Zirconium dioxide

Endpoint summary

Additional information

Short-term toxicity to fish:

The 96-h acute toxicity of zirconium dioxide to Brachydanio rerio was studied under static conditions, according to OECD Guideline 203. Fish were exposed to control and test chemical at a nominal concentration of 100 mg/L. Mortality/immobilization were monitored daily. No mortality was observed during the test, neither in the control nor in the group exposed to the test item. The 96-h LC50 and NOEC were thus > 100 mg/L.

Short-term toxicity to aquatic invertebrates:

The acute toxicity of zirconium dioxide to Daphnia magna was studied under static conditions according to EU method C2. Daphnids were exposed to control and test chemical at an initial loading rate of 100 mg/L for 48 hours. Mortality and immobilization were monitored after 24 and 48 hours. No significant immobilization was observed at the loading rate of 100 mg/L. The 48-h NOEC and 48-h EC50 were thus superior to this value.

Long-term toxicity to fish and aquatic invertebrates:

As zirconium dioxide is not classified for any endpoint, exposure assessment and risk characterization according to REACH Annex I do not need to be conducted. In view of the lack of effects in the available acute aquatic toxicity tests, its extremely low water solubility and its tendency to form complexes with (an)organic molecules in water (and thus to become non-bioavailable), there is no need to investigate further the effects on aquatic organisms. Based on this justification, these endpoints are waived.

Toxicity to aquatic algae and cyanobacteria:

In the absence of a study on zirconium dioxide itself a weight of evidence approach was proposed using two studies with other insoluble zirconium compounds (zirconium basic carbonate and a reaction mass of zirconium dioxide and cerium dioxide) and one study with a 'water soluble' zirconium compound (zirconium dichloride oxide). In all three studies, the observed growth inhibitory effects were attributed to phosphate depletion. Zirconium forms strong complexes with phosphate and therefore, when in excess, precipitates all phosphate from the test medium. No evidence has been found for direct toxic effects to occur to algae upon exposure to zirconium compounds. The phosphate depletion effect in limited systems such as used during aquatic ecotoxicity tests is not considered environmentally relevant and therefore zirconium dioxide and the tested zirconium compounds are not considered toxic to algae.

Toxicity to microorganisms:

No reliable studies were available for this endpoint.

Microorganisms in an STP will not be exposed to zirconium dioxide, as it will either be removed in the primary settling tank before reaching the microorganisms, or it will not be bioavailable due to complexation. In addition, testing is waived based on the following justification in accordance with REACH Annex VIII, 9.1.4 Column 2: the study does not need to be conducted if the substance is highly insoluble in water.