Activated carbon fiber loaded nano zero-valent iron for Microcystis aeruginosa removal: Performance and mechanisms

Cyanobacterial blooms caused by Microcystis aeruginosa threaten environmental safety and daily life. In this study, an activated carbon fiber-supported nano zero-valent iron composite (ACF-nZVI) was developed to remove Microcystis aeruginosa. The results showed that nZVI was evenly distributed on the activated carbon fibers, preventing aggregation and oxidation. ACF-nZVI achieved a removal efficiency of more than 90 % within a pH range of 3-7. During the reaction, H2O2, which was generated by Fe0, was activated to form ·OH and ·O-2, which dismantled antioxidant enzymes and induced lipid peroxidation. Additionally, ACF-nZVI destroyed the cell wall and membrane, resulting in protein and humus leakage and causing 92.34 % cell damage and death. In this study, an environmentally friendly and stable nanomaterial was developed, offering a novel approach for the safe, cost-effective, and efficient removal of cyanobacteria.

Evaluating the safety and efficiency of nanomaterials: A focus on mitochondrial health

Nanomaterials (NMs) have extensive application potential in drug delivery, tissue engineering, and various other domains, attributable to their exceptional physical and chemical properties. Nevertheless, an increasing body of literature underscores the diverse safety risks are associated with NMs upon interaction with the human body, including oxidative stress and programmed cell death. Mitochondria, serving as cellular energy factories, play a pivotal role in energy metabolism and the regulation of cell fate. Organs with substantial energy demands, including the heart and brain, are highly sensitive to mitochondrial integrity, with mitochondrial impairment potentially resulting in significant dysfunction and pathologies such as as heart failure and neurodegenerative disease. This review elucidates the pathways by which NMs translocate into mitochondria, their intracellular dynamics, and their impact on mitochondrial morphology, respiratory chain activity, and metabolic processes. We further investigate associated molecular mechanisms, including mitochondrial dynamic imbalance, calcium overload, and oxidative stress, and elucidate the pivotal roles of mitochondria in different forms of programmed cell death such as apoptosis and autophagy. Finally, we offer recommendations regarding the safety and efficacy of NMs for medical applications. By systematically analyzing the interactions and molecular mechanisms between NMs and mitochondria, this paper aims to enhance the toxicological evaluation framework of NMs and provide a foundational reference and theoretical basis for their clinical utilization.

Transcriptomic analysis and cellular responses to nanoscale zero-valent iron in green microalga Raphidocelis subcapitata

Nanoscale zero valent iron (nZVI) is used to remediate aquifers polluted by organochlorines or heavy metals and was also suggested to eliminate harmful algal blooms. nZVI can therefore affect microorganisms in the vicinity of the application area, including microalgae. However, studies on early transcriptomic effects of microalgae after exposure to nZVI are rare. Here, we described the early physiological and transcriptomic response of the freshwater ecological indicator green microalga, Raphidocelis subcapitata ATCC 22662, to 100 mg/L of reactive nZVI and non-reactive nano-magnetite (nFe3O4). The combined effect of shading and the release of total iron from nZVI posed a short-term inhibition effect leading to 15 % of deformed cells and cytosol leakage, while cells viability increased after 24 h. nZVI triggered a more pronounced transcriptomic response with (7380 differentially expressed genes [DEGs]) compared to nFe3O4 (4601 DEGs) after 1 h. nZVI, but not nFe3O4 increased the expression of genes function in DNA repair and replication, while deactivated carbohydrate-energy metabolisms, mitochondria signaling, and transmembrane ion transport. This study highlights an early fate assessment of algal cells under nZVI and nFe3O4 exposure using next-generation risk assessment methods and will serve as valuable information for safe and sustainable application of nZVI in water remediation.

The Green Synthesis of Silver Nanoparticles from Avena fatua Extract: Antifungal Activity against Fusarium oxysporum f.sp. lycopersici

Using plant extracts as eco-friendly reducing and stabilizing agents for the synthesis of nanoparticles has gained significant attention in recent years. The current study explores the green synthesis of silver nanoparticles (AgNPs) using the Avena fatua extract and evaluates their antifungal activity against Fusarium oxysporum f.sp. lycopersici (Fol), a fungal plant pathogen. A green and sustainable approach was adopted to synthesize silver nanoparticles before these nanoparticles were employed for anti-fungal activity. The primary indication that AgNPs had formed was performed using UV-vis spectroscopy, where a strong peak at 425 nm indicated the effective formation of these nanoparticles. The indication of important functional groups acting as reducing and stabilizing agents was conducted using the FTIR study. Additionally, morphological studies were executed via SEM and AFM, which assisted with more effectively analyzing AgNPs. Crystalline behavior and size were estimated using powder XRD, and it was found that AgNPs were highly crystalline, and their size ranged from 5 to 25 nm. Synthesized AgNPs exhibited significant antifungal activity against Fol at a concentration of 40 ppm. Furthermore, the inhibitory index confirmed a positive correlation between increasing AgNPs concentration and exposure duration. This study suggests that the combined phytochemical mycotoxic effect of the plant extract and the smaller size of synthesized AgNPs were responsible for the highest penetrating power to inhibit Fol growth. Moreover, this study highlights the potential of using plant extracts as reducing and capping agents for the green synthesis of AgNPs with antifungal properties. The study concludes that A. fatua extract can synthesize antifungal AgNPs as a sustainable approach with robust antifungal efficacy against Fol, underscoring their promising potential for integration into plant protection strategies.

Adverse effects of iron-based nanoparticles on freshwater phytoplankton Scenedesmus armatus and Microcystis aeruginosa strains

Zero-valent nano-iron particles (nZVI) are increasingly present in freshwater aquatic environments due to their numerous applications in environmental remediation. However, despite the broad benefits associated with the use and development of nZVI nanoparticles, the potential risks of introducing them into the aquatic environment need to be considered. Special attention should be focused on primary producer organisms, the basal trophic level, whose impact affects the rest of the food web. Although there are numerous acute studies on the acute effects of these nanoparticles on photosynthetic primary producers, few studies focus on long-term exposures. The present study aimed at assessing the effects of nZVI on growth rate, photosynthesis activity, and reactive oxygen activity (ROS) on the freshwater green algae Scenedesmus armatus and the cyanobacteria Microcystis aeruginosa. Moreover, microcystin production was also evaluated. These parameters were assessed on both organisms singly exposed to 72 h-effective nZVI concentration for 10% maximal response for 28 days. The results showed that the cell growth rate of S. armatus was initially significantly altered and progressively reached control-like values at 28 days post-exposure, while M. aeruginosa did not show any significant difference concerning control values at any time. In both strains dark respiration (R) increased, unlike net photosynthesis (Pn), while gross photosynthesis (Pg) only slightly increased at 7 days of exposure and then became equal to control values at 28 days of exposure. The nZVI nanoparticles generated ROS progressively during the 28 days of exposure in both strains, although their formation was significantly higher on green algae than on cyanobacteria. These data can provide additional information to further investigate the potential risks of nZVI and ultimately help decision-makers make better informed decisions regarding the use of nZVI for environmental remediation.

Priming effects of nZVI on carbon sequestration and iron uptake are positively mediated by AM fungus in semiarid agricultural soils

We investigated the priming effect of nanoscale zero-valent iron (nZVI) on carbon sink and iron uptake, and the possible mediation by AMF (arbuscular mycorrhizal fungi, Funneliformis mosseae) in semiarid agricultural soils. Maize seed dressings comprised of three nZVI concentrations of 0, 1, 2 g·kg^-1 and was tested with and without AMF inoculation under high and low soil moistures, respectively. The ICP-OES observations indicated that both low dose of nZVI (1 g·kg^-1) and high dose of nZVI (2 g·kg^-1) significantly increased the iron concentrations in roots (L: 54.5-109.8 %; H: 119.1-245.4 %) and shoots (L: 40.8-78.9 %; H: 81.1-99.4 %). Importantly, the absorption and translocation rate of iron were substantially improved by AMF inoculation under the low-dose nZVI. Yet, the excess nanoparticles as a stress were efficiently relieved by rhizosphere hyphae, and the iron concentration in leaves and stems can maintain as high as about 300 mg·kg^-1 while the iron translocation efficiency was reduced. Moreover, next-generation sequencing confirmed that appropriate amount of nZVI clearly improved the rhizosphere colonization of Funneliformis mosseae (p < 0.001) and the development of soil fungal community. Soil observations further showed that the hyphae development and GRSP (glomalin-related soil protein) secretion were significantly promoted (p < 0.05), with the increased R_0.25 (< 0.25 mm) by 35.97-41.16 %. As a return, AMF and host plant turned to input more organic matter into soils for microbial growth and Fe uptake, and such interactions became more pronounced under drought stress. In contrast, high dose of nZVI (2 g·kg^-1) tended to agglomerate on the surface of hyphae and spores, causing severe deformation and inactivation of AMF symbionts. Therefore, the priming effects of nZVI on carbon sequestration and Fe uptake in agricultural soils were positively mediated by AMF via the feedback loop of the plant-soil-microbe system for enhanced adaptation to global climate change.

