Toxicity of TiO2 nanoparticles to Escherichia coli: effects of particle size, crystal phase and water chemistry

Advanced In Vitro Testing Strategies and Models of the Intestine for Nanosafety Research

There is growing concern about the potential adverse effects of oral exposure to engineered nanomaterials (ENM). Recent years have witnessed major developments in and advancement of intestinal in vitro models for nanosafety evaluation. The present paper reviews the key factors that should be considered for inclusion in nonanimal alternative testing approaches to reliably reflect the in vivo dynamics of the physicochemical properties of ENM as well the intestinal physiology and morphology. Currently available models range from simple cell line-based monocultures to advanced 3D systems and organoids. In addition, in vitro approaches exist to replicate the mucous barrier, digestive processes, luminal flow, peristalsis, and interactions of ENM with the intestinal microbiota. However, while the inclusion of a multitude of individual factors/components of particle (pre)treatment, exposure approach, and cell model approximates in vivo-like conditions, such increasing complexity inevitably affects the system's robustness and reproducibility. The selection of the individual modules to build the in vitro testing strategy should be driven and justified by the specific purpose of the study and, not least, the intended or actual application of the investigated ENM. Studies that address health hazards of ingested ENM likely require different approaches than research efforts to unravel the fundamental interactions or toxicity mechanisms of ENM in the intestine. Advanced reliable and robust in vitro models of the intestine, especially when combined in an integrated testing approach, offer great potential to further improve the field of nanosafety research.

Impact of the production method and diagnostics conditions on the compositions and structure of nanodimensional anatase

The detail investigation of the samples with nanodimensional anatase, formed by hydrolysis of TiOSO4 × xH2O without or in the presence of polymer poly(N-vinyl caprolactam), physical precipitation of the polymer followed by the capture of commercial Hombifine N are performed by X-ray powder diffraction using laboratory and synchrotron radiation sources, transmission electron microscopy with the diffraction, and elemental analysis. The two «core»-«shell» models with nanoparticles and their associates as a core can be applied to samples produced. The synchrotron and electron radiation change the degree of crystallinity and the imperfection of anatase, isolate of TiO2−x(OH)2x × yH2O from the nanoparticle shell with a decrease in its thickness, lead to the anatase – rutile phase transition. The double diffraction effect on the appearance of kinematically forbidden reflections caused by the dynamic character of the electron diffraction. The photoactivity depends on microstructural characteristics (specific surface, nanoobjects sizes). The structure and elemental composition of nanoparticles (associates) affect antimicrobial activity against Staphylococcus aureus and Escherichia coli.

Age-related physicochemical differences in ZnO nanoparticles in the seawater and their bacterial interaction

To assess the fate and behavior of engineered nanoparticles in the environment, it is important to examine the physicochemical and toxicological transformation of nanoparticles as they age in seawater. In this study, we investigated how aging and seawater conditions altered the physiochemical structure of nanoparticles and affected their interactions with bacteria. For this purpose, zinc oxide nanoparticles were aged under different seawater conditions by keeping them in 1%, 10%, and 100% seawater for 1 day and 20 days. The main physicochemical parameters (surface chemistry, chemical composition, particle size, and zeta potential) and toxicity of aged nanoparticles towards gram-negative Pseudomonas aeruginosa and gram-positive Staphylococcus aureus were examined. The results indicated that aged zinc oxide nanoparticles in various concentrations of seawater changed their surface chemistry, chemical composition, particle size, and zeta potentials. Growth inhibition results were observed in that the inhibition of gram-negative (Pseudomonas aeruginosa) bacteria was higher compared with the gram-positive (Staphylococcus aureus) bacteria, and Staphylococcus aureus activated with the aged zinc oxide nanoparticles. Also, the results showed that the key biochemical factors affected by the aging and seawater concentration.

Synthesis and Photocatalytic Sterilization Performance of SA/TiO2

The photocatalyst sorbic acid (SA)/titanium dioxide (TiO₂) was successfully synthesized by sol–gel method and characterized. The composite exhibited regularly spherical particles with the size of 50 nm and the specific surface area of 90.3 m² g⁻¹, furthermore, it showed mesoporous structure and significantly improved dispersion. SA was grafted on TiO₂ surface by –COOTi and TiO₂ existed as pure anatase phase in the composite. The addition of SA made the band gap of TiO₂ increased from 3.03 to 3.35 eV, which indicting that the composite exhibited a strong response to the ultraviolet light. The optimum preparation parameters of the catalyst were as follows: n(Ti):n(SA) = 1:0.05, ethanol 60 mL, glacial acetic acid 40 mL, hydrothermal temperature 180 °C, hydrothermal time 12 h. The composite could reach the 4.31 log reduction of E. coli, with the optimum catalyst dosage of 0.7 g L⁻¹, irradiated by UV light for 60 min. SA/TiO₂ was an environmentally friendly, non-toxic and safe sterilized nanocomposite material appropriate for future bactericidal applications, providing a new way to effectively increase the dispersion of TiO₂ particles to achieve superior photocatalytic sterilization efficiency.

Effect of oral exposure to titanium dioxide nanoparticles on lipid metabolism in Sprague-Dawley rats

Ingestion of titanium dioxide nanoparticles (TiO2 NPs) via dietary and environmental exposure may pose health risks. The research about the potential effect of orally ingested nanoparticles on nutritional metabolism has been limited. We conducted an animal experiment to investigate the effect of oral exposure to TiO2 NPs on lipid metabolism in Sprague-Dawley rats. The rats were treated with TiO2 NPs (29 ± 9 nm) orally at doses of 0, 2, 10, 50 mg per kg bw daily for 90 days. Lipid metabolism is evaluated by biomarkers of serum lipids and lipidomics. TiO2 NPs caused a significant decrease of body weight in rats after exposure at doses of 10 and 50 mg kg-1 from the 8th to 13th week. The level of triglycerides (TG) decreased (0.398 ± 0.114 vs. 0.248 ± 0.058 nmol L-1) and the lipidomic signature changed significantly in the serum of rats treated with TiO2 NPs (50 mg kg-1). Sixty-nine well-matched lipophilic metabolites were differentially expressed and the glycerophospholipid metabolism pathway significantly changed. The concentrations of 32 metabolites including 19 kinds of phosphatidylcholines (PCs) increased and 37 metabolites including lysophosphatidylcholines (LysoPCs) and glycerophosphocholine decreased significantly in the TiO2 NP exposed group (50 mg kg-1). The accumulation of the lipid peroxidation product (malondialdehyde, MDA) and the decreased activity of the antioxidant enzyme SOD were observed and closely related to differential metabolites. In conclusion, orally ingested TiO2 NPs (50 mg kg-1) could have an impact on lipid metabolism, for which the strong induction of oxidative stress may be the main reason. The present study led to a better understanding of the oral toxicity of food-related TiO2 NPs.

Bacterial interactions of microplastics extracted from toothpaste under controlled conditions and the influence of seawater

Microplastics have become a global concern due to their increasing use and discharge into the environment. These ubiquitous particles are known to have extremely low degradation rates and accumulate mostly in the marine environment. The evidence for bioaccumulation and indicators of stress linked to microplastics is also stated in the literature. However, the real environmental impact of microplastics has not yet been revealed. Therefore, it is crucial to understand the interaction mechanisms between microplastics and (micro)organisms under controlled (standard) laboratory conditions and environmentally relevant conditions to reflect the true environmental -situation. In this study, we aimed to understand how microplastics extracted from commercially available toothpaste samples interacted with four types of bacteria under both standard and seawater conditions. For this purpose, bacterial inhibitions were examined, and mechanisms of inhibition were evaluated by biochemical parameters (total protein, lipid peroxidase, total antioxidant capacity, and extracellular carbohydrate levels) of bacteria and physicochemical properties (zeta potential, particle size, surface chemistry) of microplastics. Results showed that gram-positive Bacillus subtilis and gram-negative Pseudomonas aeruginosa were affected in controlled and sea water media, respectively. The inhibition of the bacteria relied on the high zeta potentials of the microplastics, and, biochemically, protein and lipid peroxidase activity of bacteria were important in both media. On the other hand, while biochemical responses were similar in both media, the difference between the cell wall and microplastics surface charge was important only in seawater.

