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A number of studies have focused on the effects of rare earth elements (REEs) on crop plants, while little attention has been paid on how tolerant plant species respond to increasing mixed REE concentrations. In this study, ramie (Boehmeria nivea L.) was exposed to a series of REE concentrations prepared with equimolar mixtures of 16 REEs (i.e. 0, 1.6, 8, 16, 80, 160, 400, 800 μmol/L) in order to explore REE accumulation and fractionation characteristics in ramie and the responses of this plant to mixed REEs. Results show that ramie root and shoot biomasses are unaffected under lower REE concentrations (1.6–80 μmol/L), while the growth of ramie and the uptake of nutrients especially Ca and Mn are largely inhibited under higher REE concentrations (160–800 μmol/L). The P and Mo concentrations in the roots increase with the increasing REE concentrations in the solution, suggestive of an involvement of P and Mo in dealing with the high concentrations of REEs in this plant. The preferential uptake of Ce and heavy REEs (HREEs) and the preferential transport of HREEs within the plant lead to a positive Ce anomaly and a HREE enrichment in ramie leaves. Our study suggests that ramie could be a good candidate for the phytoremediation of heavily REE-contaminated soils (e.g., REE mine tailings in southern China). Our results also shed light on points of taking into account phytoremediation management strategies of REE-contaminated soils (e.g., P and Mo fertilization).

Hyperaccumulator plants are able to tolerate extremely high concentrations of metals/metalloids in the soil in which they grow and to accumulate high concentrations in their shoots. To date, a total of 31 hyperaccumulator plant species have been identified in the Balkans, the centre of diversity and speciation in the European flora which is particularly rich in ultramafic areas. A further 8 species have yet to be confirmed through additional studies. Most of the 31 hyperaccumulator taxa (13 taxa or 41.9%) are species of the genus Odontarrhena, all hyperaccumulating Ni, but concentrations of this element above the hyperaccumulation threshold were also found in the genera Bornmuellera and Noccaea (all Brassicaceae), Orobanche (Orobanchaceae), Centaurea (Asteraceae) and Viola (Violaceae). The existence of hyperaccumulators of Tl and Zn is of particular interest because very few species worldwide hyperaccumulate these elements. Multiple metal hyperaccumulation was found in Noccaea kovatsii, as the hyperaccumulation of Zn was found in this species in addition to Ni, the primary accumulated element. Metal hyperaccumulation is discussed in terms of phylogenetic relationships and species distributions, with special attention to their systematics, the detection and recognition of new hyperaccumulating species and the possibilities for their future practical applications in phytotechnologies.

Rare earth elements (REEs) are critical for numerous modern technologies, and demand is increasing globally; however,production steps are resource-intensive and environmentally damaging.Some plant species are able to hyper accumulate REEs, and understanding the biology behind this phenomenon could play a pivotal role in developing more environmentally friendly REE recovery technologies. Here, we identified a REE transporter NRAMP REE Transporter 1 (NREET1)from the REE hyper accumulator fern Dicranopteris linearis. AlthoughNREET1 belongs to the natural resistance-associated macrophage protein(NRAMP) family, it shares a low similarity with other NRAMP members.When expressed in yeast, NREET1 exhibited REE transport capacity, but itcould not transport divalent metals, such as zinc, nickel, manganese, or iron.NREET1 is mainly expressed in D. linearis roots and predominantly localized in the plasma membrane. Expression studies in Arabidopsis thaliana revealed that NREET1 functions as a transporter mediating REE uptake and transfer from root cell walls into the cytoplasm. Moreover, NREET1 has a higher affinity for transporting light REEs compared to heavy REEs, which is consistent to the preferential enrichment of light REEs in field-grown D. linearis. We therefore conclude that NREET1 may play an important role in the uptake and consequently hyper accumulation of REEs in D.linearis. These findings lay the foundation for the use of synthetic biology techniques to design and produce sustainable, plant-based REE recovery systems.

International audience; Ramie plants (Boehmeria nivea) have been cultivated on ion-adsorption rare earth elements (REEs) mine tailings and showed a low ability to accumulate REEs, especially in the stems (REE= 24±17 mg kg-1) with higher concentration in leaves and roots (REE= 57 to 66 mg kg-1). Ramie individual fibers were isolated using three degumming processes: a traditional alkali treatment (AT), a steam explosion (SE) treatment after a neutral (SEN) or after a basic (SEB) impregnation. Cellulose-rich (> 80%) fine fibers with very low amounts of non-cellulosic sugars (

The increasing demand for Rare Earth Elements (REEs) and the depletion of mineral resources motivate sustainable strategies for REE recovery from alternative unconventional sources, such as REE hyperaccumulator. The greatest impediment to REE agromining is the difficulty in the separation of REEs and other elements from the harvested biomass (bio-ore). Here, we develop a sulfuric acid assisted ethanol fractionation method for processing D. linearis bio-ore to produce the pure REE compounds and value-added chemicals. The results show that 94.5% of REEs and 87.4% of Ca remained in the solid phase, and most of the impurities (Al, Fe, Mg, and Mn) transferred to the liquid phase. Density functional theory calculations show that the water-cation bonds of REEs and Ca cations were broken more easily than the bonds of the cations of key impurities, causing lower solubility of REEs and Ca compounds. Subsequent separation and purification led to a REE-oxide (REO) product with a purity of 97.1% and a final recovery of 88.9%. In addition, lignin and phenols were obtained during organosolv fractionation coupled with a fast pyrolysis process. This new approach opens up the possibility for simultaneous selective recovery of REEs and to produce value-added chemicals from REE bio-ore refining.

