Calcium fluoride

Endpoint summary

Additional information

Terrestrial toxicity

The toxicity of CaF₂is primarily expected from the fluoride ions which will be released upon dissolution of CaF₂. Similarly, toxicity of the more soluble NaF is determined by the released F^- ions. As such, the extensive dataset available for NaF has been used to assess the aquatic toxicity of CaF₂. The read-across approach is sufficiently conservative since the water solubility of CaF₂is lower than that of NaF. More information on the read-across can be found in the read-across justification in section 13.

Toxicity to soil macro-organisms

The toxicity of various fluoride compounds to Eisenia fetida was investigated over a period of 22 weeks. At higher concentrations sodium fluoride, potassium fluoride and the sodium salt of fluoroacetic acid reduced growth significantly. Calcium fluoride had no effect. The rate of maturity of the earthworms was also significantly reduced when sodium fluoride and potassium fluoride was used. The number of hatchlings was reduced in the presence of sodium fluoride, while the number of cocoons was reduced in the presence of a low concentration of sodium fluoride and potassium fluoride (Vogel & Ottow, 1992).

Toxicity to terrestrial arthropods

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 the 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 F-/kg (Beyer et al, 1987).

Toxicity to terrestrial plants

The substance is used in fertiliser preparations for application to various plant species. Toxicity of CaF₂ applied during fertilisation is therefore not expected when applied as instructed. However at elevated concentrations fluoride contaminated soils may inhibit growth and transpiration of planted trees as demonstrated in a study by Clausen et al. (2015) on willow trees and cress.

Toxicity to soil micro-organisms

The EU RAR (2001) reports NOEC values from 106 to 3000 mg F-/kg. The 63 day experiments were carried out in a micro-ecosystem containing poplar litter (30% o.m) and the isopod Porcellio scaber. Nitrification was found to be the most sensitive endpoint investigated in the micro-ecosystem test.

Toxicity to birds

Various studies are summarised in the WHO (2002) review. In feeding studies with different bird species, thicker egg shells, depressed weight gain and increased mortality rate was observed at elevated F- doses.

For Sturnus vulgaris, intubated with fluoride doses up to 160 mg F-/kg bw for 16 days, a NOEC of 10 mg F-/kg bw was derived for mortality and LD50 was calculated to be 17 mg F-/kg bw.

Toxicity to wildlife

The WHO document (2002) provides an overview of studies reporting effects on teeth and skeleton development at elevated fluoride concentrations.

In white-tailed deer (Odocoileus virginianus) mottling of the enamel of the incisors, distinct large areas of enamel hypoplasia and periosteal hyperosteosis of the metacarpal bones was observed at dietary fluoride concentrations of 25 mg F-/kg (24 months).

In areas with fluorosis in mule deer, elk and bison, fluoride levels of vegetation and water were up to 430 mg/kg and 24 mg/l, respectively (Janssen et al. 1989).

Foxes fed a diet containing 98 to 136 mg F/kg showed reduced milk production which caused mortality of kits (Janssen et al. 1989).