Predatory bacteria in combination with solar disinfection and solar photocatalysis for the treatment of rainwater

The predatory bacterium, Bdellovibrio bacteriovorus, was applied as a biological pre-treatment to solar disinfection and solar photocatalytic disinfection for rainwater treatment. The photocatalyst used was immobilised titanium-dioxide reduced graphene oxide. The pre-treatment followed by solar photocatalysis for 120 min under natural sunlight reduced the viable counts of Klebsiella pneumoniae from 2.00 × 10⁹ colony forming units (CFU)/mL to below the detection limit (BDL) (<1 CFU/100 μL). Correspondingly, ethidium monoazide bromide quantitative PCR analysis indicated a high total log reduction in K. pneumoniae gene copies (GC)/mL (5.85 logs after solar photocatalysis for 240 min). In contrast, solar disinfection and solar photocatalysis without the biological pre-treatment were more effective for Enterococcus faecium disinfection as the viable counts of E. faecium were reduced by 8.00 logs (from 1.00 × 10⁸ CFU/mL to BDL) and the gene copies were reduced by ∼3.39 logs (from 2.09 × 10⁶ GC/mL to ∼9.00 × 10² GC/mL) after 240 min of treatment. Predatory bacteria can be applied as a pre-treatment to solar disinfection and solar photocatalytic treatment to enhance the removal efficiency of Gram-negative bacteria, which is crucial for the development of a targeted water treatment approach.

An insight into the dependency on sample preparation for (eco) toxicity assessment of TiO2 nanoparticles

Assessing the environmental hazard of nanoparticles can be a challenging task using various testing strategies. However, to our knowledge, no information is available about the impact of the sample preparation on the toxicity and toxicity mechanism of nanoparticles. For this aim, three sample preparation methods and their available toxicity procedures were conducted to examine the (eco) toxicity of TiO₂ nanoparticles using bacteria model system. To detail understanding of the effect of sample preparation, the key events on the inhibition were examined by physicochemical and antioxidant responses. The findings showed that the physicochemical and toxicological behavior of the tested TiO₂ NPs varied according to the sample preparation method.

Visible-Light Active Titanium Dioxide Nanomaterials with Bactericidal Properties

This article provides an overview of current research into the development, synthesis, photocatalytic bacterial activity, biocompatibility and cytotoxic properties of various visible-light active titanium dioxide (TiO2) nanoparticles (NPs) and their nanocomposites. To achieve antibacterial inactivation under visible light, TiO2 NPs are doped with metal and non-metal elements, modified with carbonaceous nanomaterials, and coupled with other metal oxide semiconductors. Transition metals introduce a localized d-electron state just below the conduction band of TiO2 NPs, thereby narrowing the bandgap and causing a red shift of the optical absorption edge into the visible region. Silver nanoparticles of doped TiO2 NPs experience surface plasmon resonance under visible light excitation, leading to the injection of hot electrons into the conduction band of TiO2 NPs to generate reactive oxygen species (ROS) for bacterial killing. The modification of TiO2 NPs with carbon nanotubes and graphene sheets also achieve the efficient creation of ROS under visible light irradiation. Furthermore, titanium-based alloy implants in orthopedics with enhanced antibacterial activity and biocompatibility can be achieved by forming a surface layer of Ag-doped titania nanotubes. By incorporating TiO2 NPs and Cu-doped TiO2 NPs into chitosan or the textile matrix, the resulting polymer nanocomposites exhibit excellent antimicrobial properties that can have applications as fruit/food wrapping films, self-cleaning fabrics, medical scaffolds and wound dressings. Considering the possible use of visible-light active TiO2 nanomaterials for various applications, their toxicity impact on the environment and public health is also addressed.

Effect of TiO2-nanoparticles on copper toxicity to bacteria: role of bacterial surface

The impact of titanium dioxide nanoparticles (nano-TiO₂) on the aquatic environment is an important issue due to their increasing application. Although nano-TiO₂ was reported to show an effect on heavy metal toxicity to aquatic organisms, the underlying mechanism is not well understood. In this study, two bacterial species (Bacillus thuringiensis (B. thuringiensis) and Bacillus megaterium (B. megaterium)) from sediment were selected to study the effects of nano-TiO₂ on copper toxicity. Nano-TiO₂ was found to inhibit the growth of B. thuringiensis and enhance the oxidative stress damage caused by copper, whereas these effects were not observed for B. megaterium. Transmission electron microscopy and flow cytometry showed that B. thuringiensis has stronger association ability to nano-TiO₂ than B. megaterium. The existence of the S-layer on the surface of B. thuringiensis might be the possible reason, leading to the difference in copper toxicity. This indicates that the characteristics of bacterial surfaces might be important to the toxicity responses of nanoparticles.

Different surface characteristics of bacteria, for example, S-layer or exopolysaccharides, might lead to different effects of nanomaterials on metal toxicity.

Hepatotoxicity and the role of the gut-liver axis in rats after oral administration of titanium dioxide nanoparticles

Background

Due to its excellent physicochemical properties and wide applications in consumer goods, titanium dioxide nanoparticles (TiO₂ NPs) have been increasingly exposed to the environment and the public. However, the health effects of oral exposure of TiO₂ NPs are still controversial. This study aimed to illustrate the hepatotoxicity induced by TiO₂ NPs and the underlying mechanisms. Rats were administered with TiO₂ NPs (29 nm) orally at exposure doses of 0, 2, 10, 50 mg/kg daily for 90 days. Changes in the gut microbiota and hepatic metabolomics were analyzed to explore the role of the gut-liver axis in the hepatotoxicity induced by TiO₂ NPs.

Results

TiO₂ NPs caused slight hepatotoxicity, including clear mitochondrial swelling, after subchronic oral exposure at 50 mg/kg. Liver metabolomics analysis showed that 29 metabolites and two metabolic pathways changed significantly in exposed rats. Glutamate, glutamine, and glutathione were the key metabolites leading the generation of energy-related metabolic disorders and imbalance of oxidation/antioxidation. 16S rDNA sequencing analysis showed that the diversity of gut microbiota in rats increased in a dose-dependent manner. The abundance of Lactobacillus_reuteri increased and the abundance of Romboutsia decreased significantly in feces of TiO₂ NPs-exposed rats, leading to changes of metabolic function of gut microbiota. Lipopolysaccharides (LPS) produced by gut microbiota increased significantly, which may be a key factor in the subsequent liver effects.

Conclusions

TiO₂ NPs could induce slight hepatotoxicity at dose of 50 mg/kg after long-term oral exposure. The indirect pathway of the gut-liver axis, linking liver metabolism and gut microbiota, played an important role in the underlying mechanisms.

