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The post-mining landscape of Freiberg, Saxony, Germany is characterized by soils with elevated concentrations of non-essential elements, particularly arsenic (As), cadmium (Cd) and lead (Pb). While literature on soil mineralization and factors influencing the soil-plant transfer in managed agroecosystems is extensive, information on the accumulation in native woody plant species, including soil-associated factors influencing their accumulation, is still lacking. In this study, we evaluated the concentrations of 24 elements, including As, Cd and Pb in leaves and branches of three taxa of tree species (Betula pendula, Populus tremula and Salix spec.) throughout the study area and compared the results with data on potentially plant available element concentrations in soil (sequential extraction), total element concentrations as well as with remote sensing data on surface soil moisture and water availability in the root-zone. Populus tremula and Salix spec. were identified as plant species that are suitable for bioindication of soil pollution. Leaf concentrations were substantially higher compared to branches. The concentrations in leaves largely reflected the availability of elements in soil. Concomitantly, higher soil-plant-transfer of elements correlated with remote sensing data, onsurface water accumulation and water content in the root-zone. This suggests that higher soil water contents increase the availability of the toxic elements to plants and/or impacts the translocation of elements to aboveground plant parts. The contribution of soil-associated factors and plant-associated factors to the hyperaccumulation observed remains a field for further research. Nevertheless, we could demonstrate that coupling leaf analysis with remote sensing data on soil moisture could be a promising approach in environmental assessments as well as in phytoremediation and phytomining approaches.

International audience; AimsRare earth elements (REEs) and normalized REE patterns determined in plant and soil samples represent powerful tools to trace biogeochemical processes during weathering, soil genesis and processes in the rhizosphere, and thus publications reporting REE concentrations and normalized REE patterns in soil systems and plants are rapidly increasing.MethodsA normalized REE pattern allows for the recognition of anomalous concentrations of an individual REE. In the literature, anomalies are predominantly reported/focused for/on the redox-sensitive elements cerium (Ce) and europium (Eu) that can shift their oxidation state during interactions with organic and inorganic soil phases and the biological processes affecting their mobility in soil and uptake by plants. Thus positive Eu anomalies in plants are often interpreted as a consequence of reduction of Eu3+ to Eu2+ in the rhizosphere followed by a preferential uptake of Eu2+.ResultsDue to an analytical artefact in ICP-MS analysis, a false Eu anomaly may be reported. This can be avoided by using a barium (Ba) interference correction. We draw attention to the possibility of this problem and to being aware of its potential occurrence when Eu anomalies are reported.ConclusionsWe recommend (i) including information on how this potential problem was dealt with in the Materials and Methods section of articles and (ii) how to implement Findable Accessible Interoperable and Reusability (FAIR) guiding principles in that section (including data availability in an open repository).

Maize (Zea mays) is one of the most important staple food and primary source of livestock feed in the world. As the consumption of maize grown on the selenium-enriched soils of Naore Valley is one of the apparent causes of selenosis in the area, this work collected and analyzed total Se, Se fractions, and Se species distributions in maize plant samples, including grains, leaves, stalks, roots, rhizosphere soils, and the most representative parent rock materials from Naore Valley, Ziyang County, China. The Se distribution in soils markedly correlated with the weathered Se-enriched bedrocks, but most of the Se in the analyzed soils is enclosed as recalcitrant residual Se and organic-sulfide bound Se. In contrast, Se in rocks had a comparatively higher bioavailability and is bounded mainly to organic matter and sulfides minerals, with very few of the Se enclosed in the residual fraction. Maize plants might take a large amount of Se from the organic-sulfide bound Se fraction in the Se-rich soils, the weathered products from bedrocks or plant litters. Total Se concentrations in the collected samples were observed in descending order soil>leaf>root>grain>stalk. The predominant Se species detected in maize plants was SeMet. Se inorganic forms, mainly Se(VI), decreased from root to grain and were possibly assimilated into organic forms. Se (IV) was barely present. The natural increases in Se concentration affected mainly leaf and root dry-weight biomass as they are the organs that coped with the highest Se accumulation. This paper offers an insight into the uptake, accumulation, and distribution of Se forms in natural Se-rich maize crops and an opportunity for shifting Se-rich soils from menaces to valuable resources for growing Se-rich agricultural products.

Background and Aims A split-root approach was used to explore how phosphorus (P) nutrition influences accumulation of rare earth elements (REE) in plant species with different P-acquisition strategies beyond the commonly explored REE-phosphate precipitation. Methods Six species (Triticum aestivum, Brassica napus, Pisum sativum, Cicer arietinum, Lupinus albus, and Lupinus cosentinii) were cultivated with a split-root system on two sand types. Phosphorus availability was controlled on one root side by watering the plants with different P-containing solutions (100 µM P, 0 µM P). Carboxylate release and changes in pH were measured on both sides. Concentrations of nutrients, cadmium (Cd), aluminium (Al), light REE (LREE: La–Eu), and heavy REE (HREE: Gd–Lu, including Y) in roots and shoots were analyzed by ICP-MS. Results Triticum aestivum, B. napus and C. arietinum did not respond to a low P supply with elevated carboxylate release. These species accumulated more REE when the P supply was low and higher REE concentrations were proportional to declining plant growth. However, P. sativum, L. albus and L. cosentiniiaccumulated less REE when P-supply was low. Plants that strongly acidified the rhizosphere and released low quantities of dicarboxylates accumulated more REE (with higher LREE/HREE ratios) than species that released tricarboxylates. Conclusion Our findings suggest that REE accumulation strongly depended on rhizosphere acidification, in concert with the amount and composition of carboxylates determining the exclusion of REE-carboxylate complexes. Leaf REE signatures may be a promising indicator as a screen tool for carboxylate-based processes in the rhizosphere using an ionomic approach.

Groundwater contamination is a critical issue in Hanoi because it affects the water supply and treatment of a crowded city. This study aimed to explore the groundwater quality across the whole area of Hanoi city and identify potential contamination sources. 206 groundwater samples were collected in the Holocene and Pleistocene aquifers during two consecutive seasons (rainy 2015 and dry 2016) to assess the groundwater contamination and understand which elements can be used as tracers for future monitoring. As a result, the spatial distributions of major ions (Na, K, Ca, Mg, Cl−, and SO42−) and some selected elements (As, Li, Sr, Ba, Mn, Fe, Al, B, Br, total nitrogen (TN), and P) were obtained. Distributions of elements and contaminants varied not only on depth and regions (aquifers) but also season-wise. In the upper aquifer, SO42−, B, As, Br−, TN, and P concentrations were significantly higher than the common range. In the south of Hanoi city, we found elevated Li, Na, K, Mg, Cl− and Br concentrations in the Pleistocene aquifer. Additionally, the concentrations of such as As, Sr, Ba, Mn, Fe did not follow a clear pattern. Their concentrations seem to be predominantly influenced by geological processes controlling the study area's hydro-geochemical environment. However, high concentrations of SO42−, B, Br−, TN, and P, particularly in central Hanoi, supported the idea of contamination from the surface. This study's results might help managers foster sustainable groundwater resource strategies.

