Bis(4-tert-butylcyclohexyl) peroxydicarbonate

Toxicity to aquatic algae and cyanobacteria

Description of key information

The EC(50) based on growth rate was determined for the test item bis(4-tert-butylcyclohexyl) peroxydicarbonate, based on geometric mean measured concentrations (sum) of the breakdown products cis- and trans-4-tert-butylcyclohexanol: 39 mg/L. The NOEC was determined to be 17 mg/L. 

Key value for chemical safety assessment

EC50 for freshwater algae:

39 mg/L

EC10 or NOEC for freshwater algae:

17 mg/L

Additional information

The 72-h toxicity of bis-(4-tert-butylcyclohexyl)-peroxydicarbonate against Desmodesmus subspicatus was determined according to OECD 201 resp. EU C.3. The main study was performed using five concentrations ranging from 10000 to 460 mg/L nominal concentration.

For preparation of test solutions, the test item was mixed with nutrient medium (demineralised water enriched with minerals but without algae) at a nominal loading of 10 g/L, followed by vigorous stirring at 37 ± 2 °C for 7 days. This procedure was chosen to maximise concentrations of the poorly soluble test item.

Since volatilisation from the aqueous phase (most likely attributable to the degradation products) was observed in pilot studies, the dissolution and equilibration procedure was performed in tightly sealed vessels. The lower treatments were prepared by diluting with nutrient medium.

Incubation time of the test species Desmodesmus subspicatus was 72 hours. The cell concentration of each replicate was determined by measuring the absorption of the solutions at 440 nm every 24 hours with a spectral photometer. The cell density of the cultures was calculated based on the correlation curve between the absorption and the cell density of the cultures determined by microscope counts. Growth rate µ, area under the growth curve (AUC) and the yield were determined from the cell densities at the respective observation times. Three concentrations showed significant toxicity. The concentration-response curve was extremely steep.

Actual test concentrations (geometric means of 0-hour and 72-hour samples), were determined by GC-measurement of the breakdown products cis- and trans-4-tert-butylcyclohexanol, (aggregate concentrations of parent substance including potentially formed hydrolysis products).

The chemical identity of the dissolved test item being present in test media is unclear. This is due to the fact that the location of decomposition (aqueous test solutions or analytical equipment) cannot be discriminated. Since one additional peak (other than cis- and trans-4-tert-butylcyclohexanol) was detected in the chromatograms, but not identified and quantified, the total concentration of test item is probably higher than the values reported. The effect concentrations determined in this study are therefore conservative.

With the exception of treatment 2200 mg/L, the recovery after 72 hours was acceptable (73 % to 84 % of the measured start concentration). Therefore, the aggregate test item concentrations (bis(4-tert-butylcyclohexyl) peroxydicarbonate including potentially formed hydrolysis products) can be considered as stable under the test conditions. The measured concentration after 72 hours in the treatment 2200 mg/L was unexplainably low (only 10 % recovery compared to the start concentration). As significant growth inhibition was observed in this treatment and a plausible value was measured at the start of the test, for evaluation of the results a calculated value based on the mean recovery of the other treatments (80 %) was used for calculation of the concentration at the end of the test.

The determination of the biological results for the other treatments was based on the geometric mean of the measured concentrations.

The EC50s of the reference substance potassium dichromate were tested in a separate test. The values lay within the normal range of the laboratory.