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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
May 26, 1999 - Oct 29, 1999
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method C.4-E (Determination of the "Ready" Biodegradability - Closed Bottle Test)
Deviations:
no
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
other: mixed population of aquatic microorganisms
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): secondary effluent of a domestic sewage treatment plant (Kläranlage Odenthal)
- Storage conditions: not reported
- Storage length: not reported
- Preparation of inoculum for exposure: separation of coarse particles by filtration
- Pretreatment: none
- Preconditioning: aeration for 5 days
- Water filtered: not reported
Duration of test (contact time):
28 d
Initial conc.:
2.6 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: not reported
- Additional substrate: no
- Solubilising agent (type and concentration if used): no
- Test temperature: 20 ± 1 °C
- pH: not reported
- pH adjusted: no
- Aeration of dilution water: not reported
- Suspended solids concentration: not reported
- Continuous darkness: yes

TEST SYSTEM
- Number of culture flasks/concentration: 10
- Method used to create aerobic conditions: aeration of inoculum prior to test
- Measuring equipment: not reported
- Test performed in closed vessels: yes
- Test performed in open system: no

SAMPLING
- Sampling frequency: day 0, 7, 14, 21, 28
- Sampling method: two vessels per sampling day


CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Toxicity control: yes
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (O2 consumption)
Value:
48
Sampling time:
28 d
Details on results:
48% of the test substance were degraded after 48 days. The test substance was not readily biodegradable under the conditions of the test. The test substance was not inhibitory at tested concentrations of 2.6 mg/L.

Details of the degradation test with the test substance

Test substance

Test concentration: 2.6 mg/L

ThOD: 2663 mg/g

COD: -- mg/g

DO depletion after n days [mg/L]

7 d

14 d

21 d

28 d

No.1: (mt0 - mtx) -(mb0 - mbx)

1.13

1.36

2.55

3.23

No.2: (mt0 - mtx) -(mb0 - mbx)

1.06

1.50

2.42

3.37

Dl: % Degradation

16

20

37

47

Dl: % Degradation

15

22

35

49

D, Mean

16

21

36

48

 

Details of the degradation tests with the reference substance

Reference substance

Test concentration: 2.9 mg/L

ThOD: 1665 mg/g

COD: -- mg/g

DO depletion after n days [mg/L]

7 d

14 d

21 d

28 d

No.1: (mt0 - mtx) -(mb0 - mbx)

3.17

3.74

3.72

3.84

No.2: (mt0 - mtx) -(mb0 - mbx)

3.15

3.79

3.63

3.89

Dl: % Degradation

66

77

77

80

Dl: % Degradation

65

78

75

81

D, Mean

66

78

76

81

Details of the degradation test with the toxicity control

Toxicity control (2.6 mg/L test substance and 2.9 mg/L reference substance)

 

DO depletion after n days [mg/L]

7 d

14 d

21 d

28 d

No.1: (mt0 - mtx) -(mb0 - mbx)

4.05

4.94

5.45

6.59

No.2: (mt0 - mtx) -(mb0 - mbx)

3.86

5.06

5.29

6.42

Dl: % Degradation

34

42

46

56

Dl: % Degradation

33

43

45

55

D, Mean

34

43

46

56

Validity criteria fulfilled:
yes
Interpretation of results:
inherently biodegradable, not fulfilling specific criteria
Conclusions:
The test substance is regarded as not readily biodegradable but considered to be inherently biodegradable, not fulfilling specific criteria.
Executive summary:

The ready biodegradability of the substance was studied under GLP conditions in the closed bottle test according to EU Method C.4-E over a period of 28 days. The inoculum was taken from runoff of a municipal sewage treatment plant, filtered and aerated for five days prior to the test. 2.6 mg/L test substance was suspended in a mineral medium, inoculated with a mixed population of aquatic microorganisms and incubated for 28 days under aerobic conditions in the dark at 20 ± 1°C. The dissolved oxygen concentration was measured in two test bottles at the beginning of the test and in another two testing vessels at a frequency of once per week. A fraction of 48% of the substance had been degraded at the end of the observation period. A parallel degradation test was conducted with sodium benzoate, which resulted in a fraction of 81% of the reference substance being biodegraded showing the suitability of the inoculum. A toxicity control containing both test and reference substance was tested in parallel showing that the test substance was not inhibitory to the inoculum. In conclusion, the substance must be regarded as not readily biodegradable under the conditions of this test. But can be regarded as biodegradable as it degraded between 40 and 60 %, which is a clear indication that extensive primary biodegradation has occured.

Endpoint:
biodegradation in water: screening tests
Type of information:
(Q)SAR
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with limited documentation / justification
Justification for type of information:
QSAR prediction: migrated from IUCLID 5.6
Principles of method if other than guideline:
Calculation based on BIOWIN v4.10, Estimation Programs Interface Suite™ for Microsoft® Windows v 4.11. US EPA, United States Environmental Protection Agency, Washington, DC, USA.
GLP compliance:
no
Details on results:
For detailed description on the model and its applicability, see "Any other information on materials and methods incl. tables".

SMILES : O=C(C)OC1CC(C)CCC1C(C)C

MOL FOR: C12 H22 O2

MOL WT : 198.31

--------------------------- BIOWIN v4.10 Results ----------------------------

Biowin1 (Linear Model Prediction) : Biodegrades Fast

Biowin2 (Non-Linear Model Prediction): Biodegrades Fast

Biowin3 (Ultimate Biodegradation Timeframe): Weeks

Biowin4 (Primary Biodegradation Timeframe): Days

Biowin5 (MITI Linear Model Prediction) : Readily Degradable

Biowin6 (MITI Non-Linear Model Prediction): Not Readily Degradable

Biowin7 (Anaerobic Model Prediction): Does Not Biodegrade Fast

Ready Biodegradability Prediction: YES

----------------------------------------------

Biowin1 (Linear Biodeg Probability): 0.8273

Biowin2 (Non-Linear Biodeg Probability): 0.9862

A Probability Greater Than or Equal to 0.5 indicates --> Biodegrades Fast A Probability Less Than 0.5 indicates --> Does NOT Biodegrade Fast

----------------------------------------------

Biowin3 (Survey Model - Ultimate Biodeg): 2.9011

Biowin4 (Survey Model - Primary Biodeg): 3.7906

Result Classification: 5.00 -> hours 4.00 -> days 3.00 -> weeks (Primary & Ultimate) 2.00 -> months 1.00 -> longer

----------------------------------------------

Biowin5 (MITI Linear Biodeg Probability): 0.5134

Biowin6 (MITI Non-Linear Biodeg Probability): 0.3884

A Probability Greater Than or Equal to 0.5 indicates --> Readily Degradable A Probability Less Than 0.5 indicates --> NOT Readily Degradable

----------------------------------------------

Biowin7 (Anaerobic Linear Biodeg Prob): 0.2821

A Probability Greater Than or Equal to 0.5 indicates --> Biodegrades Fast A Probability Less Than 0.5 indicates --> Does NOT Biodegrade Fast

----------------------------------------------

Criteria for the YES or NO prediction: If the Biowin3 (ultimate survey model) result is "weeks" or faster (i.e. "days", "days to weeks", or "weeks" AND the Biowin5 (MITI linear model) probability is >= 0.5, then the prediction is YES (readily biodegradable). If this condition is not satisfied, the prediction is NO (not readily biodegradable). This method is based on application of Bayesian analysis to ready biodegradation data (see Help). Biowin5 and 6 also predict ready biodegradability, but for degradation in the OECD301C test only; using data from the Chemicals Evaluation and Research Institute Japan (CERIJ) database.

