Bis(α,α-dimethylbenzyl) peroxide

Endpoint summary

Description of key information

Dicumyl peroxide is hydrolytically stable (DT50 > 77 d) and not readily biodegradable. The biodegradation half-life in pelagic freshwater systems is DT50 = 142 d.

The growth- and lipid-corrected kinetic bioconcentration factor as determined in an OECD 305 study is BCF = 747 L/kg.

The adsorption/desorption coefficient was determined at Koc = 9550.

Therefore, the available information indicates that the substance is not bioaccumulative and can be considered as slightly mobile in soil. 

Additional information

Hydrolysis of dicumyl peroxide was tested in a study according to OECD test guideline 111. The shortest half-life at environmentally relevant temperatures was found to be 77 days at pH 7 and 10 °C. Degradation products could not be detected.

Several studies are available investigating the potential of dicumyl peroxide for ready biodegradability. The most recent and reliable study, following OECD guideline 301F (manometric respirometry test) identified mineralisation rates after 28 days of, on average, 20 % at a test substance concentration of 100 mg/L, and of 44 % at 20 mg/L, however with high variability. Accordingly, although dicumyl peroxide fails the criterion for being regarded as “readily biodegradable” the test result shows that the substance is susceptible to mineralisation by biological processes.

In a previous study according to OECD guideline 301 D (closed bottle test) dicumyl peroxide was not biodegradable after 28 days, but biodegradation was observed in a prolonged test for up to 57 days. This study is considered to be of limited reliability since employing an unsuitably high nominal test concentration (1000 mg/L) and lacking a toxicity control. Nevertheless, also this somewhat deficient study confirms the potential of dicumyl peroxide for biological degradability.

The primary degradation half-life of dicumyl peroxide (bis(α,α-dimethylbenzyl) peroxide) in surface water was estimated at DT50 = 142 d in a study according to OECD guideline 309, based on (poorly fitting) single first-order kinetics. Mineralisation reached a maximum of 12.9 % after 90 days (50 µg/L).

Simulation testing of degradation in soil, however, is not considered to be required, since exposure of soil is expected to be negligible based on the chemical safety assessment.

Bioaccumulation of dicumyl peroxide was determined in a study according to OECD guideline 305. Growth-corrected and lipid-normalised BCF values of 493 L/kg (3.0 µg/L, nominal) and 747 L/kg (15 µg/L) were determined, the latter being more robust for analytical reasons, and more conservative. These results indicate a low to moderate potential for accumulation of dicumyl peroxide in fish and are supported by QSAR calculations.

The Koc of dicumyl peroxide was determined to be 9550 in a study prepared according to EU method C.19 OECD guideline 121 (HPLC method).

In conclusion, dicumyl peroxide is potentially biodegradable, although failing the criteria for being regarded as not persistent. Based on the Koc value the substance is expected to adsorb to suspended solids, soil and sediment. According to the results of the BCF study, supported by QSAR calculations, the potential for bioaccumulation is low. Therefore, test dicumyl peroxide is not considered a PBT substance.