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Short-term toxicity to aquatic invertebrates

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The study from Harris (2014b) using zirconium sulfate as test substance indicates that zirconium was not available to the aquatic test organisms because all zirconium precipitated from the water column. The study yielded a 48-h EC50 > 100 % v/v saturated solution. A study with the insoluble read across substance zirconium dioxide yielded a similar 48-h EC50 of 100 mg/L (Bazin, 1994). These two studies were used in a weight of evidence approach to cover the endpoint.

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Three studies were included in the dossier, two of which were used in a weight of evidence approach for endpoint coverage.

In the study of Harris (2014b), in which the acute toxicity of zirconium sulfate to Daphnia magna was investigated, the range finding test indicated no mortality at the highest concentration tested, i.e. a 100 % v/v saturated solution. Since no dissolved zirconium above the LOQ (20 µg Zr/L) could be detected in the 100% v/v saturated solution, no final test was performed and the 48-h EC50 was considered to be > 100 % v/v saturated solution of zirconium sulfate.

Because of the precipitation of zirconium at environmentally relevant conditions, it is considered justified to perform read across from insoluble zirconium substances such as zirconium dioxide (for further argumentation reference can be made to the read across document attached to IUCLID Section 13). Therefore, a weight of evidence approach is suggested using the study from Harris (2014b) described above and a study performed with the insoluble zirconium dioxide (Bazin, 1994). This study yielded a 48-h EC50 of > 100 mg/L (based on nominal initially added zirconium dioxide) and confirms that the toxicity of the 'water soluble' zirconium sulfate and the insoluble zirconium dioxide is very similar.

Finally, 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.