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The area of soils polluted with heavy metals is increasing due to industrialization and globalization. Aromatic plant species can be a suitable alternative way for agricultural valorization and phytomanagement of such soils by the commercialization of essential oils avoiding risks for the food chain. The potential of growing Helianthus petiolaris in heavy metal polluted soils was assessed in pot experiments using spiked soils and soils from a shooting range. In terms of phytostabilization, H. petiolaris could grow in soils containing 1000 mg/kg Pb2+, 50 mg/kg Cd2+, accumulating more than three times the soil Cd content in the aerial parts and translocating significant amounts of Pb to the aerial parts when growing in soils polluted with up to 500 mg/kg Pb. When phytostabilization is considered, phytotoxicity of heavy metals strongly depends on the rhizospheric microbial communities, either by mitigating trace element phytotoxicity or promoting plant growth via phytohormone production. So, the effects of heavy metals on the diversity of the rhizospheric bacterial community were assessed using DNA-fingerprinting. [ABSTRACT FROM AUTHOR]

ABSTRACT Phytoextraction has a promising potential as an environmentally friendly clean-up method for soils contaminated with toxic metals. To improve the development of efficient phytoextraction strategies, better knowledge regarding metal uptake, translocation and detoxification in planta is a prerequisite. This review highlights our current understanding on these mechanisms, and their impact on plant growth and health. Special attention is paid to the central role of glutathione (GSH) in this process. Because of the high affinity of metals to thiols and as a precursor for phytochelatins (PCs), GSH is an essential metal chelator. Being an important antioxidant, a direct link between metal detoxification and the oxidative challenge in plants growing on contaminated soils is observed, where GSH could be a key player. In addition, as redox couple, oxidized and reduced GSH transmits specific information, in this way tuning cellular signalling pathways under environmental stress conditions. Possible improvements of phytoextraction could be achieved by using transgenic plants or plant-associated microorganisms. Joined efforts should be made to cope with the challenges faced with phytoextraction in order to successfully implement this technique in the field. [ABSTRACT FROM AUTHOR]

This paper deals with the economic viability of using energy maize as a phytoremediation crop in a vast agricultural area moderately contaminated with metals. The acceptance of phytoremediation as a remediation technology is, besides the extraction rate, determined by its profitability, being the effects it has on the income of the farmer whose land is contaminated. This income can be supported by producing renewable energy through anaerobic digestion of energy maize, a crop that takes up only relatively low amounts of metals, but that can be valorised as a feedstock for energy production. The effect on the income per hectare of growing energy maize instead of fodder maize seems positive, given the most likely values of variables and while keeping the basic income stable, originating from dairy cattle farming activities. We propose growing energy maize aiming at risk-reduction, and generating an alternative income for farmers, yet in the long run also generating a gradual reduction of the pollution levels. In this way, remediation is demoted to a secondary objective with sustainable risk-based land use as primary objective. [ABSTRACT FROM AUTHOR]

A soil column leaching experiment was used to gain insight into the long-term metal immobilization capacity of cyclonic ashes (CAH) compared to lime (LIME). Twenty six years of rainfall were simulated. Initially, all amended soils were brought to an equal soil pH. This was done to obtain optimal conditions for the detection of metal immobilization mechanisms different from just a pH effect. During the simulation period, soil pH in all treatments decreased in parallel. However, the evolution of metal mobility and phytoavailability showed a clearly distinct pattern. The strong reduction in metal immobilizing efficiency observed in the lime treatment at the end of the simulation period was much less pronounced, or even absent, in the CAH treatments. Moreover, metal accumulation in plants grown on the CAH amended soil was significantly lower compared to the untreated and the lime treated soil. CAH + SS treatment delivered the strongest reductions in metal mobility and bioavailability. [Copyright &y& Elsevier]

