Safety issues relating to nanomaterials for construction applications - Nanotechnology in Eco-efficient Construction - page 136

mammalian cells. While these particular nanomaterials do not contain
heavy metals, toxic effects have nonetheless been associated with them, as
demonstrated by several studies: bacteria, algae, and mammalian cells are
all targets of its ROS mediated cytotoxicity and membrane damage and
carcinogenic effects have been observed.

Silicon dioxide nanoparticles

Studies indicate that exposure to SiO 2 NPs can cause lipid peroxidation and
membrane damage to human lung cell lines (Lin et al. , 2006). In the rodent
model, experiments indicate that these particles may induce tumor necrosis
genes and might have carcinogenic activity. The generation of ROS appears
to be a large contributor to the toxicity of SiO 2 . Interestingly, the relative
surface area of the particles is related to the toxicity effects in as much as
a larger surface area caused stronger cytotoxicity effects in mammalian and
algal cells. In microorganisms, experiments suggest that the direct interac-
tions of SiO 2 particles attached to cell membranes are related to the mecha-
nism of cellular toxicity. Additionally, the cell division of microalgae is
hindered by the presence of SiO 2 NPs.

Nanoclay particles

Nanoclays are an umbrella term for a diverse group of MNMs and range
in chemical makeup and crystalline structure. These particles are often used
in polymer matrices to increase fl exibility, durability, and strength but can
be found as well as fi ller materials in construction nanocomposites. Studies
in the rodent model indicate toxic effects via cell membrane damage. Spe-
cifi cally, sepiolite nanoclays have been found to elicit multinucleated mac-
rophage agglomerates. In vitro studies on human cell lines demonstrate
intracellular ROS generation, leading to oxidative stress and cell death.

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7.2.4 Bimetallic alloys

In construction, this category of nanomaterials consists of semiconducting
alloys in a core/shell confi guration called quantum dots, which usually
contain toxic heavy metals like cadmium. These quantum dots can dissolve
in the digestive tract of rats upon ingestion and release these toxic compo-
nents (Karabanovas et al. , 2008).

Quantum dots

Quantum dots may be toxic due to a variety of mechanisms depending on
their composition. Most common is the release of toxic ions from the heavy