Carbon Nanotubes Profile

Carbon Nanotubes Profile

QUICK SUMMARY

  • Manufactured materials commonly used for structural reinforcement because they result in a product with high strength and low weight; has applications in nanotechnology, electronics, and optics
  • Associated cancer: Specific types of CNTs are linked to lung cancer in animals
  • Most important routes of exposure: Inhalation, skin contact
  • Occupational exposures: Workers may be exposed when generating and applying the material, especially when handling it as a dry powder
  • Environmental exposures: The general public may be exposed as CNT-containing consumer products weather over time
  • Fast fact: CNTs have been called the “new asbestos”, but while they share similar properties to asbestos fibres, usage is not as widespread and the health risks are less well-understood.

General Information

Carbon nanotubes (CNTs) are a diverse group of materials made from graphene sheets, which are hollow filaments of carbon one-atom in thickness. They can be various lengths and sizes, depending on their end purpose and how they are produced. Single walled carbon nanotubes (SWCNT) are constructed with one cylindrical sheet of graphene, while multi walled carbon nanotubes (MWCNT) consist of multiple concentric tubes or layers of graphene.[1] In general, the outer diameter of MWCNT is 10–200 nm,[2] however this can vary based on the number of layers and atomic structure.

There is currently little evidence of carcinogenicity for SWCNT and MWCNT, which are currently classified by IARC as Group 3 (not classifiable as to their carcinogenicity to humans). One specific type of MWCNT called MWCNT-7 is classified as Group 2B (possibly carcinogenic to humans).[3,4] The MWCNT-7 type of nanotubes are long and narrow with similarities in form to asbestos fibres.[5] Research on rodents found that exposure to MWCNTs can cause mesothelioma (a cancer of the organ linings, especially lung) and lung cancer.[6,7,8] The ratio of nanotube length to width and curvature of the CNTs seems to be an important factor in determining carcinogenicity.[9]

Since nanotechnology is a relatively new field and there are many different types of carbon nanotubes, it is challenging to classify potential health risks. CNTs are different than carbon nano-fibres (CNFs) which are much larger and do not always have the same structure.[10] To date there is limited evidence of human health effects of CNTs, but studies on animals have found adverse pulmonary effects including inflammation, granulomas, and pulmonary fibrosis.[10]

Regulations and Guidelines

Carbon nanotubes were not included in the Canadian government environmental guidelines reviewed.[11,12,13,14,15,16,17,18]

Other organizations have recommended occupational exposure limits within the range of 1–50 μg/m3, but as of yet, these are guidelines only.[19,20,21]

Main Uses

CNTs are strong, flexible, lightweight, heat resistant, and have high electrical conductivity,[22,23] which makes them ideal for use in electronics (including tablets and phones), batteries, solar cells, automotive parts, sporting goods (tennis rackets, baseball bats, bicycle frames), bulletproof vests, polymer composites, adhesives, electronics, imaging, and inks.[10] CNTs are also used in pharmaceutical and biomedical devices for bone grafting, tissue repair, medical diagnosis, and drug delivery.[24] Another use of CNTs is in water filters to clean pollutants out of contaminated water,[25] however further research is needed to determine whether there are health and/or environmental consequences associated with this application. The physical properties of CNTs make them an ideal material for many applications and these uses are likely to continue to expand in the coming years.

Canadian Production and Trade

No information was available on the production and trade of carbon nanotubes in Canada.[26]

Environmental Exposures Overview

The most significant route of CNT exposure for the general Canadian population is likely inhalation.[27,28] This may occur through wear and tear of CNT products via contact with CNTs during usage or disposal.[29] Release of CNTs has also been reported during the burning of natural gas, propane, and methane gases via indoor gas stoves for cooking, but also via outdoor industrial burning sites.[30,31]

Occupational Exposures Overview

The main route of occupational exposure is inhalation, however dermal exposure may also occur. Research and development along with manufacturing and applications are sites where higher airborne exposure may occur.[10] CNTs can enter the air during activities such as drilling and cutting, and while transferring, blending, and mixing the powders.[10] Having proper ventilation, using a respirator, wearing protective clothing (gloves, eyewear), showering, and changing clothes at the end of the workday are recommended methods to minimize exposure in the occupational setting. It’s also important to not consume food or beverages in areas where CNTs are constructed or handled, as this is another way they can enter your body.[10]

