磷改性生物炭对Pb、Cd复合污染土壤的钝化效果

中国存在着较大面积受重金属污染土壤,尤其是Pb、Cd两种重金属的复合污染较常见。利用磷改性生物炭对Pb、Cd复合污染土壤展开修复研究。结果表明:(1)磷改性生物炭可使土壤中Pb、Cd由弱酸提取态向可氧化态、残渣态转变,Pb的可氧化态和残渣态分别增加了19.4、16.9百分点,Cd的可氧化态、残渣态分别增加了17.4、9.9百分点;(2)磷改性生物炭可提高土壤有效磷,有效磷最终稳定在39 mg/kg左右;(3)磷改性生物炭能显著增加土壤阳离子交换量至19.3 cmol/kg。磷改性生物炭不仅能有效钝化重金属,还能有效改善土壤质量。     

不同钝化剂对外源铅在土壤中的钝化效果及粒径分布的影响

通过室内钝化培养实验比较了羊厩肥、石灰和磷酸盐对土壤外源Pb的钝化效果和钝化修复后Pb的粒径分布特征。结果表明:3种钝化剂均能显著降低土壤中DTPA-Pb的含量,且钝化效果与钝化剂添加量成正比;磷酸盐对外源Pb钝化效果最好,P10处理下土壤中DTPA-Pb的含量降幅达80.53%,羊厩肥钝化效果最差,GM1对DTPA-Pb含量的降幅为6.51%;羊厩肥与磷酸盐将弱酸提取态Pb和可还原态Pb转变为活性更低的可氧化态Pb和残渣态Pb,以降低其活性,石灰将可还原态Pb转化为可氧化态Pb,以降低其活性;3种钝化剂添加均会提升土壤Olsen-P的含量。土壤磷淋溶临界值模型显示,当土壤Olsen-P含量124.25 mg·kg~(-1)时,会发生磷素淋溶现象;Pb在土壤粗砂粒、细沙粒、粉粒和黏粒中的含量差别很大,但赋存形态无明显差异,钝化剂添加会影响外源Pb在各粒级颗粒中的富集及形态分布。相关性分析结果表明,钝化剂主要通过将细沙粒、粉粒和黏粒中的可还原态Pb转化为粉粒和黏粒中的可氧化态Pb来降低土壤Pb的毒害性。研究结果可为3种钝化剂在Pb污染土壤修复中的高效利用及修复后土壤的潜在生态风险管控提供参考。     

氯化铁和硫酸铁对酸性土壤中有效态镉和铅污染的修复作用

采用浸泡实验法研究了氯化铁和硫酸铁对酸性土壤中有效态镉和铅污染的修复效果,结果表明,氯化铁和硫酸铁均能有效去除土壤有效态镉和铅污染,Fe(Ⅲ)用量为50～100 mmol/kg时,有效态Cd和Pb的去除效果可达70％～96％.氯化铁和硫酸铁能去除土壤中的水溶态、碳酸盐结合态、腐殖酸结合态、铁锰氧化物结合态和强有机结合态Cd和Pb及交换态Cd.氯化铁和硫酸铁对Cd均既有洗脱修复作用又有固定修复作用,且洗脱修复作用的贡献稍大;氯化铁用量较小时(50 mmol/kg)对Pb既有固定修复又有洗脱修复作用,固定修复作用稍大;用量较大时(100 mmol/kg),对Pb只有洗脱修复作用.硫酸铁对Pb的修复作用则以固定修复作用为主,洗脱修复作用很小.     

