As part of our ongoing surveillance of Canadians exposures to carcinogens, the CAREX team monitors evaluations by the International Agency for Research on Cancer (IARC). In October 2014, IARC gathered 21 experts from 10 countries to evaluate whether a selection of nanomaterials and fibers cause cancer.
The expert team looked specifically at fluoro-edenite, silicon carbide fibres and whiskers, and carbon nanotubes (including single-walled and multi-walled varieties). A summary of their conclusions for each nanomaterial is summarized below.
- Occupational exposures associated with manufacturing silicon carbide particles, called the Acheson process, were classified as carcinogenic (Group 1) based on sufficient evidence that they cause lung cancer in humans.
- Fibrous silicon carbide was classified as possibly carcinogenic (Group 2B) based on limited evidence in humans that it causes lung cancer.
- Silicon carbide whiskers were classified as probably carcinogenic to humans (Group 2A), rather than possibly carcinogenic to humans (Group 2B), because the physical properties of the whiskers resemble those of asbestos fibres, which are known carcinogens.
Virtually all the silicon carbide sold in the world is manufactured. This substance occurs in three forms: particles that are used in industry as an abrasive, fibres that are a by-product of particle manufacturing, and whiskers that are used as durable substitutes for asbestos.
- These fibres were classified as carcinogenic (Group 1) based on sufficient evidence that human exposure causes mesothelioma.
Fluoro-edenite is a mineral that can take the form of fibres similar to asbestos. Quarry products from Biancavilla in Italy, used to make unpaved roads in the area since the 1950s, are a source for airborne fluoro-edenite fibres. Exposures have also occurred via indoor air, as a result of the quarry’s products being used in building materials.
- A specific nanotube, multi-walled carbon nanotube-7 was classified as possibly carcinogenic(Group 2B) based on evidence showing that they caused mesotheliomas in male and female rats.
- All other multi-walled and single-walled carbon nanotubes were categorised as not classifiable as to their carcinogenicity to humans (Group 3) due to insufficient evidence.
Carbon nanotubes consist of either a single cylinder of carbon (single-walled), with an outer diameter of 1–3 nm, or of multiple carbon cylinders arranged in layers (multi-walled) with diameters of 10–200 nm. The characteristics of carbon nanotubes vary depending on how they’re produced. They can be used to improve the structural integrity of fabrics, plastics, rubbers, electronics (i.e. in transistors and solar cells), and structural materials, as well as in medicine (i.e. drug delivery and bone tissue engineering). More information can be found on our carbon nanotubes profile.
The full IARC Monograph Volume 111: Some Nanomaterials and Some Fibres is available here.
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