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The aquatic toxicity of zirconium acetate (a 'water soluble' zirconium compound) is evaluated using data for zirconium acetate as well as data from read across substances such as zirconium basic carbonate (a sparingly soluble zirconium compound) and zirconium dioxide (an insoluble zirconium compound). 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 (Fox, 2013), stirring experiments in fish, algal and daphnid test media (Harris, 2014a,b; Vryenhoef, 2014)) indicated that zirconium from the 'water soluble' zirconium acetate 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 acetate 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 acetate is concluded not to be toxic (acutely) to fish and aquatic invertebrates. The studies that were used for endpoint coverage (performed with zirconium acetate and/or read across substances) were performed according to internationally accepted guidelines and did not report any acute adverse effects (mortality in fish, immobilization 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 acetate was not found to be toxic to aquatic microorganisms in an activated sludge respiration inhibition test.