Science Editor

In the May 21, 2008, online edition of Nature Nanotechnology, British and American researchers reported that long carbon nanotubes can cause damage in animal studies that is similar to that caused by asbestos, causing inflammation and scarring in the tissue that surrounds the lung after being injected abdominally.

Though the researchers stressed that it still is necessary to confirm that the same damage would occur after inhalation, they also suggested that the current light regulation of nanotubes, which are presumed to be harmless because they are made of carbon, needs to be re-evaluated.

Co-author Anthony Seaton, a scientist at the Edinburgh's Institute of Occupational Medicine, refrained from saying, 'I told you so,' at the press conference announcing the findings.

But Seaton did note that he and colleagues warned in a report released in 2004 that carbon nanotubes might act like asbestos. "There was a little bit of lack of support" for that conclusion, he said.

To Seaton, the current findings are not surprising. "It was foreseen," he told reporters at a press conference. The material "behaves the way we expected."

The reason that some scientists suspected that carbon nanotubes could spell trouble for the lungs is that they share some key properties of asbestos, as well as other fibers that damage the lungs. To cause injury, inhaled particles have to be long, thin and remain stable in the slightly acidic environment of the lungs, rather than being dissolved.

The researchers tested long and short nanotubes, as well as carbon nanoparticles that are not long and tubular, for their effects after injection into the abdominal cavity. Senior author Ken Donaldson of the University of Edinburgh succinctly summed up their results as "the long nanotubes were pathogenic - they caused inflammation and scarring. The short nanotubes were not."

The scientists cautioned that they did not observe mesothelioma - the cancer of the lung lining that is asbestos exposure's most feared consequence - itself, though Seaton characterized the damage they observed as "a starting point that may lead to mesothelioma." But he also noted that what he termed "a proper inhalation study," as opposed to injecting the nanotubes, has yet to be done.

"We're a long way from saying that any form of carbon nanotubes cause mesothelioma," senior author Donaldson said. "But what we think we have shown is that if they do find their way to the mesothelium, then they will be pathogenic there."

For the time being, their results by no means lead the authors to conclude that carbon nanotubes should be relegated to the trash heap of once-promising but toxic innovations. Nanotubes, which are an irresistible combination of light, strong, and great conductors of both heat and electricity, are being tested in a wide variety of applications. Possible biomedical applications include imaging and drug delivery.

Co-author Andrew Maynard, chief science advisor to the Project on Emerging Nanotechnologies at the Woodrow Wilson Center for Scholars, called them "one of the most unique materials that has come along in a long time," and added that "nothing comes along like this that is completely free from risk."

But, he added, society needs to get a better handle on the risks associated with the tubes. He pointed out that nanotubes of differing lengths are freely available on the Internet, and quoted from a material safety data sheet that said only that "irritation might occur" in response to inhalation.

Nanotubes, Donaldson said, "are useful materials that we need to use and develop . . . but we need information on exposure to these materials in workplaces."

Otherwise, he added, the risk of public disillusionment might become a greater threat to the technology than the risk of injury.

"It seems like we're beginning to crack the challenge of how to put [carbon nanotubes] into commercially viable products," he said. "But if investors, and the public, lose trust in the technology because of the stigma of asbestos, then chances are we're not going to see that return."