Phytoextraction Options.

Wastewaters often contain an array of economically valuable elements, including elements considered critical raw materials and elements for fertilizer production. Plant-based treatment approaches in constructed wetlands, open ponds, or hydroponic systems represent an eco-friendly and economical way to remove potentially toxic metal(loid)s from wastewater (phytoextraction). Concomitantly, the element-enriched biomass represents an important secondary raw material for bioenergy generation and the recovery of raw materials from the harvested plant biomass (phytomining). At present, phytoextraction in constructed wetlands is still considered a nascent technology that still requires more fundamental and applied research before it can be commercially applied. This chapter discusses the different roles of plants in constructed wetlands during the phytoextraction of economically valuable elements. It sheds light on the utilization of plant biomass in the recovery of raw materials from wastewater streams. Here, we consider phytoextraction of the commonly studied water pollutants (N, P, Zn, Cd, Pb, Cr) and expand this concept to a group of rather exotic metal(loid)s (Ge, REE, PGM) highlighting the role of phytoextraction in the face of climate change and finite resources of high-tech metals.

Lead toxicity in plants: mechanistic insights into toxicity, physiological responses of plants and mitigation strategies.

Soil toxicity is a major environmental issue that leads to numerous harmful effects on plants and human beings. Every year a huge amount of Pb is dumped into the environment either from natural sources or anthropogenically. Being a heavy metal it is highly toxic and non-biodegradable but remains in the environment for a long time. It is considered a neurotoxic and exerts harmful effects on living beings. In the present review article, investigators have emphasized the side effects of Pb on the plants. Further, the authors have focused on the various sources of Pb in the environment. Investigators have emphasized the various responses including molecular, biochemical, and morphological of plants to the toxic levels of Pb. Further emphasis was given to the effect of elevated levels of Pb on the microbial population in the rhizospheres. Further, emphasized the various remediation strategies for the Pb removal from the soil and water sources.

Potential strategies for phytoremediation of heavy metals from wastewater with circular bioeconomy approach.

Water pollution is an inextricable problem that stems from natural and human-related factors. Unfortunately, with rapid industrialization, the problem has escalated to alarming levels. The pollutants that contribute to water pollution include heavy metals (HMs), chemicals, pesticides, pharmaceuticals, and other industrial byproducts. Numerous methods are used for treating HMs in wastewater, like ion exchange, membrane filtration, chemical precipitation, adsorption, and electrochemical treatment. But the remediation through the plant, i.e., phytoremediation is the most sustainable approach to remove the contaminants from wastewater. Aquatic plants illustrate the capacity to absorb excess pollutants including organic and inorganic compounds, HMs, and pharmaceutical residues present in agricultural, residential, and industrial discharges. The extensive exploitation of these hyperaccumulator plants can be attributed to their abundance, invasive mechanisms, potential for bioaccumulation, and biomass production. Post-phytoremediation, plant biomass can be toxic to both water bodies and soil. Therefore, the circular bioeconomy approach can be applied to reuse and repurpose the toxic plant biomass into different circular bioeconomy byproducts such as biochar, biogas, bioethanol, and biodiesel is essential. In this regard, the current review highlights the potential strategies for the phytoremediation of HMs in wastewater and various strategies to efficiently reuse metal-enriched biomass material and produce commercially valuable products. The implementation of circular bioeconomy practices can help overcome significant obstacles and build a new platform for an eco-friendlier lifestyle.

Controlling In Planta Gold Nanoparticle Synthesis and Size for Catalysis.

Gold nanoparticles (Au-NPs) are used as catalysts for a diverse range of industrial applications. Currently, Au-NPs are synthesized chemically, but studies have shown that plants fed Au deposit, this element naturally as NPs within their tissues. The resulting plant material can be used to make biomass-derived catalysts. In vitro studies have shown that the addition of specific, short (∼10 amino acid) peptide/s to solutions can be used to control the NP size and shape, factors that can be used to optimize catalysts for different processes. Introducing these peptides into the model plant species, Arabidopsis thaliana (Arabidopsis), allows us to regulate the diameter of nanoparticles within the plant itself, consequently influencing the catalytic performance in the resulting pyrolyzed biomass. Furthermore, we show that overexpressing the copper and gold COPPER TRANSPORTER 2 (COPT2) in Arabidopsis increases the uptake of these metals. Adding value to the Au-rich biomass offers the potential to make plant-based remediation and stabilization of mine wastes financially feasible. Thus, this study represents a significant step toward engineering plants for the sustainable recovery of finite and valuable elements from our environment.

