Strontium fluoride

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

5.9 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

4.3 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.59 mg/L

Assessment factor:

100

Extrapolation method:

assessment factor

PNEC marine water (intermittent releases):

0.105 mg/L

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

47 mg/L

Assessment factor:

1

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

95.9 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

95.9 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

assessment factor

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

70.1 mg/kg soil dw

Assessment factor:

10

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

PNEC oral

PNEC value:

17.9 mg/kg food

Assessment factor:

30

Additional information

Read-across justification

Strontium difluoride – general considerations:

Strontium difluoride is an inorganic solid at room temperature and consists of the strontium cation and fluoride anions. Based on the solubility of strontium difluoride in water (210 mg/L at 25°C) according to handbook data (CRC handbook, 2008), a complete dissociation of strontium difluoride resulting in the release of strontium ions and fluoride ions may be assumed under environmental conditions.

 

Strontium(II):

Read-across to environmental fate and toxicity studies of different inorganic strontium substances, including strontium dichloride and strontium dinitrate is appropriate and scientifically justified.

 

Strontium is a natural element. All environmental concentration data are expressed as “Sr”, and environmental toxicity (if any) would be caused by strontium ions.Thus, ecotoxicity of soluble strontium substances are applicable to all strontium compounds that release strontium ions into the environment.

 

The behaviour of the dissociated strontium ions in the environment determines the fate of strontium upon dissolution with regard to (bio)degradation, bioaccumulation, partitioning as well as the distribution in environmental compartments (water, air, sediment and soil) and subsequently the ecotoxicological potential.

 

Fluoride:

Fluoride is a natural element. All environmental concentration data are expressed as “F”, and environmental toxicity (if any) would be caused by fluoride ions. Thus, ecotoxicity of soluble fluoride substances are applicable to all fluoride compounds that release fluoride ions into the environment.Further, read-across to environmental fate and toxicity studies of soluble fluoride salts (predominantly sodium fluoride) and acid is appropriate and scientifically justified. This read-across approach was already applied in the 2001 EU Risk Assessment of hydrogen fluoride as follows: “All reported tests with aquatic organisms were performed with NaF. Because HF occurs in the aquatic compartment mainly as fluoride ion, the NaF tests can be used for the evaluation of HF effects in aquatic organisms. All reported test results were corrected for the fluoride ion.”

 

In solution, fluoride ions form strong complexes with other ions, particularly Ca²⁺, Al³⁺, Fe³⁺, PO₄³- and B(OH)^4-.Fluorine, however, is an essential micronutrient for mammals, serving to strengthen the apatite matrix of skeletal tissues and teeth (Salminen et al. 2005 and references therein).

 

The behaviour of the dissociated fluoride ions in the environment determines the fate of fluoride upon dissolution with regard to (bio)degradation, bioaccumulation, partitioning as well as the distribution in environmental compartments (water, air, sediment and soil) and subsequently the ecotoxicological potential.

 

 

Therefore, the assessment of the ecotoxicity of strontium difluoride is based on elemental strontium and fluoride concentrations. Read-across of ecotoxicity data available for soluble strontium substances and soluble fluoride substances is applied since the strontium ions and fluoride ions determine the ecotoxicological potential of strontium difluoride.

Conclusion on classification

For the assessment of the environmental hazard potential of strontium difluoride, the category approach is applied and data for fluoride and soluble strontium substances are read-across since only the ions of strontium difluoride, Sr2+ + F- are available in an aqueous environment and determine the toxicity.

Based on aquatic toxicity data of its moieties, i.e. strontium and fluoride, strontium difluoride appears to be toxic to aquatic organisms. Short-term toxicity data of strontium are available for freshwater organisms covering three trophic levels. The respective reliable IC/LC/EC50 values are above 1 mg/L. Hence, no classification and labelling for aquatic acute toxicity is required.

Based on the EU RAR "hydrogen fluoride" (2001), EC50-values of fluoride toxicity for algae range from 43 - 122 mg/L, for daphnids from 97 - 352 mg/L, and for fish from 51 - 340 mg/L.

