Brownfields to green fields: Realising wider benefits from practical contaminant phytomanagement strategies

Utilization of phosphogypsum and red mud in alfalfa cultivation

In this work, the utilization of phosphogypsum (PG), a waste coming from the manufacture of phosphate fertilizers, as fertilizer for alfalfa (Medicago sativa L.) crops was investigated using pot experiments. The objective of this study was to evaluate the effects of both phosphogypsum and red mud (RM) in two soils representative of the pasture production area in Southern Spain. The morpho-physiological parameters of biomass, plant height, number of stems and number of leaves, as well as the chemical parameters of soil content, were measured. High doses of PG inhibited seed germination in some treatments. In addition, the treatment substrate (2550 g soil + 50 g kg-1 PG + 100 g kg-1 RM) also affected seed germination, possibly due to the large amount of RM. The application of PG and RM to the soil increased the availability of important nutrients for alfalfa, such as phosphorus (P), calcium (Ca2+) and magnesium (Mg2+). The results demonstrate that the treatment with PG significantly improved the uptake of P in alfalfa.

Maintaining the cultivation of vegetables with low Pb accumulation while remediating the soil of an allotment garden (Nantes, France) by phytoextraction

Lead (Pb) is commonly found in urban soils and can transfer to vegetables. This entails a health risk for consumers of garden crops. The increasing demand of gardening on urban soil linked to the population increase and concentration in urban areas induces an increase in the risk, as people could be forced to cultivate contaminated soils. The aim of this study was to evaluate the performance of a cropping system that allows simultaneously (i) growing eatable vegetables that accumulate few Pb and (ii) cleaning up the soil with other plants by phytoextraction. The tests were carried out in an allotment garden (Nantes, France) where soils are moderately enriched by Pb from geogenic origin (178 mg.kg-1 of dry soil on average). Four vegetables known to accumulate slightly Pb (Solanum lycopersicum, Brassica oleracea cv. "Capitata," Solanum tuberosum, and Phaseolus vulgaris) were grown. The in situ ability of Brassica juncea L. to progressively absorb the phytoavailable Pb of the soil was assessed during four seasons. Analyses of the edible parts of the four vegetables confirmed that they can all be safely cultivated. The accumulation of Pb in B. juncea shoots was too low (ca. 1 mg.kg-1 of dry matter at best) for phytoextraction purposes. Our results confirm that it is possible to grow very low Pb-accumulating vegetables on soils moderately contaminated with Pb, although it was not possible to reduce phytoavailable Pb rapidly enough with B. juncea. This study identifies possible avenues of research to improve this cropping system by using appropriate vegetables that will allow food production to continue on moderately contaminated soil while cleaning it up.

Metal-non-tolerant ecotypes of ectomycorrhizal fungi can protect plants from cadmium pollution

The application of mycorrhizal fungi as a bioaugmentation technology for phytoremediation of heavy metal (HM) contaminated soil has attracted widespread attention. In order to explore whether the adaptation of Pinus massoniana (P. massoniana) to metal polluted soil depends on the metal adaptation potential of their associated ectomycorrhizal fungi (ECMF), we evaluated the cadmium (Cd) tolerance of 10 ecotypes of Cenococcum geophilum (C. geophilum) through a membership function method, and P. massoniana seedlings were not (NM) or inoculated by Cd non-tolerant type (JaCg144), low-tolerant (JaCg32, JaCg151) and high-tolerant (JaCg205) isolates of C. geophilum were exposed to 0 and 100 mg·kg-1 for 3 months. The result showed that, each ecotype of C. geophilum significantly promoted the growth, photosynthesis and chlorophyll content, proline (Pro) content and the activity of peroxidase (POD) of P. massoniana seedlings, and decreased malonaldehyde (MDA) content and catalase (CAT) and superoxide dismutase (SOD) activity. The comprehensive evaluation D value of the tolerance to Cd stress showed that the order of the displaced Cd resistance of the four ecotypic mycorrhizal P. massoniana was: JaCg144 > JaCg151 > JaCg32 > JaCg205. Pearson correlation analysis showed that the Sig. value of the comprehensive evaluation (D) values of the strains and mycorrhizal seedlings was 0.077 > 0.05, indicating that the Cd tolerance of the the C. geophilum isolates did not affect its regulatory effect on the Cd tolerance of the host plant. JaCg144 and JaCg151 which are non-tolerant and low-tolerant ecotype significantly increased the Cd content in the shoots and roots by about 136.64-181.75% and 153.75-162.35%, indicating that JaCg144 and JaCg151 were able to effectively increase the enrichment of Cd from the soil to the root. Transcriptome results confirmed that C. geophilum increased the P. massoniana tolerance to Cd stress through promoting antioxidant enzyme activity, photosynthesis, and lipid and carbohydrate synthesis metabolism. The present study suggests that mental-non-tolerant ecotypes of ECMF can protect plants from Cd pollution, providing more feasible strategies for ectomycorrhizal-assisted phytoremediation.

Thermal evaluation of plant biomass from the phytostabilisation of soils contaminated by potentially toxic elements

The combination of phytoremediation of soils contaminated by potentially toxic elements with energy production by combustion of the generated biomass can be a sustainable land management option, combining the production of renewable bioenergy with soil restoration while minimising energy consumption and CO2 emission. In this work, plant biomass from phytoremediation of soils contaminated by potentially toxic elements was studied as solid biofuel for combustion by thermal analysis and biomass composition. Six plant species were grown in two soils with differing degrees of contamination: Brassica juncea, Cynara cardunculus, Atriplex halimus, Nicotiana glauca, Dittrichia viscosa, Retama sphaerocarpa and Salvia rosmarinus. The composition of the plant biomass was characterised chemically and thermogravimetric analyses were performed for the mass loss (TG), derivative curves of mass loss (DTG) and temperature difference (DTA) signal. The cellulose concentration correlated with the parameters of the thermal analysis in the low temperature range (150-350 °C), while lignin correlated with the thermal parameters of the second peak in the high temperature range. Salvia rosmarinus and R. sphaerocarpa showed the best combustion characteristics according to the thermal profile and mineral residue results. The accumulation of potentially toxic elements in B. juncea grown in heavily contaminated soil led to a higher amount of residue at 750 °C, with a global activation energy lower than the one obtained when this species was grown in a soil with lower contamination. Therefore, the most beneficial combination of soil phytoremediation and energy production (combustion) that can be suggested would depend on the level of soil contamination: in heavily contaminated soil, phytostabilisation using R. sphaerocarpa and S. rosmarinus; in slightly contaminated soil, B. juncea due to its high energy of activation, although the concentrations of potentially toxic elements in the residue must be controlled, as well as possible particulate matter emissions during combustion.

Comparison of PFAS soil remediation alternatives at a civilian airport using cost-benefit analysis

Contamination of soil and water systems by per- and polyfluoroalkyl substances (PFAS) due to uncontrolled use of aqueous film-forming foams (AFFFs) at firefighting training sites at civilian and military airports is a universal issue and can lead to significant human health and environmental impacts. Remediation of these sites is often complex but necessary to alleviate the PFAS burden and minimise the risks of exposure by eliminating the hotspot/source from which the PFAS spreads. This study presents a probabilistic cost-benefit analysis (CBA) for evaluating PFAS remediation alternatives, which includes monetisation of both direct costs and benefits as well as externalities. The method is applied for a case study to compare five remediation alternatives for managing PFAS contaminated soil at Stockholm Arlanda Airport in Sweden. The social profitability, or the net present value (NPV), of each remediation alternative was calculated in comparison to two reference alternatives - 'total excavation' of the site (Alt 0) or 'do nothing'. Sensitivity analyses and model scenarios were tested to account for uncertainties, including small or large PFAS spreading and simulating different values for the magnitude of annual avoided cost of inaction (i.e., aggregate benefit) from PFAS remediation. In comparison to total excavation, four of the five studied remediation alternatives resulted in a positive mean NPV. Excavation and stabilization/solidification of the hotspot on-site combined with stabilization using activated carbon for the rest of site (Alt 2) had the highest NPV for both spreading scenarios, i.e., Alt 2 was the most socially profitable alternative. Simulations of the annual avoided cost of inaction enabled estimation of the breakeven point at which a remediation alternative becomes socially profitable (NPV > 0) compared to 'do nothing'. Alt 2 had the lowest breakeven point: 7.5 and 5.75 millions of SEK/year for large and small spreading, respectively.

Drivers to improve metal(loid) phytoextraction with a focus on microbial degradation of dissolved organic matter in soils

Bioaugmentation of soils can increase the mobilization of metal(loid)s from the soil-bearing phases. However, once desorbed, these metal(loid)s are mostly complexed to the dissolved organic matter (DOM) in the soil solution, which can restrict their availability to plants (roots mainly taking up the free forms) and then the phytoextraction performances. Firstly the main drivers influencing phytoextraction are reminded, then the review focuses on the DOM role. After having reminding the origin, the chemical structure and the lability of DOM, the pool of stable DOM (the most abundant in the soil) most involved in the complexation of metal(loid)s is addressed in particular by focusing on carboxylic and/or phenolic groups and factors controlling metal(loid) complexation with DOM. Finally, this review addresses the ability of microorganisms to degrade metal(loid)-DOM complexes as an additional lever for increasing the pool of free metal(loid) ions, and then phytoextraction performances, and details the origin of microorganisms and how they are selected. The development of innovative processes including the use of these DOM-degrading microorganisms is proposed in perspectives.

