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Wednesday, 21 May 2008 18:47

Possible cancer from nanotubes studied

U.K./U.S. toxicologists studied carbon nanotubes and their effect on the abdomens of mice. They found, in the first study of its kind, that nanotubes could potentially cause cancer from actions similar to asbestos fibers inhaled into the lungs of humans.

Lead researcher in the study was Ken Donaldson, from the MRC/University of Edinburgh Center for Inflammation Research, Queen’s Medical Research Institute, Edinburgh, United Kingdom.

The conclusions of the Donaldson study are stated online in the journal Nature Nanotechnology under the title “Carbon nanotubes introduced into the abdominal cavity of mice show asbestos-like pathogenicity in a pilot study.”

The researchers involved in the study and the paper are: Craig A. Poland, Rodger Duffin, William A. H. Wallace, Simon Brown, William MacNee, Ken Donaldson (all from MRC/University of Edinburgh, Centre for Inflammation Research, Queen's Medical Research Institute, Edinburgh, UK), Ian Kinloch (from the School of Materials, University of Manchester, Manchester, UK), Andrew Maynard (from Woodrow Wilson International Center for Scholars, Washington, DC, U.S.A.), Anthony Seaton (from Institute of Occupational Medicine, Edinburgh, UK), and Vicki Stone (from School of Life Sciences, Napier University, Edinburgh, UK).

They state in the abstract of their paper, “Carbon nanotubes have distinctive characteristics, but their needle-like fibre shape has been compared to asbestos, raising concerns that widespread use of carbon nanotubes may lead to mesothelioma, cancer of the lining of the lungs caused by exposure to asbestos.”

Nanotubes are shaped like rolled-up sheets of carbon. Their length can be one million times longer than their width. They do not weigh very much but are stronger than steel. Nanotubes are considered to have been discovered in the early 1990s, although research was performed as early as the 1950s in the Soviet Union and the United States, and nanotubes produced between the 1950s and 1990s.

They are now used in such industries as electronics, nanotechnology, optics, and materials science to produce very strong materials. Nanotubes are efficient conductors of heat, along with their property of having extraordinary strength.

To study if long straight carbon nanotubes can cause mesothelioma, the Donaldson team “injected multi-walled carbon nanotubes and asbestos fibres between the membranes lining the lungs and abdominal organs in mice.” [Chemistry World: “Carbon nanotubes behave like asbestos”]

Specifically, they injected four groups of mice. One group was injected with short nanotubes, only about five microns in length. A second group received long nanotubes about twenty microns in length. A third group was injected with asbestos, and a fourth group with small carbon clumps. Some of the mice were analyzed the next day, while others were studied after one week.

They found, “… that exposing the mesothelial lining of the body cavity of mice, as a surrogate for the mesothelial lining of the chest cavity, to long multiwalled carbon nanotubes results in asbestos-like, length-dependent, pathogenic behaviour. This includes inflammation and the formation of lesions known as granulomas.”

Specifically, the mice injected with long nanotubes or asbestos developed lesions on the tissue lining. The other mice, those injected with short nanotubes or small carbon clumps, did not.

Donaldson says that macrophages, which are cells whose job is to contact and destroy foreign bodies, are unable to eliminate the nanotubes because they are too long. With more nanotubes appearing in the abdomen (and macrophages unable to get rid of them), inflammation results and eventually leads to tumors.

Such action is similar to asbestos fibers that get caught in the outer lining of the lungs after being inhaled by humans. Donaldson states, “Anything that's thin, long, and doesn't easily dissolve in body fluids has got to come under suspicion as behaving like asbestos.” [Chemistry World]

They concluded: “This is of considerable importance, because research and business communities continue to invest heavily in carbon nanotubes for a wide range of products under the assumption that they are no more hazardous than graphite. Our results suggest the need for further research and great caution before introducing such products into the market if long-term harm is to be avoided.”

Donaldson states, "We need more research on the toxicology of these materials, and the exposure to them in workplaces.” [Chemistry World]

Donaldson performed earlier research on nanotubes and their similarity to asbestos. Please read on.

In 2006, Donaldson and Stone also published the related article “Nanotoxicology: Signs of stress” in the journal Nature Nanotechnology.

The researchers stated, “The rapid expansion of nanotechnology has resulted in a vast array of nanoparticles that vary in size, shape, charge, chemistry, coating and solubility. Take carbon nanotubes, for example, which have been intensively studied because they have new and unusual mechanical, electronic and other properties.”

They added, “The potential toxicity of these materials has attracted attention because of their apparent similarities to asbestos and other carcinogenic fibres. Carbon nanotubes are long, thin (just nanometres in diameter) and insoluble — all factors that contribute to fibre toxicity in the lungs. A study by Andre Nel of the University of California, Los Angeles and co-workers now suggests that the hazards are best predicted by examining which nanomaterials cause most oxidative injury within cells.”

The 2008 pilot study of the Donaldson team provides a good indication into the potential problems that could be caused by carbon nanotubes. Further studies are needed to verify the team's conclusions and to perform more detailed studies of the potential association of nanotubes and cancer.


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