In search of the most relevant parameter for quantifying lung inflammatory response to nanoparticle exposure: particle number, surface area, or what?

Assessing the inhaled dose of nanomaterials by nanoparticle tracking analysis (NTA) of exhaled breath condensate (EBC) and its relationship with lung inflammatory biomarkers

The widespread and increasing use of nanomaterials has resulted in a higher likelihood of exposure by inhalation for nanotechnology workers. However, tracking the internal dose of nanoparticles deposited at the airways level, is still challenging. To assess the suitability of particle number concentration determination as biomarker of internal dose, we carried out a cross sectional investigation involving 80 workers handling nanomaterials. External exposure was characterized by portable counters of particles DISCminiTM (Testo, DE), allowing to categorize 51 workers as exposed and 29 as non-exposed (NE) to nanoparticles. Each subject filled in a questionnaire reporting working practices and health status. Exhaled breath condensate was collected and analysed for the number of particles/ml as well as for inflammatory biomarkers. A clear-cut relationship between the number of airborne particles in the nano-size range determined by the particle counters and the particle concentration in exhaled breath condensate (EBC) was apparent. Moreover, inflammatory cytokines (IL-1β, IL-10, and TNF-α) measured in EBC, were significantly higher in the exposed subjects as compared to not exposed. Finally, significant correlations were found between external exposure, the number concentration of particles measured by the nanoparticle tracking analysis (NTA) and inflammatory cytokines. As a whole, the present study, suggests that NTA can be regarded as a reliable tool to assess the inhaled dose of particles and that this dose can effectively elicit inflammatory effects.

The size-dependent in vivo toxicity of amorphous silica nanoparticles: A systematic review

The extensive application of amorphous silica nanoparticles (aSiNPs) in recent years has resulted in unavoidable human exposure in daily life, thus raising widespread concerns regarding the safety of aSiNPs on human health. The particle size is one of the important characteristics of nanomaterials that could influence their toxicity. For the reason that particles with smaller sizes possess larger surface area, which may lead to higher surface activity and biological reactivity. However, due to the complexity of experimental conditions and biological systems, the relationship between the particle size and the toxic effect of aSiNPs remains unclear. Therefore, this systematic review aims to investigate how particle size influences the toxic effect of aSiNPs in vivo and to analyze the relevant experimental factors affecting the size-dependent toxicity of aSiNPs in vivo. We found that 83.8% of 35 papers included in the present review came to the conclusion that smaller-sized aSiNPs exhibited stronger toxicity, though a few papers (6 papers) put forward different opinions. The reasons for smaller aSiNPs manifested greater toxicity were summarized. In addition, certain important experimental factors could influence the size-dependent effects and in vivo toxicity of aSiNPs, such as the synthesis method of aSiNPs, disperse medium of aSiNPs, administration route of aSiNPs, species or strain of experimental animals, sex of experimental animals, aggregation/agglomeration and protein corona of aSiNPs.

Synthesis and Characterization of Rutile TiO2 Nanoparticles for the Toxicological Effect on the H9c2 Cell Line from Rats

The widespread use of titanium dioxide (TiO₂) has raised concerns about potential health risks associated with its cytotoxicity in the cardiovascular system. To evaluate the cytotoxicity of TiO₂ particles, the H9c2 rat cardiomyoblasts were used as a biological model, and their toxicological susceptibility to TiO₂-anatase and TiO₂-rutile particles was studied in vitro. The study examined dose and time exposure responses. The cell viability was evaluated based on metabolic inhibition and membrane integrity loss. The results revealed that both TiO₂-anatase and TiO₂-rutile particles induced similar levels of cytotoxicity at the inhibition concentrations IC₂₅ (1.4-4.4 μg/cm²) and IC₅₀ (7.2-9.3 μg/cm²). However, at more significant concentrations, TiO₂-rutile appeared to be more cytotoxic than TiO₂-anatase at 24 h. The study found that the TiO₂ particles induced apoptosis events, but necrosis was not observed at any of the concentrations of particles used. The study considered the effects of microstructural properties, crystalline phase, and particle size in determining the capability of TiO₂ particles to induce cytotoxicity in H9c2 cardiomyoblasts. The microstress in TiO₂ particles was assessed using powder X-ray diffraction through Williamson-Hall and Warren-Averbach analysis. The analysis estimated the apparent crystallite domain and microstrain of TiO₂-anatase to be 29 nm (ε = 1.03%) and TiO₂-rutile to be 21 nm (ε = 0.53%), respectively. Raman spectroscopy, N₂ adsorption isotherms, and dynamic light scattering were used to identify the presence of pure crystalline phases (>99.9%), comparative surface areas (10 m²/g), and ζ-potential values (-24 mV). The difference in the properties of TiO₂ particles made it difficult to attribute the cytotoxicity solely to one variable.

Monitoring and apportioning sources of indoor air quality using low-cost particulate matter sensors

Air quality is one of the most important factors in public health. While outdoor air quality is widely studied, the indoor environment has been less scrutinised, even though time spent indoors is typically much greater than outdoors. The emergence of low-cost sensors can help assess indoor air quality. This study provides a new methodology, utilizing low-cost sensors and source apportionment techniques, to understand the relative importance of indoor and outdoor air pollution sources upon indoor air quality. The methodology is tested with three sensors placed in different rooms inside an exemplar house (bedroom, kitchen and office) and one outdoors. When the family was present, the bedroom had the highest average concentrations for PM_2.5 and PM₁₀ (3.9 ± 6.8 ug/m³ and 9.6 ± 12.7 μg/m³ respectively), due to the activities undertaken there and the presence of softer furniture and carpeting. The kitchen, while presenting the lowest PM concentrations for both size ranges (2.8 ± 5.9 ug/m³ and 4.2 ± 6.9 μg/m³ respectively), presented the highest PM spikes, especially during cooking times. Increased ventilation in the office resulted in the highest PM₁ concentration (1.6 ± 1.9 μg/m³), highlighting the strong effect of infiltration of outdoor air for the smallest particles. Source apportionment, via positive matrix factorisation (PMF), showed that up to 95 % of the PM₁ was found to be of outdoor sources in all the rooms. This effect was reduced as particle size increased, with outdoor sources contributing >65 % of the PM_2.5, and up to 50 % of the PM₁₀, depending on the room studied. The new approach to elucidate the contributions of different sources to total indoor air pollution exposure, described in this paper, is easily scalable and translatable to different indoor locations.

Physicochemical properties of nanosized biochar regulated by heat treatment temperature dictates algal responses: From the perspective of fatty acid metabolism

Nanosized biochar (NBC) is an important fraction of biochar (BC) as it can exert nano-scale effects on aquatic organisms, attracting increasing research attention. However, effects of different physicochemical properties of NBC on biological responses at the metabolic and gene expression level are not comprehensively understood. Here, biological effects of NBCs pyrolyzed at different heat treatment temperatures (HTTs, 350-700 °C) were evaluated using freshwater algae Chlorella vulgaris, from the perspectives of growth and fatty acid (FA) profile changes. NBC pyrolyzed at 700 °C (N700) induced the greatest algal growth inhibition and oxidative stress than N350 and N500. In addition, NBC exposure to 50 mg/L increased saturated and monounsaturated FAs, along with a decrease in polyunsaturated FAs (PUFAs). Exposure to NBC also significantly influenced the expression of key FA metabolism genes (3fad, sad, kasi and accd), demonstrating the potential role of reactive oxygen species-mediated PUFA reduction accompanied by increased membrane permeability in algal toxicity upon NBC exposure. The observed differences in response to N700 were attributed to its smaller particle size and higher abundance of -COOH. These findings reveal the underlying mechanisms in the algal response to NBCs and provide valuable guidance for the safe design and application of BC materials.

