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Short-term toxicity to aquatic invertebrates

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Description of key information

The 48-hour EC50 of cyclohexylidenebis[tert-butyl] peroxide in a static test system is > 1000 mg/L expressed as initial loading rate (EL50), corresponding to 0.598 mg/L expressed as actual concentration (measured concentration at the beginning of the test in the saturated solution obtained from the loading rate 1000 mg/L) for Daphnia magna.

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
0.598 mg/L

Additional information

The acute toxicity of cyclohexylidenebis[tert-butyl] peroxide was evaluted in the Cladoceran Daphnia magna Straus (clone 5) using a 48 -hour static test according to OECD guideline No. 202 and EU method C.2. The study included a limit test and a range-finding test. In the limit test, twenty daphnids (in four replicates of five) were exposed to a nominal loading rate of 1000 mg/L for 48 hours while a second group of 20 daphnids (in four replicates of five) was exposed to test dilution water (M4) only (control solution).

In the range-finding test, three groups of 20 daphnids (in four replicates of five) were subjected to nominal loading rates of 1, 10, 100 and 1000 mg/L for a period of 48 hours. The solutions remained unchanged for the duration of the test. Immobilization at each loading rate was recorded at 0, 24 and 48 hours. Chemical analysis was undertaken to measure the concentration of the test item, based on the peroxide, in limit test solution (loading rate of 1000 mg/L) throughout the test. In the limit test, immobilizations were 0 % in the control and the limit test solution (1000 mg/L nominal) after 48 hours.

In the range-finding test, no immobilization was observed at 1, 10,100 and 1000 mg/L nominal throughout the test. As the test item was not found to be toxic at the nominal loading rate of 1000 mg/L (limit test solution), chemical analysis was undertaken to measure the concentration of cyclohexylidenebis[tert-butyl] peroxide in this solution. The initial concentration of the test item measured in the limit test solution was 0.598 mg/L. The test item was not stable under the experimental conditions since its concentration fell below 80 % of the initial value during the test. The measured concentration was 0.0415 mg/L after 24 hours, corresponding to 7% of the initial concentration, and < 0.0394 mg/L (limit of quantification) after 48 hours. The measured concentration of the test item in the limit test solution at the beginning of the test (0.598 mg/L) was retained for data interpretation since a geometric mean of measured concentrations throughout the test could not be determined.

Hence, the highest concentration resulting in no immobilization at 48 hours was >= 1000 mg/L expressed as initial loading rate, corresponding to 0.598 mg/L expressed as actual concentration. The 48-hour EC50 of cyclohexylidenebis[tert-butyl] peroxide in a static test system is > 1000 mg/L expressed as initial loading rate (EL50), corresponding to 0.598 mg/L expressed as actual concentration (measured concentration at the beginning of the test in the saturated solution obtained from this loading rate of 1000 mg/L) for Daphnia magna.