Environmental Engineering Reference
In-Depth Information
2008a) and will lead to the formation of porous microstructures of both natural
colloids and nanomaterials that can change their structure. The structure of such
natural microstructures/aggregates controls the transport of sorbed trace contami-
nants and, thus, the potential receptor organisms. Nano- to micro-sized or larger
structures that form natural colloidal and nanoparticulate material in the environ-
ment may be altered by the aggregation or other effects of natural waters. As these
structures are vital for the maintenance of life through being direct energy and
carbon sources, as pH and metal ion buffers and other properties, the effects of
nanoparticles on these may have considerable adverse effects (Buffl e, 2006 ). This
possible impact is likely to occur on only a very small scale and at high concentra-
tions of nanoparticles.
1.8.2
Human Health
There is now a substantial literature showing that some nanoparticles may have a
toxic effect and there is a cause for concern as to their effect on human health,
which has largely developed out the voluminous literature on the health impacts
of adventitious nanoparticles (usually termed ultrafi ne, derived from combustion
and other industrial processes). For instance, sunscreen titanium dioxide and zinc
oxide can cause oxidative damage to DNA in vitro and in cultured human fi bro-
blasts (Dunford et al. , 1997 ). Nano - cerium - element doped titanium dioxide induces
apoptosis of Bel 7402 human hepatoma (liver) cells in the presence of visible light
(Wang et al. , 2007 ). Inhaled ultrafi ne particles (UFPs) can gain access to the blood
stream and can then be distributed to other organs in the body; this has been shown
for synthetically produced UFPs (nanoparticles) such as C 60 fullerenes which accu-
mulate in the liver. Even large particles outside the ' nano ' range can penetrate the
stratum corneum of human skin and reach the epidermis and, occasionally, the
dermis and may be taken up into the lymphatic system, while larger particles cannot
(Tinkle et al. , 2003). This means that there is a strong possibility that nanoparticles
can be assimilated into the body through the skin, especially damaged skin. Chapter
9 details the potential effect of nanoparticles on human health.
1.9
Classifi cation
Currently, there are hundreds of nanomaterials in use or under development that
can be classifi ed in different ways according to their chemistry, origin, size, or their
state. Other nanomaterials are expected to appear in the future.
1.9.1
Chemistry
The most common method of classifying nanoparticles is by the chemistry of the
core material. Carbon-based materials are mainly composed of carbon in the form
of a hollow spheres, ellipsoids or tubes such as carbon black (generally not classed
as a manufactured nanoparticle), carbon nanotubes (single wall (SW), multiple wall
(MW)) and fullerenes (generally denoted C n , where n may be 60, 70 or higher
numbers). Metal-based nanomaterials, including quantum dots, metals (nanogold,
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