Contributions of ectomycorrhizal fungi in a reclaimed poplar forest (Populus yunnanensis) in an abandoned metal mine tailings pond, southwest China

Reclamation using fast-growing trees has great potential for agroforestry development on former non-ferrous metal mining areas. However, the functional traits of ectomycorrhizal fungi (ECMF) and the relationship between ECMF and reclaimed trees remain unknown. Here, the restoration of ECMF and their functions in reclaimed poplar (Populus yunnanensis) growing in a derelict metal mine tailings pond were investigated. We identified ECMF belonging to 15 genera in 8 families, suggesting the occurrence of spontaneous diversification as poplar reclamation progressed. We described a previously unknown ectomycorrhizal relationship between poplar roots and Bovista limosa. Our results showed that B. limosa PY5 alleviated the phytotoxicity of Cd and enhanced poplar heavy metal tolerance, resulting in increased plant growth due to reduced Cd accumulation in host tissues. As part of the improved metal tolerance mechanism, PY5 colonization activated antioxidant systems, enhanced the conversion of Cd into inactive chemical forms, and promoted the compartmentalization of Cd into host cell walls. These results suggest that introducing adaptative ECMF may be an alternative to bioaugmenting reforestation and phytomanagement programs of fast-growing native trees in the barren metal mining and smelting areas.

Field evaluation of industrial non-food crops for phytomanaging a metal-contaminated dredged sediment

Phytomanagement is a concept fit for a bio-based circular economy that combines phytotechnologies and biomass production for non-food purposes. Here, ten annual and perennial industrial non-food crops (Sorghum Biomass 133, Sorghum Santa Fe red, Linum usitatissimum L., Eucalyptus sp., Salix Inger, Salix Tordis, Beta vulgaris L., Phacelia tanacetifolia Benth., Malva sylvestris L., and Chenopodium album L.) were studied under field conditions for phytomanaging a metal (Cd, Cu, Pb, and Zn)-contaminated dredged sediment in the North of France. The crops were selected according to their relevance to pedoclimatic and future climatic conditions, and one or more non-food end-products were proposed for each plant part collected, such as biogas, bioethanol, compost, natural dye, ecocatalyst, and fiber. Based on the soil-plant transfer of metals, eight out of the crops cultivated on field plots exhibited an excluder behavior (bioconcentration factor, BCF < 1), a trait suitable for phytostabilization. However, these crops did not change the metal mobilities in the dredged sediment. The BCF < 1 was not sufficient to characterize the excluder behavior of crops as this factor depended on the total dredged-sediment contaminant. Therefore, a BCF group ranking method was proposed accounting for metal phytotoxicity levels or yield decrease as a complemental way to discuss the crop behavior. The feasibility of the biomass-processing chains was discussed based on these results and according to a survey of available legislation in standard and scientific literature.

Beyond Cleansing: Ecosystem Services Related to Phytoremediation

Phytotechnologies used for cleaning up urban and suburban polluted soils (i.e., brownfields) have shown some weakness in the excessive extent of the timeframe required for them to be effectively operating. This bottleneck is due to technical constraints, mainly related to both the nature of the pollutant itself (e.g., low bio-availability, high recalcitrance, etc.) and the plant (e.g., low pollution tolerance, low pollutant uptake rates, etc.). Despite the great efforts made in the last few decades to overcome these limitations, the technology is in many cases barely competitive compared with conventional remediation techniques. Here, we propose a new outlook on phytoremediation, where the main goal of decontaminating should be re-evaluated, considering additional ecosystem services (ESs) related to the establishment of a new vegetation cover on the site. The aim of this review is to raise awareness and stress the knowledge gap on the importance of ES associated with this technique, which can make phytoremediation a valuable tool to boost an actual green transition process in planning urban green spaces, thereby offering improved resilience to global climate change and a higher quality of life in cities. This review highlights that the reclamation of urban brownfields through phytoremediation may provide several regulating (i.e., urban hydrology, heat mitigation, noise reduction, biodiversity, and CO₂ sequestration), provisional (i.e., bioenergy and added-value chemicals), and cultural (i.e., aesthetic, social cohesion, and health) ESs. Although future research should specifically be addressed to better support these findings, acknowledging ES is crucial for an exhaustive evaluation of phytoremediation as a sustainable and resilient technology.

Transforming brownfields into urban greenspaces: A working process for stakeholder analysis

Urban greenspaces (UGS) provide a range of ecosystem services and are instrumental in ensuring the liveability of cities. Whilst incorporating UGS in increasingly denser cities is a challenge to planners, brownfields form a latent resource with the potential of being converted into UGS. Transformation of brownfields to greenspaces, however, requires engagement of a variety of stakeholders, from providers to users. The overall aim of this study was to support effective and realistic realisations of UGS in the context of urban brownfields' regeneration and stakeholder engagement. A working process was developed to: 1) integrate methods relevant for UGS realisation for a) identification and categorising of relevant stakeholders, b) mapping their interests and resources, c) identifying various challenges, and d) matching those challenges with the mapped resources over the timeline of UGS development; and 2) apply these methods to assess relevance and shortcomings. The methods were applied to a study site in Sweden, and data was collected using a questionnaire survey. The survey received 31 responses and the respondents' comments indicated that the combination of several uses, especially integrated with an urban park, is preferable. Visualisation was an important component for data analysis: stakeholder categorisation was effectively visualised using a Venn diagram, and the needed mobilisation of resources among stakeholders to manage identified challenges was visualised using a timeline. The analysis demonstrates the need for collaboration between stakeholders to achieve an effective realisation of UGS and how multiple methods can be used in concert to map stakeholders, preferences, challenges, and resources for a particular site. The application at a study site provided site-specific data but the developed stakeholder categorisation, and the method for matching identified challenges with the stakeholders' resources using a timeline, can be generalised to applications at other sites.

Field assessment of organic amendments and spring barley to phytomanage a Cu/PAH-contaminated soil

The INTENSE project, supported by the EU Era-Net Facce Surplus, aimed at increasing crop production on marginal land, including those with contaminated soils. A field trial was set up at a former wood preservation site to phytomanage a Cu/PAH-contaminated sandy soil. The novelty was to assess the influence of five organic amendments differing in their composition and production process, i.e. solid fractions before and after biodigestion of pig manure, compost and compost pellets (produced from spent mushroom substrate, biogas digestate and straw), and greenwaste compost, on Cu availability, soil properties, nutrient supply, and plant growth. Organic amendments were incorporated into the soil at 2.3% and 5% soil w/w. Total soil Cu varied from 179 to 1520 mg kg^-1, and 1 M NH₄NO₃-extractable soil Cu ranged from 4.7 to 104 mg kg^-1 across the 25 plots. Spring barley (Hordeum vulgare cv. Ella) was cultivated in plots. Changes in physico-chemical soil properties, shoot DW yield, shoot ionome, and shoot Cu uptake depending on extractable soil Cu and the soil treatments are reported. Shoot Cu concentration varied from 45 ± 24 to 140 ± 193 mg kg DW^-1 and generally increased with extractable soil Cu. Shoot DW yield, shoot Cu concentration, and shoot Cu uptake of barley plants did not significantly differ across the soil treatments in year 1. Based on soil and plant parameters, the effects of the compost and pig manure treatments were globally discriminated from those of the untreated, greenwaste compost and digested pig manure treatments. Compost and its pellets at the 5% addition rate promoted soil functions related to primary production, water purification, and soil fertility, and the soil quality index.

Assessment for combined phytoremediation and biomass production on a moderately contaminated soil

Once previous industrial activity has ceased, brownfields are found in urban and suburban environments and managed in different ways ranging from being left untouched to total reconversion. These situations apply to large surface areas often impacted by residual diffuse pollution. Though significant and preventing any sensitive use, residual contamination does not necessarily require treatment. Moreover, conventional treatments show their technical and economic limits in these situations and gentle remediation options such as phytomanagement might appear more relevant to the management of those sites. Thus, these sites face up two major issues: managing moderate contamination levels and providing an alternative use of economic interest. This work proposes to assess a management strategy associating the phytoremediation of organic pollution along with the production of biomass for energy generation production. A 16-week controlled growth experiment was conducted on a soil substrate moderately impacted by multiple pollution (trace elements, mainly Zn and Pb, and hydrocarbons), by associating rhizodegradation with Medicago sativa or biomass production with Robinia pseudoacacia or Alnus incana in monocultures. The effect of a microbial inoculum amendment on the performances of these treatments was also evaluated. Results showed total hydrocarbons (TH), and to a lesser extent polycyclic aromatic hydrocarbons (PAH), concentrations decreased over time, whatever the plant cover. Good biomass production yields were achieved for both tree species in comparison with the control sample, even though R. pseudoacacia seemed to perform better. Furthermore, the quality of the biomass produced was in conformity with the thresholds set by the legislation concerning its use as a renewable energy source.

