The chromium detoxification pathway in the multimetal accumulator Silene vulgaris

Removal and reduction mechanism of Cr (VI) in Leersia hexandra Swartz constructed wetland-microbial fuel cell coupling system

Cr (VI) is extremely harmful to both the environment and human health, and it can linger in the environment for a very long period. In this research, the Leersia hexandra Swartz constructed wetland-microbial fuel cell (CW-MFC) system was constructed to purify Cr (VI) wastewater. By comparing with the constructed wetland (CW) system, the system electricity generation, pollutants removal, Cr enrichment, and morphological transformation of the system were discussed. The results demonstrated that the L. hexandra CW-MFC system promoted removal of pollutants and production of electricity of the system. The maximum voltage of the system was 499 mV, the COD and Cr (VI) removal efficiency was 93.73% and 97.00%. At the same time, it enhanced the substrate and L. hexandra ability to absorb Cr and change it morphologically transformation. Additionally, the results of XPS and XANES showed that the majority of the Cr in the L. hexandra and substrate was present as Cr (III). In the L. hexandra CW-MFC system, Geobacter also functioned as the primary metal catabolic reducing and electrogenic bacteria. As a result, L. hexandra CW-MFC system possesses the added benefit of removing Cr (VI) while producing energy compared to the traditional CW system.

Multi-Responsive Sensor Based on Porous Hydrogen-Bonded Organic Frameworks for Selective Sensing of Ions and Dopamine Molecules

Hydrogen-bonded organic frameworks (HOFs), as an emerging porous material, have attracted increasing research interest in fluorescence sensing due to their inherent fluorescence emission units with unique physicochemical properties. Herein, based on the organic building block 3,3',5,5'-tetrakis-(4-carboxyphenyl)-1,1'-biphenyl (H₄TCBP), the porous material HOF-TCBP was successfully synthesized using hydrogen bond self-assembly in a DMF solution. The fluorescence properties of the HOF-TCBP solution showed that when the concentration was high, excimers were easily formed, the PL emission was red-shifted, and the fluorescence intensity became weaker. HOF-TCBP showed good sensitivity and selectivity to metal ions Fe³⁺, Cr³⁺, and anion Cr₂O₇^2-. In addition, HOF-TCBP can serve as a label-free fluorescent sensor material for the sensitive and selective detection of dopamine (DA). HOF-based DA sensing is actually easy, low-cost, simple to operate, and highly selective for many potential interfering substances, and it has been successfully applied to the detection of DA in biological samples with satisfactory recoveries (101.1-104.9%). To our knowledge, this is the first report of HOF materials for efficient detection of the neurotransmitter dopamine in biological fluids. In short, this work widely broadens the application of HOF materials as fluorescent sensors for the sensing of ions and biological disease markers.

Iron nanoparticles to recover a co-contaminated soil with Cr and PCBs

Little attention has been given to the development of remediation strategies for soils polluted with mixture of pollution (metal(loid)s and organic compounds). The present study evaluates the effectiveness of different types of commercial iron nanoparticles (nanoscale zero valent iron (nZVI), bimetallic nZVI-Pd, and nano-magnetite (nFe₃O₄)), for the remediation of an industrial soil co-contaminated with Cr and PCBs. Soil samples were mixed with nZVI, nZVI-Pd, or nFe₃O₄ at doses selected according to their reactivity with PCBs, homogenized, saturated with water and incubated at controlled conditions for 15, 45 and 70 days. For each sampling time, PCBs and chromium were analyzed in aqueous and soil fractions. Cr(VI) and Cr leachability (TCLP test) were determined in the soil samples. The treatment with the three types of iron nanoparticles showed significant reduction in Cr concentration in aqueous extracts at the three sampling times (> 98%), compared to the control samples. The leachability of Cr in treated soil samples also decreased and was stable throughout the experiment. Results suggested that nZVI and nZVI-Pd immobilized Cr through adsorption of Cr(VI) on the shell and reduction to Cr(III). The mechanism of interaction of nFe₃O₄ and Cr(VI) included adsorption and reduction although its reducing character was lower than those of ZVI nanoparticles. PCBs significantly decreased in soil samples (up to 68%), after 15 days of treatment with the three types of nanoparticles. However, nFe₃O₄ evidenced reversible adsorption of PCBs after 45 days. In general, nZVI-Pd reduced PCB concentration in soil faster than nZVI. Control soils showed a similar reduction in PCBs concentration as those obtained with nZVI and nZVI-Pd after a longer time (45 days). This is likely due to natural bioremediation, although it was not effective for Cr remediation. Results suggest that the addition of nZVI or nZVI-Pd and pseudo-anaerobic conditions could be used for the recovery of soil co-contaminated with Cr and PCBs.