Decoupling Fe0 Application and Bioaugmentation in Space and Time Enables Microbial Reductive Dechlorination of Trichloroethene to Ethene: Evidence from Soil Columns

Fe⁰ is a powerful chemical reductant with applications for remediation of chlorinated solvents, including tetrachloroethene and trichloroethene. Its utilization efficiency at contaminated sites is limited because most of the electrons from Fe⁰ are channeled to the reduction of water to H₂ rather than to the reduction of the contaminants. Coupling Fe⁰ with H₂-utilizing organohalide-respiring bacteria (i.e., Dehalococcoides mccartyi) could enhance trichloroethene conversion to ethene while maximizing Fe⁰ utilization efficiency. Columns packed with aquifer materials have been used to assess the efficacy of a treatment combining in space and time Fe⁰ and aD. mccartyi-containing culture (bioaugmentation). To date, most column studies documented only partial conversion of the solvents to chlorinated byproducts, calling into question the feasibility of Fe⁰ to promote complete microbial reductive dechlorination. In this study, we decoupled the application of Fe⁰ in space and time from the addition of organic substrates andD. mccartyi-containing cultures. We used a column containing soil and Fe⁰ (at 15 g L^-1 in porewater) and fed it with groundwater as a proxy for an upstream Fe⁰ injection zone dominated by abiotic reactions and biostimulated/bioaugmented soil columns (Bio-columns) as proxies for downstream microbiological zones. Results showed that Bio-columns receiving reduced groundwater from the Fe⁰-column supported microbial reductive dechlorination, yielding up to 98% trichloroethene conversion to ethene. The microbial community in the Bio-columns established with Fe⁰-reduced groundwater also sustained trichloroethene reduction to ethene (up to 100%) when challenged with aerobic groundwater. This study supports a conceptual model where decoupling the application of Fe⁰ and biostimulation/bioaugmentation in space and/or time could augment microbial trichloroethene reductive dechlorination, particularly under oxic conditions.

Ahmed E, Battah B, Abd Ellah NH, Zanetti S, Donadu MG. Nanotechnology as a Promising Approach to Combat Multidrug Resistant Bacteria: A Comprehensive Review and Future Perspectives

The wide spread of antibiotic resistance has been alarming in recent years and poses a serious global hazard to public health as it leads to millions of deaths all over the world. The wide spread of resistance and sharing resistance genes between different types of bacteria led to emergence of multidrug resistant (MDR) microorganisms. This problem is exacerbated when microorganisms create biofilms, which can boost bacterial resistance by up to 1000-fold and increase the emergence of MDR infections. The absence of novel and potent antimicrobial compounds is linked to the rise of multidrug resistance. This has sparked international efforts to develop new and improved antimicrobial agents as well as innovative and efficient techniques for antibiotic administration and targeting. There is an evolution in nanotechnology in recent years in treatment and prevention of the biofilm formation and MDR infection. The development of nanomaterial-based therapeutics, which could overcome current pathways linked to acquired drug resistance, is a hopeful strategy for treating difficult-to-treat bacterial infections. Additionally, nanoparticles' distinct size and physical characteristics enable them to target biofilms and treat resistant pathogens. This review highlights the current advances in nanotechnology to combat MDR and biofilm infection. In addition, it provides insight on development and mechanisms of antibiotic resistance, spread of MDR and XDR infection, and development of nanoparticles and mechanisms of their antibacterial activity. Moreover, this review considers the difference between free antibiotics and nanoantibiotics, and the synergistic effect of nanoantibiotics to combat planktonic bacteria, intracellular bacteria and biofilm. Finally, we will discuss the strength and limitations of the application of nanotechnology against bacterial infection and future perspectives.

Nanoparticle surface coatings produce distinct antibacterial effects that are consistent across diverse bacterial species

Nanoparticles have been proposed as tunable delivery vehicles for targeted treatments and, in some cases, the active therapeutic agents themselves. Despite the promise of such customizable impacts, little evidence exists to support these claims in the realm of antibiotics. Exploration of the silver and copper nanoparticle antibacterial impacts have been reported with inconsistent results. Here, we investigate the physical, chemical, and bacterial properties of silver and copper core particles stabilized with commonly used surface coatings, namely, polyvinylpyrrolidone (PVP, to confer a neutrally charged surface), cetrimonium bromide (CTAB, positively charged surface), citrate (Cit, negatively charged surface for silver nanoparticles), and ascorbic acid (AA, negatively charged surface for copper nanoparticles. The impacts of these potential antibacterial nanoparticles are measured against three bacterial species spanning deep divisions in the bacterial tree of life and include Escherichia coli, Staphylococcus aureus, and Sphingobacterium multivorum. Varying dose, core composition, surface coating, and bacterial species revealed that nanoparticle surfaces accounted for most of the variation in antibacterial activity. In all experiments, dose produced a linear inhibitory effect. Surprisingly, bacterial species reacted similarly regardless of evolutionary relatedness. There is a high degree of consistency, effectiveness, and efficacy among PVP silver and copper nanoparticle. These findings have implications for the intentional use of nanotechnology in environmental systems.

Nanoparticles, a Double-Edged Sword with Oxidant as Well as Antioxidant Properties—A Review

The usage of nanoparticles became inevitable in medicine and other fields when it was found that they could be administered to hosts to act as oxidants or antioxidants. These oxidative nanoparticles act as pro-oxidants and induce oxidative stress-mediated toxicity through the generation of free radicals. Some nanoparticles can act as antioxidants to scavenge these free radicals and help in maintaining normal metabolism. The oxidant and antioxidant properties of nanoparticles rely on various factors including size, shape, chemical composition, etc. These properties also help them to be taken up by cells and lead to further interaction with cell organelles/biological macromolecules, leading to either the prevention of oxidative damage, the creation of mitochondrial dysfunction, damage to genetic material, or cytotoxic effects. It is important to know the properties that make these nanoparticles act as oxidants/antioxidants and the mechanisms behind them. In this review, the roles and mechanisms of nanoparticles as oxidants and antioxidants are explained.

Dissolved iron released from nanoscale zero-valent iron (nZVI) activates the defense system in bacterium Pseudomonas putida, leading to high tolerance to oxidative stress

Nanoscale zero-valent iron (nZVI) has increasingly been applied to remediate aquifers polluted by organochlorines or heavy metals. As a result, bacteria in the vicinity of remediate action can be stressed by surplus iron released from nZVI. However, the understanding of the iron stress defense pathways during this process is currently incomplete. Therefore, we aimed to elucidate the physiological and transcriptomic response of the bacterium, Pseudomonas putida NCTC 10936, to 100 mg/L of nZVI and 44.5 µg/L of dissolved iron obtained from nZVI suspension. Cell viability was neither affected by nZVI nor dissolved iron, although the dissolved iron caused stress that altered the cell physiology and caused the generation of smaller cells, whereas cells were elongated in the presence of nZVI. Transcriptomic analysis confirmed the observed stronger physiological effect caused by dissolved iron (in total 3839 differentially expressed genes [DEGs]) than by nZVI (945 DEGs). Dissolved iron (but not nZVI) activated genes involved in oxidative stress-related pathways, antioxidant activity, carbohydrate and energy metabolism, but downregulated genes associated with flagellar assembly proteins and two-component systems involved in sensing external stimuli. As a result, bacteria very effectively faced oxidative insults and cell viability was not affected.