Aims: Dicranopteris linearis is a rare earth element (REE), aluminium (Al) and silicon (Si) hyperaccumulator plant which occurs in southern China. To date, there have been no studies on the variation in elemental accumulation among populations of Dicranopteris linearis occurring on REE-enriched and non-REE enriched soils. Methods: In total 43 Dicranopteris linearis individuals and the corresponding rhizosphere soils from 7 populations in southern China were sampled and the plant material and soil composition were chemically analysed for REE and other elements. Results: Dicranopteris linearis populations from REE-enriched soils and non-REE enriched soils both have the ability to accumulate high concentrations of REE (> 1000 mg kg− 1), Al (> 1000 mg kg− 1) and Si (> 10 000 mg kg− 1). The ratios of light REEs (LREEs) to heavy REEs (HREEs) in Dicranopteris linearis pinnae are consistently > 1, regardless of their ratios in the corresponding soils. Concentrations of REE in Dicranopteris linearis pinnae vary significantly among populations and have positive correlations with total and extractable soil REE concentrations. The plant Al and Si concentrations in Dicranopteris linearis populations are uncoupled from variations in soil Al and Si concentrations. The plant REE concentrations have no obvious relationships with the prevailing Al concentrations, but are positively correlated with plant Si and Mn, and negatively correlated with soil extractable P concentrations. Conclusions: The hyperaccumulation of REEs (LREE > HREE), Al and Si in non-REE enriched soils is a species-wide trait. The accumulation of REEs is highly variable and associated with soil REE concentrations, nutrients status, and other soil properties.

Background The fern Dicranopteris linearis is a hyperaccumulator of rare earth elements (REEs), aluminium (Al) and silicon (Si). However, the physiological mechanisms of tissue-level tolerance of high concentrations of REE and Al, and possible interactions with Si, are currently incompletely known. Methods A particle-induced X-ray emission (μPIXE) microprobe with the Maia detector, scanning electron microscopy with energy-dispersive spectroscopy and chemical speciation modelling were used to decipher the localization and biochemistry of REEs, Al and Si in D. linearis during uptake, translocation and sequestration processes. Results In the roots >80 % of REEs and Al were in apoplastic fractions, among which the REEs were most significantly co-localized with Si and phosphorus (P) in the epidermis. In the xylem sap, REEs were nearly 100 % present as REEH3SiO42+, without significant differences between the REEs, while 24–45 % of Al was present as Al-citrate and only 1.7–16 % Al was present as AlH3SiO42+. In the pinnules, REEs were mainly concentrated in necrotic lesions and in the epidermis, and REEs and Al were possibly co-deposited within phytoliths (SiO2). Different REEs had similar spatial localizations in the epidermis and exodermis of roots, the necrosis, veins and epidermis of pinnae of D. linearis. Conclusions We posit that Si plays a critical role in REE and Al tolerance within the root apoplast, transport within the vascular bundle and sequestration within the blade of D. linearis.

International audience; AbstractPurposeUrban soil contamination by heavy metals is one of the foremost challenges for urban soil quality, especially in the urban agriculture context. Urban gardening is a common practice in many industrialized and developing countries. How sources of soil contamination relate to inputs and influence the heavy metal content in soils, however, is not established yet.Materials and methodsThis study aims to assess the potential of pesticide applications (such as Bordeaux mixture) on soil quality. A set of 104 allotment gardens was selected in three cities in France, and topsoil was sampled and analyzed.Results and discussionThe four most abundant metals in urban vegetable garden topsoils were Zn, Pb, Cu, and Cr. The past and/or present industrial and urban activities are not the only cause of the metal contamination in urban vegetable garden soils. Gardens, where pesticides such as the Bordeaux mixture are being used showed significantly higher total Cu values in soils (78 mg kg−1 compared with 49 mg kg−1 for untreated gardens).ConclusionsEven though the risk of metal contamination through vegetable consumption is usually considered low, we clearly identified indicators of anthropogenic Cd, Cu, Pb, and Zn pollution due to pesticides inputs. This link was particularly strong between the use of Bordeaux mixture and increases Cu levels.

The exploitation of ion-adsorption rare earth element (REE) deposits has resulted in large quantities of abandoned mine tailings, which pose significant risks to the surrounding environment. However, the natural evolutional patterns at early successional stages and related biogeochemical dynamics (e.g. nutrient and REE cycling) on such mine tailings remains poorly understood. To this end, a chronosequence of REE mine tailings abandoned for up to 15 years was investigated in a post-mining site in south China. Our results showed that biocrusts were the earliest colonizers on these tailings, reaching a peak of 10% of surface coverage after 10 years of abandonment. Later on, after 15 years, the biocrusts began to be replaced by pioneer plants (e.g. Miscanthus sinensis), suggesting a rather rapid succession. This ecological succession was accompanied by obvious changes in soil nutrients and microbial community structure. Compared to bulk soils, both the biocrusts and rhizospheric soils favored an accumulation of nutrients (e.g. P, S, N, C). Notably, the autotrophic bacteria (e.g. Chloroflexi and Cyanobacteria) with C and N fixation abilities were preferentially enriched in biocrusts, while heterotrophic plant growth promoting bacteria (e.g. Pseudoocardiaceae and Acidobacteriales) were mainly present in the rhizosphere. Moreover, the biocrusts showed a remarkably high concentration of REEs (up to 1820 mg kg

The exploitation of ion-adsorption rare earth element (REE) deposits in South China has left large areas of mine tailings. However, limited remediation practices on these tailings have been reported, and how the remediation strategies and economic plants cultivation affect the biogeochemical cycles of nutrients, REEs and Al remains unclear. The aim of the present study was to investigate the effects of the combination of the addition of soil amendment and the root development and activity of a fiber plant ramie (Boehmeria nivea L.) on the availability and distribution of nutrients, as well as of REEs and other potentially toxic elements (e.g. Al) in the soil-plant system. The results showed that the application of organic amendment and ramie planting induced a significant increase in soil pH, total carbon (C), nitrogen (N), and other nutrient (e.g. P and Ca) concentrations, while led to a decrease of 80-90% and 60-90% in soil extractable REE and Al concentrations respectively. Matrices of correlation showed that soil pH, total C, N, and P concentrations were among the most important factors controlling the availability of soil REEs and Al, and root characteristics (e.g. fine root length). The total C, N, P and extractable nutrient concentrations, and electrical conductivity were higher in the rhizosphere soils of ramie than those in the bulk soils. Moreover, more than 60% of the quantity of REE and Al in the whole ramie plant was stored within the thick roots. These results showed that, in addition to amendment, the effects induced by the roots of ramie could further improve soil properties through C input, nutrient mobilization and toxic element stabilization. Our study concludes that ramie planting with organic amendment is a promising phytostabilization strategy for the remediation of REE mine tailings in South China.

