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EC number: 231-131-3
CAS number: 7440-22-4
Table 1: Measured concentrations of silver (Ag) in soils used for
the plant toxicity tests (inhibition of root growth). Values in
parentheses represent the measured concentration as a percentage of the
expected nominal concentration
Nominal concentration (mg/kg)
Average measured concentration (mg/kg)
The toxicity of Ag to barley (Hordeum vulgare), was tested
according to ISO guideline 11269-1. For the inhibition of root growth
test, both root and shoot length were measured as endpoints. In most
cases the root length data were found to provide the most sensitive
endpoint when deriving EC10 and EC50 values. Overall the EC10 values for
root length were found to range from 13 (Houthalen) to 176 (Millicent)
mg Ag/kg in the unleached treatment and organic carbon was found to be
the soil property responsible for influencing the toxicity of Ag to
barley. The EC10 based on shoot length were between 2.3 mg Ag/kg
(Kingaroy) and 301 mg Ag/kg (Millicent) in the unleached treatments.
Table1: Results from analyses of the selected study soils for pH,
organic carbon, cation exchange capacity, particle size distribution and
total silver concentration.
Cation exchange capacity
Particle size distribution (%)
Total Silver (mg/kg)
* note that particle size distribution
for Port Kenny is equal to 37.2% due to the high concentration of CaCO3that
is present in this soil (60%)
Table 2: Silver (Ag) concentrations corresponding to a 10% and 50%
reduction in plant biomass (EC10 and EC50, respectively) in soils aged
12 months and 1 month. All concentrations are shown as mg Ag/kg and
values in parentheses represent the 95% confidence intervals.
* indicate significantly
(p < 0.05) lower values when the leached and unleached ECx values are
AF: ageing factor
calculated as 12 month ECx/1 month ECx
interval(s) not available due to large variability in data
Effect of soil ageing on plant uptake of silver
The BAFs that were calculated from the Ag concentrations in the above
ground plant tissue showed a general decreasing trend when the 1 month
results were compared to the 12 month results. Due to the high
variability in the data, significantly lower BAFs were only evident in
the Bordeaux and Port Kenny soils. In contrast, at one Ag rate in the
Houthalen and two rates in the Kingaroy soils, the opposite trend was
significant, whereby a significantly lower BAF was observed in the 1
month samples compared to the 12 month samples. Overall, there was an
average 15% reduction in BAF values of the 12 month aged samples
compared to the 1 month aged samples. The overall decreasing trend in
the BAFs values indicates that there is a decrease in the uptake of Ag
into the plants with time, which is also consistent with the decreasing
toxicity that was observed as evidenced by the AFs greater than 1.
An affect of soil ageing on the toxicity of silver, using tomatoes (Lycopersicum
esculentum) as the test species was tested using soils spiked with
silver that were subsequently allowed to age for either one or 12
months. In all cases, the EC10 and EC50 values were significantly lower
or there was no significant difference compared to those generated in
soils that had been aged for one month. EC10 values for plant height in
soil aged for one month ranged between 2.3 (Houthalen) and 62 mg Ag/kg
(Millicent), whilst EC10 vales in soils aged for 12 months were between
7.6 mg Ag/kg (Houthalen) and 180 mg Ag/kg (Bakalava) .For biomass, the
EC10 values ranged from 0.47 (Houthalen) to 108 mg Ag/kg (Port Kenny)
and from 1 mg Ag/kg (Houthalen) to 253 mg Ag/kg (Port Kenny) in one and
12 months aged soils, respectively. The Aging Factors (AFs) determined
in the study were found to range from 1.7 to 22 for the EC10 values and
1.3 to 2.8 for the EC50 values with an overall average AF of 2.4 (the
Bordeaux EC10 AF of 22 was removed from the calculation of average value
as it was considerably higher than the other values). The results
indicate that after a 12-month ageing period the toxicity of Ag
decreased by a factor of approximately two.
TableA.2: Measured concentrations of silver (Ag) in soils used for
the plant toxicity tests (inhibition of root growth and seedling
emergence and early growth). Values in parentheses represent the
measured concentration as a percentage of the expected nominal
The toxicity of Ag to plants was tested according to OECD guideline 208
using tomatoes (Lycopersicum esculentum) as the test species. The
tests were conducted in eight different soils representing a wide range
of soil properties (pH 3.6 – 8.0, organic carbon 0.9 – 12% and clay 1.4
– 60%). Results from leached and unleached soil treatments are reported.
