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Ecotoxicological information

Endpoint summary

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No reliable data were available for the endpoints toxicity to soil macroorganisms except arthropods, toxicity to terrestrial arthropods and toxicity to soil microorganisms. These endpoints are waived based on following justification: as ZrO2 is not classified and consequently no exposure assessment needs to be done, there is currently no reason that triggers the performance of a soil macroorganisms study. Furthermore, a plant growth study with both insoluble and soluble Zr compounds did not show any adverse effects.

Toxicity to terrestrial plants:

As no reliable studies were available on zirconium dioxide, read-across data from a structural analogue were evaluated to support data waiving for this endpoint.

Ferrand (2006) performed a plant growth study with zirconium oxychloride according to EPA OPPTS guideline 850.4230. 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 Zr compound (ZrOCl2 or Zr acetate) or an insoluble Zr 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 lowest unbound NOEC was >= 264 mg Zr/kg dw for the calcareous soil (164 mg Zr/kg background) amended with 100 mg Zr/kg ZrOCl2 or Zr acetate. The highest unbound NOEC was >= 703.4 mg Zr/kg dw for the acidic soil (417.4 mg Zr/kg background) amended with 286 mg Zr/kg Zr(OH)4. Because ZrO2 is also a highly insoluble Zr compound and background Zr in soils is also assumed to be present as insoluble Zr compounds such as ZrO2 and ZrSiO4, the unbound NOECs for the experiments with Zr(OH)4 are more relevant for ZrO2.