International audience; The efficiency of zero-valent iron (Fe-0)for the degradation of contaminants in water or soil can be highly reduced by side reactions with oxygen or water. This work was conducted to test whether this drawback can be effectively suppressed by the carbonation of Fe-0 with pyrolyzed biomass, which forms a Fe3C composite. The composite Fe3C was characterized and its reactivity and stability were assessed in batch tests with methyl orange (MO) as a model pollutant. The results indicated that the removal rate of MO on Fe3C composite was higher than that of Fe-0 (7.587 mg/(g.min) vs. 4.306 mg/(g.min)) at pH 4, where the degradation mechanism was confirmed by high-performance liquid chromatography-mass spectrometry. More importantly, the produced iron oxide in the Fe3C composite was highly suppressed. Regeneration studies showed that after three times of cycling, the removal efficiency of MO on Fe3C composite was kept to 99.42%, but Fe-0 almost lost its reactivity. In situ chemical reduction of a colorimetric redox probe (indigo-5, 5'-disulfonate, I2S) quantitatively demonstrated that Fe3C composite has the reduction kinetics of I2S obviously slower than Fe-0, indicating that Fe3C composite improved the stability of incorporated Fe-0 to resist the side oxidation.

Ultramafic (i.e. serpentine) soils are widespread in the Balkans and particularly in Albania. They account for a large part of plant endemism in that region and host several hyperaccumulator species, which are characterized by leaf nickel concentrations frequently above 1%. This rich nickel hyperaccumulating flora could serve as candidate to be used in phytoextraction and agromining. Despite recent interest in metal hyperaccumulating plants and agromining, very few studies have investigated the bacterial diversity and the influence of environmental factors on microbial gene profiles in the rhizosphere of hyperaccumulator plants growing on ultramafic soils. Because rhizospheric bacteria could be crucial to the success of phytoremediation, we studied a total of 48 nickel-hyperaccumulating plants which were sampled from four species that are widespread in Albania: Noccaea ochroleuca, Odontarrhena smolikana, O. rigida and O. chalcidica. All samples were taken from the ultramafic regions of Librazhd and Pogradec in eastern Albania in October 2015. Our study shows that Proteobacteria, Actinobacteria and Acidobacteria dominated the soil bacterial communities. Of these three phyla, only Proteobacteria was relatively abundant. This study underlines the influence of soil Cation Exchange Capacity on the bacterial community's diversity and structure. Based on the predicted metagenomes, the genes belonging to amino acid, lipid and carbohydrate metabolisms were identified as major gene families. Our study sheds some light on our understanding of how bacterial communities are structured within and affect the rhizosphere of hyperaccumulator plants from ultramafic soils in Albania.

In this study, N-functionalized biochars with varied structural characteristics were designed by loading poplar leaf with different amounts of urea at 1:1 and 1:3 ratios through pyrolysis method. The addition of urea significantly increased the N content of biochar and facilitated the formation of amine (-NH-, -NH2), imine (-HC NH), benzimidazole (-C7H5N2), imidazole (-C3H3N2), and pyrimidine (-C4H3N2) groups due to substitution reaction and Maillard reaction. The effect of pH on Cr(VI) removal suggested that decrease in solution pH favored the formation of electrostatic attraction between the protonated functional groups and HCrO4−. And, experimental and density functional theory study were used to probe adsorption behaviors and adsorption mechanism which N-functionalized biochars interacted with Cr(VI). The protonation energy calculations indicated that N atoms in newly formed N-containing groups were better proton acceptors. Adsorption kinetics and isotherm experiments exhibited that N-functionalized biochars had greater removal rate and removal capacity for Cr(VI). The removal rate of Cr(VI) on N-functionalized biochar was 10.5–15.5 times that of untreated biochar. Meanwhile, N-functionalized biochar of NB3 with the largest number of adsorption sites for -C7H5N2, -NH2, -OH, -C3H3N2, and phthalic acid (-C8H5O4) exhibited the supreme adsorption capacity for Cr(VI) through H bonds and the highest adsorption energy was −5.01 kcal/mol. These mechanistic findings on the protonation and adsorption capacity are useful for better understanding the functions of N-functionalized biochars, thereby providing a guide for their use in various environmental applications.

Hyperaccumulators have exceptional phloem translocation capability for heavy metals. This study aims at quantifying the mobility and accumulation of Ni and Co via the phloem in the model hyperaccumulator Noccaea caerulescens. “Phloem loading capability (PLC),” which is calculated by the “Metal content in phloem sap/Metal content in leaves,” was introduced to evaluate the metal phloem mobility, while “Phloem mobility value (PMV)” was used for the normalization of PLC, which sets the PLC of Sr as PMV 0 and that of Rb as 100. The results showed that the PMVs of Ni and Co were 63 and 47, respectively. And the phloem mobility of Rb, Ni, Co, and Sr could be graded as highly mobile, mobile, intermediate, and immobile accordingly. The phloem stream can supply up to 19.1% and 16.0% of the total Ni and Co accumulated in the young leaves, respectively, while for Rb and Sr, the phloem contributes to 29% and 1.4% of the total Rb or Sr, indicating phloem contribution of certain metal is directly linked with its mobility. The results of this study raise the importance of phloem translocation on metal accumulation in shoots and provide insights on the metal cycling process in hyperaccumulators.

