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EC number: 231-131-3
CAS number: 7440-22-4
The reported BCF at a steady state was ~70. This study does not follow a
standard guideline and only tests one concentration. However, the method
is acceptable and therefore this study is considered suitable for use
for this endpoint.
of available data for uncoated and coated nanosilver
relevant to the bioaccumulation of uncoated and coated nanosilver are
available from 12 studies. However, whilst none of these studies are
consistent with standard assessments of bioaccumulation as outlined in
REACH endpoint specific guidance, i.e. studies conducted according to
the principles outlined in OECD guidance document 305 (exposure up to
28 days followed by 14 days depuration with measurement of whole body
concentrations), the study by Griffitt et al. (2013) provides useful
and relevant information for the comparative assessment of the
relative bioaccumulation potential of ionic and nanosilver obtained
from a study that most closely resembles a standard method.
et al. (2013) undertook a comparative assessment of the accumulation
of silver in zebra fish (Danio rerio), alongside concurrent
effects on gene expression, after exposure to either ionic or
nanosilver. Adult zebra fish were subject to a 32 day flow-through
exposure (0-28 days with silver) to four concentrations of
commercially obtained nanosilver (5, 15, 25 and 50 µg/L) and a single
concentration of silver nitrate (5 µg/L). Each treatment comprised
four replicates of 20 fish. Nanosilver was characterised in stock
solutions to have a particle size of 3.1 ± 2.23 nm or 1.7 nm by TEM
and DLS methods, respectively. Measured silver concentrations in
exposure media stock solutions were 40-50 % of nominal concentrations.
Accumulation of silver was measured in gills and carcass tissue at
days 7, 14, 21 and 28. Mean BCF values (with 95% confidence intervals)
for silver after exposure to nanosilver and ionic silver were
calculated using data on individual carcass burden (µg/L wet weight)
versus water concentrations presented in the paper. The mean BCF value
for nanosilver was 6.61 (4.68 – 9.12), whilst the mean BCF value for
ionic silver was 95.50 (66.07-138.04). BCF was significantly greater
in ionic silver exposures than in nanosilver exposures (p<0.0001). The
maximum BCF value reported for nanosilver based on an individual
measurement of carcass burden versus water concentration was 46.82.
addition, three studies (Scown et al. 2010, Gaiser et al. 2012,
Schäfers and Weil 2013) contain sufficient information to calculate
tissue-specific BCF values for silver nanomaterials, which can be used
as “worst-case” surrogates for comparison with whole-body BCF data
available for ionic silver.
et al. (2012) investigated the fate and effects of three sizes of
commercially available silver particles (including two nanoparticles:
10 and 35 nm) and ionic silver (as silver nitrate) using 10 day
exposures with Oncorhynchus mykiss (rainbow trout). Uptake into
the gills, liver and kidneys was quantified by inductively coupled
plasma-optical emission spectrometry (ICP-OES). Maximum
tissue-specific BCF values for nanomaterials in gills were 17.2 (10
nm) and 27.7 (35 nm), whilst maximum tissue-specific BCF values in
liver were 26 (10 nm) and 42 (35 nm). Concentrations of silver in
kidneys were below the analytical limit of detection, which precluded
calculation of tissue-specific BCF values.
et al. (2012) investigated the accumulation and effects of nanosilver
and bulk silver (35 and 600–1,600 nm) in 21 day sub-chronic exposures
with Cyprinus carpio. The authors report that an equivalent
mass dose of silver nanoparticles was more toxic than larger
micro-sized material. In addition, silver was found to accumulate in
the liver, gallbladder and gills of carp exposed via the water.
Greater accumulation was observed in fish exposed to 0.1 mg/L than
0.01 mg/L. Maximum tissue-specific BCF values for the 35 nm nanosilver
particles were calculated as 6.18 and 2.92 for liver and gills,
respectively. These measurements are based on total silver and no
characterisation of silver nanoparticles in these tissues is reported.
