Prospecting for rare earth element (hyper)accumulators in the Paris Herbarium using X-ray fluorescence spectroscopy reveals new distributional and taxon discoveries.

BACKGROUND: Rare earth elements (REEs) are increasingly crucial for modern technologies. Plants could be used as a biogeochemical pathfinder and a tool to extract REEs from deposits. However, a paucity of information on suitable plants for these tasks exists. METHODS: We aimed to discover new REE-(hyper)accumulating plant species by performing an X-ray fluorescence (XRF) survey at the Herbarium of the Muséum national d'Histoire naturelle (MNHN, Paris, France). We selected specific families based on the likelihood of containing REE-hyperaccumulating species, using known taxa that accumulate REEs. A total of 4425 specimens, taken in the two main evolutionary lineages of extant vascular plants, were analysed, including the two fern families Blechnaceae (n = 561) and Gleicheniaceae (n = 1310), and the two flowering plant families Phytolaccaceae (n = 1137) and Juglandaceae (n = 1417). KEY RESULTS: Yttrium (Y) was used as a proxy for REEs for methodological reasons, and a total of 268 specimens belonging to the genera Blechnopsis (n = 149), Dicranopteris (n = 75), Gleichenella (n = 32), Phytolacca (n = 6), Carya (n = 4), Juglans (n = 1) and Sticherus (n = 1) were identified with Y concentrations ranging from the limit of detection (LOD) >49 µg g-1 up to 1424 µg g-1. Subsequently, analysis of fragments of selected specimens by inductively coupled plasma atomic emission spectroscopy (ICP-AES) revealed that this translated to up to 6423 µg total REEs g-1 in Dicranopteris linearis and up to 4278 µg total REEs g-1 in Blechnopsis orientalis which are among the highest values ever recorded for REE hyperaccumulation in plants. It also proved the validity of Y as an indicator for REEs in XRF analysis of herbarium specimens. The presence of manganese (Mn) and zinc (Zn) was also studied by XRF in the selected specimens. Mn was detected in 1440 specimens ranging from the detection limit at 116 µg g-1 up to 3807 µg g-1 whilst Zn was detected in 345 specimens ranging from the detection limit at 77 µg g-1 up to 938 µg g-1. CONCLUSIONS AND IMPLICATIONS: This study led to the discovery of REE accumulation in a range of plant species, substantially higher concentrations in species known to be REE hyperaccumulators, and records of REE hyperaccumulators outside of the well-studied populations in China.

DNA-SIP delineates unique microbial communities in the rhizosphere of the hyperaccumulator Sedum alfredii which are beneficial to Cd phytoextraction.

Rhizo-microbe recruited by hyperaccumulating plants are crucial for the extraction of metals from contaminated soils. It is important, but difficult, to identify the specific rhizosphere microbes of hyperaccumulators shaped by root exudation. Continuous 13CO2 labeling, microbial DNA-based stable isotope probing (DNA-SIP), and high throughput sequencing were applied to identify those rhizosphere microorganisms using exudates from the Cd hyperaccumulator Sedum alfredii. In contrast to its non-hyperaccumulating ecotype (NAE), the hyperaccumulating ecotype (HAE) of S. alfredii strongly changed the rhizosphere environment and extracted a 5-fold higher concentration of Cd from contaminated soil. Although both HAE and NAE harbored Streptomyces, Massilia, Bacillus, and WPS-2 Uncultured Bacteria with relative abundance of more than 1% in the rhizosphere associated with plant growth and immunity, the HAE rhizosphere specifically recruited Rhodanobacter (2.66%), Nocardioides (1.16%), and Burkholderia (1.01%) through exudates to benefit the extraction of Cd from soil. Different from the bacterial network with weak cooperation in the NAE rhizosphere, a closed-loop bacterial network shaped by exudates was established in the HAE rhizosphere to synergistically resist Cd. This research reveals a specific rhizosphere bacterial community induced by exudates assisted in the extraction of Cd by S. alfredii and provides a new perspective for plant regulation of the rhizo-microbe community beneficial for optimizing phytoremediation.

