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Trace elements pollution of soils became a global concern because of their persistence in the environment which can lead to accumulation in food chains up to toxic levels. At the same time, there is a shortage of arable land for growing food, fodder and industrial crops, which highlights the need for remediation/use of polluted land. Restoration of degraded lands has been included as a vital component of UN Sustainable Development Goals (SDGs). We summarize various sources of entry of important trace elements in the environment, available biological reclamation and management strategies and their limitations. Recent advances in phytomanagement approaches using aromatic crops to obtain economically valuable products such as essential oils and revalorize such polluted areas are reviewed. The worldwide application of this strategy in the last 10 years is illustrated through a choropleth map. Finally, the emerging concept of phytomanagement as a restorative and regenerative circular bio-economy is also discussed.

It has been speculated that selenium (Se) supply can affect cadmium (Cd) 'availability' and increase the Cd tolerance of plants used for phytoextraction, in a pH-dependent process. Thus, we evaluated the interaction Cd-Se and the effects of soil pH in this interaction on plant availability of Cd and phytoextraction efficiency of Urochloa decumbens cv. Basilisk grown in Oxisol. Two soil concentrations of Cd (0.93 and 3.6 mg kg -1 ) and Se (<0.2 and 1 mg kg -1 ) and two soil pH (0.01 mol L -1 CaCl 2 ) conditions (4.1 and 5.7) were considered. At both pH, Se supply increased the exchangeable fraction of Cd and decreased the residual Cd fraction. At pH 4.1, the growth of U. decumbens was impaired by Se addition, regardless of Cd exposure. The lower root growth and tillering of U. decumbens exposed to Cd disappeared at pH 5.7 due to uptake of low Se concentrations. Thus, the toxic or beneficial effects of Se on growth of U. decumbens used for Cd phytoextraction depend on the amount of Se assimilated. The Cd phytoextraction efficiency of U. decumbens was not improved by Se supply, regardless of soil pH. Therefore, we cannot recommend the application of Se to increase Cd phytoextraction by this grass., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Natural plant-associated microorganisms are of critical importance to plant growth and survival in field conditions under toxic concentrations of trace elements (TE) and these plant-microbial processes can be harnessed to enhance phytoremediation. The total bacterial diversity from grey willow (Salix atrocinerea) on a brownfield heavily-polluted with lead (Pb) and arsenic (As) was studied through pyrosequencing. Culturable bacteria were isolated and in vitro tested for plant growth-promotion (PGP) traits, arsenic (As) tolerance and impact on As speciation. Two of the most promising bacterial strains - the root endophyte Pantoea sp. AV62 and the rhizospheric strain Rhodococcus erythropolis AV96 - were inoculated in field to S. atrocinerea. This bioaugmentation resulted in higher As and Pb concentrations in both, roots and leaves of bacterial-inoculated plants as compared to non-inoculated plants. In consequence, bacterial bioaugmentation also affected parameters related to plant growth, oxidative stress, the levels of phytochelatins and phenylpropanoids, together with the differential expression of genes related to these tolerance mechanisms to TE in leaves. This study extends our understanding about plant-bacterial interactions and provides a solid basis for further bioaugmentation studies aiming to improve TE phytoremediation efficiency and predictability in the field., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Elsevier B.V. All rights reserved.)

We evaluated the mechanisms that control Cd accumulation and distribution, and the mechanisms that protect the photosynthetic apparatus of Brachiaria decumbens Stapf. cv. Basilisk and Panicum maximum Jacq. cv. Massai from Cd-induced oxidative stress, as well as the effects of simulated summer or winter conditions on these mechanisms. Both grasses were grown in unpolluted and Cd-polluted Oxisol (0.63 and 3.6 mg Cd kg -1 soil, respectively) at summer and winter conditions. Grasses grown in the Cd-polluted Oxisol presented higher Cd concentration in their tissues in the winter conditions, but the shoot biomass production of both grasses was not affected by the experimental conditions. Cadmium was more accumulated in the root apoplast than the root symplast, contributing to increase the diameter and cell layers of the cambial region of both grasses. Roots of B. decumbens were more susceptible to disturbed nutrients uptake and nitrogen metabolism than roots of P. maximum. Both grasses translocated high amounts of Cd to their shoots resulting in oxidative stress. Oxidative stress in the leaves of both grasses was higher in summer than winter, but only in P. maximum superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities were increased. However, CO 2 assimilation was not affected due to the protection provided by reduced glutathione (GSH) and phytochelatins (PCs) that were more synthesized in shoots than roots. In summary, the root apoplast was not sufficiently effective to prevent Cd translocation from roots to shoot, but GSH and PCs provided good protection for the photosynthetic apparatus of both grasses., (© 2020 Scandinavian Plant Physiology Society.)

Arsenic (As)-reducing bacteria are able to influence As-speciation and, in this way, change As bio-availability. In consequence, this has an impact on As uptake by plants growing on polluted soil and on the effectiveness of the phytoremediation process. To be able to efficiently utilize these bacteria for As-phytoremediation in the field, a better understanding of the plant-bacterial interactions involved in As-tolerance or toxicity is needed. In this work, seedlings of a clone of Salix atrocinerea derived from a specimen naturally growing on an As-polluted brownfield were grown under gnotobiotic conditions exposed to As, and in the presence or absence of two of its field-associated and in vitro characterized plant growth-promoting (PGP) bacteria. The inoculation with Pantoea sp., induced a moderate reduction of AsV to AsIII in the exposure medium that, together with a coordinated plant response of As uptake, chelation and sequestration, increased As accumulation in roots; which is reflected into a higher phytostabilization. However, inoculation with Rhodococcus erythropolis due to a higher disproportionate reduction of AsV to AsIII in the medium caused less As accumulation in roots that non-bioaugmented plants and despite the lower As content, the concentrations of AsIII present in the medium and the damage suffered in roots and leaves, indicated that As tolerance mechanisms (such as prevention of AsIII uptake and efflux) did not occur in time to avoid physical disturbance and plants growth reduction. Interestingly, by two different metabolic pathways -coordinated by different key transporters mediating As uptake, tolerance, distribution and vacuolar accumulation at the roots- both bacteria limited As accumulation in Salix shoots. Our results provide for the first time a detailed insight in the plant-bacterial responses and physiological changes contributing to As tolerance in S. atrocinerea, that will facilitate the design of effective strategies for exploitation of plant-associated microorganisms for phytoremediation., Competing Interests: Declaration of competing interest The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Elsevier B.V. All rights reserved.)

Heavy metals polluting the 100-year-old waste heap in Bolesław (Poland) are acting as a natural selection factor and may contribute to adaptations of organisms living in this area, including Trifolium repens and its root nodule microsymbionts-rhizobia. Exopolysaccharides (EPS), exuded extracellularly and associated with bacterial cell walls, possess variable structures depending on environmental conditions; they can bind metals and are involved in biofilm formation. In order to examine the effects of long-term exposure to metal pollution on EPS structure and biofilm formation of rhizobia, Rhizobium leguminosarum bv. trifolii strains originating from the waste heap area and a non-polluted reference site were investigated for the characteristics of the sugar fraction of their EPS using gas chromatography mass-spectrometry and also for biofilm formation and structural characteristics using confocal laser scanning microscopy under control conditions as well as when exposed to toxic concentrations of zinc, lead, and cadmium. Significant differences in EPS structure, biofilm thickness, and ratio of living/dead bacteria in the biofilm were found between strains originating from the waste heap and from the reference site, both without exposure to metals and under metal exposure. Received results indicate that studied rhizobia can be assumed as potentially useful in remediation processes.

