Tin difluoride

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

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 Guideline 209 and EU Method C.11

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Test organisms (species):

activated sludge of a predominantly domestic sewage

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

21.5 - 22 °C

pH:

range between 6.0 and 8.0

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

40.35 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

other: EC20

Effect conc.:

57.64 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

114.91 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

16.52 other: mg Sn/L

Nominal / measured:

nominal

Conc. based on:

element

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Validity criteria fulfilled:

yes

Conclusions:

An inhibiting effect of tin (Sn) in the form of tin(II)methanesulfonate on the respiration rate of activated sludge (predominantly domestic sewage) was observed in this 3 h respiration inhibition test according to OECD 209 and EC method C.11. A 3 h EC50 of 114.91 mg Sn/L (nominal) for the respiration rate of the activated sludge was determined. Furthermore, a 3 h EC10 of 40.35 mg Sn/L (nominal), EC20 of 57.64 mg Sn/L (nominal) and a NOEC of 16.52 mg Sn/L (nominal) were reported.

Description of key information

Sn has a low toxic potential to microorganisms of activated sludge, as indicated by A 3 h EC50 of 114.91 mg Sn/L (nominal) and a 3 h EC10 of 40.35 mg Sn/L (nominal).

Key value for chemical safety assessment

EC50 for microorganisms:

114.91 mg/L

EC10 or NOEC for microorganisms:

40.35 mg/L

Additional information

One reliable (RL1), GLP confirm activated sludge respiration test for Sn was performed with tin(II)methanesulfonate. In a worst-case approach, all observed toxicity is attributed to Sn:

 

An inhibiting effect of tin (Sn) in the form of tin(II)methanesulfonate on the respiration rate of activated sludge (predominantly domestic sewage) was observed in a 3 h respiration inhibition test according to OECD 209 and EC method C.11. A 3 h EC50 of 114.91 mg Sn/L (nominal) for the respiration rate of the activated sludge was determined. Furthermore, a 3 h EC10 of 40.35 mg Sn/L (nominal), EC20 of 57.64 mg Sn/L (nominal) and a NOEC of 16.52 mg Sn/L (nominal) were reported (Simon et al. 2006).

 

Hence, it is concluded, that Sn has a low toxic potential to microorganisms of activated sludge, as indicated by A 3 h EC50 of 114.91 mg Sn/L (nominal) and a 3 h EC10 of 40.35 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.