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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
Posted November 4th, 2009
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