低系统养分过量盈余,又可控制土壤重金属的积累。     

朝天委陵菜的重金属耐性与吸收性研究

利用植物生长室水培试验和温室土培盆栽试验的方法,研究了朝天委陵菜在不同浓度Pb水培条件下和Cu、Zn、Pb、Cd复合污染土壤条件下的重金属耐性和吸收性,结果表明,水培条件下随着处理浓度的增加,朝天委陵菜均生长良好,虽高浓度Pb处理下出现植株矮小、叶渐黄、根系变黑等毒害症状,但植株并未死亡,表明在水培条件下朝天委陵菜对Pb具有极强的耐性;在最高浓度3 600μmol/L Pb处理下地上部和根中Pb浓度达到最大值,分别为947 mg/kg和71 053 mg/kg。在温室土培盆栽条件下,朝天委陵菜在外加Cu、Zn、Pb和Cd分别为200、1 000、1 000和5 mg/kg的土壤上较对照生长受到抑制,地上部Cu、Zn、Pb和Cd浓度分别达到741±164、18 248±2 222、1 543±483和29.4±5.2 mg/kg;外加重金属更高时则导致植株死亡。朝天委陵菜对Pb胁迫和Cu、Zn、Pb、Cd复合污染土壤具有较强的耐受性,可作为重金属尤其是Pb污染土壤的修复植物。     

Microbial biomass,activity, and organic matter accumulation in soils contaminated with heavy metals

Chemical characteristics and some parameters related to biological components were determined in 16 soils from a fairly homogeneous area in the north of Italy, contaminated with different levels of heavy metals. Correlation analysis of the parameters studied showed close positive relationships among the metals and with the organic C content in the soils studied. Negative relationships were observed among the heavy metals, soil respiration, and the ratio between evolved CO₂–C and microbial biomass C per unit time (specific respiratory activity). This was ascribed to an adverse heavy metal effect on the soil microflora, which appeared to increase the accumulation of organic matter as the heavy metal content increased, probably because the biomass was less effective in mineralising soil organic matter under these conditions.     

中国农田重金属问题的若干思考

在对我国若干典型区域调研及资料分析的基础上,作出了当前我国耕地重金属“主产区基本安全,重点区域风险较大”的基本判断,提出了针对农田土壤采用“重金属含量超标”替代“重金属污染”的观点,指出我国农业主产区农田重金属存在明显的累积趋势.同时,在对我国土壤重金属钝化和活化、植物吸收和阻控、微生物转化和利用等研究成果进行总结和借鉴基础上,提出了强化重金属超标农田安全利用、重金属含量阈值制订、重金属污染源头和过程阻控、超标农田修复以及产地环境安全保障体系等系列建议.     

Characterization of soil heavy metal pools in paddy fields in Taiwan: chemical extraction and solid-solution partitioning

Background, aim, and scope  Ongoing industrialization has resulted in an accumulation of metals like Cd, Cu, Cr, Ni, Zn, and Pb in paddy fields across Southeast Asia. Risks of metals in soils depend on soil properties and the availability of metals in soil. At present, however, limited information is available on how to measure or predict the directly available fraction of metals in paddy soils. Here, the distribution of Cd, Cu, Cr, Ni, Zn, and Pb in 19 paddy fields among the total, reactive, and directly available pools was measured using recently developed concepts for aerated soils. Solid-solution partitioning models have been derived to predict the directly available metal pool. Such models are proven to be useful for risk assessment and to derive soil quality standards for aerated soils. Material and methods  Soil samples (0–25 cm) were taken from 19 paddy fields from five different communities in Taiwan in 2005 and 2006. Each field was subdivided into 60 to 108 plots resulting in a database of approximately 3,200 individual soil samples. Total (Aqua Regia (AR)), reactive (0.43 M HNO₃, 0.1 M HCl, and 0.05 M EDTA), and directly available metal pools (0.01 M CaCl₂) were determined. Solid-solution partitioning models were derived by multiple linear regressions using an extended Freundlich equation using the reactive metal pool, pH, and the cation exchange capacity (CEC). The influence of Zn on metal partitioning and differences between both sampling events (May/November) were evaluated. Results  Total metals contents range from background levels to levels in excess of current soil quality standards for arable land. Between 3% (Cr) and 30% (Cd) of all samples exceed present soil quality standards based on extraction with AR. Total metal levels decreased with an increasing distance from the irrigation water inlet. The reactive metal pool relative to the total metal content is increased in the order Cr << Ni = Zn < Pb < Cu < Cd and ranged from less than 10% for Cr to more than 70% for Cd. Despite frequent redox cycles, Cd, Pb, and Cu appear to remain rather reactive. The methods to determine the reactive metal pool in soils yield comparable results, although the 0.43 M HNO₃ extraction is slightly stronger than HCl and EDTA. The close correlation between these methods suggests that they release similar fractions from soils, probably those reversibly sorbed to soil organic matter (SOM) and clay. The average directly available pool ranged from less than 1% for Cu, Pb, and Cr to 10% for Ni, Zn, and Cd when compared to the reactive metal pool. For Cd, Ni, Zn, and to a lesser extent for Cu and Pb, solid-solution partitioning models were able to explain up to 93% (Cd) of the observed variation in the directly available metal pool. CaCl₂ extractable Zn increased the directly available pool for Ni, Cd, and Cu but not that of Pb and Cr. In the polluted soils, the directly available pool was higher in November compared to that in May. Differences in temperature, rainfall, and changes in soil properties such as pH are likely to contribute to the differences observed within the year. The solid-solution partitioning model failed to explain the variation in the directly available Cr pool, probably because Cr is present in precipitates rather than being adsorbed onto SOM and clay. Despite obvious differences in parent material, source of pollution, climate, and land use, solid-solution partitioning of Cd in paddy fields studied here was similar to that in soils from Belgium and the Netherlands. Discussion  To assess risks of metals in soils, both analytical procedures as well as models are needed. The three methods tested here to determine the reactive metal pool are highly correlated and either of these can be used. The directly available pool was predicted most accurately by the 0.43 M HNO₃ method. The similarity of metal partitioning in paddy soils compared to well-drained soils suggests that changing redox conditions in paddy fields have a limited effect on the geochemical behavior of metals like Cd, Ni, and Zn. Small but significant differences in the directly available metal pool during the year suggest that redox cycles as well as differences in rainfall and temperature affect the size of the directly available metal pool. The large observed spatial heterogeneity of contaminant levels requires ample attention in the setup of soil monitoring programs. Conclusions  The directly available pool (0.01 M CaCl₂) of Cd, Zn, and Ni in paddy fields can be described well by an extended Freundlich model. For Cu and Pb, more information on dissolved organic carbon is needed to obtain a more accurate estimate of the directly available pool. Recommendations and perspectives  Soil testing protocols and models used in risk assessment consider the availability of pollutants rather than the total metal content. Results from extensive testing indicate that approaches developed for nontropical regions can be applied in paddy fields as well for metals like Cd, Ni, and Zn. This study shows that the chemical behavior under drained conditions in paddy fields is comparable to that observed in soils across the European Union, which allows regions with large scale soil pollution including Taiwan to apply such concepts to derive meaningful experimental protocols and models to assess risks of metals in soils.     

