tert-butyl peroxyisobutyrate

Short-term toxicity to fish

Description of key information

The EC50-96h value obtained for t-butylperoxyisobutyrate was determined to be 8.7 mg/L .The 96 h-EC50 value corresponding to a solution containing 75 % t-butylperoxyisobutyratewas estimated to be 11.6 mg/L.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

11.6 mg/L

Additional information

The acute toxicity (lethality) of the test substance used in the study to Danio rerio (freshwater fish) was assessed according to the EU method C.1 and OECD guideline 203.

Fish were exposed to a range of concentrations of the test substance dissolved in dilution water. The definitive test was performed under semi-static conditions, with a renewal of test solutions every 24 hours. The measured toxic effect was the mortality after 24, 48, 72, and 96 hours.

Two vessels, each containing 5 fish, were prepared per concentration. The fish were exposed to a concentration range of 10.5 to 30 mg/L, forming a geometric progression with a factor of 1.3. Since the test item is a non-stable substance in water, the solutions were renewed every 24 hours during the test period. Testing flasks were incubated at 23.3 ± 0.5°C, under controlled lighting (darkness 12 hours/24hours).

For each exposure concentration, the percentage of dead fish after 24, 48, 72, and 96 hours was recorded. Visible abnormalities and physical-chemical measurements (pH and dissolved oxygen) were recorded every 24 hours. Analytical determinations were carried out at the beginning, at renewal times, and at the end of the test.

The concentrations killing 50 % of fish at times 24h, 48h, 72h, and 96h (LC50-24h, LC50-48h, LC50-72h and LC50-96h) were calculated by regression analysis using the Probit/log model. The EC50-96h value obtained for t-butyl peroxy isobutyrate was determined to be 8.7 mg/L .

The test concentrations of the test substance were measured by, high pressure liquid chromatography coupled with mass spectrometry. Lethal concentrations were calculated using measured concentrations.

Visible abnormalities (loss of equilibrium, changes in swimming behaviour, respiratory function, pigmentation, etc.) were not observed in the control vessels. At the highest concentrations, surviving fishes got very red gills. Some of them showed a red colouring of the whole body. They showed low reactivity. The study was carried out in compliance with its quality criteria: mortality in the control did not exceed 10 % at the end of the test; the concentration of dissolved oxygen in the test vessels remained above 60 % of the air saturation value at the end of the test; the pH did not vary by more than 1 unit. The concentrations of the test substance were not maintained within 80 % of the initial concentration throughout the duration of the test.

Since the substance t-butyl peroxy isobutyrate will be registred as 75 % solution, the effect concentration (96h-EC50) was extrapolated for a solution containing 75 % t-butyl peroxy isobutyrate (starting from the 96h-EC50 of 100 % t-butyl peroxy isobutyrate). The 96 h-EC50 of 75 % t-butyl peroxy isobutyrate was estimated to be 11.6 mg/L. This value will be used as key value for chemical safety assessment and for classification and labelling.