Nature Nanotechnol. doi:10.1038/nnano.2009.305 (2009)

When inhaled by mice, multiwalled carbon nanotubes (CNTs) can embed themselves in the lining of the lung (pictured).

James Bonner at North Carolina State University in Raleigh and his colleagues exposed mice to nanoparticle aerosols of either 30 milligrams per cubic metre or 1 milligram per cubic metre for six hours. In the mice exposed to the higher level, immune cells called macrophages (pictured) engulfed the nanotubes and carried them to the lung lining.

Within weeks of exposure, those mice also developed a condition called subpleural fibrosis, which causes localized fibrous lesions. This work does not confirm the suggestion made by other studies that nanotubes may cause lung tumours, but the authors say they urge caution be taken when people are exposed to nanotubes in the air.