Showing papers in "Environmental science. Nano in 2015"

Catalytic Properties and Biomedical Applications of Cerium Oxide Nanoparticles

Abstract: Cerium oxide nanoparticles (nanoceria) have shown promise as catalytic antioxidants in the test tube, cell culture models and animal models of disease However given the reactivity that is well established at the surface of these nanoparticles, the biological utilization of nanoceria as a therapeutic still poses many challenges Moreover the form that these particles take in a biological environment, such as the changes that can occur due to a protein corona, are not well established This review aims to summarize the existing literature on biological use of nanoceria, and to raise questions about what further study is needed to apply this interesting catalytic material to biomedical applications These questions include: 1) How does preparation, exposure dose, route and experimental model influence the reported effects of nanoceria in animal studies? 2) What are the considerations to develop nanoceria as a therapeutic agent in regards to these parameters? 3) What biological targets of reactive oxygen species (ROS) and reactive nitrogen species (RNS) are relevant to this targeting, and how do these properties also influence the safety of these nanomaterials?

Toxicity of halloysite clay nanotubes in vivo: a Caenorhabditis elegans study

Abstract: Here we investigated the toxicity of halloysite clay nanotubes in vivo employing a Caenorhabditis elegans nematode as a model organism Using enhanced dark-field microscopy and physiological tests, we found that halloysite is localised exclusively in the alimentary system and does not induce severe toxic effects on nematodes

Plasmonic colorimetric and SERS sensors for environmental analysis

Abstract: The potential for water pollution outbreaks requires the development of rapid, yet simple detection methods for water quality monitoring. Plasmonic nanostructures such as gold (AuNPs) and silver (AgNPs) nanoparticles are compelling candidates for the development of highly sensitive biosensors due to their unique localized surface plasmon resonances (LSPRs). The LSPR of AuNPs and AgNPs lies in the visible and infrared light range and is sensitive to the composition, size, shape, surrounding medium, and aggregation state of these NPs. This plasmonic behavior provides the basis for fabrication of colorimetric sensors for environmental analyses. Furthermore, the LSPR also enhances the electromagnetic field near the NP surface, which provides the basis for surface-enhanced Raman spectroscopy (SERS) based detection. Organic or inorganic pollutants and pathogens can be detected and differentiated based upon the finger-print spectra that arise when they enter SERS-active hot spots. In this tutorial review, we summarize progress made towards environmental analysis based on LSPR-based colorimetric and SERS detection. The problems and challenges that have hindered the development of LSPR-based nanosensors for real-world environmental pollutant monitoring are extensively discussed.

Toxicity of 12 metal-based nanoparticles to algae, bacteria and protozoa

Abstract: The use of metal-based nanoparticles (NPs) is increasing which leads to their release in water bodies via various waste streams, and thus warrants risk assessment. Consistent biological-effect data of NPs for environmentally relevant test species, which are accompanied by thorough characterization of NPs, are scarce but indispensable for understanding the possible risks of NPs. We composed and tested a library of 12 metal-based nanoparticles (Al2O3, Co3O4, CuO, Fe3O4, MgO, Mn3O4, Sb2O3, SiO2, ZnO, TiO2, WO3 and Pd) using the alga Pseudokirchneriella subcapitata, three bacterial species (Vibrio fischeri, Escherichia coli, Staphylococcus aureus) and the protozoa Tetrahymena thermophila. The NPs were characterized for their physico-chemical properties, solubility and abiotic reactive oxygen species (ROS) production. Also, respective soluble salts were analysed for toxic effects. The algal growth inhibition assay has proven to be the most sensitive and yielded EC50 values for 10 NPs ranging from 0.1 to 58 mg l−1. Algal toxicity correlated with abiotic ROS production of NPs, and the majority of the NPs formed agglomerates that entrapped algal cells. Despite the different sensitivities, there was a common trend in the toxicity of the NPs across different species and test formats: CuO and ZnO had the highest toxicity (EC50 values below 1 mg l−1) among all organism groups except for the protozoa. The high toxicity was mostly due to the shedding of toxic concentrations of Zn and Cu ions; for most of the test species, Al2O3, SiO2, WO3 and Sb2O3 were not toxic below 100 mg l−1 and MgO showed no adverse effects below 100 mg l−1 to any test species in any test setting.

