•Chlorpyrifos adsorption to TiO2 NPs is not observed to any appreciable extent.•Loss of chlorpyrifos is predominantly due to photocatalytic degradation.•Association with TiO2 results in greater ...hydroxyl radical delivery.•Bacterial inactivation is unaffected by system complexity due to NP proximity.•Simplified systems may overestimate photocatalytic efficiency for some targets.
High concentrations of pesticides enter surface waters following agricultural application, raising environmental and human health concerns. The use of photoreactive nanoparticles has shown promise for contaminant degradation and surface water remediation. However, it remains uncertain how the complexity of natural waters will impact the photodegradation process. Here, we investigate the photoreactivity of titanium dioxide nanoparticles, the capability to degrade the pesticide chlorpyrifos, and the effect of and impact on bacteria during the photodegradation process. Loss of chlorpyrifos in solution resulted solely from photocatalytic oxidation, with 80% degradation observed after 24 h in our reactor, either in the presence or absence of bacteria. Degradation of chlorpyrifos to chlorpyrifos oxon and 3,5,6-trichloro-2-pyridinol was observed via LC/MS-MS and effectively modeled for the given reactor conditions. Bacterial inactivation occurred over 60 min and was not impacted by the presence of chlorpyrifos. The relative affinity of bacteria and chlorpyrifos for the nanoparticle surface decreased the amount of Reactive Oxygen Species (ROS) detected in the bulk by up to 94%, suggesting that ROS measurements in simplified systems may overestimate the reactivity of photoreactive nanoparticles in complex environments.
Multi-wall carbon nanotube (MWCNT)/aromatic polyamide (PA) nanocomposite membranes were synthesized by a polymer grafting process. Surface morphology, roughness, and mechanical strength of the ...resultant nanocomposite membranes were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), and micro-strain analysis, respectively. SEM and AFM images showed that MWCNTs were well dispersed in the PA matrix. Measurements of mechanical properties of this composite showed increasing membrane strength with increasing MWCNT content with monotonic increases in Young's modulus, toughness, and tensile strength. The addition of MWCNTs also improved the rejection of both salt and organic matter relative to the 10% PA membrane base case. The nanocomposite membrane synthesized with 15
mg/g MWCNT in a 10% PA casting solution rejected NaCl and humic acid by factors of 3.17 and 1.67 respectively relative to the PA membrane without MWCNTs, while membrane permeability decreased by 6.5%.
► Multi-wall carbon nanotube (MWCNTs)/aromatic polyamide (PA) nanocomposite membranes by polymer grafting. ► SEM, AFM, FTIR and mechanical for membrane characterization. ► RO performance by permeability of ultrapure water and rejection of salts. ► Humic acid for water treatment.
The influence of inorganic anions on the photoreactivity and aggregation of titanium dioxide nanoparticles (NPs) was assessed by dosing carbonate, chloride, nitrate, phosphate, and sulfate as ...potassium salts at multiple concentrations. NP stability was monitored in terms of aggregate morphology and electrophoretic mobility (EPM). Aggregate size and fractal dimension were measured over time by laser diffraction, and the isoelectric point (IEP) as a function of anion and concentration was obtained by measuring EPM versus pH. Phosphate, carbonate, and to a lesser extent, sulfate decreased the IEP of TiO2 and stabilized NP suspensions owing to specific surface interactions, whereas this was not observed for nitrate and chloride. TiO2 NPs were exposed to UV-A radiation, and the photoreactivity was assessed by monitoring the production of reactive species over time both at the NP surface (photogenerated holes) and in the bulk solution (hydroxyl radicals) by observing their reactions with the selective probe compounds iodide and terephthalic acid, respectively. The generation of photogenerated holes and hydroxyl radicals was influenced by each inorganic anion to varying degrees. Carbonate and phosphate inhibited the oxidation of iodide, and this interaction was successfully described by a Langmuir–Hinshelwood mechanism and related to the characteristics of TiO2 aggregates. Chloride and nitrate do not specifically interact with TiO2, and sulfate creates relatively weak interactions with the TiO2 surface such that no decrease in photogenerated hole reactivity was observed. A decrease in hydroxyl radical generation was observed for all inorganic anions. Quenching rate constants for the reaction of hydroxyl radicals with each inorganic anion do not provide a comprehensive explanation for the magnitude of this decrease, which arises from the interplay of several physicochemical phenomena. This work shows that the reactivity of NPs will be strongly influenced by the makeup of the waters they are released into. The impact of anion species on hydroxyl radical inhibition was as follows: carbonate > chloride > phosphate > nitrate > sulfate.