The reduction of Cr(VI) in Salvinia minima, possible involvement of an h-type thioredoxin

Hexavalent chromium [Cr(VI)] is extremely toxic to plant cells and has been recognized to possess a high redox potential. Tolerant plant species have shown the ability to reduce Cr(VI), but the operating mechanism involved in this process is not elucidated. Thus, the aim of this study was to investigate the possible involvement of thiolic and phenolic compounds and thioredoxin expression during Cr(VI) reduction in S. minima. In addition, a probable enzymatic reduction of Cr(VI) was investigated. Plants were exposed to 20 mg L^-1 Cr(VI) concentration during 7 days under controlled conditions. The amount of metal accumulated in lacinias (root-like submerged leaves) and fronds (floating leaves) indicated that a low percentage of absorbed Cr(VI) was mobilized from lacinias to fronds. X-ray absorption near-edge structure (XANES) analysis revealed that Cr(III) was the only chromium species occurring in S. minima plants. Thiols and phenolics of lacinias and fronds were increased significantly by Cr(VI) treatment, but accumulation patterns were different. The expression of an h-type thioredoxin (Trx h) was demonstrated for the first time in Cr-exposed lacinias. Enzymatic reduction showed a low contribution to the Cr(VI) reduction. Data of this study provide evidences on the involvement of thiols, thioredoxin, and phenolics in the reduction of Cr(VI) to Cr(III) in S. minima tissues.

3D Ln-MOFs as multi-responsive luminescent probes for efficient sensing of Fe3+, Cr2O72−, and antibiotics in aqueous solution

Two families of Ln-based MOFs with 3D structures have been synthesized under solvothermal conditions. Eu-MOF (4) can act as a multi-responsive luminescent probe in water systems and Dy-MOF (6) shows slow magnetic relaxation behaviors.

Bioelectrochemical remediation of Cr(VI)/Cd(II)-contaminated soil in bipolar membrane microbial fuel cells

Heavy-metal contaminated soils post great environmental and health concerns. In this study, Cr and Cd which are frequently observed in contaminated soils, were selected as representatives of hazardous heavy metals because of their different redox potentials and electric charges. Cr(VI)-, Cd(II)-, Cr(VI)/Cd(II)-contaminated soils were remediated in two-chamber air-cathode MFCs, in order to investigate the remediation of soil contaminated by single heavy metal and mixed heavy metals. Four ion exchange membranes (IEMs) were first evaluated to find out that bipolar membrane (BPM) was able to well maintain pH in both anolyte and catholyte, which was beneficial to support biological metabolism and heavy metal removal. It was also found that heavy metal ions (Cr, Cd or Cr/Cd) could migrate toward the cathode forming a concentration gradient under the weak electric field. The interaction between negatively charged Cr and positively charged Cd had no major effect to hinder each other on the migration, suggesting that the reduction reaction and electric field should be the main motivation for metal ion migration. The remediation performance of mixed heavy metal contaminated soil was superior to that of single heavy metal contaminated soil, for the possible reason of smaller internal resistance under mixed heavy metal condition.

Erythrocyte Membrane-Wrapped Magnetic Nanotherapeutic Agents for Reduction and Removal of Blood Cr(VI)

The hazard of hexavalent chromium (Cr(VI)) from environmental pollution and medical implanted metal has been recognized widely. However, removal of trace amount of Cr(VI) in the blood circumstance faces tremendous difficulties for that most of Cr(VI) located in erythrocytes, thus there is almost no literature to report the removal of Cr(VI) in blood. Herein, a removal strategy, named as reduction-adsorption-separation, is proposed to realize the removal of Cr(VI) in blood. First, magnetic core-shell mesoporous nanocomposite is fabricated by using Fe₃O₄ nanoparticles as magnetic core and mesoporous silica (MS) as shell, hyperbranched polyamide (HPA) as mesoporous channel modifier and ascorbic acid (ASC) as the reductant drug loaded in the mesoporous channels, which is also denoted as Fe/MS/HPA/ASC. Then, on the basis of the bionic idea, the erythrocyte membrane (EM)-wrapped Fe/MS/HPA/ASC to protect ASC from deactivation is obtained and named as the therapeutic agent (Fe/MS/HPA/ASC@EM). During removal process, the therapeutic agent can enter in erythrocytes to use ASC to reduce Cr(VI) to Cr(III) and HPA in mesoporous channels to adsorb Cr(III) and can then be recollected from blood by magnetic separation. Finally, an animal model of blood Cr(VI) poisoning is constructed and used to test the removal ability of Cr(VI) from pig blood in vivo, verifying the effectiveness of this blood Cr(VI) removal strategy, providing a possible way to design more efficient and biosafe therapeutic agents for blood purification.