Accumulation, speciation and uptake pathway of ZnO nanoparticles in maize

Abstract: Engineered nanomaterials such as ZnO nanoparticles (NPs) will inevitably enter the environment because of the large quantities produced and their widespread application. Plants comprise a fundamental living component of terrestrial ecosystems; thus, understanding the interaction between ENMs and plants is important. In the present study we conducted an integrated study by employing a combination of microscopic and spectroscopic techniques to comparatively investigate the uptake of ZnO NPs and Zn2+ ions by maize in order to further elucidate plant uptake pathways of ZnO NPs. The results demonstrate that the majority of Zn taken up was derived from Zn2+ released from ZnO NPs, and Zn accumulated in the form of Zn phosphate. ZnO NPs were observed mainly in the epidermis, a small fraction of ZnO NPs were present in the cortex and root tip cells, and some further entered the vascular system through the sites of the primary root-lateral root junction. However, no ZnO nanoparticle was observed to translocate to shoots, possibly due to the dissolution and transformation of ZnO NPs inside the plants.

Surface modification of thin film composite forward osmosis membrane by silver-decorated graphene-oxide nanosheets

Abstract: Forward osmosis (FO), as an emerging technology for seawater desalination and wastewater reuse, has been attracting significant interest because of its energy efficiency. However, membrane fouling represents one of the major limitations for this technology, notably for thin film composite (TFC) polyamide (PA) membranes, which are prone to chlorine attack. In this study, silver nanoparticle (AgNPs)-decorated graphene oxide (GO) nanosheets (as an effective biocidal material) were covalently bonded to the PA surface to impart improved hydrophilicity and antibacterial properties to the membrane. AgNPs were synthesized in situ by the wet chemical reduction of silver nitrate onto the surface of GO nanosheets. The formation of the composite was verified by UV-vis spectroscopy, X-ray diffraction, and transmission electron microscopy techniques. The synthesized GO/Ag nanocomposites were then covalently bonded onto the TFC PA membrane surface using cysteamine through an amide forming condensation reaction. ATR-FTIR and XPS results confirmed the covalent bonding of the nanocomposite onto the TFC PA surface. Overall, the GO/Ag nanocomposite functionalized membranes exhibited super-hydrophilic properties (contact angles below 25°) and significant bacterial (E. coli) inactivation (over 95% in static bacterial inactivation tests) without adversely affecting the membrane transport properties.

Progress towards the validation of modeled environmental concentrations of engineered nanomaterials by analytical measurements

Abstract: Environmental exposure modeling has been used extensively in the last years to obtain estimates of environmental concentrations of engineered nanomaterials (ENMs). In this perspective piece, we explore the issues when aiming to validate modeled environmental concentrations and propose options for both modelers and analytical chemists on how to proceed in the future to better compliment one another's efforts. In this context, validation means to determine the degree to which the simulation results from a model are accurate representations of the real world by comparison with analytical data. Therefore, for such a model validation procedure, analytical methods need to be available which provide information in the same subject area. Currently, a major issue with nanometrology is that a multitude of nanomaterials are present in natural systems but only some are ENMs; various other particles of natural origin are abundant in the same systems. The analytical tools available are not yet capable to distinguish the natural from engineered nanomaterials at the low ENM concentrations expected in complex environmental matrices. However, both modeling and analytical studies are able to provide an orthogonal view on nanomaterials: modeling is able to yield estimates of the presence of ENMs in various environmental compartments while analytics can provide physical characterization of ENMs in these systems with hints towards the total nanomaterial concentration. While we need to make strides to improve the two approaches separately, using the resulting data together in a mutually supportive way will advance the field of ENM risk assessment.

Toxicity of engineered metal oxide nanomaterials mediated by nano–bio–eco–interactions: a review and perspective

Abstract: Along with the expanding use of engineered metal oxide nanomaterials (MONMs), there is a growing concern over their unintentional adverse toxicological effects on human health and the environment upon release and exposure. It is inevitable that biota will be exposed to nanomaterials, through intentional administration or inadvertent contact under such circumstances. Therefore, a thorough investigation of the potential nanotoxicity of MONMs at the nano–bio–eco interface is urgently needed. In general, nanomaterials interact with their surrounding environments, biotic and abiotic, immediately upon introduction into the environment. The behavior and fate of MONMs are influenced by the dynamics of the environment. Thus, understanding the interactions at the nano–bio–eco interface is necessary for selecting and designing MONMs with minimum adverse impacts. Despite the limitations of currently available techniques, careful characterization of nanomaterials and the choosing of methodologies that promote further risk assessment promise more reliable and accurate data output. Conventional toxicological analysis techniques lack the power to handle the large datasets generated from in vitro/in vivo observations. This paper provides a comprehensive review of the recent experimental and theoretical studies on the toxicity of MONMs mediated by two-way or three-way interactions. In the Perspectives, we also call for more open collaborations between industry, academia, and research labs to facilitate nanotoxicological studies focused specifically on interactions at the nano–bio–eco interface, leading to safe and effective nanotechnology for commercial, environmental, and medicinal use.

