Phytoremediation is a plant-driven process, widely regarded as a cost-effective and environmentally friendly in situ approach for remediating contaminated soil and water by taking up contaminants including potentially toxic elements (PTEs). In the last two decades, substantial research has focused on elucidating the mechanisms of phytoremediation and enhancing its efficiency, primarily through the identification of optimal plant species and the use of various amendments. Nevertheless, real-scale application of phytoremediation remains rare, and several critical questions need to be addressed, including selection of most effective species, improved effectiveness of phytoremediation process, and managing the safe utilisation of contaminated biomass. This review specifically focuses on phytoremediation of potentially toxic metals and metalloids in major metallophyte groups (wild herbaceous species, trees, and agricultural crops) recognizing the most efficient species for the anthropogenically influenced soils in Europe. It summarises the current state of knowledge regarding the use of respective plant species, highlighting the phytoremediation efficiency, critically examining existing and novel phytoremediation enhancement strategies and biomass utilisation pathways for each particular group. Future perspectives and research needed to refine the efficiency and economic viability of the phytoremediation process in Europe lay in better recognition of underlying physiological mechanism for metal stress tolerance, particularly among the most effective species and genera, application of synergistic enhancing techniques for delineated group of metallophytes and development of sustainable and cost-effective biomass utilisation routes.

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.

The cultivation of aromatic plants for the extraction of essential oils has been presented as an innovative and economically viable alternative for the remediation of areas polluted with trace elements (TE). Therefore, this study focuses on the contribution of the cultivation of coriander and the use of arbuscular mycorrhizal fungi (AMF) in combination with mineral amendments (steel slag) on the bacterial function of the rhizosphere, an aspect that is currently poorly understood and studied. The introduction of soil amendments, such as steel slag or mycorrhizal inoculum, had no significant effect on coriander growth. However, steel slag changed the structure of the bacterial community in the rhizosphere without affecting microbial function. In fact, Actinobacteria were significantly less abundant under slag-amended conditions, while the relative proportion of Gemmatimonadota increased. On the other hand, the planting of coriander affects the bacterial community structure and significantly increased the bacterial functional richness of the amended soil. Overall, these results show that planting coriander most affected the structure and functioning of bacterial communities in the TE-polluted soils and reversed the effects of mineral amendments on rhizosphere bacterial communities and their activities. This study highlights the potential of coriander, especially in combination with steel slag, for phytomanagement of TE-polluted soils, by improving soil quality and health.

AimsAfforestation of trace-element contaminated soils, notably with fast growing trees, has been demonstrated to be an attractive option for bioremediation due to the lower costs and dispersion of contaminants than conventional cleanup methods. Mycorrhizal fungi form symbiotic associations with plants, contributing to their tolerance towards toxic elements and actively participating to the biorestoration processes. The aim of this study was to deepen our understanding on the effects of mycorrhizal inoculation on plant development and fungal community at two trace-element contaminated sites (Pierrelaye and Fresnes-sur-Escaut, France) planted with poplar (Populus trichocarpa x Populus maximowiczii).MethodsThe 2 sites were divided into 4 replicated field blocks with a final plant density of 2200 tree h-1. Half of the trees were inoculated with a commercial inoculum made of a mix of mycorrhizal species. The sites presented different physico-chemical characteristics (e.g., texture: sandy soil versus silty-loam soil and organic matter: 5.7% versus 3.4% for Pierrelaye and Fresnes-sur-Escaut, respectively) and various trace element contamination levels.ResultsAfter 7 years of plantation, inoculation showed a significant positive effect on poplar biomass production at the two sites. Fungal composition study demonstrated a predominance of the phylum Ascomycota at both sites, with a dominance of Geopora Arenicola and Mortierella elongata, and a higher proportion of ectomycorrhizal and endophytic fungi (with the highest values observed in Fresnes-sur-Escaut: 45% and 28% for ECM and endophytic fungi, respectively), well known for their capacity to have positive effects on plant development in stressful conditions. Furthermore, Pierrelaye site showed higher frequency (%) of mycorrhizal tips for ectomycorrhizal fungi (ECM) and higher intensity (%) of mycorrhizal root cortex colonization for arbuscular mycorrhizal fungi (AMF) than Fresnes-sur-Escaut site, which translates in a higher level of diversity.ConclusionsFinally, this study demonstrated that this biofertilization approach could be recommended as an appropriate phytomanagement strategy, due to its capacity to significantly improve poplar productivity without any perturbations in soil mycobiomes.

