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The aquatic toxicity of zirconium dinitrate oxide (a 'water soluble' zirconium compound) is evaluated using data for zirconium dinitrate oxide as well as data from read across substances such as zirconium acetate and zirconium dichloride oxide (other 'water soluble' zirconium compounds which behave similarly in aqueous media), zirconium basic carbonate (a sparingly soluble zirconium compound), and insoluble zirconium compounds such as zirconium dioxide and a reaction mass of cerium dioxide and zirconium dioxide. Read across from insoluble or sparingly soluble zirconium substances is considered acceptable because several experiments (e.g., water solubility study and study on pH-dependency of water solubility (Bauer, 2015), and an acute toxicity to fish study (Sipos, 2015)) indicated that zirconium from the 'water soluble' zirconium dinitrate oxide does not stay in solution at environmentally relevant pH levels. Rapid hydrolysis occurs, resulting in precipitation of zirconium hydroxides or zirconium dioxide. Further, heavy complexing will occur with phosphates, which results in 100% precipitation whenever phosphate is present in excess. Complexation with carbonates may also result in progressive precipitation with increasing pH levels. As a result, at environmentally relevant conditions, zirconium dinitrate oxide cannot be considered as a water soluble compound. Overall, zirconium is not bioavailable in the aquatic environment and therefore no adverse effects are to be expected on aquatic organisms.

Further argumentation for the read across approach is given in the read across document attached to IUCLID Section 13.

Zirconium dinitrate oxide is concluded not to be harmful or toxic (acutely) to fish and aquatic invertebrates. The studies that were used for endpoint coverage (performed with zirconium dinitrate oxide and/or read across substances) were performed according to internationally accepted guidelines and did not report any acute adverse effects (mortality in fish, immobilisation in daphnids) at the limit test concentration of 100 mg/L. In algal growth experiments with read across substances, it was demonstrated that the observed growth inhibition was concurrent with phosphate depletion. Toxicity to algae is therefore due to phosphate deprivation as no primary toxic effects have been observed. Phosphate deprivation is a secondary effect which is not considered relevant at a normal environmental scale. Therefore, no effects on algae are expected in the environment either. Finally, zirconium dinitrate oxide was concluded not to be toxic to aquatic microorganisms based on the results of an activated sludge respiration inhibition test performed with the read across substance zirconium acetate.

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