As described by Scown et al. (2010), silver was not detected above the
analytical limit of detection in kidneys. Silver was also detected in
the intestines of C. carpio, resulting in a maximum
tissue-specific BCF value of 997. However, no depuration phase was
reported in the study and it is not clear if intestine samples would
include material present within the gut lumen, rather than accumulated
material in mesentery. The former scenario would result in the
calculation of greatly enhanced BCF values that are not consistent
with true accumulation.
an supplementary study to a conventional early life-stage toxicity
test with nanosilver, Schäfers and Weil (2013) exposed juvenile zebra
fish (Danio rerio) to 25 and 100 µg/L NM-300K nanosilver for 21
days (semi-static exposure regime with renewal of test dispersions on
days seven and 14) and determined differential tissue uptake of silver
in: 1) head, skin and gills; 2) intestines and stomach; and 3)
remaining fish (fillet, organs, bones). Tissue-specific BCF values in
head, skin and gills were 8.76 and 8.31 after exposure to 15.3 and
67.3 µg/L NM-300K, respectively. Tissue-specific BCF values in
intestines and stomach were 327.0 and 302.0 after exposure to 15.3 and
67.3 µg/L NM-300K, respectively. Tissue-specific BCF values in the
remainder of the fish were 7.58 and 6.17 after exposure to 15.3 and
67.3 µg/L NM-300K, respectively. The values for head, gills and skin
and the remainder of the fish agree well with the BCF values for
nanosilver calculated from the data presented in Griffitt et al.
(2013). However, as observed in Gaiser et al. (2012), BCF values in
intestines and stomach were higher than in other tissues. As discussed
above, it is not clear if intestine samples would include material
present within the gut lumen, rather than accumulated material in
mesentery, which would confound BCF value calculation.
addition, several additional studies describe the behaviour of
nanosilver relevant to an assessment of bioaccumulation but which do
not report BCF data or data from which either whole-body or
tissue-specific BCF values can be calculated.
et al. (2012) report that hyperspectral imaging of Japanese medaka
embryos exposed to nanosilver for 21 days revealed the presence of
nanosilver and their aggregates in tissues of fish. Gill distribution
was ubiquitous, while small amounts were also found in the liver and
brain. No nanosilver particles were detected in/on the epidermis,
spine, skeletal muscle, kidney or gonad of fish. Nanosilver particles
were observed in the gut lumen but rarely in mural elements or
mesentery. The authors conclude that gills were the principal sites of
nanosilver uptake, although ingestion was common.
et al. (2011) report the results of a comparative assessment of the
uptake of nanosilver and ionic silver in cultured rainbow trout (Oncorhynchus
mykiss) gill cells. The largest amount of silver was found in gill
cells exposed to ionic silver. However, citrate and PVP coated
nanosilver were both observed to be taken up by gill cell monolayers,
although uptake was significantly less for the slightly smaller PVP
coated nanosilver particles. In contrast, once accumulated, PVP coated
nanosilver particles were transported across cultured multilayers to a
greater extent than citrate coated nanosilver particles and ionic
silver, although the authors of the study conclude that additional
work is required to confirm these observations.
et al. (2012c/d) undertook studies of the real-time uptake of various
sizes of nanosilver particles (41.6 nm and 11.6 nm average diameter)
in early developing (cleavage-stage) zebrafish embryos. Single
nanosilver particles were observed to passively diffuse into embryos
through chorionic pores via random Brownian motion. Dose and size
dependent effects on embryonic development were observed. Nanosilver
particles were observed in eye (retina), brain, heart and tail.