Rhizospheric soil chromium toxicity and its remediation using plant hyperaccumulators.

The hyper-accumulation of chromium in its hexavalent form is treated as a hazardous soil pollutant at industrial and mining sites. Excessive accumulation of Cr6+ in soil threatens the environmental health and safety of living organisms. Out of two stable forms of chromium, Cr6+ is highly responsible for ecotoxicity. The expression of the high toxicity of Cr6+ at low concentrations in the soil environment indicates its lethality. It is usually released into the soil during various socio-economic activities. Sustainable remediation of Cr6+ contaminated soil is of utmost need and can be carried out by employing suitable plant hyperaccumulators. Alongside the plant's ability to sequester toxic metals like Cr6+, the rhizospheric soil parameters play a significant role in this technique and are mostly overlooked. Here we review the application of a cost-effective and eco-friendly remediation technology at hyperaccumulators rhizosphere to minimize the Cr6+ led soil toxicity. The use of selected plant species along with effective rhizospheric activities has been suggested as a technique to reduce Cr6+ toxicity on soil and its associated biota. This soil rectification approach may prove to be sustainable and advantageous over other possible techniques. Further, it may open up new solutions for soil Cr6+ management at polluted sites.

Phytoremediation is an eco-friendly technology that has been widely used for the treatment of Cr⁶⁺ contaminated soils. Most of the phytoremedial studies either focus on the ability of plant hyperaccumulators alone or in association with rhizospheric microbes for the successful remediation of Cr⁶⁺. The current study lays emphasis on different soil parameters and interactions (both biotic and abiotic) at the plant rhizosphere that is much essential for providing a sustainable remedial solution for Cr⁶⁺ contaminated soils.

Diversity and activity of soil biota at a post-mining site highly contaminated with Zn and Cd are enhanced by metallicolous compared to non-metallicolous Arabidopsis halleri ecotypes.

Hyperaccumulators' ability to take up large quantities of harmful heavy metals from contaminated soils and store them in their foliage makes them promising organisms for bioremediation. Here we demonstrate that some ecotypes of the zinc hyperaccumulator Arabidopsis halleri are more suitable for bioremediation than others, because of their distinct influence on soil biota. In a field experiment, populations originating from metal-polluted and unpolluted soils were transplanted to a highly contaminated metalliferous site in Southern Poland. Effects of plant ecotypes on soil biota were assessed by measurements of feeding activity of soil fauna (bait-lamina test) and catabolic activity and functional diversity of soil bacteria underneath A. halleri plants (Biolog® ECO plates). Chemical soil properties, plant morphological parameters, and zinc concentration in shoots and roots were additionally evaluated. Higher soil fauna feeding activity and higher bacterial community functional diversity were found in soils affected by A. halleri plants originating from metallicolous compared to non-metallicolous ecotypes. Differences in community-level physiological profiles further evidenced changes in microbial communities in response to plant ecotype. These soil characteristics were positively correlated with plant size. No differences in zinc content in shoots and roots, zinc translocation ratio, and plant morphology were observed between metallicolous and non-metallicolous plants. Our results indicate strong associations between A. halleri ecotype and soil microbial community properties. In particular, the improvement of soil biological properties by metallicolous accessions should be further explored to optimize hyperaccumulator-based bioremediation technologies.

Gene Identification, expression analysis and molecular docking of ATP sulfurylase in the selenization pathway of Cardamine hupingshanensis.

BACKGROUND: ATP sulfurylase (ATPS) is a crucial enzyme for the selenate assimilation pathway in plants. RESULTS: In this study, genome-wide and comparative analyses of ATPS in Cardamine hupingshanensis, including sequence and structural analyses, were performed. The expression of ChATPS gene family members in C. hupingshanensis under selenium (Se) stress was also investigated, and our results suggest that ChATPS1-2 play key roles in the response to Se stress. Nine ATPS genes were found from C. hupingshanensis, which share highly conserved sequences with ATPS from Arabidopsis thaliana. In addition, we performed molecular docking of ATP sulfurylase in complex with compounds ATP, selenate, selenite, sulfate, and sulfite. ChAPS3-1 was found to have stronger binding energies with all compounds tested. Among these complexes, amino acid residues Arg, Gly, Ser, Glu, and Asn were commonly present. CONCLUSION: Our study reveals the molecular mechanism of C. hupingshanensis ATP sulfurylase interacting with selenate, which is essential for understanding selenium assimilation. This information will guide further studies on the function of the ChATPS gene family in the selenium stress response and lay the foundation for the selenium metabolic pathway in higher plants.