The Effect of Silica Nanoparticles (SiNPs) on Cytotoxicity, Induction of Oxidative Stress and Apoptosis in Breast Cancer Cell Lines

Breast cancer is one of the most common cancers in women. Silica nanoparticles (SiNPs) belong to the group of often-used nanoparticles in biomedical applications. The mechanisms of the cytotoxicity, apoptosis, and oxidative stress induced by the 5-15 nm SiNPs still remain unclear. The aim of the study was to evaluate the anti-cancer effect and mechanism of action of SiNPs in breast cancer cell lines. The breast cancer MDA-MB-231 and ZR-75-1 cell lines were analyzed using MTT assay, flow cytometry, and spectrophotometric methods. In this paper, we presented findings about the cytotoxicity, apoptosis, and oxidative stress in both breast cancer cell lines. We indicated that 5-15 nm SiNPs induced dose-dependent cytotoxicity in MDA-MB-231 and ZR-75-1 cells. Moreover, we demonstrated that the process of apoptosis in the studied cell lines was associated with a decrease in the mitochondrial membrane potential (ΔΨ_m) and an increase in the activity of caspase-9 and caspase-3. Based on the obtained results, 5-15 nm SiNPs are able to induce the mitochondrial apoptosis pathway. Analyzed nanoparticles have also been found to cause an increase in selected oxidative stress parameters in both breast cancer cell lines. The presented study provides an explanation of the possible mechanisms of 5-15 nm SiNPs action in breast cancer cells.

Toxicokinetics, dose-response, and risk assessment of nanomaterials: Methodology, challenges, and future perspectives

The rapid growth of nanomaterial applications has raised safety concerns for human health. A number of studies have been conducted to assess the toxicokinetics, toxicology, dose-response, and risk assessment of different nanomaterials using in vitro and in vivo animal and human models. However, current studies cannot meet the demand for efficient assessment of toxicokinetics, dose-response relationships, or the toxicological risk arising from the rapidly increasing number of newly synthesized nanomaterials. In this article, we review the methods for conducting toxicokinetics, hazard identification, dose-response, exposure, and risk assessment studies of nanomaterials, identify the knowledge gaps, and discuss the challenges remaining. We provide the rationale behind the appropriate design of nanomaterial plasma toxicokinetic and tissue distribution studies, including caveats on the interpretation and correlation of in vitro and in vivo toxicology studies. The potential of using physiologically based pharmacokinetic (PBPK) models to extrapolate toxicokinetic and toxicity findings from in vitro to in vivo and from animals to humans is discussed, and the knowledge gaps of PBPK modeling for nanomaterials are identified. While challenges still exist, there has been progress in the toxicokinetics, hazard identification, and risk assessment of nanomaterials in the past two decades. Recent advancements in the field are highlighted with relevant examples. We also share latest guidelines as well as our perspectives on future studies needed to characterize the toxicokinetics, toxicity, and dose-response relationship in support of nanomaterial risk assessment. This article is categorized under: Toxicology and Regulatory Issues in Nanomedicine > Toxicology of Nanomaterials Toxicology and Regulatory Issues in Nanomedicine > Regulatory and Policy Issues in Nanomedicine.

Changes of diesel particle diameter and surface area distributions by non-thermal plasma

A wide literature has demonstrated that internal combustion engines are the main responsible for the emission of fine particles in urban areas. Within this scope, ultrafine particles within diesel exhausted gas have been widely proven to exert a significantly harmful impact on human health and environment. This scenario has led the research community to turn the attention from particle mass to diameter and surface area. In this paper, non-thermal plasma (NTP) technology was applied to a heavy duty diesel engine. Chemical reactions of diesel particles in plasma zone were analyzed. Additionally, variation in diesel particles' number and surface area distributions, engendered by above reactions, were thoroughly investigated. The results showed that diesel exhausted particles experienced oxidation, aggregation, and crush because of enhanced plasma transports and active species in plasma zone. NTP presents excellent reduction effectiveness of diesel particles covering different sizes. Being more than 50%, the most considerable surface area concentration drop was found in correspondence of 1800 RPM. Differently, the lowest drop of surface area concentration was seen at 1200 RPM. As a result of the NTP actions, surface area concentration distributions were almost the same for diameters being larger than 0.5 μm at different engine modes, except at 900 RPM. This research made a foundation of dropping particle emissions and evaluating the effectiveness of NTP dropping particle harms to human health.

Deployment of a mobile platform to characterize spatial and temporal variation of on-road fine particles in an urban area

Traffic-related air pollutants (TRAPs) pose a serious health hazard for residents and commuters in urban areas. In this study, a real-time mobile monitoring system was deployed in Taipei, a typical East Asian city with an overlap of high population density, traffic, and special structures (e.g., viaducts), to capture the on-road TRAPs at different times of the day. In general, black carbon, ultrafine particles (UFPs), CO concentrations, and lung deposition surface area (LDSA) were positively correlated with traffic flow, and for PM_2.5, a more independent fluctuating concentration was observed. During rush-hour periods, the mean concentrations of UFPs, PM_2.5, and LDSA were 6.12 × 10⁴ ± 3.83 × 10⁴ cm^-3, 23 ± 8 μg/m³, and 2.29 × 10² ± 1.20 × 10² μm²/cm³, respectively. Additionally, the UFP number concentration and LDSA were two times higher along the high-traffic commuting route than along the lower traffic route. Pollutants tended to accumulate at sites near viaducts and high buildings and were significantly influenced by vehicle composition. In this study, the ratio of LDSA to total particle surface area concentration was used as an indicator of the degree of particle irregularity, which was directly related to aging during transport.

Ingested Engineered Nanomaterials Affect the Expression of Mucin Genes-An In Vitro-In Vivo Comparison

The increasing use of engineered nanomaterials (ENM) in food has fueled the development of intestinal in vitro models for toxicity testing. However, ENM effects on intestinal mucus have barely been addressed, although its crucial role for intestinal health is evident. We investigated the effects of ENM on mucin expression and aimed to evaluate the suitability of four in vitro models of increasing complexity compared to a mouse model exposed through feed pellets. We assessed the gene expression of the mucins MUC1, MUC2, MUC5AC, MUC13 and MUC20 and the chemokine interleukin-8 in pre-confluent and confluent HT29-MTX-E12 cells, in stable and inflamed triple cultures of Caco-2, HT29-MTX-E12 and THP-1 cells, and in the ileum of mice following exposure to TiO₂, Ag, CeO₂ or SiO₂. All ENM had shared and specific effects. CeO₂ downregulated MUC1 in confluent E12 cells and in mice. Ag induced downregulation of Muc2 in mice. Overall, the in vivo data were consistent with the findings in the stable triple cultures and the confluent HT29-MTX-E12 cells but not in pre-confluent cells, indicating the higher relevance of advanced models for hazard assessment. The effects on MUC1 and MUC2 suggest that specific ENM may lead to an elevated susceptibility towards intestinal infections and inflammations.

Multiple pathways of alveolar macrophage death contribute to pulmonary inflammation induced by silica nanoparticles

In our previous study, 20 nm-sized amorphous silica nanoparticles (20-SiNPs), but not 50 nm-sized amorphous silica nanoparticles (50-SiNPs), induced pulmonary inflammatory response in rats exposed repeatedly for 14 days (12.5, 25, and 50 μg/time, total six times). In this study, we tried to clarify the causes of different responses induced by both SiNPs using mice (12.5, 25, and 50 μg/lung) and mouse alveolar macrophage cells. When exposed to alveolar macrophage cells for 24 h, both SiNPs decreased cell viability and enhanced ROS generation compared to controls. The 20- and 50-SiNPs also formed giant and autophagosome-like vacuoles in the cytoplasm, respectively. Structural damage of organelles was more pronounced in 20-SiNPs-treated cells than in 50-SiNPs-treated cells, and an increased mitochondrial membrane potential and mitochondrial calcium accumulation were observed only in the 20-SiNPs-treated cells. Additionally, a single intratracheal instillation of both sizes of SiNPs to mice clearly elevated the relative proportion of neutrophils and inhibited differentiation of macrophages and expression of an adhesion molecule. Meanwhile, interestingly, the total number of pulmonary cells and the levels of pro-inflammatory mediators more notably increased in the lungs of mice exposed to 20-SiNPs compared to 50-SiNPs. Given that accumulation of giant vacuoles and dilation of the ER and mitochondria are key indicators of paraptosis, we suggest that 20-SiNPs-induced pulmonary inflammation may be associated with paraptosis of alveolar macrophages.