Assessment of chromium species dynamics in root solutions using isotope tracers

BACKGROUND

Chromium (Cr) exists in the environment in two chemical forms; CrIII is an essential micronutrient for glucose and lipid metabolism, whereas CrVI is toxic and a recognised carcinogen through inhalation. Numerous studies have attempted to evaluate their transfer mechanisms from soil and solution media into plants, usually with respect to the hyperaccumulation, detoxification and tolerance of the plant to CrVI.

METHODS

Isotopically enriched species of Cr, added as 50CrIII and 53CrVI, were used to investigate transfer from solution into the root systems of Spinacia oleracea. In addition the effect of sulphate (SO42-), as a competitor for CrVI uptake, was investigated. Separation of 50CrIII and 53CrVI was undertaken using HPLC-ICP-QQQ following isolation of root solutions using freeze/thaw centrifugation.

RESULTS

Irrespective of supplied CrVI concentration (250, 500 or 1000 μg L-1), the dominant species in both apoplastic (routed through cell wall and intercellular space as a passive mechanism) and symplastic (routed through cytoplasm as an active mechanism) root solutions was CrIII. There was evidence for CrVI reduction in the rhizosphere prior to uptake as an additional detoxification mechanism. Sulphate promoted uptake of CrVI through the active pathway, although increases in SO42- concentration did not yield a proportional increase in Cr symplastic solution concentration; CrIII was also the dominant species in these root solutions.

CONCLUSION

The results indicate that Spinacia oleracea plants can effectively reduce CrVI to CrIII and that the uptake pathways for both CrIII and CrVI are more complex than previously reported. Further work is required to understand the physiological processes that result in the reduction of CrVI prior to, and during, uptake. The efficacy of sulphate to augment existing agricultural management strategies, such as liming and organic reincorporation, also requires further investigation to establish suitable application rates and applicability to other environmental contaminants.

Multi-omics response of Pannonibacter phragmitetus BB to hexavalent chromium

The release of hexavalent chromium [Cr(VI)] into water bodies poses a major threat to the environment and human health. However, studies of the biological response to Cr(VI) are limited. In this study, a toxic bacterial mechanism of Cr(VI) was investigated using Pannonibacter phragmitetus BB (hereafter BB), which was isolated from chromate slag. The maximum Cr(VI) concentrations with respect to the resistance and reduction by BB are 4000 mg L^-1 and 2500 mg L^-1, respectively. In the BB genome, more genes responsible for Cr(VI) resistance and reduction are observed compared with other P. phragmitetus strains. A total of 361 proteins were upregulated to respond to Cr(VI) exposure, including enzymes for Cr(VI) uptake, intracellular reduction, ROS detoxification, DNA repair, and Cr(VI) efflux and proteins associated with novel mechanisms involving extracellular reduction mediated by electron transfer, quorum sensing, and chemotaxis. Based on metabolomic analysis, 174 metabolites were identified. Most of the upregulated metabolites are involved in amino acid, glucose, lipid, and energy metabolisms. The results show that Cr(VI) induces metabolite production, while metabolites promote Cr(VI) reduction. Overall, multi-enzyme expression and metabolite production by BB contribute to its high ability to resist/reduce Cr(VI). This study provides details supporting the theory of Cr(VI) reduction and a theoretical basis for the efficient bioremoval of Cr(VI) from the environment.

Removal of dissolved chromium from synthetic mine effluent: A mesocosm experiment

