Silicic acid (H4SiO4), zirconium(4+) salt (1:1), reaction products with sodium hydroxide

Short-term toxicity to aquatic invertebrates

Description of key information

A Water Accommodated fraction (WAF) was prepared at a loading rate of 100 mg/L applying a 30 minute period of ultrasonic waves followed by a two-day period of magnetic stirring. Thereafter, the resulting mixture was filtered over a 0.45 µm membrane filter and used as limit concentration. The final test solution was clear and colourless. The pH of the WAF was set from 10.3 to 8.6 with 1 M HCl. 
A limit test was performed, based on the results of a preceding combined limit/range-finding test. In the limit test, twenty Daphnia per group (four replicates, 5 daphnids per vessel) were exposed to an untreated control and to a WAF prepared at a loading rate of 100 mg/L. The total exposure period was 48h. No samples were taken to analytically confirm exposure concentrations.
The study met the acceptability criteria prescribed by the study plan and was considered valid.
The 48h-EL50 for Daphnia was beyond the range tested, i.e. exceeded loading rate of 100 mg/L for the water accommodating fraction (WAF) of the test substance.

Additional information

The key study using the water accommodating fraction (WAF) of the test substance was prepared at a loading rate of 100 mg/L applying a 30 minute period of ultrasonic waves followed by a two-day period of magnetic stirring. Thereafter, the resulting mixture was filtered over a 0.45 µm membrane filter and used as limit concentration. The final test solution was clear andcolourless. The pH of the WAF was set from 10.3 to8.6 with 1 M HCl.

 

A limit test was performed, based on the results of a preceding combined limit/range-finding test. In the limit test, twenty Daphnia per group (four replicates, 5 daphnids per vessel) wereexposed to an untreated control and to a WAF prepared at a loading rate of 100 mg/L. The total exposure period was 48h. No samples were taken to analytically confirm exposure concentrations. The study met the acceptability criteria prescribed by the study plan and was considered valid. The 48h-EL50 was beyond the range tested, i.e. exceeded loading rate of 100 mg/L.

 

For supporting data, three relevant studies were identified, of which two were used in a weight of evidence approach to cover this endpoint.

 

Two reliable studies were available. In the study of Harris (2013), preliminary stirring experiments were executed with test concentrations of 100 mg/L of test item (referring to anhydrous zirconium acetate), this to determine the dissolved zirconium in solution. After prolonged stirring of the test item, a measurable amount of zirconium could not be obtained in solution. Therefore no toxicity testing was performed and the 48-h EC50 was set at > 100 mg/L.

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. Therefore, read across can be done from tests with similar 'soluble' zirconium substances, as well as 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 48h-EC50 was thus superior to this value. This study result can be used for read across purposes to indicate that zirconium acetate is not toxic to aquatic invertebrates either at equivalent doses.

The third study (Borgman 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 considered as a supporting study.