Agriculture Reference
In-Depth Information
concentration in the culture media. Therefore,
L. minor
was more sensitive to TiO
2
nanoparticles than to bulk TiO
2
.
Dalai et al. (
2013
) focused on the cytotoxicity potential of TiO
2
nanoparticles
toward a dominant freshwater crustacean,
Ceriodaphnia dubia
, in a lake water
system. The studies were carried out under a 16:8-h light and dark photoperiod.
Commercial dry titanium (IV) oxide nanopowder (99.7 % anatase, particle size:
<
25 nm) was used. The photoperiod toxicity experiments showed a concentration-
dependent reduction in viability until 16 mg L
1
(viability 20
10 %). However, at
32 mg L
1
, a slightly higher organism viability was noted (30
10 %) as compared
to 16 mg L
1
<
0.05) at
64 mg L
1
. The increased survival of daphnids at higher concentrations could be
attributed to the reduced nanoparticle toxicity owing to its rapid aggregation at
higher concentrations. A 50 % reduction in viable (mobile) organisms was recorded
around 8 mg L
1
[EC
50
¼
(
p
>
0.05), which further increased until 65
10 % (
p
8.26 mg L
1
, photoperiod]. Under dark conditions, the
maximum toxicity was observed at 32 mg L
1
, where nearly 50 % (
10 %)
27.45 mg L
1
, dark]. As observed for
photoperiod experiments, in dark conditions, an increase in viability was observed
at 64 mg L
1
concentrations, showing nearly 80 % (
reduction in viability was noted [EC
50
¼
0.05).
This work is relevant because it showed reactivity of TiO
2
nanoparticles both in the
photoperiod and in dark conditions. They concluded that although aggregation may
limit nanoparticle mobility in the environment, it may facilitate ingestion or
adhesion by aquatic organisms.
The authors also cite works on daphnids for comparison: Lovern and Klaper
(
2006
) reported concentration-dependent mortality of
Daphnia magna
on exposure
to filtered TiO
2
NPs (~30 nm), with an LC
50
of 5.5 mg L
1
; Warheit et al. (
2007
)
and Zhu et al. (
2010
) found EC
50
greater than 100 mg L
1
for TiO
2
(100-140 nm)
for
D. magna
after 48 h of exposure; and Amiano et al. (
2012
) showed the EC
50
value of 3.4 mg L
1
TiO
2
after exposure to 0.56 mW cm
2
UVA radiation using
river water as the matrix.
Cardinale et al. (
2012
) examined how TiO
2
nanoparticles impacted the growth
and metabolism of three species of freshwater green algae (
Scenedesmus
quadricauda
,
Chlamydomonas moewusii
, and
Chlorella vulgaris
). They exposed
the cultures to five concentrations of TiO
2
(0, 50, 100, 200, and 300 ppm) and
measured impacts on species population growth rates, as well as on metabolic rates
of gross primary production (GPP) and respiration (R). Population growth rates
were reduced by nano-TiO
2
, but the reduction mechanisms differed among species.
For
Chlamydomonas
, nano-TiO
2
reduced both GPP and R, but effects on GPP were
stronger, and then carbon was respired more quickly than it was fixed, leading to
reduced growth. In
C. vulgaris
, the TiO
2
stimulated both GPP and R, but, because R
was more stimulated than GPP, carbon loss exceeded fixation, leading to reduced
growth. For
Scenedesmus
, nano-TiO
2
had no significant impact on R, but reduced
GPP. This pattern also caused carbon loss to exceed fixation.
Basniwal et al. (
2014
) also reported TiO
2
nanoparticle toxicity to
Chlorella
sp. Nanoparticle suspensions were prepared in various concentrations from 0.03
to 0.12 g L
1
. They observed that with the increase of
10 %) survival (
p
>
the nanoparticle