The contamination of soils by trace metals has been an unfortunate sideeffect of industrialization. Some of these contaminants can interfere with vulnerable enduses of soil, such as agriculture or nature, already at relatively low levels of contamination. Reversely, conventional civil-technical soil-remediation techniques are too expensive to remediate extended areas of moderately contaminated soil. Phytoextraction has been proposed as a more economic complementary approach to deal with this specific niche of soil contamination. However, phytoextraction has been shown to be a slow-working process due to the low amounts of metals that can be annually removed from the soil under normal agronomic conditions. Therefore, extensive research has been conducted on process optimization by means of chemically improving plant availability and the uptake of heavy metals. A wide range of potential amendments has been proposed in the literature, with considerable attention being spent on aminopolycarboxylic acids such as ethylenediaminetetraacetic acid (EDTA). However, these compounds have received increasing criticism due to their environmental persistence and associated risks for leaching. This review presents an overview of potential soil amendments that can be employed for enhancing metal uptake by phytoextraction crops, with a distinct focus on more degradable alternatives to persistent compounds such as EDTA. [ABSTRACT FROM AUTHOR]

• The effects of environmental heavy metal pollution on the genetic structure of pioneer populations of the ectomycorrhizal basidiomyceteSuillus luteuswere assessed.• Sporocarps were collected from nine different locations and characterized by amplified fragment length polymorphism (AFLP) markers. Six of the sampling sites were contaminated with heavy metals and were dominated by tolerant individuals.Considerable genetic diversity was found within geographic subpopulations, but no reduction of the genetic diversity of populations inhabiting contaminated soils was observed. Neither did significant clustering of subpopulations inhabiting contaminated soils occur. Overall, the genetic differentiation between subpopulations was low, but Bayesian inference indicated the presence of two genetically differentiated clusters of individuals, which may correspond to different intercompatibility groups inS. luteus.• Heavy metal contamination seems to have a limited influence on the genetic structure of populations ofS. luteus. Loss of diversity may have been prevented by sexual reproduction and rapid evolution of the tolerance trait or initial genetic bottlenecks may have been reduced by admixture and recurrent migration from surrounding populations colonizing noncontaminated soils.New Phytologist(2004)doi: 10.1111/j.1469-8137.2004.01190.x© New Phytologist(2004) [ABSTRACT FROM AUTHOR]

In order to evaluate the possible use of hydroxyapatite (HA) as a soil additive for the in situ remediation of metal contaminated soils, the immobilizing capacity of this product was investigated. Three different concentrations of HA (0.5%, 1%, and 5% by weight (w/w)) were applied to a metal (Zn, Pb, Cu, Cd) and As contaminated soil originating from an old zinc smelter site in Belgium. After a three weeks equilibration period, exchangeable metal concentrations of the soils weredetermined using 0.1 M Ca(NO3)2 extraction. Test plants (Zea mays cv. Volga and Phaseolus vulgaris cv. Limburgse vroege) were grown on all soils. Growth parameters were determined and mineral analysis (Cu, Zn, Pb, Cd, Ni, Mn, Mg, Ca, K, As and P) of plants was performed. Exchangeable metal contents in soil decreased withincreasing HA application. Plant growth was partly restored on the 0.5% and 1% HA treated soils. However, at the 5% HA application rate growth was inhibited again. Plant mineral analysis showed that concentrations of 'toxic' metals in the leaves of the test plants decreased after HA application. However, the uptake of essential trace elementsalso decreased and probably led to Mn-deficiency in maize. In bean, addition of 0.5% and 1% HA resulted in a gradual decrease of metal uptake. At the 5% application level an increase of Zn, Cu, and Ni uptake was observed compared to the 0.5% and 1% application rate. In contrast to metal uptake, As uptake was found to increase after HA treatment. The increased PO42- concentration in the soil may be responsible for this. These results illustrate that HA application for the remediation of metal contaminated soils can be effective, but is not self evident. Strong immobilization of essential nutrients may lead to deficiency problems and mobilization of As may leadto an increased transfer to plants and animals and to an increased percolation of this element to the ground water. (c) 1999 Elsevier Science [ABSTRACT FROM AUTHOR]

Metal concentrations in soils are locally quite high, and are still increasing due to many human activities, leading to elevated risk forhealth and the environment. Phytoremediation may offer a viable solution to this problem, and the approach is gaining increasing interest. Improvement of plants by genetic engineering, i.e. by modifying characteristics like metal uptake, transport and accumulation as well asmetal tolerance, opens up new possibilities for phytoremediation. Sofar, only a few cases have been reported where one or more of these characteristics have been successfully altered; e.g. mercuric ion reduction causing improved resistance and phytoextraction, and metallothionein causing enhanced cadmium tolerance. These, together with otherapproaches and potentially promising genes for transformation of target plants are discussed. [ABSTRACT FROM AUTHOR]