Biocrust-mediated in situ bioremediation could be an alternative strategy to mitigate metal(loid) pollution in aquatic habitats. To better understand the roles of biocrusts in regulating the fate of metal(loid)s, we examined the morphology, composition and structure of biological aqua crusts (BAC) developed in the mine drainage of a representative Pb/Zn tailing pond, and tested their effectiveness for immobilizing typical metal(loid)s. Unlike terrestrial biocrusts, BAC results from an assembly of compounds produced by the strong microbial activity and mineral compounds present in the aquatic environment. The BAC exhibited a unique flexible, spongy and porous structure with a specific surface area of 12-22 m2 g-1, and was able to effectively concentrate various metal(loid)s (e.g. Cd, 0.26-0.60 g kg-1; Pb, 0.52-0.66 g kg-1; As, 10.4-24.3 g kg-1). The concentrations of metal(loid)s (e.g. Cd and As) in the BAC were even three to seven times higher than those in the source tailings, and more than 98% of immobilized metal(loid)s were present as the highly stable non-EDTA-exchangeable fraction. Adsorption on the well distributed micro-particles of the clay minerals (e.g. kaolinite) and the organic matters (2.0-2.7 wt.%) were found to be the major mechanisms for BAC to bind metal cations, whereas adsorption and coprecipitation on Fe/Mn oxide (e.g. FeOOH), was proposed to be the dominant pathway for accumulating metal(loid)s, especially As. The decrease in aqueous concentrations of the metal(loid)s along the drainage could be attributed in part to the scavenging effects of the BAC. These findings therefore provide new insights into the possible and efficient strategy for metal(loid) removal from water bodies, and highlighted the important role of BAC as a nature-based solution to benefit the bioremediation of mining area.

International audience

International audience; The growing demand for strategic resources such as rare earth elements (REEs) for development of modern technologies has spurred an increase in mining activities and consequently a release of REEs into the environment, posing a potential threat to human health. Phytoextraction or phytomining, regarded as an in situ and low-cost means to use the growth and harvest of hyperaccumulator plants that take up high concentrations of metals in their shoots, allowing metal removal from contaminated soil (phytoextraction) or commercial production of high value metals (phytomining). In this chapter, we review the discovery of REE hyperaccumulators worldwide, focusing on the fern species Dicranopteris linearis (synonym D. dichotoma) that preferentially takes up light REEs and Phytolacca americana that preferentially incorporates heavy REEs. Although less well understood, mechanisms of REE uptake, translocation, and distribution in hyperaccumulator plants are discussed. Finally, we analyze the challenge of improving REE yield by phytomining, and taking D. linearis and P. americana as examples, estimate the phytomining potential for REEs using these species based on their biomass production, REE concentrations in the ash and current market prices for REEs.; La demande croissante de ressources stratégiques telles que les éléments de terres rares (ETR) pour le développement de technologies modernes a entraîné une augmentation des activités minières et, par conséquent, un rejet d'ETR dans l'environnement, ce qui constitue une menace potentielle pour la santé humaine. La phytoextraction ou phytomining, considérée comme un moyen in situ et peu coûteux d'utiliser la croissance et la récolte de plantes hyperaccumulatrices qui absorbent de fortes concentrations de métaux dans leurs pousses, permet d'éliminer les métaux des sols contaminés (phytoextraction) ou de produire commercialement des métaux de grande valeur (phytomining). Dans ce chapitre, nous passons en revue la découverte des hyperaccumulateurs d'ETR dans le monde, en nous concentrant sur les espèces de fougères Dicranopteris linearis (synonyme D. dichotoma) qui absorbe préférentiellement les ETR légers et Phytolacca americana qui incorpore préférentiellement les ETR lourds. Bien que moins bien compris, les mécanismes d'absorption, de translocation et de distribution des ETR dans les plantes hyperaccumulatrices sont discutés. Enfin, nous analysons le défi d'améliorer le rendement des ETR par phytomining, et en prenant D. linearis et P. americana comme exemples, nous estimons le potentiel de phytomining pour les ETR en utilisant ces espèces sur la base de leur production de biomasse, des concentrations en ETR dans les cendres et des prix actuels du marché pour les ETR.

Substantial unrealized opportunities exist for economic Ni agromining in the tropics. However, until recently this technology has remained relatively unexploited in this part of the world. In this chapter, we discuss the progress of tropical Ni agromining in two regions, namely Southeast Asia and the neotropical region. Significant advances have been made in Ni agromining operations in Southeast Asia, particularly Sabah (Malaysia), in the past few years: (i) exploring for suitable locations, (ii) screening for hyperaccumulator plants in native flora, (iii) selecting candidate hyperaccumulator species with high biomass production and shoot Ni concentrations (‘metal crops’), (iv) testing the agronomy of ‘metal crops’ to be used in viable agromining operations, and (v) demonstration of real-life agromining operations at field scale. The two most promising ‘metal crops’ in Sabah are Phyllanthus rufuschaneyi and Rinorea cf. bengalensis. However, Ni agromining developments in neotropical regions are still in their infant stages. Preliminary investigations have led to the discovery of a potential ‘metal crop’, Blepharidium guatemalense, having highly desirable attributes for possible Ni agromining. It is envisaged that tropical Ni agromining could be a productive alternative land use in these regions, and as such will significantly improve the livelihood of potential local ‘metal farmers’.