Ore-mining industry produces a waste, which belongs to the main sources of potentially toxic elements (PTEs). One of the initial steps necessary for remediation project of contaminated sites is the research of PTEs mobile forms that are very capable to enter trophic chain mainly through plants. Great abandoned copper deposit São Domingos (Portugal) was selected as a representative area since the presence of high PTEs contents was proved there in previous research activities.The presented work is focused on efficiency of natural sorbents on the immobilisation of PTEs in copper-polluted soil developed on tailings taken from the mine district, and to compare the treated soils as habitats of vascular plants. Several natural sorbents were selected for the adequate realization of experimental part: bentonite, charcoal, calcium carbonate, phosphate, chicken manure, and organo-zeolitic substrate (mixture of perlite, chicken manure, and calcium carbonate; 5:1:3).From the whole area of the mine-dump, 10 sites were chosen as the representatives of not-so-heterogenic soil conditions, where the sampling itself was realized. As the representative PTEs; Cr, Mn, Co, Ni, Cu, Zn, As, Cd, and Sb were chosen. The sorbents were added to composite soil sample. Ex situ experiments were realized from 1st of June to 30th of September 2020. At the end of experiments, a soil sample from each pot were taken, dried and grained into the fine powder. For assessment of total concentration of elements, microwave digestion was performed, with 100 mg of grained powder dissolution in aqua regia. For the purpose to assess the forms of PTEs with the ability to be assimilated by plant roots, the extraction from 1 g of sample was executed in the sequence: I. deionized water; II. 1M ammonium acetate solution by pH 7 (both mixed for 12 hours); 0.01M citric acid solution (mixed for 2 hours). First two fractions can be referred as mobile / exchangeable. The prcessed soil solutions were measured by Inductively Coupled Plasma Mass Spectrometry (ICP-MS).The technosol was contamined mainly by As, Cu, and Zn. Obtained results show that neither As nor Sb are present in inverstigated francions, whereas the concentrations of Cr is also very low. The other PTEs are contained in significat concentrations, mostly in mobile fraction, especially Co (36 %); Mn (27 %); Cu (25 %); and Cd (15 %). Among the natural sorbents, the only ones efficient in reducting the mobile forms were charcoal and organo-zeolitic substrate. These pots were also the only suitable habitats for mixture of grass species. In both cases, the mobile contents of Ni, Cu, and Zn were practically reduced to zero since the mobile contents of Co, Mn and Cd decreased to minimum. For better understanding of habitat-suitability after application of those sorbents, the plant-nutrient characterisation should be included in further research. Based on those results, both natural sorbents could be considered for application in remediation techniques aimed on those PTEs.

Background: Silicon (Si) is one of the elements whose role in plant nutrition and development is not fully defined and has become of great interest as of recent. The presence of Si, is, however, known to extend several benefits to plants, which include increased biomass production and tolerance against both biotic and abiotic stressors, furthermore, it improves plant rigidity.Aim: This study represents a greenhouse experiment that was designed to explore the effects of Si accumulation and its relationship with the uptake of essential and nonessential elements while alleviating toxicity in plants with different nutrition strategies.Methods: Four plant species, Brassica napus (B. napus, a hyperaccumulator), Lupinus albus (L. albus, an excluder), Cucumis sativus, and Zea mays (C. sativus and Z. mays, both Si accumulators), were cultivated on a semi hydroponic substrate under greenhouse conditions. The plants were treated with a variation between a solution made of a trace element mix (Al, Cd, Mn and REE) without Si (further denoted TE-mix) and a similar mix with Si- fertilizer as silicic acid (further denoted Si+). The solution concentrations were varied between 10 and 100 µM, to investigate the effect of Si. After harvest, the concentration of Ca, Mn, Fe, P, Al, Cd and REE were determined using IC-PMS. Results: Treatment with 10 µM TE-mix and Si+ showed a decrease in biomass on the biomass of B. napus and L. albus. The effect of Si on the biomass of Si accumulators (C. sativus and Z. mays) decreased with the increasing concentration of the TE application. Treating the plants with Si+ at both low and high concentrations resulted in low Ca concentration in B. napus and C. sativus when compared to the concentrations from TE-mix treatment which are up to fivefold higher. The influence of Si+ on the concentration of Mn, and Fe increased (≥150 % and ≥10% respectively) with increased Si+ concentration. The results further indicated that treating the plants with Si+ increased the concentration of Al and Cd accumulated in B. napus, C. sativus and Z. mays. Higher concentrations of LREE were accumulated when compared to LREE in all species when treated either with TE-mix or Si+ (at both 10 and 100 µM). The highest REE concentration was accumulated in B. napus (21.4 µg /g LREE and 17.4 µg /g HREE) when the plants were treated with 100µM Si+. Conclusion: The results from this study provide further insight into the benefits of supplementing Si as fertilizer, toward plant development and nutrition. Even when utilized on plants with different nutrition strategies, Si may assist the plants in biomass production and to acquire nutrients such as Fe and Mn. Furthermore, the use of Si can assist plants in resisting high concentrations of toxic trace elements such as Al and Cd while also accumulating nonessential but valuable elements such as rare earth elements when implementing phytoremediation.

Phosphorus (P) and iron (Fe) are limiting nutrients in many (agro-)ecosystems. Due to P-sorption under most soil conditions, the current P-fertilization practices are inefficient, since large quantities of the P fertilizer applied remain in the soil as a residual part. Therefore, the development of sustainable agricultural practices urgently needs to improve nutrient-acquisition efficiencies of crop species through rhizosphere engineering and breeding of low-input strains. The availability of nutrients in the rhizosphere, especially that of P, is dependent on the activity of roots and associated microbes, particularly their ability to acidify the surrounding soil and release chelating compounds such as carboxylates. Therefore, there is a growing interest among plant ecologists, breeders and agronomists in “easily-measurable” tools to trace belowground functional traits in nutrient acquisition under soil conditions. Here, we explore the idea to use rare earth elements (REEs) in plant material to evaluate the nutrient-acquisition strategy, particularly under nutrient limitation. The rationale behind this hypothesis is that i) REEs are present in almost all soils at quantities similar to some plant nutrients such as Cu and Zn, ii) REEs interact with nutrient-bearing soil phases (phosphates, Fe-oxyhydroxides), iii) root exudates released under P/Fe deficiency strongly mobilize REEs in soil, and iv) the uptake of mobilized REEs in plants depends on their chemical form, which is a function of rhizosphere chemistry. Preliminary results from greenhouse and large-scale field experiments indicate that P-inefficient species show different REE-concentrations in their leaves than P-efficient species, and that the pattern of REEs is related to the composition of root exudates. In ongoing experiments, this hypothesis will be rigorously tested by coupling a field sampling campaign of plant material from species with contrasting nutrient-acquisition strategies along soils with changing nutrient availability (Western Australian chronosequences) as well as controlled greenhouse experiments for mechanistic elucidation of processes involved.

