Enhancing iron biogeochemical cycling for canga ecosystem restoration: insights from microbial stimuli

Introduction

The microbial-induced restoration of ferruginous crusts (canga), which partially cover iron deposits and host unique ecosystems, is a promising alternative for reducing the environmental impacts of the iron mining industry.

Methods

To investigate the potential of microbial action to accelerate the reduction and oxidation of iron in substrates rich in hematite and goethite, four different microbial treatments (water only as a control - W; culture medium only - MO; medium + microbial consortium - MI; medium + microbial consortium + soluble iron - MIC) were periodically applied to induce iron dissolution and subsequent precipitation. Except for W, all the treatments resulted in the formation of biocemented blocks.

Results

MO and MI treatments resulted in significant goethite dissolution, followed by precipitation of iron oxyhydroxides and an iron sulfate phase, due to iron oxidation, in addition to the preservation of microfossils. In the MIC treatment, biofilms were identified, but with few mineralogical changes in the iron-rich particles, indicating less iron cycling compared to the MO or MI treatment. Regarding microbial diversity, iron-reducing families, such as Enterobacteriaceae, were found in all microbially treated substrates.

Discussion

However, the presence of Bacillaceae indicates the importance of fermentative bacteria in accelerating the dissolution of iron minerals. The acceleration of iron cycling was also promoted by microorganisms that couple nitrate reduction with Fe(II) oxidation. These findings demonstrate a sustainable and streamlined opportunity for restoration in mining areas.

Mechanism of escape from the antibacterial activity of metal-based nanoparticles in clinically relevant bacteria: A systematic review

The emergency of antibiotic-resistant bacteria in severe infections is increasing, especially in nosocomial environments. The ESKAPE group is of special importance in the groups of multi-resistant bacteria due to its high capacity to generate resistance to antibiotics and bactericides. Therefore, metal-based nanomaterials are an attractive alternative to combat them because they have been demonstrated to damage biomolecules in the bacterial cells. However, there is a concern about bacteria developing resistance to NPs and their harmful effects due to environmental accumulation. Therefore, this systematic review aims to report the clinically relevant bacteria that have developed resistance to the NPs. According to the results of this systematic review, various mechanisms to counteract the antimicrobial activity of various NP types have been proposed. These mechanisms can be grouped into the following categories: production of extracellular compounds, metal efflux pumps, ROS response, genetic changes, DNA repair, adaptative morphogenesis, and changes in the plasma membrane.

Preventing Antibiotic-Resistant Infections: Additively Manufactured Porous Ti6Al4V Biofunctionalized with Ag and Fe Nanoparticles

Implant-associated infections are highly challenging to treat, particularly with the emergence of multidrug-resistant microbials. Effective preventive action is desired to be at the implant site. Surface biofunctionalization of implants through Ag-doping has demonstrated potent antibacterial results. However, it may adversely affect bone regeneration at high doses. Benefiting from the potential synergistic effects, combining Ag with other antibacterial agents can substantially decrease the required Ag concentration. To date, no study has been performed on immobilizing both Ag and Fe nanoparticles (NPs) on the surface of additively manufactured porous titanium. We additively manufactured porous titanium and biofunctionalized its surface with plasma electrolytic oxidation using a Ca/P-based electrolyte containing Fe NPs, Ag NPs, and the combinations. The specimen’s surface morphology featured porous TiO2 bearing Ag and Fe NPs. During immersion, Ag and Fe ions were released for up to 28 days. Antibacterial assays against methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa showed that the specimens containing Ag NPs and Ag/Fe NPs exhibit bactericidal activity. The Ag and Fe NPs worked synergistically, even when Ag was reduced by up to three times. The biofunctionalized scaffold reduced Ag and Fe NPs, improving preosteoblasts proliferation and Ca-sensing receptor activation. In conclusion, surface biofunctionalization of porous titanium with Ag and Fe NPs is a promising strategy to prevent implant-associated infections and allow bone regeneration and, therefore, should be developed for clinical application.

Can water composition and weather factors predict fecal indicator bacteria removal in retention ponds in variable weather conditions?