Effects of Linoleic Acid on Gut-Derived Bifidobacterium breve DSM 20213: A Transcriptomic Approach

Bacterial production of conjugated linoleic acid (CLA) has recently received great attention because of the potential health benefits of this fatty acid. Linoleic acid (LA) can be converted to CLA by several microorganisms, including bifidobacteria, possibly as a detoxification mechanism to avoid the growth inhibition effect of LA. In the present in vitro study, we investigated the gene expression landscape of the intestinal strain Bifidobacterium breve DSM 20213 when exposed to LA. Transcriptomic analysis using RNA-seq revealed that LA induced a multifactorial stress response in the test strain, including upregulation of genes involved in iron uptake and downregulation of genes involved in sugar and oligopeptide transport. We also observed reduced transcription of genes involved in membrane and pili biosynthesis. The upregulation of iron uptake was not related to any putative ability of LA to chelate Fe²⁺, but was somewhat linked to stress response. Furthermore, we demonstrated that LA increased reactive oxygen species (ROS) production in bacterial cells, activating an oxidative stress response. This response was proved by thioredoxin reductase transcription, and was primarily evident among bacteria cultured in the absence of cysteine. This is the first report of the potential mechanisms involved in bacterial LA transport and stress response in B. breve.

Untouchability of natural spa waters: Perspectives for treatments within a personalized water safety plan

Natural SPA waters and their environments were known since ancient times and used for health or recreational purposes in different societies, worldwide. The composition and uses of these spring waters may not allow standard disinfection in pools, representing a challenge for hygiene management. Several safety and quality procedures were proposed, but a systematic approach is still needed. Here, we focus on alternative strategies to provide hints for developing a sustainable Water Safety Plan, based on intrinsic water properties and photocatalytic materials. The antimicrobial activity of four different SPA waters with high mineral content and one drinkable spring water with a low mineral content, was assessed and then tested for the additional bactericidal activity of Titanium Dioxide (TiO₂) nanomaterials and/or light exposure at different wavelengths (200-635 nm). A native antibacterial activity was observed in all high mineral content waters, with a CFU reduction of 75-80%. The bactericidal action of TiO₂ showed an additional incremental effect, with a reduction of over 99% within 2-5 h. Interestingly, the antibacterial photocatalytic effect was detected also in the visible light range, with a possible pick around 450-455 nm, blue-light. Based on observed results, we propose a model for developing a water safety plan, considering water properties and bather exposure. This candidate approach is personalized on water composition and pool use, trying to avoid chemical disinfectants. Photocatalytic nanotechnologies represent one of the promising alternative treatments and can provide novel perspectives for a sustainable managing of natural SPA water hygiene.

Effects of oral exposure to titanium dioxide nanoparticles on gut microbiota and gut-associated metabolism in vivo

The antibacterial activity of titanium dioxide nanoparticles (TiO2 NPs) has been extensively documented and applied to food packaging or environmental protection. Ingestion of TiO2 NPs via dietary and environmental exposure may pose potential health risks by interacting with gut microbiota. We conducted an animal experiment to investigate the effects of oral exposure to TiO2 NPs on gut microbiota and gut-associated metabolism in Sprague-Dawley rats. Rats were administered with TiO2 NPs (29 ± 9 nm) orally at population-related exposure doses (0, 2, 10, 50 mg kg-1) daily for 30 days. Changes in the gut microbiota and feces metabolomics were analyzed through bioinformatics. TiO2 NPs caused significant changes of colon morphology in rats, manifested as pathological inflammatory infiltration and mitochondrial abnormalities. 16S rDNA sequencing analysis showed that the structure and composition of gut microbiota in rats were modulated after exposure to TiO2 NPs. Monitoring data demonstrated that differentially expressed bacterial strains were obtained until exposure for 14 days and 28 days, including increased L. gasseri, Turicibacter, and L. NK4A136_group and decreased Veillonella. Fecal metabolomics analysis showed that 25 metabolites and the aminoacyl-tRNA biosynthesis metabolic pathway have changed significantly in exposed rats. The increased metabolites were represented by N-acetylhistamine, caprolactam, and glycerophosphocholine, and the decreased metabolites were represented by 4-methyl-5-thiazoleethanol, l-histidine, and l-ornithine. Metabolic disorders of gut microbiota and subsequently produced lipopolysaccharides (LPS) led to oxidative stress and an inflammatory response in the intestine, which was considered to be a key and primary indirect pathway for toxicity induced by oral exposure to the TiO2 NPs. In conclusion, orally ingested TiO2 NPs could induce disorders of gut microbiota and gut-associated metabolism in vivo. The indirect pathway of oxidative stress and inflammatory response, probably due to dysbiosis of gut microbiota primarily, played an important role in the mechanisms of toxicity induced by oral exposure to TiO2 NPs. This may be a common mechanism of toxicity caused by oral administration of most nanomaterials, as they usually have potential antimicrobial activity.

Antibacterial effects of graphene- and carbon-nanotube-based nanohybrids on Escherichia coli: Implications for treating multidrug-resistant bacteria

Some nanomaterials including Fe⁰, Ag⁰, and ZnO are well known for their antibacterial effects. However, very few studies have examined antibacterial effects of nanohybrids. Given that metal oxides, mainly ZnO and TiO₂, are known to increase mobility, surface area, and photocatalysis when combined with carbon-based nanomaterials, ZnO- and TiO₂-conjugated carbon nanotube and graphene oxide nanohybrids were investigated for their antibacterial effects on Escherichia coli (DH5α, a multidrug-resistant coliform bacterium). Graphene-oxide (GO)-based nanohybrids (ZnO-GO and TiO₂-GO) induced increased dispersion compared to carbon-nanotube (CNT)-based nanohybrids (ZnO-CNT and TiO₂-CNT). Among the four types of nanohybrids, ZnO-conjugated nanohybrids exhibited a higher antibacterial property, resulting in the antibacterial effect (measured with growth inhibition of cells) in the order ZnO-GO > ZnO-CNT > TiO₂-GO > TiO₂-CNT. Among four possible antibacterial mechanisms (generation of reactive oxygen species (ROS), physicochemical characteristics, the steric effect, and release of metal ions), a primary mechanism-ROS generation-was identified; whereas, physicochemical characteristics and the steric effect were part of contributing mechanisms. The increasing dispersion of TiO₂/ZnO on GO may have contributed to the antibacterial effects due to increasing surface areas. Similarly, significant damages to E. coli cell membranes were found by the GO sheet with its sharp edges. Our results suggest that applying GO-based ZnO or TiO₂ could be an effective antibacterial method, especially for the treatment of multidrug-resistant bacteria in the water.

Treatment of antibiotic-resistant bacteria by encapsulation of ZnO nanoparticles in an alginate biopolymer: Insights into treatment mechanisms

Treating multidrug-resistant bacteria has been a challenging task, although the bacteria have been reported as a trace contaminant present in tap water. Given emerging issues on antibiotic-resistant bacteria, the present study investigated a novel treatment method in which ZnO nanoparticles (NPs) are encapsulated in an alginate biopolymer solution to explore primary antibacterial mechanisms. The antibacterial effects of this technology on two model antibiotic-resistant bacteria (Escherichia coli DH5-α and Pseudomonas aeruginosa) were found to be highly effective, with the removal rates of 98% and 88%, respectively, at the initial bacteria concentration of 10⁸ CFU mL^-1 over 6 h. The inactivation of antibiotic-resistant bacteria by ZnO NP-alginate beads was improved by increasing the nanocomposite amount (4, 10, and 20 mg) and contact time. The primary mechanism involved the generation of reactive oxygen species (ROS). The ZnO NP-alginate beads were demonstrated to be highly promising for different applications in water treatment, especially for point-of-use in the perspectives of reusability, antibacterial property of ZnO, immobilizing NPs, and utilizing high surface area of NPs, with a slight release of zinc ions.

