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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
(Q)SAR
Adequacy of study:
supporting study
Study period:
Not applicable
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Remarks:
The value is not an experimental result, however the QSAR model is well documented with regard to validation parameters according to OECD principles. Moreover, the substance is fully characterised and falls within the applicability domain.
Justification for type of information:
1. SOFTWARE
OASIS CATALOGIC v.5.11.19

2. MODEL (incl. version number)
CATALOGIC Kinetic 301F v.13.16 (June, 2016)

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
CC1(C)CCCC(=O)C1

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
See attached QMRF

5. APPLICABILITY DOMAIN
See attached QPRF

6. ADEQUACY OF THE RESULT
See attached QPRF
Qualifier:
according to guideline
Guideline:
other: Reach Guidance on QSAR - R.6
Deviations:
no
Principles of method if other than guideline:
QSAR, CATALOGIC Kinetic 301F v.13.16 within LMC OASIS CATALOGIC v5.11.15.
More details are given in QMRF/QPRF attached to the dossier.
GLP compliance:
no
Specific details on test material used for the study:
No additional information
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
Aerobic microorganisms: activated sludge taken from a treatment plant or laboratory-scale unit receiving predominantly domestic sewage. Inoculum may be pre-conditioned to the experimental conditions, but not pre-adapted to the test substance. Pre-conditioning consists of aerating activated sludge in mineral medium or secondary effluent for 5-7 days at the test temperature.
Duration of test (contact time):
28 d
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
not applicable
Preliminary study:
not applicable
Test performance:
not applicable
Key result
Parameter:
% degradation (O2 consumption)
Value:
55
Sampling time:
28 d
Remarks on result:
not readily biodegradable based on QSAR/QSPR prediction
Key result
Parameter:
% degradation (O2 consumption)
Value:
62
Sampling time:
60 d
Remarks on result:
other: predicted ultimate half-life = 19 days
Details on results:
The chemical fulfils the general properties requirements (log Kow, molecular weight and water solubility). The chemical is in the interpolation structural space and in the metabolic domain.
For additional informations, see the attached QPRF.
Results with reference substance:
not applicable

Prediction percentage of biodegradation after 28d:

%BOD [28d] = 0.55 ± 0.17

Start day of Calc. 10 days window = 3

%BOD calc at 10 days window = 0.4387

Classification of Calc. 10 days window = Not Ready

Prediction of biodegradation after 60d:

%BOD [60d] = 0.62 ± 0.423

Concomitant predictions: Primary Half Life = 1.24 days; Ultimate Half Life = 19.82 days

Validity criteria fulfilled:
not applicable
Interpretation of results:
not readily biodegradable
Conclusions:
The substance achieves 55% and 62% biodegradation after 28 and 60 days, respectively. Therefore, the substance is not readily biodegradable but is not persistent (not P).
Executive summary:

The ready biodegradation property of 3,3 -dimethyl cyclohexanone (DMCH), the relevant degradation product of the registered substance, was investigated using QSAR approach with CATALOGIC Kinetic 301F v.13.16, plug-in from OASIS CATALOGIC v.5.11.19.

The model indicates that DMCH achieves 55% biodegradation (BOD) after 28 days, not exceeding the 60 % pass level set by the OECD Guidelines for testing of Chemicals (301) for ready biodegradability of a substance. It can be concluded that DMCH is not ready biodegradable.

The prediction of the biodegradability at 60 days is used for the Persistence assessment. DMCH achieves 62% of biodegradation after 60d, exceeding the 60 % pass level set in REACH Guidance on Information Requirements and Chemical Safety Assessment Chapter R.11: PBT/vPvB assessment. Additionally, the predicted ultimate half life is 19d, well below the threshold value of 40d and 60d for Persistence and very Persistence, therefore it can be concluded that DMCH is not persistent.

This compound fulfills the general properties requirements (in terms of log Kow, molecular weight and water solubility) and is in the interpolation structural space and in the metabolic domain.

In conclusion, DMCH is not readily biodegradable but is not persistent (not P).

Description of key information

Registered substance

OECD Guideline 301C, GLP, Key study, validity 1:

19% biodegradation after 28 days, calculated from oxygen consumption.

100% biodegradation after 28 days, calculated from direct quantitative analysis by GC method.

The registered substance is not considered readily biodegradable but primarily degrades totally to form two degradation products: succinic acid (degraded and mineralized completely) and DMCH (which is present at 100% after 28 days).

Degradation product (DMCH)

QSAR, CATALOGIC Kinetic 301F v.13.16, Supporting study, validity 1:

55% biodegradation after 28 days.

62% of biodegradation after 60 days.

Predicted ultimate half life = 19 days.

The relevant degradation product of the registered substance is not persistent in the environment.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria

Additional information

To assess the ready biodegradability of the registered substance, one valid study is available.

This study (Institute of Ecotoxicology Co. Ltd., 2014), assessed as the key study, was performed on the registered substance according to OECD Guideline 301C with GLP compliance. The test substance at a concentration of 100 mg/L was exposed to activated sludge with culture medium for 28 days, in aerobic condition. According to this test, the mean degradability of the test substance were determined at 19% and 100% after 28 days, calculated from the oxygen consumption and from direct quantitative analysis by the GC/MS method, respectively. According to the results of the direct quantitive analysis by the GC/MS method, in the test suspensions, the degradation product 3,3-dimethyl cyclohexanone (DMCH) was detected at 100% (mean), relative to the molar quantities of the test substance supplied. On the other hand, in the abiotic control, the test substance remained quantitatively and DMCH was not detected demonstrating biodegradation and not hydrolysis. Furthermore, on the test solution after 28 days culture, succinic acid, that was presumed to be generated considering the degradation course of the test substance, was also analyzed by the direct quantification (HPLC method). As a result, in the test suspensions and in the abiotic control, succinic acid was not detected. Therefore, it was confirmed that the test substance was degraded and the only degradation product DMCH remained quantitatively. The succinic acid was degraded and then mineralized completely.

In conclusion, the registered substance is not considered readily biodegradable but disappears totally to form two degradation products: succinic acid (degraded and mineralized completely) and DMCH (which is present at 100% after 28 days).

To conclude on the persistence of the relevant remaining degradation product, DMCH, the ready biodegradation property of this compound was investigated using a QSAR approach with CATALOGIC Kinetic 301F v.13.16, plug-in from OASIS CATALOGIC v.5.11.19. The model indicates that DMCH would achieve 55% biodegradation after 28 days, not exceeding the 60 % pass level set by the OECD Guidelines for testing of Chemicals (301) for ready biodegradability of a substance. However, DMCH would achieve 62% of biodegradation after 60 days, exceeding the 60 % pass level set in REACH Guidance on Information Requirements and Chemical Safety Assessment Chapter R.11: PBT/vPvB assessment. Additionally, the predicted ultimate half-life is 19 days, well below the threshold value of 40 days and 60 days for Persistence and very Persistence, therefore it can be concluded that DMCH is not persistent in the environment.