Dual effects of nZVI on maize growth and water use are positively mediated by arbuscular mycorrhizal fungi via rhizosphere interactions

Nanoscale zero-valent iron (nZVI) might generate positive and negative effects on plant growth, since it acts as either hazardous or growth-promotion role. It is still unclear whether such dual roles can be mediated by arbuscular mycorrhizal fungi (AMF) in plant-AMF symbiosis. We first identified that in 1.5 g kg^-1 nZVI (≤1.5 g kg^-1 positively), maize biomass was increased by 15.83%; yet in 2.0 g kg^-1 nZVI, it turned to be declined by 6.83%, relative to non-nZVI condition (CK, p < 0.05), showing a negative effect. Interestingly, the inoculation of AMF massively improved biomass by 45.18% in 1.5 g kg^-1 nZVI, and relieved the growth inhibition by 2.0 g kg^-1 nZVI. The event of water use efficiency followed similar trend as that of biomass. We found that proper concentration of nZVI can positively interact with rhizosphere AMF carrier, enabling more plant photosynthetic carbon to be remobilized to mycorrhiza. The scanning of transmission electron microscopy showed that excessive nZVI can infiltrate into root cortical cells and disrupt cellular homeostasis mechanism, significantly increasing iron content in roots by 76.01% (p < 0.05). Simultaneously, the images of scanning electron microscopy showed that nZVI were attached on root surface to form an insoluble iron ion (Fe³⁺) layer, hindering water absorption. However, they were efficiently immobilized and in situ intercepted by extraradical hyphae in mycorrhizal-nZVI symbiosis, lowering iron translocation efficiency by 6.07% (p < 0.05). Herein, the optimized structure remarkably diminished aperture blockage at root surface and improved root activities by 30.06% (p < 0.05). Particularly, next-generation sequencing demonstrated that appropriate amount of nZVI promoted the colonization and development of Funneliformis mosseae as dominant species in rhizosphere, confirming the positive interaction between AMF and nZVI, and its regulatory mechanism. Therefore, dual effects of nZVI can be actively mediated by AMF via rhizosphere interactions. The findings provided new insights into the safe and efficient application of nanomaterials in agriculture.

Zero-Valent Iron Nanoparticles Induce Reactive Oxygen Species in the Cyanobacterium, Fremyella diplosiphon

Nanoscale zero-valent iron nanoparticles (nZVIs) are known to boost biomass production and lipid yield in Fremyella diplosiphon, a model biodiesel-producing cyanobacterium. However, the impact of nZVI-induced reactive oxygen species (ROS) in F. diplosiphon has not been evaluated. In the present study, ROS in F. diplosiphon strains (B481-WT and B481-SD) generated in response to nZVI-induced oxidative stress were quantified and the enzymatic response determined. Lipid peroxidation as a measure of oxidative stress revealed significantly higher malondialdehyde content (p < 0.01) in both strains treated with 3.2, 12.8, and 51.2 mg L^-1 nZVIs compared to untreated control. In addition, ROS in all nZVI-treated cultures treated with 1.6-25.6 mg L^-1 nZVIs was significantly higher than the untreated control as determined by the 2',7'-dichlorodihydrofluorescein diacetate fluorometric probe. Immunodetection using densitometric analysis of iron superoxide dismutase (SOD) revealed significantly higher SOD levels in both strains treated with nZVIs at 51.2 mg L^-1. In addition, we observed significantly higher (p < 0.001) SOD levels in the B481-SD strain treated with 6.4 mg L^-1 nZVIs compared to 3.2 mg L^-1 nZVIs. Validation using transmission electron microscopy equipped with energy-dispersive X-ray spectroscopy (EDS) revealed adsorption of nZVIs with a strong iron peak in both B481-WT and B481-SD strains. While the EDS spectra showed strong signals for iron at 4 and 12 days after treatment, a significant decrease in peak intensity was observed at 20 days. Future efforts will be aimed at studying transduction mechanisms that cause metabolic and epigenetic alterations in response to nZVIs in F. diplosiphon.

In situ nanoremediation of soils and groundwaters from the nanoparticle's standpoint: A review

Anthropogenic pollution coming from industrial processes, agricultural practices and consumer products, results in the release of toxic substances into rural and urban environments. Once released, these chemicals migrate through the atmosphere and water, and find their way into matrices such as sediments and groundwaters, thus making large areas potentially uninhabitable. Common pollutants, including heavy metal(loid)s, radionuclides, aliphatic hydrocarbons and halogenated organics, are known to adversely affect physiological systems in animal species. Pollution can be cleaned up using techniques such as coagulation, reverse osmosis, oxidation and biological methods, among others. The use of nanoparticles (NPs) extends the range of available technologies and offers particular benefits, not only by degrading, transforming and immobilizing contaminants, but also by reaching inaccessible areas and promoting biotic degradation. The development of NPs is understandably heralded as an environmentally beneficial technology; however, it is only now that the ecological risks associated with their use are being evaluated. This review presents recent developments in the use of engineered NPs for the in situ remediation of two paramount environmental matrices: soils and groundwaters. Emphasis will be placed on (i) the successful applications of nano-objects for environmental cleanup, (ii) the potential safety implications caused by the challenging requirements of [high reactivity toward pollutants] vs. [none reactivity toward biota], with a thorough view on their transport and evolution in the matrix, and (iii) the perspectives on scientific and regulatory challenges. To this end, the most promising nanomaterials will be considered, including nanoscale zerovalent iron, nano-oxides and carbonaceous materials. The purpose of the present review is to give an overview of the development of nanoremediators since they appeared in the 2000s, from their chemical modifications, mechanism of action and environmental behavior to an understanding of the problematics (technical limitations, economic constraints and institutional precautionary approaches) that will drive their future full-scale applications.

The role of soils in provision of genetic, medicinal and biochemical resources

Intact, 'healthy' soils provide indispensable ecosystem services that largely depend on the biotic activity. Soil health is connected with human health, yet, knowledge of the underlying soil functioning remains incomplete. This review highlights selected services, i.e. (i) soil as a genetic resource and hotspot of biodiversity, forming the basis for providing (ii) biochemical resources and (iii) medicinal services and goods. Soils harbour an unrivalled biodiversity of organisms, especially microorganisms. Some of the abilities of autochthonous microorganisms and their relevant enzymes serve (i) to improve natural soil functions and in particular plant growth, e.g. through beneficial plant growth-promoting, symbiotic and mycorrhizal microorganisms, (ii) to act as biopesticides, (iii) to facilitate biodegradation of pollutants for soil bioremediation and (iv) to yield enzymes or chemicals for industrial use. Soils also exert direct effects on human health. Contact with soil enriches the human microbiome, affords protection against allergies and promotes emotional well-being. Medicinally relevant are soil substrates such as loams, clays and various minerals with curative effects as well as pharmaceutically active organic chemicals like antibiotics that are formed by soil microorganisms. By contrast, irritating minerals, soil dust inhalation and misguided soil ingestion may adversely affect humans. This article is part of the theme issue 'The role of soils in delivering Nature's Contributions to People.

Single-cell Raman micro-spectroscopy for tracking of carotenoids in cyanobacteria exposed to Mn and Zn doped ferrite nanoparticles

Ferrite nanoparticles are increasingly produced and exploited as adsorbents for environmental pollutants. However, their impact on the aquatic microbiota such as cyanobacteria, are not yet investigated. Targeting the environmental monitoring context, in this paper we explored for the first time if any change in the carotenoid signal from cyanobacteria Coelomoron pussilum (AICB 1012) exposed to non-lethal doses of Mn and Zn doped ferrite nanoparticles (NPs) can be associated with the nano-aggression on single-cell level, using micro-Raman spectroscopy. UV-Vis absorption spectroscopy of the bulk culture and single-cell Raman microscopy showed that the carotenoid signal increases relative to the chlorophyll contribution upon exposure of the cells to the Mn-ferrite NPs throughout the 7 days of the experiment. The red-shift and broadening of the strongest carotenoid Raman band arising from (CC) stretching modes indicates the change of carotenoid profile towards increased amount of β-carotene in answer to the NPs stress. The increase of this band intensity relative to the fluorescence background was also observed in Zn-ferrite NPs treatment. Using a simplified and rapid sample preparation procedure, electron microscopy in both transmission and scanning modes, showed greater coverage of the cells by the stable colloidal AgNPs than by the magnetic ferrite NPs. The latter mostly clumped together rather than adhering to the cells. The combined single-cell micro-Raman tracking of physiological response of the unicellular photosynthetic microorganisms coupled with electron microscopy approach to visualise cell-NPs interaction and the extracellular polymeric substance secretion holds the promise for rapid assessment of the NPs-induced environmental stress acting on the unicellular organisms.

