Exposure assessments for a cross-sectional epidemiologic study of US carbon nanotube and nanofiber workers

Quantile regression for longitudinal data with values below the limit of detection and time-dependent covariates-application to modeling carbon nanotube and nanofiber exposures

BACKGROUND

In studies of occupational health, longitudinal environmental exposure, and biomonitoring data are often subject to right skewing and left censoring, in which measurements fall below the limit of detection (LOD). To address right-skewed data, it is common practice to log-transform the data and model the geometric mean, assuming a log-normal distribution. However, if the transformed data do not follow a known distribution, modeling the mean of exposure may result in bias and reduce efficiency. In addition, when examining longitudinal data, it is possible that certain covariates may vary over time.

OBJECTIVE

To develop predictive quantile regression models to resolve the issues of left censoring and time-dependent covariates and to quantitatively evaluate if previous and current covariates can predict current and/or future exposure levels.

METHODS

To address these gaps, we suggested incorporating different substitution approaches into quantile regression and utilizing a method for selecting a working type of time dependency for covariates.

RESULTS

In a simulation study, we demonstrated that, under different types of time-dependent covariates, the approach of multiple random value imputation outperformed the other approaches. We also applied our methods to a carbon nanotube and nanofiber exposure study. The dependent variables are the left-censored mass of elemental carbon at both the respirable and inhalable aerosol size fractions. In this study, we identified some potential time-dependent covariates with respect to worker-level determinants and job tasks.

CONCLUSION

Time dependency for covariates is rarely accounted for when analyzing longitudinal environmental exposure and biomonitoring data with values less than the LOD through predictive modeling. Mistreating the time-dependency as time-independency will lead to an efficiency loss of regression parameter estimation. Therefore, we addressed time-varying covariates in longitudinal exposure and biomonitoring data with left-censored measurements and illustrated an entire conditional distribution through different quantiles.

Human and environmental impacts of nanoparticles: a scoping review of the current literature

Use of nanoparticles have established benefits in a wide range of applications, however, the effects of exposure to nanoparticles on health and the environmental risks associated with the production and use of nanoparticles are less well-established. The present study addresses this gap in knowledge by examining, through a scoping review of the current literature, the effects of nanoparticles on human health and the environment. We searched relevant databases including Medline, Web of Science, ScienceDirect, Scopus, CINAHL, Embase, and SAGE journals, as well as Google, Google Scholar, and grey literature from June 2021 to July 2021. After removing duplicate articles, the title and abstracts of 1495 articles were first screened followed by the full-texts of 249 studies, and this resulted in the inclusion of 117 studies in the presented review.In this contribution we conclude that while nanoparticles offer distinct benefits in a range of applications, they pose significant threats to humans and the environment. Using several biological models and biomarkers, the included studies revealed the toxic effects of nanoparticles (mainly zinc oxide, silicon dioxide, titanium dioxide, silver, and carbon nanotubes) to include cell death, production of oxidative stress, DNA damage, apoptosis, and induction of inflammatory responses. Most of the included studies (65.81%) investigated inorganic-based nanoparticles. In terms of biomarkers, most studies (76.9%) used immortalised cell lines, whiles 18.8% used primary cells as the biomarker for assessing human health effect of nanoparticles. Biomarkers that were used for assessing environmental impact of nanoparticles included soil samples and soybean seeds, zebrafish larvae, fish, and Daphnia magna neonates.From the studies included in this work the United States recorded the highest number of publications (n = 30, 25.64%), followed by China, India, and Saudi Arabia recording the same number of publications (n = 8 each), with 95.75% of the studies published from the year 2009. The majority of the included studies (93.16%) assessed impact of nanoparticles on human health, and 95.7% used experimental study design. This shows a clear gap exists in examining the impact of nanoparticles on the environment.

A new capacity of gut microbiota: Fermentation of engineered inorganic carbon nanomaterials into endogenous organic metabolites

Carbon-based nanomaterials (CNMs) have recently been found in humans raising a great concern over their adverse roles in the hosts. However, our knowledge of the in vivo behavior and fate of CNMs, especially their biological processes elicited by the gut microbiota, remains poor. Here, we uncovered the integration of CNMs (single-walled carbon nanotubes and graphene oxide) into the endogenous carbon flow through degradation and fermentation, mediated by the gut microbiota of mice using isotope tracing and gene sequencing. As a newly available carbon source for the gut microbiota, microbial fermentation leads to the incorporation of inorganic carbon from the CNMs into organic butyrate through the pyruvate pathway. Furthermore, the butyrate-producing bacteria are identified to show a preference for the CNMs as their favorable source, and excessive butyrate derived from microbial CNMs fermentation further impacts on the function (proliferation and differentiation) of intestinal stem cells in mouse and intestinal organoid models. Collectively, our results unlock the unknown fermentation processes of CNMs in the gut of hosts and underscore an urgent need for assessing the transformation of CNMs and their health risk via the gut-centric physiological and anatomical pathways.

Oxidative Stress and Inflammatory Biomarkers for Populations with Occupational Exposure to Nanomaterials: A Systematic Review and Meta-Analysis

Exposure to nanomaterials (NMs) is suggested to have the potential to cause harmful health effects. Activations of oxidative stress and inflammation are assumed as main contributors to NM-induced toxicity. Thus, oxidative stress- and inflammation-related indicators may serve as biomarkers for occupational risk assessment. However, the correlation between NM exposure and these biomarkers remains controversial. This study aimed to perform a meta-analysis to systematically investigate the alterations of various biomarkers after NM exposure. Twenty-eight studies were found eligible by searching PubMed, EMBASE and Cochrane Library databases. The pooled results showed NM exposure was significantly associated with increases in the levels of malonaldehyde (MDA) [standardized mean difference (SMD) = 2.18; 95% confidence interval (CI), 1.50-2.87], 4-hydroxy-2-nonhenal (HNE) (SMD = 2.05; 95% CI, 1.13-2.96), aldehydes C6-12 (SMD = 3.45; 95% CI, 2.80-4.10), 8-hydroxyguanine (8-OHG) (SMD = 2.98; 95% CI, 2.22-3.74), 5-hydroxymethyl uracil (5-OHMeU) (SMD = 1.90; 95% CI, 1.23-2.58), o-tyrosine (o-Tyr) (SMD = 1.81; 95% CI, 1.22-2.41), 3-nitrotyrosine (3-NOTyr) (SMD = 2.63; 95% CI, 1.74-3.52), interleukin (IL)-1β (SMD = 1.76; 95% CI, 0.87-2.66), tumor necrosis factor (TNF)-α (SMD = 1.52; 95% CI, 1.03-2.01), myeloperoxidase (MPO) (SMD = 0.25; 95% CI, 0.16-0.34) and fibrinogen (SMD = 0.11; 95% CI, 0.02-0.21), and decreases in the levels of glutathione peroxidase (GPx) (SMD = -0.31; 95% CI, -0.52--0.11) and IL-6 soluble receptor (IL-6sR) (SMD = -0.18; 95% CI, -0.28--0.09). Subgroup analysis indicated oxidative stress biomarkers (MDA, HNE, aldehydes C6-12, 8-OHG, 5-OHMeU, o-Tyr, 3-NOTyr and GPx) in exhaled breath condensate (EBC) and blood samples were strongly changed by NM exposure; inflammatory biomarkers (IL-1β, TNF-α, MPO, fibrinogen and IL-6sR) were all significant in EBC, blood, sputum and nasal lavage samples. In conclusion, our findings suggest that these oxidative stress and inflammatory indicators may be promising biomarkers for the biological monitoring of occupationally NM-exposed workers.