Can rare earth elements be recovered from abandoned mine tailings by means of electrokinetic-assisted phytoextraction?

Given the high impact of traditional mining, the recovery of rare earth elements (REEs) from hazardous waste materials could become an option for the future in accordance with the principles of the circular economy. In this work, the technical feasibility of REEs recovery from metal mine tailings has been explored using electrokinetic-assisted phytoremediation with ryegrass (Lolium perenne L.). Phytoextraction combined with both AC current and DC current with reversal polarity was applied (1 V cm-1, 8 h day-1) to real mine tailings containing a total concentration of REEs (Sc, Y, La, Ce, Pr, and Nd) of around 146 mg kg-1. Changes in REEs geochemical fractionation and their concentrations in the soil pore water showed the mobilization of REEs caused by plants and electric current; REE availability was increased to a higher extent for combined electrokinetic-assisted phytoextraction treatments showing the relevant role of plants in the process. Our results demonstrated the initial hypothesis that it is feasible to recover REEs from real metal mining waste by phytoextraction and that the performance of this technology can be significantly improved by applying electric current, especially of the AC type, which increased REE accumulation in ryegrass in the range 57-68% as compared to that of the treatment without electric field application.

Phytoremediation technology for recovery of Ni by Acacia plants in association with Bacillus amyloliquefaciens isolated from E-waste contaminated site.

Electronic waste (e-waste) illegally disposal in Thailand is becoming more widespread. A sustainable metal recovery technology is needed. A phytotechnology called "phytomining" of metals such as nickel (Ni) is a promising technology providing a sustainable solution to the growing e-waste problems. This study investigated the ability of Acacia species in association with e-waste site isolated, plant growth-promoting rhizobacteria (PGPR), Bacillus amyloliquefaciens. Acacia mangium accumulated higher Ni in their tissues when Ni concentrations in soil were lower than 200 mg kg-1. The inoculation of PGPR B. amyloliquefaciens enhanced Ni uptake and accumulation in the leaves, stem, and root. The results showed that the highest Ni concentration was found in the root ash (825.50 mg kg-1) when inoculated plants were grown in soil containing 600 mg kg-1 Ni. Hence, the Ni recovery process and mass balance were performed on root ashes. The highest Ni recovery was 91.3% from the acid (H2SO4) leachate of the ash of inoculated plant treated with 600 mg kg-1 Ni. This demonstrates the feasibility of PGPR-assisted phytomining from Ni-contaminated soil. Phytomining of Ni from any e-waste contaminated sites using Acacia mangium in combination with B. amyloliquefaciens can promote plant growth and improve the uptake of Ni.

Phytomining from electronic waste is an appealing technology that can provide a long-term waste management strategy while valuable trace metals can be recovered. In this study, we evaluated the nickel phytomining ability of Acacia mangium in association with PGPR Bacillus amyloliquefaciens. The results from this study showed that Ni recovery from phytomass using A. mangium with B. amyloliquefaciens can be further improved leading to a sustainable waste management strategy.

Influence of subsoil and soil volume on the accumulation of nickel by Odontarrhena corsica grown on a serpentine soil.

Odontarrhena corsica was grown for three months on Chrome loam topsoil and subsoil from near Reisterstown, MD, to examine the effects of varying soil masses (2.8 and 5.6 kg pot-1) and soil layers (topsoil vs. subsoil) on plant growth and Ni accumulation. The subsoil position effect was simulated by placing a pot of topsoil on top of a pot filled with subsoil. Shoot Ni concentrations were similar for all treatments at 7 g Ni kg-1. Shoot yield was significantly higher in the 5.6 kg treatments compared to the 2.8 kg treatments (>18 g pot-1 vs. ∼12 g pot-1) and also greater in the topsoil treatment compared to the subsoil treatment (24.0 g pot-1 vs. 18.6 g pot-1), resulting in significantly higher phytomining. Soil depth had no statistically significant effect on shoot and root yield. Subsoil fertilization increased yield (25.8 g pot-1 vs. 19.7 g pot-1), enough to suggest that further research is warranted to optimize Ni phytomining. This study confirms the importance of soil volume and root access to the subsoil when evaluating the potential for Ni phytomining by Odontarrhena species. The use of small pots may lead to an underestimation of phytomining potential.