Impact of Polyethylene Glycol Functionalization of Graphene Oxide on Anticoagulation and Haemolytic Properties of Human Blood

Graphene oxide (GO) is one of the most explored nanomaterials in recent years. It has numerous biomedical applications as a nanomaterial including drug and gene delivery, contrast imaging, cancer treatment, etc. Since most of these applications need intravenous administration of graphene oxide and derivatives, the evaluation of their haemocompatibility is an essential preliminary step for any of the developed GO applications. Plentiful data show that functionalization of graphene oxide nanoparticles with polyethylene glycol (PEG) increases biocompatibility, thus allowing PEGylated GO to elicit less dramatic blood cell responses than their pristine counterparts. Therefore, in this work, we PEGylated graphene oxide nanoparticles and evaluated the effects of their PEGylation on the structure and function of human blood components, especially on the morphology and the haemolytic potential of red blood cells (RBCs). Further, we studied the effect of PEGylation on some blood coagulation factors, including plasma fibrinogen as well as on the activated partial thromboplastin (aPTT), prothrombin time (PT) and platelet aggregation. Our findings provide important information on the mechanisms through which PEGylation increases GO compatibility with human blood cells. These data are crucial for the molecular design and biomedical applications of PEGylated graphene oxide nanomaterials in the future.

Understanding nano-engineered particle-cell interactions: biological insights from mathematical models

Understanding the interactions between nano-engineered particles and cells is necessary for the rational design of particles for therapeutic, diagnostic and imaging purposes. In particular, the informed design of particles relies on the quantification of the relationship between the physicochemical properties of the particles and the rate at which cells interact with, and subsequently internalise, particles. Quantitative models, both mathematical and computational, provide a powerful tool for elucidating this relationship, as well as for understanding the mechanisms governing the intertwined processes of interaction and internalisation. Here we review the different types of mathematical and computational models that have been used to examine particle-cell interactions and particle internalisation. We detail the mathematical methodology for each type of model, the benefits and limitations associated with the different types of models, and highlight the advances in understanding gleaned from the application of these models to experimental observations of particle internalisation. We discuss the recent proposal and ongoing community adoption of standardised experimental reporting, and how this adoption is an important step toward unlocking the full potential of modelling approaches. Finally, we consider future directions in quantitative models of particle-cell interactions and highlight the need for hybrid experimental and theoretical investigations to address hitherto unanswered questions.

Counting Nanoplastics in Environmental Waters by Single Particle Inductively Coupled Plasma Mass Spectroscopy after Cloud-Point Extraction and In Situ Labeling of Gold Nanoparticles

The globally raising concern for nanoplastics (NPs) pollution calls for analytical methods for investigating their occurrence, fates, and effects. Counting NPs with sizes down to 50 nm in real environmental waters remains a great challenge. Herein, we developed a full method from sample pretreatment to quantitative detection for NPs in environmental waters. Various NPs of common plastic types and sizes (50-1200 nm) were successfully labeled by in situ growth of gold nanoparticles and counted by single particle inductively coupled plasma mass spectrometry. Sucrose density gradient centrifugation enables the isolation of gold-labeled NPs from homogeneously nucleated Au nanoparticles, enhancing the particle number detection limit to 4.6 × 10⁸ NPs/L for 269 nm spherical polystyrene NPs. For real environmental water samples, the pretreatment of acid digestion with a mixture of 5 mM HNO₃ and 40 mM HF eliminates the coexisting inorganic nanoparticles, while the following dual cloud-point extraction efficiently isolates NPs from various matrices and thus improves the Au-labeling efficiency. The high spiked recoveries (72.9%-92.8%) of NPs in different waters demonstrated the applicability of this method in different scenarios.

Laminar air flow reduces particle load in TKA-even outside the LAF panel: a prospective, randomized cohort study

PURPOSE

Released particles are a major risk of airborne contamination during surgery. The present prospective study investigated the quantitative and qualitative particle load in the operating room (OR) depending on location, time of surgery and use of laminar air flow (LAF) system.

METHODS

The particle load/m³ was measured during the implantation of 12 total knee arthroplasties (6 × LAF, 6 × Non-LAF) by using the Met One HHPC 6 + device (Beckmann Coulter GmbH, Germany). Measurement was based on the absorption and scattering of (laser) light by particles and was performed at three different time-points [empty OR, setting up, ongoing operation) at 3 fixed measurement points [OR table (central LAF area), anaesthesia tower (marginal LAF area), surgical image amplifier (outside LAF area)].

RESULTS

Independent of time and location, all measurements showed a significantly higher particle load in the Non-LAF group (p < 0.01). With ongoing surgical procedure both groups showed increasing particle load. While there was a major increase of fine particles (size < 1 µm) with advancing activity in the LAF group, the Non-LAF group showed higher particle gain with increasing particle size. The lowest particle load in the LAF group was measured at the operating column, increasing with greater distance from the operating table. The Non-LAF group presented a significantly higher particle load than the LAF group at all locations.

CONCLUSION

The use of a LAF system significantly reduces the particle load and therefore potential bacterial contamination regardless of the time or place of measurement and therefore seems to be a useful tool for infection prevention. As LAF leads to a significant decrease of respirable particles, it appears to be a protective factor for the health of the surgical team regardless of its use in infection prevention.

LEVEL OF EVIDENCE

I.

Size-Dependent Interactions of Lipid-Coated Gold Nanoparticles: Developing a Better Mechanistic Understanding Through Model Cell Membranes and in vivo Toxicity

Introduction

Humans are intentionally exposed to gold nanoparticles (AuNPs) where they are used in variety of biomedical applications as imaging and drug delivery agents as well as diagnostic and therapeutic agents currently in clinic and in a variety of upcoming clinical trials. Consequently, it is critical that we gain a better understanding of how physiochemical properties such as size, shape, and surface chemistry drive cellular uptake and AuNP toxicity in vivo. Understanding and being able to manipulate these physiochemical properties will allow for the production of safer and more efficacious use of AuNPs in biomedical applications.

Methods and Materials

Here, AuNPs of three sizes, 5 nm, 10 nm, and 20 nm, were coated with a lipid bilayer composed of sodium oleate, hydrogenated phosphatidylcholine, and hexanethiol. To understand how the physical features of AuNPs influence uptake through cellular membranes, sum frequency generation (SFG) was utilized to assess the interactions of the AuNPs with a biomimetic lipid monolayer composed of a deuterated phospholipid 1.2-dipalmitoyl-d62-sn-glycero-3-phosphocholine (dDPPC).

Results and Discussion

SFG measurements showed that 5 nm and 10 nm AuNPs are able to phase into the lipid monolayer with very little energetic cost, whereas, the 20 nm AuNPs warped the membrane conforming it to the curvature of hybrid lipid-coated AuNPs. Toxicity of the AuNPs were assessed in vivo to determine how AuNP curvature and uptake influence cell health. In contrast, in vivo toxicity tested in embryonic zebrafish showed rapid toxicity of the 5 nm AuNPs, with significant 24 hpf mortality occurring at concentrations ≥20 mg/L, whereas the 10 nm and 20 nm AuNPs showed no significant mortality throughout the five-day experiment.

Conclusion

By combining information from membrane models using SFG spectroscopy with in vivo toxicity studies, a better mechanistic understanding of how nanoparticles (NPs) interact with membranes is developed to understand how the physiochemical features of AuNPs drive nanoparticle-membrane interactions, cellular uptake, and toxicity.

