Real-Time Emission and Exposure Measurements of Multi-walled Carbon Nanotubes during Production, Power Sawing, and Testing of Epoxy-Based Nanocomposites (original) (raw)
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The Annals of occupational hygiene, 2014
While production and use of carbon nanotubes (CNTs) is increasing, workers exposure to CNTs is expected to increase as well, with inhalation being potentially the main pathway for uptake. However, there have been few studies reporting results about workers' personal exposure to CNTs. In this study, worker exposure to single-walled CNTs (SWCNTs) during the production of conductive films in a modern up-scaling factory was assessed. Particulate matter concentrations (2.5-10 μm) and concentrations of CO and CO2 were monitored by using real-time instruments. Workers' exposure levels to SWCNTs were qualitatively estimated by analyzing particle samples by transmission electron microscopy (TEM). TEM samples identified high aspect ratio (length/width > 500) SWCNTs in workplace air. SWCNT concentrations estimated from micrographs varied during normal operation, reactor use without local exhaust ventilation (LEV), and cleaning between 1.7×10(-3), 5.6 and 6.0×10(-3) SWCNT cm(-3), res...
Detection of Carbonaceous Aerosols Released in CNT Workplaces Using an Aethalometer
The Annals of occupational hygiene, 2016
Black carbon (BC) originating from various combustion sources has been extensively surveyed to characterize the effects of BC on global warming and human health, and many online monitors are available. In this study, BC was considered as a surrogate for carbon-based nanomaterials in an occupational health study. Specifically, BC concentrations were monitored continuously with an aethalometer for 24h at four carbon nanotube (CNT) workplaces located in rural, urban, and industrial areas, which had different background air pollution levels. Average BC concentrations for both nonworking (background) and working periods were compared with the recommended exposure limit (REL) of 1 μg m(-3) for elemental carbon that was suggested by the National Institute for Occupational Safety and Health (NIOSH). Diurnal variation of BC concentrations indicated that BC measurements corresponded well with carbonaceous aerosols such as vehicle exhaust particles and CNT aerosols. In the rural CNT workplace,...
Exposure assessment of carbon nanotube manufacturing workplaces
Inhalation Toxicology, 2010
Seven CNT (carbon nanotube) handling workplaces were investigated for exposure assessment. Personal sampling, area sampling, and real-time monitoring using an SMPS (scanning mobility particle sizer), dust monitor, and aethalometer were performed to characterize the mass exposure, particle size distribution, and particle number exposure. No workplace was found to exceed the current ACGIH (American Conference of Governmental Industrial Hygienists) TLVs (threshold limit values) and OELs (occupational exposure levels) set by the Korean Ministry of Labor for carbon black (3.5 mg/m 3), PNOS (particles not otherwise specified; 3 mg/m 3), and asbestos (0.1 fiber/cc). Nanoparticles and fine particles were most frequently released after opening the CVD (chemical vapor deposition) cover, followed by catalyst preparation. Other work processes that prompted nanoparticle release included spraying, CNT preparation, ultrasonic dispersion, wafer heating, and opening the water bath cover. All these operation processes could be effectively controlled with the implementation of exposure mitigation, such as engineering control, except at one workplace where only natural ventilation was used.
Annals of Work Exposures and Health
To date there is no consensus about the most appropriate analytical method for measuring carbon nanotubes (CNTs), hampering the assessment and limiting the comparison of data. The goal of this study is to develop an approach for the assessment of the level and nature of inhalable multi-wall CNTs (MWCNTs) in an actual workplace setting by optimizing and evaluating existing analytical methods. In a company commercially producing MWCNTs, personal breathing zone samples were collected for the inhalable size fraction with IOM samplers; which were analyzed with carbon analysis, inductively coupled plasma mass spectrometry (ICP-MS) and scanning electron microscopy/ energy dispersive X-ray spectroscopy (SEM/EDX). Analytical methods were optimized for carbon analysis and SEM/EDX. More specifically, methods were applied and evaluated for background correction using carbon analyses and SEM/EDX, CNT structure count with SEM/EDX and subsequent mass conversion based on both carbon analyses and SEM/EDX. A moderate-to-high concordance correlation coefficient (R C) between carbon analyses and SEM/EDX was observed [R C = 0.81, 95% confidence interval (CI): 0.59-0.92] with an absolute mean difference of 59 µg m −3. A low R C between carbon analyses and ICP-MS (R C = 0.41, 95% CI: 0.07-0.67) with an absolute mean difference of 570 µg m −3 was observed. The large absolute difference between EC and metals is due to the presence of non-embedded inhalable catalyst particles, as a result of which MWCNT concentrations were over-This article contains public sector information licensed under the Open Government Licence v3.0(http://www.nationalarchives.gov.uk/doc/ open-government-licence/version/3/).