Retention ponds provide benefits including flood control, groundwater recharge, and water quality improvement, but changes in weather conditions could limit the effectiveness in improving microbial water quality metrics. The concentration of fecal indicator bacteria (FIB), which is used as regulatory standards to assess microbial water quality in retention ponds, could vary widely based on many factors including local weather and influent water chemistry and composition. In this critical review, we analyzed 7421 data collected from 19 retention ponds across North America listed in the International Stormwater BMP Database to examine if variable FIB removal in the field conditions can be predicted based on changes in these weather and water composition factors. Our analysis confirms that FIB removal in retention ponds is sensitive to weather conditions or seasons, but temperature and precipitation data may not describe the variable FIB removal. These weather conditions affect suspended solid and nutrient concentrations, which in turn could affect FIB concentration in the ponds. Removal of total suspended solids and total P only explained 5% and 12% of FIB removal data, respectively, and TN removal had no correlation with FIB removal. These results indicate that regression-based modeling with a single parameter as input has limited use to predict FIB removal due to the interactive nature of their effects on FIB removal. In contrast, machine learning algorithms such as the random forest method were able to predict 65% of the data. The overall analysis indicates that the machine learning model could play a critical role in predicting microbial water quality of surface waters under complex conditions where the variation of both water composition and weather conditions could deem regression-based modeling less effective.

Fabrication of the Ordered Mesoporous nZVI/Zr-Ce-SBA-15 Composites Used for Crystal Violet Removal and Their Optimization Using RSM and ANN–PSO

Crystal violet (CV), a triphenylmethane dye, is widely used in the textile, printing, paper, leather, and cosmetics industries. However, due to its higher chemical stability and lower biodegradability, CV has teratogenic and carcinogenic toxic effects on animals and humans. Therefore, the objective of the present study was to investigate whether or not the as-prepared nZVI supported on an ordered mesoporous Zr-Ce-SBA-15 composite (nZVI/Zr-Ce-SBA-15) had more potential for CV removal from simulated wastewater in comparison with Zr-Ce-SBA-15. Meanwhile, the parameters of CV adsorption onto nZVI/Zr-Ce-SBA-15 composites were optimized by a response surface methodology (RSM) and an artificial neural network combined with particle swarm optimization (ANN–PSO). According to XRD, FTIR, SEM, and TEM, N2 adsorption, and thermogravimetric analyses, nZVI was supported successfully on Zr-Ce-SBA-15 composites, becoming an ordered mesoporous material. The results of RSM indicated that the order of the effects of the four parameters on CV removal was, successively, initial pH, contact time, temperature, and initial CV concentration. ANN–PSO was more suitable, in comparison to RSM, to optimize the experimental parameters for CV removal from simulated wastewater using ordered mesoporous nZVI/Zr-Ce-SBA-15 composites. The optimized removal rate of CV was 93.87% under an initial pH of 3.00, a contact time of 20.00 min, an initial CV concentration of 261.00 mg/L, and a temperature of 45. Pseudo-second-order kinetics can better describe the behavior of CV adsorption onto nZVI/Zr-Ce-SBA-15 composites. The process of CV adsorption onto Zr-Ce-SBA-15 composites was followed by the Langmuir model, and its maximum adsorption capacity was 105 mg/g in 213 K. It was indirectly confirmed that the maximum adsorption capacity of nZVI/Zr-Ce-SBA-15 exceeded this value because the removal efficiency of CV using nZVI/Zr-Ce-SBA-15 was obviously higher than that of using Zr-Ce-SBA-15. The thermodynamics results indicated that CV adsorption onto nZVI/Zr-Ce-SBA-15 was a spontaneous, endothermic, and entropy-driven process. The dissolution of Fe ions and light/dark experiments confirmed nZVI/Zr-Ce-SBA-15 was simultaneously of adsorption and catalysis in the process of CV removal. The effect of removal CV was still maintained in the first four experiments (removal rate > 78%), and our suggestion is that nZVI/Zr-Ce-SBA-15 is a potential adsorbent for CV remediation from wastewater compared to Zr-Ce-SBA-15 and other adsorbents.