A green and effective approach for the synthesis of structurally diversed α-hydroxyphosphonates via hydrophosphonylation of aldehydes under solventless conditions and promoted by biosourced catalysts, called ecocatalysts “Eco-MgZnOx” is presented. Ecocatalysts were prepared from Zn-hyperaccumulating plant species Arabidopsis halleri, with simple and benign thermal treatment of leaves rich in Zn, and without any further chemical treatment. The elemental composition and structure of Eco-MgZnOx were characterized by MP–AES, XRPD, HRTEM, and STEM–EDX techniques. These analyses revealed a natural richness in two unusual and valuable mixed zinc–magnesium and iron–magnesium oxides. The ecocatalysts were employed in this study to demonstrate their potential use in hydrophosphonylation of aldehydes, leading to various α-hydroxyphosphonate derivatives, which are critical building blocks in the modern chemical industry. Computational chemistry was performed to help discriminate the role of some of the constituents of the mixed oxide ecocatalysts. High conversions, broad substrate scope, mild reaction conditions, and easy purification of the final products together with simplicity of the preparation of the ecocatalysts are the major advantages of the presented protocol. Additionally, Eco-MgZnOx-P could be recovered and reused for up to five times.

Moderately contaminated garden soils can benefit from gentle remediation options such as soil amendments, which improve soil functions and agronomic potentialities while decreasing environmental and human risk. This study aimed to analyze the effects of doses of various common soil amendments generally applied by gardeners on the predicted bioavailability (i.e., extractability) of metal(loid)s (i.e., As, Cd, Pb, and Zn) in contaminated kitchen garden soils. Fourteen different amendment mixes (i.e., a green waste compost with two degrees of maturity used alone and in combination with zeolite, three organic fertilizers, two calcareous amendments, two natural siliceous or alumino-silicate amendments, and one potting soil) were tested on three different garden soils with diverse sources of contamination and physico-chemical characteristics. Chemically extractable metal(loid)s were analyzed using 0.05 M EDTA extraction and 1 M NH4NO3 extraction. In one soil sample, potting soil showed significant potential to reduce the availability of As, as analyzed by both extractants. This amendment also effectively reduced the Pb extractability in the geogenic-contaminated soil, as did other high-organic matter amendments such as various application rates of composts. Zeolite and zeolite-compost mixes demonstrated success on various metal(loid)s and therefore could be a promising emerging amendment mix. Other efficient amendments include crushed horn, which effectively reduced available Zn in all soils, as well as available Pb. The application of bone meal similarly reduced the extractable As, Pb, and Zn in various soils. The two applications of limes were effective against Cd, As, Pb, and Zn in the different soils studied. This study provided evidence that it is possible to reduce the extractability and thus the environmental availability of the metal(loid)s applied with available and affordable amendments. The results depended on the physico-chemical soil parameters and metal(loid)s considered. There is no single solution, which implies that tests must be carried out before any implementation activities on the kitchen gardens.

The current work aims to investigate the influence of fertilization (fertilizer) and fungal inoculation (Funneliformis mosseae and Serendipita indica (formerly Piriformospora indica), respectively arbuscular mycorrhizal (AMF) and endophytic fungi) on the phytoextraction potential of Arabidopsis halleri (L.) O'Kane & Al-Shehbaz (biomass yield and/or aboveground part Zn and Cd concentrations) over one life plant cycle. The mycorrhizal rates of A. halleri were measured in situ while the fungal inoculation experiments were carried out under controlled conditions. For the first time, it is demonstrated that the fertilizer used on A. halleri increased its biomass not only at the rosette stage but also at the flowering and fruiting stages. Fertilizer reduced the Zn concentration variability between developmental stages and increased the Cd concentration at fruiting stage. A. halleri roots did not show AMF colonization at any stage in our field conditions, neither in the absence nor in the presence of fertilizer, thus suggesting that A. halleri is not naturally mycorrhizal. Induced mycorrhization agreed with this result. However, S. indica has been shown to successfully colonize A. halleri roots under controlled conditions. This study confirms the benefit of using fertilizer to increase the phytoextraction potential of A. halleri. Overall, these results contribute to the future applicability of A. halleri in a phytomanagement strategy by giving information on its cultural itinerary.

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.

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.

The study of different possible biomass valorization routes is crucial in order to diversify phytomanagement options, allowing the landowner/stakeholder to choose the best option based on site characteristics and the benefits of local value chains. In the current study, field and laboratory experiments were conducted to assess the suitabilitity of Malva sylvestris L. for the phytoattenuation of a dredged sediment disposal site contaminated with trace elements (trace element (Cd, Cu, Pb, and Zn). The selected crop was Malva sylvestris, a flowering plant from which a colourant can be extracted to be used in dying of textiles as a way to valorize the produced biomass grown on this contaminated land. Under the conditions of the investigated site, the analysis of TE in the sediment and the biomass matrix showed no effect of M. sylvestris on the sediment TE contamination mobility with an excluder phenotype (Bioconcentration factor < 1). Metal concentrations were found to be the highest in the leaves followed by in the stem and flower. The dye extract obtained from the flower part of M. sylvestris permitted the silk alum-pretreated fabric to be dyed yellow, and the TE concentration in the dyed textile fabrics respected the threshold values set by OEKO-Tex standard 100.