Evaluation of potential immunotoxic effects of iron oxide nanoparticles (IONPs) on antioxidant capacity, immune responses and tissue bioaccumulation in common carp (Cyprinus carpio)

Nanoparticles can be toxic and put human and animals' life at risk. The present work was carried out to evaluate the possible immunosuppressive effects of water borne iron oxide nanoparticles (IONPs) and the FeCl₃ on immune components of common carp (Cyprinus carpio). Fish were exposed to a series of chronic levels of 25%, 50%, and 75% of IONPs LC₅₀ 96 h concentration (referred to as control, NP1, NP2, and NP3 respectively) or FeCl₃ (same concentrations as IONPs referred to as S1, S2, and S3 respectively) for 21 days. Results revealed alterations in blood parameters, where IONPs significantly decreased number of white blood cells at all concentrations. Glucose and cortisol increased in all exposed fish after 21 days, suggesting activation of the maintenance mechanism cascade against a chronic stressor. IONPs or FeCl₃ significantly accumulated in liver tissue of exposed fish. Immune responses were remarkably decreased in serum and skin mucus in response to IONPs or FeCl₃. These components were at lowest levels in fish exposed to the highest concentrations of IONPs and FeCl₃. The findings of the present study suggested that IONPs is accumulated in fish liver and intestine, where they may exhibit immunotoxicity.

Mechanism of nanotoxicity in Chlorella vulgaris exposed to zinc and iron oxide

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Growth kinetics of C. vulgaris is influenced by NPs exposure.

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NPs exposure influence proline, carotenoid, activity of SOD, CAT and LDH.

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NPs exposure disintegrate cellular membrane.

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Zinc and iron oxide NPs are more toxic to C. vulgaris compared to bulk counterpart.

Usage of nanoparticle in various products has increased tremendously in the recent past. Toxicity of these nanoparticles can have a huge impact on aquatic ecosystem. Algae are the ideal organism of the aquatic ecosystem to understand the toxicity impact of nanoparticles. The present study focuses on the toxicity evaluation of zinc oxide (ZnO) and iron oxide (Fe₂O₃) nanoparticles towards freshwater microalgae, Chlorella vulgaris. The dose dependent growth retardation in Chlorella vulgaris is observed under ZnO and Fe₂O₃ nanoparticles and nanoform attributed more toxicity than their bulk counterparts. The IC₅₀ values of ZnO and Fe₂O₃ nanoparticles was reported at 0.258 mg L⁻¹ and 12.99 mg L^-1 whereas, for the bulk-form, it was 1.255 mgL^-1 and 17.88 mg L⁻¹, respectively. The significant decline in chlorophyll content and increase in proline content, activity of superoxide dismutase and catalase, indicated the stressful physiological state of microalgae. An increased lactate dehydrogenase level in treated samples suggested membrane disintegration by ZnO and Fe₂O₃ nanoparticles. Compound microscopy, scanning electron microscopy and transmission electron microscopy confirm cell entrapment, deposition of nanoparticles on the cell surface and disintegration of algal cell wall. Higher toxicity of nanoform in comparison to bulk chemistry is a point of concern.

Impact of Zero-Valent Iron on Freshwater Bacterioplankton Metabolism as Predicted from 16S rRNA Gene Sequence Libraries

The application of zero-valent iron particles (ZVI) for the treatment of heavily polluted environment and its biological effects have been studied for at least two decades. Still, information on the impact on bacterial metabolic pathways is lacking. This study describes the effect of microscale and nanoscale ZVI (mZVI and nZVI) on the abundance of different metabolic pathways in freshwater bacterial communities. The metabolic pathways were inferred from metabolism modelling based on 16S rRNA gene sequence data using paprica pipeline. The nZVI changed the abundance of numerous metabolic pathways compared to a less influencing mZVI. We identified the 50 most affected pathways, where 31 were related to degradation, 17 to biosynthesis, and 2 to detoxification. The linkage between pathways was two times higher in nZVI samples compared to mZVI, and was specifically higher considering the arsenate detoxification II pathway. Limnohabitans and Roseiflexus were linked to the same pathways in both nZVI and mZVI. The prediction of metabolic pathways increases our knowledge of the impacts of nZVI and mZVI on freshwater bacterioplankton.

Synergistic Zerovalent Iron (Fe0) and Microbiological Trichloroethene and Perchlorate Reductions Are Determined by the Concentration and Speciation of Fe

Trichloroethene (TCE) and perchlorate (ClO₄^-) are cocontaminants at multiple Superfund sites. Fe⁰ is often used during TCE bioremediation with Dehalococcoides mccartyi to establish anoxic conditions in the aquifer. However, the synergy between Fe⁰ abiotic reactions and microbiological TCE and ClO₄^- reductions is poorly understood and seldom addressed in the literature. Here, we investigated the effects of Fe⁰ and its oxidation product, Fe²⁺, at field-relevant concentrations in promoting microbial TCE and ClO₄^- reductions. Using semibatch microcosms with a Superfund site soil and groundwater, we showed that the high Fe⁰ concentration (16.5 g L^-1) expected during Fe⁰in situ injection mostly yielded TCE abiotic reduction to ethene/ethane. However, such concentrations obscured dechlorination by D. mccartyi, impeded ClO₄^- reduction, and enhanced SO₄^2- reduction and methanogenesis. Fe²⁺ at 0.25 g L^-1 substantially delayed conversion of TCE to ethene when compared to no-Fe controls. A low concentration of aged-Fe⁰ synergistically promoted microbiological TCE dechlorination to ethene while achieving complete ClO₄^- reduction. Collectively, these results illustrate scenarios relevant at or downstream of Fe⁰ injection zones when Fe⁰ is used to facilitate microbial dechlorination. Results also underscore the potential detrimental effects of Fe⁰ and bioaugmentation cultures coinjection for in situ treatment of chlorinated ethenes and ClO₄^-.

Transcriptomics Uncovers the Response of Anammox Bacteria to Dissolved Oxygen Inhibition and the Subsequent Recovery Mechanism

Understanding the recovery of anaerobic ammonium-oxidizing (anammox) bacteria after inhibition by dissolved oxygen (DO) is critical for the successful applications of anammox-based processes. Therefore, the effects of oxygen exposure (2 mg L^-1 DO for 90 min) and subsequent recovery treatments [N₂ purging or nano zero-valent iron (nZVI) addition] on the activity and gene expression in a Kuenenia stuttgartiensis enrichment culture were examined. Combining the self-organizing map clustering and enrichment analysis, we proposed the oxidative stress response of anammox bacteria based on the existing concepts of oxidative stress in microbes: the DO exposure triggered a stringent response in K. stuttgartiensis, which downregulated the transcription levels of genes involved in the central metabolism and diverted energy to a flagellar assembly and metal transport modules; these changes possibly promoted survival during the inhibition of anammox activity. According to the cotranscription with central catabolism genes, putative reactive oxygen species (ROS) scavenger genes (kat and sod) were presumed to detoxify the anammox intermediates rather than ROS. In addition, both activity and mRNA profiles with appropriate amount of nZVI addition (5 and 25 mg L^-1) were close to that of control, which proved the effectiveness of nZVI addition in anammox recovery. These results would be relevant to the physio-biochemistry development of anammox bacteria and further enhancement of nitrogen removal in wastewater treatment.

In Vitro Study of the Toxicity Mechanisms of Nanoscale Zero-Valent Iron (nZVI) and Released Iron Ions Using Earthworm Cells

During the last two decades, nanomaterials based on nanoscale zero-valent iron (nZVI) have ranked among the most utilized remediation technologies for soil and groundwater cleanup. The high reduction capacity of elemental iron (Fe⁰) allows for the rapid and cost-efficient degradation or transformation of many organic and inorganic pollutants. Although worldwide real and pilot applications show promising results, the effects of nZVI on exposed living organisms are still not well explored. The majority of the recent studies examined toxicity to microbes and to a lesser extent to other organisms that could also be exposed to nZVI via nanoremediation applications. In this work, a novel approach using amoebocytes, the immune effector cells of the earthworm Eisenia andrei, was applied to study the toxicity mechanisms of nZVI. The toxicity of the dissolved iron released during exposure was studied to evaluate the effect of nZVI aging with regard to toxicity and to assess the true environmental risks. The impact of nZVI and associated iron ions was studied in vitro on the subcellular level using different toxicological approaches, such as short-term immunological responses and oxidative stress. The results revealed an increase in reactive oxygen species production following nZVI exposure, as well as a dose-dependent increase in lipid peroxidation. Programmed cell death (apoptosis) and necrosis were detected upon exposure to ferric and ferrous ions, although no lethal effects were observed at environmentally relevant nZVI concentrations. The decreased phagocytic activity further confirmed sublethal adverse effects, even after short-term exposure to ferric and ferrous iron. Detection of sublethal effects, including changes in oxidative stress-related markers such as reactive oxygen species and malondialdehyde production revealed that nZVI had minimal impacts on exposed earthworm cells. In comparison to other works, this study provides more details regarding the effects of the individual iron forms associated with nZVI aging and the cell toxicity effects on the specific earthworms' immune cells that represent a suitable model for nanomaterial testing.