Soil inoculation with plant growth promoting rhizobacteria (PGPR) promises benefits for agriculture as well as phytoremediation and phytomining of potentially toxic elements (PTEs) and critical raw materials (CRMs) in soil. Thus, we investigated on a field scale the effects of soil inoculation on biomass production as well as on phytoextraction of germanium (Ge), sum total of rare earth elements (REET), copper (Cu), lead (Pb), zinc (Zn), cadmium (Cd), cobalt (Co), nickel (Ni), Iron (Fe), calcium (Ca) and phosphorus (P). Zea mays (ZM) and Helianthus annuus (HA) were used as test plants and the commercially available PGPR RhizoVital®42 containing Bacillus amyloliquefaciens FZB42 as source of inoculum. Post-harvest, biomass/m2, shoot element content/m2, root concentration and water-soluble soil element fraction of root soils were compared for plants grown on inoculated versus uninoculated reference soil. Results indicated increase of 24 % and 26 % for ZM and HA grown on inoculated soils respectively, albeit insignificant at p ≤ 0.05. Inoculation with PGPR enhanced the ZM shoot content of P, K, Co, Cd and Ge by percentages between 20 and 80 % (significant only for Ge) and decreased shoot content of Pb, REET and Cu by 35 %, 28 % and 59 % respectively. For HA grown on inoculated soil, shoot content of Ca, Ni, Cu, Zn, Ge, REET and Pb increased by over 28 % with negligible decrease observed for Cd. Water soluble element concentrations revealed increased concentrations of more than 15 % for K, Fe, Zn, Cd, Pb, Ge and REET in inoculated post-harvest root soils of ZM with negligible changes of less than ≤ 5% observed for P, Ca, Co, Ni and Cu. For HA , increase of ≥ 28 % for water soluble element concentrations occurred only for P and Ca, with concentrations of Ni, Cu, Zn, Cd, Pb and REET decreasing by percentages between 11 and 41 %. Also, increased root concentrations of ≥ 22 % for ZM growing on inoculated soils occurred only for P, Ca, Cu and Cd while decreased concentration of ≥ 12 % occurred only for Fe, Co, Ni, Pb and REET. Summarily, results suggest that bioaugmentation with commercially available PGPR RhizoVital®42, containing Bacillus amyloliquefaciens FZB42 has the potential to enhance biomass production as well as enhance or inhibit phytoextraction of some elements. Also, effects of PGPR on phytomining and phytoremediation is plant specific for some elements, depending mostly on plant physiological characteristics.

Anaerobic digestion technique and production of bioenergy from biogas is an important contribution to achieving the targets of climate protection. Concomitantly, the use of digestates as secondary raw material for the production of fertilizers and the extraction of economic valuable elements are increasingly considered. The latter requires profound knowledge on the element concentrations in digestates and how changes in process parameters affect their enrichment. In this study a lab scale continuous anaerobic digestion with different organic loading rates (ORL) were performed to explore effects of loading rate on biogas production and concentration of heavy metals (Zn, Cr, Ni) and valuable elements (Ge, REEs) in digestate. The pH was 6.8–7.2 throughout the whole process. In a 30 liter reactor with working volume of 25 liter grass (Phalaris arundinaceae) and manure (20/80, 30/70, 40/60, 50/50, 60/40 ) were added as a substrate at different OLR (1, 2, 2.5, 3, 3.5, 4 kg VS m-3 d-1). The digestate of each organic loading rate was analyzed by ICP-MS. Increasing the OLR significantly increased gas production by 64%, 12%, 8%, 16% and 20%, respectively. While biogas production increased, concentration of heavy metals (Zn, Cr, Ni) and valuable elements (Ge, REEs) decreased at each level of OLR increase except between OLR 2 and OLR 3. The increased biogas production was most likely caused by higher amounts of readily degradable organics in the fermenter, while decreasing concentrations of elements in digestates result from a dilution of initially high element concentrations in the manure with low concentrated grass biomass. In fact, we could say that the concentrations of elements in manure were by far higher compared to the grass. However, there was OLR 3 where higher inputs of biomass did not negatively affect element concentrations in digestate. Surprisingly at this OLR highest relative increase in gas production was observed. This suggests that at this loading rate enrichment of elements through losses of carbon and dilution with increasing contents of low concentrated biomass was balanced. We could demonstrate that OLR fundamentally impacts gas production and mineral element concentrations in digestate. The effects depend initially on element concentrations in biomass and gas production which potentially offers novel perspectives for optimization of biogas process towards a phytomining of valuable elements and use of digestates as secondary raw materials.

Given the possible benefits of phytoextraction, this study evaluated the potential of nine plant species for phytoaccumulation/co-accumulation of selected nutrients, rare earth elements, germanium, and potentially toxic elements. Plants were grown on 2 kg potted soils for 12 weeks in a greenhouse, followed by a measurement of dry shoot biomass. Subsequently, elemental concentrations were determined using inductively coupled mass spectrometry, followed by the determination of amounts of each element accumulated by the plant species. Results show varying accumulation behavior among plants for the different elements.This is a novel study because it focuses on evaluating plant species not only the accumulation behavior but the possibilities of co-accumulation of elements comprising selected nutrients, PTEs and CRMs (Ge and REEs) by plants. It provides new information on the biomass production and accumulation behavior of some plant species for some elements, some of which have not been previously studied. It also provides information on the possibility of predicting species accumulation behavior for some elements based on similarities in the source of origin, chemical similarities, or antagonism.

This study presents how nutrient availability and intercropping may influence the migration of REE when cultivated under P-deficient conditions. In a replacement model, Hordeum vulgare was intercropped with 11% Lupinus albus cv. Feodora and 11% L. angustifolius cv. Sonate. They were cultivated on two substrates, A (pH = 7.8) and B (pH = 6.6). Two nutrient solutions were supplied, with N, K, Mg and high P-supply (P+), the other with N, K, Mg, and one-third of P-supply (P-, applied to L0 and Lan only). Simultaneously, a greenhouse experiment was conducted to quantify carboxylate release. There, one group of L. albus and L. angustifolius was supplied with 200 µM K2HPO4 (P+) together with the other nutrients while a second group received 20 µM P (P-). L. albus released higher carboxylates at low P-supply than L. angustifolius. Higher P-supply did not influence the P concentrations and contents of H. vulgare neither on substrate A nor on substrate B. However, addition of P decreased the concentrations of REEs, especially in plants cultivated on alkaline soil. Nutrient accumulation decreased in H. vulgare in intercropping with L. angustifolius when cultivated on the alkaline substrate A with high P-supply. In the same conditions, the accumulation of REE in H. vulgare significantly increased. Conversely, on the acidic substrate B intercropping with L. albus decreased REE contents and concentrations in H. vulgare. Intercropping with L. angustifolius opens an opportunity for enhanced phytomining and accumulation of REE. Furthermore, intercropping with L. albus on REE polluted soils may be utilized to restrict REE accumulation in crops used for food production.

Bioaugmentation promises benefits for agricultural production as well as for remediation and phytomining approaches. Thus, this study investigated the effect of soil inoculation with the commercially available product RhizoVital®42, which contains Bacillus amyloliquefaciens FZB42, on nutrient uptake and plant biomass production as well as on the phytoaccumulation of potentially toxic elements, germanium, and rare earth elements (REEs). Zea mays and Fagopyrum esculentum were selected as model plants, and after harvest, the element uptake was compared between plants grown on inoculated versus reference soil. The results indicate an enrichment of B. amyloliquefaciens in inoculated soils as well as no significant impact on the inherent bacterial community composition. For F. esculentum, inoculation increased the accumulation of most nutrients and As, Cu, Pb, Co, and REEs (significant for Ca, Cu, and Co with 40%, 2042%, and 383%, respectively), while it slightly decreased the uptake of Ge, Cr, and Fe. For Z. mays, soil inoculation decreased the accumulation of Cr, Pb, Co, Ge, and REEs (significant for Co with 57%) but showed an insignificant increased uptake of Cu, As, and nutrient elements. Summarily, the results suggest that bioaugmentation with B. amyloliquefaciens is safe and has the potential to enhance/reduce the phytoaccumulation of some elements and the effects of inoculation are plant specific.

