Mechanisms of Spirodela polyrhiza tolerance to FGD wastewater-induced heavy-metal stress: Lipidomics, transcriptomics, and functional validation

Unlike terrestrial angiosperm plants, the freshwater aquatic angiosperm duckweed (Spirodela polyrhiza) grows directly in water and has distinct responses to heavy-metal stress. Plantlets accumulate metabolites, including lipids and carbohydrates, under heavy-metal stress, but how they balance metabolite levels is unclear, and the gene networks that mediate heavy-metal stress responses remain unknown. Here, we show that heavy-metal stress induced by flue gas desulfurization (FGD) wastewater reduces chlorophyll contents, inhibits growth, reduces membrane lipid biosynthesis, and stimulates membrane lipid degradation in S. polyrhiza, leading to triacylglycerol and carbohydrate accumulation. In FGD wastewater-treated plantlets, the degraded products of monogalactosyldiacylglycerol, primarily polyunsaturated fatty acids (18:3), were incorporated into triacylglycerols. Genes involved in early fatty acid biosynthesis, β-oxidation, and lipid degradation were upregulated while genes involved in cuticular wax biosynthesis were downregulated by treatment. The transcription factor gene WRINKLED3 (SpWRI3) was upregulated in FGD wastewater-treated plantlets, and its ectopic expression increased tolerance to FGD wastewater in transgenic Arabidopsis (Arabidopsis thaliana). Transgenic Arabidopsis plants showed enhanced glutathione and lower malondialdehyde contents under stress, suggesting that SpWRI3 functions in S. polyrhiza tolerance of FGD wastewater-induced heavy-metal stress. These results provide a basis for improving heavy metal-stress tolerance in plants for industrial applications.

Novel Phosphate Transporter-B PvPTB1;1/1;2 Contribute to Efficient Phosphate Uptake and Arsenic Accumulation in As-Hyperaccumulator Pteris vittata

Arsenic (As) contamination in soil poses a potential threat to human health via crop uptake. As-hyperaccumulator Pteris vittata serves as a model plant to study As uptake and associated mechanisms. This study focuses on a novel P/AsV transport system mediated by low-affinity phosphate transporter-B 1 family (PTB1) in P. vittata. Here, we identified two plasma-membrane-localized PTB1 genes, PvPTB1;1/1;2, in vascular plants for the first time, which were 4.4-40-fold greater in expression in P. vittata than in other Pteris ferns. Functional complementation of a yeast P-uptake mutant and enhanced P accumulation in transgenic Arabidopsis thaliana confirmed their role in P uptake. Moreover, the expression of PvPTB1;1/1;2 facilitated the transport and accumulation of As in both yeast and A. thaliana shoots, demonstrating a comparable AsV uptake capacity. Microdissection-qPCR analysis and single-cell transcriptome analysis collectively suggest that PvPTB1;1/1;2 are specifically expressed in the epidermal cells of P. vittata roots. PTB1 may play a pivotal role in efficient P recycling during phytate secretion and hydrolysis in P. vittata roots. In summary, the dual P transport mechanisms consisting of high-affinity Pht1 and low-affinity PTB1 may have contributed to the efficient P/As uptake in P. vittata, thereby contributing to efficient phytoremediation for As-contaminated soils.

Chemical analysis of wetland plants to evaluate the bioaccumulation and metabolism of hexachlorocyclohexane (HCH)

Hexachlorocyclohexanes (HCH) belong to the banned pesticides with short-time production and use during the last century. However, the consequences of this short period are still present as persistent environmental contamination. This study represents the large lab-scale experiment focused on the HCH accumulation and metabolism in selected wetland plants (Juncus effuses, Typha latifolia, Phragmites australis) and trees (Alnus glutinosa) after the exposure to the technical mix of HCH isomers (t-HCH) or δ-HCH at three different concentration. During the three-month exposure, morphological (biomass, height, relative chlorophyll content) and physiological (photosynthetic measurements - photosynthetic rate, stomatal conductance, transpiration and dark transpiration) parameters were measured to assess the HCH effect on plant's growth. The results showed that all selected plant species supported HCH removal from the soil. The total removal efficiency was lower for the t-HCH than for δ-HCH exposure, and the best results were provided by Alnus glutinosa tree. Also, no isomer preference was observed in plants exposed to t-HCH. Most HCH remained accumulated in the root biomass, and mainly α-HCH and δ-HCH were transported to the above-ground parts due to their physicochemical properties. Simultaneously, HCH uptake and metabolization to chlorobenzenes (CB) and chlorophenols (CP) occur. Non-targeted analysis showed that CP could be conjugated to glucose and malonyl in plant tissue, and secondary plant metabolism is affected positively and negatively after exposure to t-HCH depending on plant species and chemical concentration. Luteolin, quercetin and quercetin-3-O-glucoside found common to all species showed quantitative changes due to HCH. Nevertheless, most morphological and physiological parameters were adversely affected without statistical significance. This large-scale study provides information on the fate of HCH in the soil-plant system, the suitability of selected plants and their adaptation to chemical stress for use in the phytoremediation process.

Effects of sulfur nanoparticles on rhizosphere microbial community changes in oilseed rape plantation soil under mercury stress

In the present study, experiments were conducted to assess the influence of nanoscale sulfur in the microbial community structure of metallophytes in Hg-contaminated rhizosphere soil for planting rapeseed. The results showed that the richness and diversity of the rhizobacteria community decreased significantly under Hg stress, but increased slightly after SNPs addition, with a reduction in the loss of Hg-sensitive microorganisms. Moreover, all changes in the relative abundances of the top ten phyla influenced by Hg treatment were reverted when subjected to Hg + SNPs treatment, except for Myxococcota and Bacteroidota. Similarly, the top five genera, whose relative abundance decreased the most under Hg alone compared to CK, increased by 19.05%-54.66% under Hg + SNPs treatment compared with Hg alone. Furthermore, the relative abundance of Sphingomonas, as one of the dominant genera for both CK and Hg + SNPs treatment, was actively correlated with plant growth. Rhizobacteria, like Pedobacter and Massilia, were significantly decreased under Hg + SNPs and were positively linked to Hg accumulation in plants. This study suggested that SNPs could create a healthier soil microecological environment by reversing the effect of Hg on the relative abundance of microorganisms, thereby assisting microorganisms to remediate heavy metal-contaminated soil and reduce the stress of heavy metals on plants.

Uptake of perfluoroalkyl substances PFOS and PFOA by free-floating hydrophytes Pistia stratiotes L. and Eichhornia crassipes (Mart.) Solms

The phytoremediation potential of floating aquatic plants to accumulate and remove two common PFAS from contaminated water was investigated. Free-floating hydrophytes Eichhornia crassipes and Pistia stratiotes were grown in water spiked with 0.5, 1, or 2 ppm perfluorooctanoic acid (PFOA) or perfluorooctanesulfonic acid (PFOS) for seven days. Both species were able to accumulate PFOA and PFOS in this time frame, with translocation factors (TF) ranging from 0.13 to 0.57 for P. stratiotes and 0.18 to 0.45 for E. stratiotes, respectively. E. crassipes accumulated a greater amount of PFOA and PFOS than P. stratiotes, with 178.9 ug PFOA and 308.5 ug PFOS removed by E. crassipes and 98.9 ug PFOA and 137.8 ug PFOS removed by P. stratiotes at the highest concentrations. Root tissue contained a higher concentration of PFOA and PFOS than shoot tissue in both species, and the concentration of PFOS was generally significantly higher than PFOA in both E. crassipes and P. stratiotes, with concentrations of 15.39 and 27.32 ppb PFOA and 17.41 and 80.62 ppb PFOS in shoots and roots of P. stratiotes and 12.59 and 37.37 ppb PFOA and 39.92 and 83.40 ppb PFOS in shoots and roots of E. crassipes, respectively. Both species may be candidates for further phytoremediation studies in aquatic ecosystems.

Assessment of medicinal plants colonizing abundantly on metal-enriched fly ash deposits: phytoremediation prospective

Heavy metal-enriched fly ash (FA) deposits are recognized as hazardous contaminated sites on the earth, which pollute our ecosystems. Consequently, the present investigation was carried out to explore the phytoremediation potential of naturally growing medicinal plants in the FA dumpsite. This present study chose two native medicinal plants i.e., Bacopa monnieri and Acmella oleracea found to be naturally colonizing abundantly on FA dumpsite to assess heavy metal accumulation. FA sample of B. monnieri thriving sites found to have metal content in order Mn (216.6)> Cr (39.27)> Zn (20.8)> Ni (16.1)> Cu (15.03)> Co (6.7)> Pb (5.43) whereas for A. oleracea FA dumpsites, the order of metal availability was Mn (750.3)> B (54.5)>Cr (37.2)>Zn (31.33)> Cu (18.7)> Ni (16.93)> Co (7.7)>Pb (4.23). In B. monnieri, higher concentrations of Cr and Mn were observed in the shoot in comparison to the root, indicative of its potential as a hyperaccumulator plant. Conversely, in A. oleracea, greater amounts of Pb were detected in the shoot relative to the root. Hence, it is recommended that B. monnieri and A. oleracea grow on such heavy metal-enriched substrates should be avoided for medicinal purposes; however, these plants can be used for phytoremediation purposes.

