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

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

no hazard identified

Marine water

Hazard assessment conclusion:

no hazard identified

STP

Hazard assessment conclusion:

PNEC STP

PNEC value:

100 mg/L

Assessment factor:

10

Extrapolation method:

assessment factor

Sediment (freshwater)

Hazard assessment conclusion:

PNEC sediment (freshwater)

PNEC value:

0.102 mg/kg sediment dw

Assessment factor:

50

Extrapolation method:

assessment factor

Sediment (marine water)

Hazard assessment conclusion:

PNEC sediment (marine water)

PNEC value:

0.01 mg/kg sediment dw

Assessment factor:

500

Extrapolation method:

assessment factor

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

PNEC soil

PNEC value:

5.29 mg/kg soil dw

Assessment factor:

10

Extrapolation method:

assessment factor

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

insufficient hazard data available (further information necessary)

Additional information

In light of the newly conducted water solubility study and review of all existing data new hydrolysis screenings are in progress due to conflicting data currently being available.

In a study the biotic degradation of the test material containing 90% pure test substance and 10% of isododecane was assessed performing a Closed Bottle Test according to slightly modified OECD 301D test guidelines and according to GLP. Analyses of the dissolved oxygen concentration were performed on days 7, 14, 21, and 28. 2% biodegradation was determined at day 28 and 37% at day 112. The test meets the validity criteria of the Guideline method. The test material is expected to be inherently biodegradable and has been shown to primarily degrade rapidly in sediment water systems. Moreover, 3,3,5 -trimethylcyclohexanone (CAS 873-94-9), which is a degradation product of the test substance, was also monitored in a study. After 14 days of incubation, an average of 10.7 ng/mL was detected in the test system extracts, 63% of recovered mass in extracts the water layer. Tert-butanol, another degradation product of the test substance, was detected on days 7 and 14 in both water layers and sediment layers, but the day 14 water layers were the only samples that contained enough to quantify, with an average of 1005 ng/L. 3,3,5-trimethylcyclohexylidene)bis[(1,1 dimethylethyl)peroxide] can currently be considered non Persistent in a sediment water screening study. However new studies are ongoing as requested by authorities.

 

An in vitro study was performed using the trout S9 in vitro metabolism 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 hepatocyte in vitro study, BCFs are calculated as 766 and 443 L/Kg respectively.

 