Selenium (Se) enrichments or deficiency in maize (Zea mays L.), one of the world’s most important staple foods and livestock feeds, can significantly affect many people’s diets, as Se is essential though harmful in excess. In particular, Se-rich maize seems to have been one of the factors that led to an outbreak of selenosis in the 1980s in Naore Valley in Ziyang County, China. Thus, this region’s geological and pedological enrichment offers some insight into the behavior of Se in naturally Se-rich crops. This study examined total Se and Se species in the grains, leaves, stalks, and roots of 11 maize plant samples, Se fractions of soils around the rhizosphere, and representative parent rock materials from Naore Valley. The results showed that total Se concentrations in the collected samples were observed in descending order of soil > leaf > root > grain > stalk. The predominant Se species detected in maize plants was SeMet. Inorganic Se forms, mainly Se(VI), decreased from root to grain, and were possibly assimilated into organic forms. Se(IV) was barely present. The natural increases of Se concentration in soils mainly affected leaf and root dry-weight biomasses of maize. In addition, Se distribution in soils markedly correlated with the weathered Se-rich bedrocks. The analyzed soils had lower Se bioavailability than rocks, with Se accumulated predominantly as recalcitrant residual Se. Thus, the maize plants grown in these natural Se-rich soils may uptake Se mainly from the oxidation and leaching of the remaining organic-sulfide-bound Se fractions. A viewpoint shift from natural Se-rich soils as menaces to possibilities for growing Se-rich agricultural products is also discussed in this study.

This study presents how phosphate (P) availability and intercropping may influence the migration of rare earth elements (REEs) in legume–grass associations. In a replacement model, Hordeum vulgare was intercropped with 11% Lupinus albus and 11% Lupinus angustifolius. They were cultivated on two substrates, A (pH = 7.8) and B (pH = 6.6), and treated with 1.5 g P m−2 or 3 g P m−2. Simultaneously, a greenhouse experiment was conducted to quantify carboxylate release. There, one group of L. albus and L. angustifolius was supplied with either 200 µmol L-1 P or 20 µmol L-1 P. L. albus released higher amounts of carboxylates at low P supply than L. angustifolius, while L. angustifolius showed the opposite response. Plants cultivated on substrate B accumulated substantially higher amounts of nutrients and REE, compared to substrate A. Higher P supply did not influence the leaf and stem P concentrations of H. vulgare. Addition of P decreased REE accumulation in barley monocultures on alkaline soil A. However, when H. vulgare was cultivated in mixed culture with L. angustifolius on alkaline substrate A with high P supply, the accumulation of REE in H. vulgare significantly increased. Conversely, on acidic substrate B, intercropping with L. albus decreased REE accumulation in H. vulgare. Our findings suggest a predominant effect of soil properties on the soil–plant transfer of REEs. However, in plant communities and within a certain soil environment, interspecific root interactions determined by species-specific strategies related to P acquisition in concert with the plant’s nutrient supply impact REE fluxes between neighbouring plants.

In this study three hydrometallurgical methods are described for leaching of a eudialyte concentrate with H2SO4: (i) direct leaching, (ii) fast leaching and (iii) water leaching of dehydrated acid/concentrate mixture. It is demonstrated how to obtain a silica free solution, how parameter variations impact the properties of precipitated silica and which processes lead to losses of valuable components during leaching. Furthermore, the acid solubility of gangue minerals in the concentrate is analyzed and the resulting consequences in terms of leach solution contamination and acid consumption are discussed. The best result in terms of the average yield of value components (REEs, Zr(+Hf), Mn and Nb) of 86% is obtained by direct leaching under mild conditions (cH2SO4 = 1 mol/L; TL = 60 °C). However, released silicic acid does not precipitate and aggregates at pulp density ρPD,L = 100 kg/m3 by gelling. Fast leaching allows the efficient removal of silica at high solid-liquid ratios in the pre-treatment stage. Due to mass transfer limitations, high efficiency stirrers are crucial for achieving high yields in short reaction times. Dehydration of the acid/concentrate mixture before water leaching can be a good alternative if well-defined amount of acid is used; however, high energy input is needed.

Arsenic is one of the main contaminants in soil, especially in (former) mining areas, but arsenic can also be a source of exploitable metals, if present as arsenides. In the following paper we report the microbial leaching of an arsenide (e.g. safflorite (CoAs2)) for the first time. Bioleached cobalt yielded up to 92% in presence of citric acid, while the non-inoculated and chemical controls yielded in merely 4% and 10%, respectively. Even though high yields were achieved, the arsenide turned out to be a difficult leaching substrate, leading to a diverse activity. While the addition of citric acid improved the cobalt liberation and resulted in a more stable activity, the absence led to yields ranging from 35% to 82%, depending on the ability to cope with the arsenide. From the comparison of the leaching with 1% and 2% (w/v) ore, it can be concluded that the decreased activity resulted in an unfinished leaching. Furthermore, the typestrains of Acidithiobacillus ferrooxidans and Leptospirillum ferriphilum were not able to grow in presence of the arsenide.

There are several regions of the world where soils are contaminated with potentially toxic elements (PTE) and/or have critical raw materials (CRM) that cannot be extracted through conventional raw material extraction techniques because of their low amounts. Phytoextraction- a kind of phytoremediation- offers good option or method to sustainably remediate these contaminated soils and extract these CRM from soils. The successful phytoextraction of these elements of interest from soil is dependent on their bioavailability for plant uptake and biomass production which could be increased by inoculating soil with plant growth promoting rhizobacteria (PGPR) and the element acquisition characteristics of the plant species used for phytoextraction. This study investigated the effect of the PGPR Bacillus amyloliquefaciens - FZB42 also called Rhizovital produced as spore’s formulation by ABiTEP on the phytoextraction efficiency of two selected species, Zea mays and Fagopyrum esculentum grown in potted soils under artificial lighting conditions for about 8 weeks in a laboratory. Results showed that for Fagopyrum esculentum, the inoculation of soil with Rhizovital increased the uptake of As, Cu, Pb and Co, Ni, Mg, K, P, La, Ce, Y, sum of Heavy Rare Earth Elements (HREE), sum of Light Rare Earth Elements (LREE) but significantly only for Cu and Co at alpha level 0.05 and insignificantly decreased the uptake for Ge. For Zea mays, results showed that inoculating soil with Rhizovital decreased uptake for all elements investigated and significantly so for only Co but showed an insignificant increasing effect on the uptake of Cu. For the two test species, similarity in effects of inoculation of soil with Rhizovital on uptake of elements only existed for Cu (increasing effect) and Ge (decreasing effect) suggesting that the addition of Rhizovital to soil could increase the Cu phytoextraction efficiency of Zea mays and Fagopyrum esculentum and decrease the phytoextraction efficiency of Germanium in both plants. Results from this research suggest that inoculation of soil with the PGPR Bacillus amyloliquefaciens - FZB42 could increase the phytoextraction of Copper by Zea mays and Fagopyrum esculentum respectively, thus enhancing the phytoextraction efficiency of both plants in soils contaminated by copper. Also, results suggest that inoculation of soil with Rhizovital could increase the phytoextraction efficiency of Fagopyrum esculentum for most of the PTEs and CRM investigated in this experiment and that Fagopyrum esculentum is a good candidate for PGPR assisted phytoextraction of PTE and CRM

