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Toxicity to aquatic algae and cyanobacteria

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Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Substance considered to fall within the scope of the read-across 'Silver metal: Justification of a read-across approach for environmental information requirements' (document attached in IUCLID section 13).
Reason / purpose for cross-reference:
read-across source
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.41 µg/L
95% CI:
>= 0.29 - <= 0.52
Nominal / measured:
meas. (TWA)
Conc. based on:
element (dissolved fraction)
Basis for effect:
growth rate
Details on results:
The calibration curve used to determine cell densities in the algae exposures shows a clear linear relationship between cell densities and fluorescence intensity (R² = 0.998).
Reported statistics and error estimates:
Effect concentrations (NOEC, lowest-observed-effect concentration [LOEC], and ECx) were calculated based on measured dissolved Ag concentrations. All effect concentrations were calculated based on relative responses (expressed relative to the mean control response of the respective experiment). The EC10, EC20, and EC50 values were calculated based on the 2-parameter Weibull concentration–response model using the “drc” package in R, Ver 3.3.2 (R Development Core Team 2016).
The NOECs and LOECs were calculated with the Williams (1971) test, after evaluation of the data for adherence to the underlying assumptions of normality and homogeneity of variances.

Overview of cell density and growth ratesain the different exposure treatments of the 72h-Anabaena flos-aquae growth inhibition test

Nominal Ag

Dissolved Ag

(µg/L)

Time- weighted average

Cell density

(x104cells/mL)

Growth rate

(d-1)

(µg/L)

t 0h

t 1hb

t 24h

t 48h

t 72h

dissolved Agc

Day 1

Day 2

Day 3

t 0h – t 72h

 

 

 

 

 

 

(µg/L)

 

 

Control

<0.01

<0.01

<0.01

<0.01

<0.01

<0.01

3.91±0.34

10.4±1.6

22.5±4.4

1.03±0.05

0.22

0.16

0.16

0.12

0.10

0.09

0.11

3.66±1.00

10.4±2.4

23.4±4.1

1.05±0.06

0.46

0.28

0.28

0.17

0.12

0.10

0.16

3.52±0.38

9.29±1.36

24.4±4.2

1.05±0.05

1

0.6

0.5

0.41

0.27

0.22

0.35

1.90±0.18

6.11±1.58

18.5±3.9

0.99±0.10

2.2

1.4

1.1

1.1

0.66

0.44

0.84

1.99±0.28

1.27±1.21

0.63±0.4

-0.24±0.18

4.6

2.9

2.4

2.1

2.0

1.8

2.0

1.57±0.29

0.40±0.09

0.15±0.03

-0.71±0.06

10

7.5

6.5

4.1

3.7

4.0

4.3

1.20±0.20

0.42±0.08

0.08±0.06

-0.96±0.31

22

11

10

6.5

5.6

5.6

6.6

1.32±0.17

0.56±0.04

0.16±0.05

-0.66±0.10

aAverage of all replicates ± standard deviation is reported.

bSample taken in the exposure vessels approximately 1h after the inoculation with cyanobacteria.

cTime-weighted average of dissolved silver concentrations in fresh solutions at t 0h and those measured in the algae exposures (1h, 24h, 48h & 72h).

Above table shows that a clear concentration–response behavior was observed with increasing Ag doses. At the 3 lowest silver doses, growth was comparable to the control growth. In the higher Ag doses, a negative growth was observed during the 72-h growth inhibition test (i.e., lower cell densities than the inoculum density at test initiation), suggesting that A. flos-aquae was dying in these Ag treatments. Algal clusters were observed at the control and 3 lowest Ag doses but were absent in the higher Ag doses.

Effect concentrations(expressed as measured dissolved silver concentrations) of ionic silver (Ag) to the aquatic speciesAnabaena flos-aquae.