The toxic metal cadmium (Cd) is a major soil pollutant. Knowledge on the acute Cd-induced stress response is required to better understand the triggers and sequence of events that precede plant acclimation. Therefore, we aimed to identify the pressure points of Cd stress using a short-term exposure set-up ranging from 0 h to 24 h. Acute responses related to glutathione (GSH), hydrogen peroxide (H 2 O 2 ), 1-aminocyclopropane-1-carboxylic acid (ACC), ethylene and the oxidative challenge were studied at metabolite and/or transcript level in roots and leaves of Arabidopsis thaliana either exposed or not to 5 µM Cd. Cadmium rapidly induced root GSH depletion, which might serve as an alert response and modulator of H 2 O 2 signalling. Concomitantly, a stimulation of root ACC levels was observed. Leaf responses were delayed and did not involve GSH depletion. After 24 h, a defined oxidative challenge became apparent, which was most pronounced in the leaves and concerted with a strong induction of leaf ACC synthesis. We suggest that root GSH depletion is required for a proper alert response rather than being a merely adverse effect. Furthermore, we propose that roots serve as command centre via a.o. root-derived ACC/ethylene to engage the leaves in a proper stress response.

The interactions between soil properties, microorganisms, plant species and climate affect cadmium (Cd) availability in tropical soils. In this study, we investigated the effects of simulated summer and winter conditions on Cd fractionation and bacterial communities in Oxisols and on growth of two high biomass production-grasses (Brachiaria decumbens and Panicum maximum) that were evaluated for their Cd phytoextraction potential. We also assessed how these interactions could influence the availability of Cd and its possible phytoextraction by these grasses. The Cd fraction bound to carbonates was higher in the winter conditions, while Cd bound to Fe- and Mn oxides was higher in the summer conditions, which resulted in a higher Cd availability in winter compared to summer conditions. B. decumbens and P. maximum took up more Cd when grown in the winter conditions, but their biomasses were not affected by the higher Cd uptake. The occurrence and relative abundance of bacterial taxa in the bare soil differed from the soils cultivated with grasses, where the Gammaproteobacteria predominated. However, no positive correlations were observed between the rhizosphere bacterial community in the cultivated soils and Cd availability, irrespective of the season conditions., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Bioremediation is a soil clean-up technique which exploits the metabolic capacity of microorganisms to degrade soil contaminants. A model was developed to simulate the ex situ bioremediation of a diesel-contaminated soil in a bio-slurry reactor inoculated with a diesel-degrading bacterial strain. Mass transfer processes involving desorption of diesel from soil to water and volatilization of diesel from water, and biodegradation by the bacterial inoculant were included in the model by using Weibull sigmoid kinetics and logistic/Monod kinetics respectively. Model parameters were estimated in batch-based abiotic and biodegradation experiments. Sensitivity analysis revealed the importance of maintaining a high bacterial density in the system for maximum bioremediation efficiency. The model was validated using a pilot bioreactor monitored for 528 h, which removed almost 90% of the diesel present in the system. The results revealed the capacity of the model to predict the bioremediation efficiency under different scenarios by adapting the input parameters to each system., (Copyright © 2019 Elsevier Ltd. All rights reserved.)

Hydrocarbon-degrading bacteria are important resources for use in phytoremediation applications. Yet, for many hydrocarbonoclastic strains the genetic information regarding pollutant degradation and detoxification has not been thoroughly revealed. In this study, hydrocarbon-degrading bacteria were isolated from a long-term oil-polluted soil in Bóbrka, Poland. Pseudomonas spp. was the most dominant species. Of all 69 isolated strains tested in the laboratory using qualitative biochemical assays, 61% showed the capability to use diesel as sole carbon source, 33% could produce indole, 19% produced siderophores, 36% produced organic acids, and 54% were capable of producing 1-aminocyclopropane-1-carboxylate (ACC)-deaminase. From all morphologically and genetically different strains, two representative Pseudomonas spp., strain VI4.1 and VI4T1, were selected for genome sequencing. Genomic analyses indicated the presence of the full naphthalene dioxygenase operon (plasmid and chromosomal), of genes involved in the degradation of BTEX compounds (Benzene, Toluene, Ethylbenzene, Xylene) and alkanes ( alkB gene) as well as the anthranilate degradation pathway (strain VI4T1) and terephthalate dioxygenase protein (strain VI4.1). Proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) analyses confirmed naphthalene and BTEX degradation within seven days. Motility, resistance to abiotic stresses, high and low temperatures, low pH, and salinity were confirmed at the genetic level and experimentally verified. The presence of multiple degradative and plant growth promotion genes, together with the in vitro experimental evidence, indicates the high value of these two strains and their potential use for sustainable site clean-up.

The natural accession Columbia (Col-0) is considered as the reference genome of the model plant Arabidopsis thaliana. Nonetheless, Col-0 plants are more sensitive to excess copper (Cu) and cadmium (Cd) than other widely used accessions such as Wassilewskija (Ws) plants. In the current study, this accession-specific metal sensitivity is further explored by comparing the responses in leaves of Col-0 and Ws plants exposed to excess Cu and Cd. Our results suggest that different life strategies favored by both accessions under physiological conditions affect their response to metal exposure. While Col-0 plants mainly invest in metal detoxification, Ws plants center on nutrient homeostasis. In particular, the higher expression of genes related to Cu homeostasis genes in non-exposed conditions indicates that Ws plants possess a constitutively efficient metal homeostasis. On the other hand, oxidative stress-related MAPK signaling appears to be boosted in leaves of Col-0 plants exposed to excess Cu. Furthermore, the upregulation of the glutathione (GSH) biosynthesis GSH2 gene and the increased GSH concentration after Cd exposure suggest the activation of detoxification mechanisms, such as phytochelatin production, to counteract the more severe Cd-induced oxidative stress in leaves of Col-0 plants. Exposure to Cd also led to a more pronounced ethylene signaling response in leaves of Col-0 as compared to Ws plants, which could be related to Cd-induced GSH metabolism. In conclusion, accession-specific life strategies clearly affect the way in which leaves of A. thaliana plants cope with excess Cu and Cd., (Copyright © 2018. Published by Elsevier GmbH.)

Efficient N 2 -fixing Leguminosae nodulating bacteria resistant to As may facilitate plant growth on As-contaminated sites. In order to identify bacteria holding these features, 24 strains were isolated from nodules of the trap species Crotalaria spectabilis (12) and Stizolobium aterrimum (12) growing on an As-contaminated gold mine site. 16S rRNA gene sequencing revealed that most of the strains belonged to the group of α-Proteobacteria, being representatives of the genera Bradyrhizobium, Rhizobium, Inquilinus, Labrys, Bosea, Starkeya, and Methylobacterium. Strains of the first four genera showed symbiotic efficiency with their original host, and demonstrated in vitro specific plant-growth-promoting (PGP) traits (production of organic acids, indole-3-acetic-acid and siderophores, 1-aminocyclopropane-1-carboxylate deaminase activity, and Ca 3 (PO 4 ) 2 solubilization), and increased resistance to As, Zn, and Cd. In addition, these strains and some type and reference rhizobia strains exhibited a wide resistance spectrum to β-lactam antibiotics. Both intrinsic PGP abilities and multi-element resistance of rhizobia are promising for exploiting the symbiosis with different legume plants on trace-element-contaminated soils.

