Trisodium hexafluoroaluminate

Endpoint summary

Additional information

For cryolite 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 cryolite 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 cryolite itself occurs in soil.

Based on the information of U.S. EPA (1996), cryolite is applied in dust and in suspended form where much of cryolite can expected to remain in particulate form. Ingestion of cryolite is expected to be the relevant route of exposure. The substance 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). The available two studies on the target organisms beet armyworm (Spondoptera exigua; Yee and Toscano, 1998) and tobacco caterpillar (Spodoptera litura; Prasad et al., 2000) provide evidence on that ingestion as route of exposure and particulate form as form of exposure in combination cause increased response to increased dose.

Two other studies with honeybee (Apis mellifera; Atkins and Kellum, 1986) and blueberry flea beetle larvae (Altica sylvia;Forsythe and Collins, 1994) 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 and an assessment factor of 100 is chosen for the risk characterisation. This factor is deemed appropriate due to following reasons:

• two short-term field studies are available on invertebrates; one of them has used target species, the other has employed sensitive larval stages of a non-target species (honey bee);

• a variety of plant species are not expected to show effects at application levels of cryolite as insecticide hence excluding the apparent need to test plants in this assessment.

With the above given assumptions, a tentative PNEC related to the exposure route deposition, “no-effect-deposition” (NEdep) can be obtained. It should be noted, that although the units refer to exposure via air, this value reflects effects caused by cryolite deposited from air into soil or onto plants’ surface. It is considered not relevant to derive from the critical deposition PNECsoil, because cryolite can be expected to dissolve as soon as it gets into contact with porewater. It is also noted, that the “no-effect-deposition” could be related to short-term exposure.