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EC number: 231-141-8 | CAS number: 7440-31-5
Table 3. Mortality of Fathead Minnow Pimephales promelas during a 96-Hour static exposure to aged solutions of Tin(IV) Chloride Pentahydrate
Cumulative Number Dead (Percent Mortality)
Notes: Seven fish were placed into each test treatment at initiation. No sublethal effects were observed
The conditions used in this test have been developed following difficulties encountered during earlier toxicity tests with precipitation of tin hydroxides. The objective of this and the other key aquatic toxicity tests is to assess any adverse effects from soluble tin released from tin metal. Attempts to investigate the potential toxicity from tin ions using salts such as tin (IV) chloride have been confounded by lack of stability of tin ions in solution. This instability produces dissolved tin concentrations of only 10 to 20 µg/L against a nominal total tin concentration of 1 mg/L. The high concentrations of precipitated tin hydroxides and the associated pH effects at higher doses do not reflect the true behaviour of tin ions released from the transformation and dissolution of tin metal. Therefore, to overcome these difficulties, aged solutions containing tin concentrations approaching a steady state condition have been prepared just prior to the testing. The maximum measured concentration of tin this test achieved after ageing is lower than the ABC 2010 growth inhibition test with Pseudokirchneriella subcapitata with an identical ageing protocol. This may be due to the effects of the specific water chemistry of the the different test media on the speed and degree of precipitation of tin (IV) from solution.
No mortality or sub-lethal effects were observed on Pimephales promelas at all strengths of aged solutions of tin (IV) chloride including at 100 %. This test is interpreted as demonstrating that acute effects will not be observed at concentrations of soluble tin that could arise from the dissolution of tin metal in the environment.
The objective of the Parametrix 2009 study was to determine the toxicity of tin (IV) ions to the fathead minnow Pimephales promelas under a variety of test conditions. Tests were run at two pH, each with five nominal loading rates. In addition, after preparation of the stock solution the test media was split in half, and one half used unfiltered, whilst the other was filtered before the addition of the test fish. Tin (IV) chloride was used to supply tin ions for the test and as a surrogate for tin ions released on the dissolution of tin metal. However, as in other preliminary toxicity tests using tin (IV) chloride the test results are difficult to interpret due to hydrolysis and precipitation effects which proceed over a matter of hours and days. This results in tests being undertaken in unstable conditions and makes it difficult to distinguish whether effects are due to soluble or particulate tin species.
For example, at the highest concentration treatment in the pH 8.5 filtered test, the average dissolved tin was 17.5 µg/L whereas the total measured tin was 828 µg/L. This was only concentration at which a survival effect was noted in the pH 8.5 filtered category. This study also has the added complication of uncertain analytical data with contamination effects observed possibly due to insufficient flushing of the analytical instrument between assays.
Due to these issues, the Parametrix 2009 study was used to inform the design of the key fat head minnow acute toxicity test (ABC 2010) but is not relevant for use in the aquatic toxicity assessment of tin metal.
The definitive short term toxicity fish test (ABC 2010) was undertaken in October 2010. The conditions used in this test have been developed following the difficulties encountered during earlier toxicity tests with precipitation of tin hydroxides. Earlier attempts to investigate the potential toxicity from tin ions using salts such as tin (IV) chloride have been confounded by lack of stability of tin ions in solution and consequential precipitation. This instability produces dissolved tin concentrations of 10 to 20 µg/L against a nominal tin concentration of 1 mg/L. The high concentrations of precipitated tin hydroxides and the associated low pH effects at higher doses do not reflect the true behaviour of tin ions released from the transformation and dissolution of tin metal.
The objective of this and the other key aquatic toxicity tests is to assess any adverse effects from soluble tin released from tin metal and not tin (IV) chloride. Therefore, to overcome these difficulties, aged solutions containing more stable tin concentrations have been prepared just prior to the testing. However, even after a total of seven days of ageing the tin (IV) ions are not yet at equilibrium conditions as slow precipitation and mineralisation reactions continue to take place.However, the aged solutions are considered to represent the maximum dissolved tin that can be achieved in the test media, and therefore a worst case exposure to dissolved tin.
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