Investigation of the Dynamism of Nanosized SOA Particle Formation in Indoor Air by a Scanning Mobility Particle Sizer and Proton-Transfer-Reaction Mass Spectrometry

Terpenes are VOCs of particular importance, since they are emitted from a wide range of indoor sources and are considered to be precursors of Secondary Organic Aerosol (SOA) formation. It has been proven that SOA particles, especially nanosized ones, pose a threat to human health. In this research, experiments with the application of an environmental chamber and real-time measurement techniques were carried out to investigate in a complimentary way the formation of monoterpene oxidation products and nanosized SOA particles initiated by monoterpene ozonolysis. Proton-Transfer-Reaction Mass Spectrometry with a Time-Of-Flight analyzer (PTR-TOF-MS) and a Scanning Mobility Particle Sizer (SMPS) were applied to determine in real time the dynamism of the formation of the corresponding terpene ozonolysis products and submicron SOA particles. Results proved that firstly, oxidation products were formed, and then, they underwent nucleation and condensation, forming particles whose diameters grew with time. The oxidation products formed were different depending on the type of terpenes applied. The comparison of the results obtained during the experiments with gaseous standard mixtures and real samples commonly present and used in indoor air revealed that the diversified chemical composition of the emission source had implications for both the particle formation initiated by the oxidation of essential oil components and the chemical reactions occurring via the oxidation process. With the instrumentation utilized, the concentration changes at the level of a few ppbv could be monitored.

Nanoparticle exposure and hazard in the ceramic industry: an overview of potential sources, toxicity and health effects

The ceramic industry is an industrial sector of great impact in the global economy that has been benefiting from advances in materials and processing technologies. Ceramic manufacturing has a strong potential for airborne particle formation and emission, namely of ultrafine particles (UFP) and nanoparticles (NP), meaning that workers of those industries are at risk of potential exposure to these particles. At present, little is known on the impact of engineered nanoparticles (ENP) on the environment and human health and no established Occupational Exposure Limits (OEL) or specific regulations to airborne nanoparticles (ANP) exposure exist raising concerns about the possible consequences of such exposure. In this paper, we provide an overview of the current knowledge on occupational exposure to NP in the ceramic industry and their impact on human health. Possible sources and exposure scenarios, a summary of the existing methods for evaluation and monitoring of ANP in the workplace environment and proposed Nano Reference Values (NRV) for different classes of NP are presented. Case studies on occupational exposure to ANP generated at different stages of the ceramic manufacturing process are described. Finally, the toxicological potential of intentional and unintentional ANP that have been identified in the ceramic industry workplace environment is discussed based on the existing evidence from in vitro and in vivo inhalation toxicity studies.

Moving beyond Fine Particle Mass: High-Spatial Resolution Exposure to Source-Resolved Atmospheric Particle Number and Chemical Mixing State

BACKGROUND

Most epidemiological studies address health effects of atmospheric particulate matter (PM) using mass-based measurements as exposure surrogates. However, this approach ignores many critical physiochemical properties of individual atmospheric particles. These properties control the deposition of particles in the human lung and likely their toxicity; in addition, they likely have larger spatial variability than PM mass.

OBJECTIVES

This study was designed to quantify the spatial variability in number, size, source, and chemical mixing state of individual particles in a populous urban area. We quantified the population exposure to these detailed particle properties and compared them to mass-based exposures.

METHODS

We performed mobile sampling using an advanced single-particle mass spectrometer to measure the spatial variability of number concentration of source-resolved 50-1,000 nm particles and particle mixing state in Pittsburgh, Pennsylvania. We built land-use regression (LUR) models to estimate their spatial patterns and coupled them with demographic data to estimate population exposure.

RESULTS

Particle number concentration had a much larger spatial variability than mass concentration within the city. Freshly emitted particles from traffic and cooking drive the variability in particle number, but mass concentrations are dominated by aged background particles composed of secondary materials. In addition, people exposed to elevated number concentrations of atmospheric particles are also exposed to more externally mixed particles.

CONCLUSIONS

Our advanced measurement technique provides a new exposure picture that resolves the large intra-city spatial heterogeneity in traffic and cooking particle number concentrations in the populous urban area. Our results provide a complementary and more detailed perspective compared with bulk measurements of composition. In addition, given the influence of particle mixing state on properties such as particle deposition in the lung, the large spatial gradients of chemical mixing state may significantly influence the health effects of fine PM. https://doi.org/10.1289/EHP5311.

Different metrics (number, surface area, and volume concentration) of urban particles with varying sizes in relation to fractional exhaled nitric oxide (FeNO)

Background

There have been increasing concerns on potential health effects of ultrafine particles (UFP); but little is known as to what are the most biologically relevant metrics for these particles that make up very little mass concentration. We examined a range of particle metrics (number, surface area, active surface area, and volume concentration) in relation to fractional exhaled nitric oxide (FeNO), a well-established biomarker of pulmonary inflammation.

Methods

We conducted a panel study in 17 non-asthmatic children who attended schools and resided near a monitoring site at which particles in the size range of 3-800 nm were measured using a TDMPS and particles in the size range of 0.5 to 10 µm were measured using an APS. Particles were classified by size into the nucleation, Aitken, accumulation, or coarse mode, respectively, for calculating mode-specific number, surface area, active surface area, and volume concentrations. Each participating child was measured for FeNO daily for 30 days. We used linear mixed-effects models to assess the associations between various particle metrics and FeNO.

Results

In terms of number concentration, ambient particles in the Aitken mode and in the accumulation mode were significantly and positively associated with FeNO; but particles in the nucleation mode were significantly and negatively associated with FeNO. Moreover, UFP as a lump sum of both nucleation-mode and Aikten-mode particles did not show a significant association with FeNO. In terms of surface area concentration, ambient particles only in the accumulation mode were significantly and positively associated with FeNO. In terms of volume concentration, ambient particles in both the accumulation mode and the coarse mode were significantly and positively associated with FeNO. Analyses of the relationships between FeNO and metrics for particles deposited in the respiratory tract generated consistent findings, showing a negative association for the number concentration of deposited particles (driven by nucleation-mode particles), a positive association for the surface area concentration of deposited particles (driven by accumulation-mode particles), and a positive association for the volume concentration of deposited particles (driven by accumulation-mode and coarse-mode particles).

Conclusions

Particles contributing largely to the surface area concentration and/or the volume concentration of ambient particles or particles deposited in the respiratory tract had a significant positive association with pulmonary inflammation. Nucleation-mode particles, that have large number concentrations but contribute little to the surface area or volume concentration of ambient or deposited particles, had a significant negative association with FeNO. This may indicate a different biological process or may simply be due to the negative and strong correlation between nucleation-mode and accumulation-mode particles. Given that particles in different modes may have different biological actions, measuring UFP as a whole may not necessarily be useful from a biological effect standpoint.

Assessing the bioactivity of crystalline silica in heated high-temperature insulation wools

High-Temperature Insulation Wools (HTIW), such as alumino silicate wools (Refractory Ceramic Fibers) and Alkaline Earth Silicate wools, are used in high-temperature industries for thermal insulation. These materials have an amorphous glass-like structure. In some applications, exposure to high temperatures causes devitrification resulting in the formation of crystalline species including crystalline silica. The formation of this potentially carcinogenic material raises safety concerns regarding after-use handling and disposal. This study aims to determine whether cristobalite formed in HTIW is bioactive in vitro. Mouse macrophage (J774A.1) and human alveolar epithelial (A549) cell lines were exposed to pristine HTIW of different compositions, and corresponding heat-treated samples. Cell death, cytokine release, and reactive oxygen species (ROS) formation were assessed in both cell types. Cell responses to aluminum lactate-coated fibers were assessed to determine if responses were caused by crystalline silica. DQ12 α-quartz was used as positive control, and TiO₂ as negative control. HTIW did not induce cell death or intracellular ROS, and their ability to induce pro-inflammatory mediator release was low. In contrast, DQ12 induced cytotoxicity, a strong pro-inflammatory response and ROS generation. The modest pro-inflammatory mediator responses of HTIW did not always coincide with the formation of cristobalite in heated fibers; therefore, we cannot confirm that devitrification of HTIW results in bioactive cristobalite in vitro. In conclusion, the biological responses to HTIW observed were not attributable to a single physicochemical characteristic; instead, a combination of physicochemical characteristics (cristobalite content, fiber chemistry, dimensions and material solubility) appear to contribute to induction of cellular responses.