Impact of Zero-Valent Iron Nanoparticles on Fremyella diplosiphon Transesterified Lipids and Fatty Acid Methyl Esters

Efforts to enhance the transformative potential of biofuels is an important step to achieving an environment-friendly and sustainable energy source. Fremyella diplosiphon is an ideal third-generation biofuel agent due to its ability to produce lipids and desirable essential fatty acids. In this study, the impact of Nanofer 25s nanoscale zero-valent iron nanoparticles (nZVIs) on total lipid content and fatty acid composition of F. diplosiphon strains SF33 and B481 was investigated. We observed significant increases (P < 0.05) in the growth of F. diplosiphon treated with 0.2-1.6 mg L^-1 Nanofer 25s, indicating that trace concentrations of nZVIs were not toxic to the organism. Chlorophyll a, carotenoids, and phycobiliprotein levels were not altered in F. diplosiphon treated with nZVIs ranging from 0.4 to 1.6 mg L^-1, confirming that these concentrations did not negatively impact photosynthetic efficacy. In addition, Nanofer 25s ranging from 0.2 to 1.6 mg L^-1 had an optimal impact on SF33 and B481 total lipid content. We identified significant increases in unsaturated fatty acid methyl esters (FAMEs) from F. diplosiphon Nanofer 25s-treated transesterified lipids. Theoretical chemical and physical biofuel properties revealed a product with elevated cetane number and oxidative stability for both strains. Scanning electron microscopy and energy-dispersive X-ray spectroscopy validated the localization of nZVIs. Our findings indicate that Nanofer 25s nZVIs significantly enhance F. diplosiphon total lipid content and essential FAMEs, thus offering a promising approach to augment the potential of the cyanobacterium as a large-scale biofuel agent.

Impact of different environmental particles on degradation of dibutyl phthalate in coastal sediments with and without Cylindrotheca closterium

This study investigated the impact of different environmental particles at different concentrations (0.2% and 2%, w/w) on biodegradation of dibutyl phthalate (DBP) in sediments with and without Cylindrotheca closterium, a marine benthic diatom. The particles included biochar pyrolyzed at 400 °C, multi-walled carbon nanotube (MWNT), nanoscale zero-valent iron (nZVI) and polyethylene microplastic. In treatments without C. closterium, inhibition effect of the particles on degradation percentage of DBP (up to 15.7% decrement except 1.7% increment for 0.2% nZVI) increased with the increase of particle sorption ability to DBP and particle concentration in general. The results of 16s rDNA sequencing showed that C. closterium was probably the most abundant DBP-degrader, accounting for 20.0-49.3% of the total taxon read numbers. In treatments with C. closterium, inoculation of C. closterium increased the degradation percentage of DBP in all treatments with particle addition by 0.0-11.3%, which increased with the increase of chlorophyll a content in general but decreased with the increase of particle concentration from 0.2% to 2%. The increment was the highest for treatment with 0.2% nZVI addition due to its highest promotion effect on algal growth. In contrast, the increment was the lowest for treatments with MWNT addition due to its strong sorption to DBP and strong inhibition on the growth of C. closterium. Our findings suggested that the environmental particles could influence bioavailability of DBP by sorption and biomass of C. closterium, and thus degradation of DBP in sediments.

Modification of zero valent iron nanoparticles by sodium alginate and bentonite: Enhanced transport, effective hexavalent chromium removal and reduced bacterial toxicity

The rapid aggregation/sedimentation and decreased transport of nanoscale zero-valent iron (nZVI) particles limit their application in groundwater remediation. To decrease the aggregation/sedimentation and increase the transport of nZVI, sodium alginate (a natural polysaccharide) and bentonite (one type of ubiquitous clay) were employed to modify nZVI. Different techniques were utilized to characterize the modified nZVI. We found that modification with either sodium alginate or bentonite could disperse nZVI and shifted their zeta potentials from positive to negative. Comparing with the bare nZVI, the sedimentation rates of modified nZVI either by sodium alginate or bentonite are greatly decreased and their transport are significantly increased. The transport of modified nZVI can be greatly increased by increasing flow rate. Furthermore, Cr(VI) can be efficiently removed by the modified nZVI (both sodium alginate and bentonite modified nZVI). Comparing with bare nZVI, the two types of modified nZVI contain lower toxicities to Escherichia coli. The results of this study indicate that both sodium alginate and bentonite can be employed as potential stabilizers to disperse nZVI and improve their application feasibility for in situ groundwater remediation.

Augmenting Fremyella diplosiphon Cellular Lipid Content and Unsaturated Fatty Acid Methyl Esters Via Sterol Desaturase Gene Overexpression

Cyanobacteria have immense prospective as a platform for renewable energy; however, a major barrier in achieving optimal productivity is the low lipid yield. Fremyella diplosiphon, a model cyanobacterium, is an ideal biofuel agent due to its desirable fatty acid methyl esters (FAMEs). To enhance lipid content, we overexpressed the sterol desaturase (SD) gene in F. diplosiphon B481 wild type by genetic transformation. This effort resulted in a transformant (B481-SD) with a 64-fold increase in the SD gene at the mRNA transcript level, with no loss in growth and pigmentation. The transformant was persistently grown for over 32 generations indicating long-term stability and vitality. We observed 27.3% and 23% increases in total lipid content and unsaturated FAMEs respectively in B481-SD transesterified lipids with methyl octadecadienoate as the most abundant unsaturated component. In addition, we detected an 81% increase in FAME composition in the transformant compared with the wild type. Theoretical physical and chemical properties confirmed a FAME profile with very high cetane number (65.972-67.494) and oxidative stability (50.493-18.66 h) in the engineered strain. Results of the study offer a promising approach to augment F. diplosiphon total lipid content and unsaturated FAMEs, thus paving the way to enhance biofuel capacity of the organism.

Oxidative stress in microbes after exposure to iron nanoparticles: analysis of aldehydes as oxidative damage products of lipids and proteins

Due to their enhanced reactivity, metal and metal-oxide nanoscale zero-valent iron (nZVI) nanomaterials have been introduced into remediation practice. To ensure that environmental applications of nanomaterials are safe, their possible toxic effects should be described. However, there is still a lack of suitable toxicity tests that address the specific mode of action of nanoparticles, especially for nZVI. This contribution presents a novel approach for monitoring one of the most discussed adverse effects of nanoparticles, i.e., oxidative stress (OS). We optimized and developed an assay based on headspace-SPME-GC-MS analysis that enables the direct determination of volatile oxidative damage products (aldehydes) of lipids and proteins in microbial cultures after exposure to commercial types of nZVI. The method employs PDMS/DVB SPME fibers and pentafluorobenzyl derivatization, and the protocol was successfully tested using representatives of bacteria, fungi, and algae. Six aldehydes, namely, formaldehyde, acrolein, methional, benzaldehyde, glyoxal, and methylglyoxal, were detected in the cultures, and all of them exhibited dose-dependent sigmoidal responses. The presence of methional, which was detected in all cultures except those including an algal strain, documents that nZVI also caused oxidative damage to proteins in addition to lipids. The most sensitive toward nZVI exposure in terms of aldehyde production was the yeast strain Saccharomyces cerevisiae, which had an EC₅₀ value of 0.08 g/L nZVI. To the best of our knowledge, this paper is the first to document the production of aldehydes resulting from lipids and proteins as a result of OS in microorganisms from different kingdoms after exposure to iron nanoparticles.

Investigation of Zearalenone Adsorption and Biotransformation by Microorganisms Cultured under Cellular Stress Conditions

The zearalenone binding and metabolization ability of probiotic microorganisms, such as lactic acid bacteria, Lactobacillus paracasei, Lactococcus lactis, and yeast Saccharomyces cerevisiae, isolated from food products, were examined. Moreover, the influence of cellular stress (induced by silver nanoparticles) and lyophilization on the effectiveness of tested microorganisms was also investigated. The concentration of zearalenone after a certain time of incubation with microorganisms was determined using high-performance liquid chromatography. The maximum sorption effectiveness for L. paracasei, L. lactis, and S. cerevisiae cultured in non-stress conditions was 53.3, 41.0, and 36.5%, respectively. At the same time for the same microorganisms cultured at cellular stress conditions, the maximum sorption effectiveness was improved to 55.3, 47.4, and 57.0%, respectively. Also, the effect of culture conditions on the morphology of the cells and its metabolism was examined using microscopic technique and matrix-assisted laser desorption ionization-time of flight mass spectrometry, respectively.

