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EC number: 231-131-3
CAS number: 7440-22-4
See CSR Annex 4 - PNEC Summary Report
the below table, the ERV values, TDp data and derived classifications
(incl. M-factors) for Ag metal in massive form (≥1 mm), powder form
(>100 nm - <1 mm) and nanoform (≥1 nm - ≤100 nm) are summarised.
Table 1a: Ag metal in massive and powder form are assessed aspoorly soluble substance.Basis for classification: CLP Guidance Fig IV.1 for acute endpoint, CLP Guidance Fig IV.2 for chronic endpoint (ECHA 2017)
(all values in µg Ag/L)
Rapid environmental transformation?
Not considered for classification
1.3 - 2.6**
3.55 - 5.7**
* extrapolated value based on average dissolution rate for the 3 replicates
** range of values obtained for different samples and pHs
Table 1b: Ag metal in nanoform is assessed asreadily soluble substance.Basis for classification: CLP Guidance Fig IV.4 for acute endpoint, CLP Guidance Fig IV.5 for chronic endpoint (ECHA 2017)
assuming 100% solubility
and chronic ERV values for silver
and chronic aquatic toxicity data are available for a range of different
freshwater and marine species. For silver metal and silver compounds,
the acute ecotoxicity reference value (ERV) is 0.22 µg Ag/L and the
chronic ERV is 0.1 µg Ag/L.
line with the risk assessment/classification approach adopted for other
metals and inorganic metal compounds (ECHA 2017), ecotoxicity data are
reported in terms of the concentration of dissolved silver ions from
soluble inorganic silver species. Predominantly, these are studies that
used silver nitrate (AgNO3) as the source of dissolved silver
ions. Silver nitrate is considered as the silver substance with the
greatest toxicity as it dissociates rapidly and completely in aqueous
media. Where data for silver nitrate was not available, data derived
from other inorganic silver salts (e.g. silver chloride) were used, but
only after the exposure conditions were determined to be acceptable
(e.g. testing was conducted within the limits of solubility and the Ag+
ion was likely to be the dominant dissolved species).
complete base set of acute ecotoxicity studies is available for soluble
inorganic silver species, comprising numerous studies for fish,
invertebrates and algae. The lowest reliable acute value is an EC50 of
0.22 µg Ag/L for the invertebrateDaphnia magna(pH 8.2, total
organic carbon <0.1 mg/L; Bianchini et al. 2002).
complete chronic data set is also available for soluble inorganic silver
species, with chronic ecotoxicity data available for various species of
fish, invertebrates and algae. The lowest reliable chronic value is an
EC10 of 0.1 µg Ag/L for the algaePseudokirchneriella subcapitata(pH
7.2-8.5, DOC 0.38-0.88 mg/L; Fraunhofer 2017). Additional chronic
toxicity data of similar sensitivity are also available forIsonychia
bicolor(14 day NOEC of 0.16 µg Ag/L; Diamond et al, 1990),Salmo
trutta(217 day EC10 of 0.23 µg Ag/L; Davies et al, 1998) andBrachionus
calyciflorus(EC10 of 0.31 µg Ag/L; Arijs et al. 2021).
Acute ERV = 0.22 µg Ag/L, Chronic ERV = 0.1 µg Ag/L
metal - Transformation/Dissolution tests
massive and powder forms of silver metal are poorly/sparingly soluble.
The environmental hazard of poorly/sparingly soluble forms of metals is
associated with their potential to release metals ions (Ag+ ions in this
case) as most relevant toxic moiety (ECHA 2013). The potential for
aqueous transformation or dissolution of elemental or sparingly soluble
forms of metals is measured using standardised
Transformation/Dissolution (T/D) tests (as described in OECD TG29).
tests have been performed on silver metal in both massive and powder
forms (cfr details below).
2: TDp data for silver metal powder, Ag metal flake and silver metal
massive generated according to OECD TG29 (Ag release, expressed as
average value of 3 replicate vessels in µg Ag/L).
Ag metal powder
Ag metal flake
Ag metal massive
= no data
classification of silver metal
classification strategy for poorly soluble silver substances has been
based on CLP guidance (ECHA 2017). Annex IV in this guidance describes
in detail the environmental classification of metals and inorganic metal
compounds and how to determine the appropriate M factors for poorly
soluble substances like silver metal in powder and massive form. Key
figures in the CLP guidance document used in the below environmental
hazard assessment are figures IV.1 and IV.2, and considers the acute and
chronic ERVs and the results of T/D testing. Note that the
(experimental) evidence for environmental transformation (‘rapid removal
from the water column’) of silver has not been considered for
classification in the below assessment.
that the chronic classification for silver metal in massive and powder
form has been derived using the chronic ERV and 28-day T/D data. The
available 28-day T/D data for silver metal (powder and massive form) is
restricted (for technical reasons) to a minimum loading rate of 1 mg/L.