Developing field-scale, gentle remediation options for nuclear sites contaminated with 137Cs and 90Sr: The role of Nature-Based Solutions

The remediation of contaminated land using plants, bacteria and fungi has been widely examined, especially in laboratory or greenhouse systems where conditions are precisely controlled. However, in real systems at the field scale conditions are much more variable and often produce different outcomes, which must be fully examined if 'gentle remediation options', or GROs, are to be more widely implemented, and their associated benefits (beyond risk-management) realized. These secondary benefits can be significant if GROs are applied correctly, and can include significant biodiversity enhancements. Here, we assess recent developments in the field-scale application of GROs for the remediation of two model contaminants for nuclear site remediation (⁹⁰Sr and ¹³⁷Cs), their risk management efficiency, directions for future application and research, and barriers to their further implementation at scale. We also discuss how wider benefits, such as biodiversity enhancements, water filtration etc. can be maximized at the field-scale by intelligent application of these approaches.

Potential ability of tobacco (Nicotiana tabacum L.) to phytomanage an urban brownfield soil

The ability of tobacco (Nicotiana tabacum L. cv. Badischer Geudertheimer) for phytomanaging and remediating soil ecological functions at a contaminated site was assessed with a potted soil series made by fading an uncontaminated sandy soil with a contaminated sandy soil from the Borifer brownfield site, Bordeaux, SW France, at the 0%, 25%, 50%, 75%, and 100% addition rates. Activities of sandblasting and painting with metal-based paints occurred for decades at this urban brownfield, polluting the soil with metal(loid)s and organic contaminants, e.g., polycyclic aromatic hydrocarbons, in addition to past backfilling. Total topsoil metal(loid)s (e.g., 54,700 mg Zn and 5060 mg Cu kg-1) exceeded by seven- to tenfold the background values for French sandy soils, but the soil pH was 7.9, and overall, the 1M NH4NO3 extractable soil fractions of metals were relatively low. Leaf area, water content of shoots, and total chlorophyll (Chl) progressively decreased with the soil contamination, but the Chl fluorescence remained constant near its optimum value. Foliar Cu and Zn concentrations varied from 17.8 ± 4.2 (0%) to 27 ± 5 mg Cu kg-1 (100%) and from 60 ± 15 (0%) to 454 ± 53 mg Zn kg-1 (100%), respectively. Foliar Cd concentration peaked up to 1.74 ± 0.09 mg Cd kg-1, and its bioconcentration factor had the highest value (0.2) among those of the metal(loid)s. Few nutrient concentrations in the aboveground plant parts decreased with the soil contamination, e.g., foliar P concentration from 5972 ± 1026 (0%) to 2861 ± 334 mg kg-1 (100%). Vulnerability to drought-induced embolism (P50) did not differ for the tobacco stems across the soil series, whereas their hydraulic efficiency (Ks) declined significantly with increasing soil contamination. Overall, this tobacco cultivar grew relatively well even in the Borifer soil (100%), keeping its photosynthetic system healthy under stress, and contaminant exposure did not increase the vulnerability of the vascular system to drought. This tobacco had a relevant potential to annually phytoextract a part of the bioavailable soil Zn and Cd, i.e., shoot removals representing here 8.8% for Zn and 43.3% for Cd of their 1M NH4NO3 extractable amount in the potted Borifer soil.

Field Studies on the Effect of Bioaugmentation with Bacillus amyloliquefaciens FZB42 on Plant Accumulation of Rare Earth Elements and Selected Trace Elements

This study is an investigation of the effect of soil bioaugmentation (inoculation) on a field scale with the commercially available product RhizoVital®42, containing Bacillus amyloliquefaciens FZB4, on element bioavailability, plant biomass production, as well as accumulation of rare earth elements (REEs), germanium, and selected trace elements. Zea mays and Helianthus annuus were selected as test plants. Post-harvest, results showed inoculation increased biomass production of Z. mays and H. annuus by 24% and 26%, albeit insignificant at p ≤ 0.05. Bioaugmentation enhanced Z. mays shoot content of P, Cd, and Ge by percentages between 73% and 80% (significant only for Ge) and decreased shoot content of REET, Pb, and Cu by 28%, 35%, and 59%, respectively. For H. annuus grown on bioaugmented soil, shoot content of Ca, Cu, Ge, REET, and Pb increased by over 40%, with a negligible decrease observed for Cd. Summarily, results suggest that bioaugmentation with Bacillus amyloliquefaciens FZB42 could enhance biomass production, increase soil element bioavailability enhance, and increase or reduce plant accumulation of target elements. Additionally, differences in P use efficiency could influence bioaugmentation effects on P accumulation.

A critical review of phytoremediation for acid mine drainage-impacted environments

Acid mine drainage (AMD), a waste product of mining activities containing sulfates, iron and heavy metals, causes severe environmental degradation and pose risks to human health and sustainable development. Areas impacted by AMD are lacking remediation techniques that holistically address the ecologic, social, and economic needs of affected communities, for which phytoremediation is a promising solution. This review article introduces AMD and AMD-impacted environments and critically discusses phytomanagement, phytoprotection, and phytorestoration approaches towards AMD-impacted environments. Continued research and application of such approaches will help optimize resource and revenue-generating potentials, address biodiversity loss and carbon storage concerns of climate change, and promote sustainable agricultural management. With a focus on energy crops, phytomining critical elements, carbon storage, co-cropping, allelopathy, and ecosystem restoration, this review examines phytoremediation research that addresses positive economic and environmental opportunities for AMD-impacted environments.

A combined approach utilizing UAV 3D imaging methods, in-situ measurements, and laboratory experiments to assess water evaporation and trace element uptake by tree species growing in a red gypsum landfill

The extractive industry is increasingly faced with problems of managing contaminated sites. The red gypsum landfill at the Ochsenfeld site is representative of the typology byproduct storage of the Ti-extraction activity. The management of the elemental content and the water body are the issues at this site. The aim of this study was to evaluate the canopy conductance (g_cmax) of various tree species and the content of elements in the leaves, utilizing the opportunity of a demonstration plantation setup in 2014 with sixteen tree species, combined with a growth chamber experiment. We combined the gas exchange measurements with the data from two multispectral cameras with RGB and NIR bands embarked on an unmanned aerial vehicle (UAV). In the field, Ostrya carpinifolia, Maclura pomifera, and Rhus copallina had the highest g_cmax of all planted tree species, and the high transpiration rate in O. carpinifolia was confirmed in a pot-based controlled experiment. Except R. copallina, the species with a high Mn content (O. carpinifolia, Betula pendula, and Salix aquatica grandis) had high stomatal conductance. O. carpinifolia could therefore be a species to exploit in the management of landfill leachates, especially in the context of climate change since this species is well adapted to dry environments.

Harnessing an arbuscular mycorrhizal fungus to improve the adaptability of a facultative metallophytic poplar (Populus yunnanensis) to cadmium stress: Physiological and molecular responses

Populus yunnanensis Dode, a facultative metallophytic poplar, exhibits afforestation potential in barren mine tailing areas. However, the interactions and functional roles of arbuscular mycorrhizal fungus (AMF) in P. yunnanensis adaptability to heavy metal stress remain unclear. Physiological and molecular responses of P. yunnanensis plantlets to AMF (Funneliformis mosseae) under cadmium (Cd) stress (50 mg kg^-1) were investigated. Results showed attenuation of Cd phytotoxicity effects on cell organelles upon AMF inoculation, which also reduced the Cd concentration in the poplar leaves, stems, and roots. Under Cd stress, AMF-blocking of metal transporter (e.g., Ca²⁺ channel) activity occurred, decreasing root cell Cd influx by reducing H⁺ efflux. Bioaugmentation of rhizosphere sediments by AMF to stabilize metals with a decreasing DTPA-extractable Cd also occurred. The AMF inoculation promoted Cd conversion into inactive, less phytotoxic forms, and helped to maintain ion homeostasis and relieve nutritional ion (e.g., Ca, Mg) disorders caused by excessive Cd. Leaf enzyme and non-enzyme antioxidant systems were triggered. Root and leaf physiological response patterns differed. The AMF regulated the poplar functional genes, and nine metal-responsive gene clusters were identified. We suggest that AMF is a functional component of P. yunnanensis phenotype extension, contributing to strong adaptability to unfavorable mine tailings conditions.