We introduce a novel methodology based on hyperspectral imagery with enhanced Darkfield microscopy for detection, characterization, and analysis of engineered nanoparticles in both ultrapure water ...and in complex waters, such as simulated-wetland ecosystem water and wastewater. Hyperspectral imagery analysis of 12 different nanoparticle sample types, scattering the obliquely incident visible and near-infrared light (VNIR: 400–1000 nm) in an enhanced Darkfield background, showed that the sample information in terms of the spatial distribution as well as spectral characteristics unique to each nanoparticle types, at a sensitivity of single nanoparticle (size ≥10 nm) can be obtained. Hyperspectral imagery and Raman spectral analyses of the silver nanoparticles (AgNPs) revealed that the apparent hydrodynamic size of the particle increased while the primary size remained unchanged in the presence of coatings, which is further confirmed by dynamic light scattering measurements. Similar in size, AgNPs with different coatings exhibited similar spectral color (or peak position) but a red-shift in the peak positions by same amount relative to Bare AgNPs was observed. In conclusion, hyperspectral imagery with enhanced Darkfield microscopy can be a promising tool for detection and characterization of engineered nanoparticles in environmental systems, facilitating studies on fate and transformation of these particles in various types of water samples.
Nanomaterial properties differ from those bulk materials of the same composition, allowing them to execute novel activities. A possible downside of these capabilities is harmful interactions with ...biological systems, with the potential to generate toxicity. An approach to assess the safety of nanomaterials is urgently required. We compared the cellular effects of ambient ultrafine particles with manufactured titanium dioxide (TiO2), carbon black, fullerol, and polystyrene (PS) nanoparticles (NPs). The study was conducted in a phagocytic cell line (RAW 264.7) that is representative of a lung target for NPs. Physicochemical characterization of the NPs showed a dramatic change in their state of aggregation, dispersibility, and charge during transfer from a buffered aqueous solution to cell culture medium. Particles differed with respect to cellular uptake, subcellular localization, and ability to catalyze the production of reactive oxygen species (ROS) under biotic and abiotic conditions. Spontaneous ROS production was compared by using an ROS quencher (furfuryl alcohol) as well as an NADPH peroxidase bioelectrode platform. Among the particles tested, ambient ultrafine particles (UFPs) and cationic PS nanospheres were capable of inducing cellular ROS production, GSH depletion, and toxic oxidative stress. This toxicity involves mitochondrial injury through increased calcium uptake and structural organellar damage. Although active under abiotic conditions, TiO2 and fullerol did not induce toxic oxidative stress. While increased TNF-α production could be seen to accompany UFP-induced oxidant injury, cationic PS nanospheres induced mitochondrial damage and cell death without inflammation. In summary, we demonstrate that ROS generation and oxidative stress are a valid test paradigm to compare NP toxicity. Although not all materials have electronic configurations or surface properties to allow spontaneous ROS generation, particle interactions with cellular components are capable of generating oxidative stress.
The study of nanomaterial impacts on environment, health and safety (nanoEHS) has been largely predicated on the assumption that exposure and hazard can be predicted from physical–chemical properties ...of nanomaterials. This approach is rooted in the view that nanoöbjects essentially resemble chemicals with additional particle-based attributes that must be included among their intrinsic physical–chemical descriptors. With the exception of the trivial case of nanomaterials made from toxic or highly reactive materials, this approach has yielded few actionable guidelines for predicting nanomaterial risk. This article addresses inherent problems in structuring a nanoEHS research strategy based on the goal of predicting outcomes directly from nanomaterial properties, and proposes a framework for organizing data and designing integrated experiments based on functional assays (FAs). FAs are intermediary, semi-empirical measures of processes or functions within a specified system that bridge the gap between nanomaterial properties and potential outcomes in complex systems. The three components of a functional assay are standardized protocols for parameter determination and reporting, a theoretical context for parameter application and reference systems. We propose the identification and adoption of reference systems where FAs may be applied to provide parameter estimates for environmental fate and effects models, as well as benchmarks for comparing the results of FAs and experiments conducted in more complex and varied systems. Surface affinity and dissolution rate are identified as two critical FAs for characterizing nanomaterial behavior in a variety of important systems. The use of these FAs to predict bioaccumulation and toxicity for initial and aged nanomaterials is illustrated for the case of silver nanoparticles and Caenorhabditis elegans.
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•Approaches to predict risk directly from nanomaterial (NM) properties are problematic.•We propose functional assays (FAs) to measure nanomaterial behavior in systems.•FAs measure NM processes in prescribed systems; parameterize exposure, hazard models.•FAs can support near-term nanoEHS guidance and sustainable product development.•Surface affinity & dissolution illustrated as FAs to forecast NM fate, effects.