The lowest reported EC50 values are applied in the hazard assessment. Thus, short-term toxicity data covering three trophic levels are available for strontium and fluoride and are summarized as follows:

 

Table: Short-term toxicity data of strontium and fluoride for freshwater organisms

Trophic level	lowest EC value for strontium	lowest EC value for fluoride
Algae	72-h ErC50 Pseudokirchneriella subcapitata; > 43.3 mg Sr/L (arithm. mean; Tobor-Kaplon, 2010) > 62 mg SrF2/L	96-h EbC50 43 mg F/L 284 mg SrF2/L
Daphnia	48h-EC50 (mobility) Daphnia magna; 125 mg Sr/L (Biesinger & Christensen; nominal test concentration) 179 mg SrF2/L	48-h EC50 97 mg/L 641 mg SrF2/
Fish	96-h LC50 Cyprinus carpio, > 40.3 mg Sr/L (arithm. mean; Tobor-Kaplon, 2010) > 58 mg SrF2/L	96-h LC50 51 mg/L 337 mg SrF2/L

 

Aquatic toxicity data of strontium and fluoride when expressed as strontium difluoride are available for algae, daphnia and fish; respective EC/LC50 values are > 1 mg/L. Therefore, strontium difluoride does not meet classification criteria as short-term hazard to the aquatic environment under Regulation (EC) No 1272/2008 and subsequent adaptations and should not be labelled.

Based on aquatic toxicity data of its moieties, i.e. strontium and fluoride, strontium difluoride appears to have a no potential for long-term toxicity to aquatic organisms.

Long-term toxicity data are available for strontium and fluoride and are summarized as follows:

Table: Long-term toxicity data of strontium and fluoride for freshwater organisms

Trophic level	lowest EC value for strontium	lowest EC value for fluoride
Algae	NOErC Pseudokirchneriella subcapitata; ≥ 43.3 mg Sr/L (arithm. mean; Tobor-Kaplon, 2010) ≥ 62 mg SrF2/L	7-d NOEbC 50 mg F/L 331 mg SrF2/L
Daphnia	Chronic data are not required according to Annex VIII.	21-d NOEC (reproduction) 3.7 mg F/L 25 mg SrF2/L
Fish	Chronic data are not required according to Annex VIII.	21-d NOEC 4.0 mg F/L 26 mg SrF2/L

 

Based on the EU RAR “hydrogen fluoride” (2001), a long-term NOEC-value is available for fish; i.e. 21-d LC5 of 4 mg/L. For daphnia, NOEC-values of fluoride toxicity range from 3.7 to 14.1 mg/L and for algae from 50 - 249 mg/L. The lowest reported NOEC values are applied in the hazard assessment.

Data submitted with this dossier for strontium difluoride addresses information requirements according to Annex VIII of Regulation (EC) No 1907/2006 but does not include long-term (chronic) toxicity data for aquatic invertebrates and fish. However, the registrant of this dossier for strontium difluoride acquired a Letter of Access, including access to the following aquatic hazard conclusions as already submitted for other soluble strontium substances, including strontium chloride (EC number: 233-971-6):

 

“Short-term toxicity EC/LC50 values of Sr available for 3 trophic levels are situated between >40.3 mg Sr/L and >125 mg Sr/L, corresponding to > 72.9 mg/L and 226.2 mg/L strontium chloride based on an average Sr content of 55%. In accordance with Regulation (EC) No 1272/2008, Table 4.1.0 (a), classification for acute aquatic hazard is not required for strontium chloride as all EC50/LC50 values are above the classification criteria of 1 mg/L.

 

Long-term toxicity data are available for three trophic levels and range from 21 mg Sr/L to ≥ 43.3 mg Sr/L, corresponding to 38.0 mg/L and 78.3 mg/L strontium chloride based on an average Sr content of 55%. In accordance with Regulation (EC) No 1272/2008, Table 4.1.0 (b) (i), classification for chronic aquatic hazard is not required for strontium chloride as all chronic EC10/NOEC values are above the classification criteria of 1 mg/L.”

 

Thus, the following is concluded for the aquatic hazard potential of strontium difluoride:

 

Taking into account the lowest chronic ecotoxicity value observed on a wide variety of species of different taxonomic groups (25 mg SrF2/L), chronic aquatic toxicity classification of the substance in accordance to regulation (EC) No 1272/2008 is not required.