Dispersion of hexavalent chromium (Cr(VI)) in streams around nickel laterite mines, which are mostly located in the tropics, may pose serious risks for the environment and human health. In an earlier study, a local natural wetland effectively removed Cr from a nickel mine environment in Indonesia. In order to understand the processes and conditions that would facilitate the establishment of operational constructed wetlands that would remove Cr from mine water discharge, we used two native macrophyte species from the same wetland, Lepironia articulata and Machaerina rubiginosa, in a series of mesocosm experiments to follow the distribution of Cr species in water, substrate and plants. A 1 m³ mesocosm was charged with a sand/compost mixture to a depth of 0.5 m, filled to within 0.1 m from the top by water with Cr concentrations of about 1.0 mg L^-1, similar to mine discharge water, and plants were introduced to part of the substrate surface. Stage 1 of the experiment supplied and removed fresh water continuously by surface flow, maintaining a residence time of 12 h. In stages, the water was recirculated (Stage 2), more plants were added (Stage 3) and outflow conditions were changed from totally surface to partially from beneath the substrate (Stage 4). All stages lowered Cr concentrations at the surface water outflow, but Cr concentrations were lower again close to the sediment/water interface. Due to the reduction of Cr(VI), the Cr concentrations in substrate pore water were higher near the surface compared to those at depth, and the pore water concentrations of Cr(VI) and total Cr were higher in the vegetated area compared to the non-vegetated area. Higher plant density and mixed species composition of the macrophytes did not increase the efficiency of Cr(VI) removal from the system. The hybrid system, comprising surface and below-substrate outflow (Stage 4), removed hexavalent chromium at a much higher rate than surface outflow only.

Localization and Speciation of Chromium in Coptis chinensis Franch. using Synchrotron Radiation X-ray Technology and Laser Ablation ICP-MS

Coptis chinensis Franch. is one of the most important medicinal plants globally. However, this species contains relatively high concentrations of chromium (Cr) which potentially detrimental to human health. It is important to understand Cr localization and speciation in order to evaluate its accumulation and transportation mechanisms and minimize Cr transfer to humans. As little previous work in this area has been carried out, we utilized synchrotron radiation microscopic X-ray fluorescence (SR-μXRF) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) to spatially locate Cr, X-ray absorption near-edge spectroscopy (XANES) to analyze Cr speciation, and inductively coupled plasma mass spectrometry (ICP-MS) to detect Cr subcellular concentration. Micromapping results showed that Cr was distributed predominantly within the vascular cylinder, the periderm and some outer cortex, and the cortex and some vascular bundles in root, rhizome, and petiole, respectively. XANES data showed that Cr(VI) can be reduced to Cr(III) when grown with Cr(VI), and yielded a novel conclusion that this plant contain elemental chromium. ICP-MS data showed that Cr was primarily compartmentalized in cell walls in all tissues. The new insights on Cr accumulation in C. chinensis Franch. provide a theoretical basis for the evaluation of Cr in other medicinal plants.

3D water-stable europium metal organic frameworks as a multi-responsive luminescent sensor for high-efficiency detection of Cr2O72−, MnO4−, Cr3+ ions and SDBS in aqueous solution

A 3D water-stable europium metal organic framework has been synthesized. Fluorescence measurements show that the MOF can selectively and sensitively detect Cr₂O₇²⁻, MnO₄⁻, Cr³⁺ ions and SDBS in aqueous solutions.

Different genotypes of Silene vulgaris (Moench) Garcke grown on chromium-contaminated soils influence root organic acid composition and rhizosphere bacterial communities

Plant-microbe interactions are considered to be important processes determining the efficiency of phytoremediation of heavy metal-contaminated soils. However, relatively little is known about how these interactions are influenced by chromium (Cr) contamination. The effect of Cr stress on metal uptake, root organic acid composition, and rhizosphere bacterial communities was studied using two genotypes of the metallophyte Silene vulgaris, which have shown different tolerance to Cr(VI). The results indicated that root biomass and shoot biomass were not significantly influenced by Cr treatment, but metal uptake in shoots and roots was significantly impacted by the genotype. Principal component analyses (PCA) showed that variation in organic acids oxalic, citric, malic, formic, lactic, acetic, and succinic differed between genotypes. Changes in root organic acid contents in response to Cr revealed a significant increase of oxalic acid in genotype SV-21. The denaturing gradient gel electrophoresis (DGGE) cluster analysis showed that the community structure (determined by PCR-DGGE) was affected by plant genotype and, to a lesser extent, by Cr contamination, the first being the most influential factor shaping the rhizosphere microbiome. Under Cr pollution, a shift in the relative abundance of specific taxa was found and dominant phylotypes were identified as Variovorax in SV-21 and Chitinophaga niastensis, Pontibacter sp., and Ramlibacter sp. in SV-38. These results provided the basis for further studies aimed at the combined use of plants and soil microorganisms in the remediation of Cr-polluted soils.