Bioremediation of potentially toxic elements of sewage sludge using sunflower (Heliantus annus L.) in greenhouse and field conditions.

The bioremediation of sewage sludge, containing potentially toxic elements (heavy metals), by the hyperaccumulator sunflower (Helianthus annus L.), was determined in greenhouse (G) and field (F) conditions in Isfahan, Iran. The soil pots, mixed with dried sewage sludge at 0, 15, 30, 45, and 60 mg/kg, were planted with sunflower seedlings and kept in the greenhouse (G) and in the field (F). Different soil physicochemical and plant biochemical properties including heavy metal uptake of nickel (Ni), chromium (Cr), lead (Pb), and cadmium (Cd) were determined. In contrast with the soil pH, soil salinity, organic matter, nitrogen, and not soil CaCO3, were significantly enhanced by increasing sewage sludge. Sewage sludge was significant on plant uptake of Ni (2.27-4.25 mg/kg), Cr (3.27-4.75 mg/kg), Cd (13.85-15.27 mg/kg), and total chlorophyll (1.69-1.99 mg/g) in the greenhouse, and plant uptake of Ni (1.75-2.75 mg/kg) and Cd (1.37-2.25 mg/kg), and chlorophyll b (0.06-0.26 mg/g), total chlorophyll (0.57-1.16 mg/g), and carotenoids (1.10-1.61 mg/g) in the field. Although Pb was not significantly affected by sewage sludge, it showed the highest bioaccumulation factor of 0.96 at 15 mg/kg. Interestingly, the heavy metals were all positively and significantly correlated with each other and with plant carotenoids, similar to the positive and significant correlations between Pb with chlorophyll a and b. Accordingly, the increased levels of carotenoids, acting as antioxidant, may be an indicator of oxidative stress. Sunflower plants can be used as an efficient method for the bioremediation of the soils polluted with sewage sludge including Ni, Cr, and Cd.

Molecular identification and evaluation of gamma irradiation effect on modulating heavy metals tolerance in some of novel endophytic fungal strains.

Heavy metal (HM) pollution is a worldwide environmental issue. Given the urgent need to develop more powerful approaches for effective phytoremediation of HMs, isolation of novel endophytic strains from hyperaccumulator plants having potent HM tolerance is the main objective in this research. Moreover, the recovered strains were characterized and subjected to radiation mutagenesis to enhance their tolerance to HMs. Among 105 isolates, Alternaria alternata AUMC14431 was identified as the most effective Cd+2 tolerant strain having high recorded tolerance index (TI) (76.24%); in addition, the recorded minimum inhibitory concentration (MIC) was 300 ppm. Meanwhile, Chaetomium globosum AUMC14432 was identified as the most effective Pb+2 and Ni+2 tolerant strain having high recorded TI (97.46 and 93.34%, respectively); in addition, the evaluated MICs were 250 and 200 ppm, respectively. UV and gamma irradiation of the tested strains enhanced their Cd+2 and Pb+2 tolerance significantly (P ≤ 0.05). Meanwhile, irradiation had a negative impact on Ni+2 tolerance of C. globosum. The mutation incidence at the molecular level arising from exposure to irradiation was investigated. Genomic DNA of both the wild and mutated endophytic strains were isolated followed by random amplified polymorphic DNA (RAPD-PCR) analysis, using two short primers. A remarkable difference in DNA gel pattern between the wild type and mutated strains was observed. In conclusion, the novel isolated and irradiated endophytic strains, A. alternata S5 and C. globosum El26, having high efficiency in Cd+2 and Pb+2 tolerance, respectively, are considered to be prospective and powerful bioremediation candidates for potential application in microbially assisted phytoremediation.