Hydrothermal treatment of alkaline red mud and sewage sludge: formation of a soil-like matrix

Increasing attention has been focused on the comprehensive utilisation of alkaline red mud (RM) derived from the aluminium industry. Phytoremediation serves as an effective strategy, but it is limited by the drawbacks of red mud. This study proposed 'co-hydrothermally treating red mud and sewage sludge (SS)' for producing a soil-like matrix, and explored the impacts of SS addition on the characteristics of hydrothermal solid and liquid products of RM. The results showed that the introduction of SS could improve the characteristics of hydrothermal products, including pH, the particle aggregation, and organic components. During hydrothermal treatment, the acid components released from SS could neutralise the alkalinity of RM, reducing the pH of hydrothermal product from 10.1 (without SS) to and 8.2 (80% SS), respectively. With the increase of addition ratio of SS, the main range of particle size distribution in hydrothermal solid products changed from 0.1∼1 μm to 10∼100 μm, suggesting the positive role of SS in improving the particle aggregation. XRD analysis showed that the addition of SS hindered the mineral crystallization of RM during hydrothermal treatment, while FTIR and XPS analysis confirmed that SS could serve as a 'supply source' of organic components, which created favourable conditions for hydrothermal solid products as soil-like matrix. The addition ratio of SS presented the negative correlation with the pH value and positive relative with chemical oxygen demand of hydrothermal liquid products. The hydrothermal liquid product modified by SS was beneficial to further improve soil-like matrix. The strategy of co-hydrothermal treating RM and SS to produce the soil-like matrix could massively consume solid wastes, which is a prospective approach to deal with the trouble of the aluminium industry and sewage treatment plants.

Exploring the combined effect of heavy metals on accumulation efficiency of Salix alba raised on lead and cadmium contaminated soils

The present study illustrated that Salix alba can accumulate high level of Pb and Cd in different plant parts, with maximum accumulation in roots followed by stem and leaves in the order Cd > Pb > Cd + Pb. The phytoremediation evaluation factors such as bioconcentration factor (BCF) and translocation factor (TF) was higher for Cd over Pb in all plant parts, further the BCF for both Pb and Cd was maximum in root (BCF > 1) followed by stem and leaves. Higher accumulation of Cd over the Pb was observed inside the plant tissues due to Cd mimics with other elements and gets transported through respective transporters. The combined treatment of Pb and Cd affected the bioaccumulation at every treatment level suggesting the negative effect among both elements. Higher survival rate (>85%) was recorded up to 200mgPb/kg and 15mgCd/kg, while further increase in metal concentration reduced the plant efficiency to remediate contaminated soils, hence results in declined survival rate. The FTIR analysis revealed that Pb and Cd accumulation in plants induced changes in carboxy, amino, hydroxyl and phosphate groups that ultimately caused alteration in physiological and biochemical processes of plant and thus provided an insight to the interaction, binding and accumulation of heavy metals.

Perfluorooctanesulfonic Acid Alters the Plant's Phosphate Transport Gene Network and Exhibits Antagonistic Effects on the Phosphate Uptake

Per- and polyfluoroalkyl substances (PFASs), with significant health risks to humans and wildlife, bioaccumulate in plants. However, the mechanisms underlying plant uptake remain poorly understood. This study deployed transcriptomic analysis coupled with genetic and physiological studies using Arabidopsis to investigate how plants respond to perfluorooctanesulfonic acid (PFOS), a long-chain PFAS. We observed increased expressions of genes involved in plant uptake and transport of phosphorus, an essential plant nutrient, suggesting intertwined uptake and transport processes of phosphorus and PFOS. Furthermore, PFOS-altered response differed from the phosphorus deficiency response, disrupting phosphorus metabolism to increase phosphate transporter (PHT) transcript. Interestingly, pht1;2 and pht1;8 mutants showed reduced sensitivity to PFOS compared to that of the wild type, implying an important role of phosphate transporters in PFOS sensing. Furthermore, PFOS accumulated less in the shoots of the pht1;8 mutant, indicating the involvement of PHT1;8 protein in translocating PFOS from roots to shoots. Supplementing phosphate improved plant's tolerance to PFOS and reduced PFOS uptake, suggesting that manipulating the phosphate source in PFOS-contaminated soils may be a promising strategy for minimizing PFOS uptake by edible crops or promoting PFOS uptake during phytoremediation. This study highlighted the critical role of phosphate sensing and transport system in the uptake and translocation of PFOS in plants.

Growth and Phytochemistry of Cymbopogon citratus Stapf Inoculated with Plant Growth-Promoting Bacteria under Different Lead Levels

This study aimed to investigate the phytochemistry of lemongrass (Cymbopogon citratus) inoculated with Azospirillum brasilense and grown in lead (Pb)-contaminated soil to assess its responses to inoculation under different Pb levels. The experimental design was completely randomized in a 2 × 5 factorial scheme: two levels of A. brasilense (absence or presence) and five Pb levels. After four months of treatment, the following were analyzed: total and reducing sugars, total phenolic content, flavonoids, antioxidant activity, antioxidant enzymes, proline, and essential oil (EO) content and composition. Soil Pb levels and A. brasilense inoculation affected phytochemicals in lemongrass plants. Azospirillum inoculation reduced total sugars in the roots at all soil Pb levels, while increasing Pb levels favored a rise in sugar contents. There was an increase in flavonoid content in treatments associated with Pb and inoculated with A. brasilense. Antioxidant capacity was lower at lower Pb levels, regardless of bacterial inoculation. Enzymatic response was mainly affected by Pb concentrations between 50 and 100 mg kg-1 soil. EO content was influenced by soil Pb levels, with higher EO production at 500 mg Pb kg-1 soil and without A. brasilense inoculation. Overall, lemongrass cultivation in Pb-contaminated areas can be an alternative to phytoremediation and EO production for the industry.

Mitigation strategies for heavy metal toxicity and its negative effects on soil and plants

Heavy metal pollution threatens food security by accumulating in crops and soils, posing a significant challenge to modern agriculture due to its high toxicity. Urgent action is needed to restore affected agricultural fields. An efficient way to remove toxins is by bioremediation, which uses microorganisms. With the purpose of restoring soil in agriculture, this research attempts to assemble a consortium of microorganisms isolated from techno-genic soil. A number of promising strains, including Pseudomonas putida, Pantoea sp., Pseudomonas aeruginosa, Klebsiella oxytoca, and Agrobacterium tumefaciens were chosen based on their capacity to eliminate heavy metals from tests. Heavy metal removal (Cd, Hg, As, Pb, and Ni) and phytohormone production have been shown to be effective using consortiums (Pseudomonas aeruginosa, Klebsiella oxytoca, and Agrobacterium tumefaciens in a 1:1:2). In instances with mixed heavy-metal contamination, aeruginosa demonstrated efficacy because of its notable ability to absorb substantial quantities of heavy metals. The capacity of the cooperation to improve phytoremediation was investigated, with an emphasis on soil cleanup in agricultural areas. When combined with Sorghum bicolor L., it was able to remove roughly 16% As, 14% Hg, 32% Ni, 26% Cd, and 33% Pb from the soil.

Enhancing Native Plant Establishment in Mine Tailings under Drought Stress Conditions through the Application of Organo-Mineral Amendments and Microbial Inoculants

The implementation of phytoremediation strategies under arid and semiarid climates requires the use of appropriate plant species capable of withstanding multiple abiotic stresses. In this study, we assessed the combined effects of organo-mineral amendments and microbial inoculants on the chemical and biological properties of mine tailings, as well as on the growth of native plant species under drought stress conditions. Plants were cultivated in pots containing 1 kg of a mixture of mine tailings and topsoil (i.e., pre-mined superficial soil) in a 60:40 ratio, 6% marble sludge, and 10% sheep manure. Moreover, a consortium of four drought-resistant plant growth-promoting rhizobacteria (PGPR) was inoculated. Three irrigation levels were applied: well-watered, moderate water deficit, and severe water deficit, corresponding to 80%, 45%, and 30% of field capacity, respectively. The addition of topsoil and organo-mineral amendments to mine tailings significantly improved their chemical and biological properties, which were further enhanced by bacterial inoculation and plants' establishment. Water stress negatively impacted enzymatic activities in amended tailings, resulting in a significant decrease in acid and alkaline phosphatases, urease, and dehydrogenase activities. Similar results were obtained for bacteria, fungi, and actinomycete abundance. PGPR inoculation positively influenced the availability of phosphorus, total nitrogen, and organic carbon, while it increased alkaline phosphatase, urease (by about 10%), and dehydrogenase activity (by 50%). The rhizosphere of Peganum harmala showed the highest enzymatic activity and number of culturable microorganisms, especially in inoculated treatments. Severe water deficit negatively affected plant growth, leading to a 40% reduction in the shoot biomass of both Atriplex halimus and Pennisetum setaceum compared to well-watered plants. P. harmala showed greater tolerance to water stress, evidenced by lower decreases observed in root and shoot length and dry weight compared to well-watered plants. The use of bioinoculants mitigated the negative effects of drought on P. harmala shoot biomass, resulting in an increase of up to 75% in the aerial biomass in plants exposed to severe water deficit. In conclusion, the results suggest that the combination of organo-mineral amendments, PGPR inoculation, and P. harmala represents a promising approach to enhance the phytoremediation of metal-polluted soils under semiarid conditions.

