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Toxicity to terrestrial plants

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Endpoint:
toxicity to terrestrial plants: short-term
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
1. HYPOTHESIS FOR THE READ-ACROSS APPROACH (ENDPOINT LEVEL)
The REACH registration of silver (powder and massive forms of zero-valent, elemental, silver) is underpinned, in common with other metals, by a read-across (or analogue) approach from the properties of the free ion. This principle of read-across from the free ion has been extended to also include nanosilver.
The scientific validity of read-across from the hazard properties of ionic silver (source) to nanosilver (target) under REACH is underpinned by both theoretical and empirical considerations.
The theoretical basis for the use of ionic silver data as the foundation of the risk assessment of nanosilver is based on the premise that the free metal ion (Me+) is the most toxic metal form/species (Starodub et al. 1987). This consideration was implicit in the development of the Free Ion Activity Model [FIAM] (Morel 1983, Paquin et al. 2002, Campbell 1985, Brown and Markich 2000) and, more recently, the Biotic Ligand Model [BLM] (Paquin et al 2002, Niyogi and Wood 2004) that has underpinned the risk assessment of several metals (e.g. Cu, Ni, Zn) under the Existing Substance Regulations and REACH; and most recently the development of the Environmental Quality Standard (EQS) for nickel and nickel substances under the Water Framework Directive (WFD). When considered on an equal mass basis ionic silver would therefore be expected to have greater toxicity than nanosilver simply on the basis that silver ions are released over time from the surface of particles (via oxidative dissolution). As the properties of nanosilver are read-across directly from ionic silver (not just to the fraction of silver ions released from nanosilver), this read-across is also expected to introduce considerable precaution into the hazard component of the risk assessment of nanosilver as all nanosilver, irrespective of coating, morphology or particle size distribution is assumed to behave similarly to the free ion.
This theoretical consideration has been tested by conducting a comprehensive review of the available scientific literature for nanosilver, with particular emphasis on the comparative effects on REACH relevant biotic systems (REACH information requirement) of ionic silver and nanosilver. This review is described for each endpoint in subsequent sections of the report ‘Nanosilver: read-across justification for environmental information requirements’ (attached in IULCID Section 13) and is summarised below. Furthermore, this theoretical consideration was confirmed by a specific ecotoxicity testing programme undertaken by the EPMF following the silver substance evaluation and designed to compare the effects of the smallest nanosilver form registered under REACH (‘Nano 8.1’ or ‘Silberpulver Typ 300-30’) and silver nitrate to algae, Daphnia (long-term) and soil microorganisms.


2. READ-ACROSS APPROACH JUSTIFICATION (ENDPOINT LEVEL)
In terms of ecotoxicity, nanosilver on an equal mass basis has been found to be significantly less toxic than ionic silver for the majority of REACH endpoints and of equivalent toxicity for some others. None of the empirical information available suggests that nanosilver is consistently more hazardous than ionic silver on an equivalent mass basis, or that “nano-specific” effects that would prejudice the validity of read across from ionic silver to nanosilver occur. In addition, with very limited exceptions which are described further in the report ‘Nanosilver: read-across justification for environmental information requirements’, none of the available data suggested consistent relationships between particle morphology, size, particle size distribution (raw or agglomerated) or coating (surface treatment) and effects.
Notter et al. (2014) presents a meta-analysis of published EC50 values for ionic silver and nanosilver. The authors demonstrate that almost 94% of acute toxicity values assessed for freshwater, seawater and terrestrial systems using algae, annelid, arthropoda, bacteria, crustacea, fish, nematoda, plant, protozoa and rotatoria show that the nanoform of silver is less toxic than the dissolved metal (when normalised for total metal concentration).
In addition, a specific ecotoxicity testing programme designed to compare the effects of the smallest nanosilver form registered under REACH (‘Nano 8.1’ or ‘Silberpulver Typ 300-30’) and silver nitrate to algae, Daphnia (long-term) and soil microorganisms was undertaken following the silver substance evaluation. This demonstrated that the nanoform of silver is less toxic than ionic silver (based on EC10 and EC50 values for total, ‘conventional’ dissolved (<0.45μm) and ‘truly’ dissolved (<3kDa) silver). Therefore, taking the full body of evidence into account, the read-across use of toxicity values from ionic to nanosilver as a ‘worst case’ approach is justified and scientifically defensible for environmental endpoints. The Substance Evaluation Conclusion document for silver agreed with this conclusion for the nanosilver forms covered in the REACH dossier (RIVM 2018).

Toxicity to terrestrial plants
There is one study reporting the toxicity of citrate coated nanosilver to two terrestrial plant species included in the REACH dossier as Endpoint Study Record. These limited data reporting the comparative toxicity of silver and nanosilver to plants, suggest that nanosilver is less hazardous to plants than ionic silver, although there is some uncertainly associated with these data. Together with the theoretical basis for read-across based on the free-ion, this supports the use of ionic silver as the ‘worst case’ basis to read across properties to nanosilver. A summary of this supporting study is available under Section 4.3.2 of the report ‘Nanosilver: read-across justification for environmental information requirements’ (attached in IUCLID Section 13).



