Fate and Transport of Nanomaterials in Aquatic Environments - Nanotechnologies for Water Environment Applications - page 512

size of large TiO2 NPs aggregates (120 nm) becomes smaller over time. Small TiO2 NPs
appear to enter the epithelium faster, and once in the epithelium, a greater proportion of
them is translocated to the subepithelial space as compared with larger TiO2 NPs.
Some researcher indicated that surface area rather than mass concentration
determines the effect of NPs (Beck-Speier et al., 2001). Others reported that, if the
volume proportion was assumed to be representative of particle numbers, the number of
particles reaching the interstitial space would be directly proportional to the numbers
applied; that is, overall, there was no preferential transport from lumen to interstitium by
size (Churg et al., 1998). In addition, there were significant species differences in the
pulmonary responses to inhaled TiO2 NPs. Under conditions where the lung TiO2 NP
burdens were equivalent, rats developed a more severe inflammatory response than mice
and, subsequently, developed progressive epithelial and fibroproliferative changes.
Clearance of particles from the lung was markedly impaired in mice and rats exposed to
10 mg/m 3 TiCh NPs, whereas clearance in hamsters did not appear to be affected at any
of the administered doses (Bermudez et al., 2004).
Two recent studies reveal that CNTs delivered to the abdominal cavity of mice
can induce asbestos-like pathogenicity (Kostarelos, 2008). In one recent study, animal
morbidity and histological examination of the mesothelium after 25 weeks showed the
carcinogenic effect of exposure to either the MWNT suspension [3 mg of
nonfunctionalized MWNTs dispersed in a surfactant (Tween 80)-containing methyl
cellulose solution] or to the positive control with blue asbestos (crocodilite) (Kostarelos,
2008). Poland et al. (2008) explored CNTs' carcinogenic risk in vivo by dispersing 50 |ig
of nonfunctionalized MWNTs of different lengths in saline using bovine serum albumin
and injecting it into normal mice intraperitoneally. The accumulation of MWNTs in the
diaphragmatic mesothelium and the subsequent degree of granuloma lesion formation
were significantly higher after injection of rigid MWNTs longer than 20 |im, as
compared to the low-aspect-ratio, tangled nanotube aggregates or a negative-control
carbon-containing compound that is not needle shaped. These results demonstrate that
asbestos-like pathogenic behavior associated with CNTs conforms to a structure-activity
relationship based on length, to which asbestos and other pathogenic fibers conform
(Poland et al., 2008). These results have disapproved the assumption that CNTs are no
more hazardous than graphite (Poland et al., 2008), and raised concern that NMs may
cause damage to biological systems through oxidative stress (OS) pathways (Samet et
al., 2004; Long et al., 2006).
The second set of evidence is obtained from studies on cytotoxicity of NPs in
different cells. Starting soon after the production of fullerenes in 1990, many efforts
have been devoted to the application of Ceo and its derivatives. Ceo fullerene possesses a
variety of interesting biological properties, such as HIV-P inhibition, DNA
photocleavage, neuroprotection, apoptosis, etc. (da Ros et al., 2001). However, fullerene