Enhancing Phytoextraction Potential of Brassica napus for Contaminated Dredged Sediment Using Nitrogen Fertilizers and Organic Acids

Dredged sediment contaminated with heavy metals can be remediated through phytoremediation. The main challenge in phytoremediation is the limited availability of heavy metals for plant uptake, particularly in multi-contaminated soil or sediment. This study aimed to assess the effect of the nitrogen fertilizers (ammonium nitrate (AN), ammonium sulfate (AS), and urea (UR)), organic acids (oxalic (OA) and malic (MA) acids), and their combined addition to sediment on enhancing the bioavailability and phytoremediation efficiency of heavy metals. The sediment dredged from Begej Canal (Serbia) had high levels of Cr, Cd, Cu, and Pb and was used in pot experiments to cultivate energy crop rapeseed (Brassica napus), which is known for its tolerance to heavy metals. The highest accumulation and translocation of Cu, Cd, and Pb were observed in the treatment with AN at a dose of 150 mg N/kg (AN150), in which shoot biomass was also the highest. The application of OA and MA increased heavy metal uptake but resulted in the lowest biomass production. A combination of MA with N fertilizers showed high uptake and accumulation of Cr and Cu.

[Effect of EDDS Application on Soil Cu/Cd Availability and Uptake/transport by Castor]

To investigate the effect of chelating agents on plant uptake of heavy metals, castor (Ricinus communis L.) was used as the test plant. Soil culture and pot experiments were conducted to study the effects of different concentrations of ethylenediamine disuccinic acid (EDDS) on the forms of Cu and Cd in soil and their absorption and transport by castor. The results showed that the application of EDDS significantly increased the content of available Cu and Cd. After 15 days of cultivation, the available Cu and Cd concentrations in the soil increased by 43.01%-103.55% and 51.78%-69.43%, respectively. EDDS promoted the conversion of reducible Cu to weak acid extractable and increased the mobility of Cu. Meanwhile, the application of EDDS promoted the absorption, transport, and enrichment of Cu in castor. Under the application of 2.5 mmol·kg-1 EDDS and 5.0 mmol·kg-1 EDDS, the Cu concentrations in the shoots were 4.88 times and 16.65 times higher than that of the control (P< 0.05), and the Cu concentrations in the roots were 2.89 times and 3.60 times higher than that of the control (P< 0.05), respectively. The Cu transport coefficient significantly increased by 72.73% and 381.82% when treated with EDDS 2.5 and EDDS 5.0. Simultaneously, the phytoextraction of Cu in shoots, roots, and their sum were 14.08, 2.16, and 4.70 times higher than that of the control (P<0.05), respectively, when treated with EDDS 5.0. Furthermore, EDDS significantly increased the Cd concentrations in castor. When treated with EDDS 2.5 the shoots and roots increased by 15.15% and 57.42%, respectively, and the phytoextraction of total Cd significantly increased by 13.44%. Generally, the EDDS treatment could increase the available Cu and Cd in soil, promote the uptake of Cu and Cd, and improve the phytoremediation efficiency of castor. Among them, the addition of 5.0 mmol·kg-1 EDDS had the best effect for Cu, whereas the addition of 2.5 mmol kg-1 EDDS had a higher increase in the phytoextraction of Cd.

viminalis

Elevated concentrations of heavy metals result in soil degradation, a reduction in plant yields, and a lower quality of agricultural products, which directly endangers people, animals, and the ecosystem. The potential of three clones of Salix alba (347, NS 73/6, and B-44) and one genotype of S. viminalis for the phytoextraction of heavy metals was investigated, with the aim of identifying the most physiologically suitable willow genotypes for use in soil phytoremediation. The experiment was placed on the contaminated soil substrate collected in Kolubara Mining Basin (Serbia), enriched by high loads of heavy metal salts, and a control medium. Significant differences in the concentrations of heavy metals were recorded between the contaminated and control plant material, especially when it comes to nickel (Ni), copper (Cu), cadmium (Cd), and lead (Pb), confirming that S. alba and S. viminalis are hyperaccumulator species of heavy metals. Clone 347 shows the greatest uptake of Cd and chromium (Cr), and clone B-44 takes up these metals only to a lesser extent, while clone NS 73/6 shows a less pronounced uptake of Cr. The roots have the greatest ability to accumulate Ni and Pb, Cu is absorbed by all plant organs, while Cd is absorbed by the leaves. The organ that showed the greatest ability to accumulate heavy metals was the root, which means that willows have a limited power to translocate heavy metals to above-ground organs. The studied genotypes of S. alba have a higher potential for the phytostabilization of Cu and Cd, as well as the phytoextraction of Cd, compared with S. viminalis. The results confirm the assumption of differences between different willow genotypes in terms of the ability to phytoextract certain heavy metals from soil, which is important information when selecting genotypes for soil phytoremediation.

Phytostabilization of fly ash from a coalmine in Botswana and biovalorisation of the recovered Napier grass (Pennisetum purpureum Schumach.)

The disposal of fly ash (FA) from coal power plants polluting the air, soil, and groundwater is a major environmental concern. Phytoremediation to rehabilitate fly ash dumpsites is a promising alternative but has practical concerns about the disposal of harvested biomass. This study investigated the effect of supplementing fly ash with fresh sewage sludge (FSS), aged sewage sludge, food waste, and compost (COM) to enhance the phytoremediation potential of Napier grass and its subsequent utilization for ethanol production. The highest removal of Mn (1196.12 g ha-1) and Ni (128.06 g ha-1) from FA could be obtained when Napier is grown in the presence of FSS and inorganic fertilizer (NPK). In addition, the highest bioethanol yield (19.31 g L-1) was obtained from Napier grown in fly ash with COM + NPK, thus providing additional economic benefits aside from the remediation process. Given the significant levels of heavy metals present in the pulp and bio-slurry after ethanol production, further research is required in this area to determine the best ways to utilize this waste such as converting it into biochar.

Arabidopsis response to copper is mediated by density and root exudates: Evidence that plant density and toxic soils can shape plant communities

PREMISE

Plants grown at high densities show increased tolerance to heavy metals for reasons that are not clear. A potential explanation is the release of citrate by plant roots, which binds metals and prevents uptake. Thus, pooled exudates at high plant densities might increase tolerance. We tested this exclusion facilitation hypothesis using mutants of Arabidopsis thaliana defective in citrate exudation.

METHODS

Wild type Arabidopsis and two allelic mutants for the Ferric Reductase Defective 3 (FRD3) gene were grown at four densities and watered with copper sulfate at four concentrations. Plants were harvested before bolting and dried. Shoot biomass was measured, and shoot material and soil were digested in nitric acid. Copper contents were determined by atomic absorption.

RESULTS

In the highest-copper treatment, density-dependent reduction in toxicity was observed in the wild type but not in FRD3 mutants. For both mutants, copper concentrations per gram biomass were up to seven times higher than for wild type plants, depending on density and copper treatment. In all genotypes, total copper accumulation was greater at higher plant densities. Plant size variation increased with density and copper treatment because of heterogeneous distribution of copper throughout the soil.

CONCLUSIONS

These results support the hypothesis that citrate exudation is responsible for density-dependent reductions in toxicity of metals. Density-dependent copper uptake and growth in contaminated soils underscores the importance of density in ecotoxicological testing. In soils with a heterogeneous distribution of contaminants, competition for nontoxic soil regions may drive size hierarchies and determine competitive outcomes.

Cannabis Roots: Therapeutic, Biotechnological and Environmental Aspects

Since the legalization of recreational cannabis in Canada in 2018, the number of licenses for this crop has increased significantly, resulting in an increase in waste generated. Nevertheless, cannabis roots were once used for their therapeutic properties, indicating that they could be valued today rather than dismissed. This review will focus on both traditional therapeutic aspects and potential use of roots in modern medicine while detailing the main studies on active phytomolecules found in cannabis roots. The environmental impact of cannabis cultivation and current knowledge of the root-associated microbiome are also presented as well as their potential applications in biotechnology and phytoremediation. Thus, several high added-value applications of cannabis roots resulting from scientific advances in recent years can be considered to remove them from discarded residues.

