(1RS,4Z,8E,12RS)-13-oxabicyclo[10.1.0]trideca-4,8-diene

Endpoint summary

Description of key information

Weight of evidence : substance will rapidly (bio)degrade and mineralise with a DT50 of 10.5 to 10.8 days respectively for biotic and abiotic degradation systems at 0.5 μg/L and 12°C. This corresponds to a degradation rate of >0.043 day-1 or a degradation half-life, t½ < [ln 2/0.043] = 16 days, under environmentally realistic conditions, 2020

Key Data:

1.Biodegradation: rapidly (bio)degradable due to DT50 < 16 days for biotic mineralisation in simulated environmentally relevant conditions observed (at 0.5 μg/L and 12°C). Specifically, Simple First Order (SFO) model rate constants (k) were : 0.06624 and 0.06434 d^-1 for biotic mineralisation with equivalent DT50 = 10.5 and 10.8 days, respectively for both biotic and abiotic systems at 0.5 μg/L and 12°C. Slightly slower degradation of parent occurred in the biotic group at the higher treatment level of 2.5 μg/L with DT50 21.1 and 5.14 days respectively for biotic and abiotic systems at 2.5 μg/L and 20°C, OECD TG 309, 2020

2. Ready Biodegradation (screening): not readily biodegradable ; mean biodegradation 0 % by BOD and GC (28 -days); transformation products were detected by GC, OECD TG 301F, 2020

Additional information

1. Key study : OECD TG 309, 2019 : The aerobic mineralisation in surface water : simulation biodegradation test was carried out according to OECD TG 309 guideline under GLP. The mineralization and degradation rates of the test substance : [3H]-test item were studied in biotic (live) and abiotic (sterile) water/sediment test systems. Radiolabelled test substance was applied to appropriate test system groups at nominal concentrations of 0.5 μg/L and 2.5 μg/L for the low and high dose groups, respectively. Radiolabelled reference substance, [3H]-reference item (the identity of which is given in the full study report), was applied to appropriate test systems at a nominal concentration of 2.5 μg/L. The low dose test substance vessels were incubated at approximately 12 °C, and high dose test substance vessels were incubated at approximately 20 °C. One biotic and one abiotic group of reference item vessels were incubated at approximately 20 °C, while a second biotic group was incubated at approximately 12 °C. Vessels were incubated for up to 58 days. The radioactive distributions of parent test or reference substance and associated metabolites were determined by high performance liquid chromatography with a radio flow detector (HPLC-β-RAM). Mineralization of the radiolabelled test and reference item substances (formation of tritiated water, 3H2O) was measured, when applicable, by HPLC fractionation and was presented as the volatile loss of the selected fraction at the retention time associated with 3H2O following drying. [3H]-Benzoic acid reference substance was also applied to appropriate test systems at a nominal concentration of 2.5 μg/L and the vessels were incubated at approximately 20 °C, to assess the activity and viability of the microbial population. Overall mean mass balances were acceptable for all treatment groups, ranging from 95.5% of applied radioactivity (% AR) to 104.7% AR, with individual intervals ranging from 90.0% to 108.1% AR. Insignificant radioactivity recovery was observed in headspace traps regardless of the test systems. Parent [3H]- test item disappeared steadily from all treated test systems during the course of the study. In the biotic systems, the major transformation product was observed in the retention time region associated with 3H2O, and was present at 83.1% AR and 65.7% AR, respectively, in the low and high dose groups by Day 58. One other peak was observed at >10% AR during the course of the study, and this occurred in the retention time region of ca. 4.5 to 5 minutes, prior to the parent substance, in both the low and high dose groups. By Day 58, this peak was not detectable in the low dose group and had declined to ca. 6% AR in the high dose group. No metabolite peaks other than that associated with the retention time of 3H2O were present at >10% by the end of the study. The extent of mineralization, or tritiated water formation, as assessed by HPLC fractionation, was 79.8% and 63.1% for the low and high dose biotic test systems, respectively, by the end of the study. In the abiotic systems, major metabolites (>10% AR) were detected in several polar regions prior to the parent test substance. These metabolites were attributed to an initial brief and transient abiotic process. No peaks were detected at the typical retention time of 3H2O, with the exception of one interval for the high dose system (<5% AR), indicating that no further degradation had occurred, and no or negligible mineralization had taken place in the abiotic systems, and that the degradation and subsequent mineralization observed in the biotic systems were primarily due to microbial activity. Parent [3H]-reference item disappeared rapidly from biotic systems and was not detected in samples from either system (20 °C or 12 °C incubation) on Days 2 through 58. Major metabolite peaks (>10% AR) were observed in the polar regions prior to the parent substance, including the region associated with 3H2O. The extent of mineralization, or tritiated water formation, as assessed by HPLC fractionation was 34.8% AR and 49.7% AR, respectively, in the 20 °C and 12 °C biotic reference item systems. In the abiotic [3H]-reference item system, no metabolites were observed at any interval during the course of study, indicating that the degradation and mineralization observed in the biotic test systems was due to microbial activity. Kinetic analyses were performed to estimate disappearance rates of [3H]-test item and selected metabolites (>10% AR and exhibiting a suitable pattern of decline for modelling) using CAKE software. For the reference systems dosed with 3H-benzoic acid at a nominal concentration of 2.5 μg/L, mineralization occurred at 95.4% AR by Day 2 and 97.9% AR by Day 14. Chromatographic analysis of the Day 14 samples confirmed total mineralization of the reference substance, verifying microbial viability. Transformation and subsequent mineralization of the test substance from the biotic water/sediment systems was attributed to microbial degradation following an initial brief and transient abiotic component. Slightly slower degradation of [3H]-test item occurred in the biotic group at the higher treatment level of 2.5 μg/L. DT50 values for parent were calculated as 10.5 and 10.8 days, respectively, for the low dose biotic and abiotic systems, and 21.1 and 5.14 days, respectively, for the high dose biotic and abiotic systems.