For further information and data matrix see 'CSR Annex 9 - Read Across Justification Nanosilver ENV_SUMMARY_200706' attached in IUCLID section 13.
Reason / purpose for cross-reference:
read-across source
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
13 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: root growth
Remarks on result:
other: Houthalen soil, unleached, 95% CL = 10-16
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
20 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: root growth
Remarks on result:
other: Bordeaux soil, unleached, 95% CL = 15-25
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
146 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: root growth
Remarks on result:
other: Inman Valley soil, unleached, 95% CL = 93-210
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
60 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: root growth
Remarks on result:
other: Charleston soil, unleached, 95% CL = 50-71
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
25 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: root growth
Remarks on result:
other: Kingaroy soil, unleached, 95% CL = 18-31
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
176 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: root growth
Remarks on result:
other: Millicent soil, unleached, 95% CL = 143-214
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
61 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: root growth
Remarks on result:
other: Bakalava soil, unleached, 95% CL = 40-84
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
25 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: root growth
Remarks on result:
other: Port Kenny soil, unleached, 95% CL = 18-31
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
215 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: shoot lenght
Remarks on result:
other: Bakalava soil, unleached, 95% CL = 183-251
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
109 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: shoot lenght
Remarks on result:
other: Houthalen soil, unleached, 95% CL = 68-162
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
130 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: shoot lenght
Remarks on result:
other: Bordeaux soil, unleached, 95% CL = 93-165
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
131 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: shoot lenght
Remarks on result:
other: Inman Valley, unleached, 95% CL = 110-156
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
62 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: shoot lenght
Remarks on result:
other: Charleston soil, unleached, 95% CL = 39-90
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
2.3 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: shoot lenght
Remarks on result:
other: Kingaroy soil, unleached, 95% CL = 0.34-5.4
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
301 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: shoot lenght
Remarks on result:
other: Millicent soil, unleached, 95% CL = 220-394
Species:
Hordeum vulgare
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
45 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: shoot growth
Remarks on result:
other: Port Kenny soil, unleached, 95% CL = 35-56
Details on results:
SEED GERMINATION
- Percent seed germination: There was 100% germination observed in all of the control soils.
- Root length: The root length in the control soils varied across the different soils, however, was sufficient for all subsequent toxicity analysis. In most cases there was no significant difference in root length between the leached and unleached treatments with exceptions in the Houthalen and Charleston soils.
- Root discolouration/malformation: not reported


Reported statistics and error estimates:
No significant increase (p > 0.05) in the measured response at low Ag concentrations, a standard dose log-logistic model was used to fit the data and derive ECx values:
y=c+ (d-c)/(1+(x/e)^b )

The EC10 and EC50 values were then determined in each case through interpolation from the fitted curve at a 10% and 50% reduction from the fitted d values (i.e. fitted response in the control).

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

Soil

Nominal concentration (mg/kg)

Average measured concentration (mg/kg)

Leached

Unleached

Houthalen

5

4.3 (87)

4.3 (85)

 

10

8.8 (87)

8.5 (85)

 

20

17.0 (83)

18 (90)

 

40

32 (81)

37 (92)

 

80

62 (77)

80 (100)

 

160

107 (67)

163 (102)

 

320

185 (58)

320 (100)

 

 

 

 

Bordeaux

5

4.7 (94)

5.3 (105)

 

10

9.4 (94)

9.9 (99)

 

20

19 (97)

19 (94)

 

40

41 (102)

38 (94)

 

80

78 (97)

85 (107)

 

160

144 (90)

180 (113)

 

320

298 (93)

338 (106)

 

 

 

 

Inman Valley

25

23 (93)

20 (80)

 

50

45 (91)

44 (88)

 

100

92 (92)

93 (93)

 

200

185 (92)

201 (101)

 

400

374 (93)

370 (93)

 

800

745 (93)

775 (97)

 

1600

1430 (89)

1500 (94)

 

 

 

 

Charleston

25

23 (91)

24 (97)

 

50

47 (93)

43 (86)

 

100

80 (80)

82 (82)

 

200

161 (80)

169 (85)

 

400

368 (92)

364 (91)

 

800

758 (95)

664 (83)

 

1600

1560 (98)

1540 (96)

 

 

 

 

Kingaroy

25

26 (106)

26 (102)

 

50

53 (106)

53 (106)

 

100

97 (97)

86 (86)

 

200

198 (99)

211 (106)

Kingaroy

400

396 (99)

398 (100)

 

800

800 (100)

813 (102)

 

1600

1610 (101)

1620 (101)

 

 

 

 