This study aims to identify the effects of having narrow leaf lupine grown in a mixed culture with barley at different proportions when different treatment regimens are introduced to the plants. The effects of the usage of fertilizer, NK and NPK on the plants are determined, where the absence and presence and absence of phosphorus will be used to determine the variation in REE accumulation. Furthermore, to investigate how the carboxylate-based strategies for nutrient acquisition in the rhizosphere of Lupinus angustifolius, affect the availability of trace elements to the neighbouring species (in this case barley) and are traceable by rare earth element (REE) pattern. Barley (Hordeum vulgare L. cv. Modena) was cultivated with narrow leaf lupin (Lupinus angustifolius). The experimental design involved both a monoculture (L0) and mixed cultures, where barley was replaced with narrow leaf lupin at two different proportions 11 and 33 % (Lan 11 and Lan 33). To test the influence of fertilizer on the accumulation of REEs, the plants were further treated with two variated fertilizer options; nitrogen (N), phosphorus (P) and potassium (K) and on the contrary just N & K. Elemental concentrations within the leaves and stems of the barley were determined by ICP-MS. In the presence of P (NPK treatment) An increase in LREE is observed in the leaves of barley than in the stems. There is a statistically significant difference between L0 and Lan 11. HREE also shows an increased uptake in the leaves than in stems. The behaviour of both LREE and HREE from the NK treatment show a similar pattern for both stems and leaves, however, at lower concentrations than when P is present. From the obtained results we can conclude that the presence of P increases the availability of REEs, particularly LREE. Furthermore, intercropping with narrow leaf lupin positively influences the uptake of trace REEs, thus increasing their availability to adjacent plants.

Bioharvesting of toxic and valuable elements by growing high biomass crops in the regions with low-grade mining ores and metal-polluted soils is a new concept in the area of mining termed phytomining. The biomass is used in anaerobic digestion to produce biogas and digestate. To the best of our knowledge, there are limited studies on the enrichment and distribution of heavy metals and economically valuable elements in digestate, obtained from mesophilic and thermophilic fermentation conditions. This study conducted a laboratory experiment to recover and enrich toxic elements (Zn, Cd, Pb, As) and economically valuable elements (Ge and rare earth elements REEs) at mesophilic (37⁰C) and thermophilic (55⁰C) conditions. To analyze the distribution of these elements in the liquid and solid-state of digestate a three-step sequential extraction procedure was carried out. Microfiltration (0.2µm) was used to separate elements in the solid and liquid phases. The solid digestate was extracted with ammonium acetate (pH 7) and ammonium acetate (pH 5) to determine exchangeable and acid-soluble elements. As a result, we found that thermophilic conditions significantly enriched Zn (3%), Cd (48%), Pb (25%), As (21%), Ge (40%), and REEs (22%) compared to mesophilic conditions. The following elements were enriched in decreasing order Cd > Ge > Pb > REEs > As > Zn. This enrichment may be due to differences in availability of substrates to microorganisms and higher gas production with increased temperature. The sequential extraction revealed that the concentration of elements in dissolved form was significantly increased in thermophilic conditions. While the concentrations in exchangeable are decreased indicating that previous elements bound on exchangeable sites were removed and transferred in solution. Furthermore, the element concentration in the residue fraction was not affected by temperature. Possibly the release of secondary metabolites from microorganisms triggered by higher temperature improved the solubility of elements which is an important prerequisite for element separation and recovery.

Electronic components (EC) from waste electrical and electronic equipment (WEEE) such as resistors, capacitors, diodes and integrated circuits are a subassembly of printed circuit boards (PCB). They contain a variety of economically valuable elements e.g., tantalum, palladium, gold, and rare earth elements. However, until recently there has been no systematic dismantling and recycling of the EC to satisfy the demand for raw materials. A problem connected with the recycling of the EC is the removal of the components (dismantling) in order to recover the elements in later processing steps. The aim of the present study was to develop a new technique of dismantling using bioleaching technology to lower costs and environmental impact. In triplicate batch experiments, used PCBs were treated by bioleaching using an iron-oxidizing mixed culture largely dominated by Acidithiobacillus ferrooxidans strains supplemented with 20 mM ferrous iron sulfate at pH 1.8 and 30 &deg, C for 20 days. Abiotic controls were treated by similar conditions in two different variations: 20 mM of Fe2+ and 15 mM of Fe3+. After 20 days, successful dismantling was obtained in both the bioleaching and the Fe3+ control batch. The control with Fe2+ did not show a significant effect. The bioleaching condition presented a lower rate of dismantling which can partially be explained by a constantly higher redox potential leading to a competition of solder leaching and copper leaching from the printed copper wires. The results showed that biodismantling&mdash, dismantling using bioleaching&mdash, is possible and can be a new unit operation of the recycling process to maximize the recovery of valuable metals from PCBs.

Recent studies have shown that the metal adaptation of Actinobacteria offers a rich source of metal inducible environmentally relevant bio-compounds and molecules. These interact through biosorption towards the unique cell walls or via metal chelating activity of metallophors with trace elements, heavy metals and even with lanthanides to overcome limitations and toxic concentrations. Herein, the purpose is to investigate the adaptation potential of Gordonia rubripertincta CWB2 in dependence of the rare earths and to determine if we can utilize promising metallophore metal affinities for metal separation from aquatic solutions. For details on data interpretation and applicability of siderophores we refer to the related article entitled "Cultivation dependent formation of siderophores by Gordonia rubripertincta CWB2" [1]. The respective workflow comprises a metal adaptation method to demonstrate effects on bacterial growth, pH, metallophore production, and metabolic change. All this was evaluated by LC-MS/MS and effects on biosorption of rare earths was verified by ICP-MS. Furthermore, we were able to carry out batch metal adsorption and desorption studies of metallophores entrapped in inorganic polymers of tetramethoxysilane (TMOS) to determine metal chelating capacities and selective enrichment effects from model solutions. The adaptation potential of strain CWB2 at increased erbium and manganese concentrations was verified by increased chelating activity on agar plates, in liquid assays and demonstrated by the successful enrichment of erbium by metallophore-functionalized TMOS-polymers from an aquatic model solution. Furthermore, the number of detected compounds in dependency of rare earths differ in spectral counts and diversity compared to the wild type. Finally, the biosorption of rare earths for the selected adaptation was increased significantly up to 2-fold compared to the wild-type. Overall a holistic approach to metal stress was utilised, integrating a bacterial erbium adaptation, metal chelating, biosorption of lanthanides and immobilization as well as enrichment of metals using metallophore functionalized inorganic TMOS polymers for separation of metals from aquatic model solutions.

