Silver

Long-term toxicity to fish

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

fish early-life stage toxicity

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).

Long-term toxicity to fish
Published data from two long-term toxicity to fish studies using various sizes of nanoparticles and coating types are included in the REACH dossier as Endpoint Study Records. Neither of the studies report effects at concentrations approaching the EC10 for chronic exposure to fish of 0.17 μg/L for ionic silver (Davies et al., 1998). The EC10 for ionic silver is currently approximately 30 times more sensitive than the most sensitive chronic fish toxicity data for nanosilver. 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, irrespective of any data available describing morphology, size, size distribution or coating. A summary of these supporting studies is available under Section 4.1.5 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:

reference to same study

Reason / purpose for cross-reference:

read-across source

GLP compliance:

not specified

Duration:

217 d

Dose descriptor:

EC10

Effect conc.:

0.19 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

dissolved

Remarks:

silver

Basis for effect:

mortality

Remarks on result:

other: water hardness: soft

Duration:

217 d

Dose descriptor:

EC10

Effect conc.:

0.75 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

dissolved

Remarks:

silver

Basis for effect:

mortality

Remarks on result:

other: water hardness: medium

Duration:

217 d

Dose descriptor:

EC10

Effect conc.:

1.23 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

dissolved

Remarks:

silver

Basis for effect:

mortality

Remarks on result:

other: water hardness: hard

Details on results:

Chronic values were defined on the basis of mortality, though very similar toxic limits were also defined based on retarded embryonic development and growth of early life stages. Despite early retardation of development and growth, after more than six months of exposure, fish did not show significant differences in growth between silver exposure concentrations and controls at termination of the experiments.

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

Effect concentrations were evaluated based on moratlity with chronic values calculated from their geometric mean.

Validity criteria fulfilled:

yes

Remarks:

Validity criteria in OECD 201 met

Conclusions:

217 day early-life stage EC10 (mortality) of AgNO3 to Salmo trutta was determined to be 0.19 µg/L dissolved Ag.

Executive summary:

In a non-GLP, guideline test, the 217 day early-life stage EC10 (mortality) of AgNO3 to Salmo trutta was determined to be 0.19 µg/L dissolved Ag.

Reference 2

Endpoint:

fish early-life stage toxicity

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).

Long-term toxicity to fish
Published data from two long-term toxicity to fish studies using various sizes of nanoparticles and coating types are included in the REACH dossier as Endpoint Study Records. Neither of the studies report effects at concentrations approaching the EC10 for chronic exposure to fish of 0.17 μg/L for ionic silver (Davies et al., 1998). The EC10 for ionic silver is currently approximately 30 times more sensitive than the most sensitive chronic fish toxicity data for nanosilver. 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, irrespective of any data available describing morphology, size, size distribution or coating. A summary of these supporting studies is available under Section 4.1.5 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:

reference to same study

Reason / purpose for cross-reference:

read-across source

Duration:

196 d

Dose descriptor:

EC10

Effect conc.:

0.17 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

dissolved

Remarks:

silver

Basis for effect:

mortality

Remarks on result:

other: soft

Duration:

196 d

Dose descriptor:

EC10

Effect conc.:

0.3 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

dissolved

Remarks:

silver

Basis for effect:

mortality

Remarks on result:

other: medium

Duration:

196 d

Dose descriptor:

EC10

Effect conc.:

0.63 µg/L

Nominal / measured:

meas. (geom. mean)

Conc. based on:

dissolved

Remarks:

silver

Basis for effect:

mortality

Remarks on result:

other: hard

Details on results:

Chronic values were defined on the basis of mortality, though very similar toxic limits were also defined based on retarded embryonic development and growth of early life stages. Despite early retardation of development and growth, after more than six months of exposure, fish did not show significant differences in growth between silver exposure concentrations and controls at termination of the experiments.

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

Effect concentrations were evaluated based on moratlity with chronic values calculated from their geometric mean.

Validity criteria fulfilled:

yes

Remarks:

Validity criteria in OECD 201 met

Conclusions:

The 196 day early-life stage EC10 (mortality) of AgNO3 to Oncorhynchus mykiss was determined to be 0.17 µg dissolved Ag/L.