Endpoint

EC10

(µg Ag/L)

EC20

(µg Ag/L)

EC50

(µg Ag/L)

NOEC

(µg Ag/L)

LOEC

(µg Ag/L)

Growth rate

0.41

(0.29-0.52)

0.46

(0.25-0.67)

0.56

(0.16-0.96)

0.35

(4±10)

0.84

(100±0)

ECxvalues were calculated using a Weibull function with 2 parameters. 95% confidential intervals are reported between parentheses.

NOEC and LOECs were calculated using the Williams-test. The average growth rate inhibition ± standard deviation (%) relative to the control at the NOEC or LOEC are reported between brackets.

Validity criteria fulfilled:
yes
Remarks:
Control increased 28-fold over 72 h, i.e. in line with OECD validity criteria (≥16-fold). Average control growth rate was 1.03 ± 0.05 d–1 with CV of 5% and CV among the sectional (day-by-day) growth rates in the control was 33%.
Conclusions:
An EC10 of 0.41 μg dissolved Ag /L for the endpoint growth rate was found after 72h exposure of A. flos-aquae to silver nitrate.
Executive summary:

In a 72 hour study with the cyanobacteria Anabaena flos-aquae exposed to silver nitrate, the EC10 for growth rate was 0.41 µg dissolved Ag/L.

 

This is a guideline study considered suitable for use as a key study for this endpoint.