Evaluation of airborne particle emissions from commercial products containing carbon nanotubes
Journal of Nanoparticle Research, 2012
The emission of the airborne particles from epoxy resin test sticks with different carbon nanotube (CNT) loadings and two commercial products were characterized while sanding with three grit sizes and three disk sander speeds. The total number concentrations, respirable mass concentrations, and particle size number/mass distributions of the emitted particles were measured using a condensation particle counter, an optical particle counter, and a scanning mobility particle sizer. The emitted particles were sampled on a polycarbonate filter and analyzed using electron microscopy. The highest number concentrations (arithmetic mean = 4,670 particles/cm 3 ) were produced with coarse sandpaper, 2 % (by weight) CNT test sticks and medium disk sander speed, whereas the lowest number concentrations (arithmetic mean = 92 particles/cm 3 ) were produced with medium sandpaper, 2 % CNT test sticks and slow disk sander speed. Respirable mass concentrations were the highest (arithmetic mean = 1.01 mg/m 3 ) for fine sandpaper, 2 % CNT test sticks and medium disk sander speed and the lowest (arithmetic mean = 0.20 mg/m 3 ) for medium sandpaper, 0 % CNT test sticks and medium disk sander speed. For CNT-epoxy samples, airborne particles were primarily micrometer-sized epoxy cores with CNT protrusions. No free CNTs were observed in airborne samples, except for tests conducted with 4 % CNTepoxy. The number concentration, mass concentration, and size distribution of airborne particles generated when products containing CNTs are sanded depends on the conditions of sanding and the characteristics of the material being sanded.
Annals of Occupational Hygiene, 2011
Research Significance: Toxicological evidence suggests the potential for a wide range of health effects, which could result from exposure to carbon nanotubes (CNTs) and carbon nanofibers (CNFs). The National Institute for Occupational Safety and Health (NIOSH) has proposed a recommended exposure limit (REL) for CNTs/CNFs at the respirable size fraction. The current literature is lacking exposure information, with few studies reporting results for personal breathing zone (PBZ) samples in occupational settings. To address this gap, exposure assessments were conducted at six representative sites identified as CNT/CNF primary or secondary manufacturers.
Laboratory evaluation of a personal aethalometer for assessing airborne carbon nanotube exposures
Journal of Occupational and Environmental Hygiene
Aethalometers are direct-reading instruments primarily used for measuring black carbon (BC) concentrations in workplace and ambient atmospheres. Aethalometer BC measurements of carbon nanotubes (CNTs) were compared to measurements made by other methods when subjected to high (>30 mg/m 3) and low (1-30 mg/m 3) CNT aerosol concentrations representing worst-case and typical workplace concentrations, respectively. A laboratory-based system was developed to generate carbon black, as an example of a nearly pure carbon, micron-sized aerosol, and two forms of multi-walled carbon nanotubes (CNTs): small-diameter (<8 nm) and large-diameter (50-80 nm). High-concentration trials were conducted during which a scanning mobility particle sizer (SMPS) was used to track particle count concentrations over time. Relative to the behavior of the SMPS counts over time, aethalometer readings exhibited a downward drift, which is indicative of aethalometer response subjected to high BC loading on the receiving filter of the instrument. A postsample mathematical method was applied that adequately corrected for the drift. Low-concentration trials, during which concentration drift did not occur, were conducted to test aethalometer accuracy. The average BC concentration during a trial was compared to elemental carbon (EC) concentration sampled with a quartz-fiber filter and quantified by NIOSH Method 5040. The CB and large-diameter CNT concentrations measured with the aethalometer produced slopes when regressed on EC that were not significantly different from unity, whereas the small-diameter CNTs were under-sampled by the aethalometer relative to EC. These results indicate that aethalometer response may drift when evaluating CNT exposure scenarios, such as cleaning and powder handling, that produce concentrations >30 mg/m 3. However, aethalometer accuracy remains consistent over time when sampling general work zones in which CNT concentrations are expected to be <30 mg/m 3. A calibration check of aethalometer response relative to EC measured with Method 5040 is recommended to ensure that the aethalometer readings are not under sampling CNT concentrations as occurred with one of the CNTs evaluated in this study.
