肯尼亚水稻土和甘蔗地土壤中~(14)C-六氯苯和~(14)C-滴滴涕的自然消解

氯代持久性有机污染物的农田土壤污染呈现污染浓度低、面积大、新源污染不断输入的特点。农田土壤本身微生物种类丰富,对氯代有机污染物具有较大的降解潜力和未知性。本试验以典型高氯代和低氯代持久性有机污染物——六氯苯(HCB)和滴滴涕(DDT)为研究对象,结合~(14)C同位素示踪技术,研究HCB和DDT在热带水稻土和甘蔗地土壤的矿化现象,同时监测HCB和DDT在两种土壤中的挥发、降解产物以及结合残留。结果表明,经84 d好氧培养,HCB和DDT在两种土壤中的矿化量分别仅为0.14%和3%,低氯代有机污染物DDT的矿化速率显著高于高氯代有机污染物HCB。然而,两种土壤对HCB或DDT的矿化没有显著性差异。HCB或DDT在水稻土中的挥发量略微高于甘蔗地土壤,两种土壤中HCB和DDT的挥发量在0.1%~0.6%之间,表明挥发不是其主要的环境过程。在DDT污染水稻土和甘蔗地土壤中添加1.25%的堆肥增加了DDT在土壤中的矿化与结合残留,减少了DDT的挥发。本研究结果表明土壤在好氧条件下对氯代持久性有机污染物的自然消解能力非常弱,而有机肥的使用有助于土壤中持久性氯代有机污染物的矿化消除。     

兽药抗生素在土壤环境中的行为

兽药抗生素的环境暴露问题逐渐受到人们的极大关注。但是,以往的少数相关研究仅仅报道了某些兽药抗生素在水体环境和底泥中的存在,其中涉及土壤体系的则更少。同时,对兽药抗生素在土壤中的暴露途径和迁移、转化等了解较少。某些兽药抗生素如土霉素等,在环境中的持久性较强,对生物和环境可能存在着潜在的威胁。本文回顾了某些兽药抗生素在土壤体系(包括底泥)中的环境行为。     

铜污染农田表层土壤的持久性有机氯农药残留状况

土壤中持久性有机污染物往往与重金属共存形成混合污染,但过去的研究较少关注它们在土壤中的相互影响。本研究选择典型铜污染区农田,分析了铜不同污染程度的表层土壤中HCB、HCHs与DDTs等持久性有机氯农药的组分及含量。结果表明:DDTs在土壤中的残留量随着土壤铜污染程度的加剧而上升;土壤中铜抑止了DDT向DDE或DDD的转化,DDTs残留量相对较大。供试土壤中持久性有机氯农药含量与有机质之间的相关性分析表明,污染土壤中两者之间的相关性大于未污染土壤,说明铜促进了土壤中的DDTs和HCHs与土壤有机质结合,这可能是导致水田土壤中DDTs的平均含量显著高于旱地和林灌地土壤的原因之一。     

土壤pH对汞迁移转化的影响研究进展

近年来土壤重金属污染已经成为全球性的环境问题。而汞作为五大毒性重金属元素之一,其在土壤中的迁移转化不仅会影响作物的正常生长,还会对农产品质量和安全造成严重威胁。土壤pH是影响汞迁移转化的重要因素之一,对其作用机理的不断探索已经成为近年来的研究热点。本文在前人的研究基础上,概述了土壤中汞的来源、危害及存在形态,并从汞的生物有效性及迁移转化过程两个方面详细阐述了土壤pH对汞迁移转化的影响机制。研究表明,酸性条件可能会使土壤中有效态汞的含量增加,进而导致其生物有效性提高,迁移能力增强;土壤pH对汞迁移转化过程中吸附-解吸的影响较大;土壤pH对汞迁移转化过程中络合-螯合、氧化-还原及甲基化反应的影响机理分别体现在离子竞争吸附、价态变化及甲基化促使因子的合成等方面。最后对今后的研究方向作出展望,旨在为汞污染土壤的修复与治理及汞污染扩散模型的建立提供参考依据。     

