October 26th, 2009 · No Comments

Green Right Now Reports

Exposure to nanotubes may affect the outer lining of the lungs, according to a study by a collaboration of scientists studying the potential health effects of nanotubes on human health.

Researchers at North Carolina State University, the Hamner Institute for Health Sciences and the National Institute of Environmental Health Sciences decided to take a look at what happens when mice inhale nanotubes.

Nanotubes in the lung

What they found was that multi-walled nanotubes could reach the pleura lining of the lungs, which is the area aggravated by asbestos fibers in the development of the cancer mesothelioma.

In the studies, the researchers determined that the inhaled nanotubes travel through the lungs, where they cause a “unique pathologic reaction on the surface of the pleura.”

The infiltration caused a fibrosis that cleared up over three months. So far, the researchers are unable to say what might happen if subjects – mice or humans – were repeatedly exposed to nanotubes.

The mice used in the experiment were exposed to a single inhalation of nanotubes over six hours. The effects on the pleura were only apparent at the highest dose used by the researchers of 30 milligrams per cubic meter (mg/m3). No ill effects were noticed at lower dose levels.

The local reaction in the affected mice began within one day of the inhalation and the fibrosis or scarring began two weeks later, according to Dr. James Bonner, associate professor of environmental and molecular toxicology at NC State and senior author of the study.

While the study could not project any long-term effects, it argues for more knowledge about how nanotubes, which are used in an array of products, from sports equipment to computer and auto components. Carbon nanotubes are extremely strong and also are being studied for use in medical treatments that would enable small sensors or implants to reach otherwise unreachable areas of the body.

But nanotubes have been suspected of doing biological damage because of their thin fibrous structure, similar to the asbestos fibers that cause mesolethioma.

“The major conclusion from this study is that multiwalled carbon nanotubes, once inhaled into the lungs of mice, travel to the pleural lining surrounding the lungs and remain there for weeks,” Dr. Bonner said.

“They also cause some tissue scarring (i.e., fibrosis) at the pleural lining of the lungs. This finding has the most important implications for occupational exposures, where workers might be exposed to carbon nanotube dust. In this case I advise safe handling and for workers to avoid breathing dust containing nanotubes.”

The scientist said he was not immediately concerned about specific consumer products because those that use carbon nanotubes such as carbon tennis rackets and bike frames are likely not a threat because they are “solid packed composites.”

As for the potential of nanotubes incursions into the body to trigger cancer, the study was not definitive.

“It remains unclear whether the pleura could recover from chronic, or repeated, exposures,” Bonner said in a statement. “More work needs to be done in that area and it is completely unknown at this point whether inhaled carbon nanotubes will prove to be carcinogenic in the lungs or in the pleural lining.”

“Inhaled Carbon Nanotubes Reach the Sub-Pleural Tissue in Mice,” was co-authored by Bonner, Dr. Jessica Ryman-Rasmussen, Dr. Arnold Brody, and Dr. Jeanette Shipley-Phillips of NC State, and Dr. Jeffrey Everitt who is an adjunct faculty at NC State; Dr. Mark Cesta of the National Institute of Environmental Health Sciences (NIEHS), Earl Tewksbury, Dr. Owen Moss, Dr. Brian Wong, Dr. Darol Dodd and Dr. Melvin Andersen of The Hamner Institutes for Health Sciences. The study is published in the Oct. 25 issue of Nature Nanotechnology and was funded by The Hamner Institutes for Health Sciences, NIEHS and NC State’s College of Agriculture and Life Sciences.