Endpoint:
toxicity to aquatic algae and cyanobacteria
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Substance considered to fall within the scope of the read-across 'Silver metal: Justification of a read-across approach for environmental information requirements' (document attached in IUCLID section 13).
Reason / purpose for cross-reference:
read-across source
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.46 µg/L
95% CI:
>= 0.31 - <= 0.62
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth rate
Remarks on result:
other: based on mean measured total Ag
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
2.52 µg/L
95% CI:
>= 2.13 - <= 2.98
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth rate
Remarks on result:
other: based on mean measured total Ag
Duration:
72 h
Dose descriptor:
LOEC
Effect conc.:
2.35 µg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth rate
Remarks on result:
other: based on mean measured total Ag
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.47 µg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
growth rate
Remarks on result:
other: based on mean measured total Ag
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.36 µg/L
95% CI:
>= 0.29 - <= 0.42
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
other: yield
Remarks on result:
other: based on mean measured total Ag
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.82 µg/L
95% CI:
>= 0.73 - <= 0.92
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
other: yield
Remarks on result:
other: based on mean measured total Ag
Duration:
72 h
Dose descriptor:
LOEC
Effect conc.:
0.47 µg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
other: yield
Remarks on result:
other: based on mean measured total Ag
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.11 µg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (total fraction)
Basis for effect:
other: yield
Remarks on result:
other: based on mean measured total Ag
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.1 µg/L
95% CI:
>= 0.05 - <= 0.16
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (dissolved fraction)
Basis for effect:
growth rate
Remarks on result:
other: based on mean measured conventional dissolved Ag
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.96 µg/L
95% CI:
>= 0.72 - <= 1.32
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (dissolved fraction)
Basis for effect:
growth rate
Remarks on result:
other: based on mean measured conventional dissolved Ag
Duration:
72 h
Dose descriptor:
LOEC
Effect conc.:
0.74 µg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (dissolved fraction)
Basis for effect:
growth rate
Remarks on result:
other: based on mean measured conventional dissolved Ag
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.13 µg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (dissolved fraction)
Basis for effect:
growth rate
Remarks on result:
other: based on mean measured conventional dissolved Ag
Key result
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.1 µg/L
95% CI:
>= 0.08 - <= 0.12
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (dissolved fraction)
Basis for effect:
other: yield
Remarks on result:
other: based on mean measured conventional dissolved Ag
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.24 µg/L
95% CI:
>= 0.21 - <= 0.27
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (dissolved fraction)
Basis for effect:
other: yield
Remarks on result:
other: based on mean measured conventional dissolved Ag
Duration:
72 h
Dose descriptor:
LOEC
Effect conc.:
0.13 µg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (dissolved fraction)
Basis for effect:
other: yield
Remarks on result:
other: based on mean measured conventional dissolved Ag
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.04 µg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element (dissolved fraction)
Basis for effect:
other: yield
Remarks on result:
other: based on mean measured conventional dissolved Ag
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.005 µg/L
95% CI:
>= 0.003 - <= 0.008
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element
Basis for effect:
growth rate
Remarks on result:
other: based on mean measured truly dissolved Ag
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.285 µg/L
95% CI:
>= 0.219 - <= 0.365
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element
Basis for effect:
growth rate
Remarks on result:
other: based on mean measured truly dissolved Ag
Duration:
72 h
Dose descriptor:
LOEC
Effect conc.:
0.299 µg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element
Basis for effect:
growth rate
Remarks on result:
other: based on mean measured truly dissolved Ag
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
0.003 µg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element
Basis for effect:
growth rate
Remarks on result:
other: based on mean measured truly dissolved Ag
Duration:
72 h
Dose descriptor:
EC10
Effect conc.:
0.001 µg/L
95% CI:
>= 0.001 - <= 0.002
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element
Basis for effect:
other: yield
Remarks on result:
other: based on mean measured truly dissolved Ag
Duration:
72 h
Dose descriptor:
EC50
Effect conc.:
0.016 µg/L
95% CI:
>= 0.014 - <= 0.018
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element
Basis for effect:
other: yield
Remarks on result:
other: based on mean measured truly dissolved Ag
Duration:
72 h
Dose descriptor:
LOEC
Effect conc.:
<= 0.003 µg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element
Basis for effect:
other: yield
Remarks on result:
other: based on mean measured truly dissolved Ag
Duration:
72 h
Dose descriptor:
NOEC
Effect conc.:
< 0.003 µg/L
Nominal / measured:
meas. (geom. mean)
Conc. based on:
element
Basis for effect:
other: yield
Remarks on result:
other: based on mean measured truly dissolved Ag
Details on results:
- Exponential growth in the control (for algal test): yes
- Observation of abnormalities (for algal test): At the end of the test (day 3), the cells were normal and there was almost no cell debris in the control and at test concentration of 0.316 µg Ag/L. Slightly less intact cells but normal appearance, almost no cell debris were observed at ttest concentrations of 1.00 µg Ag/L. At 3.16 and 10.0 and 316 µg Ag/L there were clearly less intact cells and cells debris observed. At the highest test concentration of 31.6 µg Ag/L cell debris and barely intact cells were noted.
- Other: The measurements of size and zeta potential revealed at all test concentrations that the chosen concentrations, which represented an optimal range for the growth test, were not sufficient for the size and zeta potential analysis. Especially the count rate of the size measurements indicated that the test concentrations were too low.
Results with reference substance (positive control):
- Results with reference substance valid? Yes, results were in good agreement with the results of an international ring test with an ErC50 of 3.38 ± 1.30 mg/L
- EC50: ErC50 value of 3.35 mg/L (95 % confidence limits: 3.27 - 3.44 mg/L)
Reported statistics and error estimates:
For the growth test, mean average growth rates were calculated (entire exposure period of 0 - 3 d) and calculation of the percent inhibition compared to controls of growth rate or sectional growth rate [r], and yield [y] for the exposure period were performed.
The test results of the growth inhibition test were statistically analysed to determine an EC50, EC20 and EC10 value together with 95 % confidence intervals using a non-linear regression model (3-parametric cumulative distribution function according to Bruce and Versteeg (1992) for yield and linear regression (probit) for growth rate. Individual replicate responses were used for the regression analysis.
The NOEC values were determined using appropriate statistical methods (Williams` Multiple Sequential t-Test. The computer program ToxRat was used for statistical evaluations.

Effective concentrations based on mean measured total Ag concentrations

Table 1: Percent inhibition of growth rate and yield compared to controls after 72 hours.

Mean measured
total Ag
[µg Ag/L]

% Inhibition of yield

% Inhibition of growth rate

Control

0

0

0.11

0.26 (-)

0.01 (-)

0.47

19.2 (+)

4.08 (+)

2.35

94.0 (+)

53.0 (+)

11.2

99.4 (+)

85.9 (+)

28.0

99.5 (+)

88.1 (+)

(+) statistically significant difference between controls / (-) no significant difference between controls and treatments. Williams t-test (growth rate) and Welsh t-test with Bonferroni Adjustment (yield), significance level 0.05, one-sided smaller.