Initial experiments using Mediterranean Ni-hyperaccumulator plants for the purpose of phytomining were carried out in the 1990s. In order to meet commercial phytoextraction requirements, a technology has been developed using hyperaccumulator species with adapted intensive agronomic practices on naturally Ni-rich soils. Ultramafic soils in the Balkans and other parts of Europe display a great variability in Ni concentrations and available Ni levels. In Albania, Vertisols are currently being used for low-productivity agriculture (pasture or arable land) on which phytomining could be included in cropping practices. In northwestern Greece (Pindus and Vourinos mountain regions), agricultural soils may occur on ultramafic Cambisols. In Spain and Austria, these soils are much more erratically distributed and are seldom used for crops and pastures. In the Balkans, Odontarrhena chalcidica (synonym Alyssum murale) occurs widely on these ultramafic soils and is a spontaneous weed that grows among other crops. Field studies across Europe have now been carried out outside Mediterranean areas and have evaluated the Ni-hyperaccumulator O. chalcidica, as well as two other species native to northwestern Greece (Bornmuellera emarginata and B. tymphaea). At each site, local hyperaccumulator plants were tested for comparison (Noccaea goesingense in Austria and Odontarrhena serpyllifolia s.l. in Spain), in the context of two recent EUfunded projects (by Agronickel and LIFEAgromine). Soil and crop management practices are being developed in order to optimize the Ni agromining process. Field studies have evaluated the potential benefits of fertilization regimes, crop selection, and cropping patterns (introducing agroecological practices), and bioaugmentation using plant-associated microorganisms.

Dicranopteris linearis is a fern that grows naturally on the tailings of former rare earth element (REE) mines in southern China. It accumulates REEs in its aerial parts at concentrations that classify this plant as hyperaccumulator. The main objective of this research is to design a process to recover REEs directly from the dry biomass. This process involves three steps: (i) extraction of REEs from the dry plant by leaching with a solution containing acid and/or complexing agents, (ii) precipitation of REEs with oxalate and (iii) calcination to prepare REE oxide. A methodology based on speciation calculation made it possible to determine operating conditions for precipitation by accounting for the influence of the species present according to the extraction method. Simulations were carried out using Chess software, allowing the calculation of the composition of a multicomponent solution at thermodynamic equilibrium. These operating conditions were then validated experimentally. REE extraction from the dry plant was significantly improved under acid conditions (with H2SO4) or with a strong complexing agent (ethylenediaminetetraacetic acid). After optimization of the precipitation conditions, REE precipitation yields were above 90 %. After calcination, the final solid (REE oxide) contained ca 69 % of the REEs present in the initial biomass. The use of sulphuric acid as an extracting agent resulted in the recovery of a solid composed of 52 wt % of REEs (based on metal content). Thus, this study proposes a new recovery route for these strategic elements with a REE concentration factor from soil to final solid of 2500.

International audience; Increasing use of emerging per- and polyfluoroalkyl substances (PFASs) has caused extensive concerns around the world. Effective detection methods to trace their pollution characteristics and environmental behaviors in complex soil-crop systems are urgently needed. In this study, a reliable and matrix effect (ME)-free method was developed for simultaneous determination of 14 legacy and emerging PFASs, including perfluorooctanoic acid, perfluorooctane sulfonate, 6 hydrogenous PFASs, 3 chlorinated PFASs, and 3 hexafluoropropylene oxide homologues, in 6 crop (the edible parts) and 5 soil matrices using ultrasonic extraction combined with solid-phase extraction and ultraperformance liquid chromatography-mass spectrometry (MS)/MS. The varieties of extractants and cleanup cartridges, the dosage of ammonia hydroxide, and the ME were studied to obtain an optimal pretreatment procedure. The developed method had high sensitivity and accuracy with satisfactory method detection limits (2.40-83.03 pg/g dry weight) and recoveries (72-117%) of all target analytes in matrices at five concentrations, that is, 0.1, 1, 10, 100, and 1000 ng/g. In addition, the ME of this method (0.82-1.15) was negligible for all PFASs, even considering 11 different matrices. The successful application of the ME-free method to simultaneously determine the legacy and emerging PFASs in crop and soil samples has demonstrated its excellent practicability for monitoring emerging PFASs in soil-crop systems.

Aims: Dicranopteris linearis is a fern that accumulates unusually high concentrations (up to 0.3% dry weight) of rare earth elements (REEs) in China. Previously, we reported that D. linearis accumulates high concentrations of aluminium (Al) and silicon (Si) in the fronds, but the interactions between these elements and REEs were unknown. Methods: In this study, a range of analytical techniques, including chemical extractions, Scanning-Electron Microscopy with Energy-Dispersive Spectroscopy (SEM-EDS) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) were used to study the association of REEs with Al and Si. Results: The results show that D. linearis accumulates high concentrations of REEs (up to 3830 mg kg−1), Al (up to 9660 mg kg−1) and Si (up to 20,300 mg kg−1), with concentrations increasing with age and frond order of pinna. The extraction patterns suggest the existence of REEs-Si and Al-Si complexes. The SEM-EDS analysis confirmed the existence of phytoliths (Al) deposits in the protoplast and apoplast of the pinna cells. The upper epidermis of the pinnule and the pericycle of the midvein are more concentrated in phytoliths (Al) particles. The LA-ICP-MS analysis revealed that REEs and Al are preferentially compartmentalized within bio-inactive tissues of the pinnules, e.g. necrotic tissues (REEs) and in the margins (Al). Conclusions: Co-deposition of Si with REEs and Al may be a mechanism for dealing with the high concentrations of REEs and Al in D. linearis fronds.