Effects of silica nanoparticles on endolysosome function in primary cultured neurons 1

Silica nanoparticles (SiNPs) have been used as vehicles for drug delivery, molecular detection, and cellular manipulations in nanoneuromedicine. SiNPs may cause adverse effects in the brain including neurotoxicity, neuroinflammation, neurodegeneration, and enhancing levels of amyloid beta (Aβ) protein-all pathological hallmarks of Alzheimer's disease. Therefore, the extent to which SiNPs influence Aβ generation and the underlying mechanisms by which this occurs deserve investigation. Our studies were focused on the effects of SiNPs on endolysosomes which uptake, traffic, and mediate the actions of SiNPs. These organelles are also where amyloidogenesis largely originates. We found that SiNPs, in primary cultured hippocampal neurons, accumulated in endolysosomes and caused a rapid and persistent deacidification of endolysosomes. SiNPs significantly reduced endolysosome calcium stores as indicated by a significant reduction in the ability of the lysosomotropic agent glycyl-l-phenylalanine 2-naphthylamide (GPN) to release calcium from endolysosomes. SiNPs increased Aβ_1-40 secretion, whereas 2 agents that acidified endolysosomes, ML-SA1 and CGS21680, blocked SiNP-induced deacidification and increased generation of Aβ_1-40. Our findings suggest that SiNP-induced deacidification of and calcium release from endolysosomes might be mechanistically linked to increased amyloidogenesis. The use of SiNPs might not be the best nanomaterial for therapeutic strategies against Alzheimer's disease and other neurological disorders linked to endolysosome dysfunction.

Review of measurement techniques and methods for assessing personal exposure to airborne nanomaterials in workplaces

Exposure to airborne agents needs to be assessed in the personal breathing zone by the use of personal measurement equipment. Specific measurement devices for assessing personal exposure to airborne nanomaterials have only become available in the recent years. They can be differentiated into direct-reading personal monitors and personal samplers that collect the airborne nanomaterials for subsequent analyses. This article presents a review of the available personal monitors and samplers and summarizes the available literature regarding their accuracy, comparability and field applicability. Due to the novelty of the instruments, the number of published studies is still relatively low. Where applicable, literature data is therefore complemented with published and unpublished results from the recently finished nanoIndEx project. The presented data show that the samplers and monitors are robust and ready for field use with sufficient accuracy and comparability. However, several limitations apply, e.g. regarding the particle size range of the personal monitors and their in general lower accuracy and comparability compared with their stationary counterparts. The decision whether a personal monitor or a personal sampler shall be preferred depends strongly on the question to tackle. In many cases, a combination of a personal monitor and a personal sampler may be the best choice to obtain conclusive results.

Evidence of size-dependent effect of silica micro- and nano-particles on basal and specialized monocyte functions

Aim: To analyze the effect of silica particles on monocyte/macrophage functions. Materials & methods: Silica micro- and nanoparticles were obtained by the Stöber method. Their effect on monocyte/macrophage proliferation, activation, membrane integrity and metabolic activity were determined. Results: Silica particles inhibit cell proliferation while 10 nm nanoparticles (NPs) did not affect it. Similarly, silica particles induced strong cell activation. However, 10 nm NPs do not alter IL-12 or nitrite levels. Furthermore, bigger NPs and microparticles increase cell membrane damage and reduce the number of living cells but smallest NPs (10 and 240 nm) did not. Conclusion: Cell activation properties of silica particles could be useful tools for immune stimulation therapy, while 10 nm NPs would be suitable for molecule transportation.

A Novel Experimental and Modelling Strategy for Nanoparticle Toxicity Testing Enabling the Use of Small Quantities

Metallic nanoparticles (NPs) differ from other metal forms with respect to their large surface to volume ratio and subsequent inherent reactivity. Each new modification to a nanoparticle alters the surface to volume ratio, fate and subsequently the toxicity of the particle. Newly-engineered NPs are commonly available only in low quantities whereas, in general, rather large amounts are needed for fate characterizations and effect studies. This challenge is especially relevant for those NPs that have low inherent toxicity combined with low bioavailability. Therefore, within our study, we developed new testing strategies that enable working with low quantities of NPs. The experimental testing method was tailor-made for NPs, whereas we also developed translational models based on different dose-metrics allowing to determine dose-response predictions for NPs. Both the experimental method and the predictive models were verified on the basis of experimental effect data collected using zebrafish embryos exposed to metallic NPs in a range of different chemical compositions and shapes. It was found that the variance in the effect data in the dose-response predictions was best explained by the minimal diameter of the NPs, whereas the data confirmed that the predictive model is widely applicable to soluble metallic NPs. The experimental and model approach developed in our study support the development of (eco)toxicity assays tailored to nano-specific features.

The Effects of Silica Nanoparticles on Apoptosis and Autophagy of Glioblastoma Cell Lines

Silica nanoparticles (SiNPs) are one of the most commonly used nanomaterials in various medical applications. However, possible mechanisms of the toxicity caused by SiNPs remain unclear. The study presented here provides novel information on molecular and cellular effects of SiNPs in glioblastoma LBC3 and LN-18 cells. It has been demonstrated that SiNPs of 7 nm, 5–15 nm and 10–20 nm induce time- and dose-dependent cytotoxicity in LBC3 and LN-18 cell lines. In contrast to glioblastoma cells, we observed only weak reduction in viability of normal skin fibroblasts treated with SiNPs. Furthermore, in LBC3 cells treated with 5–15 nm SiNPs we noticed induction of apoptosis and necrosis, while in LN-18 cells only necrosis. The 5–15 nm SiNPs were also found to cause oxidative stress, a loss in mitochondrial membrane potential, and changes in the ultrastructure of the mitochondria in LBC3 cells. Quantitative real-time PCR results showed that in LBC3 cells the mRNA levels of pro-apoptotic genes Bim, Bax, Puma, and Noxa were significantly upregulated. An increase in activity of caspase-9 in these cells was also observed. Moreover, the activation of SiNP-induced autophagy was demonstrated in LBC3 cells as shown by an increase in LC3-II/LC3-I ratio, the upregulation of Atg5 gene and an increase in AVOs-positive cells. In conclusion, this research provides novel information concerning molecular mechanisms of apoptosis and autophagy in LBC3 cells.

Is physical activity a modifier of the association between air pollution and arterial stiffness in older adults: The SAPALDIA cohort study

INTRODUCTION AND OBJECTIVES

Air pollution and insufficient physical activity have been associated with inflammation and oxidative stress, molecular mechanisms linked to arterial stiffness and cardiovascular disease. There are no studies on how physical activity modifies the association between air pollution and arterial stiffness. We examined whether the adverse cardiovascular effects of air pollution were modified by individual physical activity levels in 2823 adults aged 50-81 years from the well-characterized Swiss Cohort Study on Air Pollution and Lung and Heart Diseases (SAPALDIA).

METHODS

We assessed arterial stiffness as the brachial-ankle pulse wave velocity (baPWV [m/s]) with an oscillometric device. We administered a self-reported physical activity questionnaire to classify each subject's physical activity level. Air pollution exposure was estimated by the annual average individual home outdoor PM₁₀ and PM_2.5 (particulate matter <10μm and <2.5μm in diameter, respectively) and NO₂ (nitrogen dioxide) exposure estimated for the year preceding the survey. Exposure estimates for ultrafine particles calculated as particle number concentration (PNC) and lung deposited surface area (LDSA) were available for a subsample (N=1353). We used mixed effects logistic regression models to regress increased arterial stiffness (baPWV≥14.4m/s) on air pollution exposure and physical activity while adjusting for relevant confounders.