Millicent

50

43 (86)

45 (90)

 

100

95 (95)

91 (91)

 

200

180 (90)

189 (95)

 

400

383 (96)

387 (97)

 

800

805 (101)

738 (92)

 

1600

1460 (91)

1650 (103)

 

3200

2900 (90)

3170 (99)

 

 

 

 

Balaklava

25

23 (93)

23 (91)

 

50

45 (90)

44.9 (90)

 

100

88 (88)

89.6 (90)

 

200

184 (92)

186 (93)

 

400

384 (96)

387 (97)

 

800

741 (93)

779 (97)

 

1600

1530 (96)

1500 (94)

 

 

 

 

Port Kenny

25

27 (109)

29.3 (117)

 

50

52 (104)

52 (105)

 

100

80 (80)

103 (103)

 

200

194 (97)

204 (102)

 

400

342 (86)

373 (93)

 

800

760 (95)

760 (95)

 

1600

1400 (88)

1420 (89)

Validity criteria fulfilled:
yes
Remarks:
100% germination was observed in all of the control soils
Conclusions:
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.
Executive summary:

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.

Endpoint:
toxicity to terrestrial plants: short-term
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
1. HYPOTHESIS FOR THE READ-ACROSS APPROACH (ENDPOINT LEVEL)
The REACH registration of silver (powder and massive forms of zero-valent, elemental, silver) is underpinned, in common with other metals, by a read-across (or analogue) approach from the properties of the free ion. This principle of read-across from the free ion has been extended to also include nanosilver.
The scientific validity of read-across from the hazard properties of ionic silver (source) to nanosilver (target) under REACH is underpinned by both theoretical and empirical considerations.
The theoretical basis for the use of ionic silver data as the foundation of the risk assessment of nanosilver is based on the premise that the free metal ion (Me+) is the most toxic metal form/species (Starodub et al. 1987). This consideration was implicit in the development of the Free Ion Activity Model [FIAM] (Morel 1983, Paquin et al. 2002, Campbell 1985, Brown and Markich 2000) and, more recently, the Biotic Ligand Model [BLM] (Paquin et al 2002, Niyogi and Wood 2004) that has underpinned the risk assessment of several metals (e.g. Cu, Ni, Zn) under the Existing Substance Regulations and REACH; and most recently the development of the Environmental Quality Standard (EQS) for nickel and nickel substances under the Water Framework Directive (WFD). When considered on an equal mass basis ionic silver would therefore be expected to have greater toxicity than nanosilver simply on the basis that silver ions are released over time from the surface of particles (via oxidative dissolution). As the properties of nanosilver are read-across directly from ionic silver (not just to the fraction of silver ions released from nanosilver), this read-across is also expected to introduce considerable precaution into the hazard component of the risk assessment of nanosilver as all nanosilver, irrespective of coating, morphology or particle size distribution is assumed to behave similarly to the free ion.
This theoretical consideration has been tested by conducting a comprehensive review of the available scientific literature for nanosilver, with particular emphasis on the comparative effects on REACH relevant biotic systems (REACH information requirement) of ionic silver and nanosilver. This review is described for each endpoint in subsequent sections of the report ‘Nanosilver: read-across justification for environmental information requirements’ (attached in IULCID Section 13) and is summarised below. Furthermore, this theoretical consideration was confirmed by a specific ecotoxicity testing programme undertaken by the EPMF following the silver substance evaluation and designed to compare the effects of the smallest nanosilver form registered under REACH (‘Nano 8.1’ or ‘Silberpulver Typ 300-30’) and silver nitrate to algae, Daphnia (long-term) and soil microorganisms.


2. READ-ACROSS APPROACH JUSTIFICATION (ENDPOINT LEVEL)
In terms of ecotoxicity, nanosilver on an equal mass basis has been found to be significantly less toxic than ionic silver for the majority of REACH endpoints and of equivalent toxicity for some others. None of the empirical information available suggests that nanosilver is consistently more hazardous than ionic silver on an equivalent mass basis, or that “nano-specific” effects that would prejudice the validity of read across from ionic silver to nanosilver occur. In addition, with very limited exceptions which are described further in the report ‘Nanosilver: read-across justification for environmental information requirements’, none of the available data suggested consistent relationships between particle morphology, size, particle size distribution (raw or agglomerated) or coating (surface treatment) and effects.
Notter et al. (2014) presents a meta-analysis of published EC50 values for ionic silver and nanosilver. The authors demonstrate that almost 94% of acute toxicity values assessed for freshwater, seawater and terrestrial systems using algae, annelid, arthropoda, bacteria, crustacea, fish, nematoda, plant, protozoa and rotatoria show that the nanoform of silver is less toxic than the dissolved metal (when normalised for total metal concentration).
In addition, a specific ecotoxicity testing programme designed to compare the effects of the smallest nanosilver form registered under REACH (‘Nano 8.1’ or ‘Silberpulver Typ 300-30’) and silver nitrate to algae, Daphnia (long-term) and soil microorganisms was undertaken following the silver substance evaluation. This demonstrated that the nanoform of silver is less toxic than ionic silver (based on EC10 and EC50 values for total, ‘conventional’ dissolved (<0.45μm) and ‘truly’ dissolved (<3kDa) silver). Therefore, taking the full body of evidence into account, the read-across use of toxicity values from ionic to nanosilver as a ‘worst case’ approach is justified and scientifically defensible for environmental endpoints. The Substance Evaluation Conclusion document for silver agreed with this conclusion for the nanosilver forms covered in the REACH dossier (RIVM 2018).

