Nanotechnology for domestic water purification - Nanotechnology in Eco-efficient Construction - page 388

Nanomaterials themselves constitute a new generation of toxic chemicals.
As particle size decreases, in many nanomaterials the production of free
radicals increases, as does toxicity. Studies have shown that nanomaterials
now in commercial use can damage human DNA, negatively affect cellular
function and even cause cell death. There is a small but growing body of
scientifi c studies (termed as nanotoxicology) showing that some nanoma-
terials are toxic to commonly used environmental indicators such as algae,
invertebrate and fi sh species (Hund-Rinke and Simon, 2006; Lovern and
Klaper, 2006; Templeton et al. , 2006; Federici et al. , 2007; Lovern et al. , 2007).
There is also evidence that some nanomaterials could impair the function
or reproductive cycles of earthworms which play a key role in nutrient
cycling that underpins ecosystem function (Fordsmand et al. , 2008).
Studies demonstrated that when introduced into the lungs of rodents,
certain carbon nanotubes cause infl ammation, granuloma development,
fi brosis, artery 'plaque' responsible for heart attacks and DNA damage
(Donaldson et al. , 2006; Lam et al. , 2006; Muller et al. , 2006). Two indepen-
dent studies have shown that some carbon nanotubes can also cause the
onset of mesothelioma - cancer previously thought to be only associated
with asbestos exposure (Poland et al. , 2008; Takagi et al. , 2008). We now
discuss in brief the toxicity of those nanomaterials (such as silver, CNT,
TiO 2 and silica) that are being used substantially in water purifi cation
applications.

16.6.2 Toxicity of silver nanoparticles

Silver nanoaprticles (Ag NPs) are, due to their antimicrobial properties, the
most widely used NPs in commercial products. Ag NPs are incorporated
into medical products like bandages as well as textiles and household items.
The toxicity of Ag NPs has also been shown by a number of in vitro studies
(Kawata et al. , 2009; Kim et al. , 2009; Foldbjerg et al. , 2009, 2011). Toxicologi-
cal investigations of NPs imply that, for example, size, shape, chemical
composition, surface charge, solubility, their ability to bind and affect bio-
logical sites as well as their metabolism and excretion infl uence the toxicity
of NPs (Schrand et al. , 2010; Castranova, 2011). The high surface area of
metal-based NPs increases the potential that metal ions are released from
these NPs (Bian et al. , 2011; Mudunkotuwa and Grassian, 2011), yet it is not
clear to what degree the toxicity of Ag NPs results from released silver ions
and how much toxicity is related to the Ag NPs themselves. It is quite pos-
sible that free silver ions in Ag NP preparations play a considerable role in
the toxicity of Ag NP suspensions. While the contribution of free silver ion
to the measured toxicity of Ag NP suspensions is an important determinant
for the toxicity, a combined effect of Ag ion and Ag NP appears for lower
concentrations of Ag ions.

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