Safety issues relating to nanomaterials for construction applications - Nanotechnology in Eco-efficient Construction - page 134

Carbon nanotubes

Available in both single-walled (SWCNT) and multi-walled (MWCNT)
forms, carbon nanotubes have been shown to exert bacterial toxicity via
direct cell wall damage or oxidative stress (Kang et al. , 2007, 2008a, 2008b,
2009). More relevantly, however, studies have shown that both types can
cause pulmonary infl ammation, fi brosis, and epithelioid granulomas in
mammalian cells when respired (Ding et al. , 2005; Jia et al. , 2005; Wei et al. ,
2007). CNTs are likely to enter unprotected lungs because they are of
breathable size and weight (Soto et al. , 2008; Herzog et al. , 2009). In a study
performed on rats, it was concluded that MWCNTs pose a carcinogenic
threat, inducing mesothelioma in exposed organisms (Basak et al. , 2010).
Other toxicological implications include damage to mitochondrial DNA
(Derno et al. , 1995), cellular apoptosis and necrosis (Hoffmann et al. , 1995,
Hoffmann, 1995), and reproductive toxicity (Hansen et al. , 2008).
Additionally, heavy metal ions often become imbedded in the CNTs
during the production phase. A common method for nanotube synthesis is
chemical vapour deposition, which employs the use of a metal or alloyed
catalyst such as iron, cobalt, or nickel. Ions from these metals will inciden-
tally become bound within the CNTs. These metallic impurities can lead to
toxic effects, which are not specifi cally 'nano' in nature; they still contribute
to overall toxicological liability of CNTs (Vecitis et al. , 2010).

C 60 fullerenes and their derivatives

C 60 fullerenes may be respired during the preparation process, causing lung
infl ammation (Park et al. , 2010). In addition to their use as raw nanomateri-
als, these fullerenes are often suspended as water-stable aggregates. The
resulting fullerene solution has been shown to have broad antimicrobial
potential (Lyon et al. , 2005, 2006). While there have been hypotheses that
this cytotoxicity is mediated by oxidative stress from ROS, recently it has
been shown that direct cell membrane oxidation from C 60 contact is likely
responsible (Lyon and Alvarez, 2007; Lyon et al. , 2008). In eukaryotes, this
oxidative stress is also responsible for cell death, leading to lipid peroxida-
tion (Oberdörster, 2004; Sayes et al. , 2005). Derivatives of C 60 fullerenes,
such as fullerol and carboxyfullerene, can cause cytotoxicity by physical
membrane damage (Tsao et al. , 2002) as well as by oxidative routes (Faruk
and Matuana, 2008).

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7.2.2 Metal-containing nanoparticles

Metals and metalloids are common components in manufactured nanoma-
terials and include titanium, copper, silver, iron, and zinc. These elements