Plant growth promoting endophytic bacteria (PGPB) isolated from Brassica napus were inoculated in two cultivars of Helianthus tuberosus (VR and D19) growing on sand supplemented with 0.1 mM Cd or 1 mM Zn. Plant growth, concentrations of metals and thiobarbituric acid (TBA) reactive compounds were determined. Colonization of roots of H. tuberosus D19 by Pseudomonas sp. 262 was evaluated using confocal laser scanning microscopy. Pseudomonas sp. 228, Serratia sp. 246 and Pseudomonas sp. 262 significantly enhanced growth of H. tuberosus D19 exposed to Cd or Zn. Pseudomonas sp. 228 significantly increased Cd concentrations in roots. Serratia sp. 246, and Pseudomonas sp. 256 and 228 resulted in significantly decreased contents of TBA reactive compounds in roots of Zn exposed D19 plants. Growth improvement and decrease of metal-induced stress were more pronounced in D19 than in VR. Pseudomonas sp. 262 - green fluorescent protein (GFP) colonized the root epidermis/exodermis and also inside root hairs, indicating that an endophytic interaction was established. H. tuberosus D19 inoculated with Pseudomonas sp. 228, Serratia sp. 246 and Pseudomonas sp. 262 holds promise for sustainable biomass production in combination with phytoremediation on Cd and Zn contaminated soils., Competing Interests: The authors declare no conflict of interest. The founding sponsors had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Many endophytic bacteria exert beneficial effects on their host, but still little is known about the bacteria associated with plants growing in areas heavily polluted by hydrocarbons. The aim of the study was characterization of culturable hydrocarbon-degrading endophytic bacteria associated with Lotus corniculatus L. and Oenothera biennis L. collected in long-term petroleum hydrocarbon-polluted site using culture-dependent and molecular approaches. A total of 26 hydrocarbon-degrading endophytes from these plants were isolated. Phylogenetic analyses classified the isolates into the phyla Proteobacteria and Actinobacteria. The majority of strains belonged to the genera Rhizobium, Pseudomonas, Stenotrophomonas, and Rhodococcus. More than 90% of the isolates could grow on medium with diesel oil, approximately 20% could use n-hexadecane as a sole carbon and energy source. PCR analysis revealed that 40% of the isolates possessed the P450 gene encoding for cytochrome P450-type alkane hydroxylase (CYP153). In in vitro tests, all endophytic strains demonstrated a wide range of plant growth-promoting traits such as production of indole-3-acetic acid, hydrogen cyanide, siderophores, and phosphate solubilization. More than 40% of the bacteria carried the gene encoding for the 1-aminocyclopropane-1-carboxylic acid deaminase (acdS). Our study shows that the diversity of endophytic bacterial communities in tested plants was different. The results revealed also that the investigated plants were colonized by endophytic bacteria possessing plant growth-promoting features and a clear potential to degrade hydrocarbons. The properties of isolated endophytes indicate that they have the high potential to improve phytoremediation of petroleum hydrocarbon-polluted soils.

Plants on contaminated mining soils often show a reduced growth due to nutrient depletion as well as trace elements (TEs) toxicity. Since those conditions threat plant's survival, plant growth-promoting rhizobacteria (PGPRs), such as rhizobia, might be of crucial importance for plant colonization on TE-contaminated soils. Native rhizobia from mining soils are promising candidates for bioaugmented phytoremediation of those soils as they are adapted to the specific conditions. In this work, rhizobia from Zn- and Cd-contaminated mining soils were in vitro screened for their PGP features [organic acids, indole-3-acetic acid (IAA), and siderophore (SID) production; 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity; and Ca 3 (PO 4 ) 2 solubilization] and Zn and Cd tolerance. In addition, some type and reference rhizobia strains were included in the study as well. The in vitro screening indicated that rhizobia and other native genera have great potential for phytoremediation purposes, by exerting, besides biological N 2 fixation, other plant growth-promoting traits. Leucaena leucocephala-Mesorhizobium sp. (UFLA 01-765) showed multielement tolerance and an efficient symbiosis on contaminated soil, decreasing the activities of antioxidative enzymes in shoots. This symbiosis is a promising combination for phytostabilization.

Phytoremediation is increasingly adopted as a more sustainable approach for soil remediation. However, significant advances in efficiency are still necessary to attain higher levels of environmental and economic sustainability. Current interventions do not always give the expected outcomes in field settings due to an incomplete understanding of the multicomponent biological interactions. New advances in -omics are gradually implemented for studying microbial communities of polluted land in situ. This opens new perspectives for the discovery of biodegradative strains and provides us new ways of interfering with microbial communities to enhance bioremediation rates. This review presents retrospectives and future perspectives for plant microbiome studies relevant to phytoremediation, as well as some knowledge gaps in this promising research field. The implementation of phytoremediation in soil clean-up management systems is discussed, and an overview of the promoting factors that determine the growth of the phytoremediation market is given. Continuous growth is expected since elimination of contaminants from the environment is demanded. The evolution of scientific thought from a reductionist view to a more holistic approach will boost phytoremediation as an efficient and reliable phytotechnology. It is anticipated that phytoremediation will prove the most promising for organic contaminant degradation and bioenergy crop production on marginal land.

The interaction between plant growth-promoting bacteria (PGPB) and plants can enhance biomass production and metal tolerance of the host plants. This work aimed at isolating and characterizing the cultivable bacterial community associated with Brassica napus growing on a Zn-contaminated site, for selecting cultivable PGPB that might enhance biomass production and metal tolerance of energy crops. The effects of some of these bacterial strains on root growth of B. napus exposed to increasing Zn and Cd concentrations were assessed. A total of 426 morphologically different bacterial strains were isolated from the soil, the rhizosphere, and the roots and stems of B. napus. The diversity of the isolated bacterial populations was similar in rhizosphere and roots, but lower in soil and stem compartments. Burkoholderia, Alcaligenes, Agrococcus, Polaromonas, Stenotrophomonas, Serratia, Microbacterium, and Caulobacter were found as root endophytes exclusively. The inoculation of seeds with Pseudomonas sp. strains 228 and 256, and Serratia sp. strain 246 facilitated the root development of B. napus at 1,000 µM Zn. Arthrobacter sp. strain 222, Serratia sp. strain 246, and Pseudomonas sp. 228 and 262 increased the root length at 300 µM Cd.

The association of plants and rhizospheric bacteria provides a successful strategy to clean up contaminated soils. The purpose of this work was to enhance diesel degradation in rhizosphere by inoculation with selected bacterial strains: a diesel degrader (D), plant growth-promoting (PGP) strains, or a combination (D+PGP). Plants were set up in pots with the A or B horizon of an umbric Cambisol (A and B) spiked with diesel (1.25%, w/w). After 1 mo, the dissipation of diesel range organics (DRO) with respect to = 0 (i.e., 1 wk after preparing the pots with the seedlings) concentration was significantly higher in inoculated than in noninoculated (NI) pots: The highest DRO losses were found in A D+PGP pots (close to 15-20% higher than NI) and in B D pots (close to 10% higher). The water-extractable DRO fraction was significantly higher at = 30 d (15-25%) compared with = 0 (<5%), probably due to the effects of plant root exudates and biosurfactants produced by the degrader strain. The results of this experiment reflect the importance of the partnerships between plants and bacterial inoculants and demonstrate the relevance of the effect of bacterial biosurfactants and plant root exudates on contaminant bioavailability, a key factor for enhancing diesel rhizodegradation. The association of lupine with D and PGP strains resulted in a promising combination for application in the rhizoremediation of soils with moderate diesel contamination., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

