Di-tert-butyl 1,1,4,4-tetramethyltetramethylene diperoxide

Endpoint summary

Additional information

Stability :

2,5-dimethyl-2,5-di(tert-butylperoxy)hexane adsorbs strongly to glassware and loss of the compound is solely or mainly due to adsorption and not to hydrolysis. Even if the compound would be susceptive to hydrolysis it would not be a significant route of degradation in the environment because the compound would adsorb to suspended solids and other organic material present in surface water.

 

Biodegradation:

One key study was available on the biodegradation of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane. This study was performed according to modified OECD 301D Test Guidelines to permit prolonged measurements with no GLP statement. In the SCAS test, 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was exposed to activated sludge maintained by daily addition of primary settled sewage for a period of 8 weeks. The test substance caused no reduction of the biodegradation of the organic compounds present in primary settled sewage. Therefore the test substance is considered to be non-inhibitory to the activated sludge. 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was not degraded in prolonged Closed Bottle tests inoculated with unacclimated and acclimated sludge from the SCAS unit. This result demonstrates that microorganisms do not have the ability to grow on this organic peroxide under aerobic conditions. Potential decomposition products of the test substance i.e. tert-butanol and 2,5-dimethyl-2,5-hexanediol were degraded in Closed Bottle tests with both acclimated and unacclimated sludge (> 80% within 56 days).The length of the lag period found with 2,5-dimethyl-2,5-hexanediol with acclimated sludge was short compared to the period obtained with unacclimated sludge. This result suggests that the peroxide bond of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane is cleaved in the SCAS unit.

In a continuous activated sludge (CAS) test 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was exposed to micro-organisms maintained by addition of domestic wastewater. 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was spiked at a nominal influent concentration of 10.0 mg/L test substance for a period of 59 days. An accurate assessment of the removal of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was established with specific analyses using LC-MS/MS.

The average removal percentage in the test unit was quantified with the specific analysis on day 58 and 59 was 99.95% and 99.89%, respectively. These analyses demonstrate that the removal of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane from the wastewater is nearly complete.

Bioaccumulation:

Two studies on bioaccumulation were available on 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane.

The first study (Erhardt, 2008) was evaluated as the key study. This study assessed the bioaccumulation of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane using the in vitro trout liver S9 metabolism assay (no standard guideline followed). The BCF value was determined with and without metabolism being taken into account. The calculation is based on the Arnot Gobas BCF mass balance model run with and without metabolism. When metabolic rate (Kmet) is set to 0, the model calculates a BCF ot 46097. When Kmet is experimentally determined using two methods: arterial hepatic and arterial hepatic and portal, blood flow extrapolation further to a trout hepatocyte in vitro study, BCFs are calculated as 766 and 443 L/Kg respectively. The in vitro rate of metabolism was determined for this organic peroxide. The substance dissipated rapidly under biologically active conditions. A half- life for metabolism was 210 min or 3.5 hours. These data were used to extrapolate in vivo rate constants of metabolism or Kmet of 0.116 day^-1or 0.189 day^-1using hepatic portal blood flow or hepatic portal and arterial blood flow, respectively. The use of these kMET values in conjunction with the Gobas model dropped the calculated BCF from 31,819.51(assuming no metabolism) to 521 or 839.

The second study (author unknown, 2004) was evaluated as the weight of evidence. This study assessed the bioconcentration of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane on Cyprinus carpio, following "Methods concerning the testing of new chemical substances" (Kanpo n°. 5, Yakuhattsu n°.615, 49th Unit, n°.392, 1974, partially revised in 1998), which is similar to OECD Guideline 305. Results demonstrated that a BCF steady-state of 3690 and 2250 L/Kg (for primary and secondary concentration areas respectively).

As the experimental BCF study was incomplete missing numerous details allowing it to be validated, the BCF and as further experimental data are available from an in vitro study which is deamed to be valid, it is concluded that the BCF is between 521 and 839.

 

Transport and distribution:

The adsorption coefficient of the substance in soil and sludge using an HPLC method was estimated in a reliable GLP study following OECD 121. Based on two measurements of the substance, and by comparison with reference substances, the Koc of the substance was calculated as 52600 at 30°C.

The Log Koc of 2,5-dimethyl-2,5-di(tert-butylperoxy)hexane was therefore approximately 4.72.