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EC number: 231-131-3
CAS number: 7440-22-4
toxicity of silver toP. promelaswas assessed in a flow through
test. For fish aged 1 -4 days, the 96 hour LC50 is 1.5 µg/L dissolved
Ag. Other LC50 values were: 3.37 (7 d old), 5.9 (27 d old), 10.4 (41 d
old) µg dissolved Ag/L. Silver toxicity varied with age and size of
fish. As fish aged and mass increased 96 h LC50 values increased
(organism sensitivity decreased). The GLP status of this study is
unknown and it is unclear which guideline was followed. However, there
is sufficient information for an assessment to be made and the study is
considered suitable for use for this endpoint.
of available data for uncoated and coated nanosilver
and relevant data on the short-term toxicity of uncoated and coated
nanosilver to fish are available from 10 studies (Griffitt et al.
2008, Kennedy et al. 2010, Bilberg et al. 2012, Farmen et al. 2012,
Kashiwada et al. 2012, George et al. 2012, Cunningham et al. 2013,
Hoheisel et al. 2012, Kim et al. 2013, Wang et al. 2012). These
studies comprise effects assessment on four species (Danio rerio,
Pimephales promelas, Salmo salar and Oryzias latipes)
after exposure to various sizes of nanoparticles and coating types.
Across these studies a total of 46 LC50 values are available, from
exposures ranging from 48 hours to 7 days. Available studies are
focussed on the effects of spherical nanoparticles, although the
characterisation of several of the test materials used by Kennedy et
al. (2010), Bilberg et al. (2012) and Cunningham et al. (2013)
describe the presence of small rods or triangular particles. All
studies were conducted in freshwater media.
particle size of raw nanomaterials across the studies ranged from 3.6
to 225.3 nm. However, the majority of studies report effects
associated with primary particle sizes between 20 and 149 nm (10th to
90th percentile, respectively). It is worth noting that some of these
materials would not be considered as nanomaterials according to the EU
definition as their median primary particle size was greater than 100
extent of aggregation/agglomeration by primary particles in
experimental media or stock solutions differed between studies but in
almost all instances authors report that some degree of
aggregation/agglomeration in test systems occurs, increasing the size
of particles in environmental media. The characterisation results for
nanosilver in test systems report particle sizes after
aggregation/agglomeration of between 3.8 and 3,078 nm, with the
majority of studies reporting particle sizes between 29.6 and 310 nm
(10th to 90th percentile, respectively). Kennedy et al. (2010), report
that PVP and citrate coated nanosilver particles appear to form
smaller aggregates in test systems than uncoated or EDTA coated
values range from 9.0 µg/L for ~30 nm particles in P. promelas
after 48 hours exposure (Kennedy et al. 2012) to 44,780 µg/L for
similar size nanoparticles in Danio rerio after a 120 hour
exposure (Kim et al. 2012). The 10th to 90th percentile range of LC50
values for all forms of nanosilver tested for acute fish toxicity is
38 to 42,490 µg/L. All of the results from nanosilver studies are at
least an order of magnitude less sensitive than the 96 hour LC50 of
1.2 µg/L used as the key data for this endpoint, based on exposure of
one day old Pimephales promelas to ionic silver in
dechlorinated tap water (Bielmyer et al. 2007).
addition, where studies undertook a comparative assessment of
nanosilver and ionic silver within their own study designs (Griffitt
et al. 2008, Kennedy et al. 2010, Bilberg et al. 2012, Farmen et al.
2012, Cunnigham et al. 2012, Hoheisel et al. 2013, Kim et al. 2013,
Wang et al. 2012) nanosilver was less sensitive than ionic silver on
six occasions and equally as sensitive, at least for a single type of
nanosilver, on two occasions.
is no statistically significant correlation between smaller particle
size and increased toxicity (Kendall test, p>0.05) between either raw
or media particle size and LC50. An additional analysis excluding LC50
values from studies with materials with primary particle size greater
than 100 nm also resulted in no statistically significant correlation
(Kendall test, p>0.05) between either raw or media particle size and
the LC50 values from materials with different coatings were compared
using a non-parametric ANOVA procedure (Kruskal-Wallis, p<0.05) a
statistically significant difference between coating material and LC50
value was identified. PVP and citrate coated materials appear to have
lower toxicity than other coating materials and uncoated materials.
However, this cannot be confirmed using a statistical post-hoc test as
the variance and normality of the different groups is homogenous.
observation is supported by data from Kevin Kwok (pers comm) on the
acute toxicity (96 hour LC50) of nanosilver particles of various sizes
and coatings (gum arabic, PVP, citrate-tannic acid,
citrate-glutathione and citrate) to Japanese medaka (Oryzias latipes).
These data describe differential toxicity on the basis of coating
material, but with limited influence of particle size. The relative
toxicity of nanomaterials, from most to least toxic, was as follows:
gum arabic < PVP < citrate-tannic acid < citrate-glutathione < citrate
< PVP (nanoamor). The toxicity of PVP coated nanoparticles was
variable, but appeared to be dependent on the manufacturer of the
nanomaterial, possibly due to differences in the chain length of PVP
polymer molecules used in the coating, although additional information
would be required to confirm this.
irrespective of coating of particle size, all forms of nanosilver were
significantly less toxic than ionic forms of silver. Of particular
significance are the conclusions for Hoheisel et al. (2012) (all
authors from the US-EPA) who state that, based on their findings,
regulatory approaches based on the toxicity of ionic silver to aquatic
life would not be under protective for environmental releases of
duration is considered as a critical factor in ecotoxicity tests with
metals as sensitivity is known to be influenced by exposure duration
(greater toxicity after longer exposure). Some of the available acute
data for nanosilver reported here are from exposure durations of 48
hours, which is significantly shorter than the standard 96 hour
exposure exposure duration for acute fish toxicity. However, these
data have not been excluded from this analysis on the basis of
exposure duration as they are otherwise “well documented and
scientifically acceptable” (Klimisch et al. 1996). As the majority of
data for nanosilver from this endpoint are from studies of at least 96
hours exposure, with many of longer duration, this is not considered
to have adversely affected the integrity of the comparison between the
relative sensitivity of ionic and nanosilver for this endpoint.
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