Abstract: Phytoremediation crop disposal is a problem inhibiting the widespread use of the remediation technique. Flash pyrolysis as processing method for metal contaminated biomass is investigated: the rather low pyrolysis temperature prevents metal compounds from volatilisation while valuable pyrolysis oil is produced. Both plant stems and leaves are pyrolysed in a lab-scale semi-continuous reactor. Parameters under investigation are pyrolysis temperature (623, 723 and 823K), the use of hot-gas filtration to prevent entrained flow and the blended pyrolysis of willow stems and leaves in their natural weight ratio. Biomass and pyrolysis products are analysed with the focus on the metal distribution; target elements include Zn, Cd, Pb and Cu. Knowledge of the metal distribution is of prime importance concerning the applications of the pyrolysis product streams. ICP-AES measurements confirm very low levels of metals in pyrolysis oil produced at 623K (Cu and Zn <5ppm; Cd and Pb <1ppm) with almost all of the metals accumulated in the char/ash residue. Pyrolysis mass and energy balances are determined providing information in view of future valorisation purposes. Flash pyrolysis can likely offer a valuable processing method for heavy metal contaminated biomass, thus limiting the waste disposal problem associated with phytoremediation. [Copyright &y& Elsevier]

Abstract: Presently, little or no information of implementing fast pyrolysis for looking into the potential valorisation of heavy metal contaminated biomass is available. Fast pyrolysis of heavy metal contaminated biomass (birch and sunflower), containing high amounts of Cd, Cu, Pb and Zn, resulting from phytoremediation, is investigated. The effect of the pyrolysis temperature (623, 673, 773 and 873K) and the type of solid heat carrier (sand and fumed silica) on the distribution of the heavy metals in birch and sunflower pyrolysis fractions are studied. The goal of the set-up is “concentrating” heavy metals in the ash/char fraction after thermal treatment, preventing them to be released in the condensable and/or volatile fractions. The knowledge of the behaviour of heavy metals affects directly future applications and valorisation of the pyrolysis products and thus contaminated biomass. They are indispensable for making and selecting the proper thermal conditions for their maximum recovery. In view of the future valorisation of these biomasses, the amounts of the pyrolysis fractions and the calorific values of the obtained liquid pyrolysis products, as a function of the pyrolysis temperature, are determined. [Copyright &y& Elsevier]

Gentle remediation options (GROs) are risk management strategies or technologies involving plant (phyto-), fungi (myco-), and/or bacteria-based methods that result in a net gain (or at least no gross reduction) in soil function as well as effective risk management. GRO strategies can be customised along contaminant linkages, and can generate a range of wider economic, environmental and societal benefits in contaminated land management (and in brownfields management more widely). The application of GROs as practical on-site remedial solutions is still limited however, particularly in Europe and at trace element (typically metal and metalloid) contaminated sites. This paper discusses challenges to the practical adoption of GROs in contaminated land management, and outlines the decision support tools and best practice guidance developed in the European Commission FP7-funded GREENLAND project aimed at overcoming these challenges. The GREENLAND guidance promotes a refocus from phytoremediation to wider GROs- or phyto-management based approaches which place realisation of wider benefits at the core of site design, and where gentle remediation technologies can be applied as part of integrated, mixed, site risk management solutions or as part of “holding strategies” for vacant sites. The combination of GROs with renewables, both in terms of biomass generation but also with green technologies such as wind and solar power, can provide a range of economic and other benefits and can potentially support the return of low-level contaminated sites to productive usage, while combining GROs with urban design and landscape architecture, and integrating GRO strategies with sustainable urban drainage systems and community gardens/parkland (particularly for health and leisure benefits), has large potential for triggering GRO application and in realising wider benefits in urban and suburban systems. Quantifying these wider benefits and value (above standard economic returns) will be important in leveraging funding for GRO application and soft site end-use more widely at vacant or underutilized sites. [ABSTRACT FROM AUTHOR]