Prior studies have demonstrated that greater soil volume enhances Ni phytomining by Odontarrhena Ni hyperaccumulators. This study investigated Ni phytomining in both serpentine subsoil and topsoil, and examined the role of soil volume in this context. Our findings indicate that root access to Ni-rich serpentine subsoil significantly enhances Ni phytomining.

A new hyperaccumulator plant (Spergularia rubra) for the decontamination of mine tailings through electrokinetic-assisted phytoextraction.

The screening of new effective metal hyperaccumulators is essential for the development of profitable phytoremediation projects in highly degraded environments such as mining areas. The goal of this research was to analyze the phytoextraction potential of the native plant Spergularia rubra to decontaminate and eventually recover metals (phytomining) from the mine tailings (belonging to an abandoned Pb/Zn Spanish mine) in which it grows spontaneously. To do so, the ability of this plant species to accumulate metals was evaluated both under natural conditions and through simple and electrokinetically assisted phytoextraction tests using alternating current and different combinations of voltage gradient (1/2 V cm-1) and application time (6/12 h per day). The complete duration of the greenhouse trial was 64 days, although alternating current was applied only during the last 14 days. The results obtained demonstrated the exceptional effectiveness of S. rubra for metal hyperaccumulation and growth without affecting toxicity in highly contaminated mining waste. Zn was the metal accumulated to a higher extent in the shoots, reaching concentrations up to 17,800 mg kg-1; Pb was mainly accumulated in the roots reaching a maximum concentration of 8709 mg kg-1. Cu and Cd were accumulated to a lesser extent but the bioconcentration factors were much >1. It has been proved that S. rubra is a hyperaccumulator species for Zn and Cd both in natural and greenhouse conditions and, very probably, Pb in wild conditions. The application of AC current did not significantly increase metal concentrations in plant tissues but it was able to increase the aerial biomass of S. rubra by 49.8 %. As a result, the phytoextraction yields of all metals were significantly improved as compared to wild conditions (up to 86 % for Zn). It could open new expectations about the economic viability of recovering high-value metals from mine tailings.

Rare earth elements detoxification mechanism in the hyperaccumulator Dicranopteris linearis: [silicon-pectin] matrix fixation.

Dicranopteris linearis is the best-known hyperaccumulator species of rare earth elements (REEs) and silicon (Si), capable of dealing with toxic level of REEs. Hence, this study aimed to clarify how D. linearis leaves cope with excessive REE stress, and whether Si plays a role in REE detoxification. The results show that lanthanum (La - as a representative of the REEs) stress led to decreased biomass and an increase of metabolism related to leaf cell wall synthesis and modification. However, the La stress-induced responses, especially the increase of pectin-related gene expression level, pectin polysaccharides concentration, and methylesterase activity, could be mitigated by Si supply. Approximately 70% of the Si in D. linearis leaves interacted with the cell walls to form organosilicon Si-O-C linkages. The Si-modified cell walls contained more hydroxyl groups, leading to a more efficient REE retention compared to the Si-free ones. Moreover, this [Si-cell wall] matrix increased the pectin-La accumulation capacity by 64%, with no effect on hemicellulose-La and cellulose-La accumulation capacity. These results suggest that [Si-pectin] matrix fixation is key in REE detoxification in D. linearis, laying the foundation for the development of phytotechnological applications (e.g., REE phytomining) using this species in REE-contaminated sites.

Plant growth-promoting bacteria in phytoremediation of metal-polluted soils: Current knowledge and future directions.

Soil metal contamination is a major concern due to the ever-rising number of areas afflicted worldwide and the detrimental effects of metals to the environment and human health. Due to their non-biodegradability and toxicity, it is paramount to prevent further metal contamination and remediate the thousands of contaminated sites across the planet. Yet, conventional reclamation based on physical and chemical methods is often expensive, impractical, and triggers secondary pollution issues. Hence, microbe-aided phytoremediation has been gaining significant traction due to its environment-friendly character, cost-effectiveness, and the breakthroughs achieved during the past few decades. Microorganisms are an essential part of natural ecosystems and play a crucial role in their restoration. Indeed, plant-microbe associations in metal-polluted soils are pivotal for plants to tolerate metal toxicity and thrive in these harsh environments. Therefore, improving the understanding of this intricate relationship is invaluable for boosting phytoremediation. In this review, we focus on the potential of plant growth promoting bacteria (PGPB) for enhancing phytoremediation of metal-polluted soils. We discuss the mechanisms employed by microbes to promote plant growth and assist the removal or immobilization of metals in soil, thereby enhancing phytoextraction and phytostabilization, respectively. Microbe-mediated metal removal and detoxification through processes entailing adsorption, chelation, transformation, and precipitation, to list but a few, are also critically examined. Moreover, this work covers the direct and indirect mechanisms used by PGPB to facilitate plant acquisition of nutrients like nitrogen and phosphorus, supply and regulate phytohormones, and exert control over antagonistic microorganisms. Lastly, we provide an outlook on the future directions of microbe-aided phytoremediation and phytomining. Clearly, to fully validate and comprehend the potential of PGPB-aided phytoremediation, a considerable shift from bench-scale to field research is necessary. What's more, it is envisaged that recent advancements in genetic engineering may soon help furthering the efficiency of microbe-assisted phytoremediation.

