Human Toxicology and Effects of Nanoparticles - Environmental and Human Health Impacts of Nanotechnology - page 365

introduced as a pure chemical. Instead, the THF is trapped within C 60 clusters, so
that the fate and distribution of the C 60 cluster determines the THF fate and dis-
tribution. Such delivery mechanisms are being used by the pharmaceutical industry
to target drugs to specifi c locations, reducing delivery to non-target sites and, there-
fore, reducing the required dose and reducing side effects. While this has not been
demonstrated for THF in C 60 preparations it needs to be considered as a potential
complicating factor. Furthermore, there could be potential for C 60 and THF to
interact (antagonistically or synergistically) to alter toxicity making such experi-
ments diffi cult to interpret or control.

9.3.2 Nanotubes and Other Fibre - Like Nanostructures

High aspect ratio nanoparticles (HARN) are long fi bre - like nanoparticles including
nanotubes, nanowires, nanorods and nanofi laments (Oberdoerster et al. , 2007 ). The
bulk manufacture and use of such nanoparticles has raised concerns because of
their resemblance to asbestos in terms of dimensions and durability; both factors
which determine fi bre toxicity leading to fi brosis and the cancer mesothelioma
(Donaldson et al. , 2006). Single- and multi-walled carbon nanotubes have received
relatively more attention than other high aspect ration particles in relation to toxi-
cology studies, probably because of the greater production volumes leading to
greater exposure risk.
Toxicology studies relating to carbon nanotubes (CNTs) appear to fall into a
number of catagories:

(i) respiratory effects
(ii) dermal effects
(iii) biomedical applications.

In addition, CNTs might have effects as particles or, because of their high aspect
ratio, they may exhibit effects as fi bres; two different paradigms dictate these two
different effects.

Paradigm I: CNT as particles
(i) Respiratory effects of carbon nanotubes
The respiratory studies are generally conducted in order to ascertain the potential
for disease resulting from occupational exposure to airborne carbon nanotubes,
since this was the most relevant route of exposure leading to asbestos induced
disease in the asbestos industry. A study published by Maynard et al. (2004) has
been widely cited with respect to the potential for nanotubes to become airborne.
This study investigated single-walled carbon nanotubes (SWCNT) but not multi-
walled carbon nanotubes (MWCNT). They found that agitation in a controlled
laboratory setting of unrefi ned SWCNT could result in fi ne particle release into air.
However, in general, airborne concentrations in the region of SWCNT production
equipment were interpreted as low (less than 53

g/m 3 ). The relevance of these
exposure concentrations is discussed further in Chapter 8. There is no information
currently available regarding the exposure to MWCNT in a laboratory, experimen-
tal or industrial setting. In our own experience, SWCNT and MWCNT vary greatly

µ