Cellulose nanomaterials: life cycle risk assessment, and environmental health and safety roadmap

Abstract: Cellulose nanomaterials (CNs) derived from wood fibers are renewable materials with wide applicability for use in consumer products as bio-based composite materials and have the potential to replace petroleum-based materials in many existing and novel applications. Because their nanoscale features may impart novel chemical properties and behaviors, it is necessary to address the environmental and safety aspects of CNs to ensure safety in commercial applications, before wide introduction into society. NANO LCRA, a proposed life cycle risk assessment framework, was used for pre-commercial screening of selected applications of CN as a method for systematically identifying and assessing potential risks of CN from occupational, consumer and environmental exposures throughout the product life cycle. The analysis identifies potential exposure scenarios, evaluates toxicity and assesses the adequacy of available data to characterize risk, highlighting data needs and gaps that must be filled to reduce current uncertainty about CN safety. The analysis revealed that occupational inhalation exposure associated with handling CN as a dry powder was the highest priority data gap including the challenge of quantitative measurement for exposure assessment, followed by gaps in knowledge about the toxicity of CN in consumer use products, such as packaging, particularly for food contact. The NANO LCRA findings were then organized into a roadmap for filling key data gaps to allow safety and sustainability assessment that prioritizes data needs according to risk significance to ensure that uncertainty about the CN safety does not interfere with the commercialization of products to market.

Silver nanoparticle toxicity and association with the alga Euglena gracilis

Abstract: The impact of silver nanoparticles (AgNPs) on aquatic algae has largely been studied with model species that possess a rigid cell wall. Here, we explored the interactions of AgNPs with Euglena gracilis, a green alga having no cell wall but a pellicle. The toxicity and silver uptake upon 1–2 h of exposure to various concentrations of AgNO3 and AgNPs, having a mean size of 47 nm measured in the exposure medium, were examined. The photosynthetic yield decreased in a concentration-dependent manner and AgNPs were less toxic than AgNO3 based on the total silver added. The cell morphology was significantly altered by AgNPs and AgNO3. The damaging effects of AgNPs on the photosynthesis and morphology were completely prevented by cysteine, suggesting that the toxicity of AgNPs was mediated by dissolved Ag. Indeed, the maximal quantity of cell-associated silver was higher upon exposure to AgNPs compared to that upon AgNO3 exposure, amounting to 5.1 × 10−4 mol Lcell−1 and 1.4 × 10−4 mol Lcell−1 for AgNPs and AgNO3, respectively. However, the difference was not caused by the cellular uptake of AgNPs, but by the strong sorption of AgNPs onto the pellicle.

Comparative life cycle assessment of silver nanoparticle synthesis routes

Abstract: Silver nanoparticles (AgNPs) can be produced through a variety of synthesis routes with differing mechanisms, inputs, yields, reaction conditions, and resulting size distributions. Recent work has focused on applying green chemistry and sustainable manufacturing principles to nanomaterial synthesis, with the goal of reducing life cycle energy use and environmental impacts. Life cycle assessment (LCA) is used here to analyze and compare the environmental impacts of AgNPs produced through seven different synthesis routes (cradle-to-gate). LCA reveals both direct and indirect or upstream impacts associated with AgNPs. Synthesis routes were chosen to represent current trends in nanoparticle synthesis and include physical, chemical and bio-based methods of production. Results show that, across synthesis routes, impacts associated with the upstream production of bulk silver itself were dominant for nearly every category of environmental impact, contributing to over 90% of life cycle burdens in some cases. Flame spray methods were shown to have the highest impacts while chemical reduction methods were generally preferred when AgNPs were compared on a mass basis. The bio-based chemical reduction route was found to have important tradeoffs in ozone depletion potential and ecotoxicity. Rescaling results by the size-dependent antimicrobial efficacy that reflects the actual function of AgNPs in most products provided a performance-based comparison and changed the rank order of preference in every impact category. Comparative results were also presented in the context of a nanosilver-doped wound dressing, showing that the overall environmental burdens of the product were highly sensitive to the synthesis route by which the AgNPs are produced.

