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Short-term toxicity to aquatic invertebrates

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Description of key information

Stirring experiments performed by Harris (2014b) to investigate the solubility of zirconium acetate in daphnid test medium indicated that zirconium is precipitated from the water column. Therefore, read across is performed from the acute daphnid toxicity study of Bazin (1994) using zirconium dioxide (an insoluble zirconium compound) as test substance. In this study no effects were observed in a limit test, yielding a 48-h EC50 of > 100 mg/L (ZrO2). Zirconium acetate is assumed to be equally non-toxic to aquatic invertebrates.

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Additional information

Three relevant studies were identified, one of which was selected as key study to cover this endpoint.

 

In the study of Harris (2014b), preliminary stirring experiments were executed with loading rates of 50 mg test item/L (corresponding to 20 mg/L of anhydrous zirconium acetate), to determine dissolved zirconium in daphnid test medium. After prolonged stirring of the test item, a measurable amount of zirconium could not be obtained in solution (dissolved Zr < LOQ, LOQ = 20 µg Zr/L). Therefore, it was decided not to perform a final ecotoxicity test with daphnids. Because the ecotoxicity experiment was not performed, no robust study summary could be included in IUCLID Section 6.1.3 (Short-term toxicity to aquatic invertebrates), but the information from the stirring experiments was included in a robust study summary under IUCLID Section 5.6 (Additional information on environmental fate and behaviour).

From both theory and experience (e.g., water solubility testing and testing of pH dependency of water solubility (Fox, 2013), stirring experiment in daphnid test medium performed by Harris, 2014b), it is clear that when zirconium acetate is added to the test medium, a pH drop occurs. When adjusting pH back to environmentally relevant levels, precipitation occurs. The zirconium acetate quickly hydrolyses and zirconium precipitates out of solution forming insoluble zirconium hydroxides or zirconium oxide, rendering the substance unavailable to the test organisms. Because precipitation appears to be complete (e.g., results from stirring experiment performed by Harris, 2014b), read across can be done not only from tests with similar 'water soluble' zirconium substances, but also from tests with insoluble zirconium substances such as zirconium dioxide.

In the study of Bazin (1994), the acute toxicity of zirconium dioxide to Daphnia magna was studied under static conditions according to EU method C2. No significant immobilization was observed at a loading rate of 100 mg/L (ZrO2). The 48-h EC50 was thus superior to this value. This study result can be used for read across purposes to justify the conclusion that zirconium acetate is not expected to be toxic to aquatic invertebrates. This is supported by the results from the stirring experiments performed by Harris (2014b). The study of Bazin (1994) can be considered as the key study for this endpoint.

The study of Borgmann et al. (2005) studied juveniles of the amphipod species Hyalella azteca, following an atypical procedure. In this study, 7-d (acute) toxicity tests were performed. The obtained LC50 values in soft water and moderately hard tap water were > 1000 and > 3150 µg Zr/L, based on nominal concentrations. However, based on analytical measurements in the soft water assay, only a limited amount of the added zirconium was present in the dissolved fraction (e.g., 4.2 µg Zr/L at the nominal concentration of 1000 µg Zr/L). Because of non-satisfactory analytical monitoring, no exact LC50 values based on measured zirconium concentrations could be calculated. Moreover, the animals were fed during the test, which is not a common practice in acute toxicity tests. The results are therefore not considered reliable (Klimisch 3). The study is therefore considered as a supporting study.