Retention of particles containing potentially toxic elements (PTEs) on plants that spontaneously colonize mine tailings was studied through comparison of washed and unwashed shoot samples. Zn, Pb, Cd, Cu, Ni, Co and Mn concentrations were determined in plant samples. Particles retained on leaves were examined by Scanning Electronic Microscopy and energy dispersive X-Ray analysis. Particles containing PTEs were detected on both washed and unwashed leaves. This indicates that the thorough washing procedure did not remove all the particles containing PTEs from the leaf surface, leading to an overestimation of the concentrations of PTEs in plant tissues. Particularly trichomes and fungal mycelium were retaining particles. The quantity and composition of particles varied among plant species and place of collection. It is obvious that plants growing on toxic mine tailings form a physical barrier against particle dispersion and hence limit the spread of PTEs by wind., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Cadmium (Cd) induces the generation of reactive oxygen species (ROS) and stimulates ethylene biosynthesis. The phytohormone ethylene is a regulator of many developmental and physiological plant processes as well as stress responses. Previous research indicated various links between ethylene signalling and oxidative stress. Our results support a correlation between the Cd-induced oxidative challenge and ethylene signalling in Arabidopsis thaliana leaves. The effects of 24 or 72 h exposure to 5 μM Cd on plant growth and several oxidative stress-related parameters were compared between wild-type (WT) and ethylene insensitive mutants (etr1-1, ein2-1, ein3-1). Cadmium-induced responses observed in WT plants were mainly affected in etr1-1 and ein2-1 mutants, of which the growth was less inhibited by Cd exposure as compared to WT and ein3-1 mutants. Both etr1-1 and ein2-1 showed a delayed response in the glutathione (GSH) metabolism, including GSH levels and transcript levels of GSH synthesising and recycling enzymes. Furthermore, the expression of different oxidative stress marker genes was significantly lower in Cd-exposed ein2-1 mutants, evidencing that ethylene signalling is involved in early responses to Cd stress. A model for the cross-talk between ethylene signalling and oxidative stress is proposed., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

The impact of metal pollution on plant communities has been studied extensively in the past, but little is known about the effects of metal pollution on fungal communities that occur in metal-polluted soils. Metal-tolerant ecotypes of the ectomycorrhizal fungus Suillus luteus are frequently found in pioneer pine forests in the Campine region in Belgium on metal-polluted soils. We hypothesized that metal pollution would play an important role in shaping below-ground fungal communities that occur in these soils and that Suillus luteus would be a dominant player. To test these hypotheses, the fungal communities in a young pine plantation in soil polluted with zinc, and cadmium were studied using 454 amplicon pyrosequencing. Results show that zinc, cadmium and soil organic matter content were strongly correlated with the fungal community composition, but no effects on fungal diversity were observed. As hypothesized, S. luteus was found to be a dominant member of the studied fungal communities. However, other dominant fungal species, such as Sistotrema sp., Wilcoxina mikolae and Cadophora finlandica were found as well. Their presence in metal-polluted sites is discussed., (© 2014 Society for Applied Microbiology and John Wiley & Sons Ltd.)

The potential use of biochar from olive mill waste for in situ remediation of metal contaminated soils was evaluated. Biochar was mixed with metal contaminated soil originating from the vicinity of an old zinc smelter. Soil-biochar mixtures were equilibrated for 30 and 90 days. At these time points, Ca(NO3)2 exchangeable metals were determined, and effects of the biochar amendment on soil toxicity were investigated using plants, bacteria, and earthworms. Bean (Phaseolus vulgaris) growth, metal content, antioxidative enzymes activities, and soluble protein contents were determined. Furthermore, effects on soil microbial communities (activity, diversity, richness) were examined using Biolog ECOplates. After 120 days of soil-biochar equilibration, effects on weight and reproduction of Eisenia foetida were evaluated. With increasing biochar application rate and equilibration period, Ca(NO3)2 exchangeable metals decreased, and growth of bean plants improved; leaf metal contents reduced, the activities of antioxidative stress enzymes decreased, and soluble protein contents increased. Soil microbial activity, richness, and diversity were augmented. Earthworm mortality lowered, and their growth and reproduction showed increasing trends.

The last few decades have seen the rise of Gentle soil Remediation Options (GRO), which notably include in situ contaminant stabilization ("inactivation") and plant-based (generally termed "phytoremediation") options. For trace element (TE)-contaminated sites, GRO aim to either decrease their labile pool and/or total content in the soil, thereby reducing related pollutant linkages. Much research has been dedicated to the screening and selection of TE-tolerant plant species and genotypes for application in GRO. However, the number of field trials demonstrating successful GRO remains well below the number of studies carried out at a greenhouse level. The move from greenhouse to field conditions requires incorporating agronomical knowledge into the remediation process and the ecological restoration of ecosystem services. This review summarizes agronomic practices against their demonstrated or potential positive effect on GRO performance, including plant selection, soil management practices, crop rotation, short rotation coppice, intercropping/row cropping, planting methods and plant densities, harvest and fertilization management, pest and weed control and irrigation management. Potentially negative effects of GRO, e.g., the introduction of potentially invasive species, are also discussed. Lessons learnt from long-term European field case sites are given for aiding the choice of appropriate management practices and plant species.

The aim of this research was to identify wild plant species applicable for remediation of mine tailings in arid soils. Plants growing on two mine tailings were identified and evaluated for their potential use in phytoremediation based on the concentration of potentially toxic elements (PTEs) in roots and shoots, bioconcentration (BCF) and translocation factors (TF). Total, water-soluble and DTPA-extractable concentrations of Pb, Cd, Zn, Cu, Co and Ni in rhizospheric and bulk soil were determined. Twelve species can grow on mine tailings, accumulate PTEs concentrations above the commonly accepted phytotoxicity levels, and are suitable for establishing a vegetation cover on barren mine tailings in the Zimapan region. Pteridium sp. is suitable for Zn and Cd phytostabilization. Aster gymnocephalus is a potential phytoextractor for Zn, Cd, Pb and Cu; Gnaphalium sp. for Cu and Crotalaria pumila for Zn. The species play different roles according to the specific conditions where they are growing at one site behaving as a PTEs accumulator and at another as a stabilizer. For this reason and due to the lack of a unified approach for calculation and interpretation of bioaccumulation factors, only considering BCF and TF may be not practical in all cases.

To examine the potential of Pseudomonas putida W619-TCE to improve phytoremediation of Ni-TCE co-contamination, the effects of inoculation of a Ni-resistant, TCE-degrading root endophyte on Ni-TCE phytotoxicity, Ni uptake and trichloroethylene (TCE) degradation of Ni-TCE-exposed poplar cuttings are evaluated. After inoculation with P. putida W619-TCE, root weight of non-exposed poplar cuttings significantly increased. Further, inoculation induced a mitigation of the Ni-TCE phytotoxicity, which was illustrated by a diminished exposure-induced increase in activity of antioxidative enzymes. Considering phytoremediation efficiency, inoculation with P. putida W619-TCE resulted in a 45% increased Ni uptake in roots as well as a slightly significant reduction in TCE concentration in leaves and TCE evapotranspiration to the atmosphere. These results indicate that endophytes equipped with the appropriate characteristics can assist their host plant to deal with co-contamination of toxic metals and organic contaminants during phytoremediation. Furthermore, as poplar is an excellent plant for biomass production as well as for phytoremediation, the obtained results can be exploited to produce biomass for energy and industrial feedstock applications in a highly productive manner on contaminated land that is not suited for normal agriculture. Exploiting this land for biomass production could contribute to diminish the conflict between food and bioenergy production.