Table 2: Effective concentrations based on mean measured total Ag concentrations for the exposure ofR. subcapitatafor 72 hours.

Mean measured test item concentrations [µg/L] - total Ag

Parametera

 

EC10

EC20

EC50

LOEC

NOEC

Growth rate (r)

Value

0.46

0.82

2.52

2.35

0.47b

 

95 %-cl lower

0.31

0.61

2.13

 

 

 

95 %-cl upper

0.62

1.03

2.98

 

 

Yield (y)

Value

0.36

0.48

0.82

0.47

0.11

 

95 %-cl lower

0.29

0.41

0.73

 

 

 

95 %-cl upper

0.42

0.55

0.92

 

 

a: ECx values for growth rate were calculated using linear regression and for yield a non-linear regression model was used.

b: The NOEC for growth rate was calculated to be at 0.11 µg Ag/L based on geometric mean measured concentrations of total Ag. However, due to the low inhibition of 4.08% at a concentration of 0.47 µg Ag/L, the NOEC was set to 0.47 µg Ag/L, since effects below 10 % compared to control are generally not considered to be ecotoxicologically relevant and it is generally recommended by OECD and EFSA to use the EC10 approach in preference to the NOEC approach for the environmental risk assessment.

Effective concentrations based on conventional dissolved Ag

Table 3: Percent inhibition of growth rate and yield compared to controls after 72 hours.

Mean measured
conventional dissolved Ag
[µg Ag/L]

% Inhibition of yield

% Inhibition of growth rate

Control

0

0

0.04

0.26 (-)

0.01 (-)

0.13

19.2 (+)

4.08 (+)

0.74

94.0 (+)

53.0 (+)

9.20

99.4 (+)

85.9 (+)

25.7

99.5 (+)

88.1 (+)

(+) statistically significant difference between controls / (-) no significant difference between controls and treatments. Williams t-test (growth rate) and Welsh t-test with Bonferroni Adjustment (yield), significance level 0.05, one-sided smaller.

Table 4: Effective concentrations based on mean measured concentrations of conventional dissolved Ag for the exposure ofR. subcapitatafor 72 hours.

Mean measured test item concentrations [µg/L] – conventional dissolved Ag

Parametera

 

EC10

EC20

EC50

LOEC

NOEC

Growth rate (r)

Value

0.10

0.22

0.96

0.74

0.13b

 

95 %-cl lower

0.05

0.14

0.72

 

 

 

95 %-cl upper

0.16

0.31

1.32

 

 

Yield (y)

Value

0.10

0.14

0.24

0.13

0.04

 

95 %-cl lower

0.08

0.11

0.21

 

 

 

95 %-cl upper

0.12

0.16

0.27

 

 

a: ECx values for growth rate were calculated using linear regression and for yield a non-linear regression model was used.

b: The NOEC for growth rate was calculated to be 0.04 µg Ag/L based on geometric mean measured concentrations of conventional dissolved Ag. However, due to the low inhibition of 4.08% at a concentration of 0.13 µg Ag/L, the NOEC was set to 0.13 µg Ag/L, since effects below 10% compared to control are generally not considered to be ecotoxicologically relevant and it is generally recommended by OECD and EFSA to use the EC10 approach in preference to the NOEC approach for the environmental risk assessment.

 

Effective concentrations based on truly dissolved Ag

Table 5: Percent inhibition of growth rate and yield compared to controls after 72 hours.

Mean measured
truly dissolved Ag
[µg Ag/L]

% Inhibition of yield

% Inhibition of growth rate

Control

0

0

0.003

19.2 (+)

4.08 (+)

0.299

94.0 (+)

53.0 (+)

8.03

99.4 (+)

85.9 (+)

24.0

99.5 (+)

88.1 (+)

(+) statistically significant difference between controls / (-) no significant difference between controls and treatments. Williams t-test (growth rate) and Welsh t-test with Bonferroni Adjustment (yield), significance level 0.05, one-sided smaller.