Room temperature seed mediated growth of gold nanoparticles: mechanistic investigations and life cycle assesment

Abstract: In this study, we report the first room temperature seed-mediated synthesis of gold nanoparticles (AuNPs) in the presence of citrate and a gold salt. In contrast to citrate-reduction in boiling water, these mild reaction conditions provide expanded capacity to probe the mechanism of seed-mediated growth following gold salt addition. Moreover, comparative life cycle assessment indicates significant reductions in the environmental impacts for the room temperature synthesis. For this study, highly uniform gold seeds with Z-average diameter of 17.7 ± 0.8 nm and a polydispersity index of 0.03 ± 0.01 were prepared by a pH controlled protocol. We investigated the AuNP growth mechanism via time resolved UV-vis spectroscopy, dynamic light scattering, and transmission electron microscopy. This study indicates that citrate and its oxidation byproduct acetone dicarboxylate serve to bridge and gather Au(III) ions around gold nanoparticle seeds in the initial growth step.

Probabilistic modelling of engineered nanomaterial emissions to the environment: A spatio-temporal approach

Abstract: For the environmental risk assessment of engineered nanomaterials (ENM) knowledge about environmental concentrations is crucial. Soils and sediments are considered sinks for ENM and thus a better understanding of the spatial and temporal variability of concentrations is needed. In this work we use South Australia as a case study for a region with significant biosolids and treated wastewater application on soils, representing a system with almost “closed loops”. The probabilistic material flow modelling approach was extended to include a temporal modelling of ENM production and biosolids handling and transfer onto soils, focusing on nano-TiO2, nano-ZnO, nano-Ag, Carbon Nanotubes(CNT) and fullerenes. The results thus not only incorporate the uncertainty on ENM flows but also the spatial and temporal variability of ENM concentrations between 2005 and 2012. The ENM concentrations in different waste amended soils vary by more than 2 orders of magnitude due to different biosolids and wastewater application rates. Because of the almost complete transformation of nano-ZnO and nano-Ag during wastewater treatment, we also modelled the total flows of Zn and Ag derived from the nanoparticles and compared their modelled concentrations to measured total Ag and Zn concentration in biosolids and soils in South Australia. The modelled Ag concentration derived from nano-Ag is 50-times smaller than measured Ag in soils and 10-times in biosolids. For Zn the respective values are 250 and 7. If in the future the accumulation continues with the same rate as in 2012 it would take about 170 years until a regulatory threshold value of 500 ug Ag per kg of soil would be reached. For Zn, it will take 930 years. The results from this modelling highlight that regional and site-specific conditions need to be considered when assessing the environmental risks of nanomaterials.

Nanotechnology: nature's gift or scientists' brainchild?

Abstract: In the field of environmental nanotechnology, opinions on the novelty of engineered nanomaterials vary; some scientists believe that many engineered nanomaterials are indeed unique, while others are convinced that we are simply fabricating structures already designed in nature. In this article, we present balanced, objective evidence on both sides of the debate. While the idea of novel nanomaterials opens the mind to imagine truly unique structures with architectures unparalleled in nature, the idea that these structures have related analogs in nature has environmental relevance as scientists and engineers aim to design and manufacture more sustainable and environmentally benign nanomaterials.

Biological and environmental media control oxide nanoparticle surface composition: the roles of biological components (proteins and amino acids), inorganic oxyanions and humic acid

Abstract: Current practices of initial nanoparticle characterization with respect to particle size, shape, surface and bulk composition prior to experiments to test, for example, cellular interaction or toxicity, will not accurately describe nanomaterials in a given medium. The use of initial characterization data in subsequent analyses inherently assumes that nanoparticles are static entities. However, nanoparticle characterization, which is crucial in all studies related to their applications and implications, should also include information about the dynamics of the interfacial region between the nanomaterial surface and the surrounding medium. The objective of this tutorial review is to highlight the importance of in situ characterization of metal oxide nanoparticle surfaces in complex media. In particular, several examples of TiO2 (5 nm) and α-Fe2O3 (2 nm) nanoparticles, in different environmental and biological media, are presented so as to show the importance of the milieu to oxide surface composition. The surface composition is shown to be controlled by the adsorption of biological components (proteins and amino acids), inorganic oxyanions (phosphates and carbonates) and environmental ligands (humic acid). The extent of surface adsorption depends on the solution phase composition and the affinity of different components to adsorb to the nanoparticle surface. The examples presented here show that there is a range of possible surface interactions, adsorption energetics and adsorption modes including reversible adsorption, irreversible adsorption and co-adsorption.