不同Cd污染特征稻田施用钝化剂对水稻吸收积累Cd的影响

选择长株潭地区典型化工点源污染、污水灌溉面源污染和大气沉降面源污染的镉(Cd)污染稻田,研究钝化剂施用对稻田土壤Cd形态、水稻Cd含量的影响。结果表明,不同Cd污染特征稻田施用石灰对水稻产量无显著影响,但能显著提高土壤pH,降低土壤有效态Cd含量和水稻稻米及茎叶Cd含量;而施用钝化剂不仅可显著提高土壤pH,降低土壤有效态Cd含量、水稻稻米与茎叶Cd含量,还可增加水稻产量。通过钝化剂用量与产量的二次拟合曲线计算可知,北山、梅林桥、大同桥三实验点最高理论产量分别为7 879、9 274和9 064 kg·hm~(-2),对应的钝化剂施用量分别为1 557、1 248和2 752kg·hm~(-2);而钝化剂用量与稻米Cd含量的二次拟合曲线计算可知,三实验点最低理论稻米Cd含量分别为0.143 8、0.063 7和0.232 4 mg·kg-1,对应的钝化剂施用量分别为2 079、1 823和1 689 kg·hm~(-2)。研究结果还表明,Cd污染源对钝化剂降低土壤Cd有效性无显著影响,但会影响水稻对Cd的吸收积累。大同桥点施用石灰和钝化剂皆可显著降低土壤有效态Cd含量,但受污水灌溉的影响,稻米Cd含量较高;化工点源污染的北山点土壤有效Cd含量虽高,因污染源已断,施用石灰和钝化剂皆能显著降低土壤Cd的有效性和稻米Cd含量;而受大气沉降污染的梅林桥点,土壤Cd含量虽高,但土壤Cd有效性较低,施用石灰和钝化剂皆可有效钝化土壤中的Cd,并显著降低稻米Cd含量。     

外源螯合剂CA和NTA对苎麻修复铅镉复合污染土壤的影响

采用盆栽实验,研究了在两组铅镉复合污染(Cd(10 mg·kg~(-1))/Pb(100 mg·kg~(-1))和Cd(50 mg·kg~(-1))/Pb(500 mg·kg~(-1)))条件下,不同浓度的柠檬酸(CA)和氮三乙酸(NTA)(0,1,5,10 mmol·kg~(-1))对苎麻生物量、地上部分丙二醛(MDA)含量和抗氧化酶活性、苎麻各部分对Pb和Cd的积累的影响。结果表明,CA和NTA的应用均能促进苎麻的生长和提高Pb和Cd在苎麻体内积累。CA在促进苎麻生长、增强了苎麻对Cd的吸收和转移方面效果显著,但是,CA对Pb的提取和转移促进效果不显著。NTA促进苎麻对Pb的吸收和转移,并且同样有助于Cd的植物修复。苎麻体内CAT,SOD,POD活性和MDA含量变化表明CA和NTA缓解了Cd和Pb对苎麻的氧化胁迫。因此,外源螯合剂CA和NTA的应用有利于铅镉复合污染土壤的植物修复。     

草炭对Cd~(2+)的吸附及其用于Cd污染土壤修复的实验研究

通过室内模拟实验研究了草炭对Cd2+的典型吸附特征,以及添加草炭对Cd污染土壤中其浸出毒性和存在形态的影响。结果表明,溶液pH为3~6时,草炭对Cd2+的吸附量随着pH升高而增加,pH为6~8时草炭对Cd2+的吸附量趋于平稳;当溶液体系Cd2+初始质量浓度不超过800mg/L时,草炭对Cd2+的吸附未达到平衡,其吸附率随Cd2+初始浓度的增大而由98.60%降低至88.53%;草炭对Cd2+的等温吸附行为可用Langmuir、Freundlich方程拟合,r均达到极显著水平;添加草炭能降低轻污染(总Cd为3.0mg/kg)土样中Cd2+浸出量,Cd2+钝化率随草炭添加量增加而增加;相对较低(1%~2%,质量分数,下同)的草炭添加量对重污染(总Cd为6.0mg/kg)土样中的Cd2+表现出活化效果,导致Cd2+浸出量增加;但较高(4%)的草炭添加量下,重污染土样中Cd2+的钝化率要明显大于轻污染土样;添加草炭能影响土样中Cd的存在形态。在2种污染程度的土样中添加草炭后,有效态、无机结合态和残留态Cd所占比例均降低,而有机结合态Cd所占比例均增加。     

