Hydroxido potassium zirconium carbonate, where there are 0, 1 or 2 hydroxide groups and 2, 3 or 4 potassium atoms and 2, 3 or 4 carbonate groups.

Short-term toxicity to aquatic invertebrates

Description of key information

48 h NOEC = 16 mg/l and the EC50 > 16 mg/l, OECD 202, EU Method C.2, Wetton  2000

Additional information

The acute toxicity of the test material to aquatic invertebrates was investigated in Daphnia magna in accordance with the standardised guidelines OECD Test Method 202 and EU Test Method C.2.

Following a preliminary range-finding study, forty daphnids (4 replicates of 10 animals) were exposed to an aqueous dispersion of the test material at a concentration of 100 mg/l for 48 hours under static test conditions. Immobilisation and any adverse reactions to exposure were recorded after 24 and 48 hours.

The 48-Hour EC₅₀ for the test material to Daphnia magna based on nominal test concentrations of the test material as received was greater than 100 mg/l and correspondingly the No Observed Effect Concentration was 100 mg/l. It was considered unnecessary and unrealistic to test at concentrations in excess of 100 mg/l.

Observations made on the prepared test media during the range-finding study showed settlement of the test material after 24 hours at the 100 mg/l test concentration. Therefore analysis was carried out to determine the zirconium concentration in the freshly prepared test media at 0 hours and in the stirred and unstirred old media at 48 hours during the definitive study.

The zirconium concentration was determined at Butterworth Laboratories Limited by measuring the zirconium concentration using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and then converting this to a concentration of test material by multiplying by the appropriate factor (eg 100 mg test material contains 28.5 mg zirconium).

Analysis of the test preparations at 0 hours for zirconium showed the measured test concentrations to be 83% of nominal (based on zirconium analysis). Analysis of the test preparations at 48 hours showed the measured test concentrations of 1% of nominal for the unstirred test media and 75% of nominal for the stirred test media.

After 48 hours, measured concentrations of zirconium were shown to be lower in the unstirred test media than in the stirred test media. This decline in measured concentrations of zirconium in the unstirred test media was considered to be due to settlement of the test material over the duration of the study. A decline was also shown in the measured concentration of the unstirred test media when compared to the 0-Hour measured values. This was considered to be due to sampling from a heterogeneous dispersion and/or the analytical method of analysis employed. During the analytical work-up procedure the sample was removed from the bottle, and evaporation and reconstitution to a known volume was conducted prior to ICP-AES analysis. As losses of test material may have occurred during any of these stages, the method of analysis as such, is considered not to be compound specific. However, it is more sensitive than Atomic Absorption (AA) and thus was the only method available for analysis of this type of test material.

Given that precipitation of the test material occurred over the study duration and settled to the bottom of the test vessels and no undissolved test material was observed in the water column after 48 hours, it was considered appropriate to base the results of the study on the time-weighted mean measured test concentration of the 0-Hour and 48-Hour unstirred test media, thus basing the results on the test material bioavailable to the test organisms.

The 48-Hour EC₅₀ based on the time-weighted mean measured test concentration of the test material as received was greater than 16 mg/l and the No Observed Effect Concentration was 16 mg/l.

The study was conducted to GLP in compliance with agreed protocols, with a high standard of reporting. The study was assigned a reliability score of 1 according to the principles for assessing data quality set out in Klimisch (1997) and considered suitable for assessment as an accurate reflection of the test material.

The available data is considered complete and the result determined, 48 h NOEC value 16 mg/l and EC₅₀ > 16 mg/l, was taken forward for risk assessment.