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Physical & Chemical properties

Water solubility

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Reference
Endpoint:
water solubility
Type of information:
other: Secondary literature
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: secondary literature, online database with authoritative values
Reason / purpose for cross-reference:
reference to same study
Qualifier:
no guideline followed
Principles of method if other than guideline:
Not applicable: secondary literature, online database with authoritative values.
GLP compliance:
no
Type of method:
other: no data
Remarks on result:
other: Reliable data from a factual database states that silver metal is practically insoluble. A figure for solubility cannot be given.
Details on results:
practically insoluble
Conclusions:
Interpretation of results (migrated information): insoluble (< 0.1 mg/L)

Description of key information

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.

Key value for chemical safety assessment

Water solubility:
0.03 µg/L

Additional information

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 vehicle.

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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