International audience; The objective of the LORVER project was the construction of fertile Technosols on an industrial brownfield using wastes and byproducts to produce biomass for industrial purposes (hemp as a fiber source and poplar for short rotation coppice). A Life Cycle Assessment (LCA) of the Technosol construction was conducted to highlight the most significant environmental contributions. Three scenarios were compared: a reference scenario (REF) without improvement of the brownfield, a Technosol scenario (LORVER) using industrial byproducts (treated excavated soil, dredging sediments, paper mill sludge, compost and green waste) and a scenario where the brownfield was covered by topsoil (TS). An LCA was performed using SimaPro 8.5, the Ecoinvent v3 database and the ILCD impact indicators. The main contributors to the LORVER scenario that affected air quality and had energy-related impacts were the indirect demand of quicklime due to the use of paper mill sludge, which would have otherwise been spread on fields to save calcic amendments, followed by the transportation of waste from its source to the brownfield site. For the REF and TS scenarios, transportation and organic material spreading caused the most significant impacts. The LORVER scenario was the best or one of the best options for the fertility, carbon and pollution regulation-related impact categories due to the high carbon storage capacity of Technosols and its potential as an alternative solution to waste landfilling. Sensitivity analyses have shown that the LORVER scenario was always the best scenario for the climate change and land-related impacts and that it outperformed alternative scenarios if their required transportation distances exceeded 200 km. This very first LCA of a constructed Technosol made of inert and organic wastes on a brownfield site has proven the merit of this new approach, provided that environmental impacts are evaluated on a case-by-case basis, with the main variability source being the used materials and their alternative management strategies. It has also been demonstrated that these unused soils and materials could provide provisioning, regulation and cultural ecosystem services.

Purpose: Journal of Soils and Sediments publishes the main outcomes of SUITMA 9 Conference in its Special Issue. SUITMA (Soils of Urban, Industrial, Traffic, Mining and Military Areas) working group organizes conferences biannually all over the world. The ninth conference organized in Moscow in May 2017 involved more than 215 speakers from 25 countries, whose presentations focused on challenges and opportunities of urbanization for soil functions and ecosystem services. Materials and methods: The main outcomes of SUITMA 9 were analyzed in comparison to the previous SUIMTA conferences and the main topics were distinguished. Manuscripts accepted for publishing in the Special Issue were reviewed and presented. Results and discussion: Comparison of the topics highlighted in different special issues highlighted the evolution of the SUITMA studies from fundamental morphological descriptions and classifications to applied studies on soil engineering, assessment of SUITMA functions and ecosystem services. Conclusions: The manuscripts accepted to the Special Issue covered included various case studies of SUITMA ecosystem services (e.g. global and local climate regulation, biodiversity maintenance and improvement, nutrients balance and recreation) and disservices (e.g. pollution by heavy metals, polycyclic aromatic hydrocarbons and sulfur). The increasing role of SUITMA studies for urban management and decision making was concluded.

International audience; Aim The identification and use of hyperaccumulator plants in mining projects has been recognized as an important component of mine planning at several sites around the world. The objective of this research was to provide information on relevant plant tissue chemistry and an indicative assessment of the potential for phytomining at Weda Bay Nickel (WBN), Halmahera. Methods The first stage was the identification of native nickel hyperaccumulator plants. In total, 280 plant tissue samples from 10 nickel accumulator species and 46 matching rhizosphere soil samples were collected. Chemical analyses of plant tissue samples were performed and physico-chemical parameters of the rhizosphere soils were also measured. Results A total of three species were considered as metal crops: Rinorea aff. bengalensis (up to 22,200 mg kg−1 dry weight at 2 m above ground level), Ficus trachypison (1060 mg kg−1) and Trichospermum morotaiense (5180 mg kg−1), but only R. aff. bengalensis has sufficiently high Ni concentrations in biomass to warrant field trials. Conclusions Utilising a successional planting strategy, F. trachypison and T. morotaiense could be used to facilitate site conditions, followed by the metal crop R. aff. bengalensis. Using this design, a nickel yield of 330 kg per hectare would be possible every 4 years. In addition to allowing the recovery of nickel, this approach could be an integrated mine site rehabilitation strategy to mitigate environmental impacts, improve soil quality and facilitate transition to other land-uses such as native forest.

Phytomining technology cultivates hyperaccumulator plants on heavy metal contaminated soils, followed by biomass harvesting and incineration to recover valuable metals, offering an opportunity for resource recycling and soil remediation. Large areas of ultramafic soils, naturally rich in nickel (Ni), are present in numerous places around the world. As an environmentally friendly and cost-effective soil remediation technology, phytomining has a broad application prospect in such areas and thus has attracted great attention from global researchers. The key processes of phytomining include: (1) high-selectivity response of hyperaccumulator plants to Ni the underlying mechanisms involved in the rhizosphere; (2) underlying mechanisms of high-efficiency uptake and translocation of Ni in hyperaccumulators; and (3) resource recycling of high-added value Ni products from the Ni-rich bio-ore of hyperaccumulators. In recent 30 years, phytomining practices have successfully carried out in United States, Albania and Malaysia. However, the research and application of this technology in China are still in the fledging stage. This paper reviews the key processes and research progress of phytomining, and points out the bottleneck, to provide theoretical basis and technical guidance for phytomining.植物采矿是利用超积累植物高量吸收土壤中的重金属，并从中提取、冶炼金属产品，在修复污染土壤的同时实现金属的资源化。全世界广泛分布着自然风化的镍污染土壤，植物采矿因其重要的环境、生态及资源价值，被作为一种环境友好且具备经济效益的土壤修复技术，在此类地区具有广阔的应用前景。该植物采矿技术关键过程主要包括超积累植物镍高选择性根际环境响应、植物镍高效吸收转运以及生物质中镍高附加值资源化等过程。近30 年，污染土壤中镍的植物采矿已经在美国、阿尔巴尼亚、马来西亚等多个国家进行了野外实践，取得了良好效果。然而，相关技术在我国的研究与应用仍然处于起步阶段。文中通过综述植物采矿技术的关键过程的研究进展，发现其中的瓶颈，为接下来植物采矿的科学研究和技术在全世界推广提供理论基础和技术指导。.

