Zinc fluoride

Endpoint summary

Description of key information

Reliable substance-specific information concerning the toxicity for zinc difluoride does not exist. Instead, toxicological information on soluble inorganic fluoride (e.g., sodium and potassium) substances and soluble inorganic zinc substances (i.e., zinc dichloride) were extrapolated to zinc(II) fluoride considering that the toxicological effects mainly based on the concentrations of the Zn2+ and F- ions.

Based on the results of the acute toxicity tests it can safely be assumed that the fluoride is the driver for acute toxicity. Hence, LC/LD50 values were re-calculated to zinc difluoride and C&L were given based on these values.

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

137 mg/kg bw

Quality of whole database:

reliable key studies for zinc and fluorides are available that enables C&L of zinc difluoride

Acute toxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LC50

Value:

2 462 mg/m³ air

Quality of whole database:

Reliable key study is available for the fluoride anion (i.e., sodium fluoride). However, there are no reliable studies available for a soluble inorganic zinc substance. A test performed with zinc dichloride results in a LC50 of ~ 2000 mg ZnCl2/m3 observing local effects. Nevertheless, read across to test results that based on local effects are considered to be inappropriate, since effects may be substance specific (e.g., shape, pH etc.). However, comparison of test results for fluorides and soluble inorganic zinc substances may lead to the conclusion that the toxic driver is the fluoride ion. To avoid further animal testing a study on acute inhalation toxicity with zinc difluoride is considered to be not necessary and results for acute inhalation toxicity of sodium fluoride were used for classification and labelling of the substance.

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

discriminating dose

Value:

2 000 mg/kg bw

Quality of whole database:

reliable key studies for zinc and fluorides are available that enables C&L of zinc difluoride

Additional information

Reliable substance-specific information concerning the toxicity for zinc difluoride does not exist. Instead, toxicological information on soluble inorganic fluoride (e.g., sodium and potassium) substances and soluble inorganic zinc substances (i.e., zinc dichloride) were extrapolated to zinc(II) fluoride considering that the toxicological effects mainly based on the concentrations of the Zn2+ and F- ions.

Acute oral toxicity:

In a weight of evidence (WoE) approach the LD50 for fluoride substances in rats and mice was reported to be 137 mg ZnF2/kg body weight.

By comparison, acute oral toxicity data for zinc rated as reliable provide an LD50 value for Zn(II) of about ≥834 mg/kg, indicating a much lower class of toxicity than the fluoride anions. Hence, the data for the fluoride anion were taken as the basis for classification purposes.

Acute inhalation toxicity:

A study performed with sodium fluoride results in an LC50 of 1,000 mg/m3 that is 2,462 mg/m3 re-calculated to ZnF2.

Acute dermal toxicity:

Neither fluoride nor soluble inorganic zinc substances causes acute dermal toxicity to animals. Hence, LD50 is established to > 2,000 mg ZnF2/kg bw.

Justification for classification or non-classification

According to EU classification, labelling and packaging of substances and mixtures (CLP) regulation (EC) no 1272/2008, zinc difluoride should be classified as follows:

Acute oral toxicity Cat. 3: "toxic via ingestion"

Acute inhalation toxicity: Cat. 4 "harmful via inhalation"

Acute dermal toxicity: no C&L