Conclusions:
The substance is likely to be biodegradable in the environment and not fulfilling the criteria for environmental persistence. It may, however, not be readily biodegradable.
Executive summary:

According to the ECHA Guidance document on the PBT assessment R.12 (ECHA 2008), the results from freely available estimation models, such as BIOWIN 2, 3 and 6, can be used to make assumptions on the potential environmental persistence of a substance when considered in a combined way. The guidance gives the following criteria for non-degradability: a) the result of the non-linear model prediction with BIOWIN 2 is < 0.5 and the ultimate timeframe prediction with BIOWIN 3 is < 2.2 (or 2.7); b) the MITI non-linear model prediction with BIOWIN 6 is < 0.5 and ultimate timeframe prediciton with BIOWIN 3 is < 2.2 (or 2.7).

The predictions for the substance menthyl acetate were 0.9862 with BIOWIN 2, 2.9011 with BIOWIN 3 and 0.3884 with BIOWIN 6. According to these model predictions, the substance is likely to be biodegraded in the environment and not fulfilling the criteria for environmental persistence. It may, however, not be readily biodegradable.

Description of key information

Inherently biodegradable, not fulfilling specific criteria: 48% (O2 consumption) after 28 days (EU Method C.4-E); read-across

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria

Additional information

Since no data for the target substance (L-menthyl acetate, CAS 2623-23-6) are available, the biodegradability is assessed on the basis of data from one structurally similar substance (stereo isomers). This read-across is in accordance with Regulation (EC) No 1907/2006 Annex XI, 1.5. The target substance L-menthylacetate is a mono-constituent substance. This allows the use of experimental data from a racemic mixture (D- and L-isomers) of menthylacetate for the assessment of the target substance. A detailed justification of the analogue approach is provided in the technical dossier (see IUCLID Section 13).

The key study with the source substance was performed as a closed bottle test according to EU Method C.4-E (GLP). Secondary effluent from a domestic sewage treatment plant treating predominantly domestic sewage was used as inoculum to determine the biodegradation of the substance. A substance concentration of 2.6 mg/L was added to the test vessels. Moreover, a toxicity control containing both, test substance and reference substance, was included in the study to assess possible toxic effects of the substance to the inoculum. The degradation rate was determined based on the measurement of the oxygen consumption. After 28 d a significant fraction of 48% was degraded (clear indication that extensive primary degradation occured) and biodegradation was still ongoing. Therefore, the substance is partly but not readily biodegradable according to the OECD criteria and menthyl acetate was classified to be “inherently biodegradable, not fulfilling specific criteria”.

A supporting QSAR estimation was performed for the target substance itself. According to the ECHA Guidance document on the PBT assessment R.12 (ECHA, 2008), the results from freely available estimation models, such as BIOWIN 2, 3 and 6, can be used to make assumptions on the potential environmental persistence of a substance if considered in a combined way. The guidance gives the following criteria for non-degradability: a) the result of the non-linear model prediction with BIOWIN 2 is < 0.5 and the ultimate timeframe prediction with BIOWIN 3 is < 2.2 (or 2.7); b) the MITI non-linear model prediction with BIOWIN 6 is < 0.5 and ultimate timeframe prediction with BIOWIN 3 is < 2.2 (or 2.7). The predictions for the target substance were 0.9862 with BIOWIN 2, 2.9011 with BIOWIN 3 and 0.3884 with BIOWIN 6. According to these model predictions, the substance is likely to be biodegraded in the environment and not fulfilling the criteria for environmental persistence. It may, however, not be readily biodegradable.

Based on the results from one structurally related source substance (in accordance to Regulation (EC) No 1907/2006 Annex XI, 1.5) it can be concluded that the target substance (L-menthyl acetate) is not readily biodegradable according to the OECD criteria but is considered as inherently biodegradable. Additional (Q)SAR estimations for the target substance indicate that the substance is not likely to be persistent under environmental conditions.