There is some unsettling news out of China for people who work with or around multi-walled carbon nanotubes.
Multi-walled carbon nanotubes (MWCNTs) are carbon-based synthetic molecules in the shape of concentric tubes. Their special shape makes them more resistant to chemicals than other types of carbon nanotubes and makes them valuable for use in electronics, optics, textiles and other areas of manufacturing.
But Chinese researchers say these tiny particles, like the sharp particles of naturally-occurring asbestos, have the potential to cause mesothelioma in people who inhale them. Lead researchers Jiegou Xu of the Anhui Medical University College of Basic Medical Sciences in Hefei, China and his colleagues exposed laboratory rats to two different kinds of MWCNTs with disturbing results.
Suspensions containing either a larger needle-like MWCNT (MWCNT-L) or a smaller MWCNT (MWCNT-S) which forms “cotton candy-like aggregates” were sprayed down the tracheas of rats every two weeks for 24 weeks. After it was inhaled, the larger molecule (MWCNT-L) was found to move over time through the lung alveoli and into the two-layered pleural lining which surrounds the lungs. There, it induced fibrosis and “patchy parietal mesothelial proliferation lesions”. MWCNT-L also triggered stronger inflammatory reactions, which have been associated with the development of mesothelioma.
In contrast, the small carbon nanotube (MWCNT-S) did not translocate out of the lungs, making it less likely to cause mesothelioma, which starts in the pleura. Inflammatory response to MWCNT-S was also not as great. “These results suggest that MWCNT-L has higher risk of causing asbestos-like pleural lesions relevant to mesothelioma development,” writes Dr. Wu.
A previous study conducted by the same team found that certain MWCNTs could translocate from the lungs into the inner or visceral pleura, but did not progress to the outer or parietal pleura where mesothelioma typically starts. They now theorize that they simply had not allowed enough time for the particles to make their way through the tissue.
More than 80% of the 2,500 mesothelioma cases that occur in the U.S. each year can be traced to exposure to asbestos. However, because of mesothelioma’s long latency, it is possible that newer particles such as MWCNTs could be found to cause mesothelioma decades from now.
Xu, J et al, “Size- and shape-dependent pleural translocation, deposition, fibrogenesis an mesothelial proliferation by multi-walled carbon nanotubes”, May 11, 2014, Cancer Science, Epub ahead of print