Deformed zebrafish were found to have accumulated higher numbers of
larger particles than control fish. In addition, at the same molar
concentrations, larger nanosilver particles (41.6 nm) were more toxic
than the smaller nanosilver particles (11.6 nm).
where silver is accumulated after exposure to nanosilver, the current
fish studies are insufficient to distinguish if nanosilver particles
are accumulated or if ionic silver has dissolved from a nanosilver
particle, which is then accumulated.
the exception of the BCF value calculated for intestines using the
data presented by Gaiser et al. (2012) and Schäfers and Weil (2013),
which may be an artefact of experimental design, none of the studies
where BCF or tissue-specific BCF values can be calculated report BCF
values for nanosilver in excess of the value of 70 used in the CSR for
silver, which is based on a whole body BCF calculated after exposure
to ionic silver (silver nitrate). Based on these data, fish would
appear more susceptible to accumulation of ionic silver rather than
nanosilver and an assessment of the bioaccumulative properties of
nanosilver based on the properties of ionic silver would be protective.
in aquatic invertebrates
bioaccumulation in fish drives the assessment of bioaccumulation under
REACH, several studies that describe the relative bioaccumulation
potential of silver from ionic and nanosilver exposures in aquatic
invertebrates are available and these data should be included in a
comparative assessment of the hazard properties of nanosilver and
et al. (2011) compared silver bioavailability and toxicity in Lymnaea
stagnalis (a freshwater gastropod) after exposure to ionic silver
and to nanosilver particles coated with either citrate (17 ± 5 nm by
TEM in test media) or humic acid (13 ± 3 nm by TEM in test media). Lymnaea
stagnalis effectively accumulate silver from both ionic and
nanoparticulate exposures via aqueous or dietary routes. However, for
both routes, uptake rates were faster for ionic silver than for
nanosilver particles. Whilst uptake was slower for nanosilver
particles, loss rates of silver after waterborne exposure were also
faster for nanosilver particles than dissolved silver. The authors
conclude that ingestion of silver associated with particulate
materials appears to be the most important vector of uptake.
a related study, Khan et al. (2012) undertook waterborne exposures
with the estuarine snail Peringia ulvae and concluded that
dissolved silver is twice as bioavailable as nanosilver (citrate
coated 16.5 ± 4.5 nm by TEM). Uptake rates in saline waters were
slower than those reported for Lymnaea stagnalis by Croteau et
al. (2011). Aggregation of nanosilver particles was observed to occur
in estuarine (17 ppt salinity = 79 ± 13 nm) and marine (33 ppt
salinity = 162 ± 21 nm) media. The authors hypothesise that
aggregation of nanosilver particles reduces, but does not eliminate,
the bioavailability of silver from nanosilver particles.
et al. 2013 investigated the biochemical and behavioural responses of
the endobenthic bivalve Scrobicularia plana to nanosilver
(40-45 nm diameter, obtained from JRC stablised in lactate) and ionic
silver in seawater and microalgal food after a 14 day semi-static
exposure. Measured bioaccumulation in the whole soft tissue after
waterborne exposure to ionic silver (10 µg/L) was significantly higher
(992 ± 382 ng/g ww) than in controls (483 ± 253 ng/g ww). However,
there was no significant difference between bioaccumulation after
exposure to 10 µg/L nanosilver (753 ± 467 ng/g ww) and the control.
There was no significant difference between soft tissue concentrations
of silver after dietary exposure to either ionic silver or nanosilver.
Waterborne exposure to either form of silver did not affect feeding
rate. Dietary exposure to either ionic silver or nanosilver resulted
in reduced feeding rate after 10 days exposure.
J, Christian P, Gallegro-Urrea JA, Roos N, Hassellov M, Tollefsen KE,
Thomas KV. 2011. Uptake and effects of manufactured silver
nanoparticles in rainbow trout. Aquatic toxicology. 101: 117-125.
KJ, Nallathamby PD, Browing LM, Osgood CJ, Xu, XN. 2007c. In vivo
imaging of transport and biocompatibility of silver nanoparticles in
early development of zebrafish embryos. ACS Nano. 1: 133-143.
KJ, Browning LM, Nallathamby PD, Desai T, Cherukuri PK, Xu XN. 2012d.
In vivo quantitative study of size-dependent transport and toxicity of
single silver nanoparticles using zebrafish embryos. Chemical research
in toxicology. 25: 1029-1046.
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