Tin difluoride

Long-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

fish, juvenile growth test

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP compliance according to OECD 215 and EC method C14; acceptability of filters for tin analysis not checked; dissolved tin concentrations below 80% of nominal value

Qualifier:

according to guideline

Guideline:

OECD Guideline 215 (Fish, Juvenile Growth Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.14 (Fish Juvenile Growth Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

At test start and thereafter twice weekly, water was sampled at all test concentrations and analysed representatively for the content of methanesulfonate, dissolved tin and total tin content. Samples were taken from the test chambers at medium depth of the water column using a Pasteur pipette by pipetting sub-samples into 20 mL polyethylene vials.

Vehicle:

no

Details on test solutions:

A stock solution was prepared by mixing or agitating the test substance in the dilution water by using mechanical meands. The stock solution was continually dispensed and diluted with dilution water using the respective equipment to deliver a series of concentrations to the test chambers.

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM
- Common name: Rainbow trout
- Strain: Walbaum
- Source: freshly fertilized eggs were obtained from the NRW Landesanstalz für Fischerei (governmental fisheries agency), Germany
- Length at study initiation (mean and range, SD): 4.7-5.8 cm
- Weight at study initiation (mean and range, SD): 1.2-1.9 g
- Holding: Rainbow trout fingerling were reared at 14 ± 2 °C under flow-through conditionsin water of the same quality as used in the test. Trout were fed a ratio of 2 % body weight per day with commercial food (Trouvit Alleinfuttermittel, Milkivit, Germany)

FEEDING DURING TEST
- Food type: Trouvit 40/2 (Milkivit, Burgheim, Germany)
- Amount: 4 % of body weight
- Frequency: Twice daily

Test type:

flow-through

Water media type:

freshwater

Limit test:

no

Total exposure duration:

28 d

Hardness:

1.0 mmol

Test temperature:

14 - 15 °C

pH:

7.7 - 8.3

Dissolved oxygen:

oxygen saturation between 76% and 96%

Conductivity:

179-181 µS/cm

Nominal and measured concentrations:

Nominal concentrations: 0.2, 0.39, 0.78, 0.156 and 3.13 mg/l

Details on test conditions:

TEST SYSTEM
- Test vessel: Full glass aquaria
- Material, size, headspace, fill volume: 42x28x28 cm (l x w x h); 25 L test solution
- Aeration: not specified
- Type of flow-through: Dilution water was pumped by a water dosage pump (membrane pump, prominent); stock solution was dispensed by a stock solution dosage pump (peristaltic pump)
- Renewal rate of test solution (flow rate): 5.2 L/h
- No. of organisms per vessel: 10
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 1
- Biomass loading rate: 0.62 g/L at test start; 2.1 g/L at test end

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Purified drinking water, filtrated with activated charcoal, passage through a lime-stone column and aeration untily oxygen saturation
- Dissolved organic carbon: 0.0 mg/L
- Alkalinity: 1.4-1.5 mmol
- Intervals of water quality measurement: Monthly

OTHER TEST CONDITIONS
- Photoperiod: light/dark 16/8 h
- Light intensity: 713-871 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Mortality; daily
- Growth; weight & lenght measurement at test start, at day 14 and 28

RANGE-FINDING STUDY
- Test concentrations: 6.25, 12.5, 25.0 50.0, 100 mg/L
- Results used to determine the conditions for the definitive study: 60-100 % mortality in all test concentrations until day 12

Reference substance (positive control):

no

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

0.3 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

growth rate

Remarks on result:

other: nominal concentrations were analytically confirmed

Duration:

28 d

Dose descriptor:

LC50

Effect conc.:

0.945 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

mortality

Remarks on result:

other: nominal concentrations were analytically confirmed

Details on results:

No clinicial signs at 0.78 mg/l (NOAEC). Precipitation of the test item occurred in the aqueous solution. Concentrations of dissolved tin ranged between 37-190 % of nominal values.

