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EC number: 231-999-3 | CAS number: 7783-47-3
Chemical characteristics of Lake Superior water were monitored during the testing period according to procedures outlined by the American Public Health Association and procedures employing atomic absorption spectroscopy.
Results of analysis for fresh media (t = 0 hr) and aged (2 - 3 days) prior to media change for dissolved tin gave the following recoveries:
6.25 mg/l test substance = 37 % recovery of expected dissolved tin at t = 0 hr (mean 0.875 mg/l tin) and 0% aged (2 -3 days)
12.5 mg/l = 29% (mean 1.354 mg/l tin) and 0% aged samples
25.0 mg/l = 18% (mean 1.706 mg/l tin) and 5% (0.498 mg/l) aged
50.0 mg/l = 2.8% (mean 0.527 mg/l) and 2.8% (0.532 mg/l) aged
100 mg/l = 0 % (< limit of quatification) and 1.4% (0.530 mg/l) aged
It is clear from this work that a long term solubility of tin salts is about 0.5 mg/l and the fact that the nominal 50 and 100 mg/l concentrations cause immobilisation and no effect to vigour was seen at 25 mg/l or lower suggests that it is not the dissolved tin that is causing the immobilisation but probably exposure to the precipitate.
It is clear from this work that the solubility of tin salts is about 0.5 mg/l and the fact that the nominal 50 and 100 mg/l concentrations cause immobilisation and no effect to vigour was seen at 25 mg/l or lower suggests that it is not the dissolved tin that is causing the immobilisation but probably exposure to the precipitate.
Sn is not acutely toxic to freshwater invertebrates up to concentrations of 38.43 mg Sn/L (unbounded 7 d EC50, nominal total tin, analytically confirmed). Above these concentrations, Sn shows a low acute toxic potential, as indicated by a 48 h EC50 value of 55 mg Sn/L (nominal) derived from supporting data.
One key study of appropriate reliability and several supporting acute freshwater invertebrate studies for Sn, tested in the form of either tin(II)methanesulfonate or tin dichloride, are available.
Due to the low acute invertebrate toxicity of methanesulfonate (Dommröse et al. 1987, 48 h EC50 of 281.8 mg MSA/L (nominal)), it is expected that potential toxicity of tin(II)methanesulfonate on daphnids is not associated with methanesulfonate but with Sn. In a worst-case approach, all toxicity observed for SnCl2 is attributed to Sn:
In a reliable (RL1), GLP confirm chronic, freshwater toxicity study with Daphnia magna (< 24 h) no immobilisation was observed after 7 d of exposure to Sn in the form of tin(II)methanesulfonate in purified drinking water in a semi-static test, conducted according to OECD guideline 211. An acute unbounded 7 d EC50 of > 38.34 mg Sn/L (nominal, total tin, chemically verified) was derived for the immobilisation of Daphnia magna. Nominal concentrations were chemically verified, with concentrations for total tin and methansulfonate > 80 % of nominal values (Schäfers et al. 2006).
Further, this low acute freshwater toxicity potential of Sn is confirmed by several supporting (RL3) acute toxicity studies with Daphnia magna, showing 48 h EC50 values ranging from > 38.43 mg Sn/L (nominal) to 55.0 mg Sn/L (nominal) and a 64 h EC50 value of 66.0 mg Sn/L (nominal).
A toxic effect of tin (Sn) in the form of tin(II)methanesulfonate on Daphnia magna (age not specified) was observed in a 48 h acute toxicity test, following EU method C.2. An unbounded 48 h EC50 of > 38.43 mg Sn/L (nominal) for the immobilisation of daphnids was determined. However, precipitation of tin salts occurred and measured concentrations were below 80 % of nominal values (measured values not reported, Hill and Williams 1988). Results and methods are not well reported and test concentrations were not chemically verified. Hence this study is only considered supporting.
Biesinger & Christensen (1972) assessed the effect of tin (Sn) in the form of tin chloride dihydrate (SnCl2 * 2 H2O) on the mobility of Daphnia magna (age: 12 ± 12 h) in a 48 h acute toxicity test conducted in Lake Superior water in a static test system, following no specific guideline. A 48 h LC50 of 55.0 mg Sn/L (nominal) was derived. Since validity of the test was not assessable and exposure concentrations were not chemically confirmed, this study is only considered supporting.
The acute effect of tin (Sn) in the form of tin(II) chloride on the mortality of Daphnia magna was assessed in a 64 h test conducted in Lake Eerie water, following no specific guideline. A 64 h LC50 value of 66.0 mg Sn/L (nominal) was reported. The reported effect concentration is however only considered supportive as no data on test method are provided, information on physicochemistry of the test medium is lacking, and statistics are not reported. Furthermore, the exposure period of 64 h is not relevant for hazard assessment purposes (Anderson et al. 1950).
Data on marine organisms is not available.
In conclusion, Sn is not acutely toxic to freshwater invertebrates up to concentrations of 38.43 mg Sn/L (unbounded 7 d EC50, nominal total tin, analytically confirmed). Above these concentrations, Sn shows a low acute toxic potential, as indicated by a 48 h EC50 value of 55 mg Sn/L (nominal).
Read across justification:
Tin difluoride is an inorganic solid at room temperature and consists of the tin cation and fluoride anions. Based on the solubility of tin difluoride in water (300-428 g/L according to handbook data (Merck, 2006; Gestis, 2015)), a complete dissociation of tin difluoride resulting in tin and fluoride ions may be assumed under environmental conditions. The respective dissociation is reversible and the ratio of the salt /dissociated ions is dependent on the metal-ligand dissociation constant of the salt, the composition of the solution and its pH. The metal-ligand equilibrium constant for the formation of tin difluoride is reported as follows (Japan Nuclear Cycle Development Institute, 1999):
Sn2++ 2F- ↔ SnF20(log K =7.74)
Thus, it may reasonably be assumed that based on the tin-difluoride formation constant, the respective behaviour of the dissociated tin cations and fluoride anions in the environment determine the fate of tin difluoride upon dissolution with regard to (bio)degradation, bioaccumulation, partitioning resulting in a different relative distribution in environmental compartments (water, air, sediment and soil) and subsequently determine its ecotoxicological potential.
Therefore, in the assessment of the ecotoxicity of tin difluoride, read-across to data for fluoride and soluble tin substances is applied since only the ions of tin difluoride are available in an aqueous environment and determine the environmental fate and toxicity. Read-across to environmental fate and toxicity studies of soluble tin salts, including tin dichloride and tin methane sulfonic acid, is therefore appropriate and scientifically justified.
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