Short rotation coppice (SRC) of willow and poplar is proposed for economic valorization and concurrently as remediation strategy for metal contaminated land in northeast-Belgium. However, metal phytoextraction appears insufficient to effectuate rapid reduction of soil metal contents. To increase both biomass production and metal accumulation of SRC, two strategies are proposed: (i) in situ selection of the best performing clones and (ii) bioaugmentation of these clones with beneficial plant-associated bacteria. Based on field data, two experimental willow clones, a Salix viminalis and a Salix alba x alba clone, were selected. Compared to the best performing commercial clones, considerable increases in stem metal extraction were achieved (up to 74% for Cd and 91% for Zn). From the selected clones, plant-associated bacteria were isolated and identified. All strains were subsequently screened for their plant growth-promoting and metal uptake enhancing traits. Five strains were selected for a greenhouse inoculation experiment with the selected clones planted in Cd-Zn-Pb contaminated soil. Extraction potential tended to increase after inoculation of S. viminalis plants with a Rahnella sp. strain due to a significantly increased twig biomass. However, although bacterial strains showing beneficial traits in vitro were used for inoculation, increments in extraction potential were not always observed.

During the past decades a number of field trials with gentle remediation options (GRO) have been established on trace element (TE) contaminated sites throughout Europe. Each research group selects different methods to assess the remediation success making it difficult to compare efficacy between various sites and treatments. This study aimed at selecting a minimum risk assessment battery combining chemical and ecotoxicological assays for assessing and comparing the effectiveness of GRO implemented in seven European case studies. Two test batteries were pre-selected; a chemical one for quantifying TE exposure in untreated soils and GRO-managed soils and a biological one for characterizing soil functionality and ecotoxicity. Soil samples from field studies representing one of the main GROs (phytoextraction in Belgium, Sweden, Germany and Switzerland, aided phytoextraction in France, and aided phytostabilization or in situ stabilization/phytoexclusion in Poland, France and Austria) were collected and assessed using the selected test batteries. The best correlations were obtained between NH4NO3-extractable, followed by NaNO3-extractable TE and the ecotoxicological responses. Biometrical parameters and biomarkers of dwarf beans were the most responsive indicators for the soil treatments and changes in soil TE exposures. Plant growth was inhibited at the higher extractable TE concentrations, while plant stress enzyme activities increased with the higher TE extractability. Based on these results, a minimum risk assessment battery to compare/biomonitor the sites phytomanaged by GROs might consist of the NH4NO3 extraction and the bean Plantox test including the stress enzyme activities., (Copyright © 2014 Elsevier B.V. All rights reserved.)

The presence of explosives in soils and the interaction with drought stress and nutrient limitation are among the environmental factors that severely affect plant growth on military soils. In this study, we seek to isolate and identify the cultivable bacteria of a 2,4-dinitrotoluene (DNT) contaminated soil (DS) and an adjacent grassland soil (GS) of a military training area aiming to isolate new plant growth-promoting (PGP) and 2,4-DNT-degrading strains. Metabolic profiling revealed disturbances in Ecocarbon use in the bare DS; isolation of cultivable strains revealed a lower colony-forming-unit count and a less diverse community associated with DS in comparison with GS. New 2,4-DNT-tolerant strains were identified by selective enrichments, which were further characterized by auxanography for 2,4-DNT use, resistance to drought stress, cold, nutrient starvation and PGP features. By selecting multiple beneficial PGP and abiotic stress-resistant strains, efficient 2,4-DNT-degrading consortia were composed. After inoculation, consortium UHasselt Sofie 3 with seven members belonging to Burkholderia, Variovorax, Bacillus, Pseudomonas and Ralstonia species was capable to successfully enhance root length of Arabidopsis under 2,4-DNT stress. After 9 days, doubling of main root length was observed. Our results indicate that beneficial bacteria inhabiting a disturbed environment have the potential to improve plant growth and alleviate 2,4-DNT stress., (© 2014 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.)

Phytoextraction has been reported as an economically and ecologically sound alternative for the remediation of metal-contaminated soils. Willow is a metal phytoextractor of interest because it allows to combine a gradual contaminant removal with production of biomass that can be valorized in different ways. In this work two willow clones growing on a metal-contaminated site were selected: 'Belgisch Rood' (BR) with a moderate metal extraction capacity and 'Tora' (TO) with a twice as high metal accumulation. All cultivable bacteria associated with both willow clones were isolated and identified using 16SrDNA ARDRA analysis followed by 16SrDNA sequencing. Further all isolated bacteria were investigated for characteristics that might promote plant growth (production of siderophores, organic acids and indol acetic acid) and for their metal resistance. The genotypic and phenotypic characterization of the isolated bacteria showed that the TO endophytic bacterial population is more diverse and contains a higher percentage of metal-resistant plant growth promoting bacteria than the endophytic population associated with BR. We hypothesize that the difference in the metal accumulation capacity between BR and TO clones might be at least partly related to differences in characteristics of their associated bacterial population., (© 2013 The Authors. Published by Society for Applied Microbiology and Blackwell Publishing Ltd. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.)

Short rotation coppice (SRC) of willow and poplar might be a promising phytoremediation option since it uses fast growing, high biomass producing tree species with often a sufficient metal uptake. This study evaluates growth, metal uptake and extraction potentials of eight willow clones (Belders, Belgisch Rood, Christina, Inger, Jorr, Loden, Tora and Zwarte Driebast) on a metal-contaminated agricultural soil, with total cadmium (Cd) and zinc (Zn) concentrations of 6.5 +/- 0.8 and 377 +/- 69 mg kg(-1) soil, respectively. Although, during the first cycle, on average generally low productivity levels (3.7 ton DM (dry matter) ha(-1) y(-1)) were obtained on this sandy soil, certain clones exhibited quite acceptable productivity levels (e.g. Zwarte Driebast 12.5 ton DM ha(-1) y(-1)). Even at low biomass productivity levels, SRC of willow showed promising removal potentials of 72 g Cd and 2.0 kg Zn ha(-1) y(-1), which is much higher than e.g. energy maize or rapeseed grown on the same soil Cd and Zn removal can be increased by 40% if leaves are harvested as well. Nevertheless, nowadays the wood price remains the most critical factor in order to implement SRC as an acceptable, economically feasible alternative crop on metal-contaminated agricultural soils.

Background and Scope: Plant responses to the toxic effects of soil contaminants, such as excess metals or organic substances, have been studied mainly at physiological, biochemical and molecular levels, but the influence on root system architecture has received little attention. Nevertheless, the precise position, morphology and extent of roots can influence contaminant uptake. Here, data are discussed that aim to increase the molecular and ecological understanding of the influence of contaminants on root system architecture. Furthermore, the potential of plant-associated bacteria to influence root growth by their growth-promoting and stress-relieving capacities is explored., Methods: Root growth parameters of Arabidopsis thaliana seedlings grown in vertical agar plates are quantified. Mutants are used in a reverse genetics approach to identify molecular components underlying quantitative changes in root architecture after exposure to excess cadmium, copper or zinc. Plant-associated bacteria are isolated from contaminated environments, genotypically and phenotypically characterized, and used to test plant root growth improvement in the presence of contaminants., Key Results: The molecular determinants of primary root growth inhibition and effects on lateral root density by cadmium were identified. A vertical split-root system revealed local effects of cadmium and copper on root development. However, systemic effects of zinc exposure on root growth reduced both the avoidance of contaminated areas and colonization of non-contaminated areas. The potential for growth promotion and contaminant degradation of plant-associated bacteria was demonstrated by improved root growth of inoculated plants exposed to 2,4-di-nitro-toluene (DNT) or cadmium., Conclusions: Knowledge concerning the specific influence of different contaminants on root system architecture and the molecular mechanisms by which this is achieved can be combined with the exploitation of plant-associated bacteria to influence root development and increase plant stress tolerance, which should lead to more optimal root systems for application in phytoremediation or safer biomass production.