Table 6: Effective concentrations based on mean measured concentrations of truly dissolved Ag for the exposure ofR. subcapitatafor 72 hours.

Mean measured test item concentrations [µg/L] – truly dissolved Ag

Parametera

 

EC10

EC20

EC50

LOEC

NOEC

Growth rate (r)

Value

0.005

0.020

0.285

0.299

0.003b

 

95 %-cl lower

0.003

0.012

0.219

 

 

 

95 %-cl upper

0.008

0.030

0.365

 

 

Yield (y)

Value

0.0014

0.0031

0.0157

≤ 0.003

< 0.003

 

95 %-cl lower

0.0012

0.0028

0.0136

 

 

 

95 %-cl upper

0.0016

0.0037

0.0183

 

 

a: ECx values for growth rate and yield were calculated using linear regression.

b: The NOEC for growth rate was calculated to be below 0.003 µg Ag/L based on geometric mean measured concentrations of truly dissolved Ag. However, due to the low inhibition of 4.08% at this concentration, the NOEC was set to 0.003 µg Ag/L, since effects below 10% compared to control are generally not considered to be ecotoxicologically relevant and it is generally recommended by OECD and EFSA to use the EC10 approach in preference to the NOEC approach for the environmental risk assessment.

Note:ECx values were calculated based on the four highest test concentrations. Since a calculation of the geometric mean measured concentration over 72 hours was not possible for the lowest test concentration, the concentrations was excluded from the evaluation.

Validity criteria fulfilled:
yes
Remarks:
The cell number in the control increased by a factor of 170.9 within 72 hour, the mean of the replicate CV % in the section-by-section growth rate of controls: 8.84 %, CV of average specific growth rate at test end in replicate control cultures: 1.4 %
Conclusions:
Based on mean measured total Ag concentrations, the 72 hour ErC50 was 2.52 µg Ag/L and ErC10 was 0.46 µg Ag/L. For yield an EyC50 and EyC10 were 0.82 and 0.36 µg Ag/L, respectively. The NOECs for growth rate and for yield were 0.47 and 0.11 µg Ag/L, respectively.

Based on mean measured conventional dissolved Ag concentrations, the 72 hour ErC50 was 0.96 µg Ag/L and ErC10 was 0.10 µg Ag/L. For yield an EyC50 and EyC10 were 0.24 and 0.10 µg Ag/L, respectively. The NOECs for growth rate and for yield were 0.13 and 0.04 µg Ag/L, respectively.

Based on mean measured truly dissolved Ag concentrations, the 72 hour ErC50 was 0.285 µg Ag/L and ErC10 was 0.005 µg Ag/L. For yield an EyC50 and EyC10 were 0.01579 and 0.0014 µg Ag/L, respectively. The NOECs for growth rate and for yield was 0.003 µg Ag/L.

Executive summary:

The 72 hour toxicity of silver nitrate to the uni-cellular green alga Raphidocelis subcapitata was determined in a static system (OECD 201) exposed to nominal concentrations of 0.316, 1.00, 3.16, 10.0 and 31.6 µg Ag/L.

The nominal test concentrations were prepared in sterile modified AAP growth medium under sterile conditions. The medium was prepared with reduced EDTA concentrations and compounds including chloride were replaced by nitrate compounds. The concentrations of the test item in the test media were determined by chemical analysis of silver in the aqueous phase of all treatment levels by ICP-MS at test initiation, after 24 h, 48 h and at the test termination of the growth test (LOQ = 0.001 µg/L). Three different types of measurements were conducted: Total Ag, Conventional dissolved Ag after filtration of a subsample through 0.45 µm PSE filters and Truly dissolved Ag after filtration with centrifugal filters at 3000 x g. The particle size and the zeta potential were measured from samples of an extra analytical vessel without algae to characterise the test item in test media at test initiation and test termination. The evaluation of the results was based on the geometric mean measured concentrations of total Ag, conventional dissolved Ag and truly dissolved Ag.

