薄膜扩散梯度技术测定水体中砷及其影响因素研究

薄膜扩散梯度技术（Diffusive Gradientsin Thin Films Technique,DGT）是近年来应用于水体、沉积物和土壤中的铜镉等重金属生物有效性研究的一种新技术。采用标准溶液培养方法研究了以氧化铁作为吸附剂的DGT测定水环境中无机砷含量的可行性,并探讨了待测介质的pH和As价态对DGT测定结果的影响。结果表明,研究所用DGT装置中的吸附凝胶对砷吸附的最大容量≤42μg,其有效容量≤13μg,为确保DGT测定值的准确性,需要对DGT装置的放置时间加以控制;当水体中砷浓度为0.1～11.0mg·L-1时,DGT测定的溶液中无机砷浓度与直接用HG-AFS测定待测水体中无机砷浓度之间有较好的响应关系,DGT测定水体中无机砷的浓度能较好反应水体中无机砷的真实浓度;当溶液的pH值为2.95～8.18时,不同pH下吸附凝胶对砷的吸附量间差异不显著,溶液pH值在一定范围不影响DGT的测定结果;As（V）、As（Ⅲ）在进行DGT试验时不存在竞争吸附关系,砷离子的价态对DGT测定水体中的无机砷的浓度没有显著影响。总之,在各种环境相关的条件下,DGT是一种可以用于测定水体中总无机砷的有效方法。     

不同浓度铜离子土壤的吸附-解吸行为——兼论弱专性吸附态的存在

研究了三种可变电荷土壤和两种恒电荷土壤不同铜离子浓度条件下的吸附-解吸行为。结果表明,不同铜离子浓度下土壤的pH-Cu2+吸附率曲线均在低pH段出现会合,且随着铜离子浓度升高,pH-Cu2+吸附率曲线有向右偏移的趋势。证实了可变电荷土壤中吸附性铜离子可被去离子水解吸,并存在解吸峰现象。针对解吸前后吸附体系pH值的变化研究结果显示,吸附时体系pH低于5.0时,解吸后pH上升;而吸附体系pH高于5.0时,解吸后pH下降,表明pH5.0可能是土壤吸附铜离子机理发生变化的又一个转折点。本文还对专性吸附中弱吸附态的存在和形成原因进行了初步探讨。     

不同NaNO_3浓度下可变电荷土壤铜离子解吸率的分配及影响因素

研究了江西红壤和昆明铁质砖红壤在去离子水中和在0.1molL-1NaNO3溶液中吸附铜离子后,依次在包括去离子水在内,浓度由低到高的NaNO3溶液中解吸时,铜离子解吸率在不同吸附pH段的分配规律。结果表明,随着吸附pH的升高,可在去离子水中解吸的铜离子解吸率变化规律与在NaNO3溶液中者完全不同。在所研究的吸附pH范围内,大致以吸附pH3.7~4.0为界,低于此值时,吸附性铜离子基本以在去离子水中解吸为主,反之则基本为交换性解吸。土壤中氧化铁含量和吸附时溶液的NaNO3浓度越高,则能被交换解吸的铜离子所占总解吸率的比例越低。其原因与不同pH段各种铜离子吸附态在不同吸附条件下的比例分配以及解吸对体系pH的影响有关。     

毒死蜱有毒代谢物3,5,6-TCP在土壤中的吸附-解吸研究

应用OECD106批平衡方法,研究了毒死蜱的有毒代谢物3,5,6-TCP在6种典型土壤中的吸附-解吸行为。结果表明：Elovich方程、双常数方程和抛物线扩散方程能较好地拟合3,5,6-TCP在第四纪红土、黑土、黄壤和褐土中的吸附动力学过程,而对紫色土和潮沙土的拟合度较低（拟合相关系数小于0.85）;应用Freundlich方程和线性方程拟合第四纪红土、黑土、黄壤和褐土的经验常数nfads均小于1（非线性吸附）,而紫色土和潮沙土的nfads值则接近于1（线性吸附）;3,5,6-TCP在6种土壤中解吸的滞后系数H值均大于1,即解吸速率大于吸附速率。6种土壤对3,5,6-TCP的吸附常数Kfads从1.37-6.74μg1-n·fmLn·fg^-1,吸附系数Kd值从0.50-1.30mL·g^-1,其中第四纪红土和黑土对其吸持力较强（Kd〉1）,因而更应注意环境安全;其他4种土壤的Kd值则均小于1,淋溶风险较大。     