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.

Contamination of vegetables with heavy metals across the globe: hampering food security goal.

Food Security is a multifaceted aspect covering nutrition, availability, sufficiency, accessibility and safety. Millennium Development Goals as framed by United Nations focused to attain food security for all. The biggest hindrance in attaining food security was less productivity due to lack of enough resources. In order to increase the availability and produce sufficient food, malpractices like growing food on contaminated land or using untreated wastewater for irrigation came into play. Such practices have led to the transfer of heavy metals, pathogens and other harmful toxins to food crops. Various studies across the world have documented high concentration of heavy metals in vegetable crops. Root tubers and succulent stems are hyperaccumulators of heavy metals and thus tend to pose health hazard to the consuming population. In many instances the content of toxic metals in vegetables is much beyond permissible limits. Hazard quotient assessment in various studies has shown that consumption of these vegetables can be toxic to both adults and children. So, the question arises are we really attaining the global food security? There is a need to find a solution to produce sufficient, safe and nutritious food for the civilization so as to meet the goal of "zero hunger".

Magnetic characterizations of nickel hyperaccumulating plants (Planchonella oxyhedra and Rinorea bengalensis) from Halmahera, Indonesia.

Magnetic minerals, such as magnetite and hematite, have been reported to be present, in particular, leaves as biogenic particles. The magnetic minerals and properties of Ni hyperaccumulators have not previously been reported in the literature. This study aimed to characterize the magnetic properties of two Ni hyperaccumulating plant species, R. bengalensis and P. oxyhedra, which grow in an ultramafic region on Halmahera Island, Indonesia. For comparison, similar characterization was carried out on two non-hyperaccumulating plant species which grow in the same region. Concentrations of Ni, Fe, and Mn in the leaves of the hyperaccumulating plants were measured using atomic absorption spectroscopy (AAS) and their magnetic properties were characterized using measurements of magnetic susceptibility, low temperature magnetic susceptibility, and hysteresis curves. The results show that, compared to the non-hyperaccumulating plants, the Ni hyperaccumulating plants have higher concentrations of Ni and similar concentration of Fe. The magnetic susceptibilities of hyperaccumulating plants are positive, and those of non-hyperaccumulating plants are negative. This suggests that the abundance of Ni, rather than Fe, may control the magnetic properties of Ni hyperaccumulating plants. This probable connection between Ni concentration and plant magnetic properties could be advantageous for identifying hyperaccumulators, and should, therefore, be explored further.

The identification of indigenous Cu and As metallophytes in the Lepanto Cu-Au Mine, Luzon, Philippines.

The mining activities in the Lepanto Cu-Au Mine which is situated within the Mankayan Mineral District in the Philippines have exposed the arsenic (As)-rich copper (Cu)-gold (Au) and polymetallic ores to surface conditions. Cu and As dispersal into nearby soils and waters could pose health hazards to the natural ecosystems and human settlements. The study focused on the identification of indigenous metallophytes thriving in the area as well as the bioavailability of Cu and As in soils and its implication to the growth of the indigenous plants. Particular interests were on plant species that are capable of Cu and As absorption and have potential applications to mine rehabilitation. The samples were analyzed for total Cu and As contents. The soil samples were also subjected to different physicochemical analyses such as pH, organic matter, and nutrient content. Fern species had relatively high Cu and As contents in their biomass than other plant species found in the study area. The Cu and As concentrations in the plants might have been strongly influenced by the bioavailability of the metal and metalloid which were dependent on the physicochemical properties of the soil such as pH, organic matter, and nutrient contents. These identified metallophytes namely Dicranopteris linearis, Histiopteris incisa, Pityrogramma calomelanos, Pteris vittata, Nephrolepis hirsutula, Pteris sp., Pinus sp., Thysanolaena latifolia, and Melastoma malabathricum have tolerated the different Cu and As concentrations in the soil thus could be useful and effective for ecological restoration as an option to post-mining rehabilitation.

Phosphorus Enhances Cr(VI) Uptake and Accumulation in Leersia hexandra Swartz.