Chemical fractionation of germanium (Ge) and rare earth elements (REEs) in biogas residue by a two-step sequential extraction procedureNazia Zaffar (1), Erik Ferchau (2), Hermann Heilmeier (1), and Oliver Wiche (1) (1) Technical University of Bergakademie, Freiberg, Institute for Biosciences, Biology/Ecology Group, Germany (naziazaffarqau@gmail.com), (2) Technical University of Bergakademie, Institute for Thermal Engineering and Thermodynamics Ge and REEs are of increasing interest in phytoremediation and phytomining research. These elements are present in almost all soils and soil-grown plants contain considerable concentrations of these elements in their biomass. The process chain of phytomining involves i) the accumulation of target elements in harvestable plant biomass (phytoextraction), ii) production of bioenergy by burning or biogas production, and iii) the recovery of the elements from bioenergy residues.Although literature on bulk concentrations of elements in fermentation residues is extensive until today there is only a little information on how the elements are bound/distributed in the solid/liquid phases of the fermentation residues, particularly for target elements in phytoremediation research such as Ge and REEs. Therefore, we conducted a laboratory experiment in which residues from anaerobic fermentation were separated into liquid/solid by microfiltration. Subsequently the solids were extracted by a two-step sequential extraction procedure. This procedure involved the extraction of solids with ammonium acetate (pH 7) and ammonium acetate (pH 5) to determine exchangeable as well as acid-soluble elements. As a result, we found that total concentrations in the residues were 0.5 µg/g for (Ge) and 8.7 µg/g for (REEs i.e sum of all lanthanides). In the liquid phase concentrations of Ge and REEs were very low ranging from 0.0001 µg/g Ge and 0.003 µg/g REEs respectively. Concentrations of elements in the liquid phase represented 0.01% Ge and 0.04% REEs of the total element concentrations of the material, indicating that most of the elements were bound to solids. Results from the sequential extraction revealed that percentage distribution of elements were 1.2% (exchangeable Ge) 0.5% (exchangeable REEs) and 0.8% (acid-soluble Ge) 3.8% (acid-soluble REEs) from the total elements of the material. However, we found 99% Ge 98% REEs in residue fractions. We can conclude that most of the Ge and REEs in digestates are most probably bound into organic structures which were not attracted by extraction solutions. This has major implications for the development of methods for the recovery of the target elements were strong acids/or oxidation of organics prior to application of separation.

To significantly contribute to the available information on potentials of different plants species for use in phytomining of Rare Earth Elements(REEs) , a screening experiment was conducted to directly compare at once 8 plant species belonging to two functional groups (herbs and grasses), grown on a soil with high REEs concentrations. The plants were grown for 10 weeks on potted soils, each containing 2kg of soil. The plants evaluated are Fagopyrum esculentum, Cannabis sativa, Brassica napus and Sinapis alba for the herbaceous species and Sorghum bicolor, Zea mays, Avena sativa and Festuca arundinacea for the grass species. Concentrations of the four REEs namely Cerium (Ce), Lanthanum (La), Neodymium (Nd) and Yttrium (Y) and amount/content of each REE contained in the species investigated were determined and the data obtained were subjected to the statistical analysis Multivariate Analysis of Variance to identify differences that exist between species, within and between functional groups. Results show that the differences observed in amount of each of the REEs phytomined by the different grass species are statistically insignificant. Contrastingly, significant differences exist between the concentrations and content of each of the REEs between the herbaceous species, with F. esculentum significantly showing higher potential for use in phytomining compared to the rest of the herbaceous species. Results from statistical comparison of all species shows that F. esculentum is the candidate that showed more potential for use in phytomining , with C. sativa also being the next specie with high potential for phytomining aside from F.esculentum when compared to the rest of the species investigated. Functional groups were compared, and results showed that the herbaceous specie have a significantly higher potential for use in phytomining of REEs compared to grass species. Results from this experiment contributes to existing knowledge on potentials of different plant species for use in phytomining and suggest possible candidates in comparison to others, for use in experiments that seek to improve the chances of using plants as an eco-friendly alternative to conventional mining of rare earth elements in commercial quantities.

Wastewater treatment always produces a large amount of sludge. The different uses of sludge disposal have negative consequences for the environment. Agricultural use may appear in some situations as an alternative to current solutions, both to optimize the degradation and recycling of organic and mineral elements. During this work, on the one hand, we investigated the effect of sludge on the growth of turnip (Brassica rapa), a plant that tolerates metallic trace elements, especially lead (Liu et al., 2000) and which is considered a model plant in eco-toxicology (Sun et al., 2010), and on the other hand to determine if it has the potential to be included in phytoremediation systems.The seeds were put in different substrates that contained three sludge doses: 20%, 40% and 60%, mixed with agricultural soil which contained high levels of metallic trace elements exceeding the standard eligible concentration by AFNOR. compared to the soil, concentrations of potentiall toxic trace elements in sludge were lower than in soil. Morphological measurements were carried out during two months of planting, showing the positive effect of the sludge on the growth of the plant. The recorded biometric values (height, number of leaves, weight, rotation and height of the bulb) for all doses, far exceed those of control plants (100% soil), with high values recorded in the mixture of soil with 60% sludge.The concentration of metallic trace elements in the different substrates and also in the leaves and the turnip bulb after two months of planting shows that the plant accumulates and tolerates hight concentrations of elements and can therefore be used as a phytoremediator for polluted soils. The highest levels of metal accumulation were observed on the substrate in the soil mixture with 60% sludge.

Until recently it has been generally assumed that Ge taken up by plants is stored in phytoliths together with Si. This assumption is mostly based on the geochemical similarities between Ge and Si, while a scientific proof was lacking. The aim of the present study is to i) compare the uptake of Si and Ge in three grass species, ii) localize Ge and Si stored in above-ground plant parts and iii) evaluate the amounts of Ge and Si sequestrated in phytoliths and plant tissues. Mays (Zea mays), oat (Avana sativa) and reed canary grass (Phalaris arundinacea) were cultivated in the greenhouse on soil and sand to control element supply. Leaf phytoliths were extracted by dry ashing. Total elemental composition of leaves, phytoliths, stems and roots were measured by ICP-MS. For the localization of phytoliths and the determination of Ge and Si within leaf tissues and phytoliths scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDX) and laser ablation ICP-MS (LA-ICP-MS) was used. The amounts of Si and Ge taken up by the species corresponded with biomass formation and decreased in the order Z. mays >P. arundinacea, A. sativa. Results from LA-ICP-MS revealed that Si was mostly localizedin phytoliths, while Ge was disorderly distributed within the leaf tissue. In fact, from the total amounts of Ge accumulated in leaves only 10% was present in phytoliths highlighting the role of organic Ge species in plant tissues and the necessity for using bulk Ge/Si instead of Ge/Si in phytoliths to trace biogeochemical cycling of Si. Moreover, our results represent important background data for the optimization of a phytomining of Ge.

Open Access (OA) describes the free, unrestricted access to and re-use of research articles. Recently, a new wave of interest, debate, and practice surrounding OA publishing has emerged. In this paper, we provide a simple overview of the trends in OA practice in the broad field of geochemistry. Characteristics of the approach such as whether or not an article processing charge (APC) exists, what embargo periods or restrictions on self-archiving’ policies are in place, and whether or not the sharing of preprints is permitted are described. The majority of journals have self-archiving policies that allow authors to share their peer reviewed work via green OA without charge. There is no clear relationship between journal impact and APC. The journals with the highest APC are typically those of the major commercial publishers, rather than the geochemistry community themselves. The rise in OA publishing has potential impacts on the profiles of researchers and tends to devolve costs from organizations to individuals. Until the geochemistry community makes the decision to move away from journal-based evaluation criteria, it is likely that such high costs will continue to impose financial inequities upon research community. However, geochemists could more widely choose legal self-archiving as an equitable and sustainable way to disseminate their research., Open access, Article processing charge, Green route, Repository; Environmental geochemistry; Earth sciences; Geochemistry; Fossil geochemistry; Biogeochemistry; Catchment geochemistry; Isotope geochemistry; Petroleum geochemistry; Trace element geochemistry; Hydrochemistry, Information science, Biogeoscience.