重金属污染土壤间作修复的研究进展

种植单一的超富集植物修复重金属污染土壤,不但中断农业生产导致经济收益降低,而且因生物量较低、修复周期长等诸多弊端导致修复效果不甚理想。间作作为一种传统的农艺管理方式,利用生态位和生物多样性原理等能提高农作物对资源的有效利用,对共植的农作物种类增量提质。在中、轻度污染土壤修复中利用间作体系,通过调控超富集植物与农作物的生长发育,促进超富集植物根系低分子量有机酸(LMWOAs)的分泌,降低其根际土壤p H,增加重金属活性,从而增加超富集植物对重金属的吸收,同时抑制农作物根系LMWOAs的分泌,以减少农作物对重金属的吸收,提高其产量和品质,实现"边生产边修复",提高土地利用率,并增加经济效益。本文根据近几年来国内外相关文献,综述了间作条件下超富集植物和农作物生物量、生理生化响应、重金属吸收、转运、富集等方面的变化,以及间作对土壤环境质量的影响,并对间作修复重金属污染土壤领域的发展趋势,如超富集植物和农作物间作的信号转导和分子生物学机制、间作体系下两类植物根际微生物类群的差异及其功能机制,以及构建高效间作体系提高重金属污染土壤的修复效率等方面进行了展望。     

Measurement of urbanization process and the paddy soil loss in Yixing city,China between 1949 and 2000

This study used GIS technology, remote sensing images of 1949, 1966, 1981, 1984, 1988, 1992, 1996 and 2000, to analyze the spatial process of urbanization and its impact on the soil resources in Yixing city, southeast China. The results showed that the urban area grew more than three-fold during 51 years and the loss of paddy soil accounted for 82.9% of all soil loss. According to the expansion dynamics and the results of spatial metrics, the urban expansion process in Yixing could be divided into four steps, the initial step (1949–1966), the almost standstill step (1966–1981), the preparation step (1981–1984) and the rapid growing step (after 1984). The study also indicated that the urban expansion was encouraged by the transportation system, however, restricted by the rivers, lakes and hills. The local government's decision also affected the spatial process of urban expansion. The spatial process of Yixing urban expansion might reflect the spatial process of urbanization of southeast China, the region with a rapidly growing economy.     

Bio-indicators to assess impacts of heavy metals in land-applied sewage sludge

Soils from a pastoral farm that had received large amounts of heavy metal contaminated sewage sludge 6-10 years previously were investigated to determine the impact of heavy metals on Rhizobium. The 8 ha application area was originally divided into five different-sized blocks (blocks 1-5), which received sludge at different times between 1991 and 1994. The response of a lux biosensor based on R. leguminosarum bv. trifolii (Rhizotox-C), was compared with more traditional techniques for measuring the presence of effective strains of Rhizobium (MPN) and nitrogen fixation (δ¹⁵N natural abundance). Although population size (MPNs), nitrogen fixation and biosensor response varied between treatment blocks, linear regression analysis determined that this block effect could not be directly linked to soil heavy metal concentrations, but was probably due to biological, physical, chemical and environmental compounding factors at the site. In this type of uncontrolled field application, the lux bioassay may provide the most useful information as it measures toxicity to any microorganism exposed to the soil solution, for example, the free living rhizobia.     

不同地区城郊用地土壤重金属含量特征的比较

对京津唐、张家港和长株潭3个地区的露天菜地、设施菜地、水田和旱地进行的调查表明,城郊区大部分农田土壤重金属含量尚低于国家相关的土壤质量二级标准,但部分重金属含量超出了当地背景值,说明重金属在城郊土壤中有所积累。菜地土壤重金属含量总体上要高于水田和旱地,说明高强度利用投入会导致土壤重金属累积。对长株潭一个污染区的研究表明,发生污染的土壤很难再恢复利用。京津唐城郊区的土壤重金属含量的变异系数总体上高于张家港地区。