农药在土壤中迁移及其影响因素的初步研究

本文运用非饱和土壤中水分运动和溶质运移基本理论,建立了非饱和土壤中农药运移的数值模拟模型.模型中考虑了农药在土壤中迁移与转化的主要过程:附土壤水分的对流;水动力弥散;土壤吸附及生物化学降解等.模型得到了室内土柱中灭幼脲-Ⅲ号杀虫剂淋溶试验的验证.文中分析了各种因素对该农药存土壤中迁移的影响,并且对两种不同的农药进行了比较.研究表明,在本文所研究的条件下影响农药在土壤中迁移与转化的主要因素是土壤吸附和农药在土壤中的降解.     

电子供体对土壤中多氯代有机化合物厌氧脱氯作用研究进展

多氯代有机化合物(PCOCs)是环境中典型的污染物,其高毒性和持久性使其对生态环境造成严重危害。土壤是PCOCs的主要贮存场所,探索土壤中PCOCs加速降解机制至关重要。氯原子强烈的吸电子性使PCOCs很难在自然条件下发生氧化降解,而在厌氧条件下,PCOCs较易获得电子同时脱去氯取代基,使其毒性和持久性大大降低。本文重点综述PCOCs厌氧脱氯过程中电子供体的作用,比较几种常用电子供体(零价金属、有机物、非金属元素)的还原脱氯效果及其作用机制,最后展望了土壤中PCOCs还原脱氯降解的下一步研究方向。     

土壤中多溴联苯醚研究进展

多溴联苯醚(Polybrominated diphenyl ethers,PBDEs)是一种新型的有机污染物,作为溴化阻燃剂被大量使用。目前,PBDEs在我国多处土壤介质中均有检出。同时由于其具有毒性、可持久性、生物蓄积性,近年来已成为环境领域关注的热点。本文分析了土壤中PBDEs的来源,总结了土壤中PBDEs的分布水平,介绍了土壤中PBDEs的迁移规律,讨论了土壤中PBDEs的降解途径,并对今后土壤中PBDEs的研究进行了展望。     

酞酸酯在土壤中的环境行为与健康风险研究进展

酞酸酯(PAEs)又称邻苯二甲酸酯,是环境激素类有机化合物,作为增塑剂在塑料、树脂和橡胶制品中的添加量一般为20%~60%。土壤中PAEs的主要来源有农用化学品、污水灌溉和大气沉降。PAEs在土壤中有较强的富集作用,并能通过一系列的环境地球化学过程进入不同的环境介质,引起环境污染和人类健康风险。本文结合国内外土壤PAEs的相关研究成果,综述了我国土壤PAEs的污染现状,分析了PAEs在土壤-大气界面(挥发、沉降)、土壤-植物系统(植物吸收、植物修复)、土壤-水界面下的环境行为(吸附-解吸)及土壤PAEs污染的环境健康风险,并指出国内土壤PAEs研究中存在的不足。研究结果显示,我国土壤环境总体上已遭受不同程度的PAEs污染;同时,土壤PAEs通过不同界面之间的迁移转化过程,也面临较高的生态环境健康风险。提出今后土壤PAEs研究应以区域土壤污染与环境行为为重点,深入研究土壤PAEs的时空传输与演变规律、多介质迁移转化机制和风险削减与修复措施,为保障土壤生态环境与健康提供理论依据。     