电解质种类和浓度影响磷酸根解吸的机理研究

本文研究了吸附性阳离子、电解质浓度和组成影响几种矿物和土壤吸附态磷的解吸的机理。结果表明,吸附性阳离子影响磷酸根解吸与离子桥有关。桥接静电场愈强,被束缚磷的释放就愈困难。电解质阳离子对磷酸根解吸的影响则取决于其对表面负电荷的屏蔽效应。阳离子电价高,屏蔽作用大,磷解吸就少。电解质浓度影响吸附态磷的解吸主要与表面电位的变化有关。当pH>PZC值时,提高电解质浓度降低表面负电位,从而减少磷的吸附;当pH<PZC时,提高电解质浓度则降低表面正电位,促进磷的解吸。磷酸根解吸盐效应零点(P_PZSE)值一般都介于土壤或矿物样品吸附磷酸根前后测得的两个PZC值之间。不同浓度电解质溶液中磷解吸量之差与吸附层电位变化量(△ψ_x)呈正相关。     

中国南方两类典型土壤对五价锑的吸附行为研究

研究我国南方两类典型土壤(红壤和棕色石灰土)对五价锑[Sb(V)]的等温吸附、动力学吸附-解吸过程,比较常用动力学方程对吸附动态曲线的拟合效果,采用分级提取方法分析锑在土壤中的结合形态。试验结果表明,酸性红壤对Sb(V)的吸附量(13.8μmol g-1)和吸附速度(0.58μmol g-1h-1)均大于棕色石灰土(9.19μmol g-1;0.38μmol g-1h-1),Sb(V)在红壤表面吸附是一个快速不可逆过程。锑主要以结合较强的Fe、Al氧化物结合态和残渣态存留在两种土壤中,专性和非专性吸附形态含量很低,也说明锑在土壤中以不可逆吸持为主。比较4种动力学吸附方程对实验结果的拟合程度发现,对于红壤而言,浓度较高的情况下Elovich方程(R2=0.96)的拟合性较好,浓度较低的情况下拟二阶动力学方程(R2=0.97、1.00)的拟合性较好;而对于棕色石灰土,在3种浓度下,双常数方程(R2=0.96、0.94、0.93)的拟合性均较好。     

可变电荷土壤中铜离子的解吸

研究了我国四种可变电荷土壤红壤、赤红壤、砖红壤和铁质砖红壤以及二种恒电荷土壤黄棕壤和黑土中吸附性铜离子的解吸特征。研究结果表明 ,可变电荷土壤吸附的一部分铜离子可以被去离子水解吸 ,而且在pH～解吸率曲线上在一定pH值时出现解吸率最大值。在最大值时不同土壤中铜离子解吸率的大小与土壤中氧化铁的含量有关。氧化铁的含量越高 ,在最大值时铜离子的解吸率越大。当用中性电解质解吸可变电荷土壤吸附的铜离子时 ,电解质的浓度越大 ,解吸率越低。与此相反 ,恒电荷土壤吸附的铜离子不能被去离子水解吸 ,只能被中性电解质解吸 ,且电解质的浓度越高 ,解吸率越大。这表明 ,可变电荷土壤中吸附性铜离子的解吸规律 ,完全不同于恒电荷土壤中者。本文初步讨论了其原因     