RESULTS

We found evidence that the association of air pollution exposure with baPWV was different between inactive and active participants. The probability of having increased baPWV was significantly higher with higher PM₁₀, PM_2.5, NO₂, PNC and LDSA exposure in inactive, but not in physically active participants. We found some evidence of an interaction between physical activity and ambient air pollution exposure for PM₁₀, PM_2.5 and NO₂ (p_interaction=0.06, 0.09, and 0.04, respectively), but not PNC and LDSA (p_interaction=0.32 and 0.35).

CONCLUSIONS

Our study provides some indication that physical activity may protect against the adverse vascular effects of air pollution in low pollution settings. Additional research in large prospective cohorts is needed to assess whether the observed effect modification translates to high pollution settings in mega-cities of middle and low-income countries.

Comparison of distribution and toxicity of different types of zinc-based nanoparticles

Zinc-based nanoparticles (Zn-NPs), mainly zinc oxide (ZnO) NPs, have promising application in a wide area, but their potential harmful effects on environment and human health have been continuously raised together with their high dissolution rate. In this study, we coated the surface of ZnO NPs with phosphate (ZnP NPs) and sulfide (ZnS NPs) which have very low solubility in water, administered orally (0.5 and 1 mg/kg) to mice for 28 days, and then compared their biodistribution and toxicity. As expected, ZnO NPs were rapidly ionized in an artificial gastric fluid. On the other hand, ZnO NPs were more particlized in an artificial intestinal fluid than ZnP and ZnS NPs. After repeated dosing, all three types of Zn-NPs the most distributed in the spleen and thymus and altered the level of redox reaction-related metal ions in the tissues. We also found that three types of Zn-NPs clearly disturb tissue ion homeostasis and influence immune regulation function. However, there were no remarkable difference in distribution and toxicity following repeated exposure of three types of Zn-NPs, although Na+ and K+ level in the spleen and thymus were notably higher in mice exposed to ZnO NPs compared to ZnP and ZnS NPs. Taken together, we suggest that all three types of Zn-NPs may influence human health by disrupting homeostasis of trace elements and ions in the tissues. In addition, the surface transformation of ZnO NPs with phosphate and sulfide may not attenuate toxicity due to the higher particlization rate of ZnO NPs in the intestine, at least in part. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1363-1374, 2017.

Particulate Matter and Subclinical Atherosclerosis: Associations between Different Particle Sizes and Sources with Carotid Intima-Media Thickness in the SAPALDIA Study

BACKGROUND

Subclinical atherosclerosis has been associated with long-term exposure to particulate matter (PM), but the relevance of particle size and sources of exposure remains unclear.

OBJECTIVES

We investigated the association of long-term exposure to PM10 (≤ 10 μm), PM2.5 (≤ 2.5 μm: total mass, vehicular, and crustal sources), and ultrafine particles [UFP < 0.1 μm: particle number concentration (PNC) and lung-deposited surface area (LDSA)] with carotid intima-media thickness (CIMT).

METHODS

We used data from 1,503 participants ≥ 50 years old who participated in the third examination of the Swiss SAPALDIA cohort. Exposures were obtained from dispersion models and land-use regression models. Covariate information, including previous cardiovascular risk factors, was obtained from the second and third SAPALDIA examinations.

RESULTS

The adjusted percent difference in CIMT associated with an exposure contrast between the 10th and 90th percentile was 1.58% (95% CI: -0.30, 3.47%) for PM10, 2.10% (95% CI: 0.04, 4.16%) for PM2.5, 1.67% (95% CI: -0.13, 3.48%) for the vehicular source of PM2.5, -0.58% (95% CI: -3.95, 2.79%) for the crustal source of PM2.5, 2.06% (95% CI: 0.03, 4.10%) for PNC, and 2.32% (95% CI: 0.23, 4.40%) for LDSA. Stronger associations were observed among diabetics, subjects with low-educational level, and those at higher cardiovascular risk.

CONCLUSIONS

CIMT was associated with exposure to PM10, PM2.5, and UFP. The PM2.5 source-specific analysis showed a positive association for the vehicular source but not for the crustal source. Although the effects of PNC and LDSA were similar in magnitude, two-pollutant and residual-based models suggested that LDSA may be a better marker for the health relevance of UFP. Citation: Aguilera I, Dratva J, Caviezel S, Burdet L, de Groot E, Ducret-Stich RE, Eeftens M, Keidel D, Meier R, Perez L, Rothe T, Schaffner E, Schmit-Trucksäss A, Tsai MY, Schindler C, Künzli N, Probst-Hensch N. 2016. Particulate matter and subclinical atherosclerosis: associations between different particle sizes and sources with carotid intima-media thickness in the SAPALDIA study. Environ Health Perspect 124:1700-1706; http://dx.doi.org/10.1289/EHP161.

Comparison of Real Time Nanoparticle Monitoring Instruments in the Workplaces

Background

Relationships among portable scanning mobility particle sizer (P-SMPS), condensation particle counter (CPC), and surface area monitor (SAM), which are different metric measurement devices, were investigated, and two widely used research grade (RG)-SMPSs were compared to harmonize the measurement protocols.

Methods

Pearson correlation analysis was performed to compare the relation between P-SMPS, CPC, and SAM and two common RG-SMPS.

Results

For laboratory and engineered nanoparticle (ENP) workplaces, correlation among devices showed good relationships. Correlation among devices was fair in unintended nanoparticle (UNP)-emitting workplaces. This is partly explained by the fact that shape of particles was not spherical, although calibration of sampling instruments was performed using spherical particles and the concentration was very high at the UNP workplaces to allow them to aggregate more easily. Chain-like particles were found by scanning electron microscope in UNP workplaces. The CPC or SAM could be used as an alternative instrument instead of SMPS at the ENP-handling workplaces. At the UNP workplaces, where concentration is high, real-time instruments should be used with caution. There are significant differences between the two SMPSs tested. TSI SMPS showed about 20% higher concentration than the Grimm SMPS in all workplaces.

Conclusions

For nanoparticle measurement, CPC and SAM might be useful to find source of emission at laboratory and ENP workplaces instead of P-SMPS in the first stage. An SMPS is required to measure with high accuracy. Caution is necessary when comparing data from different nanoparticle measurement devices and RG-SMPSs.

Mass or total surface area with aerosol size distribution as exposure metrics for inflammatory, cytotoxic and oxidative lung responses in rats exposed to titanium dioxide nanoparticles

There is currently no consensus on the best exposure metric(s) for expressing nanoparticle (NP) dose. Although surface area has been extensively studied for inflammatory responses, it has not been as thoroughly validated for cytotoxicity or oxidative stress effects. Since inhaled NPs deposit and interact with lung cells based on agglomerate size, we hypothesize that mass concentration combined with aerosol size distribution is suitable for NP risk assessment. The objective of this study was to evaluate different exposure metrics for inhaled 5 nm titanium dioxide aerosols composed of small (SA < 100 nm) or large (LA > 100 nm) agglomerates at 2, 7, and 20 mg/m3 on rat lung inflammatory, cytotoxicity, and oxidative stress responses. We found a significant positive correlation ( r = 0.98, p < 0.01) with the inflammatory reaction, measured by the number of neutrophils and the mass concentration when considering all six (SA + LA) aerosols. This correlation was similar ( r = 0.87) for total surface area. Regarding cytotoxicity and oxidative stress responses, measured by lactate dehydrogenase and 8-isoprostane, respectively, and mass or total surface area as an exposure metric, we observed significant positive correlations only with SA aerosols for both the mass concentration and size distribution ( r > 0.91, p < 0.01), as well as for the total surface area ( r > 0.97, p < 0.01). These data show that mass or total surface area concentrations alone are insufficient to adequately predict oxidant and cytotoxic pulmonary effects. Overall, our study indicates that considering NP size distribution along with mass or total surface area concentrations contributes to a more mechanistic discrimination of pulmonary responses to NP exposure.