农田中的(微)塑料污染:来源、迁移、环境生态效应及防治措施

近年来,继海洋中的微塑料污染受到广泛关注后,土壤微塑料的环境风险逐渐受到重视,有关微塑料对土壤生态环境影响的研究取得了积极进展。本文总结了迄今为止的有关农田土壤中(微)塑料的研究成果和进展,阐明了当前国内外农田微塑料污染现状;详细论述了农田土壤中(微)塑料的来源以及不同源对农田微塑料污染的潜在贡献;对农田微塑料污染现有的研究方法尤其是采样方案和微塑料的提取技术做了较为详尽的分析和论证;探讨了微塑料在土壤中的迁移、老化、与其他污染物的相互作用等环境行为和归趋,以及由此带来的环境效应和生态风险,并重点关注了微塑料污染对于农田土壤质量和食品安全带来的挑战;最后列举了部分现有的微塑料污染防治策略及其对农田中微塑料污染防治的意义,并对未来土壤中微塑料的研究方向进行展望。文章认为,农田土壤的塑料与微塑料来自多种源头,其中塑料固体废物尤其是农业地膜是农田中微塑料的主要来源之一。微塑料进入土壤后,在外界物理、化学与生物等因素扰动或作用下,会发生不同尺度的迁移转化甚至生物反应,造成广泛的环境生态影响,主要有对土壤理化性质、微生物群落、土壤动物、植物生长等的不利影响,从而损害土壤健康,影响农业生产和农产品质量;此外,细小的微塑料颗粒尤其是纳米塑料存在经由食物链向人体富集的潜在风险。塑料在土壤环境中可能被生物碎化与缓慢生物降解。考虑到微塑料在环境中的广泛分布,持久性和生态风险,结合各国现有的防治策略,提出了相关的防治建议。     

土壤环境中的多氯联苯(PCBs)及其修复技术

本文着重介绍了土壤中PCBs污染的现状及其产生的危害,总结了土壤中持久性污染物PCBs的迁移转化规律,回顾并比较了近年来国内外PCBs污染土壤的修复技术,最后对多氯联苯污染土壤的修复技术的发展趋势进行了预测和展望。     

Enhanced anaerobic degradation of hexachlorobenzene in a Hydragric Acrisol using

Humic substances acting as an electron shuttle and nitrogen transformation process influence remarkably the electron transfer in anaerobic reaction systems and thus may affect the reductive dechlorination of hexachlorobenzene(HCB). In order to develop an efficient agricultural strategy for the remediation of organochlorine-contaminated soils, a batch incubation experiment was conducted to study the effects of humic acid, urea, and their interaction on the reductive dechlorination of HCB in a Hydragric Acrisol with high iron oxide content. After 44 d of anaerobic incubation, the five treatments, sterile control,control, humic acid, urea, and humic acid + urea decreased HCB residues by 28.8%, 47.8%, 64.7%, 57.8%, and 71.3%, respectively. The amendment of humic acid or urea significantly decreased soil Eh values and accelerated Fe(Ⅲ) reduction to Fe(Ⅱ), thus promoting markedly reductive dechlorination of HCB. Humic acid had a larger dechlorination effect than urea. Since there was a synergistic interaction between humic acid and urea that accelerated HCB dechlorination, the treatment having both amendments together was the most efficient for HCB dechlorination. The results showed that the combination of NH4⁺_-N supplied by a fertilizer and humic substance is a feasible strategy for the remediation of organochlorine-contaminated soils with abundant iron oxide.     

初始浓度对六氯苯在土壤中的吸附-解吸的影响及解吸

Adsorption and desorption are important processes that influence the transport, transformation, and bioavailability of hexachlorobenzene (HCB) in soils. To examine the adsorption-desorption characteristics of HCB, equilibrium batch experiments were carried out using two soils (red soil and paddy soil) with different initial HCB concentrations (0.25, 0.50, 0.75, 1.00, 1.50, 2.50, 3.50, and 5.00 mg L^-1) by using 0.01 mol L^-1 calcium chloride as the background solution. The successive desorption experiments (48, 96, 144, 192, and 240 h) were conducted after each adsorption equilibrium experiment. The results revealed that adsorption and desorption isotherms of HCB on two soils were nonlinear, which can be best described by the Freundlich equation with the square of the correlation coefficient (r²) ranging from 0.97 to 0.99. Desorption of HCB from the two soils exhibited hysteresis at all HCB concentrations because the Freundlich desorption coefficients were always higher than the Freundlich adsorption coefficients. The hysteretic effect was enhanced with increasing initial HCB concentration, and positive hysteresis was observed at different concentrations.     