Metal Accumulation and Biomass Production in Young Afforestations Established on Soil Contaminated by Heavy Metals

The restoration of forest ecosystems on metal-contaminated sites can be achieved whilst producing valuable plant biomass. Here, we investigated the metal accumulation and biomass production of young afforestations on contaminated plots by simulating brownfield site conditions. On 16 3-m² plots, the 15 cm topsoil was experimentally contaminated with Zn/Cu/Pb/Cd = 2854/588/103/9.2 mg kg⁻¹ using smelter filter dust, while 16 uncontaminated plots (Zn/Cu/Pb/Cd = 97/28/37/< 1) were used as controls. Both the calcareous (pH 7.4) and acidic (pH 4.2) subsoils remained uncontaminated. The afforestations consisted of groups of conifers, deciduous trees, and understorey plants. During the four years of cultivation, 2254/86/0.35/10 mg m⁻² Zn/Cu/Pb/Cd were extracted from the contaminated soils and transferred to the aboveground parts of the plants (1279/72/0.06/5.5 mg m⁻² in the controls). These extractions represented 3/2/3% of the soluble soil Zn/Cu/Cd fractions. The conifers showed 4–8 times lower root-to-shoot translocation of Cu and Zn than the deciduous trees. The contamination did not affect the biomass of the understorey plants and reduced that of the trees by 23% at most. Hence, we conclude that the afforestation of brown field sites with local tree species is an interesting option for their reclamation from an ecological as well as economic perspective.

Water and soil contaminated by arsenic: the use of microorganisms and plants in bioremediation

Owing to their roles in the arsenic (As) biogeochemical cycle, microorganisms and plants offer significant potential for developing innovative biotechnological applications able to remediate As pollutions. This possible use in bioremediation processes and phytomanagement is based on their ability to catalyse various biotransformation reactions leading to, e.g. the precipitation, dissolution, and sequestration of As, stabilisation in the root zone and shoot As removal. On the one hand, genomic studies of microorganisms and their communities are useful in understanding their metabolic activities and their interaction with As. On the other hand, our knowledge of molecular mechanisms and fate of As in plants has been improved by laboratory and field experiments. Such studies pave new avenues for developing environmentally friendly bioprocessing options targeting As, which worldwide represents a major risk to many ecosystems and human health.

Potentially Toxic Elements’ Contamination of Soils Affected by Mining Activities in the Portuguese Sector of the Iberian Pyrite Belt and Optional Remediation Actions: A Review

Both sectors of the Iberian Pyrite Belt, Portuguese and Spanish, have been exploited since ancient times, but more intensively during and after the second half of the 19th century. Large volumes of polymetallic sulfide ore were extracted in open pits or in underground works, processed without environmental concerns, and the generated waste rocks and tailings were simply deposited in the area. Many of these mining sites were abandoned for years under the action of erosive agents, leading to the spread of trace elements and the contamination of soils, waters and sediments. Some of these mine sites have been submitted to rehabilitation actions, mostly using constructive techniques to dig and contain the contaminated tailings and other waste materials, but the remaining soil still needs to be treated with the best available techniques to recover its ecosystem functions. Besides the degraded physical structure and poor nutritional status of these soils, they have common characteristics, as a consequence of the pyrite oxidation and acid drainage produced, such as a high concentration of trace elements and low pH, which must be considered in the remediation plans. This manuscript aims to review the results from studies which have already covered these topics in the Iberian Pyrite Belt, especially in its Portuguese sector, considering: (i) soils’ physicochemical characteristics; (ii) potentially toxic trace elements’ concentration; and (iii) sustainable remediation technologies to cope with this type of soil contamination. Phytostabilization, after the amelioration of the soil’s properties with organic and inorganic amendments, was investigated at the lab and field scale by several authors, and their results were also considered.

Phytoattenuation of Cd, Pb, and Zn in a Slag-contaminated Soil Amended with Rice Straw Biochar and Grown with Energy Maize

Biochar has attracted interest due to its ability to improve soil fertility, soil carbon, and crop yield. Also, biochar can adsorb metals and render them less bioavailable. We investigated the soil availability, sequential extraction, and maize uptake of Cd, Pb, and Zn in a highly contaminated soil amended with rice straw biochar rates (0.0, 5.0, 10.0, 20.0, and 30.0 Mg ha^-1). We hypothesized that biochar application to the soil cultivated with maize attenuates metal toxicity and mobility in slag-polluted soils near an abandoned Pb smelting plant in Brazil. Results showed that applying biochar increased the soil organic carbon, CEC, and P up to 27, 30, and 107, respectively. Plant accumulation of P and N was 104 and 32% higher than control, while aerial and root biomasses were increased by 18 and 23%. The sequential extraction showed that Pb and Zn in the original soil were retained mainly in residual fractions (94 and 87%, respectively), while Cd was mostly allocated in the organic fraction (47%). Biochar rates increased the proportion of Cd in the organic fraction to 85%, while Pb and Zn were redistributed mainly into iron oxides. The Cd, Pb, and Zn bioavailability assessed by DTPA decreased 32% in the biochar-amended soil, reducing plants' metal uptake. The maize biomass increase, metal soil bioavailability decrease, and low metal concentration in shoots driven by biochar indicate that phytoattenuation using rice straw biochar and maize cultivation could reduce risks to humans and the environment in the polluted sites of Santo Amaro.

Hydrothermally-altered feldspar reduces metal toxicity and promotes plant growth in highly metal-contaminated soils

Novel green technologies for soil remediation have been focusing on altering soil properties and improving soil health. Hydrothermally-altered feldspar (HYP, HydroPotash), recently developed, is being related as both an efficient amendment to immobilize heavy metals in soils and a plant nutrients source, consisting in a promising technology for revegetation of contaminated sites. In order to evaluate the effectiveness of using HYP for phytostabilization programs, two different soils (Technosol and Oxisol) collected from a smelting site were amended with increasing doses of HYPs (HYP-1 and HYP-2): 15, 30, 60, and 120 Mg ha^-1. For comparison, a control (soil without amendment) and a soil amended with zeolite (clinoptilolite) were also included as treatments. After 90 days of incubation, HYPs decreased up to 83.8 % of Cd availability and reduced exchangeable Al up to 100 %. HydroPotash increased pH, cation exchange capacity, and contents of potassium, calcium, and phosphorus, as well as microbial biomass carbon, and fluorescein diacetate hydrolysis of soils. Andropogon gayanus, Eucalyptus grandis, and Heterocondylus vitalbae started growing from the dose of 15 Mg ha^-1 HYPs in the Oxisol and 60 Mg ha^-1 HYPs in the Technosol. Principal component analysis indicates that plant shoot dry weight was negatively correlated with extractable Cd and Zn and positively with pH, CEC, and Ca content. Besides promoting plant growth, HYPs reduced heavy metals (Cd and Zn) absorption by plants, indicating that HYP has potential use as an amendment in phytostabilization programs.

A risk management framework for Gentle Remediation Options (GRO)

Gentle Remediation Options (GRO) are remediation measures involving plants, fungi, bacteria, and soil amendments that can be applied to manage risks at contaminated sites. Several studies and decision-support tools promote the wider range of benefits provided by GRO, but there is still skepticism regarding GRO implementation. Key issues that need to be better communicated are the various risk mitigation mechanisms, the required risk reduction for an envisioned land use, and the time perspective associated with the risk mitigation mechanisms. To increase the viability and acceptance of GRO, the phytomanagement approach implies the combination of GRO with beneficial green land use, gradually reducing risks and restoring ecosystem services. To strengthen the decision basis for GRO implementation in practice, this paper proposes a framework for risk management and communication of GRO applications to support phytomanagement strategies at contaminated sites. The mapping of the risk mitigation mechanisms is done by an extensive literature review and the Swedish national soil guideline value model is used to derive the most relevant human health exposure pathways and ecological risks for generic green land use scenarios. Results indicate that most of the expected risk mitigation mechanisms are supported by literature, but that knowledge gaps still exist. The framework is demonstrated to support the identification of GRO options for the case study site given two envisioned land uses: biofuel park and allotment garden. A more easily understandable risk management framework, as proposed here, is expected to act as a communication tool to educate decision-makers, regulatory bodies and other stakeholders for better understanding of risk mitigation mechanisms and preliminary timeframes of various GRO, particularly in the early stages of a brownfield redevelopment project.

Phytomanagement of a metal(loid)-contaminated agricultural site using aromatic and medicinal plants to produce essential oils: analysis of the metal(loid) fate in the value chain

Phytomanagement uses plants and soil conditioners to create value on contaminated land while minimizing environmental risk. This work was carried out on a metal(loid)-contaminated site and aimed at assessing the suitability of Salvia sclarea L. (sage) and Coriandrum sativum L. (coriander) combined with an arbuscular mycorrhizal fungus (AMF) inoculant to immobilize metal(loid)s and produce essential oils (EO). The effect of the inoculant on the transfer of metal(loid)s (ML, i.e., Cd, Cu, Pb, Zn, As, Ni, and Sb) to plants and the ML soil mobility were investigated. The ML concentrations in EO from both plant species and the valorization options for the distillation residues (soil conditioner, animal fodder, and anaerobic digestion) were studied. Sage was a suitable candidate for this value chain because it presents an excluder phenotype and the residues of oil extraction could be used as a soil conditioner. The metal concentrations in the sage EO were similar to those obtained from plants cultivated on an uncontaminated soil. These results indicate the suitability of sage harvested on the contaminated soil according to the ML fate in the whole value chain. Like the EO of sage, ML concentrations in the coriander EO did not differ from those in the commercial EO that were obtained from plants grown on uncontaminated soil. However, the use of distillation residues of coriander was limited by their relatively elevated Cd concentrations. The use of a mycorrhizal inoculum did not decrease the Cd mobility in soil for the coriander.

