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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:
experimental study
Adequacy of study:
key study
Study period:
01 November to 05 December 2011
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
Not applicable



Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Worlingworth sewage treatment works (Suffolk, UK),
- Laboratory culture: Yes
- Method of cultivation:At the time of collection, the sludge was sieved (1 mm2) then transported to the laboratory and left to stand for approximately 30 minutes to allow the sewage solids to settle. A portion of the supernatant was removed and the sludge aerated until required.
- Storage conditions: Aliquots (10 mL) of the sludge were filtered through dried and preweighed Whatman GF/C filters, which were then dried again at approximately 105°C for one hour
- Preparation of inoculum for exposure: The mixed liquor suspended solids (MLSS) content of the sludge was then determined and the volume required to give a solids level of 30 mg/L in test cultures was calculated. This was added to bottles three days before test initiation to allow a period of ageing.
Duration of test (contact time):
28 d
Initial conc.:
50 other: mg O2/l
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: TCD in inoculated MSM (25 mgO2/500 mL)
- Test temperature: 22 ± 2ºC.
- pH: 7.5
- pH adjusted: no
- Aeration of dilution water: no
- Continuous darkness: no

TEST SYSTEM
- Culturing apparatus:
- Number of culture flasks/concentration:
Identity No. of vessels Contents
Blank – control 2 Inoculated MSM alone
Reference 1 Inoculated MSM + sodium benzoate (25 mgO2/500 mL)
Test 2 TCD in inoculated MSM (25 mgO2/500 mL)
Inhibition assay 1 TCD (25 mgO2/500 mL) + sodium benzoate (25 mgO2/500 mL) in inoculated MSM

- Method used to create aerobic conditions:
- Measuring equipment: Co-ordinated Environmental Services (CES) Ltd automated respirometer and associated software was used to monitor the cumulative amount of oxygen consumed by the mixtures.
- Test performed in closed vessels due to significant volatility of test substance: The CO2 absorber was replaced in each cell (to ensure the maximum adsorption capacity in the test) and the cultures were sealed and returned to the water bath to equilibrate. The cells were connected to the computer-controlled system and the test was initiated.

SAMPLING
- Sampling frequency: A record of the cumulative oxygen demand made by each cell was printed at, typically, hourly intervals.
- Sampling method: automated respirometer


CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes

STATISTICAL METHODS: Not applicable
Reference substance:
benzoic acid, sodium salt
Preliminary study:
None
Test performance:
None
Key result
Parameter:
% degradation (O2 consumption)
Value:
3
Sampling time:
1 d
Details on results:
Mean oxygen consumption in mixtures containing TCD was negligible during the test, at most, 3% of the ThOD on Day 1.
Results with reference substance:
In the presence of TCD the degradation of sodium benzoate achieved 60% after 5 days

Mean oxygen consumption in mixtures containing TCD was negligible during the test, at most, 3% of the ThOD on Day 1. Substances are considered to be readily biodegradable in this type of test if oxygen consumption is equal to or greater than 60% of the theoretical value within ten days of the level achieving 10%. Therefore, TCD was not considered to be readily biodegradable under the conditions of this test.

The results obtained for the rate of degradation of sodium benzoate (67% of its ThOD after 3 days) and for the cumulative amount of oxygen consumed by the control mixtures (26.36 and 28.40 mgO2/L) fulfilled the validity criteria for this test. In the presence of TCD the degradation of sodium benzoate achieved 60% after 5 days indicating that the test substance was not inhibitory to the microbial inoculum.

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
Substances are considered to be readily biodegradable in this type of test if oxygen consumption is equal to or greater than 60% of the theoretical value within ten days of the level achieving 10%. Therefore, TCD was not considered to be readily biodegradable under the conditions of this test.

Description of key information

The substance is not readily biodegradable  

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

In a test carried out in accordance with OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test), the test substance showed no measurable degradation over 28 days and therefore cannot be considered readily biodegradable