Phytoaccumulation potential of nine plant species for selected nutrients, rare earth elements (REEs), germanium (Ge), and potentially toxic elements (PTEs) in soil.

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. Fagopyrum esculentum and Cannabis sativa were better accumulators of most elements investigated except for chromium, germanium, and silicon that were better accumulated by Zea mays, the only grass species. F. esculentum accumulated 9, 24, and 10% of Copper, Chromium, and Rare Earth Elements in the mobile/exchangeable element fraction of the soils while Z. mays and C. sativa accumulated amounts of Cr and Ge ∼58 and 17% (for Z. mays) and 20 and 9% (for C. sativa) of the mobile/exchangeable element fraction of the soils. Results revealed co-accumulation potential for some elements e.g., (1) Si, Ge, and Cr, (2) Cu and Pb, (3) P, Ca, Co, and REEs based on chemical similarities/sources of origin.

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.

The potential of Blepharidium guatemalense for nickel agromining in Mexico and Central America.

The aim of this study was to assess the potential of the woody nickel hyperaccumulator species Blepharidium guatemalense (Standl.) Standl. for agromining in southeastern Mexico. Pot trials consisting of nickel dosing (0, 20, 50, 100, and 250 mg Ni kg-1), and synthetic and organic fertilization were conducted. Field trials were also undertaken with different harvesting regimes of B. guatemalense. Foliar nickel concentrations increased significantly with rising nickel additions, with a 300-fold increase at 250 mg Ni kg-1 treatment relative to the control. Synthetic fertilization strongly increased nickel uptake without any change in plant growth or biomass, whereas organic fertilization enhanced plant shoot biomass with a negligible effect on foliar nickel concentrations. A 5-year-old stand which was subsequently harvested twice per year produced the maximum nickel yield tree-1 yr-1, with an estimated total nickel yield of 142 kg ha-1 yr-1. Blepharidium guatemalense is a prime candidate for nickel agromining on account of its high foliar Ni concentrations, high bioconcentration (180) and translocation factors (3.3), fast growth rate and high shoot biomass production. Future studies are needed to test the outcomes of the pot trials in the field. Extensive geochemical studies are needed to identify potential viable agromining locations. Novelty Statement Our research team is a pioneer in the discovery of metal hyperaccumulator plants in Mesoamerica with at least 13 species discovered in the last 2 years. This study is the first to assess the potential of nickel agromining (phytomining) in Mexico (and in all the American continent), using one of the strongest nickel hyperaccumulators reported so far. The promising results of this study are the basis for optimal agricultural management of Blepharidium guatemalense.

Imaging Zn and Ni distributions in leaves of different ages of the hyperaccumulator Noccaea caerulescens by synchrotron-based X-ray fluorescence.

Mapping of leaves of hyperaccumulators can provide insights into the mechanisms these species utilize to accumulate high metal concentrations. We used synchrotron-based X-ray fluorescence (SXRF) to perform Zn and Ni imaging in leaves of different ages of Noccaea caerulescens. A mature leaf of the related non-hyperaccumulator Thlaspi arvense was also imaged. The concentrations of Zn, Ni, Co, and Cr in N. caerulescens grown on an ultramafic soil were 9-, 10-, 12-, and 3-fold higher than T. arvense. N. caerulescens showed an exceptional ability to accumulate Zn from the soil, posing a bioconcentration factor of 6.7. T. arvense had Zn and Ni distributed uniformly in the leaf blade with doubling fluorescence counts in the tip and margins, suggesting a strategy to excrete metals and avoid toxicity. On the other hand, N. caerulescens displayed distinctly different Zn and Ni accumulation patterns, regardless of the age or metal concentration in the leaves. Zinc was mainly distributed in the cells surrounding the central and secondary veins. Nickel accumulated in the margins and tips of the leaf blade. Given the time required to image large leaves in synchrotron facilities, small leaves can be used to represent the leaf distribution of Zn and Ni in N. caerulescens.