EDTA/纳米羟基磷灰石联合修复重金属污染土壤

土壤淋洗可能导致残留重金属活化,采用淋洗/钝化联合修复重金属污染土壤可在一定程度上减少这一影响。研究了EDTA淋洗、纳米羟基磷灰石钝化及两者联合修复对土壤重金属洗脱率、TCLP浸出浓度、化学形态分布的影响,构建了涵盖土壤重金属残留量、生物有效性和生理毒性的环境风险评价方法,对淋洗、钝化及其联合修复进行了评价。结果发现,EDTA淋洗对Pb和Cu的洗脱效果较好,对Zn浸出浓度的削减率较高。当EDTA投加量为2 g·L~(-1)时,Zn的浸出浓度降低了70.40%。纳米羟基磷灰石对Pb和Zn具有较好的钝化效果,对Cu和Cd的钝化作用相对较弱。当纳米羟基磷灰石投加量为2%时,Pb浸出浓度削减率高达89.65%。淋洗/钝化联合修复大幅度降低了Pb和Cd的浸出浓度,降低了可还原态Cu残留量、可还原态和残渣态Cd残留量,以及弱酸提取态和可还原态Zn、Pb残留量。当EDTA和纳米羟基磷灰石投加量分别为1 g·L~(-1)和1%时,土壤重金属总环境风险削减率达到74.12%。EDTA对土壤中Cu和Cd的洗脱效果较好,后续钝化修复作用有限,Pb和Zn则可通过淋洗/钝化联合修复大幅度提高削减环境风险削减率。     

微生物矿化修复重金属污染土壤

以选矿厂附近土壤为研究对象,分析了土壤中交换态重金属含量,As、Pb、Cd、Zn和Cu的交换态浓度为14.01、4.95、0.64、33.46和12.95 mg/kg。基于生物矿化原理,利用碳酸盐矿化菌生长代谢过程产生的脲酶来分解底物尿素,产生碳酸根离子,固结重金属离子,使得土壤中活泼的重金属离子转变为碳酸盐矿物态,降低其危险。研究了温度、pH和重金属离子对酶活性的影响,发现环境30℃温度有利于促进酶活性;在弱酸性条件下,底物分解量减少15%;重金属离子在低浓度时对脲酶活性影响不大,浓度提高后对酶活性抑制作用没有加剧。将制备好的微生物矿化修复制剂喷洒于1 000 m2的污染土壤中,实验结果发现,土壤中交换态重金属离子含量在0～20 cm范围内明显减少,As、Pb、Cd、Zn和Cu的交换态浓度分别减少至2.37、1.25、0.31、16.67和3.42 mg/kg。     

石灰钝化法原位修复酸性镉污染菜地土壤

在湖南省湘潭县酸性(pH=5.47±0.64)镉污染((1.06±0.08)mg·kg~(-1))菜地,进行为期1年的田间修复实验。研究施用石灰类钝化剂(石灰石或生石灰)对菜地土壤镉(Cd)的有效性、当地常见蔬菜可食部位Cd含量的影响,分析蔬菜种植过程中农业投入品对表层土壤(20 cm)Cd积累的影响,确定Cd污染菜地蔬菜安全生产的措施。结果表明:与对照相比,施加4 500 kg·hm~(-2)CaCO_3或3 000 kg·hm~(-2)CaO分别使土壤pH升高了1.48和1.73,土壤有效态Cd含量分别降低了87.8%和78.1%;叶菜类、根茎类、茄果类和豆类蔬菜可食部位Cd含量分别降低了5.9%～70.5%、59.8%～65.8%、4.0%～50.0%和35.0%～76.4%,但施用4 500 kg·hm~(-2)CaCO_3或3 000 kg·hm~(-2)CaO不能使叶菜类、茄果类蔬菜中Cd含量降低到相应的国家食品安全标准限值(叶菜类蔬菜,0.2 mg·kg~(-1);茄果类蔬菜,0.05mg·kg~(-1))以下;蔬菜种植过程中施用的基肥、灌溉水、CaCO_3或CaO不会导致表层土壤Cd含量增加。在酸性Cd污染菜地施用CaCO_3或CaO、并种植低Cd积累蔬菜,可以实现蔬菜的安全生产。     