In situ cultivation of aromatic plant species for the phytomanagement of an aged-trace element polluted soil: Plant biomass improvement options and techno-economic assessment of the essential oil production channel

Due to the presence of trace element (TE) in agricultural soils, wide areas are unproper for food production and the clean-up of soil is not a feasible option. Considering the potential remediation options, the use of aromatic plants producing a high quantity of biomass and developing high-added value sectors such as essential oil (EO) production could be valuable regarding one of the phytomanagement objectives, i.e. the restoration of an economic activity. The purpose of this study was hence to evaluate in situ the suitability of two aromatic crops, clary sage and coriander, for the phytomanagement of aged TE-polluted soils, taking into account plants' growth, development and biomass production, essential oil (EO) content and quality as well as a techno-economic feasibility analysis of the channel. In situ experiments have been carried out on two agricultural plots of 1.5 ha, a TE-polluted one (Pb: 394 ppm - Zn: 443 ppm - Cd: 7.2 ppm) and an unpolluted one (Pb: 22 ppm - Zn: 48 ppm - Cd: 0.4 ppm). Our findings have shown the ability of coriander and sage to grow similarly on both unpolluted and TE-polluted soil and to produce significant amounts of biomass. The pesticide residue and TE analyses have demonstrated that the EO only contained trace amounts of the contaminants, below or close to the limit of quantification of the method used and similar to marketed products. Mycorrhizal inoculation has also shown promising results by increasing the colonization rates of both aromatic plants, but did not result in higher biomass or EO amounts. Our study brings new evidence towards the potential of clary sage to be used for the phytomanagement of TE-polluted areas, given its perennial vegetation cover, tolerance to TE and obtained EO yields.

Chemical Composition, Antioxidant and Anti-Inflammatory Activities of Clary Sage and Coriander Essential Oils Produced on Polluted and Amended Soils-Phytomanagement Approach

The potential of essential oils (EO), distilled from two aromatic plants—clary sage (Salvia sclarea L.) and coriander (Coriandrum sativum L.)—in view of applications as natural therapeutic agents was evaluated in vitro. These two were cultivated on a trace element (TE)-polluted soil, as part of a phytomanagement approach, with the addition of a mycorrhizal inoculant, evaluated for its contribution regarding plant establishment, growth, and biomass production. The evaluation of EO as an antioxidant and anti-inflammatory, with considerations regarding the potential influence of the TE-pollution and of the mycorrhizal inoculation on the EO chemical compositions, were the key focuses. Besides, to overcome EO bioavailability and target accession issues, the encapsulation of EO in β-cyclodextrin (β-CD) was also assessed. Firstly, clary sage EO was characterized by high proportions of linalyl acetate (51–63%) and linalool (10–17%), coriander seeds EO by a high proportion of linalool (75–83%) and lesser relative amounts of γ-terpinene (6–9%) and α-pinene (3–5%) and coriander aerial parts EO by 2-decenal (38–51%) and linalool (22–39%). EO chemical compositions were unaffected by both soil pollution and mycorrhizal inoculation. Of the three tested EO, the one from aerial parts of coriander displayed the most significant biological effects, especially regarding anti-inflammatory potential. Furthermore, all tested EO exerted promising antioxidant effects (IC₅₀ values ranging from 9 to 38 g L⁻¹). However, EO encapsulation in β-CD did not show a significant improvement of EO biological properties in these experimental conditions. These findings suggest that marginal lands polluted by TE could be used for the production of EO displaying faithful chemical compositions and valuable biological activities, with a non-food perspective.

Partial overlap of fungal communities associated with nettle and poplar roots when co-occurring at a trace metal contaminated site

Stinging nettle (Urtica dioica L.) raises growing interest in phytomanagement because it commonly grows under poplar Short Rotation Coppices (SRC) set up at trace-metal (TM) contaminated sites and provides high-quality herbaceous fibres. The mycobiome of this non-mycorhizal plant and its capacity to adapt to TM-contaminated environments remains unknown. This study aimed at characterizing the mycobiome associated with nettle and poplar roots co-occurring at a TM-contaminated site. Plant root barcoding using the fungi-specific ITS1F-ITS2 primers and Illumina MiSeq technology revealed that nettle and poplar had distinct root fungal communities. The nettle mycobiome was dominated by Pezizomycetes from known endophytic taxa and from the supposedly saprotrophic genus Kotlabaea (which was the most abundant). Several ectomycorrhizal fungi such as Inocybe (Agaricomycetes) and Tuber (Pezizomycetes) species were associated with the poplar roots. Most of the Pezizomycetes taxa were present in the highly TM-contaminated area whereas Agaricomycetes tended to be reduced. Despite being a known non-mycorrhizal plant, nettle was associated with a significant proportion of ectomycorrhizal OTU (9.7%), suggesting some connexions between the poplar and the nettle root mycobiomes. Finally, our study raised the interest in reconsidering the fungal networking beyond known mycorrhizal interactions.

Clary Sage Cultivation and Mycorrhizal Inoculation Influence the Rhizosphere Fungal Community of an Aged Trace-Element Polluted Soil

Soil fungal communities play a central role in natural systems and agroecosystems. As such, they have attracted significant research interest. However, the fungal microbiota of aromatic plants, such as clary sage (Salvia sclarea L.), remain unexplored. This is especially the case in trace element (TE)-polluted conditions and within the framework of phytomanagement approaches. The presence of high concentrations of TEs in soils can negatively affect not only microbial diversity and community composition but also plant establishment and growth. Hence, the objective of this study is to investigate the soil fungal and arbuscular mycorrhizal fungi (AMF) community composition and their changes over time in TE-polluted soils in the vicinity of a former lead smelter and under the cultivation of clary sage. We used Illumina MiSeq amplicon sequencing to evaluate the effects of in situ clary sage cultivation over two successive years, combined or not with exogenous AMF inoculation, on the rhizospheric soil and root fungal communities. We obtained 1239 and 569 fungal amplicon sequence variants (ASV), respectively, in the rhizospheric soil and roots of S. sclarea under TE-polluted conditions. Remarkably, 69 AMF species were detected at our experimental site, belonging to 12 AMF genera. Furthermore, the inoculation treatment significantly shaped the fungal communities in soil and increased the number of AMF ASVs in clary sage roots. In addition, clary sage cultivation over successive years could be one of the explanatory parameters for the inter-annual variation in both fungal and AMF communities in the soil and root biotopes. Our data provide new insights on fungal and AMF communities in the rhizospheric soil and roots of an aromatic plant, clary sage, grown in TE-polluted agricultural soil.

Successful remediation of soils with mixed contamination of chromium and lindane: Integration of biological and physico-chemical strategies

Soils contaminated by organic and inorganic pollutants like Cr(VI) and lindane, is currently a main environmental challenge. Biological strategies, such as biostimulation, bioaugmentation, phytoremediation and vermiremediation, and nanoremediation with nanoscale zero-valent iron (nZVI) are promising approaches for polluted soil health recovery. The combination of different remediation strategies might be key to address this problem. For this reason, a greenhouse experiment was performed using soil without or with an organic amendment. Both soils were contaminated with lindane (15 mg kg^-1) and Cr(VI) (100 or 300 mg kg^-1). After one month of aging, the following treatments were applied: (i) combination of bioaugmentation (actinobacteria), phytoremediation (Brassica napus), and vermiremediation (Eisenia fetida), or (ii) nanoremediation with nZVI, or (iii) combination of biological treatments and nanoremediation. After 60 days, the wellness of plants and earthworms was assessed, also, soil health was evaluated through physico-chemical parameters and biological indicators. Cr(VI) was more toxic and decreased soil health, however, it was reduced to Cr(III) by the amendment and nZVI and, to a lesser extent, by the biological treatment. Lindane was more effectively degraded through bioremediation. In non-polluted soils, nZVI had strong deleterious effects on soil biota when combined with the organic matter, but this effect was reverted in soils with a high concentration of Cr(VI). Therefore, under our experimental conditions bioremediation might be the best for soils with a moderate concentration of Cr(VI) and organic matter. The application of nZVI in soils with a high content of organic matter should be avoided except for soils with very high concentrations of Cr(VI). According to our study, among the treatments tested, the combination of an organic amendment, biological treatment, and nZVI was shown to be the strategy of choice in soils with high concentrations of Cr(VI) and lindane, while for moderate levels of chromium, the organic amendment plus biological treatment is the most profitable treatment.

