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Toxicity to aquatic plants other than algae

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Endpoint:
toxicity to aquatic plants other than algae
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 aquatic plants other than algae
Gubbins et al. (2011) reported 14d EC10 (dry weight) values for Lemna minor for various sizes of citrate capped nanomaterials in the same order of magnitude as EC10 values for ionic silver (silver nitrate). Based on these data, citrate coated nanosilver particles, irrespective of size, would appear to be of similar toxicity as ionic silver to Lemna minor. Oukarroum et al. (2013) reports a 7d EC10 (growth rate) for nanosilver of 3.6 μg/L for macrophytes. This EC10 is marginally (< factor of 2) lower than the EC10 results reported for ionic silver by both Naumann et al. (2007) and Gubbins et al. (2011) study. However, as Oukarroum et al. (2013) do not report the results of a comparative test with ionic silver in the same test system, and the available comparative data for silver and nanosilver in macrophytes (Gubbin et al. 2011) do not suggest that nanosilver is of greater toxicity than ionic silver, these data in isolation are not sufficient to suggest that nanosilver should be considered more toxic to macrophytes than ionic silver under REACH. A summary of these supporting studies is available under Section 4.1.7 of the report ‘Nanosilver: read-across justification for environmental information requirements’ (attached in IUCLID Section 13). 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.


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
Duration:
3 wk
Dose descriptor:
EC10
Effect conc.:
14.8 µg/L
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
silver
Basis for effect:
frond number
Details on results:
Total silver.
Results with reference substance (positive control):
Not applicable

Treatment

(µg Ag/L)

Number of fronds after 3 weeks

0

133

5

136

10

125

50

110

500

80

Validity criteria fulfilled:
no
Remarks:
No applicable validity criteria
Conclusions:
The 3 week EC10 (growth) of AgNO3 to Salvinia natans was determined to be 14.8 μg Ag/L.
Executive summary:

In a non-GLP, non-guideline, test the 3 week EC10 of AgNO3 to Salvinia natanswas determined to be 14.8 μg Ag/L.

Endpoint:
toxicity to aquatic plants other than algae
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 aquatic plants other than algae
Gubbins et al. (2011) reported 14d EC10 (dry weight) values for Lemna minor for various sizes of citrate capped nanomaterials in the same order of magnitude as EC10 values for ionic silver (silver nitrate). Based on these data, citrate coated nanosilver particles, irrespective of size, would appear to be of similar toxicity as ionic silver to Lemna minor. Oukarroum et al. (2013) reports a 7d EC10 (growth rate) for nanosilver of 3.6 μg/L for macrophytes. This EC10 is marginally (< factor of 2) lower than the EC10 results reported for ionic silver by both Naumann et al. (2007) and Gubbins et al. (2011) study. However, as Oukarroum et al. (2013) do not report the results of a comparative test with ionic silver in the same test system, and the available comparative data for silver and nanosilver in macrophytes (Gubbin et al. 2011) do not suggest that nanosilver is of greater toxicity than ionic silver, these data in isolation are not sufficient to suggest that nanosilver should be considered more toxic to macrophytes than ionic silver under REACH. A summary of these supporting studies is available under Section 4.1.7 of the report ‘Nanosilver: read-across justification for environmental information requirements’ (attached in IUCLID Section 13). 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.


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:
reference to same study
Reason / purpose for cross-reference:
read-across source
Duration:
7 d
Dose descriptor:
EC10
Effect conc.:
6.4 µg/L
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
silver
Basis for effect:
frond number
Details on results:
Total silver
Results with reference substance (positive control):
Not applicable

Experiments repeated at least twice

Validity criteria fulfilled:
not applicable
Remarks:
No applicable validity criteria
Conclusions:
The 7 day EC10 (growth) of AgNO3 to Lemna paucicostata was determined to be 6.4 μg Ag/L.
Executive summary:

In a non-GLP, non-guideline, test the 7 day EC10 (growth) of AgNO3 to Lemna paucicostata was determined to be 6.4 μg Ag/L.

Endpoint:
toxicity to aquatic plants other than algae
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 aquatic plants other than algae
Gubbins et al. (2011) reported 14d EC10 (dry weight) values for Lemna minor for various sizes of citrate capped nanomaterials in the same order of magnitude as EC10 values for ionic silver (silver nitrate). Based on these data, citrate coated nanosilver particles, irrespective of size, would appear to be of similar toxicity as ionic silver to Lemna minor. Oukarroum et al. (2013) reports a 7d EC10 (growth rate) for nanosilver of 3.6 μg/L for macrophytes. This EC10 is marginally (< factor of 2) lower than the EC10 results reported for ionic silver by both Naumann et al. (2007) and Gubbins et al. (2011) study. However, as Oukarroum et al. (2013) do not report the results of a comparative test with ionic silver in the same test system, and the available comparative data for silver and nanosilver in macrophytes (Gubbin et al. 2011) do not suggest that nanosilver is of greater toxicity than ionic silver, these data in isolation are not sufficient to suggest that nanosilver should be considered more toxic to macrophytes than ionic silver under REACH. A summary of these supporting studies is available under Section 4.1.7 of the report ‘Nanosilver: read-across justification for environmental information requirements’ (attached in IUCLID Section 13). 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.


