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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

Zirconium acetate did not cause any adverse effects on aquatic microorganisms in the key activated sludge respiration inhibition study performed according to OECD guideline 209 (Bayliss, 2013). The key EC50 and NOEC are > 1000 mg/L and >= 1000 mg/L anhydrous zirconium acetate (i.e., the highest test concentration used).

Key value for chemical safety assessment

Additional information

There are two studies available.

The study from Borne and Humphrey (1977) has a Klimisch score of 3 and is not considered reliable. In this study, the effect of zirconium acetate on activated sludge organisms was investigated in fill-and-draw tests as well as in respirometer tests. The results of the study can only be used as supporting information giving an indication of the toxicity. No statistics have been applied to the test results, however, indicative NOEC and LOEC values for carbonaceous oxidation and nitrification are 200 and 500 mg Zr/L and 50 and 100 mg Zr/L, respectively. The EC75 values reported are 400 mg Zr/L for carbonaceous oxidation and 150 mg Zr/L for nitrification. The results of the respirometer tests cannot be used because of confounding effects through precipitation of Zr and/or phosphate depletion.

A new activated sludge respiration inhibition study was executed according to OECD guideline 209 (Bayliss, 2013). A relatively large increase in respiration rate was observed in the test vessels at 1000 mg/L (anhydrous zirconium acetate), which was considered to be due to metabolism of the acetate component of the test item. No statistically significant toxic effects were shown at any of the test concentrations. The 3-h EC50 for zirconium acetate was > 1000 mg/L, and the 3-h NOEC was >= 1000 mg/L (anhydrous zirconium acetate). This study is considered as key study to cover the endpoint.