Potential Occupational Risks Associated with Pulmonary Toxicity of Carbon Nanotubes

Our plain-English summary of Potential Occupational Risks Associated with Pulmonary Toxicity of Carbon Nanotubes, by A. Manke, S. Luanpitpong, Y. Rojanasakul (Occupational Medicine & Health Affairs, 2014).

The study

• Authors: A. Manke, S. Luanpitpong, Y. Rojanasakul
• Journal: Occupational Medicine & Health Affairs
• Published: 2014;2
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Given their remarkable properties, carbon nanotubes (CNTs) have made their way through various industrial and medicinal applications and the overall production of CNTs is expected to grow rapidly in the next few years, thus requiring an additional recruitment of workers. However, their unique applications and desirable properties are fraught with concerns regarding occupational exposure. The concern about worker exposure to CNTs arises from the results of recent animal studies. Short-term and sub-chronic exposure studies in rodents have shown consistent adverse health effects such as pulmonary inflammation, granulomas, fibrosis, genotoxicity and mesothelioma after inhalation or instillation of several types of CNTs. Furthermore, physicochemical properties of CNTs such as dispersion, functionalization and particle size can significantly affect their pulmonary toxicity. Risk estimates from animal studies necessitate implementation of protective measures to limit worker exposure to CNTs. Information on workplace exposure is very limited, however, studies have reported that CNTs can be aerosolized and attain respirable airborne levels during synthesis and processing activities in the workplace. Quantitative risk assessments from sub-chronic animal studies recommend the health-based need to reduce exposures below the recommended exposure limit of 1 µg/m3. Practice of prevention measures including the use of engineering controls, personal protective equipment, health surveillance program, safe handling and use, as well as worker training can significantly minimize worker exposure and improve worker health and safety.

In plain English

This article was a narrative review of published research on the lung effects of carbon nanotubes (CNTs). CNTs are very thin, fiber-like materials made in two forms, single-walled (SWCNT) and multi-walled (MWCNT). It is not a study of asbestos. Asbestos appears only as a point of comparison. The authors searched PubMed, Ebscohost, Web of Science and Medline. They reported that there were no published reports of health effects in workers handling CNTs, and that risk estimates for workers were extrapolated from rodent studies. The animal studies they reviewed described lung inflammation, granulomas and fibrosis in mice. They also described mesothelioma after MWCNT was injected into the peritoneal cavity of mice or rats. Studies they cited measured airborne CNT levels of 0.7 to 53 µg/m3, and as high as 430 µg/m3 during some laboratory tasks. They described a NIOSH recommended exposure limit of 1 µg/m3. The authors concluded that the key is to prevent and minimize exposure through workplace controls, safety equipment and worker training. They noted that information on workplace exposure is limited.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: narrative review of published literature
• Who was studied: Published studies, mainly animal (rodent) and laboratory cell studies plus workplace and laboratory air measurements, identified through searches of PubMed, Ebscohost, Web of Science and Medline; no human health studies of CNT workers were available
• Exposure: Carbon nanotubes, both single-walled (SWCNT) and multi-walled (MWCNT); not asbestos
• Main results:
  • The authors stated there were no published reports of adverse health effects in workers handling CNTs
  • In a reviewed mouse study, pharyngeal aspiration of SWCNT at 10–40 µg per mouse induced acute inflammation, early granulomas, alveolar wall thickening and progressive fibrosis
  • In reviewed animal studies, MWCNT injected into the peritoneal cavity of mice or rats produced fiber length-dependent inflammation or genetic damage and mesothelioma
  • An initial workplace and laboratory measurement study cited in the review found CNT mass concentrations of 0.7 to 53 µg/m3
  • Later cited studies found airborne CNT levels as high as 430 µg/m3 during weighing, transfer, cutting and sonication in a laboratory setting
  • Cited studies indicated that conventional industrial measures such as local exhaust ventilation, wet cutting and fume hoods or enclosures reduced airborne levels
  • NIOSH proposed a recommended exposure limit (REL) of 1 µg/m3 for CNTs, based on animal studies
  • As described by the authors, the NIOSH report stated that workers exposed at the REL over a working lifetime of about 45 years may have a more than 10% higher risk of early-stage pulmonary fibrosis
  • Early studies proposed a benchmark occupational exposure limit of 0.01 fiber/cm3 for CNT, based on an existing asbestos limit
  • Later studies suggested occupational exposure limits for CNT ranging from 1 to 50 µg/m3
• The authors' conclusion: The authors concluded that the key is to prevent and minimize inadvertent exposure now through workplace controls, safety equipment and worker training
• Limitations the authors state:
  • Occupational risk estimates are extrapolated from rodent models because safety guidelines and biomarkers for workplace exposure are lacking
  • Information on how much workers are actually exposed is limited
  • It is not known how airborne CNTs in workplaces compare in size and structure to CNTs used in animal and laboratory studies

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Inflammation, Granuloma, Fibrosis, Genotoxicity, Mesothelioma, Engineering Controls.

Related studies

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• Mechanisms of pulmonary toxicity and medical applications of carbon nanotubes: Two faces of Janus? — A.A. Shvedova, E.R. Kisin, et al. (2009)
• Comparative proteomics and pulmonary toxicity of instilled single-walled carbon nanotubes, crocidolite asbestos, and ultrafine carbon black in mice — J.G. Teeguarden, B.J. Webb-Robertson, et al. (2011)
• Conventional and novel "omics"-based approaches to the study of carbon nanotubes pulmonary toxicity — C. Ventura, A. Sousa-Uva, et al. (2018)
• Review of carbon nanotubes toxicity and exposure--appraisal of human health risk assessment based on open literature — K. Aschberger, H.J. Johnston, et al. (2010)
• Effect of surface functionalizations of multi-walled carbon nanotubes on neoplastic transformation potential in primary human lung epithelial cells — T.A. Stueckle, D.C. Davidson, et al. (2017)

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