Zirconium acetate

Short-term toxicity to fish

Description of key information

The endpoint is covered using a weight of evidence approach including a study on zirconium acetate (Abram, 1978) yielding a 7-d LC50 of 58.7 mg Zr/L (> 100 mg/L anhydrous zirconium acetate) for rainbow trout and a study on zirconium dioxide (Bazzon, 2000) reporting a 96-h LC50 > 100 mg/L (as ZrO2) for zebra fish. The results from a stirring experiment with zirconium acetate in fish test medium (Harris, 2014a, included in IUCLID Section 5.6) further support this weight of evidence approach. In this experiment no measurable dissolved zirconium levels could be obtained because of precipitation of all zirconium from the water column, justifying the use of the study from Abram (1978) - which is a Klimisch 3 study due to absence of analytical measurements - in the weight of evidence approach together with the read across study from Bazzon (2000) performed with zirconium dioxide, an insoluble zirconium compound which is formed when dissolving a 'water soluble' compound such as zirconium acetate in aqueous media at environmentally relevant pH levels. Based on this weight of evidence approach, zirconium acetate is concluded to be non-toxic to fish.

Additional information

Three studies were identified as containing relevant information for this endpoint.

The first study from Abram (1978) yielded a 7-d LC50 for rainbow trout of 58.7 mg Zr/L. The test substance was an aqueous solution of zirconium acetate. Therefore, the LC50 is > 100 mg/L when expressed as zirconium acetate. Precipitation was observed after introduction of the test substance. Since no analytical monitoring results of the test substance in dissolution have been presented in the study report, the study cannot be considered reliable (Klimisch 3).

In the second study (Harris, 2014a) with zirconium acetate, preliminary stirring experiments were conducted with a loading rate of 50 mg test item/L (corresponding to 20 mg/L anhydrous zirconium acetate) to determine dissolved zirconium in the test medium. After prolonged stirring of the test item, a measurable amount of zirconium could not be obtained in solution (dissolved Zr < LOQ, LOQ = 49 µg Zr/L). Therefore, it was decided not to perform a final ecotoxicity test with fish. Because the ecotoxicity experiment was not performed, no robust study summary could be included in IUCLID Section 6.1.1 (Short-term toxicity to fish), 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 fish test medium performed by Harris, 2014a), 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, 2014a), 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 from Bazzon (2000), the toxicity of zirconium dioxide to zebra fish (Brachydanio rerio) was studied under static conditions, according to OECD Guideline 203. No mortality was observed during the test, neither in the control nor in the group exposed to the test item. The 96 hour LC50 was > 100 mg/L (ZrO2). The study from Bazzon (2000) is used in a weight of evidence approach with the study from Abram (1978) to demonstrate that zirconium acetate is not toxic to fish at least up to and including the limit concentration (100 mg/L) for testing toxicity to aquatic organisms.