UPDATE to nanopublic post from 5/20/08:
ICON at Rice University has produced an excellent background document, discussing the methodologies and adequate interpretations of the two studies comparing responses in mice to multi-walled carbon nanotubes (MWCNT or MWNT) and certain asbestos fibers
Here's the section from the ICON report on interpreting the results :
"These studies do not address whether humans may be exposed to MWCNT in a way that causes disease. While more research is needed to understand the potential implications of this work for human health, the two studies taken together point to the need for a careful assessment of the potential for MWCNT to cause injury to humans. The many outstanding questions that these papers raise include(Click here for Kristen Kulinowski's full report.)
* How dose is measured for MWCNT and what constitutes an appropriate dose in mice to correlate with human risk;
* The role of metals within the nanotube samples. (The Nature Nanotechnology study found that metals derived from the MWCNT could not explain the different effects of exposure to long straight vs. short tangled MWCNT. The J. Tox. Sci. study did not rule out the iron contaminant within the MWCNT samples as the agent responsible for promoting the formation of the cancerous lesions.)
* Whether short, tangled MWCNT, which are non-fibrous, have a toxic effect unrelated to effects associated with exposure to fiber-like particles;
* Whether MWCNT can persist long enough in the body and migrate to the mesothelium to induce the effects seen here in mice;
* Whether humans can be exposed to MWCNT in quantities sufficient to induce the effect seen here in mice.
Despite these caveats both groups of authors believe that their findings are important for understanding the potential hazards of MWCNT and should inform industrial risk management practices so that exposure to humans is limited. As they note, without exposure there is no risk, even if the substance is very hazardous."