International audience; Amendments of biochar, the residual solid of biomass pyrolysis, have been shown to enhance metal phytoextraction from contaminated soils with hyperaccumulating plants in specific situations. In order to investigate this phenomenon over successive harvests in field conditions, two identical undisturbed soil cylinders (1-m2 section × 1.85-m height) were excavated from a contaminated agricultural plot and monitored with instrumented lysimeters. Wood-derived biochar was added at a rate of 5% (w/w) in the first 30 cm of one of the two lysimeters. The Cd/Zn-hyperaccumulator Noccaea caerulescens was then grown for the next four years on both lysimeters. Our results showed that the hyperaccumulating plant was able to remove about 2 g m−2 of Cd and 12–16 g m−2 of Zn within four years, representing about 40% and 4% of the initial Cd and Zn soil contamination, respectively. Biochar amendment improved plant germination and survival and increased root surface density. However, no significant effect of biochar on shoot metal content of N. caerulescens was observed. Mass balances suggested that up to 10% the metal contamination moved from the disturbed Ap horizon to the deeper horizons, particularly in the biochar-amended soil profile. Furthermore, shoot Cd and Zn concentration generally decreased over the successive harvests, together with soil metal availability. Depending on the way to account for this progressive decrease in efficiency, our estimations of the time necessary to remove the excess of metals in the topsoil in these conditions ranged from 11 to 111 years for Cd and from 97 years to an infinite time for Zn. In conclusion, the simultaneous use of N. caerulescens and biochar amendment can lead to a significant removal of specific metallic elements from the topsoil, but the risk of metal movement down the soil profile and the observed decrease in phytoextraction efficiency over time deserve further investigations.

The widespread use of rare earth elements (REEs) has resulted in problems for soil and human health. Phytolacca americana L. is a herbaceous plant widely distributed in Dingnan county of Jiangxi province, China, which is a REE mining region (ion absorption rare earth mine) and the soil has high levels of REEs. An investigation of REE content of P. americana growing naturally in Dingnan county was conducted. REE concentrations in the roots, stems, and leaves of P. americana and in their rhizospheric soils were determined. Results showed that plant REEs concentrations varied among the sampling sites and can reach 1040 mg/kg in the leaves. Plant REEs concentrations decreased in the order of leaf > root > stem and all tissues were characterized by a light REE enrichment and a heavy REE depletion. However, P. americana exhibited preferential accumulation of light REEs during the absorption process (from soil to root) and preferential accumulation of heavy REEs during the translocation process (from stem to leaf). The ability of P. americana to accumulate high REEs in the shoot makes it a potential candidate for understanding the absorption mechanisms of REEs and for the phytoremediation of REEs contaminated soil.

Chromium (Cr) is a toxic heavy metal that is heavily discharged into the soil environment due to its widespread use and mining. High Cr levels may pose toxic hazards to plants, animals and humans, and thus have attracted global attention. Recently, much progress has been made in elucidating the mechanisms of Cr uptake, transport and accumulation in soil-plant systems, aiming to reduce the toxicity and ecological risk of Cr in soil; however, these topics have not been critically reviewed and summarised to date. Accordingly, based on available data-especially from the last five years (2017-2021)-this review traces a plausible link among Cr sources, levels, chemical forms, and phytoavailability in soil; Cr accumulation and translocation in plants; and Cr phytotoxicity and detoxification in plants. Additionally, given the toxicity and hazard posed by Cr(VI) in soils and the application of reductant materials to reduce Cr(VI) to Cr(III) for the remediation of Cr(VI)-contaminated soils, the reduction and immobilisation mechanisms by organic and inorganic reductants are summarised. Finally, some priority research challenges concerning the biogeochemical behaviour of Cr in soil-plant systems are highlighted, as well as the environmental impacts resulting from the application of reductive materials and potential research prospects.

The fern

The Island of Borneo is a major biodiversity hotspot, and in the Malaysian state of Sabah, ultramafic soils are extensive and home to more than 31 endemic nickel hyperaccumulator plants. The aim of this study was to characterize the structure and the diversity of the rhizosphere bacterial communities of several of these nickel hyperaccumulator plants and factors that affect these bacterial communities in Sabah. The most abundant phyla were Proteobacteria, Acidobacteria and Actinobacteria. At family level, Burkholderiaceae and Xanthobacteraceae (Proteobacteria phylum) were the most abundant families in the hyperaccumulator rhizospheres. Redundancy analysis based on soil chemical analyses and relative abundances of the major bacterial phyla showed that abiotic factors of the studied sites drove the bacterial diversity. For all R. aff. bengalensis rhizosphere soil samples, irrespective of studied site, the bacterial diversity was similar. Moreover, the Saprospiraceae family showed a high representativeness in the R. aff. bengalensis rhizosphere soils and was linked with the nickel availability in soils. The ability of R. aff. bengalensis to concentrate nickel in its rhizosphere appears to be the major factor driving the rhizobacterial community diversity unlike for other hyperaccumulator species.

International audience; Hyperaccumulator plants have the ability to efficiently concentrate metallic elements, e.g. nickel, from low-grade sources into their living biomass. Although the majority of nickel hyperaccumulator plant species restrict cobalt uptake, some species are able to co-accumulate cobalt when growing in ultramafic soils. The asteraceous perennial herb Berkheya coddii from South Africa is one of the most promising agromining crops known globally. It may accumulate nickel in excess of 30 000 mg g À1 in dry leaves, while co-accumulating up to 600 mg g À1 cobalt. This study aimed to elucidate the interactions between nickel and cobalt for uptake by and translocation into B. coddii through a pot experiment including various cobalt/nickel treatment combinations in soil, after which uptake and localisation were recorded. Cobalt in the substrate limits nickel uptake by B. coddii plants and is mainly retained in the basal leaves in contrast to Ni that is rapidly transferred to the top of the plant. B. coddii was more tolerant to high Ni concentration, whether in the substrate or internally but remains a promising crop which could be used, with suitable agronomic measures and practices, for cobalt agromining in areas with high soil cobalt but low soil nickel. A yield of 77 kg ha À1 nickel and 16.5 kg ha À1 cobalt may be attainable under optimum conditions. Significance to metallomics The hyperaccumulator plant Berkheya coddii from South Africa is one of the most promising 'agromining crops' known globally. This article reports on the interactions between cobalt and nickel for uptake and translocation in this species. Cobalt in the substrate inhibits nickel uptake in plants, and while nickel is rapidly transferred to the top of the plant, cobalt is mainly retained in the basal leaves.