  

2. Key study : OECD TG 301F, 2020 : The ready biodegradability test was carried out according to Japanese guidelines and OECD TG 301F guideline under GLP. The test item, at a concentration of 100 mg/L was exposed to mixed activated sewage sludge micro-organisms obtained from the activated sludge from an aeration tank of a sewage treatment plant treating predominantly domestic sewage in Kurume-shi, Fukuoka, Japan. The sample was collected the day before test item exposure. The activated sludge, was prepared in laboratory according to Japan guidelines. The test item was exposed in culture medium in sealed culture vessels in the dark at 22°C ± 1°C for 28 days. The sludge was diluted in the BOD bottles to 30 mg SS/L at exposure volume of 300 mL. The degradation of the test item was assessed by the measurement of oxygen consumption (BOD) on days 0 through 28 using a closed system oxygen consumption apparatus. DOC was determined quantitatively by TOC analyser. The test item degradation was determined directly quantitatively by Gas Chromatography (GC-FID) and/or DOC analysis. Control solutions with inoculum and the reference substance, sodium benzoate, together with blank controls were used for validation purposes. In the test inoculum blank the oxygen uptake was 29 mg O2/L. The pH value at the end of the test period 28 days did not exceed 7.3 in the test item system and the blank control system. The repeatability validity criterion of not more than 20% difference between replicates was fulfilled. Therefore, the test is considered valid. The test system met the validation criteria of the guideline. Sodium benzoate attained 87% degradation after 14 days thereby confirming the suitability of the inoculum and test conditions. The mean biodegradation for duplicate test flasks at 28 days for the test item was 0% (actual -5% and -7%) by BOD. The mean biodegradation by direct analysis by GC was 0% at day 28. No degradation products were detected within the chromatograms. Detected DOC corresponded to the test item dissolved in the test solutions. Under the conditions of the study, test item is not considered as readily biodegradable.

 

Conclusion:

Substance will rapidly (bio)degrade and mineralise with a DT50 of 10.5 to 10.8 days respectively for biotic and abiotic degradation systems at 0.5 μg/L and 12°C. This corresponds to a degradation rate of > 0.043 day-1 or a degradation half-life, t½ < [ln 2/0.043] = 16 days, under environmentally realistic conditions.

 

All relevant validity criteria were met and the data is suitable for use in classification and labelling under CLP Regulation (EC) 1272/2008 on the basis:

a. substance concentration that is realistic for the general aquatic environment (often in the low µg/l range);

b. inoculum from a relevant aquatic environment;

c. realistic concentration of inoculum (10^3 -10^6 cells/ml);

d. realistic temperature e.g. 5 °C to 25 °C; and

e. ultimate degradation is determined i.e. determination of the mineralisation rate or the individual degradation rates of the total biodegradation pathway.

 

References:

1. OECD TG 309 (2004)

2. ECHA Guidance R.7b, (v4.0, June 2017), Section 7.9.4

3. ECHA Guidance on Application on the CLP Criteria, (v5.0, July 2017), Annex II: Rapid Degradation and section II.2.3.1 Aquatic simulation tests

4. ECHA Guidance R.11 : PBT/vPvB assessment (v3.0, June 2017), Section 11.4.1.1.3