Toxicity of perfluorooctane sulfonate on Phanerochaete chrysosporium: Growth, pollutant degradation and transcriptomics

As a persistent organic pollutant listed in the Stockholm Convention, perfluorooctane sulfonate (PFOS) is extremely refractory to degradation under ambient conditions. Its potential ecotoxicity has aroused great concerns and research interests. However, little is known about the toxicity of PFOS on fungus. In this study, the white rot fungus Phanerochaete chrysosporium (P. chrysosporium) was adopted to assess the toxicity of PFOS in liquid culture. The addition of 100 mg/L PFOS potassium salt significantly decreased the fungal biomass by up to 76.4% comparing with un-amended control during the incubation period. The hyphostroma of P. chrysosporium was wizened and its cell membrane was thickened, while its vesicle structure was increased, based on the observation with scanning electron microscope (SEM) and transmission electron microscope (TEM). Nevertheless, the PFOS dosage of below 100 mg/L did not show a considerable damage to the growth of P. chrysosporium. The degradation of malachite green (MG) and 2,4-dichlorophenol (2,4-DCP) by P. chrysosporium was negatively affected by PFOS. At the initial dosage of 100 mg/L PFOS, the decolorization efficiency of MG and the degradation efficiency of 2,4-DCP decreased by 37% and 20%, respectively. This might be attributed to the inhibition of PFOS on MnP and LiP activities. The activities of MnP and LiP decreased by 20.6% and 43.4%, respectively. At a high dosage PFOS (100 mg/L), P. chrysosporium could show a high adsorption of MG but lose its pollutant degradation ability. Transcriptome analysis indicated that PFOS contamination could lead to the change of gene expression in the studied white rot fungus, and the genes regulating membrane structure, cell redox process, and cell transport, synthesis and metabolism were impacted. Membrane damage and oxidative damage were the two main mechanisms of PFOS' toxicity to P. chrysosporium.

Quantum dot therapeutics: a new class of radical therapies

Traditional therapeutics and vaccines represent the bedrock of modern medicine, where isolated biochemical molecules or designed proteins have led to success in treating and preventing diseases. However, several adaptive pathogens, such as multidrug-resistant (MDR) superbugs, and rapidly evolving diseases, such as cancer, can evade such molecules very effectively. This poses an important problem since the rapid emergence of multidrug-resistance among microbes is one of the most pressing public health crises of our time-one that could claim more than 10 million lives and 100 trillion dollars annually by 2050. Several non-traditional antibiotics are now being developed that can survive in the face of adaptive drug resistance. One such versatile strategy is redox perturbation using quantum dot (QD) therapeutics. While redox molecules are nominally used by cells for intracellular signaling and other functions, specific generation of such species exogenously, using an electromagnetic stimulus (light, sound, magnetic field), can specifically kill the cells most vulnerable to such species. For example, recently QD therapeutics have shown tremendous promise by specifically generating superoxide intracellularly (using light as a trigger) to selectively eliminate a wide range of MDR pathogens. While the efficacy of such QD therapeutics was shown using in vitro studies, several apparent contradictions exist regarding QD safety and potential for clinical applications. In this review, we outline the design rules for creating specific QD therapies for redox perturbation; summarize the parameters for choosing appropriate materials, size, and capping ligands to ensure their facile clearance; and highlight a potential path forward towards developing this new class of radical QD therapeutics.

Bio-interactions and risks of engineered nanoparticles

Nano technological research offered uncountable opportunities for engineered nanoparticles (ENPs) in the field of biomedical, pharmaceutical, agricultural, cosmetics, textiles, automobiles and electronic industry. Large scale commercial production and use of nanoparticles with smaller size and characteristic physico-chemical properties enhance the possibility of amenable toxicity to the environment. Primary important species of the ecosystem like bacteria, algae, fishes and plants are at high risk with nanoparticle (NP) toxicity. ENP distributed in air, water and soil can directly affect the livelihood or even the existence of smaller organisms. In day-today life, human beings are getting exposed to thousands of NPs via dermal contact, inhalation or ingestion. Topical application of sunscreens and cosmetics containing ENPs has the potential to induce photo toxicity under ultra violet irradiation. ENP intentionally or non-intentionally enter into the body will affect the entire organ system and execute their toxicity even in reproduction and fetal developmental stages. Unfortunately the existing researches to evaluate the in vivo and in vitro toxic effects of ENPs are inefficient to give the exact nature and depth of toxicity. Hence an effort was made to discuss on the characteristics, classification, synthesis, applications and toxic potentials of various classes of commercially relevant ENPs along with a detailed review on currently available literatures.

Impact of humic acid on the fate and toxicity of titanium dioxide nanoparticles in Tetrahymena pyriformis and zebrafish embryos

The extensive usage of titanium dioxide (TiO2) nanoparticles in daily usage products have increased their release into the environment. The present study has attempted to investigate the behaviour of titanium dioxide (TiO2) nanoparticles in different experimental buffers in the presence of humic acid. Also, the effect of TiO2 nanoparticles was assessed in different aquatic organisms with and without the presence of humic acid. The results demonstrate that humic acid increases the dispersion of TiO2 nanoparticles via its adsorption on the surface of the nanoparticles, mainly due to electrostatic interactions. The maximum aggregation was observed in the zebrafish growth medium (E3 medium) even in the presence of humic acid. The intensity of TiO2 nanoparticle sedimentation was observed in the order: E3 media > Dryl's buffer > MilliQ water. Interestingly, the ecotoxicity results for Tetrahymena pyriformis and Danio rerio showed that the presence of humic acid reduces the toxicity of TiO2 nanoparticles.

M. Biowaste derived graphene quantum dots interlaced with SnO2 nanoparticles – a dynamic disinfection agent against Pseudomonas aeruginosa

A biocidal GQD/SnO₂ nanocomposite derived from discarded sugarcane bagasse is a cost effective, renewable and green replacement for the traditional hazardous microbicides.

Effects of Escherichia coli and phosphate on the transport of titanium dioxide nanoparticles in heterogeneous porous media

Transport behaviors of titanium dioxide nanoparticles (nTiO₂) were examined in the individual- and co-presence Escherichia (E.) coli and phosphate in heterogeneous sand (uncoated and iron oxyhydroxide-coated sand) columns. The results showed that for the individual presence of phosphate, the degree of nTiO₂ deposition was less in uncoated than in iron oxide-coated sands. In contrast, an opposite trend that greater deposition of nTiO₂ in uncoated than in coated sands occurred in the individual presence of E. coli. These observations are due to the phosphate adsorption changing the charge of NPs and iron oxyhydroxide-coated sand, or the preferential adhesion of bacterial to coated sand. In the copresence of E. coli and phosphate, interestingly, the phosphate level plays an important role in influencing nTiO₂ transport. At a high phosphate concentration (>1.0 mM), the deposition of nTiO₂ with the individual presence of E. coli was stronger than nTiO₂ in the copresence of both E. coli and phosphate, regardless of sand type. The potential mechanism was that phosphate adsorption led to the formation of more negatively charged NPs-bacteria complexes that have higher mobility in sand columns. At a low phosphate level (≤0.1 mM), a similar observation occurred in uncoated sand. Nevertheless, the deposition of nTiO₂ with copresence of E. coli and phosphate was greater than nTiO₂ with E. coli in oxyhydroxide-coated sand. It was attributed to the formation of large NPs-bacteria-phosphate clusters (less mobile) and the preferential adhesion of E. coli cells to iron oxyhydroxide coating simultaneously. Taken together, our findings provide crucial knowledge for better understanding the fate, transport, and potential risks of engineered nanoparticles in complicated environmental settings where bacteria and phosphate are ubiquitous.

