Nanotubes could pose cancer risk

Certain types of carbon nanotubes — microscopic graphite cylinders used in a small but growing number of applications — could pose a similar cancer risk as asbestos if inhaled, scientists reported Tuesday.

Researchers found that mice injected with nanotubes quickly developed the same biological damage associated with early exposure to asbestos, a carcinogen.

The study showed "the potential to cause harm if these things get into the air and into the lungs," said co-author Andrew Maynard, a physicist at the Woodrow Wilson International Center for Scholars in Washington.

He said nanotubes should be subject to the same rules and regulations as asbestos.

"That gives you a good baseline starting point. The rules could be relaxed if nanotubes turned out to be less toxic," he said.

Maynard said the nanotubes pose the greatest danger to workers, who could inhale the dustlike particles during manufacturing. In finished products, the nanotubes are embedded in other material and thus pose less risk to consumers.

The study did not look at how easily nanotubes become airborne or whether they become lodged in the lungs if inhaled. The scientists said more research was needed to determine the extent of the risk posed by nanotubes.

Sean Murdock, head of the Nanobusiness Alliance, an industry trade group based in Skokie, Ill., said precautions are in place in many factories, usually requiring workers to wear respirators. Nanotubes are largely made in closed chemical reactors, he added.

"The good news is that we're understanding the potential hazards before we have large-scale use of these products and not four decades later," he said.

From the time nanotubes were discovered in the early 1990s, they have been billed as wonder particles for their incredible strength, low weight and ability to conduct heat and electricity.

They are starting to be used in some products, including bicycle components, computer displays and car bumpers. Researchers envision them becoming common in medical devices, solar panels and hydrogen fuel cells.

But early on, scientists suspected certain types of nanotubes could pose the same danger as asbestos fibers, which stick in the outer lining of the lung known as the mesothelium.

The damage results when the body's defenses repeatedly try and fail to expel the fibers, eventually leading to mutations that can cause mesothelioma, a fatal form of cancer, decades later.

Consumers would not likely be able to inhale nanotubes embedded in a golf club or bicycle frame. But Maynard said there could be a concern that nanotubes in products could be released later, much as asbestos in concrete or automobile brake pads was inhaled by construction workers or mechanics.

In the current study, published in the journal Nature Nanotechnology, nanotubes were injected into the abdominal cavities of mice, a tissue similar to the lining of the lungs.

One group of mice received tubes at least 20 microns long with walls several atoms thick. Other mice got shorter, thinner tubes that were bundled together. A third group was injected with asbestos fibers.

Among the mice killed after 24 hours, only those that had received asbestos or the longer tubes showed cellular inflammation, the first step in a process leading to cancer.

Mice in those same groups that were killed after a week showed a buildup of scarlike tissue known as granuloma, another step in the process.

Mice that received the shorter and thinner tubes were unaffected. The researchers speculate that the fibers were small enough to be engulfed and expelled by immune cells.

Most nanotubes being used are the longer, stiffer variety, researchers said.

Brooke Mossman, a professor who heads the University of Vermont's environmental pathology program, said she was not convinced by the experiment, because no one knows if the doses used reflect realistic conditions and because the nanotubes were injected instead of inhaled.

"The system is so artificial it's hard to evaluate what to make of this," she said.

Material from The Washington Post and The New York Times

is included in this report.