Plant growth promoting bacteria and citric acid promote growth and cadmium phytoremediation in ryegrass

Based on the growth-promoting effect of plant growth promoting bacteria on plants and the mobilization of Cd by citric acid, an experiment was designed in which the combined treatment of Bacillus megaterium and citric acid promoted ryegrass to repair Cd-contaminated soil. This study aimed to evaluate the effects of different treatments on the antioxidant enzyme activity, photosynthesis intensity, Cd accumulation, and rhizosphere cadmium migration under cadmium contamination conditions. And the soil morphology and structure changes were studied by infrared spectroscopy FourierTransformInfrared(FT-IR) and scanning electron microscope Energy Dispersive Spectrometer(SEM-EDS) before and after different treatments. The results show that the combined treatment of Bacillus megaterium and citric acid significantly improved the oxidative stress defense and plant photosynthesis and increased of rye biomass. rye biomass 1.28 times higher than CK treatment. Joint treatment significantly increased the amount of shoot accumulation of Cd, 2.31 times higher than CK treatment, increased the migration and accumulation of cadmium. FTIR and SEM-EDS also showed that the organic constituents such as O-H, C-O and C-N in soils as a major mechanism for mobilization of the heavy metal Cd. Thus, the combined treatment of Bacillus megaterium and citric acid can promote plant growth, improve the damage to ryegrass caused by single organic acid addition, and improve the plant extraction efficiency, which is a feasible way to repair Cd-contaminated soil through activated extraction system.

Transcriptome Analysis Reveals Novel Insights into the Hyperaccumulator Phytolacca acinosa Roxb. Responses to Cadmium Stress

Cadmium (Cd) is a highly toxic heavy metal that causes serious damage to plant and human health. Phytolacca acinosa Roxb. has a large amount of aboveground biomass and a rapid growth rate, and it has been identified as a novel type of Cd hyperaccumulator that can be harnessed for phytoremediation. However, the molecular mechanisms underlying the response of P. acinosa to Cd2+ stress remain largely unclear. In this study, the phenotype, biochemical, and physiological traits of P. acinosa seeds and seedlings were analyzed under different concentrations of Cd2+ treatments. The results showed higher Cd2+ tolerance of P. acinosa compared to common plants. Meanwhile, the Cd2+ content in shoots reached 449 mg/kg under 10 mg/L Cd2+ treatment, which was obviously higher than the threshold for Cd hyperaccumulators. To investigate the molecular mechanism underlying the adaptability of P. acinosa to Cd stress, RNA-Seq was used to examine transcriptional responses of P. acinosa to Cd stress. Transcriptome analysis found that 61 genes encoding TFs, 48 cell wall-related genes, 35 secondary metabolism-related genes, 133 membrane proteins and ion transporters, and 96 defense system-related genes were differentially expressed under Cd2+ stress, indicating that a series of genes were involved in Cd2+ stress, forming a complex signaling regulatory mechanism. These results provide new scientific evidence for elucidating the regulatory mechanisms of P. acinosa response to Cd2+ stress and new clues for the molecular breeding of heavy metal phytoremediation.

Corrigendum: Fungal community remediate quartz tailings soil under plant combined with urban sludge treatments

[This corrects the article DOI: 10.3389/fmicb.2023.1160960.].

Determination of the Toxic Effects of Heavy Metals on the Morpho-Anatomical Responses of the Leaf of Typha latifolia as a Biomonitoring Tool

Typha latifolia leaves act as sensitive barometers for trace heavy metal pollution, as revealed by their pronounced anatomical responses in a constructed wetland. Monthly water samples and Typha latifolia leaf tissue were collected over three consecutive months in 2018 from the Burgas Lake wetlands (Taoura), northeast Algeria. While physical and chemical parameters improved after treatment, atomic absorption spectrometry (Perkin Elmer A Analyst 800 AAS) detected persistent trace levels of cadmium, chromium, and lead in both the treated water and leaf tissue, highlighting the need for continued phytoremediation efforts. Microscopic examination of leaf tissue exposed to these metals revealed distinct anatomical adaptations, including shrunken vascular bundles, altered cell shapes, and stomatal closure. These findings underscore Typha latifolia's effectiveness in accumulating heavy metals and its potential as a highly sensitive biomonitor for persistent pollution in lake ecosystems.

Differential response of biochar in mitigating salinity stress in periwinkle (Catharanthus roseus L.) as an ornamental-medicinal plant species

To investigate the effect of various levels of salinity and biochar on the growth and biochemical traits of Catharanthus roseus L., a medicinal plant, a factorial experiment with three levels of biochar (0, 2, and 4%) and four levels of salinity (0, 1,000, 2,000, and 3,000 mg/kg soil) was conducted in pots under greenhouse conditions, in three replications, 36 pots, and 6 plants/plot. Salinity reduced the vegetative and reproductive growth and Ca and K uptake, and chlorophyll content of the plants, and increased the Na+, Cl-, electrolyte leakage, and antioxidant enzyme (SOD, CAT, GPX) activities. Biochar improved all the vegetative and reproductive growth and biochemical traits of Catharanthus roseus L. and enhanced soil fertility. The application of biochar at the rate of 2% at all four levels of NaCl reduced the activity of antioxidants and decreased electrolyte leakage, reflecting the alleviation of salinity effects and the retention of cell health for survival. The application of biochar 2% was more effective than biochar 4% in alleviating salinity stress. Therefore, by using 2% biochar, it is possible to improve saline soils (soils containing 1,000 or 2,000 mg/kg NaCl) and grow periwinkle ornamental-medicinal plant in it. The plants showed acceptable performance at salinity levels of 1,000 or 2,000 mg/kg with biochar 2%.

Colonization and phytoremediation potential for Miscanthus sacchariflorus in copper tailings

A pot experiment was conducted to explore the effects of copper (Cu) tailings with various proportions in the substrate on seed germination and morphological traits of the plant. Concurrently, to identify the adaptive and tolerance strategies of the plant to Cu tailings, the uptake and accumulation of the plant to heavy metals, variations in soil enzymatic activities, and metal speciation in the blank, rhizospheric, and non-rhizospheric soils were estimated. Cu tailings at 25% proportion in the substrate exerted no significant negative effects on seed germination and seedling growth. However, Cu tailings at higher proportions (≧50%) inhibited seed germination and disturbed the plant physiological metabolism and growth. More biomass allocated to the plant roots could contribute to more heavy metals being immobilized, arresting their translocation from roots to shoots. This was accepted as a crucial defense mechanism for the plant against heavy metal co-contamination. The plant can improve the biological properties of Cu tailings in terms of enhanced invertase and phosphatase activities. And in turn, this can effectively alleviate heavy metal phytotoxicity. Simultaneously, it markedly decreased exchangeable Cu and Zn content in the rhizosphere in 25% Cu tailings treatments. In 50% Cu tailings treatment, no differences were observed in Zn speciation between rhizosphere and non-rhizosphere soils. In 75% Cu tailings, compared to the non-rhizosphere, an obvious reduction in exchangeable Cu in rhizosphere occurred, while an opposite tendency was demonstrated in carbonate-bound Zn. The plant could successfully colonize in Cu tailings, and represent a phytoremediation potential in Cu tailings.

Combined interactions of amino acids and organic acids in heavy metal binding in plants

This research focused on the different approaches to the transport and internal chelation of metals with amino acids and organic acids in plants. Therefore, in the first phase, the plants studied were identified the characteristics of the bioaccumulation factors. Steria pumila, Echium angustifolium, Typha angustifolia, Sisymbrium austriacum were identified as hyperaccumulators (Cd, Ni), accumulators (Pb, Sn, and Se), excluders (Cr, Hg). On the other hand, the Sisymbrium austriacum only showed the characteristic of the accumulator for Cr. In the second phase, the combined effects of amino acids and organic acids on the chelation of heavy metals in plants were tested by a multi-linear regression model. Related to our hypothesis, Amino acids; Gly and Leu (Cd), Trp and Ile (Pb), Asp, Ser, and Leu (Cr), Ser (Hg), Trp and Glu (Ni), Asp, Thr, and Gly (Sn), Asn and Leu (Se), Organic acids; Malonic and Malic acid (Cd), Malonic acid (Pb), Oxalic and Malic acid (Cr), Oxalic, Succinic, Citric and Butyric acid (Hg), Malonic and Malic acid (Ni), Malonic, Maleic, and Malic acid (Sn), Malonic and Citric acid (Se) were concluded that had combined effect for heavy metal's phytochelation ability into plants.

Metal-non-tolerant ecotypes of ectomycorrhizal fungi can protect plants from cadmium pollution

The application of mycorrhizal fungi as a bioaugmentation technology for phytoremediation of heavy metal (HM) contaminated soil has attracted widespread attention. In order to explore whether the adaptation of Pinus massoniana (P. massoniana) to metal polluted soil depends on the metal adaptation potential of their associated ectomycorrhizal fungi (ECMF), we evaluated the cadmium (Cd) tolerance of 10 ecotypes of Cenococcum geophilum (C. geophilum) through a membership function method, and P. massoniana seedlings were not (NM) or inoculated by Cd non-tolerant type (JaCg144), low-tolerant (JaCg32, JaCg151) and high-tolerant (JaCg205) isolates of C. geophilum were exposed to 0 and 100 mg·kg-1 for 3 months. The result showed that, each ecotype of C. geophilum significantly promoted the growth, photosynthesis and chlorophyll content, proline (Pro) content and the activity of peroxidase (POD) of P. massoniana seedlings, and decreased malonaldehyde (MDA) content and catalase (CAT) and superoxide dismutase (SOD) activity. The comprehensive evaluation D value of the tolerance to Cd stress showed that the order of the displaced Cd resistance of the four ecotypic mycorrhizal P. massoniana was: JaCg144 > JaCg151 > JaCg32 > JaCg205. Pearson correlation analysis showed that the Sig. value of the comprehensive evaluation (D) values of the strains and mycorrhizal seedlings was 0.077 > 0.05, indicating that the Cd tolerance of the the C. geophilum isolates did not affect its regulatory effect on the Cd tolerance of the host plant. JaCg144 and JaCg151 which are non-tolerant and low-tolerant ecotype significantly increased the Cd content in the shoots and roots by about 136.64-181.75% and 153.75-162.35%, indicating that JaCg144 and JaCg151 were able to effectively increase the enrichment of Cd from the soil to the root. Transcriptome results confirmed that C. geophilum increased the P. massoniana tolerance to Cd stress through promoting antioxidant enzyme activity, photosynthesis, and lipid and carbohydrate synthesis metabolism. The present study suggests that mental-non-tolerant ecotypes of ECMF can protect plants from Cd pollution, providing more feasible strategies for ectomycorrhizal-assisted phytoremediation.

