Tin difluoride

Toxicity to terrestrial arthropods

Link to relevant study record(s)

Reference

Endpoint:

toxicity to terrestrial arthropods: short-term

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Older, non-GLP publication

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Not applicable

GLP compliance:

no

Application method:

soil

Analytical monitoring:

no

Details on sampling:

Litter was collected from eight sites at distances as far as 33 km from an Al reduction plant in western Tennessee. Soil was collected at a level of 0 to 5 cm and 5 to 15 cm.

Vehicle:

no

Details on preparation and application of test substrate:

The main part of the study involves deducing whether the content of fluoride in the litter is related to the distance from thr Al reduction plant. In one test, sodium fluoride is added to the litter to determine the effect on mortality.

Test organisms (species):

Porcellus scaber

Details on test organisms:

No further details on test organisms.

Study type:

field study

Limit test:

no

Post exposure observation period:

No post observation period.

Test temperature:

Not stated

pH (if soil or dung study):

Not stated

Humidity:

Not stated

Photoperiod and lighting:

Not stated

Details on test conditions:

The test involves determining whether there is a link between distance from the Al reduction plant and concentration of fluoride ions in the soil. Litter was collected from eight sites at distances as far as 33 km from an Al reduction plant in western Tennessee. Soil was collected at a level of 0 to 5 cm and 5 to 15 cm. To determine the effect of increased fluoride concentration on mortality, a sample of litter was spiked with sodium fluoride and the mortality rate monitored.

Nominal and measured concentrations:

measured.

Reference substance (positive control):

no

Duration:

126 d

Dose descriptor:

NOEC

Effect conc.:

800 other: mg F/kg bw

Conc. based on:

element

Basis for effect:

mortality

Details on results:

Litter was collected from eight sites at various distances away from the plant. Results showed that litter collected far from the plant had a lower fibre content, was more sapric and was less acid. Total acid extractable F- in the litter and upper 15 cm of soil was about 41 times as much at the closest site (700 mg/kg) as at the most distant sites (12 and 16 mg/kg). In a bioassay of litter from our study sites, woodlice (Porcellio scaber) had an abnormally high mortality in litter that contained 440 mg/kg or more of acid extractable F-. When F- was added in the form of NaF to the litter, a significant increase in mortality was observed only in treatments exceeding 800 mg NaF/kg.

Results with reference substance (positive control):

Not applicable

Reported statistics and error estimates:

Not applicable

Results showed that litter collected far from the plant had a lower fiber content, was more sapric and was less acid. Total acid extractable F- in the litter and upper 15 cm of soil was about 41 times as much at the closest site (700 mg/kg) as at the most distant sites (12 and 16 mg/kg).

Validity criteria fulfilled:

not applicable

Conclusions:

Porcellio scaber were exposed to fluoride for a duration of 126 d and effects on the mortality of woodlice were determined. A 126 d NOEC of 800 mg F/L (nominal) was reported.

Executive summary:

The effects of fluoride concentration were investigated on the numbers of Porcellio scaber in leaf litter. Leaf litter was collected from eight sites at various distances away from an aluminium reduction plant. Results showed that litter collected far from the plant had a lower fibre content, was more sapric and was less acid. Total acid extractable F- in the litter and upper 15 cm of soil was about 41 times as much at the closest site (700 mg/kg) as at the most distant sites (12 and 16 mg/kg). In a bioassay of litter from study sites, woodlice (Porcellio scaber) had an abnormally high mortality in litter that contained 440 mg/kg or more of acid extractable F-. When F- was added in the form of NaF to the litter, a significant increase in mortality was observed only in treatments exceeding 800 mg/kg.

Description of key information

Fluoride has a low chronic toxicity potential towards terrestrial arthropods, as indicated by a 126 d NOEC value of 800 mg F/kg soil dw.

Key value for chemical safety assessment

Long-term EC10, LC10 or NOEC for soil dwelling arthropods:

800 mg/kg soil dw

Additional information

The EU Risk Assessment Report (RAR, RL2) for hydrogen fluoride reports chronic terrestrial arthropods toxicity data:

Porcellio scaber were exposed to fluoride for a duration of 126 d and effects on the mortality of woodlice were determined. A 126 d NOEC of 800 mg F/L (nominal) was reported (Beyer et al., 1987; EU RAR, 2001).

 

Hence, fluoride has a low chronic toxicity potential towards terrestrial arthropods, as indicated by a 126 d NOEC value of 800 mg F/kg soil dw.

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 fluoride salts (predominantly sodium fluoride) is therefore appropriate and scientifically justified. This read-across approach was already applied in the 2001 EU Risk Assessment of hydrogen fluoride.