In the absence of a valid in vivo study the BCF value of 766 L/Kg is currently used for risk assessment as a worst case estimate.   Acute data of various reliability, based on international guidelines, are available for three trophic levels: Algae, Invertebrates and Fish and are summarised in the table below. An effect (growth rate inhibition) was found for the algaePseudokirchneriella subcapitata. This test was performed following the OECD 201 guideline in a GLP study. As test substance was lost during the study the endpoints were based on the geometric mean of the tests, a NOEC(72h) of 0.11 mg/L was calculated (corresponding to a 1 mg/L of nominal loading) and at the maximum testable concentration for algae, well above the aqueous solubility limit. For daphnids all effects found to date were from ecotoxicity studies performed well above the true limit of solubility using high energy preparation techniques (therefore as emulsions). Under environmental conditions in which the substance would pass through a WWTP, it would not be expected to be present in the form of an emulsion but would rapidly and strongly adsorb to particulate matter (due to the log Kow >7) and therefore the results from these studies are not considered relevant for risk assessment purposes. Using a more appropriate test methodology but in a non-GLP screening study, Kean (2013) prepared series of WAFs using a slow-stir preparation method from 0.2, to 100 mg/L of which one series was centrifuged. At 48 h a maximum of 1 daphnid out of 10 was immobile and this only in WAFs of 5, 10 and 100 mg/L. In the non-centrifuged group no immobilisations were observed at a WAF of 0.2 mg/L, approximately 5 times higher than the determined solubility limit, only 3 out of 10 daphnids were immobilized at 0.5 mg/L and in contradiction with the early studies only 6 out of 10 daphnids were found immobile in the 1 mg/L WAF while only 50% were immobilised at 5 and 10 mg/L. None of the WAFs up to 100 mg/L resulted in 100 % immobilisation (maximum 80% at 100 mg/L). The most recent and key study by Harris (2013) takes a similar approach to (Kean 2013) in its preparation of the test solutions to ensure adequate removal of undissolved material or dispersions. The measured concentrations observed were considerably closer to the true solubility limit of the test material eliminating the problems observed with earlier studies. No Effects were observed up to1 mg/L of test material. Furthermore due to the potential for loss of test material in a semi static or static setup and extended flow through sub-chronic non GLP supporting study was conducted (Kean 2013) to first brood. This demonstrated that also with continual replacement no acute effects were observed. wo chronic sediment studies assessment factor used as indicated in guidance document One acute study is available on Medaka fish,Oryzias latipes, and no toxicity was observed at the highest concentrations tested. Therefore, an LC50(48h) > 500 mg/L of 3,3,5-trimethylcyclohexylidene)bis[(1,1 dimethylethyl)peroxide] was derived for the fish. The conclusion from the available acute studies is that no acute toxicity can be determined at or well above the solubility limit when some care is taken in the preparation of the tests concentrations. No EC50 can be derived from any of the acute ecotoxicity studies and no acute classification is necessary for this substance. In order to determine if chronic effects occur a flow through study (OECD 211 with Daphnia magna) with a nominal loading of 15 mg/L of the test substance was conducted using a slow stir method (WAF) and two stage separation of the stock solution to avoid the testing of dispersed material. The stock (or large WAF solution 30L) was continually pumped into the test system. The WAF itself was refreshed entirely 3 times per week to ensure continual presence of the test material. Analytical measurements demonstrated the presence of the test material in the WAF solution (33.9µg/L) throughout the test as well as in the secondary separation (12.8 µg/L) vessel at concentrations above the limit of solubility. Fed from the secondary separation vessel triplicate test vessels containing 10 test organisms were exposed to the test substance for 21 days over which primarily the effects on reproduction were assessed in comparison to an identical triplicate control. No significant effects on reproduction or body length were observed. Indicating that 1,1-Di(tert-butylperoxy)-3,3,5-trimethylcyclohexane causes no chronic effects to Daphnia magna at or as close as possible to it's water solubility limit. Due to the tendency of1,1 -Di(tert-butylperoxy)-3,3,5 -trimethylcyclohexane to partition to the sediment a chronic sediment test (OECD 225 Lumbriculus variegatus)was conducted. Data is not considered optimal for poorly water soluble substances as the spiking method may have influenced the test outcome. No better alternative method exists and data has been used for PNEC derivation. Physical chemical data suggests that the test substance will be unable to pass the water treatment plant. This has been confirmed by a sewage treatment simulation study. In order to refine the emmission data to the environment. Due to it not being possible to exclude soil exposure and due to no aquatic PNECs being available to generate a soil PNEC by EPM further soil testing has been conducted as requested. See summary table below:   Species Experimental data Algae:Pseudokirchneriella subcapitata NOEC(72h) = 0.11 mg/L  (>limit of solubility) Invertebrates:Daphnia magna EC50(48h) >limit of solubility EC50(21d) > limit of solubility Fish:Oryzias latipes LC50(48h) > 500 mg/L  (>limit of solubility) Sediment-dwelling oligochaete:Lumbriculus variegatus  NOEC (28d) 5.1 mg/kg Sediment/soil dwelling nematode:Caenorhabditis elegans     NOEC(96h) 1000 mg/kg/dw  Earthworm Reproduction :Eisenia fetida  NOEC(28d) 52.9 mg/kg/dw  Toxicity to terrestrial plants (most sensitive endpoint):Onion  NOEC(21d) 333.3 mg/kg/dw  Toxicity to soil microrganisms  NOEC(28d) 1000mg/kg/dw

 

Conclusion on classification

No toxicity to aquatic organisms has been identified at or approaching the solubility limit based on the available and valid acute and chronic aquatic data. Very low ultimate biodegradation has been observed for the substance although there is some evidence for primary biodegradation. An estimated log Kow value of 7.56 is available which is greater than the classification threshold. Moreover, some information is available on BCF but the in vivo studies are of poor quality and cannot be reliably used to estimate a quantitative BCF. An in vitro study used in conjunction with a model (Arnot-Gobas), however, provides BCF values which are more appropriate. The Trout S9 in vitro metabolic study used in conjunction with a BCF model provides BCF values of 433 to 766 L/Kg. However, no completely valid study on BCF exists to date. As these values are situated on either side of a classification threshold for CLP, a worst case value of 766 L/Kg will be used for Classification purposes.

On this basis the substance is not considered toxic to (standard) aquatic organisms (Daphnia / Algae / Fish) at its limit of solubility. Long term environmental effects cannot be currently excluded until conclusive persistance and/or bioaccumulation data become available . Some toxicity in sediment and terrestrial systems has been observed. This is currently used for PNEC derivation only and not for classification.