The fern Dicranopteris linearis (Gleicheniaceae) from China is a hyperaccumulator of rare earth element (REE), but little is known about the ecophysiology of REE in this species. This study aimed to clarify tissue-level and organ-level distribution of REEs via synchrotron-based X-ray fluorescence microscopy (XFM). The results show that REEs (La + Ce) are mainly colocalized with Mn in the pinnae and pinnules, with the highest concentrations in necrotic lesions and lower concentrations in veins. In the cross sections of the pinnules, midveins, rachis, and stolons, La + Ce and Mn are enriched in the epidermis, vascular bundles, and pericycle (midvein). In these tissues, Mn is localized mainly in the cortex and mesophyll. We hypothesize that the movement of REEs in the transpiration flow in the veins is initially restricted in the veins by the pericycle between vascular bundle and cortex, while excess REEs are transported by evaporation and cocompartmentalized with Mn in the necrotic lesions and epidermis in an immobile form, possibly a Si-coprecipitate. The results presented here provide insights on how D. linearis regulates high concentrations of REEs in vivo, and this knowledge is useful for developing phytotechnological applications (such as REE agromining) using this fern in REE-contaminated sites in China.

National audience; Phytostabilization of ionic rare earth element mine tailings in South China. Rare earth elements supply: challenges and perspectives

International audience; Gold mining generates trace elements in the environment that are often associated with adverse effects on human health. This study determines trace elements levels in water, soil and plants (Datura inoxia and Calotropis procera) in Komabangou area, the main artisanal gold mining site in Niger. The collected samples were pre-treated before trace element analysis by inductively coupled plasma mass spectrometry (ICP-MS) for soils samples and by inductively coupled plasma optical emission spectroscopy (ICP-OES) for waters and plants samples. For soils, concentrations reached up to 555 mg kg(-1) and 468 mg kg(-1) for As and Zn, respectively. In waters, highest levels were observed for Zn (540 mg L-1), followed in decreasing order by Cu (7.4 mg L-1) and Al (4.27 mg L-1). As and Zn concentrations were 134 mg kg(-1) and 388 mg kg(-1); 49 mg kg(-1) and 46 mg kg(-1) respectively in leaves of Datura inoxia and Calotropis procera from gold site, whereas As and Zn, represented only 0.56 mg kg(-1) and 0.48 mg kg(-1); 6.40 mg kg(-1) and 46 mg kg(-1) respectively in leaves of control species. In fact, results obtained revealed both contaminations by trace elements of soil and water for the majority of samples taken in gold zone with an exceeding of limit values recommended by WHO in particular for As, Cr, Ni, Pb and Zn. Therefore, the establishment of a monitoring and treatment program for polluted soils and waters in this gold zone would be necessary to preserve human health.

International audience

International audience; Artificial soils constructed from wastes and by-products have been considered as a sustainable option for land reclamation. In particular, they could contribute in a complementary manner to natural soils to global climate regulation by storing large quantities of carbon (C). However, the evolution of C stocks in such newly formed soils remains largely unknown. This work aimed at evaluating the dynamics of C in constructed Technosols, focusing on two experimental sites in Lorraine, France, where Technosols were constructed from thermally-treated industrial soil, papermill sludge and green waste compost, and planted with grasses. Soil samples were collected over 12 years, and stocks of C were calculated, taking into account the increase in soil bulk density and the associated decrease in soil thickness over the years. The evolution of the stocks of organic C was compared to the evolution reported for natural grassland soils from the same region and for other Technosols. Initial organic C stocks in the two constructed Technosols were 50% higher than in natural analog soils when calculated over 30 cm, and up to 5 times higher when calculated over 100 cm. Organic C stocks in the two Technosols decreased over the first three years, but increased during the following years, most likely due to the accumulation of plant-derived C. A similar evolution was observed in other planted Technosols. We conclude that Technosols constructed from an adequate set of parent materials can keep large amounts of organic C over time and sequester additional C under permanent plant cover.

International audience; Hyperaccumulator plants are new alternative sources for elements of interest e.g., nickel, rare-earth elements(REEs), as concentrations in their aerial parts are higher than in common low-grade ores. The fern Dicranopterislinearis naturally grows on former mine tailings in Southern China and is classified as a REE hyperaccumulator.The efficient recovery of REEs is fundamental to ensure economic viability and to limit the environmental impactof the process. This study presents a novel approach for the treatment of the Dicranopteris biomass after incinerationto ash to drastically improve the “bio-ore” grade and to generate heat. Ash structure and composition isdescribed, and challenges for efficient recovery of REEs are discussed. A pre-processing step, aiming at renderingthe REEs available for extraction, was designed to dissolve aluminum (Al) using concentrated sodium hydroxide(6 M) at an average temperature (80 ◦C). The operating parameters were investigated through experimentmethodology design and parametric studies to build an empirical model. Additional experiments revealed thatthe formation of insoluble aluminosilicate compounds limited the removal of aluminium. Rinsing the REE-richresidue proved to be effective to increase the REE concentration and was carefully designed. Subsequently,the REEs were extracted under mildly acidic conditions using nitric acid (25 ◦C, pH 4.8), producing a valuablesolution devoid of aluminium and containing 74% of the REEs.