Registration Dossier

Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
no hazard identified

Marine water

Hazard assessment conclusion:
no data: aquatic toxicity unlikely

STP

Hazard assessment conclusion:
no data: aquatic toxicity unlikely

Sediment (freshwater)

Hazard assessment conclusion:
no hazard identified

Sediment (marine water)

Hazard assessment conclusion:
no hazard identified

Hazard for air

Air

Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
no hazard identified

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
no potential for bioaccumulation

Additional information

No aquatic PNEC values were derived for tungsten zirconium oxide. The argumentation for this is described below.

No adverse effects were observed in the available toxicity studies with fish and aquatic invertebrates performed with zirconium dioxide at concentrations below or equal to the limit test dose of 100 mg/L. In algal growth inhibition tests with zirconium compounds, adverse effects on growth have been observed at concentrations (slightly) below 100 mg/L. However, the observed effects were due to phosphate deprivation of the algae, as a result of strong complexation of zirconium with the phosphate in the test medium. Anyhow, all EC50 levels were > 100 mg/L. In conclusion, zirconium dioxide should not be considered as toxic or harmful to aquatic organisms.

To demonstrate the validity of the read across assumption, i.e. that the addition of tungsten to the crystal lattice of zirconium dioxide does not alter the unhazardous character of zirconium dioxide, studies were performed with tungsten zirconium (hydroxide) oxide for basic (Annex VII) ecotoxicological endpoints, i.e. acute toxicity to aquatic invertebrates and toxicity to aquatic algae. In the study with aquatic invertebrates, no adverse effects were observed up to and including at the limit test dose of 100 mg/L (using a saturated solution with nominal loading rate of 100 mg/L), which is in agreement with the available study for zirconium dioxide. In the algal growth inhibition study, significant growth inhibition was observed in the 100% v/v saturated solution with nominal loading rate of 100 mg/L, resulting in a growth rate-based 72-h EC50 of 98% v/v of the saturated solution. Unfortunately, no phosphate measurements were performed during the test. The results of this study are however in agreement with those obtained with other zirconium compounds and are assumed to be due to phosphate deprivation of the algae as a result of strong complexation of zirconium with the phosphate in the test medium, i.e. an effect which is not considered to be environmentally relevant.

Taking all this into account, the addition of tungsten to the zirconium dioxide crystal lattice can be considered not to alter the non-hazardous properties of zirconium dioxide in the environment. The substance is therefore not classified for any environmental hazard, and no chemical safety assessment needs to be performed. Consequently, it was not considered useful to derive PNEC values for the aquatic environment. For the same reasons, no PNEC values were determined for sediment and terrestrial organisms either.

Finally, no PNEC value was determined for secondary poisoning since the available mammalian studies indicate that tungsten zirconium oxide is not a hazardous substance and because there is no concern for bioaccumulation or biomagnification of tungsten or zirconium from tungsten zirconium oxide in both the aquatic and terrestrial environment.

Conclusion on classification

Based on the available toxicity data (fish, aquatic invertebrates, and algae) for tungsten zirconium (hydroxide) oxide and/or zirconium dioxide (or its read across compounds), it was concluded that there are no indications for tungsten to change the non-hazardous properties of zirconium dioxide, when manufacturing tungsten zirconium oxide. Therefore, as is the case for zirconium dioxide, tungsten zirconium oxide is not considered to be classified for any environmental hazard either.