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Toxicity to terrestrial arthropods

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Description of key information

The LD50 value of LD50 ≤1.67 g cryolite/m2 from a field application study with blueberry flea beetle larvae is considered as the critical acute effect value for the assessment of oral exposure in terrestrial organisms. As the observed effect from cryolite as stomach poison is considered to be predominantly from the release of fluoride ions (U. S. EPA, 1996). The critical effect value of ≤1.13 g/m2 for potassium tetrafluoroaluminate is used in the assessment.

Key value for chemical safety assessment

Additional information

For potassium tetrafluoroaluminate exposure via soil (uptake from soil matrix), no data are available. However, it should be noted, that due to the dissolution behaviour, it can be expected, that when potassium tetrafluoroaluminate is mixed to soil matrix and gets in contact with pore water, it is dissolved to different aluminum and fluoride species and no exposure to dissolved potassium tetrafluoroaluminate occurs in soil.

Like cryolite, potassium tetrafluoroaluminate can also be deposited in dust and in suspended form for some uses, where a considerable amount of potassium tetrafluoroaluminate can be expected to remain in particulate form. Ingestion of potassium tetrafluoroaluminate is expected to be the relevant route of exposure. Cryolite is considered to act predominantly as stomach poison while it releases fluoride ions (U.S. EPA, 1996). Fluoride ions in turn form complexes with metal containing enzymes in stomach (Corbett et al., 1974). For cryolite, two studies are available on the target organisms beet armyworm (Spondoptera exigua; Yee and Toscano, 1998) and tobacco caterpillar (Spodoptera litura; Prasad et al., 2000) these studies provide evidence that ingestion as route of exposure and particulate form as form of exposure in combination cause increased response to increased dose.

For cryolite two other studies are available with honeybee (Apis mellifera; Atkins and Kellum, 1986) and blueberry flea beetle larvae (Altica sylvia; Forsythe and Collins, 1994) these studies could be used in a tentative manner for PNEC derivation related to exposure similar to insecticidal application. The honeybee brood LD50 of 224.5 g cryolite/m2 is related to the application rate as well as the results with the blueberry flea beetle larvae (LD50 ≤1.67 g cryolite/m2). Target species blueberry flea beetle (short term field test) seemed to be more sensitive than honeybee brood. Despite of the uncertainty regarding to whether a proper dose-response resulted in the test with blueberry flea beetle larvae, the lower application rate of 1.67 g/m2 from this study is considered as the critical acute effect value.

The contents of fluoride, expressed as a percentage of the molar weight in both substances are practically identical, namely 54% for cryolite and 53.5% for potassium tetrafluoroaluminate. Taking into account normal physiological roles of sodium and potassium cations, their presence in the structures of the substances is not expected to lead to any significant differences in the ecotoxicity of the two substances (for details see Reporting Format as attached to the respective IUCLID entry and CSR Appendix B.4). As a result no safety factor is applied. Instead, the effect concentrations will be corrected for molecular weight. Thus, the corrected critical effect value of 1.13 g/m2 is used in the assessment.