Abstract: In the central part of the Iberian Peninsula there are old sealed landfills containing soils co-contaminated by several heavy metals (Cu, Zn, Pb, Cd, Ni, As, Cr, Fe, Al, Mn) and organic pollutants of different families (hydrocarbons, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, pesticides and other organochlorinated compounds, phenols and volatile compounds), which this work will address. We have focused on phytoremedial plants that are able to deal with this type of complex pollution, not only species that tolerate the joint effect of heavy metals in the soil, but also those that can take advantage of associated bacteria to efficiently break down organic compounds. This study was carried out with Lupinus luteus and its endophytes in two greenhouse experiments: A) growing in a substrate artificially contaminated with benzo(a)pyrene (BaP), and B) using real co-contaminated landfill soils. Endophytes of roots and shoots were isolated in both bioassays. Plant growth-promotion tests and organic pollutant tolerance and degradation tests were conducted on all strains isolated in bioassay A), and on those proving to be pure cultures from bioassay B). The selected landfill is described as are isolation and test procedures. Results indicate that plants did not show toxicity symptoms when exposed to BaP but did when grown in landfill soil. Some endophytes demonstrated plant growth-promotion capacity and tolerance to BaP and other organic compounds (diesel and PCB commercial mixtures). A few strains may even have the capacity to metabolize those organic pollutants. The overall decline in plant growth-promotion capacity in those strains isolated from the landfill soil experiment, compared with those from the bioassay with BaP, may indicate that lupin endophytes are not adapted to metal concentration in roots and shoots and fail to grow. As a result, most isolated root endophytes must have colonized root tissues from the soil. While preliminary degradation tests showed promising results (some strains exhibiting the potential to use organic pollutants as their sole source of carbon), these are not conclusive and further in-depth degradation assays need to be performed. [Copyright &y& Elsevier]

Abstract: Worldwide there are numerous regions where conventional agriculture is affected by the presence of elevated amounts of plant-available trace elements, causing economic losses and food and feed quality and safety. The Belgian and Dutch Campine regions are a first-class example, with approximately 700km2 diffusely contaminated by historic atmospheric deposition of Cd, Zn and Pb. Primary land use in this region is agriculture, which is frequently confronted with crops exceeding the European standards for heavy metal contents in food and feed-stuffs. Phytoremediation as a soil remediation technology only appears feasible if the produced biomass might be valorised in some manner. In the current case, we propose the use of energy maize aiming at risk-reduction and generation of an alternative income for agriculture, yet in the long run also a gradual reduction of the pollution levels. Since the remediation aspect is demoted to a secondary objective with sustainable risk-based land use as first objective, we introduce the term ‘phytoattenuation’: this is in analogy with ‘natural attenuation’ of organic pollutants in soils where also no direct intended remediation measures but a risk-based management approach is implemented. In the current field experiment, cultivation of energy maize could result in 33,000–46,000kWh of renewable energy (electrical and thermal) per hectare per year which by substitution of fossil energy would imply a reduction of up to 21×103 kgha−1 y−1 CO2 if used to substitute a coal fed power plant. Metal removal is very low for Cd and Pb but more significant for Zn with an annual reduction of 0.4–0.7mgkg−1 in the top soil layer. [Copyright &y& Elsevier]