施加氮磷肥及Pb胁迫对小白菜Pb含量的影响研究

为了研究施肥对小白菜Pb含量的影响,采用盆栽试验种植小白菜,分析土壤中不同浓度氮肥、磷肥及Pb胁迫对小白菜地上部分和根系吸收Pb的影响。结果表明,无Pb胁迫下,在土壤中施加氮肥对小白菜株高、根长和鲜质量均有一定的促进作用,有Pb胁迫(300mg/kg,下同)下,施氮肥对小白菜株高和鲜质量有促进作用,但对根长有抑制作用。无Pb胁迫下,在土壤中施加一定量的磷肥能促进小白菜鲜质量的增长,但却对株高有一定的抑制作用;中高质量浓度施磷处理(150～225mg/kg)会抑制小白菜地上部分对Pb的吸收,低质量浓度施磷处理(≤75mg/kg)则会促进小白菜地上部分和根系对Pb的吸收;有Pb胁迫下,施加磷肥对小白菜的株高和鲜质量均有一定的促进作用,且抑制了小白菜根系对Pb的吸收。研究土壤氮肥最佳施用量为300mg/kg,磷肥最佳施用量为150mg/kg,此时小白菜的鲜质量达到最大,且小白菜地上部分对Pb的吸收量相对较小。     

Dioxin- and POP-contaminated sites—contemporary and future relevance and challenges