The ameliorating effects of different inorganic materials were investigated on a soil originating from a zinc smelter dumping site contaminated by toxic metals. Wild mustard (Sinapis arvensis L.) was used as a test plant. The soil was amended with different doses of mining sludge, Perferric Red Latosol (LVj), steel shots, cyclonic ash, silifertil, and superphosphate. The most effective amendments improved plant growth with 45% and reduced metal uptake by over 70% in comparison to untreated soil. Reductions in availability as estimated by BaCl2-extractable metals reached up to 90% for Zn and 65% for Cd as compared to unamended soil. These reductions were associated with lower shoot and root metal contents. Shoot Zn content was reduced from 1,369 microg g(-1) in plants grown on untreated soil to 377 microg g(-1) when grown on cyclonic ash amended soil while Cd decreased from 267 to 44 microg g(-1) in steel shots amended soil. Superphosphate addition had no ameliorating effect. On the contrary, it increased BaCl2-extractable amounts of Zn. Considering all parameters we determined, steel shots, cyclonic ash and silifertil are the most promising for remediating metal contaminated soil in the tropics. Further studies evaluating impacts, cost-effectiveness and durability of effects will be conducted.

Phytoremediation, more precisely phytoextraction, has been placed forward as an environmental friendly remediation technique, that can gradually reduce increased soil metal concentrations, in particular the bioavailable fractions. The aim of this study was to investigate the possibilities of growing willows and poplars under short rotation coppice (SRC) on an acid, poor, sandy metal contaminated soil, to combine in this way soil remediation by phytoextraction on one hand, and production of biomass for energy purposes on the other. Above ground biomass productivities were low for poplars to moderate for willows, which was not surprising, taking into account the soil conditions that are not very favorable for growth of these trees. Calculated phytoextraction efficiency was much longer for poplars than these for willows. We calculated that for phytoextraction in this particular case it would take at least 36 years to reach the legal threshold values for cadmium, but in combination with production of feedstock for bioenergy processes, this type of land use can offer an alternative income for local farmers. Based on the data of the first growing cycle, for this particular case, SRC of willows should be recommended.

The TCE-degrading poplar endophyte Pseudomonas putida W619-TCE was inoculated in poplar cuttings, exposed to 0, 200 and 400 mg l(-1) TCE, that were grown in two different experimental setups. During a short-term experiment, plants were grown hydroponically in half strength Hoagland nutrient solution and exposed to TCE for 3 days. Inoculation with P. putida W619-TCE promoted plant growth, reduced TCE phytotoxicity and reduced the amount of TCE present in the leaves. During a mid-term experiment, plants were grown in potting soil and exposed to TCE for 3 weeks. Here, inoculation with P. putida W619-TCE had a less pronounced positive effect on plant growth and TCE phytotoxicity, but resulted in strongly reduced amounts of TCE in leaves and roots of plants exposed to 400 mg l(-1) TCE, accompanied by a lowered evapotranspiration of TCE. Dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), which are known intermediates of TCE degradation, were not detected., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

Adaptive Zn and Cd tolerance have evolved in populations of the ectomycorrhizal fungus Suillus luteus. When exposed to high concentrations of both metals in vitro, a one-sided antagonism was apparent in the Zn- and Cd-tolerant isolates. Addition of high Zn concentrations restored growth of Cd-stressed isolates, but not vice versa. The antagonistic effect was not detected in a S. luteus isolate from non-contaminated land and in Paxillus involutus. The fungi were inoculated on pine seedlings and subsequently exposed to ecologically relevant Zn and Cd concentrations in single and mixed treatments. The applied doses severely reduced nutrient acquisition of non-mycorrhizal pines and pines inoculated with metal-sensitive S. luteus. Highest translocation of Zn and Cd to shoots occurred in the same plants. Seedlings inoculated with fungi collected from the polluted site reduced metal transfer to their host and maintained nutrient acquisition under high metal exposure. The isolate showing highest tolerance in vitro also offered best protection in symbiosis. The antagonistic effect of high Zn on Cd toxicity was confirmed in the plant experiment. The results indicate that a Zn- and Cd-polluted soil has selected ectomycorrhizal fungi that are able to survive and protect their phytobiont from nutrient starvation and excessive metal uptake., (© 2009 Society for Applied Microbiology and Blackwell Publishing Ltd.)

Background, Aim, and Scope: The use of plants and associated microorganisms to remove, contain, inactivate, or degrade harmful environmental contaminants (generally termed phytoremediation) and to revitalize contaminated sites is gaining more and more attention. In this review, prerequisites for a successful remediation will be discussed. The performance of phytoremediation as an environmental remediation technology indeed depends on several factors including the extent of soil contamination, the availability and accessibility of contaminants for rhizosphere microorganisms and uptake into roots (bioavailability), and the ability of the plant and its associated microorganisms to intercept, absorb, accumulate, and/or degrade the contaminants. The main aim is to provide an overview of existing field experience in Europe concerning the use of plants and their associated microorganisms whether or not combined with amendments for the revitalization or remediation of contaminated soils and undeep groundwater. Contaminations with trace elements (except radionuclides) and organics will be considered. Because remediation with transgenic organisms is largely untested in the field, this topic is not covered in this review. Brief attention will be paid to the economical aspects, use, and processing of the biomass., Conclusions and Perspectives: It is clear that in spite of a growing public and commercial interest and the success of several pilot studies and field scale applications more fundamental research still is needed to better exploit the metabolic diversity of the plants themselves, but also to better understand the complex interactions between contaminants, soil, plant roots, and microorganisms (bacteria and mycorrhiza) in the rhizosphere. Further, more data are still needed to quantify the underlying economics, as a support for public acceptance and last but not least to convince policy makers and stakeholders (who are not very familiar with such techniques).

Background, Aim, and Scope: Along transects under a mixed woodland of English Oak (Quercus robur) and Common Ash (Fraxinus excelsior) growing on a trichloroethylene (TCE)-contaminated groundwater plume, sharp decreases in TCE concentrations were observed, while transects outside the planted area did not show this remarkable decrease. This suggested a possibly active role of the trees and their associated bacteria in the remediation process. Therefore, the cultivable bacterial communities associated with both tree species growing on this TCE-contaminated groundwater plume were investigated in order to assess the possibilities and practical aspects of using these common native tree species and their associated bacteria for phytoremediation. In this study, only the cultivable bacteria were characterized because the final aim was to isolate TCE-degrading, heavy metal resistant bacteria that might be used as traceable inocula to enhance bioremediation., Materials and Methods: Cultivable bacteria isolated from bulk soil, rhizosphere, root, stem, and leaf were genotypically characterized by amplified rDNA restriction analysis (ARDRA) of their 16S rRNA gene and identified by 16S rRNA gene sequencing. Bacteria that displayed distinct ARDRA patterns were screened for heavy metal resistance, as well as TCE tolerance and degradation, as preparation for possible future in situ inoculation experiments. Furthermore, in situ evapotranspiration measurements were performed to investigate if the degradation capacity of the associated bacteria is enough to prevent TCE evapotranspiration to the air., Results and Discussion: Between both tree species, the associated populations of cultivable bacteria clearly differed in composition. In English Oak, more species-specific, most likely obligate endophytes were found. The majority of the isolated bacteria showed increased tolerance to TCE, and TCE degradation capacity was observed in some of the strains. However, in situ evapotranspiration measurements revealed that a significant amount of TCE and its metabolites was evaporating through the leaves to the atmosphere., Conclusions and Perspectives: The characterization of the isolates obtained in this study shows that the bacterial community associated with Oak and Ash on a TCE-contaminated site, was strongly enriched with TCE-tolerant strains. However, this was not sufficient to degrade all TCE before it reaches the leaves. A possible strategy to overcome this evapotranspiration to the atmosphere is to enrich the plant-associated TCE-degrading bacteria by in situ inoculation with endophytic strains capable of degrading TCE.