Evaluation of direct and biochar carrier-based inoculation of Bacillus sp. on As- and Pb-contaminated technosol: effect on metal(loid) availability, Salix viminalis growth, and soil microbial diversity/activity

Phytomanagement manipulates the soil-plant system to lower the risk posed by contaminated soils. In this process, the addition of amendments, such as biochar, and bacteria can improve the fertility of poor contaminated soils and consequently ameliorate plant growth. A number of studies based on the inoculation of soil with microorganisms of the genus Bacillus, previously isolated from contaminated sites, revealed positive effects on soil properties and plant growth. Furthermore, when the Bacillus isolates were used in association with biochar, better results were obtained, as biochar can ameliorate soil properties and serve as habitat for microorganisms. Accordingly, a mesocosm study was set-up using a mining technosol amended with biochar and inoculated with an endogenous Bacillus isolate, to evaluate the effect of inoculation on soil properties, metal(loid) immobilization, and Salix viminalis growth. Two inoculation methods were compared: (1) direct inoculation of bacteria (Bacillus sp.) and (2) inoculation using biochar as a carrier. Results showed that the Bacillus isolate modified soil properties and ameliorated plant growth, while having a reduced effect on metal(loid) accumulation. The microbial activity was also stimulated, and the community composition was shifted, more importantly when biochar was used as a carrier. In conclusion, this research revealed an improvement of the plant growth and microbial activity after the addition of the endogenous bacterium to the analyzed former mining soil, with better results recorded when a carrier was used.

Rhizoremediation as a green technology for the remediation of petroleum hydrocarbon-contaminated soils

Rhizoremediation is increasingly becoming a green and sustainable alternative to physico-chemical methods for remediation of contaminated environments through the utilization of symbiotic relationship between plants and their associated soil microorganisms in the root zone. The overall efficiency can be enhanced by identifying suitable plant-microbe combinations for specific contaminants and supporting the process with the application of appropriate soil amendments. This approach not only involves promoting the existing activity of plants and soil microbes, but also introduces an adequate number of microorganisms with specific catabolic activity. Here, we reviewed recent literature on the main mechanisms and key factors in the rhizoremediation process with a particular focus on soils contaminated with total petroleum hydrocarbon (TPH). We then discuss the potential of different soil amendments to accelerate the remediation efficiency based on biostimulation and bioaugmentation processes. Notwithstanding some successes in well-controlled environments, rhizoremediation of TPH under field conditions is still not widespread and considered less attractive than physico-chemical methods. We catalogued the major pitfalls of this remediation approach at the field scale in TPH-contaminated sites and, provide some applicable situations for the future successful use of in situ rhizoremediation of TPH-contaminated soils.

The Aromatic Plant Clary Sage Shaped Bacterial Communities in the Roots and in the Trace Element-Contaminated Soil More Than Mycorrhizal Inoculation - A Two-Year Monitoring Field Trial

To cope with soil contamination by trace elements (TE), phytomanagement has attracted much attention as being an eco-friendly and cost-effective green approach. In this context, aromatic plants could represent a good option not only to immobilize TE, but also to use their biomass to extract essential oils, resulting in high added-value products suitable for non-food valorization. However, the influence of aromatic plants cultivation on the bacterial community structure and functioning in the rhizosphere microbiota remains unknown. Thus, the present study aims at determining in TE-aged contaminated soil (Pb - 394 ppm, Zn - 443 ppm, and Cd - 7ppm, respectively, 11, 6, and 17 times higher than the ordinary amounts in regional agricultural soils) the effects of perennial clary sage (Salvia sclarea L.) cultivation, during two successive years of growth and inoculated with arbuscular mycorrhizal fungi, on rhizosphere bacterial diversity and community structure. Illumina MiSeq amplicon sequencing targeting bacterial 16S rRNA gene was used to assess bacterial diversity and community structure changes. Bioinformatic analysis of sequencing datasets resulted in 4691 and 2728 bacterial Amplicon Sequence Variants (ASVs) in soil and root biotopes, respectively. Our findings have shown that the cultivation of clary sage displayed a significant year-to-year effect, on both bacterial richness and community structures. We found that the abundance of plant-growth promoting rhizobacteria significantly increased in roots during the second growing season. However, we didn't observe any significant effect of mycorrhizal inoculation neither on bacterial diversity nor on community structure. Our study brings new evidence in TE-contaminated areas of the effect of a vegetation cover with clary sage cultivation on the microbial soil functioning.

Interactions of cadmium and zinc in high zinc tolerant native species Andropogon gayanus cultivated in hydroponics: growth endpoints, metal bioaccumulation, and ultrastructural analysis

Cadmium (Cd) and zinc (Zn) toxicity causes physiological disorders and harms plants, interfering with the rehabilitation of areas affected by mining activities. This study evaluated how the exposure to Zn and/or Cd affects the growth of native andropogon grass (Andropogon gayanus Kunth) plants originally found in areas contaminated with Cd and/or Zn due to zinc mining activities. Plants were cultivated for 7 weeks in a nutrient solution treated with Zn (142.3-854.0 μM) or Cd (0.9-13.3 μM) separately or combined with a molar ratio of 64:1 (Zn:Cd). A control treatment was grown in a complete Hoagland and Arnon solution (without Cd). Plant height, stem diameter, internode length, dry weight, Cd and Zn concentration, and accumulation in shoots/roots, as well as ultrastructure of roots and leaves were analyzed at the end of the experiment. The root dry weight was not significantly affected by the addition of the metals. Moreover, Zn provided higher shoot dry weight (up to 160%) relative to control. Andropogon grass tolerated both metals better separately than when applied together. Transmission electron microscopy analyses showed modifications such as vesiculation and vacuolation in the ultrastructure of andropogon tissues by Cd and/or Zn. The andropogon grass was tolerant to the doses tested, evidencing that it has potential for recovering areas contaminated with Zn and/or Cd.

Keep and promote biodiversity at polluted sites under phytomanagement

The phytomanagement concept combines a sustainable reduction of pollutant linkages at risk-assessed contaminated sites with the generation of both valuable biomass for the (bio)economy and ecosystem services. One of the potential benefits of phytomanagement is the possibility to increase biodiversity in polluted sites. However, the unique biodiversity present in some polluted sites can be severely impacted by the implementation of phytomanagement practices, even resulting in the local extinction of endemic ecotypes or species of great conservation value. Here, we highlight the importance of promoting measures to minimise the potential adverse impact of phytomanagement on biodiversity at polluted sites, as well as recommend practices to increase biodiversity at phytomanaged sites without compromising its effectiveness in terms of reduction of pollutant linkages and the generation of valuable biomass and ecosystem services.

Afforestation may influence changes in tailing heaps in a long time

A soil and plant survey was carried out in a tailing heap afforested 30 years ago to gain information about the changes in the tailing and metal uptake by plants. A poor development of Technosol was found. It was observed accumulation of OM spatio temporarily. Metal concentrations in the soil profile varied between plots. Extractable Pb concentrations ranged from 0.4 to 2.9%; extractable Cd varied 9.7-46% of the total concentration. PCA analysis shows DTPA-Zn and DTPA-Cu, Na, K, and OM have the widest concentrations range between soil layers. Casuarina equisetifolia and Pennisetum clandestinum formed a pristine uniform litter layer, whereas Eucalyptus camaldulensis did not form a litter layer. Casuarina equisetifolia has a higher population density (756 p ha^-1) compared to Populus nigra (528 p ha^-1) and E. camaldulensis (621 p ha^-1). Pennisetum clandestinum grew successfully and covered the tailing, but Cd and Pb concentrations were above the domestic animal toxicity limits, 0.5 and 10 mg kg^-1, respectively. Populus nigra absorbed more Zn than Casuarina equisetifolia and Eucalyptus camaldulensis. Trees species did not accumulate high foliar Cu and Zn concentrations, but Pb (47.7-124.3 mg kg^-1) and Cd (5.7-26.8 mg kg^-1) concentrations are over those reported for mature leaf tissues. HighlightsPennisetum clandestinum formed soil cover on remediated plots.Casuarina equisetifolia was efficient in forming a litter soil horizon.Trasdescantia fluminensis accumulated Pb.Populus nigra accumulated Zn and Cd from the tailing heap.

Gentle remediation options for soil with mixed chromium (VI) and lindane pollution: biostimulation, bioaugmentation, phytoremediation and vermiremediation

Gentle Remediation Options (GROs), such as biostimulation, bioaugmentation, phytoremediation and vermiremediation, are cost-effective and environmentally-friendly solutions for soils simultaneously polluted with organic and inorganic compounds. This study assessed the individual and combined effectiveness of GROs in recovering the health of a soil artificially polluted with hexavalent chromium [Cr(VI)] and lindane. A greenhouse experiment was performed using organically-amended vs. non-amended mixed polluted soils. All soils received the following treatments: (i) no treatment; (ii) bioaugmentation with an actinobacteria consortium; (iii) vermiremediation with Eisenia fetida; (iv) phytoremediation with Brassica napus; (v) bioaugmentation + vermiremediation; (vi) bioaugmentation + phytoremediation; and (vii) bioaugmentation + vermiremediation + phytoremediation. Soil health recovery was determined based on Cr(VI) and lindane concentrations, microbial properties and toxicity bioassays with plants and worms. Cr(VI) pollution caused high toxicity, but some GROs were able to partly recover soil health: (i) the organic amendment decreased Cr(VI) concentrations, alleviating toxicity; (ii) the actinobacteria consortium was effective at removing both Cr(VI) and lindane; (iii) B. napus and E. fetida had a positive effect on the removal of pollutants and improved microbial properties. The combination of the organic amendment, B. napus, E. fetida and the actinobacteria consortium was the most effective strategy.