Toxicity to terrestrial plants
There is one study reporting the toxicity of citrate coated nanosilver to two terrestrial plant species included in the REACH dossier as Endpoint Study Record. These limited data reporting the comparative toxicity of silver and nanosilver to plants, suggest that nanosilver is less hazardous to plants than ionic silver, although there is some uncertainly associated with these data. Together with the theoretical basis for read-across based on the free-ion, this supports the use of ionic silver as the ‘worst case’ basis to read across properties to nanosilver. A summary of this supporting study is available under Section 4.3.2 of the report ‘Nanosilver: read-across justification for environmental information requirements’ (attached in IUCLID Section 13).


For further information and data matrix see 'CSR Annex 9 - Read Across Justification Nanosilver ENV_SUMMARY_200706' attached in IUCLID section 13.
Reason / purpose for cross-reference:
read-across source
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
2.3 mg/kg soil dw
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Houthalen soil aged 1 month, 95% CL = na-4.8
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
5.2 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Bordeaux soil, aged 1 month, 95% CL =1.9-8.5
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
16 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Inman Valley soil, aged 1 month, 95% CL = na-33
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
28 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Charleston soil, aged 1 month, 95% CL = na-47
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
6.2 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Kingaroy soil, aged 1 month, 95% CL =1.4-11
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
62 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Millicent soil, aged 1 month, 95% CL = na-109
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
52 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Bakalava soil, aged 1 month, 95% CL = 36-69
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
61 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Port Kenny soil, aged 1 month, 95% CL = na-121
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
7.6 mg/kg soil dw
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Houthalen soil, aged 12 months, 95% CL = na-15
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
116 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Bordeaux soil, aged 12 months, 95% CL = 41-217
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
37 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Inman Valley, aged 12 months, 95% CL = 21-67
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
47 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Charleston soil, aged 12 months, 95% CL = na-76
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
27 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Kingaroy soil, aged 12 months, 95% CL = na-46
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
110 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Millicent soil, aged 12 months, 95% CL = 51-227
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
180 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Bakalava soil, aged 12 months, 95% CL = 134-234
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
121 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Port Kenny soil, aged 12 months, 95% CL = 74-192
Details on results:
The growth of plants in the control soils was similar in the test conducted 1 month post spiking and the test conducted in the soils that had been aged for 12 months. Some significant differences were however observed in the Inman Valley, Charleston and Balaklava soils.

In all soils clear dose response relationships were evident in the soils that had been aged 12 months. When the dose response curves for the 12 months aged soils are compared with the 1 month aged soils it is clear in all cases that there is a shift to right, indicating a decrease in the toxicity of Ag in the aged soils.
The effect of ageing on the toxicity of Ag is also evident when the EC10 and EC50 values are compared. In all cases, the ECx values are either significantly lower in the 12 months aged soils or show no significant difference. The AFs that were determined from these values were found to range from 1.7 to 22 for the EC10 values and 1.3 to 2.8 for the EC50 values. To calculate an overall average AF, the Bordeaux EC10 AF was removed as this value was considerably higher than the other values. Following the removal of this value, the average overall AF in these soils was 2.4, indicating that after a 12-month ageing period the toxicity of Ag decreased twofold.

Table1: Results from analyses of the selected study soils for pH, organic carbon, cation exchange capacity, particle size distribution and total silver concentration.

Soil

pH

(CaCl2)

pH

(water)

Organic carbon

(%)

Cation exchange capacity

(cmol+/kg)

Particle size distribution (%)

Total Silver (mg/kg)

clay

silt

Sand

Houthalen

3.6

4.9

1.5

5.3

1.4

1.7

93

< 0.04

Bordeaux

4.6

5.6

1.9

6.4

2.5

1.6

93

< 0.04

Inman Valley

5.0

6.0

5.3

25

42

22

26

< 0.04

Charleston

5.1

6.6

6.9

12

14

12

63

< 0.04

Kingaroy

5.5

6.1

0.9

13

60

17

19

< 0.04

Millicent

6.6

6.9

12

42

19

5.2

48

< 0.04

Balaklava

7.1

8.5

1.9

27

30

20

47

< 0.04

Port Kenny*

8.0

8.8

1.8

13

12

4.2

21

< 0.04

* 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.

