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Dihydrogen hexafluorozirconate is an inorganic substance which will rapidly dissociate into fluoride, hydrogen and zirconium ions upon dissolution in the environment. However, hydrogen and zironium ions will not remain as such in solution, only fluoride ions do. The hydrogen ion attaches to a hydroxide ion to form a water molecule. The analysis of dissolved zirconium levels in aquatic toxicity test solutions for algae, daphnia and fish according to OECD 201, 202 and 203 (Schlechtriem, 2013a, b; Teigeler, 2013) indicates that up to a loading of 10 mg/L dipotassium hexafluorozirconate, very low levels of zirconium remain in solution at environmentally relevant pH (< 10%) while more than 75 % of the fluoride could be recovered. Thus, regarding the environmental fate and toxicity of dihydrogen hexafluorozirconate, it can be assumed that toxicity (if any) will be driven by the fluoride anion. Therefore, full read-across to potassium fluoride (CAS #7789-23-3) and other fluorides based upon a molecular weight conversion is justified.

Potassium fluoride

A correlation between fluoride levels in earthworms and elevated soil fluoride levels from polluted sites has been demonstrated, however levels were due to the soil content of the worm gut. Elevated fluoride content in woodlice collected from the vicinity of an Al-reduction plant has been demonstrated (Janssen et al, 1989). Sloof et al(1989) note that uptake of fluoride into plants from soil is low as a consequence of the low bioavailability of fluoride in the soil and that atmospheric uptake is generally the most important route of exposure. A relatively high rate of fluoride uptake is noted for grass species, and the consumption of fluoride containing plants may lead to elevated fluoride levels in animals and humans. Sloof et al (1989) conclude that the limited data indicate that fluoride biomagnification in the aquatic environment is of little significance. Fluoride accumulates in aquatic organisms predominantly in the exoskeleton of crustacea and in the skeleton of fish; no accumulation was reported for edible tissues.

In the terrestrial environment, fluoride accumulates in the skeleton of vertebrates and invertebrates. The EU RAR (2001) notes that the lowest fluoride levels are found in herbivores, with higher levels in omnivores and highest levels in predators, scavengers and pollinators; the findings indicate a moderate degree of biomagnification. Vertebrate species store most of the fluoride in the bones and (to a lesser extent) the teeth; elevated levels of fluoride in the bones and teeth have been shown in animals from polluted areas.