WASHINGTON, D.C., May 21, 2008 – Nanotubes may be tiny, but they are super strong carbon fibers that play an important role in the advancement of nanotechnology. However, researchers are now saying that the long, thin multi-walled carbon nanotubes that look like asbestos fiber, might actually behave like asbestos fiber.
Discovered in 1991, Carbon nanotubes are atom-thick sheets of graphite formed into cylinders. They may be formed from a single layer of graphite or they may consist of multiple concentric layers of graphite, resulting in multi-walled carbon nanotubes.
While the diameter of a nanotube can vary from a few nanometers up to tens of nanometers, they can be hundreds or even thousands of nanometers long. Nanotubes can be used to produce materials that are lighter than plastic and stronger than steel, but now the question is whether or not they have potential to cause mesothelioma, a cancer of the lung lining.
When foreign particles like smoke or dust land in the lungs, cells known as macrophages engulf the particles and clear them away. Some asbestos fibers are too long for the macrophages to handle, resulting in lesions, which eventually become a deadly lung cancer. (Widespread exposure to asbestos has been described as the worst occupational health disaster in U.S. history and the cost of asbestos-related disease is expected to exceed $200 billion, according to major U.S. think tank RAND Corporation.)
In a new study by the Project on Emerging Nanotechnologies in Washington, D.C., researchers injected four groups of mice: one with short nanotubes about 5 microns in length, one with long nanotubes about 20 microns in length, one with asbestos and one with small carbon clumps. Some of the mice were killed and dissected the next day. Some were dissected a week later. The mice injected with the short nanotubes or small carbon clumps did not develop disease. Those injected with long nanotubes or asbestos developed lesions on the tissue lining.
“Long ones are harmful, and short ones are not,” says Ken Donaldson, a professor of respiratory toxicology at the University of Edinburgh in Scotland and one of the authors of the study. “It’s a good news story, not a bad one. It shows that carbon nanotubes and their products could be made to be safe.”
“In a sense, we’re forewarned and forearmed now with respect to nanotubes,” says Anthony Seaton, a professor of environmental and occupational medicine at the University of Aberdeen in Scotland.
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.
“I think there is clear evidence for caution in how they are used and handled,” said Andrew D. Maynard, chief science adviser to the Project on Emerging Nanotechnologies at the Woodrow Wilson International Center for Scholars in Washington and another author of the study.
According to Dr. Maynard nanotubes should be subject to the same rules and regulations as asbestos.
“That gives you a good baseline starting point,” Dr. Maynard said. The rules could be relaxed if nanotubes turned out to be less toxic, he said.
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