Nanotechnology for domestic water purification - Nanotechnology in Eco-efficient Construction - page 389

16.6.3 Toxicity of carbon nanotubes
Despite their many advantages, CNTs represent a hazard to the environ-
ment and human health. Like asbestos, the aspect ratio (length : diameter)
and metal components of CNTs are known to have an effect on the toxicity
of carbon nanotubes. Kim et al. (2011) evaluated the toxic potential of CNTs
in relation to their aspect ratio and metal contamination, in vivo and in vitro
genotoxicity tests were conducted using high aspect ratio (diameter:
10-15 nm, length: m) and low aspect ratio multi-wall carbon nanotubes

(MWCNTs, diameter: 10-15 nm, length:

∼ 10 μ

150 nm) according to OECD test
guidelines 471 (bacterial reverse mutation test), 473 ( in vitro chromosome
aberration test), and 474 ( in vivo micronuclei test). High aspect ratio
MWCNTs were found to be more toxic than the low aspect ratio MWCNTs.
Thus, while high aspect ratio MWCNTs do not induce direct genotoxicity
or metabolic activation-mediated genotoxicity, genotoxicity could still be
induced indirectly through oxidative stress or infl ammation.
A recent in vivo cancer therapy study using CNTs originally designed as
drug delivery enhancers was able to demonstrate that tumour cells respond
to toxicity differently than do wild type cells (Liu et al. , 2008). Lam et al.
(2004) tested a variety of SWCNT samples with varying amounts of metal
impurities and concluded that all SWCNT preparations induced dose-
dependent lung granulomas in mice. Warheit et al. (2004) reported a mild
and transient pulmonary infl ammatory response in rats instilled intratra-
cheally with SWCNTs, with subsequent development of multifocal granu-
lomas in the lungs after 1 month in a mouse instillation study using highly
purifi ed SWCNTs.
Shvedova et al. (2005) found granulomas, lung fi brosis and a signifi cant
elevation in markers of toxicity in bronchoalveolar lavage (BAL) fl uid and
concluded that SWCNTs exerted greater toxicity on a mass basis than
crystalline silica. A critical review of carbon nanotube toxicity and assess-
ment of potential occupational and environmental health risks was pro-
vided by Lam et al. (2006), where the toxicological hazard assessment of
potential human exposures to airborne CNTs and occupational exposure
limits for these novel compounds are discussed in detail.

∼

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16.6.4 Toxicity of titanium dioxide and silica
(SiO 2 ) nanoparticles
Studies with fi ne and ultrafi ne ( 100 nm) TiO 2 particles demonstrate some

respiratory toxicity and epithelial infl ammation of the lung in rodents (Ferin
and Oberdörster, 1985; Ferin et al. , 1991; Oberdörster et al. , 1992; Bermudez
et al. , 2002, 2004; Warheit et al. , 2005, 2006). Silica nanoparticles have been
shown to have a low toxicity when administered in moderate doses (W Lin

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