Effects of exogenous citric acid on the concentration and spatial distribution of Ni, Zn, Co, Cr, Mn and Fe in leaves of Noccaea caerulescens grown on a serpentine soil.

The aim of this study was to show the potential of citric acid in increasing the concentration of Ni, Zn, Co, Cr, Mn and Fe in leaves of the hyperaccumulator Noccaea caerulescens. Synchrotron x-ray fluorescence (µ-XRF) images were collected to assess the distribution of metals in leaves. Applying citric acid (20 mmol kg-1) to soil increased in 14-, 10-, 7-, 2- and 1.4- fold the concentration of Mn, Fe, Co, Ni, and Cr, respectively, compared to the control. The µ-XRF imaging revealed that Ni and Zn were not spatially correlated across the leaf. We observed a clear partitioning of Zn between veins and surrounding leaf cells while Ni was more evenly distributed between veins and leaf blade. The accumulation of metals in citric acid treated plants did not change the Ni and Zn distribution pattern in leaves but altered the Mn distribution. It seems that Mn reached toxic concentrations in leaves and we hypothesize that a mechanism driven by transpiration through the xylem was used to excrete the metal. Our results show that citric acid can enhance metal accumulation by N. caerulescens and have impact for soil remediation by either decreasing the time for clean up or increasing the access to non-labile pools of metals in soil.

[Key processes and progress in phytomining of nickel contaminated soils: a review].

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.

Phytoremediation of Heavy Metal-Contaminated Sites: Eco-environmental Concerns, Field Studies, Sustainability Issues, and Future Prospects.

Environmental contamination due to heavy metals (HMs) is of serious ecotoxicological concern worldwide because of their increasing use at industries. Due to non-biodegradable and persistent nature, HMs cause serious soil/water pollution and severe health hazards in living beings upon exposure. HMs can be genotoxic, carcinogenic, mutagenic, and teratogenic in nature even at low concentration. They may also act as endocrine disruptors and induce developmental as well as neurological disorders, and thus, their removal from our natural environment is crucial for the rehabilitation of contaminated sites. To cope with HM pollution, phytoremediation has emerged as a low-cost and eco-sustainable solution to conventional physicochemical cleanup methods that require high capital investment and labor alter soil properties and disturb soil microflora. Phytoremediation is a green technology wherein plants and associated microbes are used to remediate HM-contaminated sites to safeguard the environment and protect public health. Hence, in view of the above, the present paper aims to examine the feasibility of phytoremediation as a sustainable remediation technology for the management of metal-contaminated sites. Therefore, this paper provides an in-depth review on both the conventional and novel phytoremediation approaches; evaluates their efficacy to remove toxic metals from our natural environment; explores current scientific progresses, field experiences, and sustainability issues; and revises world over trends in phytoremediation research for its wider recognition and public acceptance as a sustainable remediation technology for the management of contaminated sites in the twenty-first century.

A review on global metal accumulators-mechanism, enhancement, commercial application, and research trend.

The biosphere is polluted with metals due to burning of fossil fuels, pesticides, fertilizers, and mining. The metals interfere with soil conservations such as contaminating aqueous waste streams and groundwater, and the evidence of this has been recorded since 1900. Heavy metals also impact human health; therefore, the emancipation of the environment from these environmental pollutants is critical. Traditionally, techniques to remove these metals include soil washing, removal, and excavation. Metal-accumulating plants could be utilized to remove these metal pollutants which would be an alternative option that would simultaneously benefit commercially and at the same time clean the environment from these pollutants. Commercial application of pollutant metals includes biofortification, phytomining, phytoremediation, and intercropping. This review discusses about the metal-accumulating plants, mechanism of metal accumulation, enhancement of metal accumulation, potential commercial applications, research trends, and research progress to enhance the metal accumulation, benefits, and limitations of metal accumulators. The review identified that the metal accumulator plants only survive in low or medium polluted environments with heavy metals. Also, more research is required about metal accumulators in terms of genetics, breeding potential, agronomics, and the disease spectrum. Moreover, metal accumulators' ability to uptake metals need to be optimized by enhancing metal transportation, transformation, tolerance to toxicity, and volatilization in the plant. This review would benefit the industries and environment management authorities as it provides up-to-date research information about the metal accumulators, limitation of the technology, and what could be done to improve the metal enhancement in the future.

