Environmental Engineering Reference
In-Depth Information
of negatively charged fl uorescent polystyrene nanoparticle beads to aquatic crus-
taceans (e.g.
D. magna
) resulted in rapid ingestion within 30 minutes of exposure
and also adsorption to the exoskeleton of the organism (Fernandes
et al.
, 2006 ).
Stone
et al.
(2006) studied marine and freshwater crustaceans (
Artemia, Daphnia
,
Gammarids) exposed to sonicated suspensions of titanium dioxide, ultrafi ne carbon
black and nC
60
. Results indicated that particles are ingested resulting in accumula-
tion in the gastrointestinal tract. The particles also adhere to the exoskeleton
surfaces of the and exposed organisms, suggesting multiple routes of exposure and
absorption. LC
50
(48 h) values ranged between 5 and 20 mg/l.
Non-rodent vertebrate studies include several publications on fi sh toxicity (e.g.
Griffi tt
et al.
, 2007; Oberdorster, 2004). Selective transport of nanoparticles to the
brain of rodents has been observed in other studies (Oberdorster
et al.
, 2005 ) and
the authors suggest that this, along with the lack of neural antioxidant defences,
could explain the enhanced brain lipid peroxidation levels observed.
Hardly any work has been done on the effects of nanoparticles on plants and
other terrestrial organisms. Possible interactions of nanoparticles with plant roots
include adsorption onto the root surface, incorporation into the cell wall and uptake
into the cell. The nanoparticle could also diffuse into the intercellular space, the
apoplast and be adsorbed or incorporated into membranes there. Yang and Watts
(2005) investigated the phytotoxicity of 13 nm alumina nanoparticles on root growth
by the seeds of fi ve different plant species in hydroponic studies. Species tested
included commercially important species used in ecological risk assessments of
pesticides: corn (
Zea mays
), cucumber (
Cucumis sativus
), soybean (
Glycine max
),
cabbage (
Brassica oleracea
), and carrot (
Daucus corota
). The alumina nanoparticles
inhibited root growth at high concentrations (2 mg/ml), while larger alumina par-
ticles of 200-300 nm had no effect, indicating that the alumina itself was not causing
the toxicity. The inhibiting effects on root growth were decreased by the addition
of dimethyl sulfoxide, a molecule that scavenges free radicals such as hydroxyl
radicals, suggesting that oxidative stress may play a role in the effects of the
nanoparticles on root elongation. A slight reduction in root elongation was found
in the presence of uncoated alumina nanoparticles but not with nanoparticles
coated with phenanthrene. The authors hypothesised that the surface charge on the
alumina nanoparticles may have played a role in the decreased plant root growth;
however, they did not measure the concentrations of soluble Al
3+
in their studies
which is a potent root toxicant and known to inhibit root growth (Murashov, 2006).
The solubility of aluminium oxide increases with decreasing particle size and modi-
fi cation of the surface by adsorbed compounds is known to affect the dissolution
rate.
7.5.2
Carbon - Based Nanoparticles
Carbon-based nanoparticles comprise amorphous carbon, graphite and fullerene-
based compounds including carbon nanotubes. The fullerene-based materials are a
rapidly expanding class of engineered nanoparticles whose production is expected
to soon exceed several thousand tonnes per annum and whose applications include
plastics, catalysts, battery and fuel cell electrodes, super-capacitors, water purifi ca-
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