Priority organic pollutants in soil of arboretum of the Botanical Garden of Moscow State University: Report 3. Specific features of vertical distribution pattern of organochlorine pesticide in profile of urbanozem

The vertical distribution pattern of dichlorodiphenyltrichloroethane (DDT) and its metabolites (hexachlorocyclohexane (HCH) isomers and hexachlorobenzene (HCB)) in the urbanozem of the arboretum of the Botanical Garden of Moscow State University at Vorob’evy Gory is studied. The highest contents of DDT, dichlorodiphenyldichloroethylene (DDE), and HCH isomers in the soil profile are found in the Au humus horizon and/or in the top part of the U technogenic 10–20-cm-thick layer. The greatest HCB content is typical of the U technogenic 20–30-cm-thick layer. The total content of DDT and its metabolites (156.2 mg/kg) in the surface layer is within the range typical of soils of old parks and recreational zones. The residual DDT content in the soil profile is 0.336–1.47 of the maximum permissible content. The ratio between metabolites and isomers of DDT points to its slight transformation (5.67–37.6%) and application as an industrial chemical. The contents of HCB (2.479–5.868 μg/kg) and the total content of HCH isomers (α + β + γ) in the profile of the urbanozem are 1–2 orders of magnitude lower than the maximum permissible contents or approximate permissible contents (0.3824–0.9863 μu/kg) and correspond to their background levels. The ratio between the HCH isomers shows that the transformation rate of the pesticide is rather high and that in the preceding period it was mainly used in the form of lindane.     

污染物和土壤类型影响吸附剂降低水稻植株对有机污染物吸收的效果

Persistent organic pollutants(POPs) in soils are an environmental concern due to their long-term bioavailability, which could be reduced by adding adsorbents. However, testing of these adsorbents is necessary prior to widespread field application. The effects of three adsorbents, nano-organic montmorillonite, nano-organic silicon dioxide(SiO_2), and activated carbon, on hexachlorobenzene(HCB) and pentachlorobenzene(Pe CB) accumulation in rice(Oryza sativa L.) plants were tested in a greenhouse experiment using two soils, a Hydragric Acrisol(Ac) and a Gleyi-Stagnic Anthrosol(An). The bioconcentration factors(BCFs) of HCB and Pe CB to rice roots were 2.3–3.7 and 2.0–3.0 times those to rice shoots, respectively. The applications of the three adsorbents decreased HCB and Pe CB extractability in Ac, while only the application of activated carbon decreased their extractability in An. The bioavailability of HCB and Pe CB to rice plants in Ac was higher than that in An. In Ac, the applications of nano-organic SiO_2 and activated carbon decreased the BCF of HCB to rice roots by 16.1% and 26.8%, respectively, whereas only the application of activated carbon decreased the BCF of Pe CB to rice roots by 31.4%, compared to the control. In An, only the application of activated carbon decreased the BCFs of HCB and Pe CB to rice roots by 22.9% and 18.2%, respectively, compared to the control. However, the application of nano-organic montmorillonite inhibited rice growth in both soils. The results of this study suggested that the effectiveness of adsorbents would vary with pollutant and soil types, providing a reference point for developing efficient adsorbents to reduce the ecological risk of POPs.     

干湿交替过程中水稻土铁形态和磷吸附解吸的变化

采用室内培养试验 ,经过连续 3次淹水 落干处理 ,研究了干湿交替过程中土壤中氧化铁形态的变化以及对土壤磷吸附和解吸的影响。结果表明 ,淹水使土壤中结晶态氧化铁含量明显减少 ,无定形氧化铁和土壤对磷的吸附量急剧增加 ,磷解吸下降 ;落干则使之发生相反的变化。土壤中的无定形氧化铁含量与土壤对磷的吸附之间存在着密切的相关关系。因此 ,淹水 落干过程中无定形氧化铁的变化是影响水稻田磷有效性的一个主导因子。     

Estimation of the thermal separation of soil particles from the thermal conductivity under reduced air pressure

