Nov 4 2009
Concerns have been raised in the scientific literature that carbon nanotubes (CNT) might behave similar like asbestos fibres when inhaled into the lungs, implying that they might be causing mesothelioma cancer as well.
To do so, CNT would need to be able to reach the pleura and remain there. Latest scientific data, published by researchers around James Bonner from the North Carolina State University, is now supporting that fact that CNT in mice are indeed able to reach the pleura after inhalation, persisting there for weeks and causing initial pathogenic effects.
The outer lining of the lungs, the so called pleura, is composed of two thin cell layers. The inner layer covers the lung; the other layer connects the lung to the chest wall. In-between these two layers resides a small fluid space that is needed to lubricate the movement of the lungs. The cells that are producing this lubricating fluid are the so called mesothelial cells. These cells are the target of cancer triggered by inhaled asbestos fibres, called mesothelioma cancer. To cause cancer, asbestos fibres need to be enriched and retained for a certain time near the mesothelial cells within the pleura.
What makes Bonners results particularly relevant for CNT risk research is the use of a true inhalation setting instead of injection of particles into the body cavity near the pleura as done previously. CNT inhalation is considered the most realistic route of exposure for humans, particularly in a workplace setting. Microscopy data from Bonner and co-workers revealed deposited multi walled CNT (MWCNT) that were localized below the pleura and near the cancer sensitive mesothelial cell layer. At high CNT doses (30 mg/m3), the researchers observed initial pathogenic effects at the outer lining of the lung such as scarring and cell aggregation which persisted for around 14 weeks.
All together Bonner and colleagues’ findings suggest that inhaled MWCNT in certain ways behave like asbestos fibres: They are able to reach the region below the pleura, they remain there intact for weeks and they are able to initiate initial pathology. On the other hand, however, the short term pathology pattern observed for MWCNT appears different compared to asbestos fibres described in other studies. Since the researchers did not observe abnormal growth of mesothelial cells within the timescale of their experiments (max. 14 weeks), these new findings are not able to declare that MWCNT could cause mesothelioma, the kind of cancer that is connected to airborne asbestos exposure. Mesothelioma is a very slow growing form of cancer, thus, to investigate whether MWCNT inhalation could lead to mesothelioma needs further long term pathology studies.
It is important not to misinterpret these new findings; while they prove a similar deposition behaviour of MWCNT and asbestos fibres which certainly gives rise to concerns, the short term pathology has not shown to be completely matching and a causal connection between MWCNT inhalation and mesothelioma still does not exist so far.
Source: The Innovation Society