Iron oxide nanoparticle phytotoxicity to the aquatic plant Lemna minor: effect on reactive oxygen species (ROS) production and chlorophyll a/chlorophyll b ratio

Although iron oxide occurs naturally in the environment, iron oxide nanoparticles have distinct mobility, reactivity, and toxicity, which can harm the human health and nature. This scenario has motivated the investigation of the toxic effects of iron oxide nanoparticles (akaganeite predominance + hematite) on the aquatic plant Lemna minor. First, nanoparticles were synthesized and characterized; then, different iron oxide NP concentrations were added to Lemna minor culture. After 7 days, all the Lemna minor leaves died, irrespective of the added NP concentration. The iron oxide NP impact on the plant was evaluated based on malondialdehyde (MDA) production from thiobarbituric acid reactive substances (TBARS), which was dose-dependent; i.e., lipid peroxidation in the plant increased with rising iron oxide NP concentration. The chlorophyll content decreased at high iron oxide NP concentrations, which disrupted the light absorption mechanism. Fe accumulation in Lemna minor roots also occurred, which can harm nutrient uptake. Therefore, the iron oxide NP toxic impact on plants and related ecosystems requires further studies in order to prevent environmental damage.

Impacts of iron oxide and titanium dioxide nanoparticles on biogas production: Hydrogen sulfide mitigation, process stability, and prospective challenges

Anaerobic digestion for biogas production is one of the most used technology for bioenergy. However, the adoption of nanoparticles still needs further studies. Therefore, this study was designed to examine the effect of metal oxide nanoparticles (MONPs) at four different concentrations in two different combinations, 20 (R1) and 100 (R2) mg/L for Fe₂O₃, 100 (R3) and 500 (R4) mg/L for TiO₂, and a mixture of Fe₂O₃ and TiO₂ at rates of 20, 500 (R5) and 100, and 500 (R6), on hydrogen sulfide (H₂S) mitigation, biogas, and methane (CH₄) yield during the anaerobic digestion of cattle manure (CM) using an anaerobic batch system. The results showed that H₂S production was 2.13, 2.38, 2.37, 2.51, 2.64, and 2.17 times lower than that of the control (R0), respectively, when the CM was treated by the aforementioned MONPs. Additionally, biogas and CH₄ production were 1.09 and 1.105, 1.15 and 1.191, 1.07 and 1.097, 1.17 and 1.213, 1.10 and 1.133, and 1.13 and 1.15 times higher than those of R0 when R1, R2, R3, R4, R5, and R6 were supplemented with MONPs, respectively. The highest specific production of biogas and CH₄ was 336.25 and 192.31 mL/gVS, respectively, which was achieved by R4 supplemented with 500 mg/L TiO₂ NPs, while the corresponding values in the case of R0 were 286.38 and 158.55 mL/gVS.

Comparison of short-term dosing ferrous ion and nanoscale zero-valent iron for rapid recovery of anammox activity from dissolved oxygen inhibition

As obligate anaerobes, anammox bacteria are sensitive to oxygen, which might hinder the maximization of anammox activity. However, there are very few effective strategies to rapidly recover anammox activity after its deterioration under exposure of oxygen. In this study, the activity recovery of anammox bacteria encountering dissolved oxygen (DO) exposure (0.2 and 2.0 mg L^-1) were compared by three strategies in short-term experiments, nZVI, Fe(II) dosing, and N₂ purging. nZVI is more effective in recovering anammox activity with a high DO exposure (2 mg L^-1), compared to a low DO exposure (0.2 mg L^-1). After inhibiting by 2.0 mg L^-1 DO, anammox activity recovery (normalized to the control) was ranked in the order of nZVI (5 mg L^-1) addition (63 ± 8.2%) > Fe(II) (5 mg L^-1) addition (41 ± 8.0%) >N₂ purging (39 ± 4.0%). In contrast to Fe(II) ion additions, the shell structure of nZVI combined with the buffering effect of biomass-extracellular polysaccharide (EPS) prevented the sharp pH variation and excessive dissolved Fe(II)/Fe(III) in solution. Under such circumstances, nZVI addition (5 and 25 mg L^-1) increased the intracellular reactive oxygen species (ROS) to a moderate level (<200%), which might be responsible for the better activity recovery of anammox than that of Fe(II) addition and N₂ purging. Specifically, 5 mg L^-1 nZVI dosage moderately enhanced the intracellular O₂^- production (∼150% of the control) after scavenging 2.0 mg L^-1 DO, and the anammox activity recovered better than that of both 5 and 25 mg L^-1 Fe(II) ions additions. However, high dosage nZVI (75 mg L^-1) inhibited anammox activity in spite of low or high DO exposure. Our findings elucidate that appropriate amount of nZVI (short-term dosing) can rapidly recover anammox activity when anammox bacteria encountering oxygen exposure accidentally and could be useful in facilitating the robust operation of anammox-based processes.

Shift in Natural Groundwater Bacterial Community Structure Due to Zero-Valent Iron Nanoparticles (nZVI)

Toxic and persistent contaminants in groundwater are technologically difficult to remediate. Remediation techniques using nanoparticles (NPs) such as nZVI (Zero-Valent Iron) are applicable as in situ reduction or oxidation agents and give promising results for groundwater treatment. However, these NP may also represent an additional contamination in groundwater. The aims of this study are to assess the impact of nZVI on the nitrate-reducing potential, the abundance and the structure of a planktonic nitrate-reducing bacterial community sampled in groundwater from a multicontaminated site. An active nitrate-reducing bacterial community was obtained from groundwater samples, and inoculated into batch reactors containing a carbon substrate, nitrate and a range of nZVI concentrations (from 0 to 70.1 mg Fe.L-1). Physical (pH, redox potential), chemical (NO 3 - concentrations) and biological (DNA, RNA) parameters were monitored during 1 week, as well as nZVI size distribution and mortality of bacteria. Nitrate-reducing activity was temporally stopped in the presence of nZVI at concentrations higher than 30 mg L-1, and bacterial molecular parameters all decreased before resuming to initial values 48 h after nZVI addition. Bacterial community composition was also modified in all cultures exposed to nZVI as shown by CE-SSCP fingerprints. Surprisingly, it appeared overall that bacteria viability was lower for lower nZVI concentrations. This is possibly due to the presence of larger, less reactive NP aggregates for higher nZVI concentrations, which inhibit bacterial activity but could limit cell mortality. After 1 week, the bacterial cultures were transplanted into fresh media without nZVI, to assess their resilience in terms of activity. A lag-phase, corresponding to an adaptation phase of the community, was observed during this step before nitrate reduction reiterated, demonstrating the community's resilience. The induction by nZVI of modifications in the bacterial community composition and thus in its metabolic potentials, if also occurring on site, could affect groundwater functioning on the long term following nZVI application. Further work dedicated to the study of nZVI impact on bacterial community directly on site is needed to assess a potential impact on groundwater functioning following nZVI application.

Responses of flocculated activated sludge to bimetallic Ag-Fe nanoparticles toxicity: Performance, activity enzymatic, and bacterial community shift

Ever-increasing production and use of nanoparticles (NPs) have aroused overarching concerns for their toxic effects on the environment and human. In the present study, the toxic effects of Silver (Ag) and Iron (Fe) NPs on the performance of activated sludge were investigated under continuous aerobic/anoxic/anaerobic conditions in laboratory-scale sequencing batch reactors (SBRs).Activated sludge was exposed to various concentrations (5-100 mg/L) of Ag-Fe NPs for 60 days and its response was assessed through the enzymatic activity, COD, nitrogen (TN) and phosphorus (TP) removal, toxicity tests, as well as variations in bacterial community. Compared with the pristine control sample, the exposure to NPs suppressed TN and TP removal efficiencies. Indeed, the respiration rate and biomass concentration were significantly affected by the NPs. Although the simultaneous exposure to Ag-Fe NPs did affect the integrity of cell membrane (LDH) and key enzymes activities, the higher concentration induced an increased generation of reactive oxygen species (ROS). The metagenome analysis revealed a marked shift in the microbial community structure suggesting that both heterotrophic and autotrophic communities were affected by the presence of Ag-Fe NPs. Our results provide some evidence for compounded effects of NPs in their simultaneous presence, and generate new leads for future research efforts.

