Researchers at North Carolina State University have made a collaborative study and found that inhaling nanotubes can affect the outer lining of the lung.
However, the researchers from The Hamner Institutes for Health Sciences, and the National Institute of Environmental Health Sciences, said that the effects of long-term exposure remain unclear.
Using mice in an animal model study, the researchers aimed to determine what happens when multi-walled carbon nanotubes are inhaled.
Specifically, they wanted to find out if the nanotubes could reach the pleura, which is the tissue that lines the outside of the lungs and is affected by exposure to certain types of asbestos fibres which cause the cancer mesothelioma.
The researchers used inhalation exposure and found that inhaled nanotubes do reach the pleura and cause health effects.
Short-term studies described in the paper do not allow 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, senior author of the study.
The "unique reaction" began within one day of inhalation of the nanotubes, when clusters of immune cells (lymphocytes and monocytes) began collecting on the surface of the pleura.
Localized fibrosis, or scarring on parts of the pleural surface that is also found with asbestos exposure, began two weeks after inhalation.
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. 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," said Bonner.