Human Toxicology and Effects of Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 368

MWCNT formed aggregates that were easily ingested by the macrophages result-
ing in little ROS or TNF production. If this observation translates to the in vivo

situation, this would suggest that carbon nanotubes behave like other pathogenic
fi bres such as asbestos.
As a consequence of the observation that MWCNT have the potential to behave
like pathogenic fi bres in vitro , an in vivo study was conducted to determine the
consequence of MWCNT interaction with the mesothelium. As a pilot study, Poland
et al. (2008) instilled a selection of entangled and relatively straight MWCNT into
the peritoneal cavity of the mouse, and compared these with carbon nanoparticles,
long fi bre amosite (LFA) (pathogenic asbestos sample) and short fi bre amosite
(SFA) (non-pathogenic). As hypothesised, the long relatively straight MWCNT
behaved similarly to LFA in that they generated an infl ammatory response that
was associated with pathological changes in the mesothelial layer lining the peri-
toneal surface of the diaphragm. In contrast, entangled and relatively short MWCNT,
as well as the nanoparticle carbon black and SFA, did not induce any signifi cant
pathological change. This data suggests that MWCNT, if long and straight conform
to the fi bre paradigm of toxicity, but this needs to be confi rmed in the pleural cavity
following exposure via inhalation.

α

(iii) Biomedical applications
There are many studies which have been conducted with the aim to investigate the
potential for use of carbon nanotubes as nanomedicines, including drug delivery,
gene delivery and nanocomposites for implantation. A full review of these applica-
tions is beyond the scope of this chapter and the reader is referred elsewhere for
this information (Lacerda et al. , 2006). Instead, this section focuses on publications
in this area that provide toxicologically relevant information. For example, Singh
et al. (2006) injected radio-labelled SWCNT into mice to identify their biodistribu-
tion and clearance. The SWCNT had been modifi ed by functionalisation in order
to make them more water soluble and, therefore, more useful in biomedical appli-
cations. Intravenous administration of the functionalised SWCNT resulted in rapid
excretion of the radioactivity from the blood with a half-life of three hours.
Clearance was via the kidney, as verifi ed by electron microscopy analysis of urine.
Functionalisation appeared to prevent uptake by the reticuloendothelial system,
including the liver and spleen. Such functionalisation is obviously useful in prevent-
ing accumulation in the body, facilitating clearance and thereby reducing the poten-
tial for toxicity. However, it is also a disadavangate if the nanotube is cleared too
rapidly from the body to allow drug or gene delivery to a specifi c target. Another
study injected intravenously unmodifi ed SWCNT into rabbits and identifi ed their
biodistribution using near - infrared fl uorescence. Again, the nanotubes were found
to clear from the blood, this time with a half-life of one hour. The nanotubes were
found accumulated in the liver 24 hours after administration, the consequences of
which remain unknown.

9.3.3 Metals

There is a wide range of metal and metal oxide nanoparticles, in fact too many
to be covered comprehensively by this chapter. Instead, the focus is on some