Understanding toxicity associated with boron nitride nanotubes: Review of toxicity studies, exposure assessment at manufacturing facilities, and read-across

Boron nitride nanotubes (BNNT) are produced by many different methods leading to variances in physicochemical characteristics and impurities in the final product. These differences can alter the toxicity profile. The importance of understanding the potential pathological implications of this high aspect ratio nanomaterial is increasing as new approaches to synthesize and purify in large scale are being developed. In this review, we discuss the various factors of BNNT production that can influence its toxicity followed by summarizing the toxicity findings from in vitro and in vivo studies conducted to date, including a review of particle clearance observed with various exposure routes. To understand the risk to workers and interpret relevance of toxicological findings, exposure assessment at manufacturing facilities was discussed. Workplace exposure assessment of BNNT from two manufacturing facilities measured boron concentrations in personal breathing zones from non-detectable to 0.95 μg/m3 and TEM structure counts of 0.0123 ± 0.0094 structures/cm3, concentrations well below what was found with other engineered high aspect ratio nanomaterials like carbon nanotubes and nanofibers. Finally, using a purified BNNT, a "read-across" toxicity assessment was performed to demonstrate how known hazard data and physicochemical characteristics can be utilized to evaluate potential inhalation toxicity concerns.

Results of the 2019 Survey of Engineered Nanomaterial Occupational Health and Safety Practices

In collaboration with RTI International, the U.S. National Institute for Occupational Safety and Health (NIOSH) administered a survey to North American companies working with nanomaterials to assess health and safety practices. The results would contribute to understanding the impact of the efforts made by the NIOSH Nanotechnology Research Center (NTRC) in communicating occupational health and safety (OHS) considerations for workers when handling these materials. The survey, developed by RAND Corporation, was conducted online from September 2019–December 2019. Forty-five companies or organizations in the U.S. and Canada that fabricate, manufacture, handle, dispose, or otherwise use nanomaterials completed the survey. The survey was designed to answer research questions regarding the nanomaterials in use, which resources the companies have consulted for OHS guidance, and the overall OHS culture at the companies. Other questions specifically addressed whether the companies interacted with NIOSH or NIOSH resources to inform OHS policies and practices. Among participating companies, 57.8% had a maximum of 50 employees. Gold nanoparticles and polymers were most common (n = 20; 45.5% each), followed by graphene (36.4%), carbon nanotubes and nanofibers (34.1%), and zinc oxide nanoparticles (31.8%). Environmental monitoring was performed by 31.8% of the companies. While 88.9% of the companies had laminar flow cabinets, only 67.5% required it to be used with ENMs. Information and training programs were indicated by 90% of the sample, and only 29.6% performed specific health surveillance for ENM workers. Personal protective equipment primarily included gloves (100%) and eye/face protection (97.7%). More than a third (37.8%) of the respondents reported using at least one NIOSH resource to acquire information about safe handling of ENMs. The small number of companies that responded to and completed the survey is a considerable limitation to this study. However, the survey data are valuable for gauging the reach and influence of the NIOSH NTRC on nano OHS and for informing future outreach, particularly to small businesses.

Applying Translational Science Approaches to Protect Workers Exposed to Nanomaterials

Like nanotechnology, translational science is a relatively new and transdisciplinary field. Translational science in occupational safety and health (OSH) focuses on the process of taking scientific knowledge for the protection of workers from the lab to the field (i.e., the worksite/workplace) and back again. Translational science has been conceptualized as having multiple phases of research along a continuum, beyond scientific discovery (T0), to efficacy (T1), to effectiveness (T2), to dissemination and implementation (D&I) (T3), to outcomes and effectiveness research in populations (T4). The translational research process applied to occupational exposure to nanomaterials might involve similar phases. This builds on basic and efficacy research (T0 and T1) in the areas of toxicology, epidemiology, industrial hygiene, medicine and engineering. In T2, research and evidence syntheses and guidance and recommendations to protect workers may be developed and assessed for effectiveness. In T3, emphasis is needed on D&I research to explore the multilevel barriers and facilitators to nanotechnology risk control information/research adoption, use, and sustainment in workplaces. D&I research for nanomaterial exposures should focus on assessing sources of information and evidence to be disseminated /implemented in complex and dynamic workplaces, how policy-makers and employers use this information in diverse contexts to protect workers, how stakeholders inform these critical processes, and what barriers impede and facilitate multilevel decision-making for the protection of nanotechnology workers. The T4 phase focuses on how effective efforts to prevent occupational exposure to nanomaterials along the research continuum contribute to large-scale impact in terms of worker safety, health and wellbeing (T4). Stakeholder input and engagement is critical to all stages of the translational research process. This paper will provide: (1) an illustration of the translational research continuum for occupational exposure to nanomaterials; and (2) a discussion of opportunities for applying D&I science to increase the effectiveness, uptake, integration, sustainability, and impact of interventions to protect the health and wellbeing of workers in the nanotechnology field.