The effects of P supplementation on chromium(VI) uptake by Leersia hexandra Swartz were studied using pot-culture experiment. P-deficiency and zero-P addition controls were included. The Cr(VI) uptake followed Michaelis-Menten kinetics. Compare with the control, the P-supply decreased the Michaelis constant (Km) by 16.9% and the P-deficiency decreased the maximum uptake velocity (Vmax) by 18%, which indicated no inhibition and competition between P and Cr(VI) uptake by L. hexandra. Moreover, there were a synergistic action between P and Cr(VI) suggests that Cr(VI) uptake by the roots of L. hexandra may be an active process. The bioconcentration factor (BCF) and the transport factor (TF') increased with the increase in P supply. The highest BCF was 3.6-folds higher than the control, indicating that the additional P contribute to a higher ability of L. hexandra transporting Cr from root to the aboveground parts.

Advances in microbe-assisted reclamation of heavy metal contaminated soils over the last decade: A review.

Contamination of agricultural soils with trace metals present lethal consequences in terms of diverse ecological and environmental problems that entail entry of metal in food chain, soil deterioration, plant growth suppression, yield reduction and alteration in microbial community. Metal polluted soils have become a major concern for scientists around the globe. Phytoremediation involves the hyperaccumulation of metals in different plant parts. Phytoremediation of metals from polluted soils could be enhanced through inoculation with metal resistant plant growth promoting (PGP) bacteria. These PGP bacteria not only promote plant growth but also enhance metal uptake by plants. There are a number of reports in the literature where PGP bacterial inoculation improves metal accumulation in different plant parts without influencing plant growth. Therefore, there is a need to select PGP bacterial strains which possess the potential to improve plant growth as well as expedite the phytoremediation of metals. In this review, we have discussed the mechanisms possessed by PGP bacteria to promote plant growth and phytoremediation of metals. The central part of this review deals with the recent advances in microbial assisted-phytoremediation of metals.

Local adaptation is associated with zinc tolerance in Pseudomonas endophytes of the metal-hyperaccumulator plant Noccaea caerulescens.

Metal-hyperaccumulating plants, which are hypothesized to use metals for defence against pests and pathogens, provide a unique context in which to study plant-pathogen coevolution. Previously, we demonstrated that the high concentrations of zinc found in leaves of the hyperaccumulator Noccaea caerulescens provide protection against bacterial pathogens, with a potential trade-off between metal-based and pathogen-induced defences. We speculated that an evolutionary arms race between zinc-based defences in N. caerulescens and zinc tolerance in pathogens might have driven the development of the hyperaccumulation phenotype. Here, we investigate the possibility of local adaptation by bacteria to the zinc-rich environment of N. caerulescens leaves and show that leaves sampled from the contaminated surroundings of a former mine site harboured endophytes with greater zinc tolerance than those within plants of an artificially created hyperaccumulating population. Experimental manipulation of zinc concentrations in plants of this artificial population influenced the zinc tolerance of recovered endophytes. In laboratory experiments, only endophytic bacteria isolated from plants of the natural population were able to grow to high population densities in any N. caerulescens plants. These findings suggest that long-term coexistence with zinc-hyperaccumulating plants leads to local adaptation by endophytic bacteria to the environment within their leaves.

Prospecting for hyperaccumulators of trace elements: a review.

Specific plant species that can take up and accumulate abnormally high concentrations of elements in their aboveground tissues are referred to as "hyperaccumulators". The use of this term is justified in the case of enormous element-binding capacity of plants growing in their natural habitats and showing no toxicity symptoms. An increasing interest in the study of hyperaccumulators results from their potential applications in environmental biotechnology (phytoremediation, phytomining) and their emerging role in nanotechnology. The highest number of plant species with confirmed hyperaccumulative properties has been reported for hyperaccumulators of nickel, cadmium, zinc, manganese, arsenic and selenium. More limited data exist for plants accumulating other elements, including common pollutants (chromium, lead and boron) or elements of commercial value, such as copper, gold and rare earth elements. Different approaches have been used for the study of hyperaccumulators - geobotanical, chemical, biochemical and genetic. The chemical approach is the most important in screening for new hyperaccumulators. This article presents and critically reviews current trends in new hyperaccumulator research, emphasizing analytical methodology that is applied in identification of new hyperaccumulators of trace elements and its future perspectives.