The endpoints measured in the seedling emergence and early growth test
included emergence, plant height and plant biomass (dry weight). Plant
emergence showed very low sensitivity, therefore, the results are not
presented. The plant growth endpoints of height and biomass both showed
high sensitivity to additions of Ag to the soil. Plant biomass showed
the highest sensitivity, however, the results were considerably more
variable than the plant height data. The EC10 values for plant height in
unleached soil ranged from 4.1 (Inman Valley) to 54 (Charleston) mg
Ag/kg. The toxicity of Ag to tomato appeared to be controlled by soil pH
and organic carbon. The EC10 values based on tomatoes weight were found
to range from 0.7 (Inman Valley) to 58 (Port Kenny) mg Ag/kg in
chronic toxicity of silver nitrate to the plant Lactuca sativa was
tested in an OECD 208 test. The test was conducted as a static exposure
with a single soil type. Six test concentrations and a control were
included, and the results are expressed based on the measured total
silver concentration at the end of the test. The emergence, survival and
shoot growth of the plants was studied over 17 days. No oberserved
effect concentrations (NOEC) were determined for each biological
endpoint. The most sensitive endpoint for this test was shoot growth,
with a 17 day NOEC of 0.16 mg Ag/kg dw for shoot length, wet and dry
weight and an EC10 of 0.13 mg Ag/kg dw for shoot dry weight.
of available data for uncoated and coated nanosilver
quality assessment only a single study reporting the effects of
nanosilver on terrestrial plants is available (Lee et al. 2012b).
There are several other studies reporting reliable data on the effects
of nanosilver on terrestrial plant species (Barrena et al. 2009, Yin
et al. 2011, Geisler-Lee et al. 2013, Le et al. 2013, Mirzajani et al.
2013, Musante and White 2012, Wang et al. 2013), however, as these
were conducted using aqueous exposure media, agar or filter paper
media they are not directly relevant to the measurement of the effects
of nanosilver in soils for REACH.
et al. (2012b) report the effects of exposure of citrate coated
nanosilver to two commercially important plant species in soil:
mungbean (Phaseolus radiates) and sorghum (Sorghum bicolour).
Lee et al. (2012b) also report the results of exposures conducted in
agar media, which are not discussed further. Exposures, based on
nominal concentrations, were conducted in synthetic OECD soil over
five days with effects on shoot and root length measured.
NOEC of >2,000 mg/kg dry weight, which was the highest concentration
of nanosilver particles tested, was reported for shoot and root length
inP. radiates. Conversely, a NOEC of <100 mg/kg dry weight,
which was the lowest concentration of nanosilver particles tested, was
reported for effects on shoot length inS. bicolor. However, an
interrupted dose-response (non-monotonic) relationship was observed in
this study as at the highest concentration tested (2,000 mg/kg dry
weight) there were no statistically significant difference between
shoot length in the experimental and control treatments. A NOEC of 100
mg/kg for root length effects inS. bicolor was also reported,
with a corresponding LOEC of 300 mg/kg. However, root length inS.
bicolor after exposure to 2,000 mg/kg dry weight nanosilver was
only slightly, but statistically significantly, reduced (i.e. by
non-monotonic results reported forS. bicolor, indicative of an
interrupted dose-response, suggest that there was some confounding
factor affecting theS. bicolor response in the test,
potentially related to soil partitioning. The NOEC of <100 mg/kg dry
weight for shoot length and 100 mg/kg for root length, should be
interpreted with a degree of caution. In their manuscript Lee et al.
(2012b) conclude that exposure ofS. bicolor to nanosilver in
soil resulted in a “slightly reduced growth rate”, rather than
ascribing any greater magnitude of effect.
et al. (2012b) also undertook a comparative assessment of the toxicity
of silver ions (as silver nitrate) and nanosilver particles to P.
radiatus and S. bicolor. NOECs for effects on root length
were reported as 200 mg/kg dry weight and 300 mg/kg dry weight for P.
radiates and S. bicolor, respectively. No effects were
observed on shoot length in either P. radiatus and S.
bicolor at the highest concentration of silver ions tested (500
on these results, P. radiates is approximately 100 times more
sensitive to ionic silver than nanosilver. In contrast, S. bicolor is
more sensitive to nanosilver than ionic silver based on the results of
the root length endpoint. However, as discussed above, these results
should be interpreted with caution as they are from a non monotonic,
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