Nanotubes Show Toxic Qualities of Asbestos

May 20, 2008 -- Strong, versatile little "nanotubes" made out of carbon are considered future stars in nanotechnology research in medicine and industry. Now a study finds that longer threads of the stuff mimic the toxic qualities of asbestos, renewing questions about how carbon nanotubes can be used safely.

Researchers with British institutes and the U.S.-based Project on Emerging Nanotechnologies injected mice with asbestos and with commercial samples of carbon nanotubes of varying sizes. When they examined the lining of the rodents' abdominal cavities, the researchers observed that longer nanotubes behaved like asbestos, provoking inflammation and lesions.

The study was reported Tuesday in Nature Nanotechnology, a scientific journal.

Carbon nanotubes are widely available for sale, but the study's authors and outside experts said they are not certain how extensively the materials have begun to be used in electronic gear, composite metal structures or consumer products. Such uses are expected eventually.

Because of that uncertainty, the researchers hope to pressure companies developing carbon nanotube-based materials to reveal whether they are using longer strands such as the ones that appear to act like asbestos -- which was once a wonder material, too, before its cancerous consequences were discovered.

"I think it ups the stakes," said one of the authors, Andrew Maynard of the Project on Emerging Nanotechnologies, a partnership of the Woodrow Wilson International Center for Scholars and the Pew Charitable Trusts. "Up to this point we could talk hypothetically about the risks, but there wasn't enough there to demand action."

Vicki Colvin, a Rice University chemist who directs the National Science Foundation-funded Center for Biological and Environmental Nanotechnology, said carbon nanotubes' potential applications -- such as cars that could be 80 percent lighter than today's models, but just as sturdy -- are too powerful to ignore. She said the new study drove home the importance of making sure "we know how to handle it." Colvin was not involved in the new research.

The researchers acknowledged their work had limitations and called for more study.

For one thing, they put nanotubes directly into the abdomens of mice and stopped their experiments after a week -- before seeing whether the nanotubes went on to induce mesothelioma, the cancer of the organ lining caused by asbestos exposure.

Mesothelioma is slow to develop; it can take 30 to 40 years in humans. But Vincent Castranova, chief of a pathology research unit at the National Institute for Occupational Safety and Health, said signs of the cancer would have been apparent in the mice after a month or two.

Whether that would have happened in a meaningful way is a vital question.

Castranova noted that earlier research in Japan, similar to Tuesday's paper, found that mice injected with carbon nanotubes did develop mesothelioma. But the doses of carbon nanotubes were so high that Castranova questioned the results.