Do not inhale: 3D models of three types of single-walled carbon nanotubes.

Credit: Michael Ströck / Wikipedia

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SYDNEY: Tests on lab mice have revealed that carbon nanotubes, which are already in commercial use, can lead to lesions similar to those caused by asbestos.

Carbon nanotubes are structures just a few billionths of a metre across, with applications in high tech materials, electronics and medicine. But the needle-like shape of some nanotubes has led to them being compared with asbestos fibres. Asbestos exposure is known to cause cancer in the lining of the lungs.

A large body of research exists about the potential of other nanoscale particles to attack the lungs. But this is the first study to show that carbon nanotubes can have the same damaging impact on the mesothelium.

Inflammation and scarring

In experiments with mice, medical researchers led by Ken Donaldson of the University of Edinburgh in Scotland, exposed the mesothelium lining that swathes the lungs, abdomen and heart to carbon nanotube dust.

The fibres resulted in the same kind of inflammation and scarring, called granulomas, that are caused by exposure to asbestos, they report in the British journal Nature Nanotechnology.

"The granulomas and the inflammation are extremely strong indicators of mesothelioma," the cancer that attacks the lining of body cavities, said co-author Andrew Maynard. If the mice had been allowed to carry on living, cancer would most probably have developed where the fibres were present, he said.

Carbon nanotubes hold great promise for applications in future technology from space elevators to hydrogen fuel cells.

"We are at the very, very beginning of using these materials commercially," said Maynard, who predicted that within half a dozen years the market for carbon nanotubes would be worth billions of dollars. "Great caution must be exercised before introducing such products into the market if long-term harm is to be avoided," he said.

Investigation is urgently needed to see whether these tiny particles can be breathed in from air, and if they can migrate to within the lungs to cause cancer, he added. The biggest potential danger is probably in the workplace, but nanotubes might also escape into the environment once the products containing them wind up in landfills as refuse.

Clarifying the issue

"We don't have enough evidence to call for a moratorium, but there is very urgent need to for action to ensure safety, by government and by industry," Maynard said.

The study showed that only so-called long carbon nanotubes, and not short ones, caused the pre-cancerous symptoms. Further experiments are needed, however, to determine if short nanotubes are entirely safe.

"Up to now, there's been considerable uncertainty about the hazards that carbon nanotubes might pose," commented Richard Jones, senior strategic advisor for nanotechnology at the University of Sheffield in England. "This research starts to clarify the issue; not all nanotubes are equal when it comes to potential toxicity, and now we know that it is the longest tubes that are most likely to cause problems."

Mark Welland, a professor of nanotechnology at the University of Cambridge in the U.K., said that though the study confirms that carbon nanotubes of a similar size and shape to asbestos fibres may be harmful if inhaled, most nanotubes are embedded within products and present little risk. "[The finding] therefore neither affects the majority of nanoproducts nor products after manufacture where nanotubes are embedded within the product," he said.

"I welcome this valuable research that represents a part of the growing scientific literature into exploring the potential toxicology of nanoparticles of various shapes, sizes and compositions," added Welland.