Executive summary:

In a non-GLP, guideline test, the 196 day early-life stage EC10 (mortality) of AgNO3 to Oncorhynchus mykiss was determined to be 0.17 µg dissolved Ag/L.

Reference 3

Endpoint:

fish early-life stage toxicity

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).

Long-term toxicity to fish
Published data from two long-term toxicity to fish studies using various sizes of nanoparticles and coating types are included in the REACH dossier as Endpoint Study Records. Neither of the studies report effects at concentrations approaching the EC10 for chronic exposure to fish of 0.17 μg/L for ionic silver (Davies et al., 1998). The EC10 for ionic silver is currently approximately 30 times more sensitive than the most sensitive chronic fish toxicity data for nanosilver. 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, irrespective of any data available describing morphology, size, size distribution or coating. A summary of these supporting studies is available under Section 4.1.5 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

Duration:

32 d

Dose descriptor:

NOEC

Effect conc.:

0.351 other: μg dissolved Ag/L

Nominal / measured:

meas. (not specified)

Conc. based on:

not specified

Basis for effect:

other: survival and growth

Duration:

32 d

Dose descriptor:

EC10

Effect conc.:

0.39 other: μg dissolved Ag/L

Nominal / measured:

meas. (not specified)

Conc. based on:

not specified

Basis for effect:

growth rate

Remarks on result:

other: EC10 value recalculated from originally reported data

Duration:

32 d

Dose descriptor:

EC10

Effect conc.:

0.44 µg/L

Nominal / measured:

meas. (not specified)

Conc. based on:

not specified

Basis for effect:

mortality

Remarks on result:

other: EC10 value recalculated from originally reported data

Duration:

33 d

Dose descriptor:

EC10

Effect conc.:

0.59 µg/L

Nominal / measured:

nominal

Conc. based on:

not specified

Basis for effect:

growth rate

Remarks on result:

other: No analytical monitoring of test concentrations. EC10 value recalculated from originally reported data

Duration:

33 d

Dose descriptor:

EC10

Effect conc.:

0.55 µg/L

Nominal / measured:

nominal

Conc. based on:

not specified

Basis for effect:

mortality

Remarks on result:

other: No analytical monitoring of test concentrations. EC10 value recalculated from originally reported data

Duration:

34 d

Dose descriptor:

EC10

Effect conc.:

1.41 µg/L

Nominal / measured:

nominal

Conc. based on:

not specified

Basis for effect:

growth rate

Remarks on result:

other: No analytical monitoring of test concentrations. EC10 value recalculated from originally reported data

Duration:

34 d

Dose descriptor:

EC10

Effect conc.:

0.95 µg/L

Nominal / measured:

nominal

Conc. based on:

not specified

Basis for effect:

mortality

Remarks on result:

other: No analytical monitoring of test concentrations. EC10 value recalculated from originally reported data

Details on results:

No data reported

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

Hypothesis testing (NOEC/LOEC) undertaken using Toxstat (version 3.5): ANOVA with Dunnett's test. EC10 by non-linear interpolation.

Validity criteria fulfilled:

yes

Conclusions:

28 day post-hatch early-life stage EC10 (growth) of AgNO3 to Pimephales promelas was determined to be 0.39 µg dissolved Ag/L.

Executive summary:

In a GLP, guideline, test the 28 days post-hatch early-life stage EC10 (growth) of AgNO3 to Pimephales promelas was determined to be 0.39 µg dissolved Ag/L.

Reference 4

Endpoint:

long-term toxicity to fish

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).

Long-term toxicity to fish
Published data from two long-term toxicity to fish studies using various sizes of nanoparticles and coating types are included in the REACH dossier as Endpoint Study Records. Neither of the studies report effects at concentrations approaching the EC10 for chronic exposure to fish of 0.17 μg/L for ionic silver (Davies et al., 1998). The EC10 for ionic silver is currently approximately 30 times more sensitive than the most sensitive chronic fish toxicity data for nanosilver. 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, irrespective of any data available describing morphology, size, size distribution or coating. A summary of these supporting studies is available under Section 4.1.5 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

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

130 other: μg dissolved Ag/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

element

Remarks:

silver

Basis for effect:

other: mortality and growth

Remarks on result:

other: at 30% salinity

Details on results:

The effect values from the toxicity test demonstrate that increasing salinity has a mitigating effect on silver toxicity if toxicity is determined using measured concentrations of dissolved silver.