BACKGROUND, AIM AND SCOPE: Once they have been generated, polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) and other persistent organic pollutants (POPs) can persist in soils and sediments and in waste repositories for periods extending from decades to centuries. In 1994, the US EPA concluded that contaminated sites and other reservoirs are likely to become the major source of contemporary pollution problems with these substances. With this in mind, this article is the first in a new series in ESPR under the title 'Case Studies on Dioxin and POP Contaminated Sites--Contemporary and Future Relevance and Challenges', which will address this important issue. The series will document various experiences from sites contaminated with PCDD/F and other POPs. This article provides an overview of the content of the articles comprising the series. In addition, it provides a review of the subject in its own right and identifies the key issues arising from dioxin/POP-contaminated sites. Additionally, it highlights the important conclusions that can be drawn from these examples. The key aim of this article and of the series as a whole is to provide a comprehensive overview of the types of PCDD/F contaminated sites that exist as a result of historical activities. It details the various processes whereby these sites became contaminated and attempts to evaluate their contemporary relevance as sources of PCDD/Fs and other POPs. It also details the various strategies used to assess these historical legacies of contamination and the concepts developed, or which are under development, to effect their remediation. MAIN FEATURES: Special sessions on 'Contaminated sites--Cases, remediation, risk and policy' were held at the DIOXIN conferences in 2006 and 2007, and this theme will be continued at DIOXIN 2008 to be held in Birmingham. Selected cases from the approximately 70 contributions made to these sessions, together with some additional invited case studies are outlined together with the key issues they raise. By evaluating these cases and adding details of experiences published in the current literature, an overview will be given of the different features and challenges of dioxin and POP-contaminated sites. RESULTS: This article provides a systematic categorisation of types of PCDD/F and POP-contaminated sites. These are categorised according to the chemical or manufacturing process, which generated the PCDD/Fs or POPs and also includes the use and disposal aspects of the product life cycle in question. The highest historical PCDD/F and dioxin-like polychlorinated biphenyl (PCB) contamination burdens have arisen as a result of the production of chlorine and of chlorinated organic chemicals. In particular, the production of chlorinated pesticides, PCBs and the related contaminated waste streams are identified being responsible for historical releases of toxic equivalents (TEQs) at a scale of many tonnes. Along with such releases, major PCDD/F contaminated sites have been created through the application or improper disposal of contaminated pesticides, PCBs and other organochlorine chemicals, as well through the recycling of wastes and their attempted destruction. In some extreme examples, PCDD/F contaminated sites have also resulted from thermal processes such as waste incinerators, secondary metal industries or from the recycling or deposition of specific waste (e.g. electronic waste or car shredder wastes), which often contain chlorinated or brominated organic chemicals. The examples of PCDD/F and dioxin-like PCB contamination of fish in European rivers or the impact of contaminated sites upon fishing grounds and upon other food resources demonstrate the relevance of these historical problems to current and future human generations. Many of the recent food contamination problems that have emerged in Europe and elsewhere demonstrate how PCDD/F and dioxin like PCBs from historical sources can directly contaminate human and animal feedstuffs and indeed highlight their considerable contemporary relevance in this respect. Accordingly, some key experiences and lessons learnt regarding the production, use, disposal and remediation of POPs from the contaminated sites are summarised. DISCUSSION: An important criterion for evaluating the significance and risks of PCDD/Fs and other POPs at contaminated sites is their present or future potential for mobility. This, in turn, determines to a large degree their propensity for off-site transport and environmental accessibility. The detailed evaluation of contaminated site cases reveals different site-specific factors, which influence the varied pathways through which poor water-soluble POPs can be mobilised. Co-contaminants with greater water solubility are also typically present at such sites. Hence, pumping of groundwater (pump and treat) is often required in addition to attempting to physically secure a site. At an increasing number of contaminated sites, securing measures are failing after relatively short time spans compared to the time horizon, which applies to persistent organic pollutant contamination. Due to the immense costs and challenges associated with remediation of contaminated sites 'monitored natural attenuation' is increasingly gaining purchase as a conceptual remediation approach. However, these concepts may well prove limited in their practical application to contaminated sites containing persistent organic pollutants and other key pollutants like heavy metals. CONCLUSIONS: It is inevitable, therefore, that dioxin/POP-contaminated sites will remain of contemporary and future relevance. They will continue to represent an environmental issue for future generations to address. The securing and/or remediation of dioxin/POP-contaminated sites is very costly, generally in the order of tens or hundreds of millions of dollars. Secured landfills and secured production sites need to be considered as constructions not made for 'eternity' but built for a finite time scale. Accordingly, they will need to be controlled, supervised and potentially repaired/renewed. Furthermore, the leachates and groundwater impacted by these sites will require ongoing monitoring and potential further remediation. These activities result in high maintenance costs, which are accrued for decades or centuries and should, therefore, be compared to the fully sustainable option of complete remediation. The contaminated site case studies highlight that, while extensive policies and established funds for remediation exist in most of the industrialised western countries, even these relatively well-regulated and wealthy countries face significant challenges in the implementation of a remediation strategy. This highlights the fact that ultimately only the prevention of contaminated sites represents a sustainable solution for the future and that the Polluter Pays Principle needs to be applied in a comprehensive way to current problems and those which may emerge in the future. RECOMMENDATIONS AND PERSPECTIVES: With the continuing shift of industrial activities in developing and transition economies, which often have poor regulation (and weak self-regulation of industries), additional global challenges regarding POPs and other contaminated sites may be expected. In this respect, a comprehensive application of the "polluter pays principle" in these countries will also be a key to facilitate the clean-up of contaminated areas and the prevention of future contaminated sites. The threats and challenges of contaminated sites and the high costs of securing/remediating the problems highlight the need for a comprehensive approach based upon integrated pollution prevention and control. If applied to all polluting (and potentially polluting) industrial sectors around the globe, such an approach will prove to be both the cheapest and most sustainable way to underpin the development of industries in developing and transition economies.     