Novelty of Bioengineered Iron Nanoparticles in Nanocoated Surgical Cotton: A Green Chemistry

The current focus of nanotechnology is to develop environmentally safe methodologies for the formulation of nanoparticles. The phytochemistry of Zingiber officinale inspired us to utilize it for the synthesis of iron nanoparticles. GC-MS analysis revealed the phytochemical profile of ginger. Out of 20 different chemicals, gingerol was found to be the most potent phytochemical with a retention time of 40.48 min. The present study reports a rapid synthesis method for the formation of iron nanoparticles and its potential efficacy as an antibacterial agent and an antioxidant. Because of its antibacterial property, ginger extract was used to coat surgical cotton. Synthesized ginger root iron nanoparticles (GR-FeNPs) were characterized by UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction analysis, and particle size analysis. XRD confirmed the crystalline structure of iron oxide nanoparticles as it showed the crystal plane (2 2 0), (3 1 1), (2 2 2), and (4 0 0). The particle size analyzer (PSA) showed the average size of the particles, 56.2 nm. The antimicrobial activity of the FeNPs was tested against different Gram-positive and Gram-negative bacteria. E. coli showed maximum inhibition as compared with the other organisms. Antioxidant activity proved the maximum rate of free radicals at 160 µg/mL produced by nanoparticles. In addition, the antimicrobial activity of nanocoated surgical cotton was evaluated on the first day and 30^th day after coating, which clearly showed excellent growth inhibition of organisms, setting a new path in the field of medical microbiology. Hence, iron-nanocoated surgical cotton synthesized using green chemistry, which is antimicrobial and cost effective, might be economically helpful and provide insights to the medical field, replacing conventional wound healing treatments, for better prognosis.

Nanoparticles in mitigating gaseous emissions from liquid dairy manure stored under anaerobic condition

A number of mitigation techniques exist to reduce the emissions of pollutant gases and greenhouse gases (GHGs) from anaerobic storage of livestock manure. Nanoparticle (NP) application is a promising mitigating treatment option for pollutant gases, but limited research is available on the mode of NP application and their effectiveness in gaseous emission reduction. In this study, zinc silica nanogel (ZnSNL), copper silica nanogel (CuSNL), and N-acetyl cysteine (NACL) coated zinc oxide quantum dot (Qdot) NPs were compared to a control lacking NPs. All three NPs tested significantly reduced gas production and concentrations compared to non-treated manure. Overall, cumulative gas volumes were reduced by 92.73%-95.83%, and concentrations reduced by 48.98%-99.75% for H₂S, and 20.24%-99.82% for GHGs. Thus, application of NPs is a potential treatment option for mitigating pollutant and GHG emissions from anaerobically stored manure.

Soil bacterial communities of Sahara and Gibson deserts: Physiological and taxonomical characteristics

The purpose of this research was to investigate the structure of soil bacteria communities present in the Gibson (Australia) and the Sahara (Egypt) deserts, as well as to estimate strain survivability under different environmental factors. It should be noticed that the screening of bacterial resistance to wide spectra of principally different stress conditions was performed for the first time. Experiments were conducted with culturable bacterial communities. Strains were identified using 16S rRNA sequencing, and stress-tolerance was estimated by growing strains in various nutrient media. In order to characterize the community the epifluorescent microscopy and multisubstrate testing were also performed. High bacterial abundance in the desert soils was detected, and there was seen a significant proportion of culturable cells. The close numbers of psychotropic and mesophilic bacteria in arid ecosystems were revealed. The representatives of the Actinobacteria phylum were dominant in the microbial communities, and Firmicutes, Proteobacteria, and Bacteroidetes phyla representatives were also identified. Tolerance of the axenic bacterial cultures, isolated from arid desert ecotopes, to temperature, pH, salts (KCl, NaCl, MgSO4, NaHCO3), strong oxidizers (Mg(ClO4)2), and antibiotics (ampicillin, cephalexin, chloramphenicol, tetracycline, doxycycline, kanamycin, rifampicin) was studied. The bacterial isolates were characterized by polyextremotolerance and by the ability to maintain metabolic activity in vitro while influenced by a wide range of physicochemical and biotic factors.

Novel assay for the toxicity evaluation of nanoscale zero-valent iron and derived nanomaterials based on lipid peroxidation in bacterial species

Nano-scale zero-valent iron (nZVI) began attracting research attention in remediation practice in recent decades as a prospective nanomaterial applicable to various contaminated matrices. Despite concerns about the negative effects of nanomaterials on ecosystems, the number of reliable toxicity tests is limited. We have developed a test based on the evaluation of oxidative stress (OS). The test employed the analysis of a typical OS marker (malondialdehyde, MDA), after exposure of six bacterial strains to the tested nanomaterial. We also attempted to use other OS and cell membrane damage assays, including the determination of glutathione and lactate dehydrogenase, respectively. However, we found that the components of these assays interfered with nZVI; therefore, these tests were not applicable. The MDA assay was tested using nZVI and three newly engineered oxide shell nZVI materials with different oxide thicknesses. Six different bacterial species were employed, and the results showed that the test was fully applicable for the concentrations of nanomaterials used in remediation practice (0.1-10 g/L). MDA was produced in a dose-response manner, and the bacteria showed a similar response toward pure pyrophoric nZVI, reaching EC₅₀ values of 0.3-1.1 g/L. We observed different responses in the absolute production of MDA; however, the MDA concentrations were correlated with the cell membrane surfaces of the individual strains (R > 0.75; P < 0.09). Additionally, the EC₅₀ values correlated with the thickness of the oxide shells (except for Escherichia coli: R > 0.95; P < 0.05), documenting the reliability of the assay, where reactivity was confirmed to be an important factor for reactive oxygen species production.

Impact of surface modification on the toxicity of zerovalent iron nanoparticles in aquatic and terrestrial organisms

Nanoscale zerovalent iron (nZVI)-based materials are increasingly being applied in environmental remediation, thereby lead to their exposure to aquatic and terrestrial biota. However, little is known regarding the toxic effects of surface-modified nZVI on multiple species in the ecosystem. In this study, we systematically compared the toxicities of different forms of nZVIs, such as bare nZVI, carboxymethyl cellulose (CMC)-stabilized nZVI, tetrapolyphosphate (TPP)-coated nZVI and bismuth (Bi)-doped nZVI, on a range of aquatic and terrestrial organisms, including bacteria (Escherichia coli and Bacillus subtilis), plant (Arabidopsis thaliana), water flea (Daphnia magna) and earthworm (Eisenia fetida). The Bi- and CMC-nZVI induced adverse biological responses across all the test systems, except E. fetida, varying from cell death in E. coli and B. subtilis to inhibition of the physiological states in D. magna and A. thaliana. The particle characterization under exposure conditions indicated that the surface modification of nZVI played a significant role in their toxicities by changing their physicochemical properties. The underlying mechanisms by which nZVI induces toxicity might be a combination of oxidative stress and another mechanism such as cell membrane disruption, chlorosis and hypoxia. Overall, our findings could provide important implications for the development of environment-friendly nanomaterials and direct further ecotoxicological researches regarding interspecies exploration.

Insight into the impact of Fe3O4 nanoparticles on anammox process of subsurface-flow constructed wetlands under long-term exposure

The increasing use of Fe₃O₄ nanoparticles (NPs) had posed an emerging challenge to wastewater treatment processes, and their potential impact on anaerobic ammonium oxidation (anammox) process of unplanted subsurface-flow constructed wetlands (USFCWs) was investigated firstly under the long-term exposure of different Fe₃O₄ NP concentrations. It was found that Fe₃O₄ NP exposure could improve total nitrogen (TN) removal. The abundance of Candidatus Anammoxoglobus increased significantly at 10 mg/L Fe₃O₄ NPs, while decreased under 1 mg/L Fe₃O₄ NP exposure. Desulfosporosinus and Exiguobacterium increased to some extent at 1 mg/L Fe₃O₄ NPs, suggesting that Fe-anammox played an important role in TN removal. The ROS production increased with the increase of Fe₃O₄ NP concentration, and the integrity of cell membrane was good under Fe₃O₄ NP exposure. The functional genes that related to inorganic ion transport and metabolism and lipid transport and metabolism were upregulated, and cell motility decreased after long-term exposure of 1 mg/L Fe₃O₄ NPs. Graphical abstract ᅟ.