SOIL

EC10

 

EC50

12 month

1 month

AF

 

12 month

1 month

AF

Houthalen

1.0

(na-3.2)

0.47

(na-1.2)

2.1

 

16

(9.8-23)

8.5

(5.7-11)

1.9

Bordeaux

8.1

(na-28)

5.3

(na-9.2)

1.5

 

77

(37-167)

19*

(14-25)

4.1

Inman Valley

11

(na-32)

6.9

(na-18)

1.6

 

85

(48-124)

50

(31-72)

1.7

Charleston

60

(43-74)

7.0*

(na-16)

8.6

 

123

(110-137)

50*

(34-68)

2.5

Kingaroy

22

(na-43)

1.1

(0.24-4.0)

20

 

58

(35-80)

12*

(5.6-18)

4.8

Millicent

41

(na-125)

34

(na-61)

1.2

 

317

(171-535)

139

(104-184)

2.3

Balaklava

17

(na-43)

45

(41-50)

0.4

 

121

(76-176)

83

(76-91)

1.5

Port Kenny

253

(203-305)

108*

(70-156)

2.3

 

371

(310-440)

282

(173-585)

1.3

* indicate significantly (p < 0.05) lower values when the leached and unleached ECx values are compared

AF: ageing factor calculated as 12 month ECx/1 month ECx

na, confidence 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.

Validity criteria fulfilled:
not specified
Conclusions:
The EC10 and EC50 values were found in all cases to increase in soils that had been aged for 12 months, compared to those generated in soils that had been aged for 1 month. Overall, the ageing factors (AFs) were found to range from 1.3 to 4.4 (and additional value of 22 was observed for one soil) with an overall average AF of 2.4.
Executive summary:

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.

Endpoint:
toxicity to terrestrial plants: short-term
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
1. HYPOTHESIS FOR THE READ-ACROSS APPROACH (ENDPOINT LEVEL)
The REACH registration of silver (powder and massive forms of zero-valent, elemental, silver) is underpinned, in common with other metals, by a read-across (or analogue) approach from the properties of the free ion. This principle of read-across from the free ion has been extended to also include nanosilver.
The scientific validity of read-across from the hazard properties of ionic silver (source) to nanosilver (target) under REACH is underpinned by both theoretical and empirical considerations.
The theoretical basis for the use of ionic silver data as the foundation of the risk assessment of nanosilver is based on the premise that the free metal ion (Me+) is the most toxic metal form/species (Starodub et al. 1987). This consideration was implicit in the development of the Free Ion Activity Model [FIAM] (Morel 1983, Paquin et al. 2002, Campbell 1985, Brown and Markich 2000) and, more recently, the Biotic Ligand Model [BLM] (Paquin et al 2002, Niyogi and Wood 2004) that has underpinned the risk assessment of several metals (e.g. Cu, Ni, Zn) under the Existing Substance Regulations and REACH; and most recently the development of the Environmental Quality Standard (EQS) for nickel and nickel substances under the Water Framework Directive (WFD). When considered on an equal mass basis ionic silver would therefore be expected to have greater toxicity than nanosilver simply on the basis that silver ions are released over time from the surface of particles (via oxidative dissolution). As the properties of nanosilver are read-across directly from ionic silver (not just to the fraction of silver ions released from nanosilver), this read-across is also expected to introduce considerable precaution into the hazard component of the risk assessment of nanosilver as all nanosilver, irrespective of coating, morphology or particle size distribution is assumed to behave similarly to the free ion.
This theoretical consideration has been tested by conducting a comprehensive review of the available scientific literature for nanosilver, with particular emphasis on the comparative effects on REACH relevant biotic systems (REACH information requirement) of ionic silver and nanosilver. This review is described for each endpoint in subsequent sections of the report ‘Nanosilver: read-across justification for environmental information requirements’ (attached in IULCID Section 13) and is summarised below. Furthermore, this theoretical consideration was confirmed by a specific ecotoxicity testing programme undertaken by the EPMF following the silver substance evaluation and designed to compare the effects of the smallest nanosilver form registered under REACH (‘Nano 8.1’ or ‘Silberpulver Typ 300-30’) and silver nitrate to algae, Daphnia (long-term) and soil microorganisms.