Impact of nanoparticles on transcriptional regulation of catabolic genes of petroleum hydrocarbon-degrading bacteria in contaminated soil microcosms

This study was conducted to determine what effects nanoparticles (NPs) like TiO₂ , ZnO, and Ag may pose on natural attenuation processes of petroleum hydrocarbons in contaminated soils. The solid NPs used were identified using x-ray diffraction technique and their average size was certified as 18.2, 16.9, and 18.3 nm for Ag-NPs, ZnO-NPs, and TiO₂ -NPs, respectively. NPs in soil microcosms behave differently where it was dissolved as in case of Ag-NPs, partially dissolved as in ZnO-NPs or changed into other crystalline phase as in TiO₂ -NPs. In this investigation, catabolic gene encoding catechol 2,3 dioxygenase (C23DO) was selected specifically as biomarker for monitoring hydrocarbon biodegradation potential by measuring its transcripts by RT-qPCR. TiO₂ -NPs amended microcosms showed almost no change in C23DO expression profile or bacterial community which were dominated by Bacillus sp., Mycobacterium sp., Microbacterium sp., Clostridium sp., beside uncultured bacteria, including uncultured proteobacteria, Thauera sp. and Clostridia. XRD pattern suggested that TiO₂ -NPs in microcosms were changed into other non-inhibitory crystalline phase, consequently, showing the maximum degradation profile for most low molecular weight oil fractions and partially for the high molecular weight ones. Increasing ZnO-NPs concentration in microcosms resulted in a reduction in the expression of C23DO with a concomitant slight deteriorative effect on bacterial populations ending up with elimination of Clostridium sp., Thauera sp., and uncultured proteobacteria. The oil-degradation efficiency was reduced compared to TiO₂ -NPs amended microcosms. In microcosms, Ag-NPs were not detected in the crystalline form but were available in the ionic form that inhibited most bacterial populations and resulted in a limited degradation profile of oil, specifically the low molecular weight fractions. Ag-NPs amended microcosms showed a significant reduction (80%) in C23DO gene expression and a detrimental effect on bacterial populations including key players like Mycobacterium sp., Microbacterium sp., and Thauera sp. involved in the biodegradation of petroleum hydrocarbons.

Factors impacting the interactions of engineered nanoparticles with bacterial cells and biofilms: Mechanistic insights and state of knowledge

Since their advent a few decades ago, engineered nanoparticles (ENPs) have been extensively used in consumer products and industrial applications and their use is expected to continue at the rate of thousands of tons per year in the next decade. The widespread use of ENPs poses a potential risk of large scale environmental proliferation of ENPs which can impact and endanger environmental health and safety. Recent studies have shown that microbial biofilms can serve as an important biotic component for partitioning and perhaps storage of ENPs released into aqueous systems. Considering that biofilms can be one of the major sinks for ENPs in the environment, and that the field of biofilms itself is only three to four decades old, there is a recent and growing body of literature investigating the ENP-biofilm interactions. While looking at biofilms, it is imperative to consider the interactions of ENPs with the planktonic microbial cells inhabiting the bulk systems in the vicinity of surface-attached biofilms. In this review article, we attempt to establish the state of current knowledge regarding the interactions of ENPs with bacterial cells and biofilms, identifying key governing factors and interaction mechanisms, as well as prominent knowledge gaps. Since the context of ENP-biofilm interactions can be multifarious-ranging from ecological systems to water and wastewater treatment to dental/medically relevant biofilms- and includes devising novel strategies for biofilm control, we believe this review will serve an interdisciplinary audience. Finally, the article also touches upon the future directions that the research in the ENP-microbial cells/biofilm interactions could take. Continued research in this area is important to not only enhance our scientific knowledge and arsenal for biofilm control, but to also support environmental health while reaping the benefits of the 'nanomaterial revolution'.

A comprehensive review on the use of second generation TiO2 photocatalysts: Microorganism inactivation

Photocatalytic disinfection practices have been applied for decades and attract current interest along with the developments in synthesis of novel photocatalysts. A survey based investigation was performed for elucidation of photocatalytic treatment details as well as disinfection mechanism of microorganisms. The present work brings significant information on the utilization of second generation TiO₂ photocatalysts for inactivation of microorganisms typically using E. coli as the model microorganism. Special interest was devoted to the role of organic matrix either generated during treatment or as a natural component. Studies on photocatalytic disinfection were extensively reviewed and evaluated with respect to basic operational parameters related to photocatalysis, and types and properties of microorganisms investigated. Degradation mechanism and behavior of microorganisms towards reactive oxygen species during disinfection and organic matrix effects were also addressed. For successful utilization and effective assessment of visible light active photocatalysts, standard protocols for disinfection activity testing have to be set. Further improvement of the efficiency of these materials would be promising for future applications in water treatment processes.

Interactions between Metal Oxides and Biomolecules: from Fundamental Understanding to Applications

Metallo-oxide (MO)-based bioinorganic nanocomposites promise unique structures, physicochemical properties, and novel biochemical functionalities, and within the past decade, investment in research on materials such as ZnO, TiO₂, SiO₂, and GeO₂ has significantly increased. Besides traditional approaches, the synthesis, shaping, structural patterning, and postprocessing chemical functionalization of the materials surface is inspired by strategies which mimic processes in nature. Would such materials deliver new technologies? Answering this question requires the merging of historical knowledge and current research from different fields of science. Practically, we need an effective defragmentation of the research area. From our perspective, the superficial accounting of material properties, chemistry of the surfaces, and the behavior of biomolecules next to such surfaces is a problem. This is particularly of concern when we wish to bridge between technologies in vitro and biotechnologies in vivo. Further, besides the potential practical technological efficiency and advantages such materials might exhibit, we have to consider the wider long-term implications of material stability and toxicity. In this contribution, we present a critical review of recent advances in the chemistry and engineering of MO-based biocomposites, highlighting the role of interactions at the interface and the techniques by which these can be studied. At the end of the article, we outline the challenges which hamper progress in research and extrapolate to developing and promising directions including additive manufacturing and synthetic biology that could benefit from molecular level understanding of interactions occurring between inanimate (abiotic) and living (biotic) materials.

Non-toxic properties of TiO2 and STiO2 nanocomposite PES ultrafiltration membranes for application in membrane-based environmental biotechnology

In membrane bioreactor (MBR) technology, nanocomposite membrane has a great potential to improve the filtration performance and antifouling. However, antibacterial activity of nanoparticles (NPs) is a significant disadvantage which can be impacted to bacterial growth and microbial community in MBRs. The modified polyethersulfone (PES) ultrafiltration (UF) membranes in the study were prepared by using TiO₂ NPs and TiO₂ NPs functionalized with sulfonation (STiO₂). The antibacterial effect of NPs and non-toxic properties of nanocomposite membranes were examined by using three different Gram-negative bacterial species isolated from a local full scale membrane bioreactor treating municipal wastewater (Escherichia coli, Pantoea agglomerans, and Pseudomonas graminis). Results are revealed that the TiO₂ and STiO₂ NPs have 60% of antibacterial activity based on disc diffusion, viability tests, and TEM analysis. However, the PES-TiO₂ and PES-STiO₂ nanocomposite UF membranes showed significantly lower antibacterial activity (<95%, significance at p < 0.0001), indicating innocuous to bacterial growth. This study highlights that the PES-TiO₂ and PES-STiO₂ nanocomposite membrane is more sustainable than PES membrane and promising materials for MBRs, by taking advantage of non-toxic properties to bacterial growth.