Knowledge of thermal conductivity of granular materials under reduced air pressure can be utilized for studying intricate mechanisms of heat transfer in two‐phase systems. We measured the thermal conductivity of three soils of varied texture and two sets of glass beads (GB) under reduced air pressure using a twin heat probe. We also predicted the thermal conductivity of a two‐phase system at reduced air pressure from the modified Woodside & Messmer equation based on the kinetic theory of gases. This equation includes a thermal separation of solid particles (d) defined by the heat conduction. We compared this separation with the geometrical mean separation of solid particles (D). The results showed a linear relation between d and D for the GB, and in all cases d was smaller than D. This suggests that conductive heat transfer in two‐phase GB takes place mainly through air spaces the dimension of which is smaller than D. The d of a Red Yellow soil and an Ando soil, however, were about 200–300 times larger than D. This result seems to be related to the soil aggregation. We showed that in soil aggregates the conduction of heat through the solid was the dominant mode of heat transfer, and the micropores in a soil aggregate had very little effect on the diminished thermal conductivity under reduced air pressure. The decrease in the thermal conductivity of two‐phase soil under reduced air pressure is probably caused by the air molecules confined in interaggregate pore spaces rather than those in the intra‐aggregate pore spaces. The d of soils can be used to represent the thermal separation of the interaggregate pore spaces, and soil aggregates can be treated as single‐grained particles in evaluating heat conduction.     

作物残体去向与利用及对土壤氮素转化的影响

近年来,作物残体还田受到了很大的关注,一方面它可以改进土壤氮素的动态变化,减少硝态氮淋失;另一方面可作为提高耕地土壤作为潜在氮储库的一种手段。作物残体是碳、氮的重要源和库,因此还田后会影响土壤中的氮素循环。本文综述了作物残体还田后对土壤氮素转化的影响及残体氮素的利用与去向问题。具体阐述了以下几个方面内容:作物残体的降解过程及影响因素,残体氮素的利用率及去向问题,以及作物残体对土壤无机氮库、有机氮库、微生物特征的影响。     

Reductive Dechlorination of Hexachlorobenzene by an Anaerobic Mixed Culture

The potential for reductive dechlorination of hexachlorobenzene (HCB) by a 1,2,3-trichlorobenzene (TCB)-adapted mixed culture was investigated. Optimal dechlorination conditions were assessed at 29 °C ～ 37 °C and pH 6.1 ～ 6.9. The observed transformation pathway was HCB → pentachlorobenzene (PCB) → 1,2,3,5-tetrachlorobenzene (TeCB) → 1,3,5-TCB. The dechlorination of HCB was delayed by the addition of ferric chloride and manganese dioxide as electron acceptors, but enhanced by the addition of lactate and pyruvate as electron donors. However, we found that the addition of acetate had no significant effect on HCB dechlorination. Following treatment with bromoethanesulfonic acid (BESA) and vancomycin, it was suggested that the methane-producing bacteria was involved in the dechlorination of CBs.     

THE RELATION BETWEEN BULK DENSITY, AVAILABLE WATER CAPACITY, AND AIR CAPACITY OF SOILS

The effect of bulk density on moisture content at 50 mb tension in four soils of different textures was studied. The volumetric water content increased linearly with bulk density over a wide range of densities. Depending on texture, a maximum bulk density was reached above which continued compaction decreased the water content. This is shown to be the point at which the air capacity of the soil at this tension approaches zero. Accepting that the gravimetric wilting point depends mainly on texture, the available water capacity varies in a manner similar to the 50 mb water content. If the relationships described are valid in the field, the available water capacity and air capacity may be optimized using cultivation techniques to adjust the bulk density. The available water capacity of coarse-textured droughty soils may be increased by increasing the bulk density provided that the air capacity remains above acceptable lower limits (10–15 per cent). Conversely, the air capacity of compacted soils with large available-water capacities could be increased by reducing the bulk density to a value corresponding to an acceptable available-water capacity. In very compacted soils a decrease in bulk density will benefit both available-water capacity and air capacity.