Towards health-based nano reference values (HNRVs) for occupational exposure: Recommendations from an expert panel

Unique physicochemical characteristics of engineered nanomaterials (ENMs) suggest the need for nanomaterial-specific occupational exposure limits (OELs). Setting these limits remains a challenge. Therefore, the aim of this study was to set out a framework to evaluate the feasibility of deriving advisory health-based occupational limit values for groups of ENMs, based on scientific knowledge. We have used an expert panel approach to address three questions: 1) What ENM-categories should be distinguished to derive advisory health-based occupational limit values (or health-based Nano Reference Values, HNRVs) for groups of ENMs? 2) What evidence would be needed to define values for these categories? And 3) How much effort would it take to achieve this? The panel experts distinguished six possible categories of HNRVs: A) WHO-fiber-like high aspect ratio ENMs (HARNs), B) Non-WHO-fiber-like HARNs and other non-spheroidal ENMs, C) readily soluble spheroidal ENMs, D) biopersistent spheroidal ENMs with unknown toxicity, E) biopersistent spheroidal ENMs with substance-specific toxicity and F) biopersistent spheroidal ENMs with relatively low substance-specific toxicity. For category A, the WHO-fiber-like HARNs, agreement was reached on criteria defining this category and the approach of using health-based risk estimates for asbestos to derive the HNRV. For category B, a quite heterogeneous category, more toxicity data are needed to set an HNRV. For category C, readily soluble spheroidal ENMs, using the OEL of their molecular or ionic counterpart would be a good starting point. For the biopersistent ENMs with unknown toxicity, HNRVs cannot be applied as case-by-case testing is required. For the other biopersistent ENMs in category E and F, we make several recommendations that can facilitate the derivation of these HNRVs. The proposed categories and recommendations as outlined by this expert panel can serve as a reference point for derivation of HNRVs when health-based OELs for ENMs are not yet available.

Abdalla M, Bechelany M. Review on Natural, Incidental, Bioinspired, and Engineered Nanomaterials: History, Definitions, Classifications, Synthesis, Properties, Market, Toxicities, Risks, and Regulations

Nanomaterials are becoming important materials in several fields and industries thanks to their very reduced size and shape-related features. Scientists think that nanoparticles and nanostructured materials originated during the Big Bang process from meteorites leading to the formation of the universe and Earth. Since 1990, the term nanotechnology became very popular due to advances in imaging technologies that paved the way to specific industrial applications. Currently, nanoparticles and nanostructured materials are synthesized on a large scale and are indispensable for many industries. This fact fosters and supports research in biochemistry, biophysics, and biochemical engineering applications. Recently, nanotechnology has been combined with other sciences to fabricate new forms of nanomaterials that could be used, for instance, for diagnostic tools, drug delivery systems, energy generation/storage, environmental remediation as well as agriculture and food processing. In contrast with traditional materials, specific features can be integrated into nanoparticles, nanostructures, and nanosystems by simply modifying their scale, shape, and composition. This article first summarizes the history of nanomaterials and nanotechnology. Followed by the progress that led to improved synthesis processes to produce different nanoparticles and nanostructures characterized by specific features. The content finally presents various origins and sources of nanomaterials, synthesis strategies, their toxicity, risks, regulations, and self-aggregation.

Pulmonary toxicity and gene expression changes in response to whole-body inhalation exposure to multi-walled carbon nanotubes in rats

Purpose: To investigate the molecular mechanisms underlying the pulmonary toxicity induced by exposure to one form of multi-walled carbon nanotubes (MWCNT-7).Materials and methods: Rats were exposed, by whole-body inhalation, to air or an aerosol containing MWCNT-7 particles at target cumulative doses (concentration x time) ranging from 22.5 to 180 (mg/m³)h over a three-day (6 hours/day) period and toxicity and global gene expression profiles were determined in the lungs.Results: MWCNT-7 particles, associated with alveolar macrophages (AMs), were detected in rat lungs following the exposure. Mild to moderate lung pathological changes consisting of increased cellularity, thickening of the alveolar wall, alveolitis, fibrosis, and granuloma formation were detected. Bronchoalveolar lavage (BAL) toxicity parameters such as lactate dehydrogenase activity, number of AMs and polymorphonuclear leukocytes (PMNs), intracellular oxidant generation by phagocytes, and levels of cytokines were significantly (p < 0.05) increased in response to exposure to MWCNT-7. Global gene expression profiling identified several significantly differentially expressed genes (fold change >1.5 and FDR p value <0.05) in all the MWCNT-7 exposed rats. Bioinformatic analysis of the gene expression data identified significant enrichment of several diseases/biological function categories (for example, cancer, leukocyte migration, inflammatory response, mitosis, and movement of phagocytes) and canonical pathways (for example, kinetochore metaphase signaling pathway, granulocyte and agranulocyte adhesion and diapedesis, acute phase response, and LXR/RXR activation). The alterations in the lung toxicity parameters and gene expression changes exhibited a dose-response to the MWCNT exposure.Conclusions: Taken together, the data provided insights into the molecular mechanisms underlying the pulmonary toxicity induced by inhalation exposure of rats to MWCNT-7.

Histopathology of the broad class of carbon nanotubes and nanofibers used or produced in U.S. facilities in a murine model

BACKGROUND

Multi-walled carbon nanotubes and nanofibers (CNT/F) have been previously investigated for their potential toxicities; however, comparative studies of the broad material class are lacking, especially those with a larger diameter. Additionally, computational modeling correlating physicochemical characteristics and toxicity outcomes have been infrequently employed, and it is unclear if all CNT/F confer similar toxicity, including histopathology changes such as pulmonary fibrosis. Male C57BL/6 mice were exposed to 40 µg of one of nine CNT/F (MW #1-7 and CNF #1-2) commonly found in exposure assessment studies of U.S. facilities with diameters ranging from 6 to 150 nm. Human fibroblasts (0-20 µg/ml) were used to assess the predictive value of in vitro to in vivo modeling systems.

RESULTS

All materials induced histopathology changes, although the types and magnitude of the changes varied. In general, the larger diameter MWs (MW #5-7, including Mitsui-7) and CNF #1 induced greater histopathology changes compared to MW #1 and #3 while MW #4 and CNF #2 were intermediate in effect. Differences in individual alveolar or bronchiolar outcomes and severity correlated with physical dimensions and how the materials agglomerated. Human fibroblast monocultures were found to be insufficient to fully replicate in vivo fibrosis outcomes suggesting in vitro predictive potential depends upon more advanced cell culture in vitro models. Pleural penetrations were observed more consistently in CNT/F with larger lengths and diameters.

CONCLUSION

Physicochemical characteristics, notably nominal CNT/F dimension and agglomerate size, predicted histopathologic changes and enabled grouping of materials by their toxicity profiles. Particles of greater nominal tube length were generally associated with increased severity of histopathology outcomes. Larger particle lengths and agglomerates were associated with more severe bronchi/bronchiolar outcomes. Spherical agglomerated particles of smaller nominal tube dimension were linked to granulomatous inflammation while a mixture of smaller and larger dimensional CNT/F resulted in more severe alveolar injury.