Thermal Characteristics of Hyperaccumulator and Fate of Heavy Metals during Thermal Treatment of Sedum plumbizincicola.

Thermal treatment is one of the most promising disposal techniques for heavy metal- (HM)-enriched hyperaccumulators. However, the thermal characteristics and fate of HMs during thermal treatment of hyperaccumulator biomass need to be known in detail. A horizontal tube furnace was used to analyze the disposal process of hyperaccumulator biomass derived from a phyto-extracted field in which the soil was moderately contaminated with heavy metals. Different operational conditions regarding temperature and gas composition were tested. A thermo-dynamic analysis by advanced system for process engineering was performed to predict HM speciation during thermal disposal and SEM-EDS, XRD and sequential chemical extraction were used to characterize the heavy metals. The recovery of Zn, Pb and Cd in bottom ash decreased with increasing temperature but recovery increased in the fly ash. Recovery of Zn, Pb and Cd fluctuated with increasing air flow rate and the metal recovery rates were higher in the fly ash than the bottom ash. Most Cl, S, Fe, Al and SiO2 were found as alkali oxides, SO2, Fe2(SO4)3, iron oxide, Ca3Al2O6, K2SiO3 and SiO2 instead of reacting with HMs. Thus, the HMs were found to occur as the pure metals and their oxides during the combustion process and as the sulfides during the reducing process.

The potential of zeolite nanocomposites in removing microplastics, ammonia, and trace metals from wastewater and their role in phytoremediation.

Nanocomposites are emerging as a new generation of materials that can be used to combat water pollution. Zeolite-based nanocomposites consisting of combinations of metals, metal oxides, carbon materials, and polymers are particularly effective for separating and adsorbing multiple contaminants from water. This review presents the potential of zeolite-based nanocomposites for eliminating a range of toxic organic and inorganic substances, dyes, heavy metals, microplastics, and ammonia from water. The review emphasizes that nanocomposites offer enhanced mechanical, catalytic, adsorptive, and porosity properties necessary for sustainable water purification techniques compared to individual composite materials. The adsorption potential of several zeolite-metal/metal oxide/polymer-based composites for heavy metals, anionic/cationic dyes, microplastics, ammonia, and other organic contaminants ranges between approximately 81 and over 99%. However, zeolite substrates or zeolite-amended soil have limited benefits for hyperaccumulators, which have been utilized for phytoremediation. Further research is needed to evaluate the potential of zeolite-based composites for phytoremediation. Additionally, the development of nanocomposites with enhanced adsorption capacity would be necessary for more effective removal of pollutants.

Reducing Heavy Metal Contamination in Soil and Water Using Phytoremediation.

The increase in industrialization has led to an exponential increase in heavy metal (HM) soil contamination, which poses a serious threat to public health and ecosystem stability. This review emphasizes the urgent need to develop innovative technologies for the environmental remediation of intensive anthropogenic pollution. Phytoremediation is a sustainable and cost-effective approach for the detoxification of contaminated soils using various plant species. This review discusses in detail the basic principles of phytoremediation and emphasizes its ecological advantages over other methods for cleaning contaminated areas and its technical viability. Much attention has been given to the selection of hyperaccumulator plants for phytoremediation that can grow on heavy metal-contaminated soils, and the biochemical mechanisms that allow these plants to isolate, detoxify, and accumulate heavy metals are discussed in detail. The novelty of our study lies in reviewing the mechanisms of plant-microorganism interactions that greatly enhance the efficiency of phytoremediation as well as in discussing genetic modifications that could revolutionize the cleanup of contaminated soils. Moreover, this manuscript discusses potential applications of phytoremediation beyond soil detoxification, including its role in bioenergy production and biodiversity restoration in degraded habitats. This review concludes by listing the serious problems that result from anthropogenic environmental pollution that future generations still need to overcome and suggests promising research directions in which the integration of nano- and biotechnology will play an important role in enhancing the effectiveness of phytoremediation. These contributions are critical for environmental scientists, policy makers, and practitioners seeking to utilize phytoremediation to maintain the ecological stability of the environment and its restoration.