2. READ-ACROSS APPROACH JUSTIFICATION (ENDPOINT LEVEL)
In terms of ecotoxicity, nanosilver on an equal mass basis has been found to be significantly less toxic than ionic silver for the majority of REACH endpoints and of equivalent toxicity for some others. None of the empirical information available suggests that nanosilver is consistently more hazardous than ionic silver on an equivalent mass basis, or that “nano-specific” effects that would prejudice the validity of read across from ionic silver to nanosilver occur. In addition, with very limited exceptions which are described further in the report ‘Nanosilver: read-across justification for environmental information requirements’, none of the available data suggested consistent relationships between particle morphology, size, particle size distribution (raw or agglomerated) or coating (surface treatment) and effects.
Notter et al. (2014) presents a meta-analysis of published EC50 values for ionic silver and nanosilver. The authors demonstrate that almost 94% of acute toxicity values assessed for freshwater, seawater and terrestrial systems using algae, annelid, arthropoda, bacteria, crustacea, fish, nematoda, plant, protozoa and rotatoria show that the nanoform of silver is less toxic than the dissolved metal (when normalised for total metal concentration).
In addition, a specific ecotoxicity testing programme designed to compare the effects of the smallest nanosilver form registered under REACH (‘Nano 8.1’ or ‘Silberpulver Typ 300-30’) and silver nitrate to algae, Daphnia (long-term) and soil microorganisms was undertaken following the silver substance evaluation. This demonstrated that the nanoform of silver is less toxic than ionic silver (based on EC10 and EC50 values for total, ‘conventional’ dissolved (<0.45μm) and ‘truly’ dissolved (<3kDa) silver). Therefore, taking the full body of evidence into account, the read-across use of toxicity values from ionic to nanosilver as a ‘worst case’ approach is justified and scientifically defensible for environmental endpoints. The Substance Evaluation Conclusion document for silver agreed with this conclusion for the nanosilver forms covered in the REACH dossier (RIVM 2018).

Toxicity to terrestrial plants
There is one study reporting the toxicity of citrate coated nanosilver to two terrestrial plant species included in the REACH dossier as Endpoint Study Record. These limited data reporting the comparative toxicity of silver and nanosilver to plants, suggest that nanosilver is less hazardous to plants than ionic silver, although there is some uncertainly associated with these data. Together with the theoretical basis for read-across based on the free-ion, this supports the use of ionic silver as the ‘worst case’ basis to read across properties to nanosilver. A summary of this supporting study is available under Section 4.3.2 of the report ‘Nanosilver: read-across justification for environmental information requirements’ (attached in IUCLID Section 13).


For further information and data matrix see 'CSR Annex 9 - Read Across Justification Nanosilver ENV_SUMMARY_200706' attached in IUCLID section 13.
Reason / purpose for cross-reference:
read-across source
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
8.7 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Houthalen soil, unleached, 95% CL = na-18
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
17 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Bordeaux soil, unleached, 95% CL = 7.9-27
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
4.1 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Inman Valley soil, unleached, 95% CL = na-11
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
54 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Charleston soil, unleached, 95% CL = 34-74
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
6.6 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Kingaroy soil, unleached, 95% CL = 0.4-13
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
30 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Millicent soil, unleached, 95% CL = na-55
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
42 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Bakalava soil, unleached, 95% CL = 26-57
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
53 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: plant height
Remarks on result:
other: Port Kenny soil, unleached, 95% CL = na-98
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
19 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: biomass
Remarks on result:
other: Bakalava soil, unleached, 95% CL = 4.7-27
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
4 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: biomass
Remarks on result:
other: Houthalen soil, unleached, 95% CL = na-11
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
0.9 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: biomass
Remarks on result:
other: Bordeaux soil, unleached, 95% CL = na-1.9
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
0.7 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: biomass
Remarks on result:
other: Inman Valley, unleached, 95% CL = na-3.4
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
21 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: biomass
Remarks on result:
other: Charleston soil, unleached, 95% CL = na-41
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
0.86 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: biomass
Remarks on result:
other: Kingaroy soil, unleached, 95% CL = na-5.6
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
5.5 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: biomass
Remarks on result:
other: Millicent soil, unleached, 95% CL = na-18
Species:
Lycopersicon esculentum
Duration:
5 d
Dose descriptor:
EC10
Effect conc.:
58 mg/kg soil dw
Nominal / measured:
nominal
Conc. based on:
element
Basis for effect:
other: biomass
Remarks on result:
other: Port Kenny soil, unleached, 95% CL = na-117
Details on results:
The growth of the plants was sufficient in all of the control soils to allow for all subsequent toxicity modelling.
Reported statistics and error estimates:
There was no significant increase (p > 0.05) in the measured response at low Ag concentrations, therefore a standard dose log-logistic model was used to fit the data and derive ECx values.
y=c+ (d-c)/(1+(x/e)^b )

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 concentration

Soil

Nominal concentration (mg/kg)

Average measured concentration (mg/kg)

Leached

Unleached

Houthalen

5

4.3 (87)

4.3 (85)

 

10

8.8 (87)

8.5 (85)

 

20

17.0 (83)

18 (90)

 

40

32 (81)

37 (92)

 

80

62 (77)

80 (100)

 

160

107 (67)

163 (102)

 

320

185 (58)

320 (100)

 

 

 

 

Bordeaux

5

4.7 (94)

5.3 (105)

 