Photocatalytic Water Disinfection under Solar Irradiation by d-Glucose-Modified Titania

Modified titania photocatalysts were synthesized by the pressure method using titanium(IV) oxide from Grupa Azoty Zakłady Chemiczne “Police” S.A., Police, Poland, and d-glucose solution. Characterization of obtained composites was performed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), elemental analysis, and measurements of zeta potential and specific surface area (SSA). The possibility of using glucose-titania composites as photocatalysts for simulated solar-assisted disinfection against gram-negative Escherichia coli and gram-positive Stapchyloccocus epidermidis bacteria were examined in two reaction systems, i.e., for suspended and immobilized photocatalysts (on the concrete). It was found that an increase in the d-glucose concentration, i.e., higher carbon content, led to a decrease in antibacterial properties. The sample obtained from 1% of d-glucose solution at 100 °C (TiO2-1%-G-100) showed superior photocatalytic activity under UV-Vis irradiation toward both bacteria species. Water disinfection was more efficient for suspended photocatalyst than that for supported one, where complete disinfection was reached during 55–70 min and 120 min of irradiation, respectively. For the first time, it has been shown that titania modified with monosaccharides can be efficiently used for water disinfection, and the immobilization of photocatalyst on the concrete might be a prospective method for public water supplies.

Environmental risk assessment of engineered nano-SiO2 , nano iron oxides, nano-CeO2 , nano-Al2 O3 , and quantum dots

Many research studies have endeavored to investigate the ecotoxicological hazards of engineered nanomaterials (ENMs). However, little is known regarding the actual environmental risks of ENMs, combining both hazard and exposure data. The aim of the present study was to quantify the environmental risks for nano-Al₂ O₃ , nano-SiO₂ , nano iron oxides, nano-CeO₂ , and quantum dots by comparing the predicted environmental concentrations (PECs) with the predicted-no-effect concentrations (PNECs). The PEC values of these 5 ENMs in freshwaters in 2020 for northern Europe and southeastern Europe were taken from a published dynamic probabilistic material flow analysis model. The PNEC values were calculated using probabilistic species sensitivity distribution (SSD). The order of the PNEC values was quantum dots < nano-CeO₂  < nano iron oxides < nano-Al₂ O₃  < nano-SiO₂ . The risks posed by these 5 ENMs were demonstrated to be in the reverse order: nano-Al₂ O₃  > nano-SiO₂  > nano iron oxides > nano-CeO₂  > quantum dots. However, all risk characterization values are 4 to 8 orders of magnitude lower than 1, and no risk was therefore predicted for any of the investigated ENMs at the estimated release level in 2020. Compared to static models, the dynamic material flow model allowed us to use PEC values based on a more complex parameterization, considering a dynamic input over time and time-dependent release of ENMs. The probabilistic SSD approach makes it possible to include all available data to estimate hazards of ENMs by considering the whole range of variability between studies and material types. The risk-assessment approach is therefore able to handle the uncertainty and variability associated with the collected data. The results of the present study provide a scientific foundation for risk-based regulatory decisions of the investigated ENMs. Environ Toxicol Chem 2018;37:1387-1395. © 2018 SETAC.

Toxicity of Food-Grade TiO2 to Commensal Intestinal and Transient Food-Borne Bacteria: New Insights Using Nano-SIMS and Synchrotron UV Fluorescence Imaging

Titanium dioxide (TiO₂) is commonly used as a food additive (E171 in the EU) for its whitening and opacifying properties. However, a risk of intestinal barrier disruption, including dysbiosis of the gut microbiota, is increasingly suspected because of the presence of a nano-sized fraction in this additive. We hypothesized that food-grade E171 and Aeroxyde P25 (identical to the NM-105 OECD reference nanomaterial in the European Union Joint Research Centre) interact with both commensal intestinal bacteria and transient food-borne bacteria under non-UV-irradiated conditions. Based on differences in their physicochemical properties, we expect a difference in their respective effects. To test these hypotheses, we chose a panel of eight Gram-positive/Gram-negative bacterial strains, isolated from different biotopes and belonging to the species Escherichia coli, Lactobacillus rhamnosus, Lactococcus lactis (subsp. lactis and cremoris), Streptococcus thermophilus, and Lactobacillus sakei. Bacterial cells were exposed to food-grade E171 vs. P25 in vitro and the interactions were explored with innovative (nano)imaging methods. The ability of bacteria to trap TiO₂ was demonstrated using synchrotron UV fluorescence imaging with single cell resolution. Subsequent alterations in the growth profiles were shown, notably for the transient food-borne L. lactis and the commensal intestinal E. coli in contact with food-grade TiO₂. However, for both species, the reduction in cell cultivability remained moderate, and the morphological and ultrastructural damages, observed with electron microscopy, were restricted to a small number of cells. E. coli exposed to food-grade TiO₂ showed some internalization of TiO₂ (7% of cells), observed with high-resolution nano-secondary ion mass spectrometry (Nano-SIMS) chemical imaging. Taken together, these data show that E171 may be trapped by commensal and transient food-borne bacteria within the gut. In return, it may induce some physiological alterations in the most sensitive species, with a putative impact on gut microbiota composition and functioning, especially after chronic exposure.

Silver-, calcium-, and copper molybdate compounds: Preparation, antibacterial activity, and mechanisms

Developing novel compounds with antimicrobial properties can be an effective approach to decreasing the number of healthcare-associated infections, particularly in the context of medical devices and touch surfaces. A variety of molybdate powders (Ag₂MoO₄, CaMoO₄, CuMoO₄ and Cu₃Mo₂O₉) were synthesized and characterized, and Escherichia coli was used as a model gram-negative bacterium to demonstrate their antimicrobial properties. Optical density measurements, bacterial colony growth, and stained gel images for protein expression clearly showed that silver- and copper molybdates inhibit bacterial growth, whereas CaMoO₄ exhibited no bactericidal effect. All tests were performed in both daylight and darkness to assess the possible contribution of a photocatalytic effect on the activity observed. The main mechanism responsible for the antibacterial effect observed for Ag₂MoO₄ is related to Ag⁺ release in combination with medium acidification, whereas for compounds containing copper, leaching of Cu²⁺ ions is proposed. All these effects are known to cause damage at the cellular level. A photocatalytic contribution to the antibacterial activity was not clearly observable. Based on the pH and solubility measurements performed for powders in contact with various media (ultrapure water and bacterial growth medium), silver molybdate (Ag₂MoO₄) was identified as the best antibacterial candidate. This compound has great potential for further use in hybrid powder-polymer/varnish systems for touch surfaces in healthcare settings.

Antimicrobial and antibiofilm efficacy of self-cleaning surfaces functionalized by TiO2 photocatalytic nanoparticles against Staphylococcus aureus and Pseudomonas putida

A photocatalytic sol of TiO₂ nanoparticles has been used for creating self-cleaning antimicrobial flat and porous glass surfaces. The substrates were irradiated to study their photocatalytic properties and behavior in the presence of biofilm-forming bacteria. Smooth glass surfaces and glass microfiber filters were covered with 1.98×10^-3±1.5×10^-4gcm^-2 and 8.55×10^-3±3.0×10^-4gcm^-2 densities, respectively. Self-cleaning properties were analyzed using the methylene blue 365nm UV-A photodegradation test. TiO₂-coated filters achieved rapid and complete photodegradation of methylene blue because of the better TiO₂ dispersion with respect to the glass slides. The effect of functionalized surfaces on the growth and viability of bacteria was studied using the strains Staphylococcus aureus and Pseudomonas putida. After irradiation (2h, 11.2Wm^-2, 290-400nm), the initially hydrophobic surface turned hydrophilic. The antibacterial effect led to extensive membrane damage and significant production of intracellular reactive oxygen species in all TiO₂-loaded irradiated specimens. The reduction of cell viability was over 99.9% (>3-log) for TiO₂ on glass surfaces. However, the polymeric extracellular matrix formed before the irradiation treatment was not removed. This study highlights the importance of bacterial colonization during dark periods and the difficulty of removing the structure of biofilms.