On the rise: Development of a multi-tiered, indoor duckweed cultivation system

Duckweed species (Lemnaceae) are suitable for remediation and valorization of agri-feed industry wastewaters and therefore can contribute to a more sustainable, circular economy where waste is a resource. Industrial applications will, however, require space efficient cultivation methods that are not affected by prevailing weather conditions. Here, the development and operation of a multi-tiered duckweed bioreactor is described. The developed prototype bioreactor depicted in this paper is composed of four cultivation layers (1 m2 each) with integrated LED lighting (generating up to 150 μmol m-2  s-1 ), a system of pumps and valves to manage the recirculatory flow (2.5 L min-1 ) of wastewater, and an automatic harvesting system. Using a nutrient poor medium, good growth of the duckweed species Lemna minor was achieved in the bioreactor, and this was matched by strong nutrient depletion from the medium, especially for phosphorus (45-mg total phosphorus [TP] removed per m-2  day-1 ). A fully automatic harvesting arm reliably captured similar amounts of duckweed biomass across multiple harvesting cycles, revealing a future scenario whereby labor and interventions by human operators are minimized. Further developments to advance the system towards fully automated operation will include, for example, the use of specific nutrient sensors to monitor and control medium composition. It is envisaged that multi-tiered, indoor bioreactors can be employed in the agri-feed industry where wastewaters are, in many cases, continuously generated throughout the year and need remediating immediately to avoid costly storage. Given the extensive use of automation technology in conventional wastewater treatment plants, multi-tiered duckweed bioreactors can be realistically integrated within the operating environment of such treatment plants. PRACTITIONER POINTS: Duckweed is suitable for remediation and valorization of agri-feed wastewater. Industrial duckweed applications require space efficient cultivation methods. Development and operation of a multi-tiered duckweed bioreactor is detailed. Flow dynamics and automatic harvesting in the bioreactor are optimized. It is concluded that a multi-tiered bioreactor can be used in industry.

Effect of endophytic bacteria on the phytoremediation potential of halophyte Tamarix smyrnensis for Sb-contaminated soils

Phytoremediation, including bacteria-assisted phytoremediation, presents a promising technology for treating shooting range soils contaminated with toxic metalloids. In this study, a pot experiment was performed using the halophyte Tamarix smyrnensis and soil collected from a shooting range and artificially spiked at two different antimonite (Sb(III)) concentrations (50 mg/kg and 250 mg/kg) with the aim to explore the Sb phytoremediation of the halophyte. The effect of salt (0.3%) and Mn addition (300 ppm) on its remediation capacity was also investigated. Moreover, the root endophytic community of the halophyte was found able to remove Sb(III) and was periodically inoculated to the plants. The consortium application increased the Sb bioavailable fraction in the soil and enhanced the Sb accumulation in root and aerial parts (up to 50% and 55% respectively at high Sb(III) concentration) compared to the uninoculated plants. Moreover, the presence of Mn increased the translocation factor (21% increase for inoculated and 46% increase for uninoculated plants) while lower TF was observed at high Sb concentrations (0,2 and 0,07 was the lowest value at low and high Sb treatments respectively). The addition of salt, Mn and root endophytic bacteria aided the halophyte to cope with elevated Sb concentrations. The total chlorophyll concentration was higher in inoculated plants compared to the uninoculated ones in all treatments, implying the positive effects of endophytic inoculation. The halophyte T. smyrnensis with the aid of endophytic community presents a promising alternative for remediating shooting range soils especially in areas impacted by salinity.

Study on the migration behaviour of heavy metals at the improved mine soil-plant rhizosphere interface

With the increasing shortage of land resources and the aggravation of soil pollution in mining areas, the remediation of soil in abandoned mining areas has gradually attracted people's attention. The remediation of heavy metal contaminated soil in mining areas is the key to reduce the harm of heavy metals to the environment and human health. In this study, municipal sludge and phytoremediation technology were combined to investigate the migration and transformation of heavy metals at the soil-plant interface in improved mining areas through indoor pot experiments. The results showed that heavy metals in non-rhizosphere soil entered the rhizosphere environment with the growth of plants, leading to the increase of heavy metal content in rhizosphere soil. The cumulative amounts of Cu, Zn, Pb and Cd were 1299.32, 832.10, 347.89 and 71.34 mg/kg, respectively. The content of oxidized Cu and Zn decreased with increasing planting days, while the oxidized Pb and Cd showed an increasing trend. Under acidic conditions, H+ is easy to compete with heavy metal ions for exchangeable positions in the clay mineral layer, so that the reducible heavy metals are easy to be converted into exchangeable states. In this paper, the effects of various factors on the distribution of heavy metals were discussed by adjusting soil pH, adding humic acid and root exudates, so as to analyse the migration and transformation mechanism of heavy metals at the soil-plant interface, and provide a reliable theoretical basis for soil remediation in mining areas.

Current Status of Biotechnological Approaches to Enhance the Phytoremediation of Heavy Metals in India-A Review

Rising waste construction, agricultural actions, and manufacturing sewages all contribute to heavy metal accumulation in water resources. Humans consume heavy metals-contaminated substances to make sustenance, which equally ends up in the food circle. Cleaning of these vital properties, along with the prevention of new pollution, has long been required to evade negative strength consequences. Most wastewater treatment techniques are widely acknowledged to be costly and out of the grasp of governments and small pollution mitigation businesses. Utilizing hyper-accumulator plants that are extremely resilient to heavy metals in the environment/soil, phytoremediation is a practical and promising method for eliminating heavy metals from contaminated environments. This method extracts, degrades, or detoxifies harmful metals using green plants. The three phytoremediation techniques of phytostabilization, phytoextraction, and phytovolatilization have been used extensively for soil remediation. Regarding their ability to be used on a wide scale, conventional phytoremediation methods have significant limitations. Hence, biotechnological attempts to change plants for heavy metal phytoremediation methods are extensively investigated in order to increase plant effectiveness and possible use of improved phytoremediation approaches in the country of India. This review focuses on the advances and significance of phytoremediation accompanied by the removal of various harmful heavy metal contaminants. Similarly, sources, heavy metals status in India, impacts on nature and human health, and variables influencing the phytoremediation of heavy metals have all been covered.

Exploring the potential of bacterial-augmented floating treatment wetlands for the remediation of detergent-contaminated water

Due to industrialization and urbanization, the use of detergents inadvertently led to contamination of aquatic environments, thus posing potential threat to aquatic organisms and human health. One of the main components of detergents is linear alkylbenzene sulfonate (LAS), which can cause toxic effects on living organisms, particularly aquatic life in the environment. In this study, floating treatment wetlands (FTWs) mesocosms were developed and augmented with LAS-degrading bacteria. The plant species, Brachiaria mutica (Para grass), was vegetated to establish FTWs and bacterial consortium (1:1:1:1) of Pseudomonas aeruginosa strain PJRS20, Bacillus sp. BRRH60, Acinetobacter sp. strain CYRH21, and Burkholderia phytofirmans Ps.JN was augmented (free or immobilized) in these mesocosms. Results revealed that the FTWs removed LAS from the contaminated water and their augmentation with bacteria slightly increased LAS removal during course of the experiment. Maximum reduction in LAS concentration (94%), chemical oxygen demand (91%), biochemical oxygen demand (93%), and total organic carbon (91%) was observed in the contaminated water having FTWs augmented with bacterial consortium immobilized on polystyrene sheet. This study highlights that the FTWs supported with immobilized bacteria on polystyrene sheets can provide an eco-friendly and sustainable solution for the remediation of LAS-bearing water, especially for developing countries like Pakistan.