In 1999, 275 poplar trees were planted on a field site near a car factory in order to install a bioscreen. The aim was to combine the biodegradation activities of poplar and its associated rhizosphere and endophytic microorganisms for containing a BTEX contaminated groundwater plume. This BTEX plume occurred as the result of leaking solvents and fuel storage tanks. Monitoring, conducted overa 6-year period (1999-2005) after the planting of the trees suggested that the poplar trees and their associated microorganisms had, once the tree roots reached the contaminated groundwater zone, an active role in the remediation of the BTEX plume, resulting in full containment of the contamination. Analysis of the microbial communities associated with poplar demonstrated that, once the poplar roots got in contact with the BTEX contaminated groundwater, enrichment occurred of both rhizosphere and endophytic bacteria that were able to degrade toluene. Interestingly, once the BTEX plume was remediated, the numbers of toluene degrading rhizosphere and endophytic bacteria decreased below the detection limit, indicating that their population resulted from selective enrichment by the presence of the contaminants.

Soil metal pollution can trigger evolutionary adaptation in soil-borne organisms. An in vitro screening test showed cadmium adaptation in populations of Suillus luteus (L.: Fr.) Roussel, an ectomycorrhizal fungus of pine trees. Cadmium stress was subsequently investigated in Scots pine (Pinus sylvestris L.) seedlings inoculated with a Cd-tolerant S. luteus, isolated from a heavy metal contaminated site, and compared to plants inoculated with a Cd-sensitive isolate from a non-polluted area. A dose-response experiment with mycorrhizal pines showed better plant protection by a Cd-adapted fungus: more fungal biomass and a higher nutrient uptake at high Cd exposure. In addition, less Cd was transferred to aboveground plant parts. Because of the key role of the ectomycorrhizal symbiosis for tree fitness, the evolution of Cd tolerance in an ectomycorrhizal partner such as S. luteus can be of major importance for the establishment of pine forests on Cd-contaminated soils.

The genetic structure of populations of the ectomycorrhizal basidiomycete Suillus luteus in heavy metal polluted and nonpolluted areas was studied. Sporocarps were collected at nine different locations and genotyped at four microsatellite loci. Six of the sampling sites were severely contaminated with heavy metals and were dominated by heavy metal-tolerant individuals. Considerable genetic diversity was found within the geographical subpopulations, but no reduction of the genetic diversity, current or historic, was observed in subpopulations inhabiting polluted soils. The genetic differentiation between the geographical subpopulations was low, and no evidence for clustering of subpopulations from polluted soils vs. subpopulations from nonpolluted soils was found. These results indicate that heavy metal pollution has a limited effect on the genetic structure of S. luteus populations, and this may be due to the high frequency of sexual reproduction and extensive gene flow in S. luteus, which allows rapid evolution of the tolerance trait while maintaining high levels of genetic diversity.

Contaminated soil particles and food are established routes of exposure. We investigated the relations between biomarkers of exposure to cadmium and lead, and the metal loading rates in house dust in the adult residents of an area with a soil cadmium concentration of > or = 3 mg/kg (n=268) and a reference area (n=205). We determined the metal concentrations in house dust allowed to settle for 3 months in Petri dishes placed in the participants' bedrooms. The continuously distributed vegetable index was the first principal component derived from the metal concentrations in six different vegetables. The biomarkers of exposure (blood cadmium 9.2 vs. 6.2 nmol/L; 24-h urinary cadmium 10.5 vs. 7.0 nmol; blood lead 0.31 vs. 0.24 micromol/L), the loading rates of cadmium and lead in house dust (0.29 vs. 0.12 and 7.52 vs. 3.62 ng/cm(2)/92 days), and the vegetable indexes (0.31 vs. -0.44 and 0.13 vs. -0.29 standardized units) were significantly higher in the contaminated area. A two-fold increase in the metal loading rate in house dust was associated with increases (P<0.001) in blood cadmium (+2.3%), 24-h urinary cadmium (+3.0%), and blood lead (+2.0%), independent of the vegetable index and other covariates. The estimated effect sizes on the biomarkers of internal exposure were three times greater for house dust than vegetables. In conclusion, in the adult population, house dust is potentially an important route of exposure to heavy metals in areas with contaminated soils, and should be incorporated in the assessment of health risks.

In order to reduce the health risks associated with historically enriched metal smelting sites in Flanders (Belgium), the capacities of a non-beringite cyclonic ash and commercial Na-silicates to fix metals and create conditions to restore vegetation cover were evaluated and compared to lime and H(3)PO(4). All tested amendments reduced Ca(NO(3))(2)-extractable soil metal concentrations and reduced metal uptake in Agrostis capillaris seedlings. Sodium released by Na-silicates was possibly toxic to bean plants while an isotopic dilution technique revealed that metals were only weakly sorbed by silicates (i.e. reversible sorption). Cyclonic ash appeared more efficient than lime in both reducing oxidative stress in beans and Zn, Cu and Pb uptake in grasses. The metal fixing mechanism for both amendments appeared similar (i.e. irreversible fixation at constant pH), in contrast to H(3)PO(4) where at least part of the immobilised Cd was irreversibly fixed across a range of pH.

A contaminated soil was collected in a field adjacent to a derelict As((III)) smelter in Reppel (Bocholt, Belgium). A single soil treatment (% by soil weight) based on either iron grit (SS, 1%), beringite (B, 5%), or iron grit (1%) + beringite (5%) (BSS) was applied. Untreated and treated Reppel soils and a control soil were placed in lysimeters inside a greenhouse and cropped annually. The efficiency of soil treatments in decreasing As and metals in exposure sources and restoring soil functions was assessed 6 years after the treatments commenced. Decreases in extractable Cd, Mn, Zn and As occurred in the BSS soil. Only BSS treatment reduced both As and metal concentrations in leachates. BSS treatment produced best growth of lettuce and cabbage, the highest shoot and pod yields for dwarf bean, the lowest As, Cd and Zn concentrations in plant tissues, and partly restored Rhizobium nodulation on bean roots. The epigeic earthworm (Dendrobaena octaedra) could only survive in the BSS soil. Depurated living worms from the BSS soil had Cd concentration similar to those in control worms, but higher As, Ca, Fe, and Zn concentrations. Based on physiologically based extraction test (PBET), As bioaccessibility was reduced from 12% (untreated soil) to 7.4% (BSS) and 3% (SS), but only the SS treatment decreased the bioaccessibility of Cd (-30%) and Pb (-35%). The range of chemical and biological indicators suggested that BSS amendment was the most effective treatment for restoration of normal soil functions 6 years after initial treatment of the Reppel soil.

