Carbon Nanotubes Exposure Risk Assessment: From Toxicology to Epidemiologic Studies (Overview of the Current Problem)

Our plain-English summary of Carbon Nanotubes Exposure Risk Assessment: From Toxicology to Epidemiologic Studies (Overview of the Current Problem), by L.M. Fatkhutdinova, T.O. Khaliullin, A.A. Shvedova (Nanotechnologies in Russia, 2015).

The study

• Authors: L.M. Fatkhutdinova, T.O. Khaliullin, A.A. Shvedova
• Journal: Nanotechnologies in Russia
• Published: 2015;10(5):501-509
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Nanoscale size and fiber like structure of carbon nanotubes (CNTs) may determine high reactivity and penetration, as well as the pathogenicity of asbestos and other mineral fibers. Despite many in vitro and in vivo studies, the absence of full-scale data on CNT effects on human health clearly point out the necessity for epidemiological studies. Currently, several projects are initiated worldwide on studying health risks associated with the inhalation of industrial CNTs, including NIOSH-promoted research (United States), the European CANTES study, and the Russian CNT-ERA project. Studies comprising several successive steps, such as CNT exposure assessment in occupational settings, toxicological evaluation, and epidemiological observations, are critical for determining material safety and use criteria.

In plain English

This article was a review, not a new study of people or animals. The authors surveyed research on carbon nanotubes, tiny carbon fibers that they noted may behave like asbestos and other mineral fibers. Reviewed animal and cell experiments included a 2008 study in which genetically tumor-prone mice were injected in the abdomen with 3 mg of multiwalled carbon nanotubes or crocidolite asbestos; mesothelioma was induced in both cases, but the study was criticized for using too high a dose. They described human reports, including World Trade Center responders: carbon nanotubes, along with other dust particles, were found in lung biopsies of four of seven severely affected people; the authors noted these tubular structures formed at high combustion temperatures. Recommended exposure levels for different carbon nanotubes worldwide ranged from 1 to 50 μg/m3 as 8-hour time-weighted averages. They also outlined their own Russian study, CNT-ERA, begun in 2011, which was repeatedly sampling workers and a control group. The authors concluded that studies of exposed people are urgently needed and that projects combining exposure measurement, toxicology and epidemiology are most promising.

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 (overview) of toxicology, workplace exposure, epidemiology and exposure-limit literature on carbon nanotubes, with a description of the authors' own ongoing study protocol (CNT-ERA)
• Who was studied: No new population was studied. The review covered published animal experiments (mice, rats), cell-culture studies, and human reports and studies. It also described the authors' Russian CNT-ERA study, begun in 2011 at enterprises producing multiwalled carbon nanotubes, which involves workers and a control group.
• Exposure: Single-walled and multiwalled carbon nanotubes (SWCNTs, MWCNTs), compared in some reviewed experiments with asbestos (crocidolite), quartz and carbon black. Exposure routes were inhalation, pharyngeal aspiration, intratracheal instillation and intraperitoneal injection.
• Main results:
  • In a 2008 experiment by Takagi et al., p53 heterozygous mice (genetically at high risk of tumors) were given 3 mg of MWCNTs or crocidolite asbestos into the abdominal cavity. Mesothelioma was induced in both cases. The experiment was criticized because the dose was too high.
  • In a 2008 study by Poland et al., in which mice were injected intraperitoneally at a dose of 50 μg, both asbestos and MWCNTs caused significant protein exudation and the formation of granulomas.
  • In November 2014, the International Agency for Research on Cancer classified MWCNT-7 (produced by Mitsui, Japan) as Group 2B, possibly carcinogenic to humans.
  • Of 12 891 people examined in the World Trade Center screening program, lung biopsy was performed in seven of the most severe cases. Four of these patients had carbon nanotubes along with other dust particles in their biopsy samples.
  • The authors stated that at the World Trade Center site, high combustion temperatures contributed to the formation of tubular carbon nanostructures that were very similar to artificial carbon nanotubes.
  • A 2009–2010 Taiwan study of 13 nanoparticle-using companies found a decrease in total antioxidant protection and an increase in cardiovascular markers. That study did not divide workers by specific type of nanoparticle.
  • Researchers on the CANTES study, whose results had not yet been published as articles, reported increased levels of proinflammatory cytokines in the study group compared to the controls.
  • Recommended exposure levels for different carbon nanotubes worldwide varied from 1 to 50 μg/m3 as 8-hour time-weighted averages. NIOSH set a recommended exposure level for all types of carbon nanotubes of 1 μg/m3 in April 2013.
  • The Russian safe exposure levels for single-walled nanotubes (2010) were guided by a level of 0.01 fibers/m3, as printed, which was suggested by the British Standards Institution and calculated as 1/10 of the maximum allowable level for asbestos fibers.
  • From their own toxicology experiments, the authors selected TGF-b, osteopontin and KL-6 as biomarkers for the CNT-ERA study. They reported that the Russian recommended method of counting nanotubes by electron microscopy did not allow an objective assessment of carbon nanotube content in air, because the particles clump together rapidly.
• The authors' conclusion: The authors concluded that experiments established pronounced local profibrogenic (scar-promoting) effects of carbon nanotubes on lung tissue. They concluded that studies in exposed people are urgently needed, that a panel study is the most favorable design at present, and that complex projects combining exposure assessment, toxicology and epidemiology are the most promising.
• Limitations the authors state:
  • The authors stated that early research used high doses and laboratory-purified rather than industrial nanotubes, used exposure models poorly related to real working conditions, and lacked data on actual exposure.
  • The authors stated that human data on carbon nanotube health effects are insufficient and that the group of exposed persons is still relatively small.

Topics

Medical terms in this study, explained in our Lexicon: Mineral Fiber, NIOSH.

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