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Environmental fate & pathways

Adsorption / desorption

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Dihydrogen hexafluorotitanate will rapidly dissociate into fluoride, hydrogen and titanium ions upon dissolution in the environment. However, hydrogen and titanium ions will not remain as such in solution, only fluoride ions do. Therefore, full read-across to potassium fluoride (CAS #7789-23-3) and other fluorides based upon a molecular weight conversion is justified. Relevant information are reported for fluoride in the EHC (2002). Fluoride strongly adsorbs to soil and is essentially immobile with very low levels of leaching. A similar conclusion can be made for dihydrogen hexafluorotitanate.

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Additional information

Dihydrogen hexafluorotitanate

Dihydrogen hexafluorotitanate is an inorganic substance which will rapidly dissociate into fluoride, hydrogen and titanium ions upon dissolution in the environment. However, hydrogen and titanium ions do 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 titanium 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 100 mg/L dipotassium hexafluorotitanate, very low levels of titanium (often < 10% or even 5%) remain in solution at environmentally relevant pH while nearly all of the fluoride (often more than 95 %) could be recovered. Indeed, under almost all environmental conditions (except the most acid conditions,i.e.,below pH 2), titanium displays a very low mobility, mainly due to the low solubility of the oxide TiO2. This limits the concentration of dissolved Ti in most natural solutions (fresh water, seawater as well as soil and sediment porewater) to <3 μg/L. Titanium only exists in a fully hydrated form, TiO(OH)2, in water above pH 2, and is, therefore, transported in a colloidal state rather than as a dissolved ion. Concentrations of ‘dissolved’ Ti generally decrease with increasing salinity. However, higher concentrations in organic rich water provide further evidence of colloidal transport. Titanium may be removed from water by flocculation of colloidal material, adsorption and scavenging by precipitation of Mn and Fe oxides. (http://www.gtk.fi/publ/foregsatlas, accessed on 12.03.2013). Thus, regarding the environmental fate and toxicity of dihydrogen hexafluorotitanate, 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

The transport and transformation of fluoride in soil are influenced by pH and the formation of predominantly aluminium and calcium complexes. Adsorption to the soil solid phase is stronger at slightly acidic pH values (5.5–6.5). Fluoride is not readily leached from soil.