This is a guideline, GLP- study and considered suitable for use as a key study for this endpoint.

For PNEC derivation, reliable EC10 for Pseudokirchneriella subcapitata on the endpoints yield and growth rate of 0.10 μg/L could be extracted from this study (expressed as conventional dissolved Ag).

Description of key information

Read across from ionic silver

Plus supporting data from a P. subcapitata study comparing the effects of the smallest nanosilver form registered under REACH previously (‘Nano 8.1’) and ionic silver (silver nitrate), demonstrating nanosilver is less toxic than ionic silver (based on EC10 and EC50 values)

Plus supporting published data from 2 studies on P. subcapitata included in the REACH dossier as Endpoint Study Records with various sizes of nanoparticles, showing that nanosilver is equally or less toxic than ionic silver

Key value for chemical safety assessment

Additional information

Summary of available data for uncoated and coated nanosilver

Reliable and relevant data on the toxicity of silver and silver-based (coated) nanomaterials to algae and cyanobacteria are available from three studies (Griffitt et al. 2008, McLaughlin and Bonzongo 2012, Schlich et al. 2017 a,b). The Griffit (2008) and McLaughlin and Bonzongo (2012) studies used uncoated spherical nanoparticles with mean particle size of >30 nm. However, the media used for toxicity testing affected the subsequent aggregation/agglomeration behaviour of nanosilver particles in test systems with mean particle sizes in test systems ranging from 35 nm to ~200 nm dependent upon the study and whether the study used natural water or artificial media e. g. McLaughlin and Bonzongo (2012). Reported EC50 values for algae (all relating to Pseudokirchneriella subcapitata) range considerably, which may reflect differences in the bioavailability of silver or nanosilver in the media used for the individual tests. The greatest toxicity (IC50 of 4.61 µg/L) was observed in artificial algal media with lowest toxicity (IC50 of 1,600 µg/L) observed in a field collected water representative of wetland conditions.

Schlich et al. (2017 a,b) undertook comparative studies for nanosilver and silver nitrate with the alga, Raphidocelis subcapitata (formerly Pseudokirchneriella subcapitata). Schlich et al. (2017a) describes the effects on Raphidocelis subcapitata exposed to silver nitrate, while Schlich et al. (2017b) describes the effects on Raphidocelis subcapitata exposed to nanosilver. Both of these studies were conducted to OECD guideline 201 according to the principles of GLP, Both studies were conducted insynthetic, modified AAP medium, in whichthe trace elements and macro nutrients containing Cl-were replaced by suitable elements containing nitrate (NO3-) and EDTA was reduced.

The nanosilver material used was a powder in aqueous suspension with the following particle size distribution: D25 = 7 nm, D50 = 8 nm, D75 = 9 nm (see section 4.5 of IUCLID), and contained 37% silver.

The EC10 values for growth rate for nanosilver were 0.37 (<0.45 µm) and 0.17 (<3kDa) µg/L measured dissolved silver. The corresponding EC10 values for algal yield for nanosilver were 0.26 (<0.45 µm) and 0.08 (<3kDa) µg/L measured dissolved silver. The comparable EC10 values for growth rate for silver nitrate were 0.1 (<0.45 µm) and 0.005 (<3kDa) µg/L measured dissolved silver. The EC10 values for algal yield for silver nitrate were 0.1 (<0.45 µm) and 0.0014 (<3kDa) µg/L measured dissolved silver. Thus, the directly comparable EC10 values reported by Schlich et al (2017 c,d) were more toxic for ionic silver than for nanosilver.

Critically, all the reliable data available for nanosilver indicate that it is less hazardous to algae than ionic silver.

These data support the read-across of properties from ionic silver to nanosilver in both the freshwater and marine compartment. At present, as the available algal dataset is small, no conclusions can be made regarding the influence of particle size or coating material on the resulting toxicity of nanosilver to algae.