Environmental Engineering Reference
In-Depth Information
fl ea) and Oncorhynchus mykiss (rainbow trout) using accepted OECD/US EPA
test protocols. The EC 50 values were
100 mg/l for O. mykiss (96 - h mortality) and
D. magna (48-h immobility) and 21 mg/l for P. subcapitata (72 - h growth inhibition),
indicating that the toxicity of ultrafi ne TiO 2 is of low to medium concern for aquatic
species. However, due to the size of the primary particles used in this study (140 nm)
they may not be considered truly nanoparticulate. Hund-Rinke and Simon (2006)
considered the effects of 25 nm (mainly anatase) and 100 nm (100% anatase) TiO 2
nanoparticles to the green alga Desmodesmus subspicatus and to D. magna . The
smaller (25 nm) particles produced a 72-h EC 50 of 44 mg/l for algal chlorophyll fl uo-
rescence, whereas no clear concentration effect curve could be determined for the
larger particles. The extent of aggregation was not determined in the test for either
size particle, making it unclear which properties contribute to toxicity. Both prod-
ucts caused a toxic response in the daphnid but no clear concentration effect was
observed with concentrations up to 3 mg/l; higher TiO 2 concentrations were not
tested. To determine if the nanoparticulate TiO 2 effects could be enhanced photo-
catalytically these tests were also repeated under UV illumination. No effects of
pre-illumination of the particles were observed for the alga and the effects were
not concentration dependent for the daphnid, suggesting that the photocatalytic
activity of TiO 2 was not a major contributor to toxicity under the conditions studied.
Another study on the effects of nano-sized TiO 2 on D. magna in US EPA medium
indicated the 48-h EC 50 was 5.5 mg/l for TiO 2 dispersed in THF and fi ltered to
remove the residual solvent (Lovern and Klaper, 2006). Conversely, no effect was
observed for TiO 2 dispersed by sonication alone (no THF). The fi ltered particles
had an average diameter of 30 nm compared to 100-500 nm for the sonicated par-
ticles. The potential toxic effects of THF were investigated by comparing fi ltered
TiO 2 with and without the solvent and no statistical differences in toxicity were
observed. Furthermore, D. magna survival was not affected in THF-treated and
evaporated water alone (Lovern and Klaper, 2006). Sub-lethal concentrations,
2 mg/l (LOEC), of TiO 2 nanoparticle showed no statistically signifi cant effects on
D. magna behaviour (hopping rate, heart rate, appendage beat and abdominal
curls) over a 60minute exposure period (Lovern et al. , 2007 ).
Federici et al. (2007) exposed rainbow trout ( Oncorhynchus mykiss ) to a sub-
lethal concentration (1 mg/l) of nanoparticulate TiO 2 with an average particle diam-
eter of 24 nm for 14 days. This comprehensive study of physiological effects showed
gill damage, disruption of copper and zinc homeostasis and increased oxidative
stress markers in the fi sh but no mortality was observed over this exposure period.
No controls for particle size were included in this study however, making it diffi cult
to conclude that the effects were specifi cally due to the properties of nanoparticu-
late TiO 2 . Other studies with the freshwater fi sh species Cyprinus carpio have
demonstrated the potential for TiO 2 nanoparticles to facilitate the transport of
other metal contaminants (Sun et al. , 2007 ; Zhang et al. , 2007). In these studies, C.
carpio were exposed to 10 mg/l TiO 2 nanoparticles for 25 days in the presence or
absence of 200
>
g/l cadmium (Zhang et al. ,
2007). TEM characterisation of the nanoparticles revealed small 50- 400 nm aggre-
gates (nominally 21 nm particles) (Sun et al. , 2007) and adsorption isotherms indi-
cated that the metals were rapidly adsorbed onto the particles with equilibrium
µ
g/l arsenic(V) (Sun et al. , 2007 ) or 100
µ
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