Multiwalled carbon nanotubes ― multiple layers of long concentric tubes of graphite ― inhaled by mice reach the outer lining of the lungs and cause unique pathological changes, reports a study published online this week in Nature Nanotechnology. This work suggests that minimizing the inhalation of nanotubes during handling of the material is necessary until further long-term assessments of the lungs' response have been conducted.
Previously, multiwalled carbon nanotubes introduced into the abdominal cavity of mice were shown to have asbestos-like pathogenic behavior. Building on this work, James Bonner and colleagues allowed mice to inhale a single dose of either a high or low concentration of multiwalled carbon nanotubes and examined their lung tissues after one day, two weeks, six weeks and fourteen weeks. The inhaled nanotubes were swallowed up by specialized white blood cells that travelled to the outer lining of the lung wall, causing scarring of the lung tissue. None of these effects were seen in mice that inhaled the lower dose of nanotubes or carbon black nanoparticles ― graphite in the form of compact particles rather than long tubes.
Although the present inhalation study is a relevant method for determining nanotube toxicity, the pathological changes seen could be unique to this specific type of nanotube and may or may not persist under repeated exposures. Nevertheless, the ability of nanotubes to reach the outer lining of the lungs calls for a better understanding of how to handle these materials.