Serum peptidome: diagnostic window into pathogenic processes following occupational exposure to carbon nanomaterials

BACKGROUND

Growing industrial use of carbon nanotubes and nanofibers (CNT/F) warrants consideration of human health outcomes. CNT/F produces pulmonary, cardiovascular, and other toxic effects in animals along with a significant release of bioactive peptides into the circulation, the augmented serum peptidome. While epidemiology among CNT/F workers reports on few acute symptoms, there remains concern over sub-clinical CNT/F effects that may prime for chronic disease, necessitating sensitive health outcome diagnostic markers for longitudinal follow-up.

METHODS

Here, the serum peptidome was assessed for its biomarker potential in detecting sub-symptomatic pathobiology among CNT/F workers using label-free data-independent mass spectrometry. Studies employed a stratified design between High (> 0.5 µg/m3) and Low (< 0.1 µg/m3) inhalable CNT/F exposures in the industrial setting. Peptide biomarker model building and refinement employed linear regression and partial least squared discriminant analyses. Top-ranked peptides were then sequence identified and evaluated for pathological-relevance.

RESULTS

In total, 41 peptides were found to be highly discriminatory after model building with a strong linear correlation to personal CNT/F exposure. The top-five peptide model offered ideal prediction with high accuracy (Q2 = 0.99916). Unsupervised validation affirmed 43.5% of the serum peptidomic variance was attributable to CNT/F exposure. Peptide sequence identification reveals a predominant association with vascular pathology. ARHGAP21, ADAM15 and PLPP3 peptides suggest heightened cardiovasculature permeability and F13A1, FBN1 and VWDE peptides infer a pro-thrombotic state among High CNT/F workers.

CONCLUSIONS

The serum peptidome affords a diagnostic window into sub-symptomatic pathology among CNT/F exposed workers for longitudinal monitoring of systemic health risks.

Pulmonary delivery of the broad-spectrum matrix metalloproteinase inhibitor marimastat diminishes multiwalled carbon nanotube-induced circulating bioactivity without reducing pulmonary inflammation

BACKGROUND

Multiwalled carbon nanotubes (MWCNT) are an increasingly utilized engineered nanomaterial that pose the potential for significant risk of exposure-related health outcomes. The mechanism(s) underlying MWCNT-induced toxicity to extrapulmonary sites are still being defined. MWCNT-induced serum-borne bioactivity appears to dysregulate systemic endothelial cell function. The serum compositional changes after MWCNT exposure have been identified as a surge of fragmented endogenous peptides, likely derived from matrix metalloproteinase (MMP) activity. In the present study, we utilize a broad-spectrum MMP inhibitor, Marimastat, along with a previously described oropharyngeal aspiration model of MWCNT administration to investigate the role of MMPs in MWCNT-derived serum peptide generation and endothelial bioactivity.

RESULTS

C57BL/6 mice were treated with Marimastat or vehicle by oropharyngeal aspiration 1 h prior to MWCNT treatment. Pulmonary neutrophil infiltration and total bronchoalveolar lavage fluid protein increased independent of MMP blockade. The lung cytokine profile similarly increased following MWCNT exposure for major inflammatory markers (IL-1β, IL-6, and TNF-α), with minimal impact from MMP inhibition. However, serum peptidomic analysis revealed differential peptide compositional profiles, with MMP blockade abrogating MWCNT-derived serum peptide fragments. The serum, in turn, exhibited differential potency in terms of inflammatory bioactivity when incubated with primary murine cerebrovascular endothelial cells. Serum from MWCNT-treated mice led to inflammatory responses in endothelial cells that were significantly blunted with serum from Marimastat-treated mice.

CONCLUSIONS

Thus, MWCNT exposure induced pulmonary inflammation that was largely independent of MMP activity but generated circulating bioactive peptides through predominantly MMP-dependent pathways. This MWCNT-induced lung-derived bioactivity caused pathological consequences of endothelial inflammation and barrier disruption.

Occupational Exposures to Engineered Nanomaterials: a Review of Workplace Exposure Assessment Methods

PURPOSE OF REVIEW

The purpose of this review is to consolidate exposure assessment methods for occupational research on engineered nanomaterials (ENMs) published within the past 5 years (2015-2020).

RECENT FINDINGS

The three ENMs that generated the highest volume of new research include titanium dioxide, graphene, and aluminum oxide. A multi-metric approach, using both online and offline instruments and analyses, has been found to be a useful method to characterize ENM workplace exposures and was commonly used in the recently published literature. Particle number concentration was the most common online exposure metric used, followed by the metrics of mass and surface area. There are currently no consensus methods for offline analyses of most ENMs. Researchers generally used gravimetric or elemental analyses for carbonaceous nanomaterials, titanium dioxide, and other nanometals, but there was little overlap between other ENM materials reviewed. Using biological markers of exposure, such as urinary oxidative stress biomarkers, as an indication of chronic exposure may also be useful for some ENMs and should be further researched. Generally, similar online instrumentation and offline electron microscopy methods were used for all ENMs. However, this consistency was not observed for offline mass analysis methods within specific ENMs. Consolidation of the most recent methods and results of exposure assessments within this broad material category can guide researchers toward future areas of study. Establishing consensus methods of exposure assessment for each individual ENM is crucial to characterizing workplace exposures, pooling data to fully understand their associated risks, and developing useful occupational exposure limits.

Tim4 recognizes carbon nanotubes and mediates phagocytosis leading to granuloma formation

Macrophage recognition and phagocytosis of crystals is critical for the associated fibrosis and cancer. Of note, multi-walled carbon nanotubes (MWCNTs), the highly representative products of nanotechnology, induce macrophage NLRP3 inflammasome activation and cause asbestosis-like pathogenesis. However, it remains largely unknown how macrophages efficiently recognize MWCNTs on their cell surfaces. Here, we identify by a targeted screening of phagocyte receptors the phosphatidylserine receptors T cell immunoglobulin mucin 4 (Tim4) and Tim1 as the pattern-recognition receptors for carbon crystals. Docking simulation studies reveal spatiotemporally stable interfaces between aromatic residues in the extracellular IgV domain of Tim4 and one-dimensional carbon crystals. Further, CRISPR-Cas9-mediated deletion of Tim4 and Tim1 reveals that Tim4, but not Tim1, critically contributes to the recognition of MWCNTs by peritoneal macrophages and to granuloma development in a mouse model of direct mesothelium exposure to MWCNTs. These results suggest that Tim4 recognizes MWCNTs through aromatic interactions and mediates phagocytosis leading to granulomas.

