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Short-term toxicity to aquatic invertebrates

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Description of key information

Under the experimental conditions, the 48-hour EL50 of the test substance (75 % t-butylperoxyisobutyrateinisododecane) in a static test system is 231 mg/L expressed as initial loading rate, corresponding to 72.5 mg/L expressed as actual concentration (calculated from geometric means of measured concentrations in the saturated solutions obtained from the loading rates tested), for Daphnia magna.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
72.5 mg/L

Additional information

The acute toxicity of the test substance (75 % t-butyl peroxy isobutyrate in isododecane) was evaluated in the Cladoceran, Daphnia magna STRAUS using a 48-hour static test according to OECD guideline No. 202 and EU method C.2. As the test item is a mixture of poorly soluble components, the water-accomodated fraction (WAF) procedure was applied to prepare the test solutions. A preliminary test which included a limit test and a range-finding test preceded the definitive test. Five loading rates of the test substance were used together with a control at: 0, 50, 100, 200, 400 and 800 mg/L. Twenty daphnids (in four replicates of five) were exposed to each loading rate for 48 hours and immobilization was recorded at 0, 24 and 48 hours.

Initial concentrations of the test item measured in the definitive test solutions were within ± 20% of the corresponding nominal values. The test item was not stable under our experimental conditions since its concentration fell below 80% of the initial value in all solutions during the test (measured concentrations ranged from 4% to 31% of the nominal values after 48 hours). All toxicity results could be based on initial loading rates and also on geometric means of measured concentrations (calculated from the test substance measurements) in test solutions during the corresponding exposure period, i.e. 24 or 48 hours.

Under our experimental conditions, the 48-hour EL50 of the test substance in a static test system is 231 mg/L expressed as initial loading rate, corresponding to (EC50) 72.5 mg/L expressed as actual concentration (calculated from geometric means of measured concentrations in the saturated solutions obtained from the loading rates tested), for Daphnia magna.