Dihydrogen hexafluorozirconate(2-)

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

PNEC aqua (freshwater)

PNEC value:

0.119 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

PNEC freshwater (intermittent releases):

0.078 mg/L

Marine water

Hazard assessment conclusion:

PNEC aqua (marine water)

PNEC value:

0.119 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

1.29 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

21.1 mg/kg sediment dw

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

4.22 mg/kg sediment dw

Assessment factor:

50

Extrapolation method:

assessment factor

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

16.5 mg/kg soil dw

Assessment factor:

10

Extrapolation method:

sensitivity distribution

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

Dihydrogen hexafluorozirconate rapidly dissociates into fluoride, hydrogen 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)₂^2-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 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.

Data of the structural analogue dipotassium hexafluorozirconate are availabe and are read-across to address the acute toxicity at three throphic levels, i.e. algae, daphnia and fish, while chronic data are only available for algae, the apparently most sensitive trophic level. Chronic toxicity data for invertebrates and fish of potassium fluoride (CAS #7789-23-3) and other fluorides are furthermore read-across. Based on available read-across data, it can be assumed that the aquatic toxicity potential of dihydrogen hexafluorozirconate is low and below relevant classification criteria of Directive 67/548 EEC and CLP Regulation (EC) No 1272/2008.

Conclusion on classification

According to Directive 67/548 EEC and CLP Regulation (EC) No 1272/2008, a classification and labelling for aquatic toxicity of dihydrogen hexafluorozirconate is not required.