Impact of ageing on the fate of molybdate-zerovalent iron nanohybrid and its subsequent effect on cyanobacteria (Microcystis aeruginosa) growth in aqueous media

Nanoscale zerovalent iron (nZVI) has been proposed to remediate heavy metal ions in the subsurface. However, the fate of metal-nZVI hybrid has not been fully investigated. In this study, we investigated (1) the long-term removal performance of nZVI for molybdate (Mo(VI)); (2) the relationship between the ageing of Mo-nZVI hybrid in specific solution chemistries and the remobilization of Mo(VI) from the hybrid; and (3) the effects of Mo-nZVI hybrid on cyanobacteria (Microcystis aeruginosa). Results showed that although common ions have limited influence on the removal ratio of Mo(VI) by nZVI, they do impact the structure evolution and transformation of the Mo-nZVI nanohybrid formed thereafter. Ageing time was crucial for the chemical stabilization of Mo-nZVI hybrid, but common groundwater ions retarded the stabilizing process, which may lead to a significant remobilization of Mo(VI) from the hybrid after exposure to water bodies. While low levels of Mo(VI) ions could stimulate the growth of M. aeruginosa, aged Mo-nZVI hybrid inhibited the growth of M. aeruginosa, except when ageing occurred in the presence of HPO₄^2-/CO₃^2- (which also retarded hybrid stabilization). This study shows that nZVI can immobilize Mo(VI) ions in groundwater, and the derived metal-nZVI hybrid can effectively suppress the potential growth of M. aeruginosa in river water.

Nano Zero-Valent Iron Mediated Metal(loid) Uptake and Translocation by Arbuscular Mycorrhizal Symbioses

Nano zero-valent iron (nZVI) has great potential in the remediation of metal(loid)-contaminated soils, but its efficiency in metal(loid) stabilization in the plant-microbe continuum is unclear. This study investigated nZVI-mediated metal(loid) behavior in the arbuscular mycorrhizal (AM) fungal-maize ( Zea mays L.) plant association. Plants with AM fungal inoculation were grown in metal(loid)- (mainly Zn and Pb) contaminated soils (Litavka River, Czech Republic) amended with/without 0.5% (w/w) nZVI. The results showed that nZVI decreased plant metal(loid) uptake but inhibited AM development and its function in metal(loid) stabilization in the rhizosphere. AM fungal inoculation alleviated the physiological stresses caused by nZVI and restrained nZVI efficiency in reducing plant metal(loid) uptake. Micro proton-induced X-ray emission (μ-PIXE) analysis revealed the sequestration of Zn (possibly through binding to thiols) by fungal structures in the roots and the precipitation of Pb and Cu in the mycorrhizal root rhizodermis (possibly by Fe compounds originated from nZVI). XRD analyses further indicated that Pb/Fe mineral transformations in the rhizosphere were influenced by AM and nZVI treatments. The study revealed the counteractive effects of AM and nZVI on plant metal(loid) uptake and uncovered details of metal(loid) behavior in the AM fungal-root-nZVI system, calling into question about nZVI implementation in mycorrhizospheric systems.

Environmentally Sustainable and Ecosafe Polysaccharide-Based Materials for Water Nano-Treatment: An Eco-Design Study

Nanoremediation, which is the use of nanoparticles and nanomaterials for environmental remediation, is widely explored and proposed for preservation of ecosystems that suffer from the increase in human population, pollution, and urbanization. We herein report a critical analysis of nanotechnologies for water remediation by assessing their sustainability in terms of efficient removal of pollutants, appropriate methods for monitoring their effectiveness, and protocols for the evaluation of any potential environmental risks. Our purpose is to furnish fruitful guidelines for sustainable water management, able to promote nanoremediation also at European level. In this context, we describe new nanostructured polysaccharide-based materials obtained from renewable resources as alternative efficient and ecosafe solutions for water nano-treatment. We also provide eco-design indications to improve the sustainability of the production of these materials, based on life-cycle assessment methodology.

Biological effects of four iron-containing nanoremediation materials on the green alga Chlamydomonas sp

As nanoremediation strategies for in-situ groundwater treatment extend beyond nanoiron-based applications to adsorption and oxidation, ecotoxicological evaluations of newly developed materials are required. The biological effects of four new materials with different iron (Fe) speciations ([i] FerMEG12 - pristine flake-like milled Fe(0) nanoparticles (nZVI), [ii] Carbo-Iron^® - Fe(0)-nanoclusters containing activated carbon (AC) composite, [iii] Trap-Ox® Fe-BEA35 (Fe-zeolite) - Fe-doped zeolite, and [iv] Nano-Goethite - 'pure' FeOOH) were studied using the unicellular green alga Chlamydomonas sp. as a model test system. Algal growth rate, chlorophyll fluorescence, efficiency of photosystem II, membrane integrity and reactive oxygen species (ROS) generation were assessed following exposure to 10, 50 and 500 mg L^-1 of the particles for 2 h and 24 h. The particles had a concentration-, material- and time-dependent effect on Chlamydomonas sp., with increased algal growth rate after 24 h. Conversely, significant intracellular ROS levels were detected after 2 h, with much lower levels after 24 h. All Fe-nanomaterials displayed similar Z-average sizes and zeta-potentials at 2 h and 24 h. Effects on Chlamydomonas sp. decreased in the order FerMEG12 > Carbo-Iron® > Fe-zeolite > Nano-Goethite. Ecotoxicological studies were challenged due to some particle properties, i.e. dark colour, effect of constituents and a tendency to agglomerate, especially at high concentrations. All particles exhibited potential to induce significant toxicity at high concentrations (500 mg L^-1), though such concentrations would rapidly decrease to mg or µg L^-1 in aquatic environments, levels harmless to Chlamydomonas sp. The presented findings contribute to the practical usage of particle-based nanoremediation in environmental restoration.

Green Synthesis of Metal and Metal Oxide Nanoparticles and Their Effect on the Unicellular Alga Chlamydomonas reinhardtii

Recently, the green synthesis of metal nanoparticles has attracted wide attention due to its feasibility and very low environmental impact. This approach was applied in this study to synthesise nanoscale gold (Au), platinum (Pt), palladium (Pd), silver (Ag) and copper oxide (CuO) materials in simple aqueous media using the natural polymer gum karaya as a reducing and stabilising agent. The nanoparticles' (NPs) zeta-potential, stability and size were characterised by Zetasizer Nano, UV-Vis spectroscopy and by electron microscopy. Moreover, the biological effect of the NPs (concentration range 1.0-20.0 mg/L) on a unicellular green alga (Chlamydomonas reinhardtii) was investigated by assessing algal growth, membrane integrity, oxidative stress, chlorophyll (Chl) fluorescence and photosystem II photosynthetic efficiency. The resulting NPs had a mean size of 42 (Au), 12 (Pt), 1.5 (Pd), 5 (Ag) and 180 (CuO) nm and showed high stability over 6 months. At concentrations of 5 mg/L, Au and Pt NPs only slightly reduced algal growth, while Pd, Ag and CuO NPs completely inhibited growth. Ag, Pd and CuO NPs showed strong biocidal properties and can be used for algae prevention in swimming pools (CuO) or in other antimicrobial applications (Pd, Ag), whereas Au and Pt lack these properties and can be ranked as harmless to green alga.

Remediation of contaminated soils by enhanced nanoscale zero valent iron

The use of nanoscale zero valent iron (nZVI) for in situ remediation of soil contamination caused by heavy metals and organic pollutants has drawn great concern, primarily owing to its potential for excellent activity, low cost and low toxicity. This reviews considers recent advances in our understanding of the role of nZVI and enhanced nZVI strategy in the remediation of heavy metals and persistent organic contaminants polluted soil. The performance, the migration and transformation of nZVI affected by the soil physical and chemical conditions are summarized. However, the addition of nZVI inevitably disturbs the soil ecosystem, thus the impacts of nZVI on soil organisms are discussed. In order to further investigate the remediation effect of nZVI, physical, chemical and biological method combination with nZVI was developed to enhance the performance of nZVI. From a high efficient and environmentally friendly perspective, biological method enhanced nZVI technology will be future research needs. Possible improvement of nZVI-based materials and potential areas for further applications in soil remediation are also proposed.

Unraveling the impact of nanoscale zero-valent iron on the nitrogen removal performance and microbial community of anammox sludge

Given the increasing use of nanoscale zero-valent iron (NZVI) particles for environmental remediation and wastewater treatment, their potential impact on anaerobic ammonium oxidation (anammox) bacteria was investigated in this study using anammox sludge. Batch assays showed that NZVI concentrations up to 200mgL^-1 did not affect anammox activity, reactive oxygen species production, and cell membrane integrity. The nitrogen removal efficiency of the continuous-flow reactor fluctuated in the presence of 20 or 50mgL^-1 NZVI, but it could return to normal over time, even at 200mgL^-1 NZVI. 16S rDNA-based high-throughput sequencing indicated that although the presence of 10, 20, 50, and 200mgL^-1 NZVI to some extent affected microbial composition, the anammox bacteria (Candidatus Kuenenia) never lost its dominance. The abundance of gene families that are related to the assimilation and utilization of iron was down-regulated in response to the stress of high-level NZVI.