Iron-based nanoparticles have been proposed for an increasing number of biomedical or environmental applications although in vitro toxicity has been observed. The aim of this study was to understand ...the relationship between the redox state of iron-based nanoparticles and their cytotoxicity toward a Gram-negative bacterium, Escherichia coli. While chemically stable nanoparticles (γFe2O3) have no apparent cytotoxicity, nanoparticles containing ferrous and, particularly, zerovalent iron are cytotoxic. The cytotoxic effects appear to be associated principally with an oxidative stress as demonstrated using a mutant strain of E. coli completely devoid of superoxide dismutase activity. This stress can result from the generation of reactive oxygen species with the interplay of oxygen with reduced iron species (FeII and/or Fe0) or from the disturbance of the electronic and/or ionic transport chains due to the strong affinity of the nanoparticles for the cell membrane.
The production of reactive oxygen species (ROS) by aqueous suspensions of fullerenes and nano-TiO2 (Degussa P25) was measured both in ultrapure water and in minimal Davis (MD) microbial growth ...medium. Fullerol (hydroxylated C60) produced singlet oxygen (1O2) in ultrapure water and both 1O2 and superoxide (O2 −•) in MD medium, but no hydroxyl radicals (OH•) were detected in either case. PVP/C60 (C60 encapsulated with poly(N-vinylpyrrolidone)) was more efficient than fullerol in generating singlet oxygen and superoxide. However, two other aggregates of C60, namely THF/nC60 (prepared with tetrahydofuran as transitional solvent) and aqu/nC60 (prepared by vigorous stirring of C60 powder in water), were not photoactive. Nano-TiO2 (also present as aggregates) primarily produced hydroxyl radicals in pure water and superoxide in MD medium. Bacterial (Escherichia coli) toxicity tests suggest that, unlike nano-TiO2 which was exclusively phototoxic, the antibacterial activity of fullerene suspensions was linked to ROS production. Nano-TiO2 may be more efficient for water treatment involving UV or solar energy, to enhance contaminant oxidation and perhaps for disinfection. However, fullerol and PVP/C60 may be useful as water treatment agents targeting specific pollutants or microorganisms that are more sensitive to either superoxide or singlet oxygen.
Chemical ingredients in consumer products are continually changing. To understand our exposure to chemicals and their consequent risk, we need to know their concentrations in products, or chemical ...weight fractions. Unfortunately, manufacturers rarely report comprehensive weight fraction data on product labels. The goal of this study was to evaluate the utility of machine learning strategies for predicting weight fractions when chemical constituent data are limited. A “data-poor” framework was developed and tested using a small dataset on consumer products containing engineered nanomaterials to represent emerging substances. A second, more traditional framework was applied to a “data-rich” product dataset comprised of bulk-scale organic chemicals for comparison purposes. Feature variables included chemical properties, functional use categories (e.g., antimicrobial), product categories (e.g., makeup), product matrix categories, and whether weight fractions were manufacturer-reported or experimentally obtained. Classification into three weight fraction bins was done using a random forest or nonlinear support vector classifier. An ablation study revealed that functional use data improved predictive performance when included alongside chemical property data, suggesting the utility of functional use categories in evaluating the safety and sustainability of emerging chemicals. Models could roughly stratify material-product observations into order of magnitude weight fractions with moderate success; the best of these achieved an average balanced accuracy of 73% on the nanomaterials product data. Framework comparisons also revealed a positive trend in sample size versus average balanced accuracy, suggesting great promise for machine learning approaches with continued investment in chemical data collection.
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•Machine learning models estimate ranges of chemical concentrations in products.•Chemical functional use data can provide insight for exposure-related endpoints.•QSAR-like models with obtainable inputs are applicable to data-poor chemicals.•Nanomaterial case study shows promise for machine learning despite small data.•Frameworks to develop chemical endpoint prediction models are customizable.
Eight types of common airborne particles were used to investigate whether the composition of dust influences its soiling potential on photovoltaic panels. Chosen model particles were roughly ...spherical, 10–30 μm in diameter to minimize the differences in size and shape. While the predicted van der Waals forces were lower than the adhesion forces measured with an atomic force microscope (AFM), the adhesion potential as a function of surface energy did follow the theoretical pattern. The organic and carbon-based materials, namely the pollen grains and spherical graphite, exhibited a significantly larger adhesion force to the glass surface, indicating high attachment efficiency. The developed generalized linear model confirmed that the type of material should be included in soiling models as a variable, as it provides information on the likelihood of particles sticking to and remaining on the surface. The adhesion force between soiled particles and the surface can be estimated based on the local ambient dust composition to predict the short-term fate of the depositing particles and develop cleaning schedules and techniques accordingly. The results also highlight the need to study dust composition to understand long-term soiling, where chemical characteristics and changing environmental conditions may lead to cementation.
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