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:
reference to same study
Reason / purpose for cross-reference:
read-across source
Duration:
7 d
Dose descriptor:
EC10
Effect conc.:
16.67 µg/L
Nominal / measured:
nominal
Conc. based on:
dissolved
Remarks:
silver
Basis for effect:
frond number
Results with reference substance (positive control):
Not applicable

Experiments repeated at least twice

Validity criteria fulfilled:
not applicable
Remarks:
No applicable validity criteria
Conclusions:
The 7 day EC10 (growth) of AgNO3 to Lemna paucicostata was determined to be 16.67 μg Ag/L.
Executive summary:

In a non-GLP, non-guideline, test the 7-day EC10 (growth) of AgNO3 to Lemna paucicostata was determined to be 16.67 μg Ag/L.

Endpoint:
toxicity to aquatic plants other than algae
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting 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 aquatic plants other than algae
Gubbins et al. (2011) reported 14d EC10 (dry weight) values for Lemna minor for various sizes of citrate capped nanomaterials in the same order of magnitude as EC10 values for ionic silver (silver nitrate). Based on these data, citrate coated nanosilver particles, irrespective of size, would appear to be of similar toxicity as ionic silver to Lemna minor. Oukarroum et al. (2013) reports a 7d EC10 (growth rate) for nanosilver of 3.6 μg/L for macrophytes. This EC10 is marginally (< factor of 2) lower than the EC10 results reported for ionic silver by both Naumann et al. (2007) and Gubbins et al. (2011) study. However, as Oukarroum et al. (2013) do not report the results of a comparative test with ionic silver in the same test system, and the available comparative data for silver and nanosilver in macrophytes (Gubbin et al. 2011) do not suggest that nanosilver is of greater toxicity than ionic silver, these data in isolation are not sufficient to suggest that nanosilver should be considered more toxic to macrophytes than ionic silver under REACH. A summary of these supporting studies is available under Section 4.1.7 of the report ‘Nanosilver: read-across justification for environmental information requirements’ (attached in IUCLID Section 13). 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.


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
Duration:
7 d
Dose descriptor:
EC50
Effect conc.:
30 - 81 µg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Remarks:
silver
Basis for effect:
growth rate
Duration:
7 d
Dose descriptor:
NOEC
Effect conc.:
6 µg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Remarks:
silver
Basis for effect:
frond number
Duration:
7 d
Dose descriptor:
NOEC
Effect conc.:
7 µg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
element
Remarks:
silver
Basis for effect:
other: weight (fw & dw)
Details on results:
Results expressed as free metal.
Results with reference substance (positive control):
Not applicable

Limited experimental detail makes it difficult to fully evaluate the study, however it is said to have been performed in accordance with ISO 20079. NOEC based on frond no. = 6 µg l-1 and weight (fw & dw) = 7 µg l-1 ; EC50s = 81 and 30 µg l-1 for same endpoints, respectively.

Validity criteria fulfilled:
not specified
Conclusions:
NOEC based on frond no. = 6 µg l-1 and weight (fw & dw) = 7 µg l-1 ; EC50s = 81 and 30 µg l-1 for same endpoints, respectively. Test is 7 d test on Lemna minor.
Executive summary:

Limited experimental detail makes it difficult to fully evaluate the study, however it is said to have been performed in accordance with ISO 20079. NOEC based on frond no. = 6 µg l-1 and weight (fw & dw) = 7 µg l-1 ; EC50s = 81 and 30 µg l-1 for same endpoints, respectively. Test is 7 d test on Lemna minor.

Description of key information

Key value for chemical safety assessment

Additional information

Summary of available data for uncoated and coated nanomaterials

Reliable and relevant data on the toxicity of nanosilver to aquatic plants are available from two studies (Gubbins et al. 2011 and Oukarroum et al. 2013). Gubbins et al. (2011) reported 14 day EC10 (dry weight) values for Lemna minor of 9.71 and 8.14 µg/L for citrate capped nanomaterials with mean particle size distribution of 29.2 and 93.52 nm (determined by TEM), respectively. A comparative exposure to ionic silver (silver nitrate) performed in the same study resulted in a 14 day EC10 (dry weight) value of 6.01 µg/L, which is comparable to the 7 day EC10 for Lemna minor of 6.0 µg/L ionic silver reported by Naumann et al. (2007), used as key data in the current silver REACH CSR. Based on these data, citrate coated nanosilver particles, irrespective of size, would appear to be of similar toxicity as ionic silver to Lemna minor, despite the differences in exposure duration.

The Oukarroum et al. (2013) macrophyte study reports a seven day EC10 (growth rate) of 3.6 µg/L for an uncoated spherical silver particle with a raw nominal particle size of 50 nm. This EC10 is marginally (< factor of 2) lower than the EC10 results reported for ionic silver by both Naumann et al. (2007) and in the Gubbins et al. (2011) study. However, as Oukarroum et al. (2013) do not report the results of a comparative test with ionic silver, these data in isolation are not sufficient to suggest that nanosilver should be considered more toxic to macrophytes than ionic silver.

These data support the precautionary read-across of properties from ionic silver to nanosilver in the freshwater 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 aquatic plants.