Three-Day Continuous Exposure Monitoring of CNT Manufacturing Workplaces
BioMed research international, 2015
Continuous monitoring for possible exposure to carbon nanotubes was conducted over a period of 2 to 3 days at workplaces that manufacture multiwall carbon nanotubes (MWCNTs) and single wall carbon nanotubes (SWCNTs). To estimate the potential emission of carbon nanotubes (CNTs) and potential exposure of workers, personal sampling, area monitoring, and real-time monitoring using an scanning mobility particle sizer (SMPS) and dust monitor were conducted at workplaces where the workers manufactured CNTs. The personal and area sampling of the total suspended particulate (TSP) at the MWCNT manufacturing facilities ranged from 0.031 to 0.254 and from N.D (not detected) to 0.253 mg/m(3), respectively. This 2- to 3-day monitoring study found that nanoparticles were released when opening the chemical vapor deposit (CVD) reactor door after the synthesis of MWCNTs, when transferring the MWCNTs to containers and during blending and grinding. However, distinguishing the background concentration ...
Carbon nanotube dosimetry: from workplace exposure assessment to inhalation toxicology
Particle and Fibre Toxicology
Dosimetry for toxicology studies involving carbon nanotubes (CNT) is challenging because of a lack of detailed occupational exposure assessments. Therefore, exposure assessment findings, measuring the mass concentration of elemental carbon from personal breathing zone (PBZ) samples, from 8 U.S.-based multi-walled CNT (MWCNT) manufacturers and users were extrapolated to results of an inhalation study in mice. Upon analysis, an inhalable elemental carbon mass concentration arithmetic mean of 10.6 mug/m3 (geometric mean 4.21 mug/m3) was found among workers exposed to MWCNT. The concentration equates to a deposited dose of approximately 4.07 mug/d in a human, equivalent to 2 ng/d in the mouse. For MWCNT inhalation, mice were exposed for 19 d with daily depositions of 1970 ng (equivalent to 1000 d of a human exposure; cumulative 76 yr), 197 ng (100 d; 7.6 yr), and 19.7 ng (10 d; 0.76 yr) and harvested at 0, 3, 28, and 84 d post-exposure to assess pulmonary toxicity. The high dose showed ...
Annals of Occupational Hygiene, 2014
The production and use of carbon nanotubes (CNTs) is rapidly growing. With increased production, there is potential that the number of occupational exposed workers will rapidly increase. Toxicological studies on rats have shown effects in the lungs, e.g. inflammation, granuloma formation, and fibrosis after repeated inhalation exposure to some forms of multi-walled CNTs (MWCNTs). Still, when it comes to health effects, it is unknown which dose metric is most relevant. Limited exposure data for CNTs exist today and no legally enforced occupational exposure limits are yet established. The aim of this work was to quantify the occupational exposures and emissions during arc discharge production, purification, and functionalization of MWCNTs. The CNT material handled typically had a mean length <5 μm. Since most of the collected airborne CNTs did not fulfil the World Health Organization fibre dimensions (79% of the counted CNT-containing particles) and since no microscopy-based method for counting of CNTs exists, we decided to count all particle that contained CNTs. To investigate correlations between the used exposure metrics, Pearson correlation coefficient was used.