Integrated Assessment of Pb(II) and Cu(II) Metal Ion Phytotoxicity on Medicago sativa L., Triticum aestivum L., and Zea mays L. Plants: Insights into Germination Inhibition, Seedling Development, and Ecosystem Health

Environmental pollution with heavy metals has become a problem of major interest due to the harmful effects of metal ions that constantly evolve and generate serious threats to both the environment and human health through the food chain. Recognizing the imperative need for toxicological assessments, this study revolves around elucidating the effects of Pb(II) and Cu(II) ions on three plant species; namely, Medicago sativa L., Triticum aestivum L., and Zea mays L. These particular species were selected due to their suitability for controlled laboratory cultivation, their potential resistance to heavy metal exposure, and their potential contributions to phytoremediation strategies. The comprehensive phytotoxicity assessments conducted covered a spectrum of critical parameters, encompassing germination inhibition, seedling development, and broader considerations regarding ecosystem health. The key metrics under scrutiny included the germination rate, the relative growth of root and stem lengths, the growth inhibition index, and the tolerance index. These accurately designed experiments involved subjecting the seeds of these plants to an array of concentrations of PbCl2 and CuCl2 solutions, enabling an exhaustive evaluation of the phytotoxic potential of these metal ions and their intricate repercussions on these plant species. Overall, this study provides valuable insights into the diverse and dynamic responses of different plant species to Pb(II) and Cu(II) metal ions, shedding light on their adaptability and resilience in metal-contaminated environments. These findings have important implications for understanding plant-metal interactions and devising phytoremediation strategies in contaminated ecosystems.

Sorption of cadmium, chromium, lead, and vanadium from artificial wetlands using Lemna aequinoctialis

The efficacy of the lesser duckweed, Lemna aequinoctialis (Welw.), to remediate varying concentrations of cadmium, chromium, lead, and vanadium from an organo-metallic contaminated media was tested in artificial surface wetland mesocosm experiment. A 100 g of fresh-weight duckweed was introduced into each of the mesocosm, except for the control setup and monitored for 120 days while the metals removal rate was quantified using an atomic absorption spectrometer. A time-dependent and partial sorption of metals was observed with the highest removal rate recorded for cadmium (71.96%), followed by lead (69.23%), vanadium (55.22%), and chromium (41.64%). The uptake and bioaccumulation of metals were reflected in the increased plant biomass (p < 0.05, F = 97.12) and relative growth rate (p < 0.05, F = 1214.35) in duckweed. A coefficient (r2) of 0.951, 0.919, 0.970, and 0.967 was recorded for cadmium, chromium, lead, and vanadium respectively, indicating that the remediation of metals followed the first-order kinetic rate model. This study highlights the efficacy of the lesser duckweed to preferentially remediate metals in an organo-metallic complex medium for potential wastewater treatment in the petrochemical industry.

Likelihood of using phytoremediation for mine-tailing management in Chile

Chile has more than 750 mine tailings across the country, mainly distributed in the northern region, which also includes a biodiversity hotspot and the driest desert in the world. So far, tailing management has included chemical and physical stabilization of tailings, exclusively. This research examined the perceived likelihood of stakeholders, namely: Academia, Industry, environmental Non-Governmental Organizations, and Government officials, in the management of tailings and explored their attitudes toward the inclusion of plants and their associated microbes, as an additional stabilization technology, through an online questionnaire (n = 43). We aimed to answer What was the perceived likelihood of stakeholders for using phytoremediation for mine-tailing management in Chile? The consensus opinion across sectors is that there is general lack of proper tailings management in Chile. There is a critical willingness to incorporate phytoremediation, with a preference for using native plants. An absence of demonstrably successful phytoremediation projects, funding and access to suitable plants are perceived to be significant limitations. Local community involvement is considered key to successful restoration of tailings.

The Potential of Bioaugmentation-Assisted Phytoremediation Derived Maize Biomass for the Production of Biomethane via Anaerobic Digestion

Anthropogenic behaviors are causing the severe build-up of heavy metal (HM) pollutants in the environment, particularly in soils. Amongst a diversity of remediation technologies, phytoremediation is an environmentally friendly technology that, when coupling tolerant plants to selected rhizospheric microorganisms, can greatly stimulate HM decontamination of soils. Maize (Zea mays) is a plant with the reported capacity for HM exclusion from contaminated soil but also has energetic importance. In this study, Zea mays was coupled with Rhizophagus irregularis, an arbuscular mycorrhizal fungus (AMF), and Cupriavidus sp. strain 1C2, a plant growth-promoting rhizobacteria (PGPR), as a remediation approach to remove Cd and Zn from an industrial contaminated soil (1.2 mg Cd kg-1 and 599 mg Zn kg-1) and generate plant biomass, by contrast to the conservative development of the plant in an agricultural (with no metal pollution) soil. Biomass production and metal accumulation by Z. mays were monitored, and an increase in plant yield of ca. 9% was observed after development in the contaminated soil compared to the soil without metal contamination, while the plants removed ca. 0.77% and 0.13% of the Cd and Zn initially present in the soil. The resulting biomass (roots, stems, and cobs) was used for biogas generation in several biomethane (BMP) assays to evaluate the potential end purpose of the phytoremediation-resulting biomass. It was perceptible that the HMs existent in the industrial soil did not hinder the anaerobic biodegradation of the biomass, being registered biomethane production yields of ca. 183 and 178 mL of CH4 g-1 VS of the complete plant grown in non-contaminated and contaminated soils, respectively. The generation of biomethane from HM-polluted soils' phytoremediation-derived maize biomass represents thus a promising possibility to be a counterpart to biogas production in an increasingly challenging status of renewable energy necessities.

Prevalence of Cobalt in the Environment and Its Role in Biological Processes

Cobalt (Co) is an essential trace element for humans and other animals, but high doses can be harmful to human health. It is present in some foods such as green vegetables, various spices, meat, milk products, seafood, and eggs, and in drinking water. Co is necessary for the metabolism of human beings and animals due to its key role in the formation of vitamin B12, also known as cobalamin, the biological reservoir of Co. In high concentrations, Co may cause some health issues such as vomiting, nausea, diarrhea, bleeding, low blood pressure, heart diseases, thyroid damage, hair loss, bone defects, and the inhibition of some enzyme activities. Conversely, Co deficiency can lead to anorexia, chronic swelling, and detrimental anemia. Co nanoparticles have different and various biomedical applications thanks to their antioxidant, antimicrobial, anticancer, and antidiabetic properties. In addition, Co and cobalt oxide nanoparticles can be used in lithium-ion batteries, as a catalyst, a carrier for targeted drug delivery, a gas sensor, an electronic thin film, and in energy storage. Accumulation of Co in agriculture and humans, due to natural and anthropogenic factors, represents a global problem affecting water quality and human and animal health. Besides the common chelating agents used for Co intoxication, phytoremediation is an interesting environmental technology for cleaning up soil contaminated with Co. The occurrence of Co in the environment is discussed and its involvement in biological processes is underlined. Toxicological aspects related to Co are also examined in this review.

Investigation of the Persistence, Toxicological Effects, and Ecological Issues of S-Triazine Herbicides and Their Biodegradation Using Emerging Technologies: A Review

S-triazines are a group of herbicides that are extensively applied to control broadleaf weeds and grasses in agricultural production. They are mainly taken up through plant roots and are transformed by xylem tissues throughout the plant system. They are highly persistent and have a long half-life in the environment. Due to imprudent use, their toxic residues have enormously increased in the last few years and are frequently detected in food commodities, which causes chronic diseases in humans and mammals. However, for the safety of the environment and the diversity of living organisms, the removal of s-triazine herbicides has received widespread attention. In this review, the degradation of s-triazine herbicides and their intermediates by indigenous microbial species, genes, enzymes, plants, and nanoparticles are systematically investigated. The hydrolytic degradation of substituents on the s-triazine ring is catalyzed by enzymes from the amidohydrolase superfamily and yields cyanuric acid as an intermediate. Cyanuric acid is further metabolized into ammonia and carbon dioxide. Microbial-free cells efficiently degrade s-triazine herbicides in laboratory as well as field trials. Additionally, the combinatorial approach of nanomaterials with indigenous microbes has vast potential and considered sustainable for removing toxic residues in the agroecosystem. Due to their smaller size and unique properties, they are equally distributed in sediments, soil, water bodies, and even small crevices. Finally, this paper highlights the implementation of bioinformatics and molecular tools, which provide a myriad of new methods to monitor the biodegradation of s-triazine herbicides and help to identify the diverse number of microbial communities that actively participate in the biodegradation process.

in abandoned mine site

Tailings and mine dumps are often pollutant sources that pose serious environmental threats to surrounding areas. The use of pioneer vascular plants to extract or stabilize metals is considered among the more effective mine tailing reclamation techniques. The study aimed at evaluating the phytoremediation potential of Pinus halepensis in abandoned mine-tailing (SW-Sardinia, Italy). Plant ability to tolerate high Zn, Pb, and Cd concentration and their accumulation in roots and aerial parts were assessed at greenhouse conditions. Experiments were performed on 45 seedlings planted in different substrates (mine-tailings, mine-tailings compost-amended, and reference) and on 15 seedlings grown spontaneously in the contaminated mine site investigated with their own substrates. The phytostabilization potential of plant was evaluated through biological accumulation and translocation indexes together with plant survival and biometric parameters. The outcomes showed the adaptability of P. halepensis to grow and survive in contaminated substrates. Compost addition did not improve plant survival and growth, however, it enhanced total carbon and nitrogen contents of soil, restricted metal bioavailability, and accumulation in plant aerial parts. These findings highlight that P. halepensis may be considered for phytostabilization given the great potential to limit Zn, Pb, and Cd toxicity in plant tissues by applying compost amendment in metal contaminated mine sites.