Synchrotron-based X-Ray Approaches for Examining Toxic Trace Metal(loid)s in Soil-Plant Systems

Elevated levels of trace metal(loid)s reduce plant growth, both in soils contaminated by industrial activities and in acid agricultural soils. Although the adverse effects of trace metal(loid)s have long been recognized, there remains much unknown both about their behavior in soils, their toxicity to plants, and the mechanisms that plants use to tolerate elevated concentrations. Synchrotron-based approaches are being utilized increasingly in soil-plant systems to examine toxic metal(loid)s. In the present review, brief consideration is given to the theory of synchrotron radiation. Thereafter, we review the use of synchrotron-based approaches for the examination of various trace metal(loid)s in soil-plant systems, including aluminum, chromium, manganese, cobalt, nickel, copper, zinc, arsenic, selenium, and cadmium. Within the context of this review, X-ray absorption spectroscopy (XAS) and X-ray fluorescence microscopy (μ-XRF) are of particular interest. These techniques can provide in situ analyses of the distribution and speciation of metal(loid)s in soil-plant systems. The information presented here serves not only to understand the behavior of trace metals in soil-plant systems, but also to provide examples of the potential applications of synchrotron radiation that can be used to advantage in other studies.

Role of the polycarboxylic compounds in the response of Silene vulgaris to chromium

This work aims to investigate the nature and the specific mechanisms by which polycarboxylic compounds participate in the tolerance of Silene vulgaris to Cr with special attention given to the rhizosphere system. This knowledge is important to use this species in the implementation of phytoremediation technologies in Cr-polluted soils. According to the results, chromium is chelated and mobilized by the citric and malic acids in plant tissues, while oxalic acid might participate in the reduction and chelation of Cr in the rhizosphere. At the applied doses, the response of both exudation rate and root exudate composition (total polyphenols and quercitin) seems to involve a rearrangement in the lignification of the plant cell wall to immobilize Cr. Quercetin-3-dirhamnosyl-galactoside and apiin (apigenin-7-O-apiosyl-glucoside) have been identified as the major polyphenols in the root exudates of S. vulgaris. The increments found in the apiin concentration in root exudates seem to be related to the protection against Cr toxicity by chelation of Cr or by free radical scavenging. Though earlier response is detected in plant tissues, results from this work together with previous studies in S. vulgaris indicate that exudation might be a regulated mechanism of protection under Cr exposition in S. vulgaris that may involve mainly Cr reduction and chelation.

Bioelectrochemical Chromium(VI) Removal in Plant-Microbial Fuel Cells

Plant-microbial fuel cell (PMFC) is a renewable and sustainable energy technology that generates electricity with living plants. However, little information is available regarding the application of PMFC for the remediation of heavy metal contaminated water or soil. In this study, the potential for the removal of heavy metal Cr(VI) using PMFC was evaluated, and the performance of the PMFC at various initial Cr(VI) contents was investigated. The Cr(VI) removal efficiency could reached 99% under various conditions. Both the Cr(VI) removal rates and the removal efficiencies increased with the increasing initial Cr(VI) concentration. Furthermore, the long-term operation of the PMFC indicated that the system was stable and sustainable for Cr(VI) removal. The mass balance results and XPS analysis results demonstrate that only a small amount of soluble Cr(III) remained in the PMFC and that most Cr(III) precipitated in the form of the Cr(OH)3(s) or was adsorbed onto the electrodes. The PMFC experiments of without acetate addition also show that plants can provide carbon source for MFC through secrete root exudates and bioelectrochemical reduction of Cr(VI) was the main mechanism for the Cr(VI) removal. These results extend the application fields of PMFC and might provide a new insight for Cr(VI) removal from wastewater or soil.

ECO-physiological response of S. vulgaris to CR(VI): Influence of concentration and genotype

The objective of this work is to study the response of Silene vulgaris to a range of environmentally relevant concentrations of Cr(VI) in order to evaluate its potential use in the phytomanagement of Cr polluted sites. Cuttings of six homogenous genotypes from Madrid (Spain) have been used as plant material. The eco-physiological response of S. vulgaris to Cr(VI) changed with the genotype. The yield dose-response curve was characterized by stimulation at low doses of Cr(VI). The effects of metal concentration were quantified on root dry weight, water content and chlorophyll content, determined by SPAD index. The response was not homogeneous for all studied genotypes. At high doses of Cr(VI), plants increased micronutrient concentration in dry tissues which suggested that nutrient balance could be implicated in the alleviation of Cr toxicity. This work highlights the importance of studying the eco-physiological response of metallophytes under a range of pollutant concentrations to determine the most favorable traits to be employed in the phytomanagement process.