Physicochemical characterization and genotoxicity of the broad class of carbon nanotubes and nanofibers used or produced in U.S. facilities

BACKGROUND

Carbon nanotubes and nanofibers (CNT/F) have known toxicity but simultaneous comparative studies of the broad material class, especially those with a larger diameter, with computational analyses linking toxicity to their fundamental material characteristics was lacking. It was unclear if all CNT/F confer similar toxicity, in particular, genotoxicity. Nine CNT/F (MW #1-7 and CNF #1-2), commonly found in exposure assessment studies of U.S. facilities, were evaluated with reported diameters ranging from 6 to 150 nm. All materials were extensively characterized to include distributions of physical dimensions and prevalence of bundled agglomerates. Human bronchial epithelial cells were exposed to the nine CNT/F (0-24 μg/ml) to determine cell viability, inflammation, cellular oxidative stress, micronuclei formation, and DNA double-strand breakage. Computational modeling was used to understand various permutations of physicochemical characteristics and toxicity outcomes.

RESULTS

Analyses of the CNT/F physicochemical characteristics illustrate that using detailed distributions of physical dimensions provided a more consistent grouping of CNT/F compared to using particle dimension means alone. In fact, analysis of binning of nominal tube physical dimensions alone produced a similar grouping as all characterization parameters together. All materials induced epithelial cell toxicity and micronuclei formation within the dose range tested. Cellular oxidative stress, DNA double strand breaks, and micronuclei formation consistently clustered together and with larger physical CNT/F dimensions and agglomerate characteristics but were distinct from inflammatory protein changes. Larger nominal tube diameters, greater lengths, and bundled agglomerate characteristics were associated with greater severity of effect. The portion of tubes with greater nominal length and larger diameters within a sample was not the majority in number, meaning a smaller percentage of tubes with these characteristics was sufficient to increase toxicity. Many of the traditional physicochemical characteristics including surface area, density, impurities, and dustiness did not cluster with the toxicity outcomes.

CONCLUSION

Distributions of physical dimensions provided more consistent grouping of CNT/F with respect to toxicity outcomes compared to means only. All CNT/F induced some level of genotoxicity in human epithelial cells. The severity of toxicity was dependent on the sample containing a proportion of tubes with greater nominal lengths and diameters.

Health and Safety Concerns Related to CNT and Graphene Products, and Related Composites

The use of Carbon Nanotubes (CNT) and Graphene increased in the last decade and it is likely to keep increasing in the near future. The attractiveness of their properties, particularly the possibility to enhance the composites performance using a tailor made methodology, brings new materials, processes and products for highly demanding industrial applications and to the market. However, there are quite a lot of health/safety issues, as well as lack of understanding and standards to evaluate their effects. This paper starts with a general description of materials, processes and products dealing with CNT and graphene. Then, an overview of concerns related to the health and safety when handling, researching, producing and using products that include these materials is presented. It follows a risk management approach with respect to simulation and evaluation tools, and considering the consensual limits already existing for research, industry and consumers. A general discussion integrating the relevant aspects of health and safety with respect to CNT and graphene is also presented. A proactive view is presented with the intention to contribute with some guidelines on installation, maintenance, evaluation, personal protection equipment (PPE) and personnel training to deal with these carbon-based nanomaterials in research, manufacture, and use with composite materials.

Estimates of carbon nanotube deposition in the lung: improving quality and robustness

Carbon nanotube (CNT) in vivo inhalation studies are increasingly providing estimates of the quantity of material deposited in the lung, generally estimated using standard formulae and pulmonary deposition models. These models have typically been developed and validated using data from studies using sphere-like particles. Given the importance of particle morphology to pulmonary deposition, the appropriateness of such an approach was explored to identify any potential limitations. Aerosolized CNT particles typically form 'fiber-like' and/or 'broadly spherical' agglomerates. A review of currently used deposition models indicates that none have been directly validated against results for CNT, however, models for spherical particles have been extensively validated against a wide range of particle sizes and materials and are thus expected to provide reasonable estimates for most 'broadly spherical' CNT particles, although experimental confirmation of this would be of benefit, especially given their low density. The validation of fiber deposition models is significantly less extensive and, in general, focused on larger particles, e.g. asbestos. This raises concerns about the accuracy of deposition estimates for 'fiber-like' CNT particles and recommendations are made for future research to address this. An appreciation of the uncertainties on CNT deposition estimates is important for their interpretation and thus it is recommended that model sensitivity and uncertainty assessments be undertaken. Issues surrounding the measurement and derivation of model input data are also addressed, including instrument responses and particle density assessment options. Recommendations are also made for aerosol characterization to 'future-proof' CNT inhalation studies regarding advances in deposition modeling and toxicological understanding.

Association of occupational exposures with ex vivo functional immune response in workers handling carbon nanotubes and nanofibers

The objective of this study was to evaluate the association between carbon nanotube and nanofiber (CNT/F) exposure and ex vivo responses of whole blood challenged with secondary stimulants, adjusting for potential confounders, in a cross-sectional study of 102 workers. Multi-day exposure was measured by CNT/F structure count (SC) and elemental carbon (EC) air concentrations. Demographic, lifestyle and other occupational covariate data were obtained via questionnaire. Whole blood collected from each participant was incubated for 18 hours with and without two microbial stimulants (lipopolysaccharide/LPS and staphylococcal enterotoxin type B/SEB) using TruCulture technology to evaluate immune cell activity. Following incubation, supernatants were preserved and analyzed for protein concentrations. The stimulant:null response ratio for each individual protein was analyzed using multiple linear regression, followed by principal component (PC) analysis to determine whether patterns of protein response were related to CNT/F exposure. Adjusting for confounders, CNT/F metrics (most strongly, the SC-based) were significantly (p < 0.05) inversely associated with stimulant:null ratios of several individual biomarkers: GM-CSF, IFN-γ, interleukin (IL)-2, IL-4, IL-5, IL-10, IL-17, and IL-23. CNT/F metrics were significantly inversely associated with PC1 (a weighted mean of most biomarkers, explaining 25% of the variance in the protein ratios) and PC2 (a biomarker contrast, explaining 14%). Among other occupational exposures, only solvent exposure was significant (inversely related to PC2). CNT/F exposure metrics were uniquely related to stimulant responses in challenged whole blood, illustrating reduced responsiveness to a secondary stimulus. This approach, if replicated in other exposed populations, may present a relatively sensitive method to evaluate human response to CNT/F or other occupational exposures.

Predicting Occupational Exposures to Carbon Nanotubes and Nanofibers Based on Workplace Determinants Modeling

BACKGROUND

Recent cross-sectional epidemiologic studies have examined the association between human health effects and carbon nanotube and nanofiber (CNT/F) workplace exposures. However, due to the latency of many health effects of interest, cohort studies with sufficient follow-up will likely be needed. The objective of this study was to identify workplace determinants that contribute to exposure and develop predictive models to estimate CNT/F exposures for future use in epidemiologic studies.