in Cadmium-contaminated Soil]

To explore the effect of exogenous plant hormone spraying on the absorption of heavy metals by hyperaccumulated plants, Bidens pilosa L. was selected as the tested plant owing to the large biomass, short growth cycle, and high accumulation efficiency. Here, the effect of foliar spraying 6-benzylaminopurine (6-BA), salicylic acid (SA), and 24-epi-brassinosteroid (24-EBR) on the remediation of cadmium (Cd)-contaminated soil by B. pilosa L. was examined. The results showed:① the efficiency of the remediation in Cd-contaminated soil by B. pilosa L. was effectively enhanced after the spraying of all three kinds of exogenous plant hormones with appropriate concentrations. The spraying of the three exogenous plant hormones could promote the cadmium concentration in the leaves of B. pilosa L. to increase by 4.21%, 31.79%, and 14.89%; promote the translocation factor (TF) to increase by 9.67%, 18.83%, and 17.85%; promote the phytoextraction rates (PR) to increase by 15.36%, 32.33%, and 64.38%, respectively. ② The growth of B. pilosa L. was significantly promoted after the spraying of the three kinds of exogenous plant hormones with appropriate concentrations. The spraying of the three exogenous plant hormones could promote plant growth under cadmium stress, and the dry weight of the plant root, stem, and leaf was increased by 37.53%, 74.50%, and 104.02%, respectively. ③ The photosynthesis of B. pilosa L. was significantly enhanced after the spraying of the three kinds of exogenous plant hormones with appropriate concentrations. The chlorophyll concentration of the plant was significantly increased after foliar spraying with plant hormones, and the concentration of chlorophyll a was increased by 79.31%, 92.27%, and 51.12%; the photochemical quenching coefficient (qP) was increased by 11.32%, 89.16%, and 78.43%; and the non-photochemical quenching coefficient (NPQ) was increased by 51.71%, 241.12%, and 27.85%, respectively, after foliar spraying with appropriate concentrations of 6-BA, SA, and 24-EBR. ④ The antioxidant capacity of B. pilosa L. was significantly strengthened after the spraying of the three kinds of exogenous plant hormones with appropriate concentrations. The malondialdehyde (MDA) concentration of the plant was reduced by 62.41%, 68.67%, and 46.76% after the application of 6-BA, SA, and 24-EBR, respectively. Meanwhile, superoxide dismutase (SOD) was increased by 68.33%, 10.28%, and 6.17%, and catalase (CAT) was increased by 31.43%, 37.87%, and 37.31%, respectively. Generally, the spraying of exogenous 6-BA, SA, and 24-EBR with the appropriate concentration under Cd stress could significantly increase the biomass of B. pilosa L. and promote the accumulation of heavy metals in the plant, improve the photosynthetic ability of the plant, reduce the oxidative damage of the plant under heavy metal stress, enhance the antioxidant capacity, and improve the absorption and tolerance of plants to Cd. It also could promote the transfer of Cd from roots to shoots, improve the phytoextraction rates of Cd from the plant, and effectively strengthen the phytoremediation efficiency. Among them, 30 mg·L-1 SA foliar spraying had the best effect.

Heavy Metal Pollution in the Environment and Its Impact on Health: Exploring Green Technology for Remediation

Along with expanding urbanization and industrialization, environmental pollution which negatively affects the surroundings, has been rising quickly. As a result, induces heavy metal contamination which poses a serious threat to living organisms of aquatic and soil ecosystems. Therefore, they are a need to ameliorate the effects cost by cost pollution on the environment. In this review, we explore methods employed to mitigate the effects caused by heavy metals on the environment. Many techniques employed to manage environmental pollution are tedious and very costly, necessitating the use of alternative management strategies to resolve this challenge. In this concept, bioremediation is viewed as a future technique, due to its environmental friendliness and cost-effective measures aligned with sustainable or climate-smart agriculture to manage contaminants in the environment. The technique involves the use of living entities such as bacteria, fungi, and plants to deteriorate toxic substances from the rhizosphere. Currently, bioremediation is thought to be the most practical, dependable, environmentally benign, and long-lasting solution. Although bioremediation involves different techniques, they are still a need to find the most efficient method for removing toxic substances from the environment. This review focuses on the origins of heavy metal pollution, delves into cost-effective and green technological approaches for eliminating heavy metal pollutants from the environment, and discusses the impact of these pollutants on human health.

Overexpression of IlHMA2, from Iris lactea, Improves the Accumulation of and Tolerance to Cadmium in Tobacco

Long-distance transport cadmium (Cd) from roots to shoots is a key factor for Cd phytoremediation. Our previous study indicated that heavy metal P1B2-ATPases, IlHMA2, was involved in improving the accumulation of Cd via mediated long-distance transport Cd, contributing to the phytoremediation in Cd accumulator Iris lactea. However, whether the overexpression of IlHMA2 could enhance the accumulation and tolerance to Cd remains unclear in plants. Here, we generated transgenic tobacco overexpressing IlHMA2 and tested its effect on the translocation and accumulation of Cd and zinc (Zn), as well as the physio-biochemical characteristics under 50 mg/L Cd exposure. The overexpression of IlHMA2 significantly increased Cd concentrations in xylem saps, resulting in enhanced root-to-shoot Cd translocation compared with wild-type. Meanwhile, overexpressing IlHMA2 promoted Zn accumulations, accompanied by elevating proline contents and antioxidant enzyme activity (SOD, POD, and CAT) to diminish the overproduction of ROS in transgenic tobacco. These pieces of evidence suggested that higher Zn concentrations and lower ROS levels could tremendously alleviate Cd toxicity for transgenic tobacco, thereby improving the growth and tolerance. Overall, the overexpression of IlHMA2 could facilitate Cd accumulation and enhance its tolerance in tobacco exposed to Cd contaminations. This would provide a valuable reference for improving Cd phytoremediation efficiency.

Effects of biochar application and nutrient fluctuation on the growth, and cadmium and nutrient uptake of Trifolium repens with different planting densities in Cd-contaminated soils

Biochar has been used to remediate contaminated-soil with heavy metals, however, less is known on how biochar interacts with planting density and nutrient fluctuation to affect the remediation. A pot experiment was conducted in the greenhouse to investigate the effects of biochar application (without vs. with 1% biochar, g/g substrate), nutrient fluctuation (constant vs. pulsed) and planting density (1-, 3- and 6-individuals per pot) on the growth, and cadmium (Cd) and nutrient uptake of Trifolium repens population. Our results found that the growth of T. repens population increased significantly with increasing planting density, and the increment decreased with increasing planting density. Both the Cd and nutrient uptake were higher at higher planting density (e.g., 3- and 6-individuals) than at lower planting density (e.g., 1-individual). Biochar application increased the biomass and shoot Cd uptake, but decreased the ratio of root to shoot and root Cd uptake of T. repens population, the effects of which were significantly influenced by planting density. Although nutrient fluctuation had no effect on the growth of T. repens population, but its interaction with planting density had significant effects on Cd uptake in tissues. Overall, the effects of biochar application and nutrient fluctuation on the growth and Cd uptake were both influenced by planting density in the present study. Our findings highlight that biochar application and constant nutrient supply at an appropriate planting density, such as planting density of 3-individuals per pot in the present study, could promote the growth, and Cd and nutrient uptake of T. repens population.

The traces elements absorption, accumulation and translocation ability of Phragmites australis

In this study, the wastewater analyses of Oued K'sob for one year showed a spatiotemporal diminution of zinc content seasonally, it rest light than copper. But Zinc and copper a threat to the environment of the region. The wastewater analyses of Oued K'sob water for one year showed a spatiotemporal diminution of zinc content seasonally, with a minimum and maximum range of 249 ± 219 µg/l and 2382 ± 3426 µg/l obtained in autumn and summer for the zinc and 75 ± 24 µg/l and 433 ± 310 µg/l obtained in winter and spring at the first and fifth station for the copper. These concentrations of zinc and copper a threat to the environment of the region. Like a solution for this problem, the absorption, accumulation and translocation abilities of Phragmites australis were determined toward iron (Fe), copper (Cu), zinc (Zn) and lead (Pb). In the soils contaminated by different concentrations (100, 200 and 500 mg/L), the absorption, accumulation and transport ability of elements were evaluated via the Bio-concentration (BCF), Bioaccumulation (BF) and Translocation (TF) factors. A proportional increase between the BCF, BFs, TFs and the irrigation concentrations, where BCFs of all metallic elements exceed 1 and the Zn BCF, BFs and TFL are the highest and exceed 1 relative to the other elements which remain lower than 1, which has a low accumulation. Therefore, according to the BCFs obtained and which exceed 1, we can consider this plant as a hyper-accumulator of Zn, Fe, Cu and Pb. Extraction of fatty and organic acids followed by HPLC confirmed the oxalic, citric, malic, succinic, fumaric, formic, acetic, propionic, and butyric acid presence, which are responsible for the transport of the metal from roots to leaves. In the light of these results, we can therefore propose Phragmites australis species as an alternative and natural solution to reduce the high concentrations of zinc and copper in the Oued k'sob (region of Bordj Bou Arreridj, Algeria).