土壤矿物和胡敏酸对阿特拉津的吸附-解吸作用研究

选取了6种土壤矿物(蒙脱石、高岭石、钙饱和处理蒙脱石、钙饱和处理高岭石、无定型氧化铁和无定型氧化铝),以及从土壤中提取纯化的3种胡敏酸为材料,采用批量吸附平衡法,研究土壤矿物和胡敏酸对阿特拉津的吸附特性。结果表明,各吸附剂对阿特拉津的吸附均能采用Frundlich方程进行较好地拟合(r≥0.982,p0.01)。胡敏酸对阿特拉津具有最大的吸附性能,其固-液分配系数(Kd值)随平衡浓度(Ce值)的变化基本恒定,吸附等温线呈线性(Frundlich方程常数N≈1),吸附以分配溶解作用为主,吸附可逆性较高。黏土矿物(特别是蒙脱石)对阿特拉津也具有较强的吸附能力,Kd值随Ce值增加而增加,吸附等温线呈S型(N1),吸附主要是通过表面亲水作用。无定型氧化铁铝的Kd值随Ce值增加而降低,当Ce达到一定水平后,Kd趋于恒定,吸附等温线呈L形(N1),吸附主要是通过无定型氧化物表面的羟基与阿特拉津分子间的化学键合作用,吸附可逆性最差。     

有机酸对几种土壤胶体吸附解吸镉离子的影响

用平衡法研究了有机酸对土壤胶体吸附 解吸Cd2 的影响。结果表明 ,黄棕壤、红壤、砖红壤胶体Cd2 最大吸附容量 (Qm)分别为 4 3 7、16 8、1 5 8mmolkg-1。在加入Cd2 浓度相同的条件下 ,土壤胶体Cd2 吸附量随有机酸浓度的升高呈峰形曲线变化。当有机酸与Cd2 共存时 (竞争吸附 ) ,低浓度的草酸 (小于0 5～ 2mmolL-1)或柠檬酸 (小于 0 0 2 5～ 0 2mmolL-1)提高Cd2 吸附量 ,高浓度的草酸或柠檬酸能降低Cd2 吸附量。吸附有机酸后的土壤胶体 (次级吸附 )对Cd2 次级吸附量的影响与竞争吸附一致 ,但两者的Cd2 吸附量变化幅度不一样。这是由于两种吸附体系液相中有机酸残留浓度不同所致。土壤胶体吸附态Cd2 的解吸结果表明 ,草酸浓度不仅影响Cd2 的总解吸量、总解吸率 ,还影响土壤胶体表面KNO3 解吸态与DTPA解吸态Cd2 的分配比例     

离子强度对可变电荷表面吸附性铜离子解吸的影响:高岭石

为了解连续性解吸对可变电荷表面吸附性铜离子解吸的影响,研究了高岭石在去离子水和0.1 mol L~(-1) NaNO_3溶液中吸附铜离子后,依次在去离子水以及浓度由低到高的NaNO_3溶液中连续解吸时,离子强度变化对不同pH段铜离子解吸的影响。结果表明:在去离子水中和不同浓度NaNO_3中解吸吸附性铜离子时,pH-解吸分值曲线的变化趋势完全不同。在去离子水中解吸时可出现重吸附现象,而在NaNO_3中解吸时出现解吸峰现象。高岭石pH-铜离子解吸分值曲线的拐点pH与pH吸附有着对应关系,且pH特征与高岭石pH0关系密切。离子强度变化导致的吸附表面电位变化、高岭石边面的诱导水解作用和土壤表面电荷性质随pH升高的变化被认为是导致这些现象的原因。     

Determination of High Resolution Pore Water Profiles of Trace Metals in Sediments of the Rupel River (Belgium) using Det (Diffusive Equilibrium in Thin Films) and DGT (Diffusive Gradients in Thin Films) Techniques

The techniques of diffusional equilibrium in thin films (DET) and diffusional gradients in thin films (DGT) were used to obtain high resolution pore water profiles of total dissolved and labile trace (mobilizable) metals in the sediments of the Rupel River, Belgium. DGT measures labile metal species in situ by immobilizing them on a resin gel after diffusion through a diffusive gel whereas for DET an equilibrium is established between the DET gel and the pore water. Concentrations of Pb and Zn obtained by DGT were in good agreement with the results obtained by centrifugation, and thus were well buffered by rapid equilibrium with the solid phase, whereas Fe, Mn and Cd were very tightly bound to the sediment phase and large differences were observed between the labile and the total metal concentrations. Cu, Zn, Co and Ni show intermediated behavior. Good correlations were found between the profiles of As and Fe and Mn and Co for DET as well as DGT showing a close link between the geochemical behavior of these elements. Cu, Zn, Pb and Cd are also influenced by the reductive mobilization of Fe and Mn oxides but are also closely linked to the bacterial degradation of organic matter in the surface sediments as to the precipitation of metal sulfides in the deeper layers.     