Greening the Browns: A Bio-Based Land Use Framework for Analysing the Potential of Urban Brownfields in an Urban Circular Economy

The Circular Economy (CE) is expected to accelerate the use of resources with bio-based origin. Cities have an important role in such an economy, not only as main consumers but also because vegetation provides numerous ecosystem services essential for the well-being of urban dwellers. Urban lands are, however, heavily burdened with both past and present activities and ongoing urbanization. Retrofitting obsolete and potentially contaminated brownfields provides an opportunity to engage with bio-based land uses within the city. At the same time, plants are an important part of Gentle Remediation Options (GROs), a more sustainable alternative for managing contamination risks and restoring soil health. This paper (1) provides a tentative selection of Urban Greenspaces (UGSs) relevant for brownfields, and a compilation of ecosystem services provided by the selected UGSs, and (2) presents a framework covering the 14 selected bio-based land uses on brownfields, including GRO interventions over time. This framework provides three practical tools: the conceptualization of linkages between GROs and prospective UGS uses, a scatter diagram for the realization of 14 UGS opportunities on brownfields, and a decision matrix to analyze the requirements for UGS realization on brownfields.

Field evaluation of one Cu-resistant somaclonal variant and two clones of tobacco for copper phytoextraction at a wood preservation site

A Cu-resistant somaclonal tobacco variant (NBCu 10-8-F1, C1), its BaG mother clone (C3), and the FoP tobacco clone (C2) were cultivated at a wood preservation site on Cu-contaminated soils (239-1290 mg Cu kg-1 soil range) and an uncontaminated control site (CTRL, 21 mg Cu kg-1) to assess their shoot DW yields and potential use for bioavailable Cu stripping. The Cu concentration in the soil pore water varied between 0.15 and 0.84 mg L-1. Influences of Cu exposure and soil treatments, i.e., untreated soil (Unt), soils amended with compost and either dolomitic limestone (OMDL) or zerovalent iron grit (OMZ), on plant growth and shoot ionome were determined. All transplants survived and grew even at high total soil Cu. Shoots were harvested after 3 months (cut 1). Subsequently, bottom suckers developed and were harvested after 2 months (cut 2). Total shoot DW yield (cuts 1 + 2) varied between 0.8 and 9.9 t DW ha-1 year-1 depending on tobacco cultivars, soil treatments, and soil Cu exposure. It peaked for all cultivars in the OMDL plots at moderate Cu exposure (239-518 mg kg-1 soil), notably for the C2 plants. Cut 2 contributed for 11-43% to total shoot DW yield. Increase in shoot DW yield diluted shoot Cu concentration. At low Cu exposure, total shoot Cu removal peaked for the variant. At moderate Cu exposure, shoot Cu concentrations were similar in all cultivars, but total shoot Cu removal was highest for the C2 plants. At high Cu exposure (753-1140 mg kg-1), shoot Cu concentrations peaked for the C2 plants in the Unt plots, the C1 and C2 plants in the OMZ plot, and the C3 ones in the OMDL plots. Shoot Cu removal (in g Cu ha-1 year-1) ranged from 15.4 (C2 on the CTRL soil) to 261.3 (C2 on moderately contaminated OMDL soils). The C2 plants phytoextracted more Cu than the C1 and C3 ones in the Unt plots and in the OMDL plots at moderate Cu exposure. In the OMDL plots with high Cu exposure, shoot Cu removal was highest for the C1 plants. Soil amendments improved shoot Cu removal through increase in either shoot DW yield (OMDL-3-fold) or shoot Cu concentration (OMZ-1.3-fold). Increased shoot Cu concentration induced an ionome imbalance with increased shoot Al, Fe, B, and Mg concentrations and decreased P and K ones. Copper concentrations in plant parts varied in decreasing order: roots > leaves > inflorescence (cymes including seeds) > stem, whereas Cu removal ranked as roots > stem = leaves > inflorescence.

Spatio-Temporal Nonstationary Effects of Impact Factors on Industrial Land Price in Industrializing Cities of China

Industrialization has brought about great differences in industrial development and land use demand among different regions and cities, especially in rapidly industrializing countries with a vast territory. In those areas, implementing local-specific policies on industrial land price is of great significance to improve industrial land use efficiency and facilitate the sustainable development of regional economy. Based on the land pricing monition files of 105 industrializing cities, geographically weighted regression (GWR) was applied to detect the spatial variation of the industrial land price and its main impact factors (for example, tax, leased land, population, and location quotient index) in China in 2009, 2011 and 2014. The results show that the relationships were generally spatio-temporally nonstationary. More specifically, while the effect of tax on industrial land price was significantly positive and spatially stable all over China in 2009, the effect varied spatially in the two later studied years, weakened in North and East China and strengthened in South China. The effect of leased land on industrial land price was generally negative; it was very weak in 2009 and 2011 but became negatively strong in most studied cities in 2014, except for a few cities in Middle China. Population had a significant positive effect on industrial land price in the cities of East and Northeast China. For the three studied years, the location quotient index always had negative effect in Bohai Economic Rim and positive effect in Yangtze River Delta Economic Zone, and the negative effect strengthened with time. Meanwhile, the underlying reasons behind the relationships were further analyzed, showing that the spatio-temporal changes of industrial land price are closely correlated with the population mobility, industrial agglomeration, government intervention and economic situation.

Management of trace element-contaminated agricultural land by in situ stabilization combined with phytoexclusion over a three years crop rotation

This study assessed in situ stabilization combined with phytoexclusion in practical application on agricultural land contaminated strongly, and spatially heterogeneous, with metals (Cd, Pb, and Zn) and As. Single and combined lime marl and phosphate treatments were consecutively planted with two cultivars each of rape, wheat, and barley differing in trace elements (TE) accumulation. The effects on soil acidity, NH₄NO₃-soluble, and straw and grain TE concentrations were evaluated. The combined fertilizer treatment most effectively reduced metals mobility, but neither amendment mitigated plant TE status, which correlated more with pseudo-total than NH₄NO₃-soluble TE in soil. The cultivar choice reduced grain Cd by 39 or 21% in barley or wheat, respectively, simultaneously decreased grain Zn, but conversely affected As uptake in wheat grains. The lack of correlations between grain TE concentrations suggests the potential for breeding cultivars with low Cd and As accumulation without causing Zn malnutrition. The cereals had relatively low yields, particularly on highly polluted areas, and only rape and barley grains unexceptionally suited for animal consumption. Agricultural measures and climatic conditions influenced TE mobility. The cultivars' TE uptake varied less than in greenhouse studies, stressing the importance of field studies for an adequate estimation of phytoexclusion potentials.

Long-term phytomanagement with compost and a sunflower - Tobacco rotation influences the structural microbial diversity of a Cu-contaminated soil

At a former wood preservation site contaminated with Cu, various phytomanagement options have been assessed in the last decade through physicochemical, ecotoxicological and biological assays. In a field trial at this site, phytomanagement with a crop rotation based on tobacco and sunflower, combined with the incorporation of compost and dolomitic limestone, has proved to be efficient in Cu-associated risk mitigation, ecological soil functions recovery and net gain of economic and social benefits. To demonstrate the long-term effectiveness and sustainability of phytomanagement, we assessed here the influence of this remediation option on the diversity, composition and structure of microbial communities over time, through a metabarcoding approach. After 9 years of phytomanagement, no overall effect was identified on microbial diversity; the soil amendments, notably the repeated compost application, led to shifts in soil microbial populations. This phytomanagement option induced changes in the composition of soil microbial communities, promoting the growth of microbial groups belonging to Alphaproteobacteria, many being involved in N cycling. Populations of Nitrososphaeria, which are crucial in nitrification, as well as taxa from phyla Planctomycetacia, Chloroflexi and Gemmatimonadetes, which are tolerant to metal contamination and adapted to oligotrophic soil conditions, decreased in amended phytomanaged plots. Our study provides an insight into population dynamics within soil microbial communities under long-term phytomanagement, in line with the assessment of soil ecological functions and their recovery.

