Published online 20 May 2008 | Nature | doi:10.1038/news.2008.845

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Calls for caution as nanotubes cause precancerous growths in mice.

Straight carbon nanotubes may have the potential to damage lung tissue. PETER HARRIS / SPL

Nanotechnology experts are calling for prompt government action to ensure that carbon nanotubes are properly regulated, after researchers discovered that some carbon nanotubes can cause precancerous growths in the same way that asbestos does.

Researchers led by Ken Donaldson of the University of Edinburgh’s Centre for Inflammation Research, UK, found that in mice, long, straight, multi-walled carbon nanotubes can cause the same kind of damage as that inflicted by asbestos fibres when they are injected into the lung's outer lining, called the mesothelium.

The lung clears out foreign bodies by wrapping them up in immune cells, which can then be flushed out of the body. But straight fibres longer than about 20 micrometres cannot be removed in this way because the cells are too small to engulf them. As a result, the cells become inflamed and form unwanted lumps, called granulomas, that can go on to cause mesothelioma, a cancer of the mesothelium.

Asbestos is a known environmental cause of lung cancer. ALFRED PASIEKA / SPL

The researchers found that carbon nanotubes of this length led to the formation of granulomas in the mice. “We have shown that if [carbon nanotubes] do find their way to the mesothelium they are pathogenic,” says Donaldson.

Toxic effects

The work doesn’t show that people exposed to nanotubes will get cancer, Donaldson and his colleagues stress. There have not yet been any studies on the effects of environmental exposure, or inhalation. “We certainly need more research on the toxicology of these materials,” says Donaldson.

The health effects of asbestos only came to light decades after workers were exposed to the fibres. This needn’t happen with nanotubes, says Anthony Seaton, a chest physician and co-author of the paper, published in Nature Nanotechnology1. “We are well ahead of the game,” he says.

“If we think carefully we can make carbon nanotubes reasonably safe.” Andrew Maynard

Woodrow Wilson International Center for Scholars

Andrew Maynard, co-author and chief scientific adviser for the project on emerging nanotechnologies at the Woodrow Wilson International Center for Scholars in Washington DC, says that he knows of 12 products that openly declare the use of carbon nanotubes, such as tennis rackets and bike components.

But Maynard suspects that this number is an underestimate. “My suspicion is that this is the tip of the iceberg,” he says.

Size matters

"Up to now there has been considerable uncertainty about the hazards that carbon nanotubes might pose," says Richard Jones, a nanotechnologist at the University of Sheffield, UK. This research begins to clarify things, he says. "Now we know that it is the longest tubes that are most likely to cause problems."

Jones adds that nanotubes aren't normally handled in a state in which they might be inhaled, but nevertheless sees a need to protect the public, and the environment from any chance of exposure to nanotubes.

Maynard expects to see carbon nanotubes used in a wide range of applications, from lightweight structural materials to water-purification systems for the developing world. To do this safely, the use of nanotubes must be properly regulated, he says.

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Maynard calls the mouse study "a wake up call". “It has occurred at an early enough stage that we can take action," he says. "If we think carefully we can make carbon nanotubes reasonably safe.” He suggests that only short, curly nanotubes, should be used. Alternatively, they could be mixed with liquids, rather than using powders containing straight nanotubes that might be inhaled.

Such regulation will require government and industry intervention, says Maynard. “There has got to be regulation, but industry has got to take responsibility.”

The UK government’s Department for Environment, Food and Rural Affairs (DEFRA) has a voluntary reporting scheme for manufacturers that use nanoscale materials in their products, and the United States has a similar system. But until this kind of reporting is made mandatory, it will be difficult to tell just where, and what kind of nanotubes are being used by manufacturers.