METHODS

Exposure measurements were compiled from 15 unique facilities for the metrics of elemental carbon (EC) mass at both the respirable and inhalable aerosol size fractions as well as a quantitative analysis performed by transmission electron microscopy (TEM). These metrics served as the dependent variables in model development. Repeated personal samples were collected from most of the 127 CNT/F worker participants for 252 total observations. Determinants were categorized as company-level or worker-level and used to describe the exposure relationship within the dependent variables. The influence of determinants on variance components was explored using mixed linear models that utilized a backwards stepwise selection process with a lowering of the AIC for model determinant selection. Additional ridge regression models were created that examined predictive performance with and without all two-way interactions. Cross-validation was performed on each model to evaluate the generalizability of its predictive capabilities while predictive performance was evaluated according to the corresponding R2 value and root mean square error (RMSE).

RESULTS

Determinants at the company-level that increased exposure included an inadequate or semi-adequate engineering control rating, increasing average CNT/F diameter/length, daily quantities of material handled from 101 g to >1 kg and >1 kg, the use of CNF materials, the industry type of hybrid producer/user, and the expert assessment of a high exposure potential. Worker-level determinants associated with higher exposure included handling the dry-powdered form of CNT/F, handling daily quantities of material >1 kg, direct/indirect exposure, having the job title of engineer, using a respirator, using a ventilated or unventilated enclosure, and the job task of powder handling. The mixed linear models explained >60% of the total variance when using all company- and worker-level determinants to create the three exposure models. The cross-validated RMSE values for each of the three mixed models ranged from 2.50 to 4.23. Meanwhile, the ridge regression models, without all two-way interactions, estimated cross-validated RMSE values of 2.85, 2.23, and 2.76 for the predictive models of inhalable EC, respirable EC, and TEM, respectively.

CONCLUSIONS

The ridge regression models demonstrated the best performance for predicting exposures to CNT/F for each exposure metric, although they only provided a modest predictive capability. Therefore, it was concluded that the models alone would not be adequate in predicting workplace exposures and would need to be integrated with other methods.

State of knowledge on the occupational exposure to carbon nanotubes

Carbon nanotubes (CNT) trigger fascination as well as anxiety, given their unique physical and chemical properties, and continuing concerns around their possible health effects. CNT exposure assessment is an integral component of occupational and environmental epidemiology, risk assessment, and management. We conducted a systematic review to analyze the quality of CNT occupational exposure assessments in field studies and to assess the relevance of available quantitative data from occupational hygiene and epidemiological perspectives. PubMed and Scopus databases were searched for the period 2000-2018. To grade the quality of each study, we used a standardized grid of seven criteria. The first criterion addressed 12 items deemed most relevant CNT physical-chemical properties with respect to their in vitro and in vivo toxicity. We included 27 studies from 11 countries in the review and graded them high (n = 2), moderate (n = 15) and low quality (n = 10). Half of the studies measured elemental carbon mass concentration (EC) using different methods and aerosol fractions. In 85% of studies, the observed values exceed the US National Institute for Occupational Safety and Health Recommended Exposure Limit. The quantification of CNT agglomerates and/or CNT contained fibers becomes increasingly common although lacking methodological standardization. Work activities with the greatest mean CNT mass concentrations were non-enclosed and included sieving, harvesting, packaging, reactor cleaning, extrusion and pelletizing. Some of the large studies defined standardized job titles according to exposure estimates at corresponding workstations and classified them by decreasing CNT exposure level: technicians > engineers > chemists. The already initiated harmonization of CNT exposure assessment and result reporting need to continue to favor not only studies in the field, but also to identify companies and workers using CNTs to characterize their exposures as well as monitor their health. This will enable an objective and realistic evaluation of risks associated with CNT applications and an appropriate risk management.

Comparative analysis of lung and blood transcriptomes in mice exposed to multi-walled carbon nanotubes

Pulmonary exposure to multi-walled carbon nanotubes (MWCNT) causes inflammation, fibroproliferation, immunotoxicity, and systemic responses in rodents. However, the search for representative biomarkers of exposure is an ongoing endeavor. Whole blood gene expression profiling is a promising new approach for the identification of novel disease biomarkers. We asked if the whole blood transcriptome reflects pathology-specific changes in lung gene expression caused by MWCNT. To answer this question, we performed mRNA sequencing analysis of the whole blood and lung in mice administered MWCNT or vehicle solution via pharyngeal aspiration and sacrificed 56 days later. The pattern of lung mRNA expression as determined using Ingenuity Pathway Analysis (IPA) was indicative of continued inflammation, immune cell trafficking, phagocytosis, and adaptive immune responses. Simultaneously, innate immunity-related transcripts (Plunc, Bpifb1, Reg3g) and cancer-related pathways were downregulated. IPA analysis of the differentially expressed genes in the whole blood suggested increased hematopoiesis, predicted activation of cancer/tumor development pathways, and atopy. There were several common upregulated genes between whole blood and lungs, important for adaptive immune responses: Cxcr1, Cd72, Sharpin, and Slc11a1. Trim24, important for T_H2 cell effector function, was downregulated in both datasets. Hla-dqa1 mRNA was upregulated in the lungs and downregulated in the blood, as was Lilrb4, which controls the reactivity of immune response. "Cancer" disease category had opposing activation status in the two datasets, while the only commonality was "Hypersensitivity". Transcriptome changes occurring in the lungs did not produce a completely replicable pattern in whole blood; however, specific systemic responses may be shared between transcriptomic profiles.

Single-walled carbon nanotubes repress viral-induced defense pathways through oxidative stress

Exposure of lung cells in vitro or mice to single-walled carbon nanotubes (SWCNTs) directly to the respiratory tract leads to a reduced host anti-viral immune response to infection with influenza A virus H1N1 (IAV), resulting in significant increases in viral titers. This suggests that unintended exposure to nanotubes via inhalation may increase susceptibility to notorious respiratory viruses that carry a high social and economic burden globally. However, the molecular mechanisms that contribute to viral susceptibility have not been elucidated. In the present study, we identified the retinoic acid-induced gene I (RIG-I) like receptors (RLRs)/mitochondrial antiviral signaling (MAVS) pathway as a target of SWCNT-induced oxidative stress in small airway epithelial cells (SAEC) that contribute to significantly enhanced influenza viral titers. Exposure of SAEC to SWCNTs increases viral titers while repressing several aspects of the RLR pathway, including mRNA expression of key genes (e.g. IFITs, RIG-I, MDA5, IFNβ1, CCL5). SWCNTs also reduce mitochondrial membrane potential without altering oxygen consumption rates. Our findings also indicate that SWCNTs can impair formation of MAVS prion-like aggregates, which is known to impede downstream activation of the RLR pathway and hence the transcriptional production of interferon-regulated anti-viral genes and cytokines. Furthermore, application of the antioxidant NAC alleviates inhibition of gene expression levels by SWCNTs, as well as MAVS signalosome formation, and increased viral titers. These data provide evidence of targeted impairment of anti-viral signaling networks that are vital to immune defense mechanisms in lung cells, contributing to increased susceptibility to IAV infections by SWCNTs.

