99 research outputs found
Toxicity of TiO2 nanoparticles to Escherichia coli: effects of particle size, crystal phase and water chemistry.
No full textControversial and inconsistent results on the eco-toxicity of TiO2 nanoparticles (NPs) are commonly found in recorded studies and more experimental works are therefore warranted to elucidate the nanotoxicity and its underlying precise mechanisms. Toxicities of five types of TiO2 NPs with different particle sizes (10∼50 nm) and crystal phases were investigated using Escherichia coli as a test organism. The effect of water chemistry on the nanotoxicity was also examined. The antibacterial effects of TiO2 NPs as revealed by dose-effect experiments decreased with increasing particle size and rutile content of the TiO2 NPs. More bacteria could survive at higher solution pH (5.0-10.0) and ionic strength (50-200 mg L(-1) NaCl) as affected by the anatase TiO2 NPs. The TiO2 NPs with anatase crystal structure and smaller particle size produced higher content of intracellular reactive oxygen species and malondialdehyde, in line with their greater antibacterial effect. Transmission electron microscopic observations showed the concentration buildup of the anatase TiO2 NPs especially those with smaller particle sizes on the cell surfaces, leading to membrane damage and internalization. These research results will shed new light on the understanding of ecological effects of TiO2 NPs
Biomacromolecular and Toxicity Responses of Bacteria upon the Nano–Bio Interfacial Interactions with Ti<sub>3</sub>C<sub>2</sub>T<sub><i>x</i></sub> Nanosheets
No full textThe biomolecular responses of bacteria to 2D nanosheets
that result
from nano–bio interfacial interactions remain to be thoroughly
examined. Herein, Fourier transform infrared (FTIR) multivariate and
2D correlation analyses were performed to assess the composition and
conformational changes in bacterial biomacromolecules (lipids, polysaccharides,
and carbohydrates) upon exposure to Ti3C2Tx nanosheets. General toxicity assays, 3D
excitation–emission matrix fluorescence analyses, extended
Derjaguin–Landau–Verwey–Overbeek theory interaction
calculations, and isothermal titration calorimetry were also performed.
Our results demonstrate that Ti3C2Tx nanosheets considerably impact Gram-positive bacteria
(Bacillus subtilis), causing oxidative damage and
inactivation by preferentially interacting with and disrupting the
cell walls. The bilayer membrane structure of Gram-negative bacteria
(Escherichia coli) endows them with increased resistance
to Ti3C2Tx nanosheets.
The unmodified nanosheets had a higher affinity to bacterial protein
components with lower toxicity due to their susceptibility to oxidation.
Surface modification with KOH or hydrazine (HMH), particularly HMH,
induced stronger dispersion, antioxidation, and affinity to bacterial
phospholipids, which resulted in severe cell membrane lipid peroxidation
and bacterial inactivation. These findings provide valuable insight
into nano–bio interfacial interactions, which can facilitate
the development of antimicrobial and antifouling surfaces and contribute
to the evaluation of the environmental risks of nanomaterials
Toxicity of ZnO Nanoparticles to<i>Escherichia coli</i>: Mechanism and the Influence of Medium Components
No full textTannic Acid Adsorption and Its Role for Stabilizing Carbon Nanotube Suspensions
No full textDissolved organic matter (DOM) has been reported to stabilize carbon nanotube (CNT) suspensions, which increases concern over the subsequent transport and behavior of CNTs. However, it is unknown exactly which compounds or functional groups cause the stabilization of CNTs in natural environments. Naturally occurring tannic acid (TA), which has a large number of aromatic functional groups, was used as a surrogate of DOM to investigate its interaction with CNTs. CNT suspendability in TA solution increased with increasing CNT diameter without the aid of sonication. Sorption affinity of CNTs for TA increased with decreasing CNT diameter, positively related to their surface area. A two-stage sorption model was proposed to illustrate the interaction between CNTs and TA. TA molecules may be adsorbed first onto CNTs with aromatic rings binding to the surface carbon rings via π−π interactions, until forming a monolayer; the TA monolayer then further sorbed the dissolved TA by hydrogen bonds and other polar interactions. The sorbed TA increased the steric repulsion between individual CNTs, which might disperse the relatively loose CNT aggregates and result in the stabilization of large-diameter CNTs in TA solution. The sorption and suspending process were also examined by transmission electron microscopy, providing further evidence for the above proposed CNT−TA interactions. This study implies that widely distributed TA may promote the mobility and transport of CNTs in natural aqueous environments