Heavy metal tolerance and accumulation in the Brassica species (Brassica chinensis var. parachinensis and Brassica rapa L.): A pot experiment.

This study delves into the heavy metal tolerance and accumulation capabilities of Brassica chinensis var. parachinensis (B. chinensis) and Brassica rapa L. (B. rapa) in a pot experiment, specifically focusing on cadmium (Cd), chromium (Cr) and lead (Pb). Agricultural topsoils were spiked with varying concentrations of these heavy metals (0 mg/kg, 75 mg/kg, 150 mg/kg, 225 mg/kg and 300 mg/kg) for each element. The experiment involved cultivating 15 pots each of B. chinensis and B. rapa over 60 days. Results indicated that both Brassica species experienced delayed germination, with B. chinensis exhibiting a significant drop in germination percentage to 53 % at the highest concentration (300 mg/kg), while B. rapa showed a tendency for an increased germination percentage of up to 80 % at elevated metal concentrations; however, these differences were not statistically significant. Both B. chinensis and B. rapa demonstrated a stable decline in growth rate from 0.05 cm/day to 0.04 cm/day with increasing heavy metal concentrations, and the he reduction in relative growth rate was significant at the highest concentration compared to the control. The stress tolerance index revealed a significant decrease in plant heights for B. chinensis, in contrast to the stable performance of B. rapa, showcasing the tolerance of B. rapa to toxic conditions. Despite insignificant differences in fresh biomass due to metal treatments, B. chinensis consistently yielded higher biomass, yet it had a lower edible index due to its higher root biomass. Leaf areas increased significantly in both species at higher soil treatments, while root lengths remained unchanged, suggesting their resilience to elevated heavy metal concentrations. Analysis of plant tissues (leaves, stems and roots) using ICP-OES revealed that B. rapa accumulated the highest Cd concentration (864 mg/kg), whereas B. chinensis accumulated the highest Pb concentration (953 mg/kg) in root parts. Both species significantly accumulated Cr in roots, demonstrating a sequestration mechanism. These findings suggest that both species, particularly, B. rapa possess strong tolerance and accumulation capabilities for non-essential heavy metals, making them potential hyperaccumulators for green remediation techniques in toxic soil environments. Understanding the molecular mechanisms driving these responses and validating phytoremediation potential in real-world scenarios is essential for developing sustainable soil management practices.

Pervasive influence of heavy metals on metabolic pathways is potentially relieved by hesperidin to enhance the phytoremediation efficiency of Bassia scoparia.

Hesperidin (HSP), a flavonoid, is a potent antioxidant, metal chelator, mediator of signaling pathways, and regulator of metal uptake in plants. The study examined the ameliorative effects of HSP (100 µM) on Bassia scoparia grown under excessive levels of heavy metals (zinc (500 mg kg-1), copper (400 mg kg-1), cadmium (100 mg kg-1), and chromium (100 mg kg-1)). The study clarifies the underlying mechanisms by which HSP lessens metabolic mayhem to enhance metal stress tolerance and phytoremediation efficiency of Bassia scoparia. Plants manifested diminished growth because of a drop in chlorophyll content and nutrient acquisition, along with exacerbated deterioration of cellular membranes reflected in elevated reactive oxygen species (ROS) production, lipid peroxidation, and relative membrane permeability. Besides the colossal production of cytotoxic methylglyoxal, the activity of lipoxygenase was also higher in plants under metal toxicity. Conversely, hesperidin suppressed the production of cytotoxic ROS and methylglyoxal. Hesperidin improved oxidative defense that protected membrane integrity. Hesperidin caused a more significant accumulation of osmolytes, non-protein thiols, and phytochelatins, thereby rendering metal ions non-toxic. Hydrogen sulfide and nitric oxide endogenous levels were intricately maintained higher in plants treated with HSP. Hesperidin increased metal accumulation in Bassia scoparia and thereby had the potential to promote the reclamation of metal-contaminated soils.