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。     

离子强度对铁质砖红壤铜离子连续解吸的影响

研究了昆明铁质砖红壤中水吸附性铜离子依次在包括去离子水在内的浓度从低到高的Na NO3溶液中连续解吸时,电解质浓度和有机质去除对不同p H段铜离子解吸率的影响。结果表明,当铁质砖红壤中水吸附性铜离子依次在去离子水、0.01 mol L-1Na NO3、0.1 mol L-1Na NO3及1 mol L-1Na NO3中连续解吸时,去离子水和Na NO3溶液对铁质砖红壤p H-铜离子解吸率曲线形状影响截然不同。在去离子水中解吸时,解吸率曲线表现为单调下降,当解吸平衡液p H达到5.3左右时,铜离子解吸率降至基本为零,且解吸次数不影响这一规律;在Na NO3溶液中解吸时,除1 mol L-1者外,对于0.01 mol L-1和0.1 mol L-1者,铜离子解吸率曲线均在p H4.4~4.6之间出现解吸峰。部分去除有机质对解吸率的整体变化趋势并无根本影响。研究结果表明,土壤中吸附性铜离子可在去离子水中解吸的原因与双电层重叠以及离子强度降低导致土壤表面对铜离子解吸势增加有关,而解吸峰产生的可能原因与在不同p H段,体系p H对铁质砖红壤中吸持铜离子的羟基化比例和表面电荷性质的综合影响有关。     

Effect of extraction techniques on soil pore‐water chemistry

Abstract

The retention of contaminants in soil and overburden is often estimated using a solid/liquid partition coefficient, Kd, which lumps all the processes into an empirical value. Determination of this value in unsaturated porous media requires the separation of the pore water from the solid phase. Soil pore‐water recovery and composition were investigated in three chemically and texturally different mineral soils and one organic soil. The removal of pore water was achieved through centrifugation at low (1000 to 2500 rpm) and ultra (10,000 to 20,000 rpm) speeds, ceramic plate extraction and immiscible displacement. Pore‐water recovery was highest using ceramic plate extraction and lowest with displacement. Pore‐water quality was not affected by centrifugation time. However, the pore‐water concentrations of F, Cl, NO₃, Fe, and Na suggest that the effect of centrifuge speed on the element or ion of interest should be determined prior to extraction. Ceramic plates retained both cations and anions, and the immiscible displacent depressed the pH of the soil slurry affecting the pore‐water composition. Comparisons between distilled water extracts, standardized to field capacity moisture, and the centrifugate for a sand and an organic soil indicated that with low solid/liquid ratios, pore‐water concentrations are influenced by dissolution or desorption. Therefore, Kd values based on centrifuged pore water will be lower than those based on extraction/ desorption.     

基于梯度扩散薄膜技术的太湖金属和营养盐区域污染特征分析

本研究利用梯度扩散薄膜技术（Diffusive gradients in thin-films,DGT）对太湖7个湖区的水体和沉积物中金属与营养盐有效态含量进行原位监测,并分析污染物的区域特征。结果表明,DGT所测有效态浓度低于传统化学方法所提取浓度,且能实现低浓度、多元素同时监测。具体来看,太湖水体中金属的DGT有效态含量较低,区域差别较小。沉积物中9种典型金属的DGT有效态含量排序为Fe>Mn>Zn>Ni>As>W>Co>Mo>Cu,其中,Fe、As、Zn、Ni和W在竺山湾、梅梁湾和贡湖污染相对较重,在湖心区、胥湖和东太湖污染相对较轻,其余金属分布较平均且含量较低。与金属不同的是,太湖水体中DGT所测的有效磷（P）含量整体较高,最高值出现在贡湖,达83.2μg·L-1。沉积物中DGT有效态P的区域分布更明显,以竺山湾、梅梁湾和沿岸区污染相对较重,最高值出现在竺山湾,达500μg·L-1。对比沉积物和水体中DGT有效态P含量发现,竺山湾、梅梁湾和沿岸区沉积物可能是P的主要储存场所,具有潜在释放风险。     