Germanium (Ge) is widespread in the Earth's crust. As a cognate element to silicon (Si), Ge shows very similar chemical characteristics. Recent use of Ge/Si to trace Si cycles and changes in weathering over time, growing demand for Ge as raw material, and consequently an increasing interest in Ge phytomining have contributed to a growing interest in this previously rather scarcely considered element in geochemical studies. This review deals with the distribution of Ge in primary minerals and surface soils as well as the factors influencing the mobility of Ge in soils including the sequestration of Ge in secondary mineral phases and soil organic matter. Furthermore, the uptake and accumulation of Ge in plants and effects of plant-soil relationships on the availability of Ge in soils and the biogeochemical cycling of Ge are discussed. The formation of secondary soil minerals and soil organic matter are of particular importance for the concentration of Ge in plant-available forms. The transfer from soil to plant is usually low and shows clear differences between species belonging to the functional groups of grasses and forbs. Possible uptake mechanisms in the rhizosphere are discussed. However, the processes that are involved in the formation of plant-available Ge pools in soils and consequently its biogeochemical cycling are not yet well understood. There is, therefore, a need for future studies on the uptake mechanisms and stoichiometry of Ge uptake under field conditions and plant-soil-microbe interactions in the rhizosphere as well as the chemical speciation in different plant parts.

Herein we demonstrate cultivation-dependent siderophore production by the actinomycete Gordonia rubripertincta CWB2. The strain produces mostly citrate, but also desferrioxamine E (DFOE) and new hydroxamate-type siderophores. The production of hydroxamate-like siderophores is influenced by cultivation conditions, for example available carbon sources or presence of metals, such as the rare earth erbium or the heavy metal lead. By cultivation with succinate and extraction with an adsorbing resin (XAD) we purified the G. rubripertincta CWB2 siderophores (yield up to 178 mg L-1). The respective workflow comprises genome mining, cultivation, and overproduction strategies, a rapid screening procedure, as well as traditional structure enrichment and structure elucidation methods. This combination of methods allows the discovery of new natural products with metal complexation capacity, also for lanthanides of commercial value. G. rubripertincta CWB2 carries a desferrioxamine-like biosynthetic gene cluster. Its transcription was proven by a transcriptomic approach comparing expression levels of the selected gene cluster during cultivation in iron-depleted and repleted media. Further investigation of the siderophores of this desferrioxamine producing Actinobacterium could lead to new structures.

Open Access (OA) describes the free, unrestricted access to and re-use of research articles. Recently, a new wave of interest, debate, and practice surrounding OA publishing has emerged. In this paper, we provide a simple overview of the trends in OA practice in the broad field of geochemistry. Characteristics of the approach such as whether or not an article processing charge (APC) exists, what embargo periods or restrictions on self-archiving’ policies are in place, and whether or not the sharing of preprints is permitted are described. The majority of journals have self-archiving policies that allow authors to share their peer reviewed work via green OA without charge. The journals with the highest APC are typically those of the major commercial publishers, rather than the geochemistry community themselves. Until the geochemistry community makes the decision to move away from journal-based evaluation criteria, it is likely that such high costs will continue to impose financial inequities upon research community. However, geochemists could more widely choose legal self-archiving as an equitable and sustainable way to progress communication of their research.

The distribution of U, Sr, V, Ni, Cr, B, and Mo in sediments of the Al-Batin Alluvial Fan in southern Iraq was investigated. A total of 18 sediment samples were collected in the study area and the clay and silt fraction was analyzed using a six-step sequential extraction method. Results of the sequential extraction were used to evaluate the potential origin and environmental impacts of the selected elements. Except for Sr, the highest average concentration of the investigated trace elements is mainly in the residual fraction with the following descending order: Cr > V > B > Ni > Mo > U. This suggests a geogenic origin of these trace elements. Sr occurs mainly in the acid soluble fraction due to its authigenic formation from the underlying carbonate beds. Anthropogenic pollution in the study area is restricted to agricultural activities and fertilizer application which adds B and Mo to the soil in some cases. The Sr elevation and fractionation within the sediments suggests a possibility of Sr accumulation in cultivated crops, and thus a potential risk to infants and children. High concentrations and fractionation pattern of U in three samples shows a considerable risk to the environment in certain areas.

This article examines phytoecological aspects of plant groups in the Chebket El Melhassa region (Tiaret-Ouest Algérien) by several types of analysis: biological, biogeographic and statistical. From the plant analysis, a list of 103 taxa distributed in 36 families was compiled, biologically characterized by a dominance of therophytes (45.6%) with species of the Mediterranean biogeographic type 20 species (19.8%) assuming particular importance. The ordination of the plant community was performed in the search for the optimum solution based on correlation with environmental factors, estimated using the phytoindication approach. The results reveal that the plants represented in the community, mostly prefer strongly lit places. Phytoindication shows a warm sub Mediterranean climate. Continentality corresponds to the sub-oceanic climate. The moisture regime ranges from strongly dry to dry soil. The plant community is formed on moderately acid soils. Plants are able to grow on both strongly acidic and neutral soils. The soil is very poor or poor in nitrogen. A four dimension variant of multidimensional scaling procedure was selected as the most appropriate decision. Dimensions selected after nonmetric multidimensional scaling were interpreted by computing weighted average scores of ecological factors for ordination configuration. Four of the plant species clusters were found to be the optimal solution on the basis of the Calinsky-Harabasz criteria. The clusters can be viewed as a functional group. Functional group A is quite diverse and represented by 42 species. This functional group is closest to the community optimum because in all four space dimensions the corresponding cluster is near the origin, which corresponds to the most typical ecological conditions. Species that constitute the group B prefer minimum values of dimension 2. This indicates a preference for illuminated sites with high temperature regime and low soil humidity. This group includes 32 species. A feature of group С is that it is located in the area of maximum values for dimension 2. Thus, this functional group is opposite to functional group B. This indicates a preference of species included in the functional group C for wetter soils. Functional group C comprises 21 species. Functional group D differs considerably from all others in its ecological characteristics. The difference is in the preference for minimum values for measurement 1. This suggests that more acid soils are optimal for a given functional group. Functional group E comprises 8 species.

Here, we explore effects of metallophore-producing rhizobacteria on the plant availability of germanium (Ge) and rare earth elements (REEs). Five isolates of the four species Rhodococcus erythropolis, Arthrobacter oxydans, Kocuria rosea and Chryseobacterium koreense were characterized regarding their production of element-chelators using genome-mining, LC-MS/MS analysis and solid CAS-assay. Additionally, a soil elution experiment was conducted in order to identify isolates that increase solubility of Ge and REEs in soil solution. A. oxydans ATW2 and K. rosea ATW4 released desferrioxamine-, bacillibactin- and surfactin-like compounds that mobilized Ge and REEs as well as P, Fe, Si and Ca in soil. Subsequently, oat, rapeseed and reed canary grass were cultivated on soil and sand and treated with cells and iron depleted culture supernatants of A. oxydans ATW2 and K. rosea ATW4. Inoculation increased plant yield and shoot phosphorus (P), manganese (Mn), Ge and REE concentrations. However, effects of the inoculation varied substantially between the growth substrates and plant species. On sand, A. oxydans ATW2 increased accumulation of REEs in all plant species and root-shoot translocation in rapeseed, while K. rosea ATW4 enhanced REE accumulation in rapeseed only, without effects on other plant species. Sand-cultured oat plants showed increased Ge accumulation and root-shoot translocation in presence of A. oxydans ATW2 cells and K. rosea ATW4 supernatant; however, there was no effect on other plant species, irrespective the growth substrate used. In contrast, soil-cultured rapeseed showed enhanced REE accumulation in presence of cells of A. oxydans ATW2 while there were no effects on other plant species and Ge. The processes involved are not yet fully understood. Nevertheless, we demonstrated that chemical microbe-soil-plant relationships influence plant availability of nutrients together with Ge and REEs, which has major implications on our understanding of biogeochemical element cycling and development of sustainable bioremediation and biomining technologies.