Inhalation exposure to multi-walled carbon nanotubes alters the pulmonary allergic response of mice to house dust mite allergen

Background: Increasing evidence from rodent studies indicates that inhaled multi-walled carbon nanotubes (MWCNTs) have harmful effects on the lungs. In this study, we examined the effects of inhalation exposure to MWCNTs on allergen-induced airway inflammation and fibrosis. We hypothesized that inhalation pre-exposure to MWCNTs would render mice susceptible to developing allergic lung disease induced by house dust mite (HDM) allergen. Methods: Male B6C3F1/N mice were exposed by whole-body inhalation for 6 h a day, 5 d a week, for 30 d to air control or 0.06, 0.2, and 0.6 mg/m³ of MWCNTs. The exposure atmospheres were agglomerates (1.4-1.8 µm) composed of MWCNTs (average diameter 16 nm; average length 2.4 µm; 0.52% Ni). Mice then received 25 µg of HDM extract by intranasal instillation 6 times over 3 weeks. Necropsy was performed at 3 and 30 d after the final HDM dose to collect serum, bronchoalveolar lavage fluid (BALF), and lung tissue for histopathology. Results: MWCNT exposure at the highest dose inhibited HDM-induced serum IgE levels, IL-13 protein levels in BALF, and airway mucus production. However, perivascular and peribronchiolar inflammatory lesions were observed in the lungs of mice at 3 d with MWCNT and HDM, but not MWCNT or HDM alone. Moreover, combined HDM and MWCNT exposure increased airway fibrosis in the lungs of mice. Conclusions: Inhalation pre-exposure to MWCNTs inhibited HDM-induced TH2 immune responses, yet this combined exposure resulted in vascular inflammation and airway fibrosis, indicating that MWCNT pre-exposure alters the immune response to allergens.

Evaluation of total and inhalable samplers for the collection of carbon nanotube and carbon nanofiber aerosols

A growing number of carbon nanotubes and nanofibers (CNT/F) exposure and epidemiologic studies have utilized 25-mm and 37-mm open-faced cassettes (OFC) to assess the inhalable aerosol fraction. It has been previously established that the 37-mm OFC under-samples particles greater than 20 μm in diameter, but the size-selective characteristics of the 25-mm OFC have not yet been fully evaluated. This article describes an experimental study conducted to determine if the 25- and 37-mm OFCs performed with relative equivalence to a reference inhalable aerosol sampler when challenged with CNT/F particles. Side-by-side paired samples were collected within a small Venturi chamber using a 25-mm styrene OFC, 37-mm styrene OFC, 25-mm aluminum OFC, and Button Inhalable Aerosol Sampler. Three types of CNT/F materials and an Arizona road dust were used as challenge aerosols for the various sampler configurations. Repeated experiments were conducted for each sampler configuration and material. The OFC samplers operated at flow rates of 2 and 5 liters per minute. Results showed that the 25-mm OFC performed comparably to the Button Sampler when challenged with CNT/F aerosols, which was demonstrated in five of the six experimental scenarios with an average error of 20%. Overall, the results of this study indicate that the sampling efficiency of the 25- and 37-mm OFCs adequately followed the ISO/ACGIH/CEN inhalable sampling convention when challenged with CNT/F aerosols. Past exposure and epidemiologic studies that used these OFC samplers can directly compare their results to studies that have used other validated inhalable aerosol samplers.

Sampling Techniques on Collecting Fine Carbon Nanotube Fibers for Exposure Assessment

Carbon nanotube (CNT) sampling using an open-faced 25 mm cassette fiber sampling method and a newly developed direct sampling device was evaluated for the size fractioned analysis of collected airborne CNT fibers to improve the sampling and analytical methods. The open-faced 25 mm cassette fiber sampling method primarily collected large agglomerates, with the majority of collected particles being larger than two micrometer in size. Most of CNT structures collected by the new direct sampling device were individual fibers and clusters smaller than one micrometer with a high particle number concentration discrepancy compared to the open-faced 25 mm cassette method raising the concern of this sampling method to representatively characterize the respirable size fraction of CNT aerosols. This work demonstrates that a specialized technique is needed for collecting small fibers to provide a more representative estimate of exposure. It is recommended that an additional sampler be used to directly collect and analyze small fibers in addition to the widely accepted sampling method which utilizes an open-faced 25 mm cassette.

Current state of knowledge on the health effects of engineered nanomaterials in workers: a systematic review of human studies and epidemiological investigations

Objectives The widespread application of nano-enabled products and the increasing likelihood for workplace exposures make understanding engineered nanomaterial (ENM) effects in exposed workers a public and occupational health priority. The aim of this study was to report on the current state of knowledge on possible adverse effects induced by ENM in humans to determine the toxicological profile of each type of ENM and potential biomarkers for early detection of such effects in workers. Methods A systematic review of human studies and epidemiological investigations of exposed workers relative to the possible adverse effects for the most widely used ENM was performed through searches of major scientific databases including Web of Science, Scopus, and PubMed. Results Twenty-seven studies were identified. Most of the epidemiological investigations were cross-sectional. The review found limited evidence of adverse effects in workers exposed to the most commonly used ENM. However, some biological alterations are suggestive for possible adverse impacts. The primary targets of some ENM exposures were the respiratory and cardiovascular systems. Changes in biomarker levels compared with controls were also observed; however, limited exposure data and the relatively short period since the first exposure may have influenced the incidence of adverse effects found in epidemiological studies. Conclusions There is a need for longitudinal epidemiologic investigations with clear exposure characterizations for various ENM to discover potential adverse health effects and identify possible indicators of early biological alterations. In this state of uncertainty, precautionary controls for each ENM are warranted while further study of potential health effects continues.

