A Mar. 11, 2013 news item on Nanowerk reveals some of the latest research performed by US National Institute of Occupational Health Safety (NIOSH) researchers into the question of whether or not multi-walled carbon nanotubes (MWCNT) cause cancer,
Earlier today, at the annual meeting of the Society of Toxicology, NIOSH researchers reported preliminary findings from a new laboratory study in which mice were exposed by inhalation to multi-walled carbon nanotubes (MWCNT). The study was designed to investigate whether these tiny particles have potential to initiate or promote cancer. By “initiate,” we mean the ability of a substance to cause mutations in DNA that can lead to tumors. By “promote,” we mean the ability of a substance to cause cells that have already sustained such DNA mutations to then become tumors.
It is very important to have new data that describe the potential health hazards that these materials might represent, so that protective measures can be developed to ensure the safe advancement of nanotechnology in the many industries where it is being applied.
The Mar. 11, 2013 posting (which originated the news item) by Vincent Castranova, PhD; Charles L Geraci, PhD; Paul Schulte, PhD on the NIOSH blog provides details about the experimental protocols and the outcome of the experiments,
In the NIOSH study, a group of laboratory mice were injected with a chemical that is a known cancer initiator, methylcholanthrene. Another group of mice were injected with a saline solution as a control group. The mice then were exposed by inhalation either to air or to a concentration of MWCNT. These protocols enabled the researchers to investigate whether MWNCT alone would initiate cancer in mice, or whether MWCNT would promote cancer where the initiator, methylcholanthrene, had already been applied.
Mice receiving both the initiator chemical plus exposure to MWCNT were significantly more likely to develop tumors (90% incidence) and have more tumors (an average of 3.3 tumors/mouse lung) than mice receiving the initiator chemical alone (50% of mice developing tumors with an average of 1.4 tumors/lung). Additionally, mice exposed to MWCNT and to MWCNT plus the initiator chemical had larger tumors than the respective control groups. The number of tumors per animal exposed to MWCNT alone was not significantly elevated compared with the number per animal in the controls. These results indicate that MWCNT can increase the risk of cancer in mice exposed to a known carcinogen. The study does not suggest that MWCNTs alone cause cancer in mice.
That last sentence is quite important because (from the NIOSH blog post),
Several earlier studies in the scientific literature indicated that MWCNT could have the potential to initiate or promote cancer. The new NIOSH study is the first to show that MWCNT is a cancer promoter in a laboratory experiment, and reports the growth of lung tumors in laboratory mice following inhalation exposure to MWCNT rather than injection, instillation, or aspiration. Inhalation exposure most closely resembles the exposure route of greatest concern in the workplace. In the study, laboratory mice were exposed to one type of MWCNT through inhalation at a concentration of 5 milligrams per cubic meter of air for five hours per day for a period of 15 days.
Risk of occupational cancer depends on the potency of a given substance to cause or promote cancer and the concentration and duration of worker exposure to that substance. This research is an important step in our understanding of the hazard associated with MWCNT, but before we can determine whether MWCNT pose an occupational cancer risk, we need more information about actual exposure levels and the types and nature of MWCNT being used in the workplace, and how that compares to the material used in this study.
This study is part of a larger program designed to establish safety practices with regard to handling nanomaterials/nanoparticles (from the NIOSH blog post),
These laboratory studies are part of a strategic program of NIOSH research to better understand the occupational health and safety implications of nanoparticle exposure, and to make authoritative science-based recommendations for controlling exposures so that the technology is developed responsibly as the research advances, and the societal benefits of nanotechnology can be realized. NIOSH has worked closely with diverse public and private sector partners over the past decade to incorporate occupational health and safety into practical strategies for safe development of this revolutionary technology. More information is available on the NIOSH nanotechnology topic page.
There is no mention in the blog post as to whether the MWCNTs in this latest work were long or short or a mixture of both. Unfortunately, the study has not yet been published in a journal, so it’s not yet available for reading purposes. I did mention carbon nanotubes and toxicity in a Jan. 16, 2013 posting about a recent study,
Researchers at the University College of London (UCL), France’s Centre national de la recherche scientifique (CNRS), and Italy’s University of Trieste have determined that carbon nanotube toxicity issues can be addressed be reducing their length and treating them chemically.
While I find this latest work from NIOSH interesting, it’s hard for me to understand why there’s no mention of length. Unless, the NIOSH work is focused on what happens when MWCNTs are inhaled along with known cancer initiators and they believe that length is not a factor.
ETA Mar. 15, 2013: I did find get some information about the length (long carbon nanotubes for the most part) as per this Mar. 14, 2013 posting or you can find the update in my Mar. 15, 2013 posting here.