Physical, chemical, and in vitro toxicological characterization of nanoparticles in chemical mechanical planarization suspensions used in the semiconductor industry: towards environmental health and safety assessments

Abstract: This tutorial review focuses on aqueous slurries of dispersed engineered nanoparticles (ENPs) used in chemical mechanical planarization (CMP) for polishing wafers during manufacturing of semiconductors. A research consortium was assembled to procure and conduct physical, chemical, and in vitro toxicity characterization of four ENPs used in CMP. Based on input from experts in semiconductor manufacturing, slurries containing fumed silica (f-SiO2), colloidal silica (c-SiO2), ceria (CeO2), and alumina (Al2O3) were selected and subsequently obtained from a commercial CMP vendor to represent realistic ENPs in simplified CMP fluids absent of proprietary stabilizers, oxidants, or other chemical additives that are known to be toxic. ENPs were stable in suspension for months, had highly positive or negative zeta potentials at their slurry working pH, and had mean diameters measured by dynamic light scattering (DLS) of 46 ± 1 nm for c-SiO2, 148 ± 5 nm for f-SiO2, 132 ± 1 nm for CeO2, and 129 ± 2 nm for Al2O3, all of which were larger than the sub 100 nm diameter primary particle sizes measured by electron microscopy. The concentration of ENPs in all four slurries that caused 50% inhibition (IC-50) was greater than 1 mg mL−1 based on in vitro assays using bioluminescence of the bacterium Aliivibrio fischeri and the proliferation, viability, and integrity of human cells (adenocarcinomic human alveolar basal epithelial cell line A549). The general practice in the CMP industry is to dilute the slurry waste stream so actual abrasive concentrations are typically orders of magnitude smaller than 1 mg mL−1, which is lower than IC-50 levels. In contrast to recent reports, we observed similar toxicological characteristics between c-SiO2 and f-SiO2, and the materials exhibited similar X-ray diffraction (XRD) spectra but different morphology observed using electron microscopy. The ENPs and CMP slurries used in this study have been made available to a number of other research groups, and it is the intention of the consortium for this paper to provide a basis for characterizing and understanding human and environmental exposures for this important class of industrial ENPs.

Toxicity of exfoliated-MoS2 and annealed exfoliated-MoS2 towards planktonic cells, biofilms, and mammalian cells in the presence of electron donor

Abstract: We demonstrate for the first time that suspensions of single-layered MoS2 nanosheets can act as photocatalytic antimicrobial materials under visible light in the presence of ethylenediaminetetraacetic acid (EDTA) as an electron donor. The antimicrobial capacity of exfoliated MoS2 (Ex-MoS2) was found to be 5.7 times higher than that of annealed exfoliated MoS2 (Ae-MoS2) against planktonic cells in the presence of 40 ppm EDTA. This difference in the antimicrobial performance was attributed to the 1T-phase of Ex-MoS2, which presents higher electron conductivity than that of Ae-MoS2. This higher electron conductivity of Ex-MoS2 led to increase generation of reactive oxygen species (ROS), as observed by the superoxide anion and hydrogen peroxide production assays under visible light. Additionally, Ex-MoS2 could also inactivate 65% of mature E. coli K12 biofilms without significant cytotoxicity to mammalian fibroblast cells. The suspension of single-layered MoS2 nanosheets opens up new opportunities for the development of advanced functional nanomaterials for biomedical and environmental applications.

Fabrication and characterization of poly(ethylene oxide) templated nickel oxide nanofibers for dye degradation

Abstract: In the present study, one dimensional nickel oxide (NiO) nanofibers were successfully fabricated using an inexpensive and simplistic electrospinning technique to evaluate their efficient applicability as a photocatalyst in dye degradation processes. The synthesis part involves the calcination of electrospun poly(ethylene oxide)/nickel acetate tetrahydrate nanofibers to obtain phase pure cubic NiO nanofibers, which were further characterized using various techniques to determine their physical and chemical properties. Furthermore, the photocatalytic activity of these NiO nanofibers along with their kinetics of degradation was studied with the photodegradation of model dye Congo red (CR) under visible light irradiation. Interestingly, the photocatalytic properties of the NiO nanofibers were found to be better than those of the nanoparticles when compared, and were found to be dependent on the concentrations of the loaded photocatalyst. Besides this, the stability of the nanofibers in aqueous solution was examined along with their reusability.

ZnO nanowire-immobilized paper matrices for visible light-induced antibacterial activity against Escherichia coli

Abstract: Paper matrices showing antibacterial activity were prepared by immobilizing ZnO nanowires (NWs) of diameter ca. 130–500 nm and length up to 2.5 μm on the surface of cellulose fibers by a single-step hydrothermal method. The antibacterial activity of the paper matrices has been investigated versus the visible light exposure time and ZnO contents (2.0 to 18.0 wt%). A complete inhibition of E. coli growth (i.e. 99.99%) was observed with the ZnO-immobilized paper matrices for 6 to 9 h exposure. A possible growth mechanism for the ZnO NW growth on the surface of the cellulose fibers has been proposed. The immobilization of ZnO NWs in paper matrices was characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoluminescence spectroscopy (XPS) and Fourier transform infrared (FTIR) spectroscopy.