Adsorption of Phenolic Compounds by Carbon Nanotubes: Role of Aromaticity and Substitution of Hydroxyl Groups
No full textWith increasing production and application of carbon nanotubes (CNTs), it becomes necessary to understand the interaction between CNTs and aromatic compounds, an important group of organic contaminants and structural components of large organic molecules in biological systems. However, so far few experimental studies have been conducted to systematically investigate the sorption mechanism of polar aromatics to CNTs. Therefore, cyclohexanol, phenol, catechol, pyrogallol, 2-phenylphenol, 1-naphthol, and naphthalene were selected to investigate the role of aromatic structure and -OH substitution in the polar aromatics-CNTs system. Sorption affinity of these compounds by CNTs increased with increasing number of aromatic rings, with an order of cyclohexanol < phenol <2-phenylphenol <1-naphthol, and was greatly enhanced by -OH substitution, with an order of phenol (1 -OH) < catechol (2 -OH) < pyrogallol (3 -OH). Four possible solute-sorbent interactions, i.e., hydrophobic effect, electrostatic interaction, hydrogen bonding, and π-π bonds, were discussed to address the underlying mechanism of the enhanced sorption affinity by -OH substitution. It was evident that electron-donating substitution on the aromatic rings strengthened the π-π interaction between the aromatics and CNTs and thus the adsorption affinity. These results will advance the understanding of the sorption behavior of CNTs in the environmental systems
Root Uptake and Phytotoxicity of ZnO Nanoparticles
No full textIncreasing application of nanotechnology highlights the need to clarify nanotoxicity. However, few researches have focused on phytotoxicity of nanomaterials; it is unknown whether plants can uptake and transport nanoparticles. This study was to examine cell internalization and upward translocation of ZnO nanoparticles by Lolium perenne (ryegrass). The dissolution of ZnO nanoparticles and its contribution to the toxicity on ryegrass were also investigated. Zn2+ ions were used to compare and verify the root uptake and phytotoxicity of ZnO nanoparticles in a hydroponic culture system. The root uptake and phytotoxicity were visualized by light, scanning electron, and transmission electron microscopies. In the presence of ZnO nanoparticles, ryegrass biomass significantly reduced, root tips shrank, and root epidermal and cortical cells highly vacuolated or collapsed. Zn2+ ion concentrations in bulk nutrient solutions with ZnO nanoparticles were lower than the toxicity threshold of Zn2+ to the ryegrass; shoot Zn contents under ZnO nanoparticle treatments were much lower than that under Zn2+ treatments. Therefore, the phytotoxicity of ZnO nanoparticles was not directly from their limited dissolution in the bulk nutrient solution or rhizosphere. ZnO nanoparticles greatly adhered onto the root surface. Individual ZnO nanoparticles were observed present in apoplast and protoplast of the root endodermis and stele. However, translocation factors of Zn from root to shoot remained very low under ZnO nanoparticle treatments, and were much lower than that under Zn2+ treatments, implying that little (if any) ZnO nanoparticles could translocate up in the ryegrass in this study
Environmental Behaviors and Biological Effects of Engineered Nanomaterials: Important Roles of Interfacial Interactions and Dissolved Organic Matter
No full textEnvironmental transformations and ecological effects of iron-based nanoparticles
No full textThe 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. Environmental transformations of iron-based NPs regulate their eco-toxicities.</p
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