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EC number: 231-131-3
CAS number: 7440-22-4
According to a reliable factual database (Gestis), silver metal is
considered as practically insoluble.
Conventional water solubility testing is not appropriate for sparingly
soluble metals and metal compounds (ECHA Guidance on information
requirements and Chemical Safety Assessment. Chapter R.7a: Endpoint
specific guidance. Version 2.1, August 2013). Therefore, Transformation
/ Dissolution (T/D) testing (OECD Series on testing and assessment No.
29) was conducted for silver massive and several examples of silver
powder and is presented in section 5.6 of IUCLID.
Two sets of full T/D test results are available for non-nano
silver powder. CIMM (2009) report T/D results for a silver powder with a
median particle size of 1.9 µm after seven (loading rates of 1, 10 and
100 mg/L) and 28 days (loading rate of 1 mg/L) in OECD media at both pH
6 and pH 8. ECTX (2010a) reports T/D results for a silver flake with a
median particle size of 2.6 µm after seven (loading rates of 1, 10 and
100 mg/L) and 28 days (loading rate of 1 mg/L) in OECD media at pH 6
only. The results of the tests performed at pH 6 on the two different
materials are similar, with average dissolved silver concentrations
after seven days of 1.25 and 1.8 µg/L (1 mg/L loading rate) and average
dissolved silver concentrations after 28 days of 3.6 and 3.7 µg/L (1
mg/L loading rate). In the CIMM study (2009), dissolved silver
concentrations were comparable at both pH values at the highest loading
rate, which suggests a limit to the solubility of silver. At lower
loading rates, silver showed somewhat greater dissolution at pH 8 than
at pH 6.
Initial studies to determine the T/D behaviour of silver in
massive form (ECTX 2010b), which were performed using an epoxy resin
carrier to control the exposed surface area of silver during the test,
indicated unusual dissolution/solubility behaviour. Dissolved silver
concentrations increased rapidly, but then declined to a steady state
concentration. Further experimentation suggested that epoxy resin could
act as an adsorbent phase for silver, which would result in the decline
in the dissolved silver concentrations observed. It was further
hypothesised that during preparation of the test item minute particles
of silver may have become embedded in the epoxy vehicle, considerably
increasing the exposed surface area during the test. Given these
complications further experiments were proposed using a quartz glass
To address the limitations of the 2010 study, a further
“definitive test” on massive silver was performed using a quartz glass
vehicle to control the available surface area to a “surface equivalent”
of 3, 9, and 27 mg l-1(ECTX 2013). This study was conducted
at pH 8 only (based on the results of silver powder T/D testing) and
used fluorinated ethylene propylene vessels to minimise adsorption of
silver to the test system during the course of the 28 days test. The
test items were also cleaned ultrasonically prior to the start of the
exposure to remove residual particles of silver from the surface of the
quartz glass tubes remaining from sample preparation. The average blank
corrected dissolved silver concentrations in the test medium after 28
days exposure were below the analytical limit of detection of 0.02 µg l-1at
loading rates of 3 and 9 mg l-1, and was 0.03 (+/- 0.07) µg l-1at
a loading rate of 27 mg l-1.
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