Sirtuin 6 inhibits MWCNTs-induced epithelial-mesenchymal transition in human bronchial epithelial cells via inactivating TGF-β1/Smad2 signaling pathway

Multi-walled carbon nanotubes (MWCNTs) have been developed with numerous beneficial applications. However, rodent models demonstrate that exposure to MWCNTs via respiratory pathways results in pulmonary fibrosis. Therefore, they could elicit a potential risk of pulmonary fibrosis in humans due to occupational or consumer exposure. Sirtuin 6 (SIRT6), a nicotinamide adenine dinucleotide (NAD)-dependent deacetylase, has been proved to prevent fibrosis in the liver, renal and myocardial tissues. In this present study, we aimed to explore the role of SIRT6 in MWCNTs-induced epithelial-mesenchymal transition (EMT), one of the major contributor of lung fibrogenesis in human bronchial epithelial BEAS-2B cells. We found that the protein level of SIRT6 was elevated after exposure to MWCNTs in BEAS-2B cells. Overexpression of SIRT6 significantly inhibited MWCNTs-induced EMT and EMT-like cell behaviors in BEAS-2B cells. Moreover, wild-type SIRT6 was found to decrease MWCNTs-induced phosphorylation of Smad2, but not mutant SIRT6 (H133Y) without histone deacetylase activity. In conclusion, our study demonstrated that SIRT6 inhibited MWCNTs-induced EMT in BEAS-2B cells through TGF-β1/Smad2 signaling pathway, which depended on its deacetylase activity, and provided evidences that targeting SIRT6 could be a potential novel therapeutic strategy for MWCNTs-induced pulmonary fibrosis.

Multi-walled carbon nanotube oxidation dependent keratinocyte cytotoxicity and skin inflammation

BACKGROUND

The effects of carbon nanotubes on skin toxicity have not been extensively studied; however, our lab has previously shown that a carboxylated multi-walled carbon nanotube (MWCNT) exacerbates the 2, 4-dinitrofluorobenzene induced contact hypersensitivity response in mice. Here we examine the role of carboxylation in MWCNT skin toxicity.

RESULTS

MWCNTs were analyzed by transmission electron microscopy, zetasizer, and x-ray photoelectron spectroscopy to fully characterize the physical properties. Two MWCNTs with different levels of surface carboxylation were chosen for further testing. The MWCNTs with a high level of carboxylation displayed increased cytotoxicity in a HaCaT keratinocyte cell line, compared to the MWCNTs with intermediate levels of carboxylation. However, neither functionalized MWCNT increased the level of in vitro reactive oxygen species suggesting an alternative mechanism of cytotoxicity. Each MWCNT was tested in the contact hypersensitivity model, and only the MWCNTs with greater than 20% surface carboxylation exacerbated the ear swelling responses. Analysis of the skin after MWCNT exposure reveals that the same MWCNTs with a high level of carboxylation increase epidermal thickness, mast cell and basophil degranulation, and lead to increases in polymorphonuclear cell recruitment when co-administered with 2, 4-dinitrofluorobenzene.

CONCLUSIONS

The data presented here suggest that acute, topical application of low doses of MWCNTs can induce keratinocyte cytotoxicity and exacerbation of allergic skin conditions in a carboxylation dependent manner.

Carbon nanotube and nanofiber exposure and sputum and blood biomarkers of early effect among U.S. workers

BACKGROUND

Carbon nanotubes and nanofibers (CNT/F) are increasingly used for diverse applications. Although animal studies suggest CNT/F exposure may cause deleterious health effects, human epidemiological studies have typically been small, confined to single workplaces, and limited in exposure assessment.

OBJECTIVES

We conducted an industrywide cross-sectional epidemiological study of 108 workers from 12 U.S. sites to evaluate associations between occupational CNT/F exposure and sputum and blood biomarkers of early effect.

METHODS

We assessed CNT/F exposure via personal breathing zone, filter-based air sampling to measure background-corrected elemental carbon (EC) (a CNT/F marker) mass and microscopy-based CNT/F structure count concentrations. We measured 36 sputum and 37 blood biomarkers. We used factor analyses with varimax rotation to derive factors among sputum and blood biomarkers separately. We used linear, Tobit, and unconditional logistic regression models to adjust for potential confounders and evaluate associations between CNT/F exposure and individual biomarkers and derived factors.

RESULTS

We derived three sputum and nine blood biomarker factors that explained 78% and 67%, respectively, of the variation. After adjusting for potential confounders, inhalable EC and total inhalable CNT/F structures were associated with the most sputum and blood biomarkers, respectively. Biomarkers associated with at least three CNT/F metrics were 72 kDa type IV collagenase/matrix metalloproteinase-2 (MMP-2), interleukin-18, glutathione peroxidase (GPx), myeloperoxidase, and superoxide dismutase (SOD) in sputum and MMP-2, matrix metalloproteinase-9, metalloproteinase inhibitor 1/tissue inhibitor of metalloproteinases 1, 8-hydroxy-2'-deoxyguanosine, GPx, SOD, endothelin-1, fibrinogen, intercellular adhesion molecule 1, vascular cell adhesion protein 1, and von Willebrand factor in blood, although directions of associations were not always as expected.

CONCLUSIONS

Inhalable rather than respirable CNT/F was more consistently associated with fibrosis, inflammation, oxidative stress, and cardiovascular biomarkers.

Association of pulmonary, cardiovascular, and hematologic metrics with carbon nanotube and nanofiber exposure among U.S. workers: a cross-sectional study

BACKGROUND

Commercial use of carbon nanotubes and nanofibers (CNT/F) in composites and electronics is increasing; however, little is known about health effects among workers. We conducted a cross-sectional study among 108 workers at 12 U.S. CNT/F facilities. We evaluated chest symptoms or respiratory allergies since starting work with CNT/F, lung function, resting blood pressure (BP), resting heart rate (RHR), and complete blood count (CBC) components.

METHODS

We conducted multi-day, full-shift sampling to measure background-corrected elemental carbon (EC) and CNT/F structure count concentrations, and collected induced sputum to measure CNT/F in the respiratory tract. We measured (nonspecific) fine and ultrafine particulate matter mass and count concentrations. Concurrently, we conducted physical examinations, BP measurement, and spirometry, and collected whole blood. We evaluated associations between exposures and health measures, adjusting for confounders related to lifestyle and other occupational exposures.

RESULTS

CNT/F air concentrations were generally low, while 18% of participants had evidence of CNT/F in sputum. Respiratory allergy development was positively associated with inhalable EC (p=0.040) and number of years worked with CNT/F (p=0.008). No exposures were associated with spirometry-based metrics or pulmonary symptoms, nor were CNT/F-specific metrics related to BP or most CBC components. Systolic BP was positively associated with fine particulate matter (p-values: 0.015-0.054). RHR was positively associated with EC, at both the respirable (p=0.0074) and inhalable (p=0.0026) size fractions. Hematocrit was positively associated with the log of CNT/F structure counts (p=0.043).

CONCLUSIONS

Most health measures were not associated with CNT/F. The positive associations between CNT/F exposure and respiratory allergies, RHR, and hematocrit counts may not be causal and require examination in other studies.