In Western Europe, policy makers are currently moving towards a more integrated risk-based approach of soil contamination assessment. As part of this approach, selective single extraction procedures have been proposed to add complementary insights regarding heavy metal behaviour and phytoavailability in soils and sediments. However, there is currently a wide range of such procedures available in literature, hampering standardisation and harmonisation of phytoavailability research of heavy metals. The current study examines shoot accumulation of Cd, Cu, Ni, Pb and Zn by the test plant Phaseolus vulgaris in 21 soils, differing in soil composition and level of contamination. On these soils, 12 different commonly used extraction procedures have been compared: soil solution extraction by Rhizon soil moisture samplers, 0.01M CaCl2, 0.1M NaNO3, 1M NH4NO3, 1M NH4NOAc, 1M MgCl2, 0.11M HOAc, 0.5M HNO3, 0.1M HCl, DTPA–TEA–CaCl2, EDTA-NH4OAc and aqua regia. The plant species used in this study has previously been proposed as a test plant in a bioassay for assessing heavy metal induced oxidative stress in contaminated soils [Van Assche, F., Clijsters, H., 1990. A biological test system for the evaluation of the phytotoxicity of metal-contaminated soils. Environ. Pollut., 66, 157–172]. Cadmium shoot accumulation correlated best with soil solution concentrations, unbuffered nitrate solutions and the dilute CaCl2 extraction procedure. The same was observed for Zn, yet for this element NH4OAc and MgCl2 also provided significant interactions. The best prediction for Ni was observed in the cluster containing CaCl2 and NH4NO3. For Cd, Zn and Ni, the pseudo-total content and the aggressive chelate based and/or acidic extractants did not correlate well with shoot accumulation. Cu and Pb uptake on the other hand was found to correlate significantly (p =0.01) with total content as well as with all aggressive extraction procedures over the range of soils used in this experiment. In general, the 0.01M CaCl2 extraction procedure proved to be the most versatile as it provided a good indication of phytoavailability for all five metals under evaluation. [Copyright &y& Elsevier]

The potential of short rotation coppice (SRC) for phytoremediation of contaminated sites and simultaneous generation of bio-energy by conversion of the produced biomass has been discussed in previous publications. The current study compares five species of Salix spp. In their ability to extract and accumulate heavy metals (Cd, Cr, Cu, Ni, Pb, Zn) in harvestable plant parts. The species used in this study were: Salix dasyclados ‘Loden’, Salix triandra ‘Noir de Villaines’, Salix fragilis ‘Belgisch Rood’, Salix purpurea × Salix daphnoides ‘Bleu’, Salix schwerinii ‘Christina’. The comparison was conducted in a pot experiment in open air over the course of a growing season on three different soil types: a moderately contaminated dredged sediment derived surface soil (A1), a heavily polluted sediment derived surface soil (A2) and a sandy soil with moderately elevated concentrations due to atmospheric deposition by historic smelter activities (A3). In addition, the effects of soil treatment with 2. 5mmolkg−1 ethylene diamine disuccinate (EDDS) on metal accumulation in stems and leaves were evaluated for one Salix clone (Loden). Of the five clones tested, Christina, Loden and Belgisch Rood exhibited the highest Cd and Zn concentrations and therefore deserve further attention in field validation. A first estimation of the order of magnitude of Cd and Zn that could potentially be annually extracted with these clones, resulted in 5–27kgha−1 for Zn and 0. 25–0. 65kgha−1 for Cd, based on the soil type. However, biomass production in field situations will mainly determine metal removal. Treatment with EDDS exhibited distinct differences in inducing metal removal on the various soils. Uptake of Cd and Zn could not be enhanced in A1, whereas in A2 and A3 removal of these metals could be increased by 50–100% after treatment. In all soils EDDS treatment also had a distinct effect on Cu uptake. [Copyright &y& Elsevier]

Abstract: Current legislative frameworks for soil pollution focus predominantly on total metal content. However, environmental risks posed by heavy metals are not only function of their overall presence in the soil, but also of their chemical speciation. Soil solution levels of Zn are indicative of its availability to plants and soil (micro)biota. In addition, levels present in the soil solution can tell us something of the potential risks for leaching and subsequently elevating ground water levels. In this research, a total of 29 polluted and unpolluted soils were characterised and assessed for the presence of Zn in the soil solution using Rhizon soil moisture samplers. Interactions between the soil properties and observed solubility of Zn was described and put into empirical multivariate formulations. All obtained equations without exception contained pH as a key factor in determining Zn solubility. Finally, soil solution speciation of Zn was assessed using 2 independent software packages (Visual Minteq 2.23 and WHAM VI), based on pH and the presence of other metals, exchangeable bases, anions, and dissolved organic matter. Both models were largely in disagreement in the fractionation between organically bound and inorganic Zn in the solution. Further investigation into the parametric background of both models will therefore be required to ascertain the cause and nature of the observed discrepancy. [Copyright &y& Elsevier]