Zirconium dioxide

Ecotoxicological Summary

Additional information

PNEC values calculated using assessment factors cannot be derived. The available acute ecotoxicity tests in fish and daphnids show L(E)C50 values which are higher than the loading rate of 100 mg/L. In view of the extremely low water solubility of zirconium dioxide, concentrations that would be toxic for aquatic organisms will never be reached. In addition, it is commonly known that many metals form complexes with (an)organic molecules present in water. This is also the case for zirconium dioxide and it can thus be argued that zirconium dioxide will not be bioavailable to aquatic organisms. Complexation has been shown in the algal growth inhibition studies where zirconium complexed all phosphate and caused phosphate depletion in the test medium. This causes a secondary effect in algae, which is not considered relevant under environmentally realistic conditions.

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. Furthermore zirconium dioxide is highly insoluble in water and consequently no study needs to be performed. No PNEC can thus be derived.

As there are no tests on sediment and soil dwelling organisms available, and as no PNEC aquatic could be derived, no PNEC values for soil and sediment can be derived either by using assessment factors or by the equilibrium partitioning method.

There is one plant study on Zr(OH)4, which is relevant for zirconium dioxide, as zirconium dioxide is also a highly insoluble zirconium compound and background zirconium in soils is also assumed to be present as insoluble zirconium compounds. In this study, tomato and pea seedlings (ca. 21 days old) were exposed for 7 days to two different soils contaminated with either a soluble zirconium compound (zirconium dichloride oxide or zirconium acetate) or an insoluble zirconium compound (Zr(OH)4). In none of the experiments adverse effects were observed on root or shoot fresh weight of the plants. Unbound NOEC values were obtained for all experiments. The highest unbound NOEC was >= 703.4 mg Zr/kg dw for the acidic soil (417.4 mg Zr/kg background) and the lowest unbound NOEC was >= 450 mg Zr/kg dw for the calcareous soil (164 mg Zr/kg background), both soils amended with 286 mg Zr/kg Zr(OH)4.

No long-term oral or dietary mammalian or avian toxicity studies are available. Therefore no PNEC oral can be derived. This route is also not relevant as it can reasonably be assumed that zirconium dioxide will not bioaccumulate in the food chain.

Conclusion on classification

As zirconium dioxide is insoluble in water, concentrations which are toxic to aquatic organisms will not be reached. This is demonstrated in the available acute ecotoxicity studies. The substance will therefore not be classified for environmental hazards, based on the available information.