Diesel exhaust exposures in port workers

Exposure to diesel engine exhaust has been linked to increased cancer risk and cardiopulmonary diseases. Diesel exhaust is a complex mixture of chemical substances, including a particulate fraction mainly composed of ultrafine particles, resulting from the incomplete combustion of fuel. Diesel trucks are known to be an important source of diesel-related air pollution, and areas with heavy truck traffic are associated with higher air pollution levels and increased public health problems. Several indicators have been proposed as surrogates for estimating exposures to diesel exhaust but very few studies have focused specifically on monitoring the ultrafine fraction through the measurement of particle number concentrations. The aim of this study is to assess occupational exposures of gate controllers at the port of Montreal, Canada, to diesel engine emissions from container trucks by measuring several surrogates through a multimetric approach which includes the assessment of both mass and number concentrations and the use of direct reading devices. A 10-day measurement campaign was carried out at two terminal checkpoints at the port of Montreal. Respirable elemental and organic carbon, PM1, PM2.5, PMresp (PM4), PM10, PMtot (inhalable fraction), particle number concentrations, particle size distributions, and gas concentrations (NO2, NO, CO) were monitored. Gate controllers were exposed to concentrations of contaminants associated with diesel engine exhaust (elemental carbon GM = 1.6 µg/m(3); GSD = 1.6) well below recommended occupational exposure limits. Average daily particle number concentrations ranged from 16,544-67,314 particles/cm³ (GM = 32,710 particles/cm³; GSD = 1.6). Significant Pearson correlation coefficients were found between daily elemental carbon, PM fractions and particle number concentrations, as well as between total carbon, PM fractions and particle number concentrations. Significant correlation coefficients were found between particle number concentrations and the number of trucks and wind speed (R(2) = 0.432; p < 0.01). The presence of trucks with cooling systems and older trucks with older exhaust systems was associated with peak concentrations on the direct reading instruments. The results highlight the relevance of direct reading instruments in helping to identify sources of exposure and suggest that monitoring particle number concentrations improves understanding of workers' exposures to diesel exhaust. This study, by quantifying workers' exposure levels through a multimetric approach, contributes to the further understanding of occupational exposures to diesel engine exhaust.

Development of land use regression models for nitrogen dioxide, ultrafine particles, lung deposited surface area, and four other markers of particulate matter pollution in the Swiss SAPALDIA regions

BACKGROUND

Land Use Regression (LUR) is a popular method to explain and predict spatial contrasts in air pollution concentrations, but LUR models for ultrafine particles, such as particle number concentration (PNC) are especially scarce. Moreover, no models have been previously presented for the lung deposited surface area (LDSA) of ultrafine particles. The additional value of ultrafine particle metrics has not been well investigated due to lack of exposure measurements and models.

METHODS

Air pollution measurements were performed in 2011 and 2012 in the eight areas of the Swiss SAPALDIA study at up to 40 sites per area for NO2 and at 20 sites in four areas for markers of particulate air pollution. We developed multi-area LUR models for biannual average concentrations of PM2.5, PM2.5 absorbance, PM10, PMcoarse, PNC and LDSA, as well as alpine, non-alpine and study area specific models for NO2, using predictor variables which were available at a national level. Models were validated using leave-one-out cross-validation, as well as independent external validation with routine monitoring data.

RESULTS

Model explained variance (R(2)) was moderate for the various PM mass fractions PM2.5 (0.57), PM10 (0.63) and PMcoarse (0.45), and was high for PM2.5 absorbance (0.81), PNC (0.87) and LDSA (0.91). Study-area specific LUR models for NO2 (R(2) range 0.52-0.89) outperformed combined-area alpine (R (2)  = 0.53) and non-alpine (R (2)  = 0.65) models in terms of both cross-validation and independent external validation, and were better able to account for between-area variability. Predictor variables related to traffic and national dispersion model estimates were important predictors.

CONCLUSIONS

LUR models for all pollutants captured spatial variability of long-term average concentrations, performed adequately in validation, and could be successfully applied to the SAPALDIA cohort. Dispersion model predictions or area indicators served well to capture the between area variance. For NO2, applying study-area specific models was preferable over applying combined-area alpine/non-alpine models. Correlations between pollutants were higher in the model predictions than in the measurements, so it will remain challenging to disentangle their health effects.

Disturbance of ion environment and immune regulation following biodistribution of magnetic iron oxide nanoparticles injected intravenously

Although it is expected that accumulation of metal oxide nanoparticles that can induce redox reaction in the biological system may influence ion homeostasis and immune regulation through generation of free radicals, the relationship is still unclear. In this study, mice received magnetic iron oxide nanoparticles (M-FeNPs, 2 and 4 mg/kg) a single via the tail vein, and their distribution in tissues was investigated over time (1, 4, and 13 weeks). In addition, we evaluated the effects on homeostasis of redox reaction-related elements, the ion environment and immune regulation. The iron level in tissues reached at the maximum on 4 weeks after injection and M-FeNPs the most distributed in the spleen at 13 weeks. Additionally, levels of redox reaction-related elements in tissues were notably altered since 1 week post-injection. While levels of K(+) and Na(+) in tissue tended to decrease with time, Ca(2+) levels reached to the maximum at 4 weeks post-injection. On 13 weeks post-injection, the increased percentages of neutrophils and eosinophils, the enhanced release of LDH, and the elevated secretion of IL-8 and IL-6 were clearly observed in the blood of M-FeNP-treated mice compared to the control. While expression of antigen presentation related-proteins and the maturation of dendritic cells were markedly inhibited following distribution of M-FeNPs, the expression of several chemokines, including CXCR2, CCR5, and CD123, was enhanced on the splenocytes of the treated groups. Taken together, we suggest that accumulation of M-FeNPs may induce adverse health effects by disturbing homeostasis of the immune regulation and ion environment.

Gaining a Critical Mass: A Dose Metric Conversion Case Study Using Silver Nanoparticles

Mass concentration is the standard convention to express exposure in ecotoxicology for dissolved substances. However, nanotoxicology has challenged the suitability of the mass concentration dose metric. Alternative metrics often discussed in the literature include particle number, surface area, and ion release (kinetics, equilibrium). It is unlikely that any single metric is universally applicable to all types of nanoparticles. However, determining the optimal metric for a specific type of nanoparticle requires novel studies to generate supportive data and employ methods to compensate for current analytical capability gaps. This investigation generated acute toxicity data for two standard species (Ceriodaphnia dubia, Pimephales promelas) exposed to five sizes (10, 20, 30, 60, 100 nm) of monodispersed citrate- and polyvinylpyrrolidone-coated silver nanoparticles. Particles were sized by various techniques to populate available models for expressing the particle number, surface area, and dissolved fraction. Results indicate that the acute toxicity of the tested silver nanoparticles is best expressed by ion release, and is relatable to total exposed surface area. Particle number was not relatable to the observed acute silver nanoparticle effects.

A critical review of in vitro dosimetry for engineered nanomaterials

A major obstacle in the development of accurate cellular models for investigating nanobio interactions in vitro is determination of physiologically relevant measures of dose. Comparison of biological responses to nanoparticle exposure typically relies on administered dose metrics such as mass concentration of suspended particles, rather than the effective dose of particles that actually comes in contact with the cells over the time of exposure. Adoption of recently developed dosimetric methodologies will facilitate determination of effective dose delivered to cells in vitro, thereby improving the accuracy and reliability of in vitro screening data, validation of in vitro with in vivo data, and comparison across multiple datasets for the large variety of nanomaterials currently in the market.