Sorption and desorption of Cu and Cd by macroalgae and microalgae

The sorption and desorption of Cu and Cd by two species of brown macroalgae and five species of microalgae were studied. The two brown macroalgae, Laminaria japonica and Sargassum kjellmanianum, were found to have high capacities at pHs between 4.0 and 5.0 while for microalgae, optimum pH lay at 6.7. The presence of other cations in solution was found to reduce the sorption of the target cation, suggesting a competition for sorption sites on organisms. Sorption isotherms obeyed the Freundlich equation, suggesting involvement of a multiplicity of mechanisms and sorption sites. For the microalgae tested, Spirulina platensis had the highest capacity for Cd, followed by Nannochloropsis oculata, Phaeodactylum tricornutum, Platymonas cordifolia and Chaetoceros minutissimus. The reversibility of metal sorption by macroalgae was examined and the results show that both HCl and EDTA solutions were very effective in desorbing sorbed metal ions from macroalgae, with up to 99.5% of metals being recovered. The regenerated biomass showed undiminished sorption performance for the two metals studied, suggesting the potential of such material for use in water and wastewater treatment.     

Persistence and dissipation kinetics of trifloxystrobin and tebuconazole in onion and soil

The persistence and dissipation kinetics of trifloxystrobin and tebuconazole on onion were studied after application of their combination formulation at a standard and double dose of 75 + 150 and 150 + 300 g a.i. ha^?1. The fungicides were extracted with acetone, cleaned-up using activated charcoal (trifloxystrobin) and neutral alumina (tebuconazole). Analysis was carried out by gas chromatograph (GC) and confirmed by gas chromatograph mass spectrometry (GC-MS). The recovery was above 80% and limit of quantification (LOQ) 0.05 mg kg^?1 for both fungicides. Initial residue deposits of trifloxystrobin were 0.68 and 1.01 mg kg^?1 and tebuconazole 0.673 and 1.95 mg kg^?1 from standard and double dose treatments, respectively. Dissipation of the fungicides followed first-order kinetics and the half life of degradation was 6–6.6 days. Matured onion bulb (and field soil) harvested after 30 days was free from fungicide residues. These findings suggest recommended safe pre-harvest interval (PHI) of 14 and 25 days for spring onion consumption after treatment of Nativo 75 WG at the standard and double doses, respectively. Matured onion bulbs at harvest were free from fungicide residues.     

Kinetic and structural relationships of transition monomeric and oligomeric carboxyl- and choline-esterases

The kinetic and structural relationships of eight electrophoretically pure mammalian serum and liver serine carboxylesterases (CE) and cholinesterases (ChE) have been studied. Eight CE's and ChE's, which were fully resolved but only partially purified, provided additional information. Five of the electrophoretically pure esterases were monomeric, and of these, four belonged to a new and widely distributed class. These four monomeric esterases hydrolyzed choline esters, but at widely differing rates. Thus two were termed monomeric butyrylcholinesterases, mBuChE I and II, and two were monomeric CE's (mCE). The rabbit liver mCE was not a subunit of the oligomeric CE (oCE), although the oCE also hydrolyzed choline esters at a very low rate. The complex kinetics of the mCE's, mBuChE's, oCE's, and of the oligomeric BuChE's of horse and human serum could be interpreted according to a single reaction scheme involving an allosteric site and the equation derived from it. Thus activation and inhibition at high substrate concentrations, together with sigmoidal activity versus substrate concentration plots, all of which characterize the reactions of these esterases, could be interpreted by a single scheme and equation. Structural and kinetic comparisons showed a progressive transition of properties from the oCE's through the mCE's to the oBuChE's. One of the purified mCE's was from horse serum, and it exhibited physical and kinetic properties unlike those of the liver mCE's or oCE's.     