Are Fungal Endophytes Merely Mycorrhizal Copycats? The Role of Fungal Endophytes in the Adaptation of Plants to Metal Toxicity.

The contamination of soil with toxic metals is a worldwide problem, resulting in the disruption of plant vegetation and subsequent crop production. Thus, remediation techniques for contaminated soil and water remain a constant interest of researchers. Phytoremediation, which utilizes plants to remove or stabilize contaminants, is perceived to be a promising strategy. However, phytoremediation's use to date is limited because of constraints associated with such factors as slow plant growth rates or metal toxicity. Microbial-assisted phytoremediation serves as an alternative solution, since the impact of the microbial symbionts on plant growth and stress tolerance has frequently been described. Endophytic fungi occur in almost every plant in the natural environment and contribute to plant growth and tolerance to environmental stress conditions. Although this group of symbiotic fungi was found to form association with a wide range of hosts, including the non-mycorrhizal Brassicaceae metallophytes, their role in the response of plants to metal toxicity has not been thoroughly elucidated to date. This review summarizes the current knowledge regarding the role of endophytic fungi in the tolerance of plants to toxic metals and highlights the similarities and differences between this group of symbiotic fungi and mycorrhizal associations in terms of the survival of the plant during heavy metal stress.

Can organic amendments replace chemical fertilizers in nickel agromining cropping systems in Albania?

In Albania, ultramafic outcrops cover 11% of the surface and have the potential to support nickel phytomining. In a large-scale in-situ experiment on an ultramafic Vertisols in Pojskë we are studying the influence of agronomical practices on Ni phytoextraction yield of Odontarrhena chalcidica (syn. Alyssum murale). Three cropping systems were compared in three plots in 2016-2017; POJ-1 Plot (0.3 ha) was established with plants that had germinated spontaneously without any treatments; POJ-2 plot (0.3 ha) was covered by plants that had germinated spontaneously and was treated with mineral fertilizer (N50P50K50 kg ha-1); and POJ-3 Plot (400 m2) was divided in four sub plots, where O. chalcidica was planted at a density of 4 plants m-2 on which, we neither applied fertilizer, nor NPK fertilizer (N65P65K65), pig (FPM; N260:P105:K260 + 15 kg ha-1N, P, K) or chicken manure (FCHM; N260:P390:K260 +15 kg ha-1 N, P, K. Irrigation and mechanical control of weeds was done on POJ-3. After 8 months, shoot Ni concentration, biomass, and Ni yields were higher in O. chalcidica treated with manure and the cost of biomass production was smaller. Nickel yield was more promising (145 kg ha-1) than in previous field trials. This study highlights that, using manure, the Ni yield increases Ni phytomining net values, thus agromining can become an economically justifiable agricultural cropping system.

The effects of rhenium accumulation on Indian mustard.

Rhenium (Re) is one of Earth's scarcest and more largely scattered elements, with an estimate concentration of 0.4-0.6 µg kg-1 in the upper crust. Still, considerable concentrations of bioavailable ReO4- ions are often found, particularly in copper-molybdenum mines, where their uptake by plants of these regions has been reported. Yet, the impact of Re on plants remains a question mark, as the only available knowledge derives from a limited investigation carried out over 60 years ago. The aim of this study was to evaluate the ecophysiological response of Brassica juncea, a species known to endure and accumulate various metals, to a broad range of Re concentrations. B. juncea plants were allowed to grow and on a substrate amended with KReO4 to attain soil Re levels ranging from 0 to 80 mg kg-1. Plants were collected 45 days after sowing for analysis. The results have shown that greater Re levels reduce growth, photosynthetic activity, soluble carbohydrate mobilization, and protein contents, and increase the plant's oxidative stress (anthocyanins, H2O2, lipid peroxidation) and corresponding response (ascorbic acid, superoxide dismutase activity). Nevertheless, B. juncea exhibited a remarkable ability to endure and uptake Re, featuring shoot Re concentrations that ranged from 1615 to 24,987 mg kg-1 among the 5 and 80 mg kg-1 treatments.