No mortality was observed up to 1.22 mg Sn/L (nominal) after 8 d of exposure and an unbounded 8 d LC50 of > 1.22 mg Sn/L (nominal) was derived.

Reported statistics and error estimates:

Survival data were analysed by means of probit analysis. NOEC and LOEC values for growth were determined by ANOVA, followed by multiple Williams-test.

Analysis of tin and methane sulphonic acid showing good recovery compared to nominal concentrations. At the highest concentration of 3.13 mg/l, recover of dissolved tin was only an average of 62%, implying up to 40% was undissolved.

At concentrations showing no effect to the fish, there was recovery of > 80% dissolved tin.

A range finding study was performed on concentrations of up to 100 mg/l and there was no mortality for the first 96 hours, confirming the acute study test results. However, fish exposed to high concentrations started to show signs of toxicity from day 5, implying a chronic effect, although at these levels, there would be a high level of precipitated tin salts in suspension.

Validity criteria fulfilled:

yes

Conclusions:

The effect of tin (Sn) in the form of tin(II)methanesulfonate on the growth of juvenile Oncorhynchus mykiss (length: 4-7-5-8 cm; weight: 1.2-.19 g) was assessed in this flow-through test with purified drinking water conducted according to OECD guideline 215. Based on analytically confirmed nominal concentrations, the no effect concentration (NOEC) was estimated to be 0.3 mg Sn/L after 28 d of juvenile growth. Further, a LC50 of 0.95 mg Sn/L (nominal, analytically confirmed) for mortality of Oncocrhynchus mykiss after 28 d could be determined.

Executive summary:

The test work was reported very well and has allowed a good insight into the behaviour of the substance in water that will impact on other endpoints and help in making conclusions to the chemical safety assessment. Of key interest is the difference between acute toxic effects (< 96 hours) with survival at 100 mg/l and how mortality started from day 5. In the definitive study, 90% mortality was observed at the highest tested concentration of 3.13 mg/l.

Analysis was performed for sulphonates (confirming the suspected degradation product that is not reported in other tests) and crucially, the dissolved and precipitated tin was measured separately using filtration. This tin analysis showed a maximum dissolved tin concentration of < 1 mg/l (corresponding to approximately 2 mg/l of Tin-MSA) and at concentrations above this figure, there could be expected to be undissolved tin salts. Precipitated tin will therefore build up in gills in fish and lead to artificially high concentrations leading to increased toxicity over time, as reflected in the results. It is also significant that the dose response curve for mortality was reported to be very steep (Litchfield and Wilcoxon method, 1.2).

Description of key information

Sn is chronically toxic to freshwater fish, which is demonstrated by a 28 d NOEC for juvenile growth of 0.3 mg Sn/L (nominal total tin, analytically confirmed).

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

0.3 mg/L

Additional information

One reliable (RL 1) chronic freshwater fish study was performed under GLP compliance to observed the effect of tin (Sn) in the form of tin(II)methanesulfonate. In a worst-case approach, all observed toxicity is attributed to Sn:

 

The effect of tin (Sn) in the form of tin(II)methanesulfonate on the growth of juvenile Oncorhynchus mykiss (length: 4-7-5-8 cm; weight: 1.2-.19 g) was assessed in a flow-through test with purified drinking water conducted according to OECD guideline 215. Based on analytically confirmed nominal total tin concentrations, the no effect concentration (NOEC) was estimated to be 0.3 mg Sn/L after 28 d of juvenile growth. Further, a 28 d LC50 of 0.95 mg Sn/L (nominal total tin, analytically confirmed) for mortality of Oncocrhynchus mykiss after 28 d could be determined. (Schäfers et a. 2006)

 

Data on marine organisms are not available.

 

In conclusion, Sn was found to be chronically toxic to freshwater fish, showing a 28 d NOEC for juvenile growth of 0.3 mg Sn/L (nominal total tin, analytically confirmed).

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.