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Environmental fate & pathways

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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.

Simulation testing on ultimate degradation in surface water and sediment is not considered to be required.

Likewise, simulation testing of degradation in soil 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 C (Bioaccumulation: Test for the Degree of Bioconcentration in Fish). BCF values of 137–1470 (0.01 mg/L) and 181–667 (0.001 mg/L) were determined. These results indicate a low potential for accumulation of dicumyl peroxide in fish. This result is supported by QSAR calculations. Not all of them are independent estimators (since dicumyl peroxide being contained in the reference data set), but the VEGA read-across model which is truly independent clearly supports a BCF of < 2000 (VEGA estimate: 517). Accordingly, there is compelling overall evidence that dicumyl peroxide has only a low to moderate bioaccumulation potential.

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 readily biodegradable. 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 as a PBT substance.