Carbon nanotubes - which are being considered for use in everything from sports equipment to medical applications - could cause lung cancer if inhaled, according to a study.
Researchers from North Carolina State University, The Hamner Institutes for Health Sciences and the National Institute of Environmental Health found that inhaled nanotubes were able to reach the pleura, which is the tissue that lines the outside of the lungs and is affected by exposure to certain types of asbestos fibers which cause the cancer mesothelioma.
The short-term studies described in the paper don't allow firm conclusions about long-term responses such as cancer. However, the inhaled nanotubes "clearly reach the target tissue for mesothelioma and cause a unique pathologic reaction on the surface of the pleura, and caused fibrosis," says Dr James Bonner, associate professor of environmental and molecular toxicology at NC State.
The reaction began within a day of inhalation, when clusters of immune cells began collecting on the surface of the pleura. Localized fibrosis - scarring on parts of the pleural surface which is also found with asbestos exposure - began two weeks later.
The study showed the immune response and fibrosis disappeared within three months of exposure. However, this study used only a single exposure to the nanotubes. "It remains unclear whether the pleura could recover from chronic, or repeated, exposures," Bonner says. "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."
The mice received a single inhalation exposure of six hours as part of the study, and the effects on the pleura were only evident at the highest dose used by the researchers – 30 milligrams per cubic meter (mg/m3). The researchers found no health effects in the mice exposed to the lower dose of one mg/m3.
The study is published in Nature Nanotechnology.