Tin difluoride

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: study conducted in GLP accreditated laboratory according to OECD 211 and EC method C.20

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.20 (Daphnia magna Reproduction Test)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

At test start and afterwards three times weekly, a sample was taken for the analysis of methanesulfonate, dissolved tin and total tin content of each test concentration from the test solution preparation (fresh solution). At each removal, aged test solutions were analysed for dissolved tin and methanesulfonate.

Vehicle:

no

Details on test solutions:

Each test concentration was prepared by weighing adequate amounts of the test item into a mixing vessel, stirring it for 20 h and distributing it to replicates. The pH of diultion water was adjustet to pH 7.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Strain/clone: Daphnia magna Straus
- Source: Umweltbundesamt (German Federal Environment Agency), bred in the laboratory of the testing facillity
- Age of parental stock: at least 3 weeks old
- Age at study initiation: < 24 h
- Feeding during test
- Food type: Suspensions of unicellular green algae
- Amount: 7 mg C/L to 15 mg C/L
- Frequency: not specified

ACCLIMATION
- Acclimation period: not specified
- Acclimation conditions (same as test or not): at room temperature, in dilution water
- Type and amount of food: algal suspension (Scenedesmus subspicatus) and LiquizeIIR
- Feeding frequency: daily

METHOD FOR PREPARATION AND COLLECTION OF EARLY INSTARS OR OTHER LIFE STAGES:
- Newborn daphnia are separated by sieving, the first generation is discarded.

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

21 d

Hardness:

total hardness 1.0 mmol/L

Test temperature:

20 +/- 0.5 °C

pH:

from 7.7 to 7.9

Dissolved oxygen:

The oxygen saturation between 85% and 121%., never below 7.0 mg/L

Salinity:

Alkalinity 1.4-1.6 mmol/L;

Conductivity:

Conductivity 181-192 microS/cm

Nominal and measured concentrations:

The study was conducted at nominal concentration of 6.25, 12.5, 25, 50 and 100 mg test item/L.

Details on test conditions:

TEST SYSTEM
- Test vessel: 60 mL glass beakers
- Type: covered with a glass pane
- Fill volume: 50 mL
- Aeration: none
- Renewal rate of test solution (frequency): three times weekly
- No. of organisms per vessel: 1
- No. of vessels per concentration (replicates): 10
- No. of vessels per control (replicates): 10

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Purified drinking water (filtration with activated charcoal, passage through a lime-stone column & aeration until oxygen saturation)
- Dissolved organic carbon: 0 mg/L
- Conductivity: 181-192 µS/cm

OTHER TEST CONDITIONS
- Photoperiod: light/dark 16/8 h
- Light intensity: 700 ± 50 lux

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Number of living offspring
- immobility of parental generation daphnids
- time to first brood
- individual lenght of adults on day 21

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 2
- Range finding study
- Test concentrations: Up to 100 mg/L
- Results used to determine the conditions for the definitive study: No toxicity at 100 mg/L in a 48 h acute toxicity test.

Reference substance (positive control):

no

Duration:

21 d

Dose descriptor:

EC10

Effect conc.:

4.3 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

other: offspring number

Remarks on result:

other: nominal concentrations were analytically confirmed

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

4.8 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

other: offspring number

Remarks on result:

other: nominal concentrations were analytically confirmed

Duration:

21 d

Dose descriptor:

EC10

Effect conc.:

11.3 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

immobilisation

Remarks on result:

other: nominal concentrations were analytically confirmed

Duration:

21 d

Dose descriptor:

EC50

Effect conc.:

19.6 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

immobilisation

Remarks on result:

other: nominal concentrations were analytically confirmed

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

9.6 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

other: body length

Remarks on result:

other: nominal concentrations were analytically confirmed

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

>= 38.43 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

other: age at first brood

Remarks on result:

other: nominal concentrations were analytically confirmed

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

9.6 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

other: intrinsic rate of natural increase

Remarks on result:

other: nominal concentrations were analytically confirmed

Duration:

21 d

Dose descriptor:

EC10

Effect conc.:

19.7 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

other: intrinsic rate of natural increase

Remarks on result:

other: nominal concentrations were analytically confirmed

Reported statistics and error estimates:

ECx values (and 95 % CLs) were determined by regression using Probit-analysis, assuming log-normal distribution of values. NOEC values were calculated by using ANOVA, followed by Williams' test.

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.

Validity criteria fulfilled:

yes

Conclusions:

The effect of long-term exposure to tin (Sn) in the form of tin(II)methanesulfonate on the reproduction of Daphnia magna (age: < 24 h) was assessed in this 21 d semi-static test conducted in purified drinking water, following OECD test guideline 211 and EU Method C.20. A NOEC of 4.8 mg Sn/L (nominal) and an EC10 of 4.3 mg Sn/L (nominal) for the number of produced offspring (reproduction) were determined. Nominal concentrations were chemically verified, with concentrations of total tin and methansulfonate > 80 % of nominal values. However, measured dissolved tin concentrations were below 80 % of nominal values. Furthermore, filters used for analysis of dissolved tin concentrations were not checked for acceptability in tin analysis.

Executive summary:

Effect values are not based on dissolved tin concentrations, since effects did not correlate with measured dissolved tin concentrations. Measured dissolved tin concentrations were highest at the intermediate nominal concentrations of tin(II)methanesulfonate. These results suggest that it is not the dissolved tin that is causing the immobilisation but probably exposure to the precipitate.

Description of key information

Sn is chronically toxic to freshwater invertebrates, as indicated by a 21 d EC10 value of 4.3 mg Sn/L (nominal total tin, chemically verified) for reproduction of D. magna.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

4.3 mg/L

Additional information

One reliable (RL1), GLP confirm chronic toxicity study for Sn performed with tin(II)methanesulfonate is available. In a worst-case approach, all observed toxicity is attributed to Sn:

 

In a reliable (RL1), GLP confirm chronic freshwater toxicity study the effect of long-term exposure to tin (Sn) in the form of tin(II)methanesulfonate on the reproduction of Daphnia magna (age: < 24 h) was assessed. In this 21 day, semi-static test conducted in purified drinking water, following OECD test guideline 211 and EU Method C.20 a 21 d NOEC of 4.8 mg Sn/L (nominal) and a 21 d EC10 of 4.3 mg Sn/L (nominal) for the number of produced offspring (reproduction) were determined. Nominal concentrations were chemically verified, with concentrations of total tin and methansulfonate above 80% of nominal values. However, measured dissolved tin concentrations were below 80% of nominal values (Schäfers et al. 2006). Effect values are not based on dissolved tin concentrations, since effects did not correlate with measured dissolved tin concentrations. Measured dissolved tin concentrations were highest at the intermediate nominal concentrations of tin(II)methanesulfonate. These results suggest that it is not the dissolved tin that is causing the immobilisation but probably exposure to the precipitate.

 

Data on marine organisms is not available.

 

Finally, it is concluded that Sn is chronically toxic to freshwater invertebrates, as indicated by a 21 d EC10 value of 4.3 mg Sn/L (nominal total tin, chemically verified) for reproduction of D. magna.

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.