In Vitro Antimicrobial Activity Of Layered Silicate Materials

Objective — to assess the presence of a direct antimicrobial effect of natural minerals (ammonite; montmorillonite of the Azerbaijani deposit; calcium montmorillonite, or light clay, and sodium montmorillonite, or dark clay, of the Gerpegezh deposit in Kabardino-Balkaria; serpentinite) against strains of Staphylococcus aureus, Escherichia coli and yeast-like Candida fungi. Material and Methods — The antimicrobial activity was investigated by qualitative and quantitative methods; the methods of X-ray diffraction and X-ray fluorescence analysis were used to assess the chemical composition of samples of natural minerals. The results were statistically processed. Results — We established that ammonite, montmorillonite of Azerbaijani origin and serpentinite did not have a direct antimicrobial effect against the studied cultures of bacteria and fungi (S. aureus, E. coli, Candida albicans). The growth of S. aureus was suppressed by calcium and sodium montmorillonite from the Gerpegezh deposit. Sodium montmorillonite had the strongest antibacterial effect, and its dose-dependent effect was revealed. According to the data of X-ray fluorescence analysis, in the structure of, trivalent iron and oxides of manganese and titanium predominated in the samples of dark Gerpegezh clay with a more pronounced anti-staphylococcal effect. Conclusion — Our study demonstrated the possibilities and limitations of using various samples of layered silicate minerals for antibacterial solutions. The spectrum of antimicrobial activity largely depends on the unique composition of mineral complexes. Samples with a high content of iron(III) can be considered promising in the development of natural antimicrobial preparations.

Bacteriostatic impact of nanoscale zero-valent iron against pathogenic bacteria in the municipal wastewater

Nanoscale zero-valent iron particles were investigated as an antibacterial agent against two Gram-positive bacteria; Staphylococcus aureus NRRL B-313 (S. aureus), Bacillus subtilus NRC (B. subtilus), and two Gram-negative bacteria; Escherichia coli NRC B-3703 (E. coli), Pseudomonas aeruginosa NRC B-32 (Ps. aeruginosa). The characterization of synthesized nZVI particles was obtained by XRD, SEM, EDX, and TG analyses. The results demonstrated that the nZVI particles have a spherical shape, mean crystalline size of 44.43 nm, and exhibited a good chemical and thermal stability performance under different physical conditions. The bacterial suspensions were subjected to the treatment using nZVI particle suspensions with a concentration of 10 mg/mL. The minimum inhibitory concentration of nZVI particles was determined using the well diffusion assay method and found to be 15, 10, 10, and 5 mg for the following four strains; S. aureus, B. subtilus, E. coli, and Ps. aeruginosa, respectively. The biological treatment results of municipal wastewater using nZVI particles revealed that the counts of total bacteria, total coliform, fecal coliform, S. aureus, fecal Streptococcus, and E. coli were decreased to 44.29%, 51.76%, 90.95%, 46.67%, 33.33%, and 93.89%, respectively, while the Ps. aeruginosa not detected in the wastewater sample. The enhanced inactivation performance of nZVI nanoparticles was mainly attributed to the reactive oxygen species (ROS) production, releasing of iron corrosion products like Fe²⁺/Fe³⁺ ions, and direct friction of nZVI particles with bacterial cells membranes. In addition, the nZVI particles presented a striking disinfection behavior in comparison with other widespread disinfection technologies such as chlorination. Accordingly, the obtained results introduce the nZVI particles as a promising disinfection technology.

Nanoparticles as antimicrobial and antiviral agents: A literature-based perspective study

The scientific explorations of nanoparticles for their inherent therapeutic potencies as antimicrobial and antiviral agents due to increasing incidences of antibiotic resistance have gained more attention in recent time. This factor amongst others necessitates the search for newer and more effective antimicrobial agents. Several investigations have demonstrated the prospects of nanoparticles in the treatment of various microbial infections. The therapeutic applications of nanoparticles as either delivery agent or broad spectrum inhibition agents in viral and microbial investigations can no longer be overlooked. Their large surface area to volume ratio made them an indispensable substance as delivery agents in many respect. Various materials have been used for the synthesis of nanoparticles with unique properties channelised to meet specific therapeutic requirement. This review focuses on the antibacterial, antifungal, and antiviral potential of nanoparticles with their probable mechanism of action.

Superior antibacterial activity of gallium based liquid metals due to Ga3+ induced intracellular ROS generation

Gallium metals demonstrate enhanced antibacterial activity compared to gallium nitrate with the same gallium ion concentration.

An insight into the mechanism of antibacterial activity by magnesium oxide nanoparticles

The exact mechanism behind the antibacterial efficacy of nanoparticles has remained unexplored to date. This study aims to shed light the mechanism adopted using magnesium oxide nanoparticles prepared in ethyl alcohol against gram-negative and gram-positive bacterial cells, and the generation of reactive oxygen species (ROS) is proposed to be the dominant mechanism. This paradigm is supported by the quantification of the hydroxyl radical and superoxide anions produced in the nanoparticle treated and untreated bacterial solutions, and by the reduction of the antibacterial efficiency after the addition of a radical scavenger. The production of free Mg2+ ions from the nanoparticle is supposed to be the causative agent behind this uncontrolled ROS generation, resulting in excessive oxidative stress, which the antioxidants of the bacterial cells are unable to nullify, leading to cell damage. The amount of proteins, carbohydrates and lipids leaked due to the distortion of the cellular membrane is also quantified, and it is observed that their leakage trend varies on the structure of the bacterial cell. FESEM images taken at certain time intervals show the gradual internalization of the nanoparticles, and increasing rupture of bacterial cell membranes, leading to cell necrosis.