Evaluation of Toxicity Ranking for Metal Oxide Nanoparticles via an in Vitro Dosimetry Model

It has been argued that in vitro toxicity testing of engineered nanoparticles (NPs) should consider delivered dose (i.e., NP mass settled per suspension volume) rather than relying exclusively on administered dose (initial NP mass concentration). Delivered dose calculations require quantification of NP sedimentation in tissue cell culture media, taking into consideration fundamental suspension properties. In this article, we calculate delivered dose using a first-principles "particles in a box" sedimentation model, which accounts for the particle size distribution, fractal dimension, and permeability of agglomerated NPs. The sedimentation model was evaluated against external and our own experimental sedimentation data for metal oxide NPs. We then utilized the model to construct delivered dose-response analysis for a library of metal oxide NPs (previously used for hazard ranking and prediction making) in different cell culture media. Hierarchical hazard ranking of the seven (out of 24) toxic metal oxide NPs in our library, using EC50 calculated on the basis of delivered dose, did not measurably differ from our ranking based on administered dose. In contrast, simplified sedimentation calculations based on the assumption of impermeable NP agglomerates of a single average size significantly underestimated the settled NPs' mass, resulting in misinterpretation of toxicity ranking. It is acknowledged that in vitro dose-response outcomes are likely to be shaped by complex toxicodynamics, which include NP/cellular association, triggering of dynamic cell response pathways involved in NP uptake, and multiple physicochemical parameters that influence NP sedimentation and internalization.

Adapting OECD Aquatic Toxicity Tests for Use with Manufactured Nanomaterials: Key Issues and Consensus Recommendations

The unique or enhanced properties of manufactured nanomaterials (MNs) suggest that their use in nanoenabled products will continue to increase. This will result in increased potential for human and environmental exposure to MNs during manufacturing, use, and disposal of nanoenabled products. Scientifically based risk assessment for MNs necessitates the development of reproducible, standardized hazard testing methods such as those provided by the Organisation of Economic Cooperation and Development (OECD). Currently, there is no comprehensive guidance on how best to address testing issues specific to MN particulate, fibrous, or colloidal properties. This paper summarizes the findings from an expert workshop convened to develop a guidance document that addresses the difficulties encountered when testing MNs using OECD aquatic and sediment test guidelines. Critical components were identified by workshop participants that require specific guidance for MN testing: preparation of dispersions, dose metrics, the importance and challenges associated with maintaining and monitoring exposure levels, and the need for reliable methods to quantify MNs in complex media. To facilitate a scientific advance in the consistency of nanoecotoxicology test results, we identify and discuss critical considerations where expert consensus recommendations were and were not achieved and provide specific research recommendations to resolve issues for which consensus was not reached. This process will enable the development of prescriptive testing guidance for MNs. Critically, we highlight the need to quantify and properly interpret and express exposure during the bioassays used to determine hazard values.

Comparative assessment of nanomaterial definitions and safety evaluation considerations

Nanomaterials continue to bring promising advances to science and technology. In concert have come calls for increased regulatory oversight to ensure their appropriate identification and evaluation, which has led to extensive discussions about nanomaterial definitions. Numerous nanomaterial definitions have been proposed by government, industry, and standards organizations. We conducted a comprehensive comparative assessment of existing nanomaterial definitions put forward by governments to highlight their similarities and differences. We found that the size limits used in different definitions were inconsistent, as were considerations of other elements, including agglomerates and aggregates, distributional thresholds, novel properties, and solubility. Other important differences included consideration of number size distributions versus weight distributions and natural versus intentionally-manufactured materials. Overall, the definitions we compared were not in alignment, which may lead to inconsistent identification and evaluation of nanomaterials and could have adverse impacts on commerce and public perceptions of nanotechnology. We recommend a set of considerations that future discussions of nanomaterial definitions should consider for describing materials and assessing their potential for health and environmental impacts using risk-based approaches within existing assessment frameworks. Our intent is to initiate a dialogue aimed at achieving greater clarity in identifying those nanomaterials that may require additional evaluation, not to propose a formal definition.

Lung biodurability and free radical production of cellulose nanomaterials

Abstract The potential applications of cellulose nanomaterials in advanced composites and biomedicine makes it imperative to understand their pulmonary exposure to human health. Here, we report the results on the biodurability of three cellulose nanocrystal (CNC), two cellulose nanofibril (CNF) and a benchmark cellulose microcrystal (CMC) when exposed to artificial lung airway lining fluid (SUF, pH 7.3) for up to 7 days and alveolar macrophage phagolysosomal fluid (PSF, pH 4.5) for up to 9 months. X-ray diffraction analysis was used to monitor biodurability and thermogravimetry, surface area, hydrodynamic diameter, zeta potential and free radical generation capacity of the samples were determined (in vitro cell-free and RAW 264.7 cell line models). The CMC showed no measurable changes in crystallinity (x(CR)) or crystallite size D in either SUF or PSF. For one CNC, a slight decrease in x(CR) and D in SUF was observed. In acidic PSF, a slight increase in x(CR) with exposure time was observed, possibly due to dissolution of the amorphous component. In a cell-free reaction with H₂O₂, radicals were observed; the CNCs and a CNF generated significantly more ·OH radicals than the CMC (p < 0.05). The ·OH radical production correlates with particle decomposition temperature and is explained by the higher surface area to volume ratio of the CNCs. Based on their biodurability, mechanical clearance would be the primary mechanism for lung clearance of cellulose materials. The production of ·OH radicals indicates the need for additional studies to characterize the potential inhalation hazards of cellulose.

Response-metrics for acute lung inflammation pattern by cobalt-based nanoparticles

Background

Although the surface area metric has been proposed as a possible dose-metric for nanoparticles (NPs), it is limited to low-solubility NPs and the dose-metric for high-solubility NPs is poorly understood. In this study, we aimed to assess the appropriate dose-metric or response-metric for NPs using two cobalt (Co)-based NPs, cobalt monoxide (CoO) and cobalt oxide (Co₃O₄), which both show distinctive solubility, and determine the role of their soluble Co ions in inflammation.

Methods

We evaluated the physicochemical properties of NPs, including solubility in artificial lysosomal fluid (ALF, pH 5.5). Acute lung inflammogenicity was evaluated by bronchoalveolar lavage fluid analysis using the rat intratracheal instillation model. The appropriate response-metric was then determined by plotting several dose-metrics against parameters for lung inflammation. To investigate the effect of the soluble fraction of CoO NPs, the equivalent doses of Co ions from CoCl₂ were instilled.

Results

The Co₃O₄ and CoO NPs showed about 11.46 % and 92.65 % solubility in ALF, respectively. Instillation of Co₃O₄ NPs produced neutrophilic inflammation, but CoO NPs induced eosinophilic inflammation. The number of eosinophils showed good correlation with the soluble Co ions dose from NPs (r² = 0.987, p <0.001), while the number of neutrophils showed good correlation with the surface area dose of the biopersistent NPs (r² = 0.876, p <0.001). Instillation of CoCl₂ showed a similar type and magnitude of inflammation as CoO NPs.

Conclusions

In the Co-based NPs, the eosinophilic inflammation was produced by Co ions based on the ion metric, while the neutrophilic inflammation was developed based on the surface area metric of the biopersistent NPs.

A practical approach to determine dose metrics for nanomaterials

Traditionally, administered mass is used to describe doses of conventional chemical substances in toxicity studies. For deriving toxic doses of nanomaterials, mass and chemical composition alone may not adequately describe the dose, because particles with the same chemical composition can have completely different toxic mass doses depending on properties such as particle size. Other dose metrics such as particle number, volume, or surface area have been suggested, but consensus is lacking. The discussion regarding the most adequate dose metric for nanomaterials clearly needs a systematic, unbiased approach to determine the most appropriate dose metric for nanomaterials. In the present study, the authors propose such an approach and apply it to results from in vitro and in vivo experiments with silver and silica nanomaterials. The proposed approach is shown to provide a convenient tool to systematically investigate and interpret dose metrics of nanomaterials. Recommendations for study designs aimed at investigating dose metrics are provided.

Molecular interactions between gold nanoparticles and model cell membranes

Direct observations of the lipid flip-flop induced by Au NP – model mammalian cell membrane interactions.