Phytoattenuation combines phytoextraction or phytostabilization with the economic valorization of the biomass produced on the contaminated soil. Sorghum bicolor is a suitable crop for this strategy, as it is known to be metal-tolerant and can be used for biogas or bioethanol production or in strategies toward biofortification. In the current investigation, two cultivars, Biomass 133 and Trudan Headless (HL), were studied in a metal-contaminated (Cd, Pb, Zn) field site located in northern France to assess their potential use in a phytoattenuation strategy. The biomass yield and the metal transfer in the produced biomass were monitored in three plots with different pollution levels. Both cultivars were tolerant to high levels of metal pollution in field conditions, with yields similar to that obtained on uncontaminated sites. Neither of the cultivars changed the metal mobility of the soil and both exhibited a metal-excluder behavior. Nevertheless, Cd concentration in the aboveground part of Trudan HL, and of Biomass 133 to a lesser extent, could restrict their use in some valorization options. However, biogas production was possible with the produced biomass, indicating anaerobic digestion to be a possible valorization route for sorghum grown on contaminated sites.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Increasing the applicability of gentle soil remediation methods : lessons from the Greenland project Markus Puschenreiter, Michel Mench, Valérie Bert, Jurate Kumpiene, Petra Kidd, Andrew Cundy

Cette etude vise a optimiser les pratiques culturales de l’arabette de Haller et des saules, afin d’augmenter le potentiel de phytoextraction du Zn et du Cd chez ces deux especes (accumulation et/ou biomasse). Differentes pratiques agronomiques sont testees pour augmenter ces parametres : l’application de fertilisant NPK, la co-culture, la fauche et l’ajout d’un amendement biologique a base de champignons mycorhiziens. Le fonctionnement biologique du sol a ete evalue par le suivi d’indicateurs microbiens (biomasse bacterienne et fongique et activites enzymatiques microbiennes) en fonction de la contamination et des modalites de culture (sol contamine non vegetalise, vegetalise par les saules seuls, l’arabette seule, ou la co-culture). L’etude a ete menee sur le site du projet PHYTOAGGLO (Montataire, Oise, France). 800 m² de terres polluees ont ete excavees et homogeneisees et reparties sur l’ensemble de la parcelle. Un taillis a tres courte rotation de 350 saules (Salix viminalis) a ete mis en place en 2013 et les premieres parcelles d’arabette de Haller ont ete mises en place en 2015. Le suivi de 100 saules (diametre, hauteur, biomasse, taux de survie, concentrations du Zn et Cd foliaires) et Le suivi des arabettes de Haller a differents stades de developpement (concentrations en Zn et Cd foliaires, biomasse) ont ete realises en 2018. La biomasse des saules produite sur le site contamine (58T/ha) est comparable a celle de sites non contamines, et les concentrations en Zn (576 mg. Kg-1) et Cd (2,14 mg. Kg-1) foliaire sont superieures aux valeurs physiologiques (Zn 70 mg. Kg-1 et Cd 2 mg. Kg-1). La biomasse des arabettes (4,7T/ha) est significativement superieure a celle mentionnee dans la litterature (Mcgrath et al., 2006 ; Wielhammer et al., 2007). Les concentrations en Zn (5259 mg. Kg-1) et en Cd (5.04 mg. Kg-1) sont superieures aux concentrations physiologiques chez les plantes. Pour augmenter la production de biomasse chez le saule, l’ajout d’un inoculum mycorhizien commercial (Ectovit® et Symbivit®) a ete teste sur des racines de bouture de saule en laboratoire. Apres 8 semaines de culture, les racines de saule sont collectees, colorees au bleu Trypan (McGonigle et al., 1990) et observees au microscope. Afin de verifier l’etat de mycorhization spontanee de l’arabette de Haller, des racines d’arabette ont ete collectees sur le site experimental a differents stades de developpement (rosette, floraison, fructification). Parallelement a cela, une experimentation de mycorhization induite de l’arabette en presence d’une plante nurse (Trifolium repens) et d’un inoculum mycorhizien commercial (Symbivit®) est mise en place. Aucune mycorhization spontanee n’a ete observee dans les racines d’arabette de Haller quel que soit le stade de developpement (rosette, floraison, fructification) sur le site contamine en presence de NPK. Aucune mycorhization dans les racines des saules et des arabettes en presence d’un inoculum commercial en laboratoire n’a ete observe. Afin d’evaluer le fonctionnement biologique du sol, des quantifications de biomasse fongique et bacterienne (via le dosage des marqueurs lipidiques specifiques : acides gras associes aux phospholipides (AGPL)) ainsi que des dosages d’activites enzymatiques microbiennes ont ete realisees en fonction des differentes modalites de culture mises en place sur le site (sols sous les arabettes, sous la saulaie, sous la coculture et sans vegetation). L’analyse des AGPL nous montre la presence d’une quantite de biomasse bacterienne et fongique identique quelles que soient la modalite de culture. En 2019, le suivi des concentrations foliaires en Cd et Zn et le developpement du saule et de l’arabette sera poursuivi. L’effet du fertilisant NPK sur la biomasse de l’arabette, et le nombre de fauches possibles par annee sera mesure. La quantification des biomasses microbiennes et les activites enzymatiques du sol vont etre re-mesurees en octobre 2019 afin de suivre les fonctionnalites du sol en fonction du temps.