Gordonia rubripertincta CWB2 produces hydroxamate-type siderophores. Therefore it was cultivated under iron limitation. Analytical reversed-phase HPLC allowed determining a single peak of ferric iron chelating compounds from culture broth. The elution profile and its absorbance spectrum were similar to those of desferrioxamine B. The latter is a commercial available metal chelating agent which is of interest for industries. We successfully developed an HPLC protocol to separate metal-free and metal-loaded desferrioxamines. Further, we aimed to increase the re-usability of desferrioxamines as metal chelators by immobilization on silica based carriers. The siderophores of strain CWB2 have been covalently linked to the carrier with a high yield (up to 95%). Metal binding studies demonstrated that metals can be bound to non-immobilized as well as to the covalently linked desferrioxamines.

In the present study we explore the idea of biotechnologically produced metallophore mixtures as selective chelating compounds for economically valuable metals from various sources. A complex soil matrix with natural levels of metal mineralization was employed as a potential source of metals. We focused on gallium-chelating metallophore preparations of two soil bacteria (Gordonia rubripertincta CWB2 and Paracoccus denitrificans PD1222) which were compared to the commercially available desferrioxamine B (DFOB). As a reference, the binding of iron was analyzed. The herein described successful mobilization of metals such as gallium from soil provides first hints towards alternative strategies, such as phytomining, sensor development, or solvent extraction based on metallophores. The metallophore mixture produced by the strains showed best results at pH 8 and allowed to mobilize gallium about three times better as the pure commercially available DFOB.

Effects of citric acid and desferrioxamine B (DFO-B) on the availability of Ge and selected rare earth elements (REEs) (La, Nd, Gd, Er) to Phalaris arundinacea were investigated. A soil dissolution experiment was conducted to elucidate the effect of citric acid and DFO-B at different concentrations (1 and 10 mmol L−1 citric acid) on the release of Ge and REEs from soil. In a greenhouse, plants of P. arundinacea were cultivated on soil and on sand cultures to investigate the effects of citric acid and DFO-B on the uptake of Ge and REEs by the plants. Addition of 10 mmol L−1 citric acid significantly enhanced desorption of Ge and REEs from soil and uptake into soil-grown plants. Applying DFO-B enhanced the dissolution and the uptake of REEs, while no effect on Ge was observed. In sand cultures, the presence of citric acid and DFO-B significantly decreased the uptake of Ge and REEs, indicating a discrimination of the formed complexes during uptake. This study clearly indicates that citric acid and th...

The total concentrations and chemical fractionation of Germanium (Ge) and selected rare earth elements (REEs) in top soils and soil-grown plants of different land use types (moist grassland, mesic grassland, arable land) were investigated in the post-mining area of Freiberg (Saxony, Germany). The study area covers approximately 1000 km 2 in the south of Central Saxony, and 138 samples from 46 sampling sites were examined. Ge and REEs in soils were partitioned by a sequential extraction procedure into mobile/exchangeable (Fraction 1), acid soluble (Fraction 2), bound to organic matter (Fraction 3), amorphous Fe/Mn-oxyhydroxides (Fraction 4), crystalline Fe/Mn-oxides (Fraction 5) and residual fractions (Fraction 6). Total concentrations of Ge and REEs in soil varied considerably ranging from 1.0 μg g − 1 to 4.3 μg g − 1 for Ge (mean 1.9 μg g − 1 ) and 97 μg g − 1 to 402 μg g − 1 (mean 168 μg g − 1 ) for total REE contents, accounting for 17% and 14% to the investigated light REEs La and Nd, respectively and 2.8% and 1.5% to the investigated heavy REEs Gd and Er, respectively. Elements in potentially plant available fractions represented 8% of total Ge and 30% of total REEs, respectively. Soils on moist grasslands characterized as acidic fluvisols and gleysols with high organic matter content contained significantly higher total concentrations of Ge and REEs and higher concentrations of Ge and REEs in the potentially plant available Fractions 1–3 compared to soils of mesic grassland and arable land. Grass species accumulated significantly higher concentrations of Ge than herb species. Highest concentrations of Ge were measured in plant species growing on moist grassland ( Phalaris arundinacea : 449 ng g − 1 ), while there were no significant differences with regard to the concentrations of REEs in plants among the different land use types. The results of this study indicate that moist grasslands may act as sinks for Ge and REEs. In these soils high amounts of soil organic matter and low pH may foster the retention of labile forms, increasing the pool of Ge and REEs accessible for phytoextraction. However, the species-specific processes involved during the uptake of REEs need to be understood in order to optimize phytomining techniques.

The geochemical behavior of rare earth elements (REE) has been mainly investigated in geological systems where they represent the best proxies for processes occurring at the interface between different media. REE concentrations, normalized with respect to the upper continental crust, were used to assess their behavior. In this study, REE geochemical behavior was investigated in plant shoots of a facultative metallophyte naturally growing in Katanga (Democratic Republic of Congo). Anisopappus chinensis and rooting zone soil samples (n=80) were collected in four natural sites with contrasting pedogeological environments (e.g., parent rock type, pH, organic matter content) and highly variable REE contents. Soil and plant REE concentrations and chemical soil factors were was analyzed by ICP-MS, to examine relationships between soil factor and REE accumulation in plants. REE uptake by plants was primarily correlated with their concentrations and/or their speciation in the soil as previously shown in the literature. Results of this study show that REE patterns in shoots are relatively flat whereas soils are enriched in middle REE. The geochemical behavior of REE illustrates that metals accumulation in aerial parts of A. chinensis is most probably driven by mechanisms involving REE complexation processes in the rhizosphere.

Salinity increase in groundwater was investigated in the area between Al-Zubair and Safwan, and close to the Khor Al-Zubair Channel of southern Iraq. Thirty-nine groundwater samples from the shallow aquifer and one sample from the Khor Al-Zubair Channel were analyzed. The mean total dissolved solids are 7556 mg/L. The δ2H and δ18O plot in two groups are below the global meteoric water line. Group A indicates the evaporation effect of irrigation return-flow, while group B is characterized by depleted δ18O values due to recharge under colder climate. Deuterium excess values plot within the region of modern precipitation and dilution of groundwater by precipitating water. The groundwater residence time is between 1000 and 2000 years and combining 14C -age with SO42− shows a contrasting effect on groundwater on both sides of Khedr Almai Fault and the Zubair anticline, which indicates the role of these geological structures on the hydrochemical evolution in the western part. Jabal Sanam shows no clear effect in this regard. The ratio Cl−/Br− and sulfate in groundwater showed that the measured salinity in groundwater is the result of a mixing process between groundwater, seawater intruding from Khor Al-Zubair Channel, and water from septic tanks in addition to dry and wet sea spray, and irrigation return-flow.