Inactivation of sulfonamide antibiotic resistant bacteria and control of intracellular antibiotic resistance transmission risk by sulfide-modified nanoscale zero-valent iron

The inactivation of a gram-negative sulfonamide antibiotic resistant bacteria (ARB) HLS.6 and removal of intracellular antibiotic resistance gene (ARG, sul1) and class I integrase gene (intI1) by nanoscale zero-valent iron (nZVI) and sulfide-modified nZVI (S-nZVI) with different S/Fe molar ratios were investigated in this study. The S-nZVI with high sulfur content (S/Fe = 0.05, 0.1, 0.2) was superior to nZVI and the treatment effect was best when S/Fe was 0.1. The ARB (2 × 10⁷ CFU/mL) could be completely inactivated by 1.12 g/L of S-nZVI (S/Fe = 0.1) within 15 min, and the removal rates of intracellular sul1 and intI1 reached up to 4.39 log and 4.67 log at 60 min, respectively. Quenching experiments and flow cytometry proved that reactive oxygen species and adsorption were involved in the ARB inactivation and target genes removal. Bacterial death and live staining experiments and transmission electron microscopy showed that the ARB cell structure and intracellular DNA were severely damaged after S-nZVI treatment. This study provided a potential alternative method for controlling the antibiotic resistance in aquatic environment.

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.

Remediation of heavy metals polluted environment using Fe-based nanoparticles: Mechanisms, influencing factors, and environmental implications

Environmental pollution by heavy metals (HMs) has raised considerable attention due to their toxic impacts on plants, animals and human beings. Thus, the environmental cleanup of these toxic (HMs) is extremely urgent both from the environmental and biological point of view. To remediate HMs-polluted environment, several nanoparticles (NPs) such as metals and its oxides, carbon materials, zeolites, and bimetallic NPs have been documented. Among these, Fe-based NPs have emerged as an effective choice for remediating environmental contamination, due to infinite size, high reactivity, and adsorption properties. This review summarizes the utilization of various Fe-based NPs such as nano zero-valent iron (NZVI), modified-NZVI, supported-NZVI, doped-NZVI, and Fe oxides and hydroxides in remediating the HMs-polluted environment. It presents a comprehensive elaboration on the possible reaction mechanisms between the Fe-based NPs and heavy metals, including adsorption, oxidation/reduction, and precipitation. Subsequently, the environmental factors (e.g., pH, organic matter, and redox) affecting the reactivity of the Fe-based NPs with heavy metals are also highlighted in the current study. Research shows that Fe-based NPs can be toxic to living organisms. In this context, this review points out the environmental hazards associated with the application of Fe-based NPs and proposes future recommendations for the utilization of these NPs.

Sustainable Synthesis of Nanoscale Zerovalent Iron Particles for Environmental Remediation

Nanoscale zerovalent iron (nZVI) particles represent an important material for diverse environmental applications because of their exceptional electron-donating properties, which can be exploited for applications such as reduction, catalysis, adsorption, and degradation of a broad range of pollutants. The synthesis and assembly of nZVI by using biological and natural sustainable resources is an attractive option for alleviating environmental contamination worldwide. In this Review, various green synthesis pathways for generating nZVI particles are summarized and compared with conventional chemical and physical methods. In addition to describing the latest environmentally benign methods for the synthesis of nZVI, their properties and interactions with diverse biomolecules are discussed, especially in the context of environmental remediation and catalysis. Future prospects in the field are also considered.

Bibliometric study of the toxicology of nanoescale zero valent iron used in soil remediation

The application of nanoscale zero-valent iron is one of the most widely used remediation technologies; however, the potential environmental risks of this technology are largely unknown. In order to broaden the knowledge on this subject, the present work consists of a bibliometric study of all of publications related to the toxicity of zero-valent iron nanoparticles used in soil remediation available from the Scopus (Elsevier) and Web of Science (Thompson Reuters) databases. This study presents a temporal distribution of the publications, the most cited articles, the authors who have made the greatest contribution to the theme, and the institutions, countries, and scientific journals that have published the most on this subject. The use of bibliometrics has allowed for the visualization of a panorama of the publications, providing an appropriate analysis to guide new research towards an effective contribution to science by filling the existing gaps. In particular, the lack of studies in several countries reveals a promising area for the development of further research on this topic.