Effects of Ultraviolet Light on Silver Nanoparticle Mobility and Dissolution

Abstract: Nanomaterials are subject to various physical, chemical, and biological transformations, necessitating a better understanding of the impact of “aging” processes on nanoparticle fate and transport in engineered and natural porous media. The objective of this study was to evaluate the mobility and dissolution of citrate-coated silver nanoparticles (nAg, 11 nm diameter) in water-saturated sand following ultraviolet (UV) irradiation with UVA (320–400 nm) or UVB (280–320 nm) light. A 3-day UV exposure resulted in up to a 5-fold increase in mean diameter, a 10 to 15 mV increase in zeta potential (i.e., less negative), red shifts in surface plasmon resonance, and up to a 25-fold increase in Ag+ release. The addition of a reactive oxygen species (OH˙) scavenger, tert-butyl alcohol, reduced aggregation and dissolution of nAg exposed to UV light up to 50%, indicating that free radical activity plays a central role in aging. Transport experiments conducted in columns packed with 40–50 mesh Ottawa sand revealed that 25 to 50% more UVA- and UVB-aged nAg were retained compared to freshly prepared (un-aged) nAg. Additionally, 35 to 50% of the applied UV-aged nAg mass eluted as Ag+, compared to less than 1% in experiments with fresh nAg. UVB exposure resulted in up to 4-fold greater Ag+ release and greater nAg retention compared with UVA exposure, consistent with the less negative zeta potential of UVB- compared to UVA-aged nAg (−31 vs. −37 mV). These findings demonstrate that exposure to UV light significantly enhances nAg retention and dissolution in porous media, and thus, oxidative aging of nAg is likely to enhance Ag+ release.

Fate descriptors for engineered nanoparticles: the good, the bad, and the ugly

Abstract: Developments in hazard identification of engineered nanoparticles (ENP) have not been met with proper fate descriptors to calculate travel distances and the bioavailable concentration of ENP Three possible fate descriptors for ENP in soils are compared – batch partitioning coefficients (Kd values), batch retention coefficients (Kr values) and column attachment efficiency – in view of both technical and practical aspects of environmental risk assessments of ENP Kd values are deemed not appropriate fate descriptors for ENP because the equilibrium assumption is not valid The kinetic interpretation of batch studies offered by Kr values bears a link to relevant ENP processes in the environment, but interpretation may be confounded by the conditions of high shear during batch tests complicating direct use in transport or bioavailability calculations Column experiments are, to some extent, also operationally defined and require a more experimentally dedicated approach that does not necessarily lead to a widely carrying physical parameter Future efforts should therefore be investigated in development of tests that strike a better balance between operational simplicity and technical accuracy

Environmental photochemistry of single layered graphene oxide in water

Abstract: Graphene oxide (GO) is a carbonaceous nanomaterial that is a precursor material in the preparation of graphene, and because of its unique properties, it will likely be used in a number of industrial and consumer products in the future. Despite its name, it contains many epoxy, hydroxyl, and carboxyl functional groups on its edges and surface, making it easy to suspend in water. However, how it is transformed or mineralized in natural aquatic environments and its effects on natural processes within these environments remain largely unknown. Therefore, in this study, we report on the photochemical reactivity of single layered GO dispersed in water and irradiated with light within the solar spectrum that reaches the water bodies at the earth's surface (λ ≥ 300 nm). Upon irradiation, the visible color of a 5 mg L−1 GO suspension shifted from pale to dark brown, possibly indicating the repair of some of the π-bond structures; however, Raman spectroscopy indicated an increase in nonaromatic defects. To further examine how oxidation or reduction of the GO surface may occur upon solar light irradiation, we probed the production of various reactive oxygen species (ROS). By monitoring ROS production with selective and highly reactive chemical probes, formation of superoxide anions (O2˙−), but not single oxygen (1O2) or hydroxyl radicals (·OH), was detected, indicating electron transfer from GO to dissolved molecular oxygen (O2). However, further electron transfer through reduction of O2˙− did occur, as hydrogen peroxide (H2O2) was found to accumulate, forming 3 μM H2O2 in a suspension of 5 mg L−1 GO after 4 hours of irradiation.