However, as chronic classification requires T/D data obtained with lower
loading rates of 0.01 and 0.1 mg/L, data for these theoretical loading
rates have been extrapolated, as detailed in the CLP guidance (footnote
93, page 585; ECHA, 2017), from tests conducted at higher loading rates
using either empirically derived relationships (i.e. linear regression)
or precautionary assumptions (i.e. based on analytical limits of
of silver in nanoform (≥1
nm - ≤100 nm)
precautionary classification for silver metal nanoparticles has been
read across from data for soluble silver and the appropriate M factors
have been derived.
for Ag nanoparticles have been generated as part of the Silver Substance
Evaluation under REACH (cfr. details in Mertens et al, 2019). On
specific request of the Evaluating Member State, this T/D study was
performed in a non-standard modified daphnia and algae medium with
chloride salts replaced by nitrate salts to maximise the concentration
of ionic Ag. These conditions are deviating from the standard medium
described in OECD Test Guideline 29. The OECD 29 Test Guideline was
developed for hazard classification purposes, and therefore any
deviation from the guideline (like changes in the medium composition
that may affect the solubility and bioavailability of the test compound)
makes the results not useable for hazard assessment. An alternative
publication by Wasmuth et al (2016) describes a TDp test, performed
according to OECD TG29, with a commonly used reference material for Ag
nanoforms (NM-300 K; 20 nm mean diameter) as test item. Although
performed in a standard medium and in compliance with the test
guideline, the authors conclude on a low Ag dissolution under all test
conditions (nominal Ag loadings of 1, 10 and 100 mg/L, pH 6 and 8,
sampling up to 7d for all loadings and up to 28d for 1 mg/L loading)
with values for ionic silver varying between 23 and 71 µg Ag/L after 7d.
No increase was observed in the next 21 days at 1 mg/L loading. This low
concentration of dissolved Ag in solution was attributed to quick and
extensive complexation and precipitation of silver as silver chloride,
which was most pronounced at higher loadings. The general conclusion of
the authors was that the observations were biased due to rapid
aggregation of silver nanoparticles and precipitation of dissolved Ag
absence of reliable T/D data for Ag metal nanoparticles (generated
according to OECD Testing Guideline 29), the environmental
classification of uncoated and coated silver metal nanomaterials has
therefore been directly read across from soluble forms of silver, as
specified in Figures IV.4-5 in the CLP guidance (ECHA, 2017), as
that the conclusion of the Silver Substance Evaluation specifically
mentions that environmental toxicity data, generated with soluble silver
substances like silver nitrate, are a suitable and conservative approach
for assessing the effects of silver nanoparticles: “Taking into
account that silver nitrate can be seen as a ‘worst case’ in the risk
assessment regarding toxicity of the nanoforms of silver that are
covered by the REACH registration dossier(s) submitted for Silver (as
shown in Section 7.8), the eMSCA can agree with the approach to use the
harmonised classification for silver nitrate (and corresponding
Mfactors) to self-classify the nanoforms of silver.”
classification under CLP
Acute ERV for silver is 0.22 µg Ag/L. This value is ≤1 mg/L and silver
metal nanoparticles are therefore classified as Aquatic Acute category
1. The appropriate acute M factor is 1000 (0.0001
< acute ERV (in mg/L) ≤ 0.001 as inCLP
Guidance Table IV.1; ECHA 2017).
classification under CLP
chronic ERV for silver is 0.1 µg Ag/L. This value is below 0.1 mg/L and
triggers a classification of silver metal nanoparticles as Aquatic
Chronic category 1. The appropriate chronic M-factor is 1000 since rapid
transformation to non-bioavailable forms is not considered for this
< chronic ERV (in mg/L) ≤ 0.0001as
in CLP Guidance Table IV.1; ECHA 2017).
Ag metal in nanoform is classified as Aquatic Acute 1 (Macute=1000) and
Aquatic Chronic 1 (Mchronic=1000).
et al (2021) Setting a Protective Threshold Value for Silver Toward
Freshwater Organisms. Environmental Toxicology and Chemistry, 40,
(2017) Guidance on the Application of the CLP Criteria. Guidance to
Regulation (EC) No 1272/2008 on classification, labelling and packaging
(CLP) of substances and mixtures. Version 5.0, July 2017.
et al (2019) Effects of Silver Nitrate Are a Conservative Estimate for
the Effects of Silver Nanoparticles on Algae Growth andDaphnia magnaReproduction.
Environmental Toxicology and Chemistry, 38, 1701–1713.
et al (2016) Assessing the suitability of the OECD 29 guidance document
to investigate the transformation and dissolution of silver
nanoparticles in aqueous media. Chemosphere 144, 2018-2023.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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