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Environmental fate & pathways

Adsorption / desorption

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Dihydrogen hexafluorozirconate will rapidly dissociate into fluoride, hydrogen and zirconium ions upon dissolution in the environment. However, zironium and hydrogen 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 hexafluorozirconate.

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Additional information

Dihydrogen hexafluorozirconate

Dihydrogen hexafluorozirconate is an inorganic substance which will rapidly dissociate into hydrogen, fluoride and zirconium ions upon dissolution in the environment. However, hydrogen and zironium 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 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.Indeed, under most environmental conditions, zirconium displays a very low mobility, mainly due to the low solubility of the hydroxide Zr(OH)4. This limits the concentration of dissolved Zr in most natural solutions (fresh water, seawater as well as soil and sediment porewater) to <0.05 μg/L. Depending on the pH of the environmental medium, different zirconium species exist in solution, including Zr4+, and various hydroxides. At pH 7, a Zr(OH)2(CO3)22-complex may form, but the complex is unstable and Zr(OH)4forms with decreasing pH. The hydro-bicarbonate (Zr(OH)4-HCO3-H2O) complex may be the most significant Zr complex in natural water (http://www.gtk.fi/publ/foregsatlas, accessed on 12.03.2013). 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

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.

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