Towards understanding the antibacterial activity of Ag nanoparticles: electron microscopy in the analysis of the materials-biology interface in the lung

Abstract: Bacterial infections of the pulmonary system are increasing. With almost half of today's infections being caused by strains of bacteria that are resistant to existing conventional antibiotics, there is an urgent need for the development of novel therapeutic platforms. Silver nanoparticles (AgNPs) have been receiving increasing attention due to their unique antibacterial properties, and whilst the biological efficacy of silver is well known, the mechanisms by which AgNPs degrade within cells and how these processes correlate to their bioreactivity are poorly understood. This review summarises the current knowledge on the bactericidal pathways of AgNPs and discusses the challenges to be faced before we are able to develop efficient and safe antibacterial agents for the treatment of bacterial infections in the lung.

Effect of N-acetyl cysteine coated CdS:Mn/ZnS quantum dots on seed germination and seedling growth of snow pea (Pisum sativum L.): imaging and spectroscopic studies

Abstract: Anthropogenic nanomaterials (ANMs), once produced, will inevitably be present in the environment. Depending on their environmental stability and level of toxicity, ANMs raise some concern regarding their potential impact on the surrounding animal, aquatic and plant life. In this study, we demonstrate for the first time the effect of ultra-small size (<5 nm) semiconductor ANMs on the germination and growth of seeds of a snow pea model plant system (Pisum sativum) using a N-acetyl cysteine (NAC) coated core–shell CdS:Mn/ZnS Qdots as a heavy metal ion containing model ANM. We present combined results of fluorescence confocal, atomic force microscopy (AFM) and Raman imaging of quantum dot (Qdot) to track the uptake and localization (translocation) in plant tissue. It was found that Qdots were localized on the surface seed coat, epidermis and intercellular regions. The germination, growth and chlorophyll content of the seedlings were found to be strongly dependent on Qdot dosage and time of seed incubation with Qdots. Interestingly, no acute Cd metal toxicity was observed at Qdot concentration below 40 μg mL−1, and seed germination and growth processes were promoted.

Much ado about α: reframing the debate over appropriate fate descriptors in nanoparticle environmental risk modeling

Abstract: Large-scale fate and transport models have used different approaches to account for engineered nanoparticle (ENP) heteroaggregation and its effects on fate. Praetorius et al. and Cornelis, in recent Perspectives in this journal, favor the use of particle number-based kinetic models and attachment efficiency, α, in place of mass-based approaches relying on partition coefficients, or Kd values, because the former is more theoretically faithful to the particulate nature of ENPs. Here, we provide perspective on these two popular modeling frameworks, particle balance and mass balance, with regards to their ability to capture ENP fate processes at large scales. We show that particle balance using α is not unique in its ability to describe ENP heteroaggregation kinetically, since mathematically equivalent rates can be created for mass balance, and that the ability of particle balance to accurately describe particle behaviors is still severely hindered by evolving scientific understanding of ENP heteroaggregation. Ultimately, we find that models at this scale are relatively insensitive to the particulate nature of ENPs. In the short term, mass-based models that rely on simple heuristics can be more practical, and less error-prone, than particle balance alternatives using α.

Chronic dosing of a simulated pond ecosystem in indoor aquatic mesocosms: fate and transport of CeO2 nanoparticles

Abstract: Indoor aquatic mesocosms were designed to mimic pond ecosystems contaminated by a continuous point-source discharge of cerium oxide nanoparticles (CeO2-NPs). Bare and citrate-coated CeO2-NPs exhibited different chemical and colloidal behaviors in the aquatic mesocosms. Bare CeO2-NPs were chemically stable but quickly homo-aggregated and settled out of the water column. Citrate-coated NPs both homo-and hetero-aggregated but only after the several days required to degrade the citrate coating. While they were more stable as a colloidal suspension, coated CeO2-NPs dissolved faster due to surface complexation with citrate, which resulted in the release of dissolved Ce into the water column. The different distributions over time between water/sediment or dissolved/particulate forms of Ce controlled the availability of Ce to benthic grazers (mollusk Planorbarius corneus) and planktonic filter feeders (copepod Eudiaptomus vulgaris).