10

9.4 (94)

9.9 (99)

 

20

19 (97)

19 (94)

 

40

41 (102)

38 (94)

 

80

78 (97)

85 (107)

 

160

144 (90)

180 (113)

 

320

298 (93)

338 (106)

 

 

 

 

Inman Valley

25

23 (93)

20 (80)

 

50

45 (91)

44 (88)

 

100

92 (92)

93 (93)

 

200

185 (92)

201 (101)

 

400

374 (93)

370 (93)

 

800

745 (93)

775 (97)

 

1600

1430 (89)

1500 (94)

 

 

 

 

Charleston

25

23 (91)

24 (97)

 

50

47 (93)

43 (86)

 

100

80 (80)

82 (82)

 

200

161 (80)

169 (85)

 

400

368 (92)

364 (91)

 

800

758 (95)

664 (83)

 

1600

1560 (98)

1540 (96)

 

 

 

 

Kingaroy

25

26 (106)

26 (102)

 

50

53 (106)

53 (106)

 

100

97 (97)

86 (86)

 

200

198 (99)

211 (106)

Kingaroy

400

396 (99)

398 (100)

 

800

800 (100)

813 (102)

 

1600

1610 (101)

1620 (101)

 

 

 

 

Millicent

50

43 (86)

45 (90)

 

100

95 (95)

91 (91)

 

200

180 (90)

189 (95)

 

400

383 (96)

387 (97)

 

800

805 (101)

738 (92)

 

1600

1460 (91)

1650 (103)

 

3200

2900 (90)

3170 (99)

 

 

 

 

Balaklava

25

23 (93)

23 (91)

 

50

45 (90)

44.9 (90)

 

100

88 (88)

89.6 (90)

 

200

184 (92)

186 (93)

 

400

384 (96)

387 (97)

 

800

741 (93)

779 (97)

 

1600

1530 (96)

1500 (94)

 

 

 

 

Port Kenny

25

27 (109)

29.3 (117)

 

50

52 (104)

52 (105)

 

100

80 (80)

103 (103)

 

200

194 (97)

204 (102)

 

400

342 (86)

373 (93)

 

800

760 (95)

760 (95)

 

1600

1400 (88)

1420 (89)

Validity criteria fulfilled:
yes
Conclusions:
The EC10 values for plant height in unleached soil ranged from 4.10 (Inman Valley) to 54.0 (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 unleached soil.
Executive summary:

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 unleached soil.

Endpoint:
toxicity to terrestrial plants: long-term
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
1. HYPOTHESIS FOR THE READ-ACROSS APPROACH (ENDPOINT LEVEL)
The REACH registration of silver (powder and massive forms of zero-valent, elemental, silver) is underpinned, in common with other metals, by a read-across (or analogue) approach from the properties of the free ion. This principle of read-across from the free ion has been extended to also include nanosilver.
The scientific validity of read-across from the hazard properties of ionic silver (source) to nanosilver (target) under REACH is underpinned by both theoretical and empirical considerations.
The theoretical basis for the use of ionic silver data as the foundation of the risk assessment of nanosilver is based on the premise that the free metal ion (Me+) is the most toxic metal form/species (Starodub et al. 1987). This consideration was implicit in the development of the Free Ion Activity Model [FIAM] (Morel 1983, Paquin et al. 2002, Campbell 1985, Brown and Markich 2000) and, more recently, the Biotic Ligand Model [BLM] (Paquin et al 2002, Niyogi and Wood 2004) that has underpinned the risk assessment of several metals (e.g. Cu, Ni, Zn) under the Existing Substance Regulations and REACH; and most recently the development of the Environmental Quality Standard (EQS) for nickel and nickel substances under the Water Framework Directive (WFD). When considered on an equal mass basis ionic silver would therefore be expected to have greater toxicity than nanosilver simply on the basis that silver ions are released over time from the surface of particles (via oxidative dissolution). As the properties of nanosilver are read-across directly from ionic silver (not just to the fraction of silver ions released from nanosilver), this read-across is also expected to introduce considerable precaution into the hazard component of the risk assessment of nanosilver as all nanosilver, irrespective of coating, morphology or particle size distribution is assumed to behave similarly to the free ion.
This theoretical consideration has been tested by conducting a comprehensive review of the available scientific literature for nanosilver, with particular emphasis on the comparative effects on REACH relevant biotic systems (REACH information requirement) of ionic silver and nanosilver. This review is described for each endpoint in subsequent sections of the report ‘Nanosilver: read-across justification for environmental information requirements’ (attached in IULCID Section 13) and is summarised below. Furthermore, this theoretical consideration was confirmed by a specific ecotoxicity testing programme undertaken by the EPMF following the silver substance evaluation and designed to compare the effects of the smallest nanosilver form registered under REACH (‘Nano 8.1’ or ‘Silberpulver Typ 300-30’) and silver nitrate to algae, Daphnia (long-term) and soil microorganisms.