Sources

Photo: Wikimedia Commons, Eric Wieser

1. Murray AR, Kisin ER, Tkach AV, Yanamala N, Mercer R, Young SH, Fadeel B, Kagan VE, Shvedova AA. “Factoring-in agglomeration of carbon nanotubes and nanofibers for better prediction of their toxicity versus asbestos”. Part Fibre Toxicol2012;9:10.
2. Hou PX, Xu ST, Ying Z, Yang QH, Liu C, Cheng HM. “Hydrogen adsorption/desorption behavior of multi-walled carbon nanotubes with different diameters”. Carbon 2003;41:2471-2476.
3. Grosse Y, Loomis D, Guyton KZ, Lauby-Secretan B, El Ghissassi F, Bouvard V, Benbrahim-Tallaa L, Guha N, Scoccianti C, Mattock H, Straif K. “Carcinogenicity of fluoro-edenite, silicon carbide fibres and whiskers, and carbon nanotubes”. Lancet Oncol2014;15:1427-1428.
5. Takagi A, Hirose A, Nishimura T, Fukumori N, Ogata A, Ohashi N, Kitajima S, Kanno J. “Induction of mesothelioma in p53+/− mouse by intraperitoneal application of multi‐wall carbon nanotube”. J Toxicol Sci 2008;33:105-116.
6. Sakamoto Y, Nakee D, Fukumori N, Tayama K, Maekawa A, Imai K, Hirose A, Nishimura T, Ohashi N, Ogata A. “Induction of mesothelioma by a single intrascrotal administration of multi-wall carbon nanotube in intact male Fischer 344 rats”. J Toxicol Sci2009;34:65-76.
8. Sargent LM, Porter DW, Staska LM, Hubbs AF, Lowry DT, Battelli L, Siegrist KJ, Kashon ML, Mercer RR, Bauer AK, Chen BT, Salisbury JL, Frazer D, McKinney W, Andrew M, Tsuruoka S, Endo M, Fluharty KL, Castranova V, Reynolds SH. “Promotion of lung adenocarcinoma following inhalation exposure to multi-walled carbon nanotubes”. Part Fibre Toxicol 2014;11:3
9. Rittinghausen S, Hackbart A, Creutzenberg O, Ernst H, Heinrich U, Leonhardt A, Schaudien D. “The carcinogenic effect of various multi-walled carbon nanotubes (MWCNTs) after intraperitoneal injection in rats”. Part Fibre Toxicol 2014;11:59.
10. Department of Health and Human Services. Occupational Exposure to Carbon Nanotubes and Nanofibers (2013) (PDF)
14. Health Canada. Cosmetic Ingredient Hotlist (2014)
16. The Canadian Legal Information Institute (CanLII). Regulation respecting the quality of drinking water, CQLR c Q-2, r 40 (2014)
17. Ontario Ministry of the Environment and Climate Change. Ontario’s Ambient Air Quality Criteria (2016)
18. Alberta Environment and Parks. Ambient Air Quality Objectives (2017)
20. Aschberger K, Johnston HJ, Stone V, Aitken RJ, Hankin SM, Peters SA, Tran CL, Christensen FM. “Review of carbon nanotubes toxicity and exposure—appraisal of human health risk assessment based on open literature”. Crit Rev Toxicol 2010;40:759-790.
22. Walters A, Ericson LM, Casavant MJ, Liu J, Col¬bert DT, Smith KA, Smalley RE. “Elastic strain of freely suspended single-walled carbon nanotube ropes”. Appl Phys Lett 1999;74:3803.
23. Yu M-F, Louire O, Dyer MJ, Moloni K, Kelly TF, Ruoff RS. “The strength and breaking mechanism of multiwalled carbon nanotubes under tensile load”. Science 2000;287:637-640.
24. Milne WI, Mann M, Dijon J, Bachmann P, McLaugh¬lin J, Robertson J, Teo KBK, Lewalter A, de Souza M, Boggild P, Briggs A, Mogensen KB, Gabriel J-CP, Roche S, Baptist R. “Carbon nanotubes”. E-Nano Newsletter 2008;13:5-32.
25. Mauter MS, Elimelech M. “Environmental applications of carbon-based nanomaterials”. Environ Sci Technol 2008;42:5843–5859.
26. International Trade Centre. TradeMap (Free subscription required)
27. Monteiro-Riviere NA, Nemanich RJ, Inman AO, Wang YY, Riviere JE. “Multi-walled carbon nanotube interactions with human epidermal keratinocytes”. Toxicol Lett 2005;155:377-384.
28. Donaldson K, Aitken R, Tran L, Stone V, Duffin R, Forrest G, Alexander A. “Carbon nanotubes: a review of their properties in relation to pulmonary toxicology and workplace safety”. Toxicol Sci 2006;92:5-22.
29. Kingston, C, Zepp R, Andrady A, Bovergof D, Fehir R, Hawkins D, Roberts J, Sayre P, Shelton B, Sultan Y, Vejins C, Wohlleben W. “Release characteristics of selected carbon nanotube polymer composites”. Carbon 2014;68:33-57.
31. Murr LE, Bang JJ, Lopez DA, Guerrero PA, Esquivel EV. “Carbon nanotubes and nanocrystals in methane combustion and the environmental implications”. J Mater Sci 2004;39:2199–2204.

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