Poplar rotation coppice at a trace element-contaminated phytomanagement site: A 10-year study revealing biomass production, element export and impact on extractable elements

Growing lignocellulosic crops on marginal lands could compose a substantial proportion of future energy resources. The potential of poplar was explored, by devising a field trial of two hectares in 2007 in a metal-contaminated site to quantify the genotypic variation in the growth traits of 14 poplar genotypes grown in short-rotation coppice and to assess element transfer and export by individual genotypes. Our data led us to conclusions about the genotypic variations in poplar growth on a moderately contaminated site, with the Vesten genotype being the most productive. This genotype also accumulated the least amounts of trace elements, whereas the Trichobel genotype accumulated up to 170 mg Zn kg^-1 DW in the branches, with large variation being exhibited among the genotypes for trace element (TE) accumulation. Soil element depletion occurred for a range of TEs, whereas the soil content of major nutrients and the pH remained unchanged or slightly increased after 10 years of poplar growth. The higher TE content of bark tissues compared with the wood and the higher proportion of bark in branches compared with the wood led us to recommend that only stem wood be harvested, instead of the whole tree, which will enable a reduction in the risks encountered with TE-enriched biomass in the valorization process.

Urban soil phytomanagement for Zn and Cd in situ removal, greening, and Zn-rich biomass production taking care of snail exposure

The phytoextraction potential of Arabidopsis halleri (L.) O'Kane & Al Shehbaz and Salix viminalis L. to partially remove Zn and Cd in soil was investigated. In an urban field site, a very short rotation coppice of willows was implemented, and growth parameters were monitored for 3 years. A. halleri was cultivated in the same site with or without fertilizer to improve biomass yield and/or Zn and Cd aerial part concentrations. Effects of harvest and co-cultivation on these two parameters were measured. To determine if willows and A. halleri leaves were risky in case of consumption by a herbivorous invertebrate like the landsnail Cantareus aspersus, metal concentrations of snails fed with Zn- and Cd-enriched and low enriched leaves were compared. Willows and A. halleri grew well on the metal-contaminated soil (1.7 and 616 mg kg^-1 Cd and Zn, respectively). The A. halleri Zn foliar concentration reached the Zn hyperaccumulation threshold (> 10,000 mg kg^-1 DW) in the presence of NPK fertilizer and although the soil was alkaline (pH > 8.2). Cd concentration increased with harvest and fertilizer. Cd and Zn foliar concentrations of willows were far above baseline values. Laboratory snails exposure revealed that willow leaves ingestion caused a moderate increase of Cd, Pb, and Zn bioaccumulation in snails compared to the one caused by A. halleri ingestion. The soil and plant metal concentrations were reflected by field snail biomonitoring. This study confirmed the interest of selecting A. halleri and willows to partially remove Zn and Cd in the soil and emphasized their potential usefulness in greening urban contaminated area and producing raw materials for green chemistry while paying attention to the environmental pollutant transfer.

Potential use of biochar, compost and iron grit associated with Trifolium repens to stabilize Pb and As on a multi-contaminated technosol

Vegetation cover can be used in the phytomanagement of polluted areas by adding value to abandoned sites and reducing the dispersion of pollutants by erosion. Appropriate amendments, that allow both efficient plant growth and the immobilization of contaminants in the soil must be chosen in order to optimize the efficiency of this process. We used a mining technosol mainly contaminated by arsenic (1068 mg kg^-1) and lead (23387 mg kg^-1) to study the effect of three amendments (biochar, compost and iron grit) on (i) physico-chemical properties of the soil and soil pore water, (ii) metal(loid) mobility, bioavailability and bioaccessibility (CaCl₂ and Simple Bioaccessibility Extraction Test (SBET)), and (iii) the capability of Trifolium repens to germinate and grow. All the amendments used increased the pH and electrical conductivity of the SPW, resulting in a 90% decrease in the concentration of lead in the soil pore water (SPW). We also demonstrated a decrease in Pb phytoavailability. The amendments allowed the establishment of a plant cover, although the addition of iron grit alone did not allow any clover germination. For the Pontgibaud technosol, the combination of the three amendments resulted in a significant decrease in As and Pb concentrations in clover tissues, mainly in the aerial organs. The amendments also made it possible for some of them to halve the phytoavailable fraction of arsenic. However, for compost, both the As concentrations in the SPW, and the bioavailable fraction of As increased. All the amendments used had contrasting effects on the bioaccessible fractions of metal(loid)s. The most efficient amendment combination was the addition of 5% biochar and 5% compost.

Best management practices from agricultural economics: Mitigating air, soil and water pollution

Often the several stakeholders involved in the agricultural sector place a greater emphasis on the negative externalities from farming production rather than on the solutions and approaches to mitigate, namely impacts from pollution. The scientific literature, in certain circumstances, follows this tendency leaving a vast chasm of enormous potential left to be explored. It is important to contribute towards the reduction of this gap, highlighting the best management practices implemented across the agricultural sector around the world, specifically to make them more visible and give incentive to the several agents in adopting and spreading their use. In this way, the main objective is to stress the best management practices presented by the global scientific literature from the farming sector. To achieve this objective methodology based on bibliometric analysis-factor-analysis-literature survey approach was considered, applied to 150 documents obtained from the Web of Science (core collection) related with the following topics: best management practice; agricultural economics; air, soil and water pollution. As main insights, it is worth referring the best management practices to deal with problems from agricultural production, such as, for example, the use of agricultural residues as feedstock for renewable energies. With regard to sustainable development in the agricultural sector, concepts such as "sustainable remediation" have their place. On the other hand, the agricultural and environmental policies and the agricultural costs associated with the several farming practices also play a determinant role here. Finally, only fraction of the scientific documents analysed (16 papers) belong to the group of studies related to policies, showing that there are potential subjects to be addressed here in future studies related with these topics. The same happens for cost-benefit analyses (24 documents).

Variation in pickleweed root-associated microbial communities at different locations of a saline solid waste management unit contaminated with petroleum hydrocarbons

The main purpose of this study was to explore the potential influences of pickleweed vegetation on the abundance, diversity and metabolic activities of microbial communities in four distinct areas of a petroleum-contaminated solid waste management unit (SWMU) located in Contra Costa County, northern California. The four areas sampled include two central areas, one of which is central vegetated (CV) and one unvegetated (UV), and two peripheral vegetated areas, one of which is located to the west side of the SWMU (V-West) and one located to the east side (V-East). Measurements were made of total petroleum hydrocarbons (TPH), polyaromatic hydrocarbons (PAH), soil physicochemical properties, and various aspects of microbial communities including metabolic activities, microbial abundances (PLFAs), diversity and composition based on amplicon sequencing. The peripheral V-East and V-West sites had 10-times lower electrical conductivity (EC) than that of the CV and UV sites. The high salinity levels of the CV and UV sites were associated with significant reductions in bacterial and fungal abundances (PLFA) when compared to V-East but not when compared to V-West. TPH levels of CV and UV were not significantly different from those of V-West but were substantially lower than V-East TPH (19,311 mg/kg of dry soil), the high value of which may have been associated with a pipeline that ran through the area. Microbial activities (in terms of soil respiration and the activities of three soil enzymes, i.e., urease, lipase, and phosphatase) were greatest in the vegetated sites compared to the UV site. The prokaryotic community was not diverse as revealed by the Shannon index with no significant variation among the four groups of samples. However, the fungal community of the peripheral sites, V-East and V-West had significantly higher OTU richness and Shannon index. Structure of prokaryotic communities inhabiting the rhizosphere of pickleweed plants at the three sites differed significantly and were also different from those found in the UV region of the central site according to pairwise, global PERMANOVA and ANOSIM analyses. The differences in OTU-based rhizosphere-associated bacterial and fungal communities’ composition were explained mainly by the changes in soil EC and pH. The results suggest that saline TPH-contaminated areas that are vegetated with pickleweed are likely to have increased abundances, diversity and metabolic activities in the rhizosphere compared to unvegetated areas, even in the presence of high salinity.

Soil microbial response to metal contamination in a vegetated and urban brownfield

The ubiquity of urban brownfields presents not only a challenge for environmental managers but also an opportunity to study the functional aspects of degraded ecosystems that are in close contact with human habitation. In this study, we investigate the soil microbial community response to heavy metal contamination at Liberty State Park (LSP), an urban brownfield in Jersey City, NJ, USA. Heavy metal contamination of the soils at LSP is heterogeneous, varying widely across site and among metals. We collected soils along a previously mapped gradient of metal contamination at LSP and sampled soil from a local and uncontaminated reference site (Hutcheson Memorial Forest (HMF)) for comparison. For all soils, we measured soil heavy metal concentrations, soil organic carbon content, bacterial density, and extracellular phosphatase activity as a proxy of ecosystem functioning. Additionally, we analyzed the microbial community composition using high-throughput sequencing. Data show that some sites within LSP have significantly higher phosphatase activity compared to HMF, indicating that some heavily contaminated LSP soils are highly functional. We also found that soil organic carbon and bacterial density have a significant and positive relationship with phosphatase activity. The microbial community analyses showed that the bacterial communities were sensitive to heavy metals and that the composition was significantly affected in particular by copper, zinc, and lead. The fungal communities, however, did not vary significantly with heavy metals. Our results shed important light on the composition and functioning of urban brownfield soils. A deeper understanding of these unique ecosystems is required for successful remediation, restoration and urban sustainability.