Inhaled Nanotubes Reach Lung Lining In Mice

If inhaled, multiwalled carbon nanotubes can travel to the lung lining of mice and cause scarring, according to a paper from James C. Bonner of North Carolina State University and coworkers (Nat. Nanotech., DOI: 10.1038/nnano.2009.305). The results suggest extra caution should be exercised to avoid inhaling carbon nanotubes when handling the material.

"This is the first published study to demonstrate that inhaled carbon nanotubes reach" the lung lining, also known as the pleura, note Ken Donaldson and Craig A. Poland of the University of Edinburgh's Center for Inflammation Research, in Scotland, in a commentary that accompanies the paper. Nanotoxicologists are particularly concerned with the pleural region because the rare cancer mesothelioma, which is frequently associated with asbestos exposure, develops there. Scientists have expressed concern that nanotubes may behave like asbestos because of their fiberlike shape.

To see how far multiwalled carbon nanotubes travel when inhaled, Bonner's team subjected mice to a single inhalation exposure to the tubes at a concentration of 30 mg/m³. They then collected lung tissue after one day, as well as after two, six, and 14 weeks of exposure. The researchers found that the nanotubes traveled to just beneath the pleura, where scarring developed after two, six, and 14 weeks of exposure. The team observed no mesothelioma but notes that the slow-growing cancer is unlikely to show up in their experimental time frame. Similar experiments carried out with carbon black nanoparticles produced no scarring.

"The take-home message is that we should be careful in the way we handle carbon nanotubes because based on our mouse study, these fiberlike structures will reach the outer lining of the lung and remain there for weeks or months," Bonner tells C&EN.

"This is an important paper because it demonstrates that inhaled multiwalled carbon nanotubes" move from airspace to the regions that line the lungs of mice, comments nanotoxicology expert David B. Warheit of the DuPont Haskell Laboratory for Health & Environmental Sciences, in Newark, Del. However, "the effects were manifested following an extremely high exposure concentration of carbon nanotubes," he adds. "It will be important to ascertain whether the observed potency occurs at relevant occupational exposure levels."