Biochar Decreases Cr Toxicity and Accumulation in Sunflower Grown in Cr(VI)-Polluted Soil

Biochar is preferentially recommended for the remediation of heavy metal-polluted soils. Sunflower is an important high-biomass oil crop with a promising potential for phytoremediation of Cr(VI)-polluted soil. However, how biochar affects sunflower growth and Cr accumulation in Cr(VI)-polluted soil needs to be elucidated. Here, a pot culture experiment was conducted to study whether soil amendment with biochar (0, 0.1%, 1%, and 5%, w/w) can mitigate Cr toxicity and accumulation in sunflower seedlings grown in soils artificially polluted with different levels of Cr(VI) (0, 50, and 250 mg Cr(VI)/kg soil). The addition of Cr(VI) exhibited significant phytotoxicity, as evidenced by inhibited plant growth and even the death of seedlings at 250 mg/kg Cr(VI). Overall, biochar amendment showed positive effects on plant growth and Cr immobilization, dependent on both the biochar dose and Cr addition level. When 50 mg/kg Cr(VI) was added, 1% biochar showed positive effects similar to 5% biochar on improving plant growth and mineral nutrition (particularly K), reducing Cr content in shoots and roots, and decreasing Cr availability and Cr(VI) content in the soil. In comparison with non-amendment, 1% and 5% biochar caused 85% and 100% increase in shoot dry weights, and 75% and 86% reduction in shoot Cr concentrations, respectively. When 250 mg/kg Cr(VI) was added, a 5% dose produced much better benefits than 1%, while a 0.1% dose did not help plants to survive. Overall, an appropriate dose of biochar enhanced Cr(VI) immobilization and subsequently decreased its toxicity and accumulation in sunflower seedlings. Our findings confirm that biochar can be used as an efficient amendment for the remediation of Cr(VI)-polluted soils and cleaner production of sunflower oil and biomass.

Evaluation of the Phytoremediation Potential of the Sinapis alba Plant Using Extractable Metal Concentrations

Testing the feasibility of soil phytoremediation requires the development of models applicable on a large scale. Phytoremediation mechanisms include advanced rhizosphere biodegradation, phytoaccumulation, phytodegradation, and phytostabilization. The aim of this study was to evaluate the phytoremediation potential of the Sinapis alba. Identification of the factors influencing the extraction process of metals from contaminated soils in a laboratory system suitable for evaluating the phytoavailability of these metals in three solutions (M1-CaCl2, M2-DTPA, and M3-EDTA) included the following: distribution of metals in solution (Kd), soil properties and mobile fractions (SOC, CEC, pH), response surface methodology (RSM), and principal component analysis (PCA). The evaluation of the phytoremediation potential of the Sinapis alba plant was assessed using bioaccumulation coefficients (BACs). The accumulation of heavy metals in plants corresponds to the concentrations and soluble fractions of metals in the soil. Understanding the extractable metal fractions and the availability of metals in the soil is important for soil management. Extractable soluble fractions may be more advantageous in total metal content as a predictor of bioconcentrations of metals in plants. In this study, the amount of metal available in the most suitable extractors was used to predict the absorption of metals in the Sinapis alba plant. Multiple regression prediction models have been developed for estimating the amounts of As and Cd in plant organs. The performance of the predictive models generated based on the experimental data was evaluated by the adjusted coefficient of determination (aR2), model efficiency (RMSE), Durbin-Watson (DW) test, and Shapiro-Wilk (SW) test. The accumulation of the analyzed metals followed the pattern Root > Pods > Leaves > Seeds, stems > Flowers for As and Leaves > Root > Stem > Pods > Seeds > Flowers for Cd in soil contaminated with different metal concentrations. The obtained results showed a phytoremediation potential of the Sinapis alba plant.

Effects of humic acid on nutrient removal efficiency of aquatic duckweed (Lemna minor) and both growth performance, and hemato-biochemical parameters of Nile tilapia (Oreochromis niloticus) cultured in water recirculating system

This study was carried out to evaluate the effects of humic acid (HA) on the nutrient removal efficiencies of aquatic duckweed plant (Lemna minor) from a water recirculating system used to culture Nile tilapia (Oreochromis niloticus) fish for 30 days. The HA was added to water at three concentrations of 0 (Control), 1.5, and 3 mg/L in triplicate. Water quality parameters, growth performance, and some hemato-biochemical parameters of the fish in variable HA concentrations were compared. The total ammonia nitrogen (TAN) and total phosphorous (TP) removal efficiency of L. minor increased with increasing the HA concentration from 0 mg/L to 3 mg/L (p < 0.05). The concentration of nitrate (NO3-) in the HA-3 mg/L was higher than that in the other groups on days 20 and 30 of the fish cultivation period (p < 0.05). The growth performance of fish improved in the HA-3 mg/L compared to the other groups. The addition of different concentrations of HA to water had no adverse effect on the hematological properties of the Nile tilapia. The plasma aspartate aminotransferase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) levels in the HA-0 mg/L and HA-1.5 mg/L groups were higher than in the HA-3 mg/L (p < 0.05). No significant differences in the plasma glucose and cholesterol levels were observed between the HA-groups (p > 0.05), while the triglyceride level increased in the HA-3 mg/L compared to the control (p < 0.05). These results indicated that adding HA to water could be an effective method to enhance the bioremediation performance of the aquatic duckweed plants as biofilter and thus improve water quality, subsequently, fish growth performance in RASs.

Harnessing Diesel-Degrading Potential of an Antarctic Microalga from Greenwich Island and Its Physiological Adaptation

Microalgae are well known for their metal sorption capacities, but their potential in the remediation of hydrophobic organic compounds has received little attention in polar regions. We evaluated in the laboratory the ability of an Antarctic microalga to remediate diesel hydrocarbons and also investigated physiological changes consequent upon diesel exposure. Using a polyphasic taxonomic approach, the microalgal isolate, WCY_AQ5_1, originally sampled from Greenwich Island (South Shetland Islands, maritime Antarctica) was identified as Tritostichococcus sp. (OQ225631), a recently erected lineage within the redefined Stichococcus clade. Over a nine-day experimental incubation, 57.6% of diesel (~3.47 g/L) was removed via biosorption and biodegradation, demonstrating the strain's potential for phytoremediation. Fourier transform infrared spectroscopy confirmed the adsorption of oil in accordance with its hydrophobic characteristics. Overall, degradation predominated over sorption of diesel. Chromatographic analysis confirmed that the strain efficiently metabolised medium-chain length n-alkanes (C-7 to C-21), particularly n-heneicosane. Mixotrophic cultivation using diesel as the organic carbon source under a constant light regime altered the car/chl-a ratio and triggered vacuolar activities. A small number of intracellular lipid droplets were observed on the seventh day of cultivation in transmission electron microscopic imaging. This is the first confirmation of diesel remediation ability in an Antarctic green microalga.

Oil-Contaminated Soil Remediation with Biodegradation by Autochthonous Microorganisms and Phytoremediation by Maize (Zea mays)

Biological methods are currently the most commonly used methods for removing hazardous substances from land. This research work focuses on the remediation of oil-contaminated land. The biodegradation of aliphatic hydrocarbons and PAHs as a result of inoculation with biopreparations B1 and B2 was investigated. Biopreparation B1 was developed on the basis of autochthonous bacteria, consisting of strains Dietzia sp. IN118, Gordonia sp. IN101, Mycolicibacterium frederiksbergense IN53, Rhodococcus erythropolis IN119, Rhodococcus globerulus IN113 and Raoultella sp. IN109, whereas biopreparation B2 was enriched with fungi, such as Aspergillus sydowii, Aspergillus versicolor, Candida sp., Cladosporium halotolerans, Penicillium chrysogenum. As a result of biodegradation tests conducted under ex situ conditions for soil inoculated with biopreparation B1, the concentrations of TPH and PAH were reduced by 31.85% and 27.41%, respectively. Soil inoculation with biopreparation B2 turned out to be more effective, as a result of which the concentration of TPH was reduced by 41.67% and PAH by 34.73%. Another issue was the phytoremediation of the pre-treated G6-3B2 soil with the use of Zea mays. The tests were carried out in three systems (system 1-soil G6-3B2 + Zea mays; system 2-soil G6-3B2 + biopreparation B2 + Zea mays; system 3-soil G6-3B2 + biopreparation B2 with γ-PGA + Zea mays) for 6 months. The highest degree of TPH and PAH reduction was obtained in system 3, amounting to 65.35% and 60.80%, respectively. The lowest phytoremediation efficiency was recorded in the non-inoculated system 1, where the concentration of TPH was reduced by 22.80% and PAH by 18.48%. Toxicological tests carried out using PhytotoxkitTM, OstracodtoxkitTM and Microtox® Solid Phase tests confirmed the effectiveness of remediation procedures and showed a correlation between the concentration of petroleum hydrocarbons in the soil and its toxicity. The results obtained during the research indicate the great potential of bioremediation practices with the use of microbial biopreparations and Zea mays in the treatment of soils contaminated with petroleum hydrocarbons.