Rapid Aerobic Inactivation and Facile Removal of Escherichia coli with Amorphous Zero-Valent Iron Microspheres: Indispensable Roles of Reactive Oxygen Species and Iron Corrosion Products

Zero valent iron (ZVI) is recently regarded as a promising alternative for water disinfection, but still suffers from low efficiency. Herein we demonstrate that amorphous zerovalent iron microspheres (A-mZVI) exhibit both higher inactivation rate and physical removal efficiency for the disinfection of Escherichia coli than conventional crystalline nanoscale ZVI (C-nZVI) under aerobic condition. The enhanced E. coli inactivation performance of A-mZVI was mainly attributed to more reactive oxygen species (ROSs), especially free •OH, generated by the accelerated iron dissolution and molecular oxygen activation in bulk solution. In contrast, C-nZVI preferred to produce surface bound •OH, and its bactericidal ability was thus hampered by the limited physical contact between C-nZVI and E. coli. More importantly, hydrolysis of dissolved iron released from A-mZVI produced plenty of loose FeOOH to wrap E. coli, increasing the dysfunction of E. coli membrane. Meanwhile, this hydrolysis process lowered the stability of E. coli colloid and caused its rapid coagulation and sedimentation, favoring its physical removal. These findings clarify the indispensable roles of ROSs and iron corrosion products during the ZVI disinfection, and also provide a promising disinfection material for water treatment.

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.

A series of water-soluble photosensitizers based on 3-cinnamoylcoumarin forin vitroantimicrobial photodynamic inactivation

Three cationic PSs (M3–M5) exhibited equivalent photodynamic inactivation (PDI) efficacies to MRSA andA. baumannii, whileM4andM5showed significantly higher PDI toC. albicans, compared to methylene blue, indicating their large potentials on PDI.

Environmental transformations and ecological effects of iron-based nanoparticles

The increasing application of iron-based nanoparticles (NPs), especially high concentrations of zero-valent iron nanoparticles (nZVI), has raised concerns regarding their environmental behavior and potential ecological effects. In the environment, iron-based NPs undergo physical, chemical, and/or biological transformations as influenced by environmental factors such as pH, ions, dissolved oxygen, natural organic matter (NOM), and biotas. This review presents recent research advances on environmental transformations of iron-based NPs, and articulates their relationships with the observed toxicities. The type and extent of physical, chemical, and biological transformations, including aggregation, oxidation, and bio-reduction, depend on the properties of NPs and the receiving environment. Toxicities of iron-based NPs to bacteria, algae, fish, and plants are increasingly observed, which are evaluated with a particular focus on the underlying mechanisms. The toxicity of iron-based NPs is a function of their properties, tolerance of test organisms, and environmental conditions. Oxidative stress induced by reactive oxygen species is considered as the primary toxic mechanism of iron-based NPs. Factors influencing the toxicity of iron-based NPs are addressed and environmental transformations play a significant role, for example, surface oxidation or coating by NOM generally lowers the toxicity of nZVI. Research gaps and future directions are suggested with an aim to boost concerted research efforts on environmental transformations and toxicity of iron-based NPs, e.g., toxicity studies of transformed NPs in field, expansion of toxicity endpoints, and roles of laden contaminants and surface coating. This review will enhance our understanding of potential risks of iron-based NPs and proper uses of environmentally benign NPs.

The application of iron-based technologies in uranium remediation: A review

Remediating uranium contamination is of worldwide interest because of the increasing release of uranium from mining and processing, nuclear power leaks, depleted uranium components in weapons production and disposal, and phosphate fertilizer in agriculture activities. Iron-based technologies are attractive because they are highly efficient, inexpensive, and readily available. This paper provides an overview of the current literature that addresses the application of iron-based technologies in the remediation of sites with elevated uranium levels. The application of iron-based materials, the current remediation technologies and mechanisms, and the effectiveness and environmental safety considerations of these approaches were discussed. Because uranium can be reduced and reoxidized in the environment, the review also proposes strategies for long-term in situ remediation of uranium. Unfortunately, iron-based materials (nanoscale zerovalent iron and iron oxides) can be toxic to microorganisms. As such, further studies exploring the links among the fates, ecological impacts, and other environmentally relevant factors are needed to better understand the constraints on using iron-based technologies for remediation.