An international inter-laboratory research program investigated the effectiveness of in situ remediation of soils contaminated by cadmium, lead and zinc, measuring changes in soil and soil solution chemistry, plants and soil microbiota. A common soil, from mine wastes in Jasper County MO, was used. The soil was pH 5.9, had low organic matter (1.2 g kg(-1) C) and total Cd, Pb, and Zn concentrations of 92, 5022, and 18 532 mg kg(-1), respectively. Amendments included lime, phosphorus (P), red mud (RM), cyclonic ashes (CA), biosolids (BIO), and water treatment residuals (WTR). Both soil solution and NH4NO3 extractable metals were decreased by all treatments. Phytotoxicity of metals was reduced, with plants grown in P treatments having the highest yields and lowest metal concentration (0.5, 7.2 and 406 mg kg(-1) Cd, Pb, and Zn). Response of soil micro-organisms was similar to plant responses. Phosphorus addition reduced the physiologically based extraction test Pb from 84% of total Pb extracted in the untreated soil to 34.1%.

The present study investigated the acute toxic effects of a metal-loaded Bauxsol reagent (MLBR), containing more than 6,450 mg kg(-1) of bound metal, on the earthworm Eisenia fetida. Bauxsol is manufactured by Virotec Global Solutions of Gold Coast, Queensland, Australia. The E. fetida were exposed to 0, 10, 20, 40, 60, and 80% treatments of MLBR plus cow manure for 28 d. Good motility and no mortality of E. fetida were found in all treatments after 28 d of exposure. The greatest bioaccumulation of metals by E. fetida occurred in the 20 and 40% MLBR treatments. The bioaccumulation of metals in the worms and bioaccumulation factors (BAFs) were less than the reported toxicity thresholds to cause mortality and less than the reported BAF for moderately contaminated soils, indicating that metals bound to Bauxsol reagents are mostly nonbioavailable. Analyses of the 20% MLBR treatment at 28 d using a sequential extraction procedure showed that more than 95% of the metals are bound within the Fe/Mn oxide fractions. However, changes occurred in metal fractionation after exposure to E. fetida for Cd/Cr, and Fe/Mn. The data also showed that the exchangeable (1 M MgCl2) and the toxicity characteristic leaching procedure extractant are useful as indicators of metal bioavailability from MLBR to E. fetida.

Total metal content by itself is insufficient as a measure to indicate actual environmental risk. Understanding the mobility of heavy metals in the soil and their speciation in the soil solution is of great importance for accurately assessing environmental risks posed by these metals. In a first explorative study, the effects of general soil characteristics on Cd mobility were evaluated and expressed in the form of empirical formulations. The most important factors influencing mobility of Cd proved to be pH and total soil content. This may indicate that current legislation expressing the requirement for soil sanitation in Flanders (Belgium) as a function of total soil content, organic matter, and clay does not successfully reflect actual risks. Current legal frameworks focusing on total content, therefore, should be amended with criteria that are indicative of metal mobility and availability and are based on physicochemical soil properties. In addition, soil-solution speciation was performed using two independent software packages (Visual Minteq 2.23 and Windermere Humic Aqueous model VI [WHAM VI]). Both programs largely were in agreement in concern to Cd speciation in all 29 soils under study. Depending on soil type, free ion and the organically complexed forms were the most abundant species. Additional inorganic soluble species were sulfates and chlorides. Minor species in solution were in the form of nitrates, hydroxides, and carbonates, the relative importance of which was deemed insignificant in comparison to the four major species.

Biosensors based on whole bacterial cells and on bacterial heavy metal binding protein were used to determine the mercury concentration in soil. The soil samples were collected in a vegetable garden accidentally contaminated with elemental mercury 25 years earlier. Bioavailable mercury was measured using different sensors: a protein-based biosensor, a whole bacterial cell based biosensor, and a plant sensor, i.e. morphological and biochemical responses in primary leaves and roots of bean seedlings grown in the mercury-contaminated soil. For comparison the total mercury concentration of the soil samples was determined by AAS. Whole bacterial cell and protein-based biosensors gave accurate responses proportional to the total amount of mercury in the soil samples. On the contrary, plant sensors were found to be less useful indicators of soil mercury contamination, as determined by plant biomass, mercury content of primary leaves and enzyme activities.

The use of green plants to remove, contain, inactivate, or degrade harmful environmental contaminants (generally termed phytoremediation) is an emerging technology. In this paper, an overview is given of existing information concerning the use of plants for the remediation of metal-contaminated soils. Both site decontamination (phytoextraction) and stabilization techniques (phytostabilization) are described. In addition to the plant itself, the use of soil amendments for mobilization (in case of phytoextraction) and immobilization (in case of phytostabilization) is discussed. Also, the economical impacts of changed land-use, eventual valorization of biomass, and cost-benefit aspects of phytoremediation are treated. In spite of the growing public and commercial interest and success, more fundamental research is needed still to better exploit the metabolic diversity of the plants themselves, but also to better understand the complex interactions between metals, soil, plant roots, and micro-organisms (bacteria and mycorrhiza) in the rhizosphere. Further, more demonstration experiments are needed to measure the underlying economics, for public acceptance and last but not least, to convince policy makers.

Nitroaromatics form an important group of recalcitrant xenobiotics. Only few aromatic compounds, bearing one nitro group as a substituent of the aromatic ring, are produced as secondary metabolites by microorganisms. The majority of nitroaromatic compounds in the biosphere are industrial chemicals such as explosives, dyes, polyurethane foams, herbicides, insecticides and solvents. These compounds are generally recalcitrant to biological treatment and remain in the biosphere, where they constitute a source of pollution due to both toxic and mutagenic effects on humans, fish, algae and microorganisms. However, relatively few microorganisms have been described as being able to use nitroaromatic compounds as nitrogen and/or carbon and energy source. The best-known nitroaromatic compound is the explosive TNT (2,4,6-trinitrotoluene). This article reviews the bioremediation strategies for TNT-contaminated soil and water. It comes to the following conclusion: The optimal remediation strategy for nitroaromatic compounds depends on many site-specific factors. Composting and the use of reactor systems lend themselves to treating soils contaminated with high levels of explosives (e.g. at former ammunition production facilities, where areas with a high contamination level are common). Compared to composting systems, bioreactors have the major advantage of a short treatment time, but the disadvantage of being more labour intensive and more expensive. Studies indicate that biological treatment systems, which are based on the activity of the fungus Phanerochaete chrysosporium or on Pseudomonas sp. ST53, might be used as effective methods for the remediation of highly contaminated soil and water. Phytoremediation, although not widely used now, has the potential to become an important strategy for the remediation of soil and water contaminated with explosives. It is best suited where contaminant levels are low (e.g. at military sites where pollution is rather diffuse) and where larger contaminated surfaces or volumes have to be treated. In addition, phytoremediation can be used as a polishing method after other remediation treatments, such as composting or bioslurry, have taken place. This in-situ treatment method has the advantage of lower treatment costs, but has the disadvantage of a considerable longer treatment time. In order to improve the cost-efficiency, phytoremediation of nitroaromatics (and other organic xenobiotics) could be combined with bio-energy production. This requires, however, detailed knowledge on the fate of the contaminants in the plants as well as the development of efficient treatment methods for the contaminated biomass that minimise the spreading of the contaminants into the environment during post harvest treatment.