Metal-Based Nanoparticles for the Treatment of Infectious Diseases

Infectious diseases can be transmitted and they cause a significant burden on public health globally. They are the greatest world killers and it is estimated that they are responsible for the demise of over 17 million people annually. The impact of these diseases is greater in the developing countries. People with compromised immune systems and children are the most affected. Infectious diseases may be caused by bacteria, viruses, and protozoa. The treatment of infectious diseases is hampered by simultaneous resistance to multiple drugs, indicating that there is a serious and pressing need to develop new therapeutics that can overcome drug resistance. This review will focus on the recent reports of metal-based nanoparticles that are potential therapeutics for the treatment of infectious diseases and their biological efficacy (in vitro and in vivo).

Interaction between bacterial cell membranes and nano-TiO2 revealed by two-dimensional FTIR correlation spectroscopy using bacterial ghost as a model cell envelope

The interaction between microorganisms and nanoparticles is a crucial step towards understanding the subsequent biological effect. In this study, the interaction between TiO₂ nanoparticles and bacterial cell membrane was investigated by Two-dimensional Correlation Fourier Transformation Infrared spectroscopy (2D-FTIR-COS) using bacterial ghosts (BGs), which are non-living bacterial cell envelopes devoid of cytoplasm. The synchronous map of 2D-FTIR-COS results indicated that the functionalities in proteins of BGs preferentially interacted with TiO₂ nanoparticles; whereas the interaction of TiO₂ nanoparticles with characteristic functionality in polysaccharides (COH) and phospholipids (PO) were very weak or insensitive. This conclusion was further corroborated by settling of TiO₂ nanoparticles in the presence of pure protein, polysaccharide and phospholipid represented by bovine serum albumin (BSA), alginate and phosphatidylethanolamine (PE). Additionally, the asynchronous map of 2D-FTIR-COS indicated a sequential order of functionalities bonded to TiO₂ nanoparticles with the order of: COO^- > aromatic CC stretching > NH, amide II > CO, ketone. These findings contribute to deeper understanding of the interaction between TiO₂ nanoparticles and bacterial cell membrane in aquatic systems.

Metabolomic and proteomic investigations of impacts of titanium dioxide nanoparticles on Escherichia coli

In a previous study, it was demonstrated that the toxic impact of titanium dioxide nanoparticles on Escherichia coli starts at 10 ppm and is closely related to the presence of little aggregates. It was also assumed that only a part of the bacterial population is able to adapt to this stress and attempts to survive. Proteomic analyses, supported by results from metabolomics, reveal that exposure of E. coli to nano-TiO2 induces two main effects on bacterial metabolism: firstly, the up-regulation of proteins and the increase of metabolites related to energy and growth metabolism; secondly, the down-regulation of other proteins resulting in an increase of metabolites, particularly amino acids. Some proteins, e.g. chaperonin 1 or isocitrate dehydrogenase, and some metabolites, e.g. phenylalanine or valine, might be used as biomarkers of nanoparticles stress. Astonishingly, the ATP content gradually rises in relation with the nano-TiO2 concentration in the medium, indicating a dramatic release of ATP by the damaged cells. These apparently contradictory results accredit the thesis of a heterogeneity of the bacterial population. This heterogeneity is also confirmed by SEM images which show that while some bacteria are fully covered by nano-TiO2, the major part of the bacterial population remains free from nanoparticles, resulting in a difference of proteome and metabolome. The use of combined-omics has allowed to better understand the heterogeneous bacterial response to nano-TiO2 stress due to heterogeneous contacts between the protagonists under environmental conditions.

TiO2-based photocatalytic disinfection of microbes in aqueous media: A review

The TiO₂ based photocatalyst has great potential for the disinfection/inactivation of harmful pathogens (such as E.coli in aqueous media) along with its well-known usefulness on various chemical pollutants. The disinfection property of TiO₂ is primarily attributed to surface generation of reactive oxygen species (ROS) as well as free metal ions formation. Furthermore, its disinfection capacity and overall performance can be significantly improved through modifications of the TiO₂ material. In this review, we provide a brief survey on the effect of various TiO₂ materials in the disinfection of a wide range of environmentally harmful microbial pathogens (e.g., bacteria, fungi, algae, and viruses) in aqueous media. The influencing factors (such as reactor design, water chemistry, and TiO₂ modifications) of such processes are discussed along with the mechanisms of such disinfection. It is believed that the combined application of disinfection and decontamination will greatly enhance the utilization of TiO₂ photocatalyst as a potential alternative to conventional methods of water purification.

Cyto-genotoxic and DNA methylation changes induced by different crystal phases of TiO2-np in bronchial epithelial (16-HBE) cells

With the increase in use of TiO₂-np, a better understanding of their safety is important. In the present study the effect of different crystal phases of TiO₂-np (anatase, rutile and anatase: rutile mixture; 20-26nm) were studied for cyto-genotoxicity and global DNA methylation and hydroxymethylation. Cytotoxic response was observed at a concentration of 25μg/ml for the particles tested. Results of comet and micronucleus (with and without CytB) assays revealed significant genotoxic effect of these particles. Flow cytometry revealed cell cycle arrest in the S-phase. Based on the results, toxicity of the particles could be correlated with their physico-chemical properties (i.e. smaller size and hydrodynamic diameter and larger surface area), anatase form being the most toxic. From the results of the cyto-genotoxicity assays, concentrations were determined for the epigenetic study. Effect on global DNA methylation and hydroxymethylation levels were studied at cyto-genotoxic (25μg/ml), genotoxic (12.5μg/ml) and sub cyto-genotoxic (3.25μg/ml) concentrations using LC-MS/MS analysis. Though no significant changes were observed for 3h treatment schedule; significant hypomethylation were observed at 24h for anatase (significant at 3.25 and 25μg/ml), rutile (significant at 3.25 and 25μg/ml) and anatase: rutile mixture (significant at 25μg/ml) forms. The results suggest that epigenetic changes could occur at sub cyto-genotoxic concentrations. And hence for complete characterization of nanoparticle toxicity, epigenetic studies should be performed along with conventional toxicity testing methods.

Behavior and Potential Impacts of Metal-Based Engineered Nanoparticles in Aquatic Environments

The specific properties of metal-based nanoparticles (NPs) have not only led to rapidly increasing applications in various industrial and commercial products, but also caused environmental concerns due to the inevitable release of NPs and their unpredictable biological/ecological impacts. This review discusses the environmental behavior of metal-based NPs with an in-depth analysis of the mechanisms and kinetics. The focus is on knowledge gaps in the interaction of NPs with aquatic organisms, which can influence the fate, transport and toxicity of NPs in the aquatic environment. Aggregation transforms NPs into micrometer-sized clusters in the aqueous environment, whereas dissolution also alters the size distribution and surface reactivity of metal-based NPs. A unique toxicity mechanism of metal-based NPs is related to the generation of reactive oxygen species (ROS) and the subsequent ROS-induced oxidative stress. Furthermore, aggregation, dissolution and ROS generation could influence each other and also be influenced by many factors, including the sizes, shapes and surface charge of NPs, as well as the pH, ionic strength, natural organic matter and experimental conditions. Bioaccumulation of NPs in single organism species, such as aquatic plants, zooplankton, fish and benthos, is summarized and compared. Moreover, the trophic transfer and/or biomagnification of metal-based NPs in an aquatic ecosystem are discussed. In addition, genetic effects could result from direct or indirect interactions between DNA and NPs. Finally, several challenges facing us are put forward in the review.

