[1,3(or 1,4)-phenylenebis(1-methylethylidene)]bis[tert-butyl] peroxide

Biodegradation in water and sediment: simulation tests

Description of key information

The ready biodegradability was evaluated in a study performed in accordance with OECD testing guideline 301 D and GLP requirements.

The test substance is not biodegraded in the closed bottle test, and thereforeshould not be classified as readily biodegradable. This lack of biodegradation is not due to toxicity of the test compound because the endogenous respiration is not inhibited by bis (tert-butyl peroxy isopropyl) benzene.

 

Based upon the adsorption potential of the substance of interest,a study was conducted to determine the biodegradation of [1,3(or 1,4)-phenylenebis(1-methylethylidene)]bis[1,1-dimethylethyl] peroxide in water/sediment simulation test, according to US EPA guideline. The substance was not found in the water layers at all time points. In the sediment layer, an average of 94.7% of the applied dose was detected at day 0. The substance has decreased to an average of 9.7% of the applied dose at day 90. The half-life in sediment/water compartment under anaerobic conditions was determined as 29 days.

Tert-butanol, the main expected breakdown product, was detected in water and sediment layers at all time point (except day 0) but below a quantifiable level until day 90: it represented an average of 61.5% of the test substance applied dose.

 

An aerobic mineralisation in surface water study (simulation biodegradation test) according to the OECD 309 Test Guideline was performed. The test system was not suitable for the test substance as the test material leaved the test system and hence, the study did not meet the validy critera for the test guideline as viable samples did not achieve acceptable mass balance. Due to the poor mass balance and the inability to allow sufficient contact time for biodegradation to occur due to the volatility, the test is concluded as unsuitable for the substance. Based on the study it is not possible to draw any conclusions with regards to surface water degradation. Hence, an OECD 308 test was initiated and the performed feasibility study shows that the sediment test is feasible for the substance.

Therefore, a feasability study for an OECD 308 was performed.  The results of this study demonstrate the feasibility of conducting a full OECD  Guideline 308 study to investigate degradation of 1,3-bis(tert-butylperoxy isopropyl)benzene and 1,4-bis(tert-butylperoxy isopropyl)benzene in the aerobic and anaerobic aquatic sediments.

Thus the fate of bis peroxide, a mixture of 1,3-bis(tert-butylperoxy isopropyl)benzene and 1,4-bis(tert-butylperoxy isopropyl)benzene, has been studied in two natural aquatic sediment systems under laboratory conditions following the OECD 308 guideline using radiolabelled substances. A mixture of 1,3 and 1,4 radiolabelled bis peroxides was applied to silica gel and added to the sediment layer of samples of two aquatic sediment types.  This method of application was used to avoid losses by volatilization and to obtain a good mass balance.  As a result, levels detected in the water phase were low compared to the sediment phase.  The total recovery of radioactivity, or mass balance, for both aquatic sediments were between 83.9% and 97.2% applied radioactivity (AR) throughout the incubation period. Bis peroxide dissipated rapidly from the water of aquatic sediment systems with none detected from 30 days after treatment onwards.  This gave an estimated DT₅₀ values of 3.4 days (Calwich Abbey Lake) and 1.0 days (Lumsdale Middle Pond).  After 100 days incubation bis peroxide accounted for 2.0 to 4.7% of applied radioactivity in the overall system, corresponding to an estimated DT₅₀ values of 10.5 days (Calwich Abbey Lake) and 12.6 days (Lumsdale Middle Pond) at 12°C. Bis peroxide was degraded to up to 5 major components and 14 minor components in the Calwich Abbey lake system.  The main component formed eluted at 3.1 minutes (component 4), accounting for a maximum of 38.7% AR in the total system at 59 days after treatment and then declined.  In the Lumsdale Middle pond 3 major and 11 minor components were formed.  The main component formed eluted at 3.2 minutes (component 3), accounting for a maximum of 40.9% AR in the total system at 30 days after treatment and then declined.  One component was identified as 2,2-(1,4-phenylene)di(propan-2-ol).  The 1,3 isomer was also shown to co-elute with this reference.

The available OECD308 data support the OECD309 data (observed in water not air) and also demonstrated rapid primary (bio)degradation. The OECD 308 showed sufficient recovery in both preliminary and definitive testing indicating a valid result according to the test guideline. Therefore, it is concluded that primary degradation of the test material will occur in the environment. Further assessment of PBT properties should therefore be based on the properties of the transformation products (2,2-(1,4-phenylene)di(propan-2-ol) and 2,2-(1,3-phenylene)di(propan-2-ol)) as indicated in Reach Guidance on PBT assessment: R11.23.2.1 Page 24 2017. If this data is not available, it should be generated. The PBT assessment cannot therefore be stopped until conclusive data on these products is available.