氧化节杆菌生物降解苯并芘

A pot experiment was conducted with multi-metal (Pb, Cd, Cu, and Zn) contaminated acidic soil to investigate changes in available metal burden resulting from the application of industrial wastes (fly ash and steel slag). The efficiency of amendments-induced metal stabilization was evaluated by diffusive gradients in thin films (DGT), sequential extraction, and plant uptake. The stability of remediation was assessed by an acidification test and by chemical equilibrium modeling. Addition of fly ash (20 g kg-1 ) and steel slag (3 g kg-1 ) resulted in similar increase in soil pH. Both amendments significantly decreased the concentrations of metals measured with DGT (C DGT) and the metal uptake by Oryza sativa L. Significant correlations were found between C DGT and the concentration of a combination of metal fractions (exchangeable, bound to carbonates, and bound to Fe/Mn oxides), unraveling the labile species that participate in the flux of metal resupply. The capability of metal resupply, as reflected by the R (ratio of C DGT to pore water metal concentration) values, significantly decreased in the amended soils. The C DGT correlated well with the plant uptake, suggesting that DGT is a good indicator for bioavailability. Acidification raised the extractable metal concentration in amended soil but the concentration did not return to the pre-amendment level. Equilibrium modeling indicated that the soil amendments induced the precipitation of several Fe, Al and Ca minerals, which may play a positive role in metal stabilization. Chemical stabilization with alkaline amendments could be an effective and stable soil remediation strategy for attenuating metal bioavailability and reducing plant metal uptake.     

The role of sediment-feeding oligochaeteTubifex on the availability of trace metals in sediment pore waters as determined by diffusive gradients in thin films (DGT)

Background  Available fractions of metal concentrations in sediment pore water are difficult to measure without disturbing the sediment core. The available fraction is an important parameter in understanding the risks for benthic organisms. Not much is known about the influence of the presence of benthic organisms to the available fraction. Objectives  The aim of this study was to discuss the dynamics of metal behaviour in natural sediments and the influence of the presence ofTubifex on sediment chemistry using DGT. Methods. DGT-probes were added to six beakers to cover a depth profile of 0 to 13 cm. The six beakers contained three different sediments. For each sediment, one beaker had 1 g ofTubifex added, the other beaker contained noTubifex. After two weeks of exposure, the probes were withdrawn and strips were analysed for their content of cadmium, copper and zinc. Results and discussion  Available concentrations were higher in the upper layer (0–1 cm) of the sediment core, where conditions are generally more oxic. The presence ofTubifex worms led to a decrease of the available concentrations in the upper layer, due to the competition of the worms with the DGT for the available metal fraction. On the other hand, the presence of the worms led, via bioturbation, to an increased oxygen penetration depth in the sediment, and, as a consequence, to an increase of the available fraction in the next-higher sediment layer. Conclusions  In sediment cores without organisms, very steep gradients of the available metal concentration in pore water have been found. The change from a high to low amount of available fraction corresponds to the change from oxidised conditions in the surficial sediment layer to reduced conditions in the lower sediment layers. The tunnelling behaviour ofTubifex worms leads to a penetration of oxygen to deeper sediment layers, and to an increase of the available metal fraction in the pore water.Tubifex competes with DGT for the available fraction, resulting in lower metal amounts accumulated in the DGT probe. Competition is the prevailing effect in the top 1 cm layer of all sediments. In the second 1 cm layer, competition, in most cases, is not strong enough to compensate the increase in metal availability due to the broadening of the oxidised zone. Recommendations  The effects of sediment organisms on the deepening of the oxidised layer and on the availability of metals in pore water need further investigations and quantification. DGT is recommended as an instrument for measuring available metal concentrations in these studies.     

Occurrence of Cu and Cr in the sedimentary humic substances and pore water from a typical sugar cane cultivation area in São Paulo,Brazil

Purpose

The purpose of this paper is to study the interactions of sedimentary humic substances (SHS) from a sugarcane cultivation area with Cu(II) and Cr(III) and to evaluate the occurrence of these metals in the pore water and SHS.