Gene expression as an indicator of the molecular response and toxicity in the bacterium Shewanella oneidensis and the water flea Daphnia magna exposed to functionalized gold nanoparticles

Abstract: Nanoparticle (NP) physiochemical properties have been shown to be important determinants of NP interactions with biological systems. Due to both nanomaterial diversity and environmental complexity, a mechanistic understanding of how physiochemical properties affect NP/organism interactions will greatly aid in the accurate assessment and prediction of current and emerging NP-induced environmental impacts. Herein, we investigated key biological apical endpoints, such as viability, growth, and reproduction and the expression of genes associated with related molecular pathways in response to exposure to gold nanoparticles (AuNPs) functionalized with either positively charged ligands, polyallyamine hydrochloride, or negatively charged ligands, mercaptopropionic acid, in two model organisms, the bacterium Shewanella oneidensis MR-1 and the water flea Daphnia magna. By linking changes in molecular pathways to apical endpoints, potential biomarkers for functionalized AuNP impacts were identified in both organisms. Specifically, act was identified as a potential biomarker in D. magna and 16S as a potential biomarker in S. oneidensis. We also revealed that changes in molecular pathways induced by ligand–NP combination were strongly dependent upon the type of ligand on the NP surface, and the effects from their respective ligands alone might predict these effects for the ligand–NP combination, but only in some cases. Lastly, we revealed that it is possible to identify similar pathways provoked upon NP exposure across organisms. This study shows that molecular pathways will help elucidate mechanisms for NP toxicity that are predictive of adverse environmental outcomes.

Research strategy to determine when novel nanohybrids pose unique environmental risks

Abstract: The production and use of increasingly complex hierarchical multifunctional ensembles of nanomaterials introduces emergent properties that will likely lead to uncertainty in the environmental health and safety (EHS) evaluation of nanohybrids (NHs). This perspective proposes principles to identify NHs with novel properties relevant to nano EHS research, and discusses specific challenges for EHS research on these materials. We propose a strategy for focusing nano EHS research efforts on relevant NH systems.

Prediction of nanoparticle transport behavior from physicochemical properties: machine learning provides insights to guide the next generation of transport models

Abstract: In the last 15 years, the development of advection–dispersion particle transport models (PTMs) for the transport of nanoparticles in porous media has focused on improving the fit of model results to experimental data by inclusion of empirical parameters. However, the use of these PTMs has done little to elucidate the complex behavior of nanoparticles in porous media and has failed to provide the mechanistic insights necessary to predictively model nanoparticle transport. The most prominent weakness of current PTMs stems from their inability to consider the influence of physicochemical conditions of the experiments on the transport of nanoparticles in porous media. Qualitative physicochemical influences on particle transport have been well studied and, in some cases, provide plausible explanations for some aspects of nanoparticle transport behavior. However, quantitative models that consider these influences have not yet been developed. With the current work, we intend to support the development of future mechanistic models by relating the physicochemical conditions of the experiments to the experimental outcome using ensemble machine learning (random forest) regression and classification. Regression results demonstrate that the fraction of nanoparticle mass retained over the column length (retained fraction, RF; a measure of nanoparticle transport) can be predicted with an expected mean squared error between 0.025–0.033. Additionally, we find that RF prediction was insensitive to nanomaterial type and that features such as concentration of natural organic matter, ζ potential of nanoparticles and collectors and the ionic strength and pH of the dispersion are strongly associated with the prediction of RF and should be targets for incorporation into mechanistic models. Classification results demonstrate that the shape of the retention profile (RP), such as hyperexponential or linearly decreasing, can be predicted with an expected F1-score between 60–70%. This relatively low performance in the prediction of the RP shape is most likely caused by the limited data on retention profile shapes that are currently available.

A multi-constituent site blocking model for nanoparticle and stabilizing agent transport in porous media

Abstract: A quantitative understanding of the potential influence of engineered and natural stabilizing agents on the transport behavior of engineered nanomaterials will be crucial to assessing their environmental fate. Column transport experiments conducted with CdSe/ZnS quantum dot nanocrystals (QD) stabilized with poly-(acrylic-acid)–octylamine (PAA–OA) yielded retention profiles that exhibited increased retention with distance from the inlet, a trend which could not be reproduced by existing nanoparticle transport models. To address this shortcoming, a new Multi-Constituent Site-Blocking (MCB) model was developed and implemented to simulate coupled transport and retention of nanoparticles and stabilizing agents. Mass balance equations for solution constituents are linked through a Langmuir-type blocking term that accounts for the surface area occupied by each constituent. The model successfully reproduced experimental observations of delayed QD breakthrough and retention profiles. These results support the hypothesis that stabilizing agents present in the nanoparticle suspension inhibit deposition, facilitating enhanced nanoparticle mobility in the columns. Inter-model comparisons and model sensitivity analyses examine the dependence of nanoparticle mobility on the relative concentration and adsorption properties of the stabilizing agents. Modeling results indicate that both synergistic and competitive interactions between nanomaterials and stabilizing agents should be accounted for in order to accurately predict nanoparticle transport behavior in subsurface environments.