Some Nanotubes Could Cause Cancer

New studies suggest that long carbon nanotubes behave like asbestos.

Certain types of carbon nanotubes could cause the same health problems as asbestos, according to the results of two recent studies. In one, published yesterday, tests in mice showed that long and straight multiwalled carbon nanotubes cause the same kind of inflammation and lesions in the type of tissues that surround the lungs that is caused by asbestos. The other study, also done in mice, showed that similar carbon nanotubes eventually led to cancerous tumors.

Dangerous nanotubes: The long, multiwalled carbon nanotubes shown here can lead to inflammation, lesions, and cancer when they come in contact with mesothelial tissues that surround organs in the body, according to new studies performed on mice. (Scale bar is 20 micrometers.) Credit: Ken Donaldson, University of Edinburgh

Carbon nanotubes, tube-shaped carbon molecules just tens of nanometers in diameter, have excellent electronic and mechanical properties that make them attractive for a number of applications. They have already been incorporated into some products, such as tennis rackets and bicycles, and eventually they could be used in a wide variety of applications, including medical therapies, water purification, and ultrafast and compact computer chips. "It's a material that's got many unique characteristics," says Andrew Maynard, a coauthor of one of the studies, which appears in the current issue of Nature Nanotechnology. "But of course nothing comes along like this that is completely free from risk."

Carbon nanotubes that are straight and 20 micrometers or longer in length--qualities that are well suited for composite materials used in sports equipment--resemble asbestos fibers. This has long led many experts to suggest that these carbon nanotubes might pose the same health risks as asbestos, a fire-resistant material that can cause mesothelioma, a cancer of a type of tissue surrounding the lungs. But until now, strong scientific evidence for this theory was lacking.

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The new studies partially confirm the carbon nanotubes' similarity to asbestos by showing that long, straight carbon nanotubes injected into mesothelial tissues in mice cause the sort of lesions and inflammation that also develop as a result of asbestos. Such reactions are a strong indicator that cancer will develop with chronic exposure. One of the studies, which appeared in the Journal of Toxicological Study and was done by researchers at Japan's National Institute of Health Sciences, also showed actual cancerous tumors. The Nature Nanotechnology study was done primarily by researchers in the United Kingdom at the University of Edinburgh and elsewhere.

What isn't known is whether, during nanotubes' manufacture, use, and disposal, they can become airborne and be inhaled in sufficient quantities to cause problems. Indeed, earlier work has shown that it is actually difficult to get carbon nanotubes airborne, since they tend to clump together, says Maynard, the chief science advisor for the Project on Emerging Nanotechnologies, at the Woodrow Wilson Center for Scholars, in Washington, DC. He says that this could decrease the chance that they will be inhaled. He adds that further research is needed to confirm this.