2. READ-ACROSS APPROACH JUSTIFICATION (ENDPOINT LEVEL)
In terms of ecotoxicity, nanosilver on an equal mass basis has been found to be significantly less toxic than ionic silver for the majority of REACH endpoints and of equivalent toxicity for some others. None of the empirical information available suggests that nanosilver is consistently more hazardous than ionic silver on an equivalent mass basis, or that “nano-specific” effects that would prejudice the validity of read across from ionic silver to nanosilver occur. In addition, with very limited exceptions which are described further in the report ‘Nanosilver: read-across justification for environmental information requirements’, none of the available data suggested consistent relationships between particle morphology, size, particle size distribution (raw or agglomerated) or coating (surface treatment) and effects.
Notter et al. (2014) presents a meta-analysis of published EC50 values for ionic silver and nanosilver. The authors demonstrate that almost 94% of acute toxicity values assessed for freshwater, seawater and terrestrial systems using algae, annelid, arthropoda, bacteria, crustacea, fish, nematoda, plant, protozoa and rotatoria show that the nanoform of silver is less toxic than the dissolved metal (when normalised for total metal concentration).
In addition, a specific ecotoxicity testing programme designed to compare the effects of the smallest nanosilver form registered under REACH (‘Nano 8.1’ or ‘Silberpulver Typ 300-30’) and silver nitrate to algae, Daphnia (long-term) and soil microorganisms was undertaken following the silver substance evaluation. This demonstrated that the nanoform of silver is less toxic than ionic silver (based on EC10 and EC50 values for total, ‘conventional’ dissolved (<0.45μm) and ‘truly’ dissolved (<3kDa) silver). Therefore, taking the full body of evidence into account, the read-across use of toxicity values from ionic to nanosilver as a ‘worst case’ approach is justified and scientifically defensible for environmental endpoints. The Substance Evaluation Conclusion document for silver agreed with this conclusion for the nanosilver forms covered in the REACH dossier (RIVM 2018).

Toxicity to terrestrial plants
There is one study reporting the toxicity of citrate coated nanosilver to two terrestrial plant species included in the REACH dossier as Endpoint Study Record. These limited data reporting the comparative toxicity of silver and nanosilver to plants, suggest that nanosilver is less hazardous to plants than ionic silver, although there is some uncertainly associated with these data. Together with the theoretical basis for read-across based on the free-ion, this supports the use of ionic silver as the ‘worst case’ basis to read across properties to nanosilver. A summary of this supporting study is available under Section 4.3.2 of the report ‘Nanosilver: read-across justification for environmental information requirements’ (attached in IUCLID Section 13).


For further information and data matrix see 'CSR Annex 9 - Read Across Justification Nanosilver ENV_SUMMARY_200706' attached in IUCLID section 13.
Reason / purpose for cross-reference:
read-across source
Species:
Lactuca sativa
Duration:
17 d
Dose descriptor:
NOEC
Effect conc.:
7.14 mg/kg soil dw
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Basis for effect:
other: emergence and survival
Species:
Lactuca sativa
Duration:
17 d
Dose descriptor:
NOEC
Effect conc.:
0.16 mg/kg soil dw
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Basis for effect:
other: shoot length, wet weight and dry weight
Species:
Lactuca sativa
Duration:
17 d
Dose descriptor:
EC10
Effect conc.:
10.03 mg/kg soil dw
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Basis for effect:
other: emergence
Species:
Lactuca sativa
Duration:
17 d
Dose descriptor:
EC10
Effect conc.:
7.84 mg/kg soil dw
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Basis for effect:
other: survival
Species:
Lactuca sativa
Duration:
17 d
Dose descriptor:
EC10
Effect conc.:
0.14 mg/kg soil dw
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Basis for effect:
other: shoot length
Species:
Lactuca sativa
Duration:
17 d
Dose descriptor:
EC10
Effect conc.:
0.41 mg/kg soil dw
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Basis for effect:
other: shoot wet weight
Species:
Lactuca sativa
Duration:
17 d
Dose descriptor:
EC10
Effect conc.:
0.13 mg/kg soil dw
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Basis for effect:
other: shoot dry weight
Details on results:
Discolouration was not a reliable indicator of significant effects, as the number of plants with discolouration was substantial for all treatments, including control.
Results with reference substance (positive control):
Results with reference substance were within historical range of laboratory
Reported statistics and error estimates:
Hypothesis testing of the NOEC was determined using Toxstat version 3.5.
Validity criteria fulfilled:
yes
Conclusions:
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.
Executive summary:

The 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.

Description of key information

Key value for chemical safety assessment

Additional information

Summary of available data for uncoated and coated nanosilver

After 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.

Lee 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.

A 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 approximately 20%).

The 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.

Lee 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 mg/kg).

Based 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, interrupted, dose-response.