Agriculture Reference
In-Depth Information
nanomaterial or even the nanomaterial itself because impurities and other compo-
nents can account for such effects (Sayes and Warheit
2009
).
Furthermore, it is essential that the material characterization is performed in
biorelevant media for the toxicity tests intended (Jiang et al.
2009
), i.e., those in
which the ecotoxicological experiments will be conducted. This is because poten-
tial physical and chemical changes (e.g., agglomeration/aggregation and change in
surface charge) may occur with the particles in different solutions, which have a
direct impact on the toxicological responses (Powers et al.
2007
).
Here, we draw attention to the importance of establishing the dispersion state of
nanomaterials. This is needed because certain particles are extremely reactive in
aqueous medium, which changes their size and shape compared to the dry powder.
The dry nanomaterials can take two forms: aggregates (strong links between
primary particles) and clusters/agglomerates (controlled by weaker forces such as
van der Waals). The state of the nanoparticles, aggregate or agglomerate, may be
controlled during synthesis (Tsantilis and Pratsinis
2004
; Jiang et al.
2007
). After
dispersing nanomaterials in solution/suspension, they can remain as singlets or
form agglomerates or remain as aggregates, surrounded by an electrical double
layer. Typically, when agglomerated nanoparticles are added to a liquid, they can
be separated to overcome the attraction of weak forces through various methods
such as the use of ultrasound. However, the aggregated nanoparticles cannot be
separated.
In order to illustrate the importance of such determinations mentioned, below we
cite some studies on selected nanomaterials.
13.5 Nanoecotoxicology of Selected Nanomaterials
13.5.1 Titanium Dioxide (TiO
2
)
Potential applications of TiO
2
include, but are not limited to, (1) solar cells (Usui
et al.
2004
); (2) food additives (Lomer et al.
2002
); (3) paints, cosmetics, and
sunscreens (Serpone et al.
2007
); (4) photocatalysts (Carp et al.
2004
); and
(5) photocatalytic water purification (Hagfeldt and Gratzel
1995
).
Without photoactivation, nano-TiO
2
is considered chemically inert (Bernard
et al.
1990
; Lindenschmidt et al.
1990
), but it becomes highly reactive under UV
irradiation and produces reactive oxygen species (ROS) (Reeves et al.
2008
), which
leads to strong antibacterial activity (Sunada et al.
2003
).
Among the nanomaterials, the production of nanoparticulate TiO
2
is the highest
in the world, an order of magnitude greater than the next most widely produced
nanomaterial, ZnO (Miller et al.
2012
). Thus, TiO
2
may reach its highest concen-
trations in surface waters and pose a significant threat to aquatic ecosystems
(Gottschalk et al.
2009
,
2010
).