Bacterial and archaeal diversity in oil fields and reservoirs and their potential role in hydrocarbon recovery and bioprospecting

Environmental Science and Pollution Research - Hydrocarbon is a primary source of energy in the current urbanized society. Considering the increasing demand, worldwide oil productions are declining...     

Sorption and Desorption Behavior of Chloroanilines and Chlorophenols on Montmorillonite and Kaolinite

The bioavailability of pollutants, pesticides and/or their degradation products in soil depends on the strength of their sorption by the different soil components, particularly by the clay minerals. This study reports the sorption-desorption behavior of the environmentally hazardous industrial pollutants and certain pesticides degradation products, 3-chloroaniline, 3,4-dichloroaniline, 2,4,6-trichloroaniline, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol on the reference clays kaolinite KGa-1 and Na-montmorillonite SWy-l. In batch studies, 2.0 g of clay were equilibrated with 100.0 mL solutions of each chemical at concentrations ranging from 10.0 to 200.0 mg/L. The uptake of the compounds was deduced from the results of HPLC-UV-Vis analysis. The lipophilic species were best retained by both clay materials. The most lipophilic chemical used in the study, 2,4,6-trichloroaniline, was also the most strongly retained, with sorption of up to 8 mg/g. In desorption experiments, which also relied on HPLC-UV-Vis technique, 2,4,6-trichloroaniline was the least desorbed from montmorillonite. However, on kaolinite all of the compounds under study were irreversibly retained. The experimental data have been modelled according to the Langmuir and Freundlich isotherms. A hypothesis is proposed concerning the sorption mechanism and potential applications of the findings in remediation strategies have been suggested.     

Sorption and desorption behavior of chloroanilines and chlorophenols on montmorillonite and kaolinite

The bioavailability of pollutants, pesticides and/or their degradation products in soil depends on the strength of their sorption by the different soil components, particularly by the clay minerals. This study reports the sorption-desorption behavior of the environmentally hazardous industrial pollutants and certain pesticides degradation products, 3-chloroaniline, 3,4-dichloroaniline, 2,4,6-trichloroaniline, 4-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol on the reference clays kaolinite KGa-1 and Na-montmorillonite SWy-l. In batch studies, 2.0 g of clay were equilibrated with 100.0 mL solutions of each chemical at concentrations ranging from 10.0 to 200.0 mg/L. The uptake of the compounds was deduced from the results of HPLC-UV-Vis analysis. The lipophilic species were best retained by both clay materials. The most lipophilic chemical used in the study, 2,4,6-trichloroaniline, was also the most strongly retained, with sorption of up to 8 mg/g. In desorption experiments, which also relied on HPLC-UV-Vis technique, 2,4,6-trichloroaniline was the least desorbed from montmorillonite. However, on kaolinite all of the compounds under study were irreversibly retained. The experimental data have been modelled according to the Langmuir and Freundlich isotherms. A hypothesis is proposed concerning the sorption mechanism and potential applications of the findings in remediation strategies have been suggested.     

Sources and fate of PCDD and PCDF

PCDD and PCDF were found in urban air particulates from St. Louis and Washington, D.C., and in sediments from the Great Lakes and Siskiwit Lake, Isle Royale. The similarity between the PCDD and PCDF found in air particulates and sediment samples and the presence of PCDD and PCDF in sediment from Siskiwit Lake (a location which can receive only atmospheric inputs) suggest that these compounds are emitted to the atmosphere from combustion sources. The historical input of PCDD and PCDF to dated sediment cores shows a strong increase since 1940, and this suggests that the incineration of chlorinated organic compounds is an important source of PCDD and PCDF to the environment.     

Synthesis and characterization of m- and p-methylbenzyl-mercapturic acids derived from m- and p-xylenes

Chemical synthesis and physical properties of two mercapturic acids suggested as urinary metabolites of m- and p-xylenes ace described. These compounds may be used for the identification and quantivative determination by high-performance liquid chromatography of the corresponding mercapturic acids in urine.