Materials and methods

For this study, the northwestern region of the State of São Paulo, Brazil, which is considered the region with the highest production of sugar cane in the state, was selected. Samples of sediment were collected from four sampling sites in the Preto, Turvo, and Grande rivers. The SHS and pore water were extracted from the sediment using the method suggested by the International Humic Substances Society and centrifugation, respectively. The complexing capacity (CC) of the SHS for Cu(II) and Cr(III) was determined by individually titrating these metals with an ultrafiltration system using tangential flow. The total concentrations of Cr and Cu were determined for the pore water, sediments, and humic substances with graphite furnace atomic absorption spectrometry and Zeeman background correction after an acid digestion, according to the methods described in US EPA Method 3050B.

Results and discussion

The SHS from a site in the Turvo River, which is typically cultivated with sugarcane, possessed the highest concentration of Cu bound to SHS (25.0%), the largest CC (0.63 mmol Cu g^?1 HS) and the highest concentration of this metal in the pore water (1.38 mg Cu Kg^?1 sed.). For Cr, the SHS collected from a location on the Preto River dam had the largest CC (0.90 mmol Cr g^?1 HS) and the lowest Cr content in the pore water (0.29 mg Cr Kg^?1 sed.), indicating that there was an inverse relationship between the CC and the concentration of metal available in the pore water.

Conclusions

Sedimentary humic substances might be one of the regulatory factors controlling the availability of Cu and Cr in the sediments found in a typical region that has been planted with sugarcane. Distinct behaviors were observed between the two elements investigated; higher CC and a larger fraction of Cu(II) were found in the pore water of samples originating from sugarcane crops. The opposite behavior was observed for the Cr(III) species.     

Phytostabilisation of a copper contaminated topsoil aided by basic slags: assessment of Cu mobility and phytoavailability

Purpose

Basic slags are alkaline by-products of the steel industry with potential properties to ameliorate nutrient supply and metal stabilisation in contaminated soils. This study aimed at investigating the potential of a P-spiked Link Donawitz slag and a conventional basic slag called Carmeuse for the aided phytostabilisation of a Cu-contaminated soil at a wood treatment site. The effects of basic slag addition on Cu fractionation, mobility and (phyto) availability were assessed.

Materials and methods

Both slags were incorporated at 1 % w/w into the Cu-contaminated soil phytostabilised with Cu-tolerant plants, using either outdoor lysimeters or a field plot. Untreated soil (UNT), amended soils with the P-spiked Link Donawitz slag (PLDS) and the conventional slag (CARM) respectively, and a control soil (CTRL) were sampled, potted and cultivated with dwarf bean. Physico-chemical analysis, determination of total soil elements and a Cu-sequential extraction scheme were carried out for all soils. Physico-chemical characteristics of soil pore water and Cu speciation (rhizon, ion selective electrode and diffusive gradient in thin film (DGT)) were determined. Shoot dry weight yield and leaf ionome (i.e. all inorganic ions present in the primary leaves) of dwarf beans were investigated.

Results and discussion

The slag incorporation at only 1 % w/w increased the soil pH from 1.5 to 2 U and electrical conductivity in soil pore water by three times. The residual Cu fraction increased for both slag amended soils compared to the UNT soil by six times in parallel to the decrease of the Cu oxidisable fraction (1.5 times) and to a less extent the reducible fraction. The incorporation of both slags did not reduce the total dissolved Cu concentration in the soil pore water but significantly reduced the real dissolved Cu concentration ca five times, the Cu labile pool as measured by DGT (at least two times) and the Cu phytoavailability. The dwarf bean total biomass was also improved with the slag addition especially for the P-spiked Linz–Donawitz slag.

Conclusions

The addition of both slags in the contaminated soil increased Cu concentration in the residual fraction and thus reduced its potential mobility. Though the total dissolved Cu soil pore water concentration remained identical, its speciation changed as the real dissolved fraction diminished and lowered the Cu bioavailability. The addition of small amount of P-spiked Linz–Donawitz and Carmeuse slags was beneficial for this Cu-contaminated soil in the context of aided phytostabilisation.