Is there evidence for man-made nanoparticles in the Dutch environment?

Only very limited information is available on measured environmental concentrations of nanoparticles. In this study, several environmental compartments in The Netherlands were probed for the presence of nanoparticles. Different types of water were screened for the presence of inorganic (Ag, Au, TiO₂) and organic nanoparticles (C₆₀, C₇₀, [6,6]-phenyl-C₆₁-butyric acid octyl ester, [6,6]-phenyl-C₆₁-butyric acid butyl ester, [6,6]-phenyl-C₆₁-butyric acid methyl ester, [6,6]-bis-phenyl-C₆₁-butyric acid methyl ester, [6,6]-phenyl-C₇₁-butyric acid methyl ester, [6,6]-thienyl-C₆₁-butyric acid methyl ester). Air samples were analysed for the presence of nanoparticulate Mo, Ag, Ce, W, Pd, Pt, Rh, Zn, Ti, Si, B as well as Fe and Cu. ICP-MS, Orbitrap-HRMS, SEM and EDX were used for this survey. Water samples included dune and bank filtrates, surface waters and ground waters as well as influents, effluents and sludge of sewage treatment plants (STPs), and surface waters collected near airports and harbours. Air samples included both urban and rural samples. C₆₀ was detected in air, sewage treatment plants, influents, effluents and sludge, but in no other aqueous samples despite the low detection limit of 0.1ng/L. C₇₀ and functionalised fullerenes were not detected at all. In STP sludge and influent the occurrence of Ag and Au nanoparticles was verified by SEM/EDX and ICP-MS. In air up to about 25m% of certain metals was found in the nanosize fraction. Overall, between 1 and 6% of the total mass from metals in the air samples was found in the size fraction <100nm.

Assessment of Crystal Morphology on Uptake, Particle Dissolution, and Toxicity of Nanoscale Titanium Dioxide on Artemia salina

Knowledge of nanomaterial toxicity is critical to avoid adverse effects on human and environment health. In this study, the influences of crystal morphology on physico-chemical and toxic properties of nanoscale TiO2 (n-TiO2) were investigated. Artemia salina were exposed to anatase, rutile and mixture polymorphs of n-TiO2 in seawater. Short-term (24 h) and long-term (96 h) exposures were conducted in 1, 10 and 100 mg/L suspensions of n-TiO2 in the presence and absence of food. Anatase form had highest accumulation followed by mixture and rutile. Presence of food greatly reduced accumulation. n-TiO2 dissolution was not significant in seawater (p<0.05) nor was influenced from crystal structure. Highest toxic effects occurred in 96h exposure in the order of anatase > mixture > rutile. Mortality and oxidative stress levels increased with increasing n-TiO2 concentration and exposure time (p<0.05). Presence of food in the exposure medium alleviated the oxidative stress, indicating that deprivation from food could promote toxic effects of n-TiO2 under long-term exposure.

Size effect of SnO2 nanoparticles on bacteria toxicity and their membrane damage

Semiconductor SnO₂ nanoparticles (NPs) are being exploited for various applications, including those in the environmental context. However, toxicity studies of SnO₂ NPs are very limited. This study evaluated the toxic effect of two sizes of spherical SnO₂ NPs (2 and 40 nm) and one size of flower-like SnO₂ NPs (800 nm) towards the environmental bacteria E. coli and B. subtilis. SnO₂ NPs were synthesized using a hydrothermal or calcination method and they were well characterized prior to toxicity assessment. To evaluate toxicity, cell viability and membrane damage were determined in cells (1 × 10⁹ CFU mL^-1) exposed to up to 1000 mg L^-1 of NPs, using the plate counting method and confocal laser scanning microscopy. Spherical NPs of smaller primary size (E2) had the lowest hydrodynamic size (226 ± 96 nm) and highest negative charge (-30.3 ± 10.1 mV). Smaller spherical NPs also showed greatest effect on viability (IC₅₀ > 500 mg L^-1) and membrane damage of B. subtilis, whereas E. coli was unaffected. Scanning electron microscopy confirmed the membrane damage of exposed B. subtilis and also exhibited the attachment of E2 NPs to the cell surface, as well as the elongation of cells. It was also apparent that toxicity was caused solely by NPs, as released Sn⁴⁺ was not toxic to B. subtilis. Thus, surface charge interaction between negatively charged SnO₂ NPs and positively charged molecules on the membrane of the Gram positive B. subtilis was indicated as the key mechanism related to toxicity of NPs.

Toxicity of iron-based nanoparticles to green algae: Effects of particle size, crystal phase, oxidation state and environmental aging

With the increasing environmental application and discharge of iron-based nanoparticles (NPs), a comprehensive understanding of their fate and ecotoxicological effect in the aquatic environment is very urgent. In this study, toxicities of 4 zero-valent iron NPs (nZVI) of different sizes, 2 Fe₂O₃ NPs of different crystal phases, and 1 type of Fe₃O₄ NPs to a green alga (Chlorella pyrenoidosa) were investigated, with a focus on the effects of particle size, crystal phase, oxidation state, and environmental aging. Results show that the algal growth inhibition of nZVI increased significantly with decreasing particle size; with similar particle sizes (20-30 nm), the algal growth inhibition decreased with oxidation of the NPs with an order of nZVI > Fe₃O₄ NPs > Fe₂O₃ NPs, and α-Fe₂O₃ NPs presented significantly higher toxicity than γ-Fe₂O₃ NPs. The NP-induced oxidative stress was the main toxic mechanism, which could explain the difference in algal toxicity of the NPs. The NP-cell heteroagglomeration and physical interactions also contributed to the nanotoxicity, whereas the effect of NP dissolution was negligible. The aging in distilled water and 3 surface water samples for 3 months increased surface oxidation of the iron-based NPs especially nZVI, which decreased the toxicity to algae. These findings will be helpful for the understanding of the fate and toxicity of iron-based NPs in the aquatic environment.

Toxicity of ZnO and TiO2 to Escherichia coli cells

We performed a comprehensive investigation of the toxicity of ZnO and TiO2 nanoparticles using Escherichia coli as a model organism. Both materials are wide band gap n-type semiconductors and they can interact with lipopolysaccharide molecules present in the outer membrane of E. coli, as well as produce reactive oxygen species (ROS) under UV illumination. Despite the similarities in their properties, the response of the bacteria to the two nanomaterials was fundamentally different. When the ROS generation is observed, the toxicity of nanomaterial is commonly attributed to oxidative stress and cell membrane damage caused by lipid peroxidation. However, we found that significant toxicity does not necessarily correlate with up-regulation of ROS-related proteins. TiO2 exhibited significant antibacterial activity, but the protein expression profile of bacteria exposed to TiO2 was different compared to H2O2 and the ROS-related proteins were not strongly expressed. On the other hand, ZnO exhibited lower antibacterial activity compared to TiO2, and the bacterial response involved up-regulating ROS-related proteins similar to the bacterial response to the exposure to H2O2. Reasons for the observed differences in toxicity and bacterial response to the two metal oxides are discussed.