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

Values for NOEC and LOEC were calculated using ANOVA and a parmetric Dunnettt's test or nonparametric William's test. The LC20 calculated by weighted least-squares nonlinear regression, and the EC50 calculated by binomial/nonlinear interpolation. (p<0.05).

Salinity	NOEC	LOEC	EC20	ACR
‰	µg/L dissolved Ag
Mysids
10	6	13	3.9	>3.2
20	34	60	60	5.8
30	19	37	35	9.3
Fish
10	26	42	38	3
20	49	100	100	1.9
30	130	290	170	> 3

Validity criteria fulfilled:

not specified

Conclusions:

The 28 day NOEC (mortality and growth) is 130 μg dissolved Ag/L.

Executive summary:

This is a GLP, guideline study and is considered reliable and fully acceptable for use for this endpoint.

Additional information

Summary of available data for uncoated and coated nanosilver

Reliable and relevant data in the long-term toxicity of uncoated and coated nanosilver to fish are available from two studies (Kwok et al. 2012, Schäfers and Weil 2013). Both studies were based on early-life stage exposure of fish embryos. Kwok et al. (2012) report the effects of various forms of nanosilver on Oryzias latipes (Japanese medaka) after 21 days exposure, whilst Schäfers and Weil (2013) report the effects of exposure to NM-300K standard nanosilver in Danio rerio (zebra fish) after a 35 day OECD 210 early life test. Both studies were conducted in freshwater media.

Kwok et al. (2012) exposed medaka embryos to two sizes of PVP coated spherical nanoparticles with mean raw materials particle sizes of 21 ± 7 and 75 ± 21 nm, as well as citrate and gum arabic coated nanosilver particles with mean particle raw materials sizes of 7 ± 11 and 6 ± 2 nm, respectively (gum arabic particle measurements are based on the silver core of the particles). All forms of nanosilver were found to aggregate/agglomerate in test systems, with aggregates/agglomerates of PVP coated silver nanoparticles reported to exceed 1 µm in size after 48 hours within the test system. NOECs for survival after 21 days exposure ranged from 150 µg/L for the larger PVP coated and citrate coated nanosilver particles, 500 µg/L for the gum arabic coated silver particles and 1,500 µg/L for the smallest PVP coated nanoparticles. The equivalent NOEC for ionic silver (silver nitrate) exposure for 21 days was 15 µg/L, approximately 10 times more toxic than the forms of nanosilver used in the study.

Schäfers and Weil (2013) exposed zebrafish embryos to uncoated NM-300K nanosilver in an OECD standard early life-stage toxicity test (OECD 210). NM-300K has a primary particle size of 15 nm (with 99% of particles below 20 nm) and is widely used in the OECD Sponsorship Programme for the testing of engineered nanomaterials. Test were semi-static with seven day renewal periods for media. Aggregates of 50-60 nm were reported in test media and were considered stable between media renewals. The test was initiated with fertilised eggs and various endpoints were monitored during the test period including hatching success, post-hatch success (survival), length, weight and abnormal development. All test validity criteria were achieved and an overall NOEC of 5.9 µg/L was reported (length and weight endpoints). An EC10 of 41 µg/L was also reported for post-hatch survival. No concurrent exposure with ionic silver was undertaken.

Neither of the studies report effects at concentrations approaching the EC10 for chronic exposure to fish of 0.17 µg/L for ionic silver used in the REACH CSR. The EC10 for ionic silver is currently approximately 30 times more sensitive than the most sensitive chronic fish toxicity data for nanosilver, although the exposure duration of the study with dissolved silver was significantly longer than the available studies with nanosilver. As such, the hazard properties of ionic silver are considered to adequately cover the potential hazard of nanosilver to fish.

There is currently insufficient information available to make any conclusions regarding the influence of particle size, morphology or coating on the long-term toxicity of nanosilver to fish.