Ecotoxicity and environmental safety related to nano-scale zerovalent iron remediation applications

This mini-review summarizes the current information that has been published on the various effects of nano-scale zerovalent iron (nZVI) on microbial biota, with an emphasis on reports that highlight the positive aspects of its application or its stimulatory effects on microbiota. By nature, nZVI is a highly reactive substance; thus, the possibility of nZVI being toxic is commonly suspected. Accordingly, the cytotoxicity of nZVI and the toxicity of nZVI-related products have been detected by laboratory tests and documented in the literature. However, there are numerous other published studies on its useful nature, which are usually skipped in reviews that deal only with the phenomenon of toxicity. Therefore, the objective of this article is to review both recent publications reporting the toxic effects of nZVI on microbiota and studies documenting the positive effects of nZVI on various environmental remediation processes. Although cytotoxicity is an issue of general importance and relevance, nZVI can reduce the overall toxicity of a contaminated site, which ultimately results in the creation of better living conditions for the autochthonous microflora. Moreover, nZVI changes the properties of the site in a manner such that it can also be used as a tool in a tailor-made approach to support a specific microbial community for the decontamination of a particular polluted site.

Cationic benzylidene cyclopentanone photosensitizers for selective photodynamic inactivation of bacteria over mammalian cells

Cationic modified benzylidene cyclopentanone photosensitizers selectively photo-inactivate bacterial cells over mammalian cells.

Antibacterial activity and cytocompatibility of titanium oxide coating modified by iron ion implantation

In this work, zero valent iron nanoparticles (Fezero-NPs) and iron oxide nanoparticles (Feox-NPs) were synthesized at the subsurface and surface regions of titanium oxide coatings (TOCs) by plasma immersion ion implantation. This novel Fe-NPs/TOC system showed negligible iron releasing, great electron storage capability and excellent cytocompatibility in vitro. Importantly, the system showed selective antibacterial ability which can kill Staphylococcus aureus under dark conditions but has no obvious antibacterial effect against Escherichia coli. Owing to a bipolar Schottky barrier between Fezero-NPs/TOC and Fezero-NPs/Feox-NPs, electrons could be captured by the Fezero-NPs bounded at the subsurface region of the coating. This electron storage capability of the Fe-NPs/TOC system induced extracellular electron transportation and accumulation of adequate valence-band holes (h(+)) at the external side, which caused oxidation damage to S. aureus cells in the dark. No obvious biocide effect against E. coli resulted from lack of electron transfer ability between E. coli and substrate materials. This work may open up a novel and controlled strategy to design coatings of implants with antibacterial ability and cytocompatibility for medical applications.

Characterizing reactive oxygen generation and bacterial inactivation by a zerovalent iron-fullerene nano-composite device at neutral pH under UV-A illumination

A nano-composite device composed of nano-scale zerovalent iron (ZVI) and C60 fullerene aggregates (ZVI/nC60) was produced via a rapid nucleation method. The device was conceived to deliver reactive oxygen species (ROS) generated by photosensitization and/or electron transfer to targeted contaminants, including waterborne pathogens under neutral pH conditions. Certain variations of the nano-composite were fabricated differing in the amounts of (1) ZVI (0.1mM and 2mM) but not nC60 (2.5mg-C/L), and (2) nC60 (0-25mg-C/L) but not ZVI (0.1mM). The generation of ROS by the ZVI/nC60 nano-composites and ZVI nanoparticles was quantified using organic probe compounds. 0.1mM ZVI/2.5mg-C/L C60 generated 3.74-fold higher O2(-) concentration and also resulted in an additional 2-log inactivation of Pseudomonas aeruginosa when compared to 0.1mM ZVI (3-log inactivation). 2mM ZVI/2.5mg-C/L nC60 showed negligible improvement over 2mM ZVI in terms of O2(-) generation or inactivation. Further, incremental amounts of nC60 in the range of 0-25mg-C/L in 0.1mM ZVI/nC60 led to increased O2(-) concentration, independent of UV-A. This study demonstrates that ZVI/nC60 device delivers (1) enhanced O2(-) with nC60 as a mediator for electron transfer, and (2) (1)O2 (only under UV-A illumination) at neutral pH conditions.

Formation of lepidocrocite (γ-FeOOH) from oxidation of nanoscale zero-valent iron (nZVI) in oxygenated water

The aging of nZVI in oxygenated water yields stable sheet-shaped and well-formed lepidocrocite crystals.