Toxicology of carbon nanomaterials
Mori et al. (2006)[3] could not find toxicity in rodents for C60 and C70 mixtures after oral administration of a dose of 2 g/kg body weight and did not observe evidence of genotoxic or mutagenic potential in vitro.
A quantitative structural analysis relationship (QSAR) study can analyze on how close the molecules under consideration are in physical and chemical properties, which can help.
This was not an inhalation study, though there have been several performed in the past, therefore it is premature to conclude that nanotubes should be considered to have a toxicological profile similar to asbestos.
Conversely, and perhaps illustrative of how the various classes of molecules which fall under the general term fullerene cover a wide range of properties, Sayes et al. found that in vivo inhalation of C60(OH)24 and nano-C60 in rats gave no effect, whereas in comparison quartz particles produced an inflammatory response under the same conditions.
However, available data clearly show that, under some conditions, nanotubes can cross membrane barriers, which suggests that, if raw materials reach the organs, they can induce harmful effects such as inflammatory and fibrotic reactions.
No human epidemiologic or cancer data was available to the IARC Working Group at the time, so the evaluation focused on the results of in vivo animal studies assessing the carcinogenicity of SWCNTs and MWCNTs in rodents.
[17] Scientists exposed the mesothelial lining of the body cavity of mice to long multiwalled carbon nanotubes and observed asbestos-like, length-dependent, pathogenic behavior that included inflammation and formation of lesions known as granulomas.
Authors of the study conclude: This is of considerable importance, because research and business communities continue to invest heavily in carbon nanotubes for a wide range of products under the assumption that they are no more hazardous than graphite.
Our results suggest the need for further research and great caution before introducing such products into the market if long-term harm is to be avoided.
[17]Although further research is required, the available data suggest that under certain conditions, especially those involving chronic exposure, carbon nanotubes can pose a serious risk to human health.
[21] Another study provided breathing zone and area sampling results from fourteen sites working with CNTs in a variety of manners for potential exposure assessment.
[23][24][25] With the limited amount of human data, scientists are more reliant on the results of current animal toxicity studies to predict adverse health effects, as well as applying what is already known about exposures to other fibrous materials such as asbestos or fine and ultra-fine particulates.
One cross-sectional study to evaluate health effects was conducted to determine associations of biomarkers in relation to measured CNT exposure.
Ultimately, the risk assessment found the most relevant data upon which to calculate the REL (recommended exposure limit) were animal studies.
Corrections for inter-species differences, and updates to reflect advancing technologies in sampling methods and detection capabilities were considered as a part of the risk assessment.
The resultant REL is several orders of magnitude smaller than those of other carbonaceous particulate matters of concern, graphite and carbon black.
[7] Several individual authors have also performed similar risk assessments using animal toxicity data and have established inhalation exposure limits ranging from 2.5 to 50 ug/m3.
