Di-tert-butyl 3,3,5-trimethylcyclohexylidene diperoxide

Endpoint summary

Description of key information

Hydrolysis:

In early studies, it was believed that rapid hydrolysis of the parent substance had been observed. This was further tested in Harlan, (2010) however, results were conflicting and after multiple attempts the final test was abandoned in the light of new solubility data which showed that all hydrolysis studies had been performed well above the water solubility level of the test substance (then thought to be 2 µg/L) Further work during solubility studies (Mead, 2013; Mullee, 2013) clarified that the expected major degradation product, trimethylcyclohexanone, was present as an impurity throughout the study but did not increase. Therefore the substance is considered hydrolytically stable at pH7 -8.

Dam (2017) further clarified the problematic endpoints in stoob (2014) and demonstrated that at lower temperatures the test material was not degrading rapidly and that degradation at higher temperatures was likely not caused by hydrolysis. Loss did occur but not as rapidly as originally indicated in earlier studies.Nevertheless, as one of the major expected degradation products was observed to increase in certain cases the following information should be considered:

Increase in the major degradation product, trimethylcyclohexanone, was not observed at pH 7 and 9 except at 50°C. The explanation for this is that thermal degradation of the substance occurs (also in water) at 50°C but not at the lower temperature used in the studies and this cannot be considered to be hydrolysis in the true sense of the term and moreover cannot be extrapolated to environmentally relevant situations.

At pH4 trimethylcyclohexanone concentrations increased over the study at all temperatures used. Thus it is likely that the substance hydrolyses, perhaps even rapidly, at pH4 but not under environmentally relevant condictions. Data from (Dam2017) will therefore be used for the environmental risk assessment due to this being generated at what is considered to be the most accurate water solubility value and without the deficiencies of the other existing hydrolysis data.

Furthermore the lack of rapid biodegradation suggests hydrolytical stability. The current half life determination of 63 days also corresponds better with the existing biodegradation data.

Biodegradation:

An anaerobic degradation study in sediment using an EPA method provides reliable evidence of rapid (half life 4.3 days at 25ºC) primary anaerobic degradation.

A continuous activated sludge simulation study demonstrated 99.5 % of the test material in the influent was removed. 2% of the test material was lost to the air and 15.4% was adsorbed to the sludge. A total of 82.6 % biodegradation was measured after correction. The test material can therfore be expected to be significantly removed from industrial waste water streams during water treatment.

A Closed Bottle Test according to a slightly modified version of OECD 310 D test guideline (use of silca gel to increase bioavailability) and according to GLP was performed. 2% biodegradation was determined at day 28 and 37% at day 112. A MITI-I study was also available indicating 8-12 % biodegradation.

OECD 308 sediment simulation testing has demonstrated that the DT50 (based on total radioactivity) in the sedment is >159d. Although the parent material appears to rapidly undergo changes and is no longer quantifiable. Radioactivity resulting from the parent in the form of bound residue and unknown degredation products have been concluded as persistant in the sediment. Some low level biodegradation (mineralization to CO2) was observed

Bioaccumulation:

An in vitro study was performed using the trout S9 assay (Erhardt 2008) and the metabolism results were combined with a BCF uptake depuration model (Arnott & Gobas, 2003, 2004). When metabolic rate (Kmet) is set to 0, the model calculates a BCF of 46097. When Kmet is experimentally determined and the values obtained from the two methods incorporated into the equation (arterial hepatic and arterial hepatic and portal blood flow) further to a trout hepatocytein vitrostudy, BCFs are calculated as 766 and 443 L/Kg respectively. 766 L/Kg will be used for risk assessment as a worst case value.

 

Additional information

This substance is the main source material in a proposed family of Peroxyketal organic peroxides with very similar / identical properties. The justification for this approach has been attached in secton 13. The intention being facilitate the timely PBT / Ecotoxicity assessment of the other members of the group without uneccesary testing.