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Environmental fate & pathways

Biodegradation in water: screening tests

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biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
according to guideline
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
GLP compliance:
Specific details on test material used for the study:
Purity not reported
Oxygen conditions:
Inoculum or test system:
activated sludge, adapted
Details on inoculum:
- Source: The aeration stage of the HRC pIc sewage treatment plant
- Preparation of inoculum for exposure: The sample was allowed to settle and the supernatant filtered through Whatman GFA filter paper (first 200 mL discarded).
Duration of test (contact time):
28 d
Initial conc.:
2 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
- Test temperature: 20 ± 1°C
- Aeration of dilution water: Yes
- Continuous darkness: Yes

- Culturing apparatus: 250-300 mL BOD bottles (darkened glass) with ground glass stoppers
- Number of culture flasks/concentration: Duplicate
- Test performed in closed vessels due to significant volatility of test substance: Yes

- Sampling frequency: 0, 5, 15, and 28 days

- Other: Dilution water without inoculum and dilution water with inoculum
Reference substance:
benzoic acid, sodium salt
Key result
% degradation (DOC removal)
Sampling time:
28 d
Results with reference substance:
Sodium benzoate attained 100% degradation after 28 days
Validity criteria fulfilled:
Interpretation of results:
not readily biodegradable
% biodegradation after 28 days was 22% (not readily biodegradable)
Executive summary:

The study was conducted to assess the ready biodegradability of the test substance following OECD guideline 301D.

2 mg/L of the test substance was used. Test media were inoculated with activated sludge filtrate at the rate of 1 drop of inoculum per litre. BOD bottles were filled, by siphon, and firmly stoppered to exclude all air bubbles. Sufficient bottles were prepared to allow a single oxygen determination per bottle to be made at 0, 5, 15 and 28 days for each test medium (duplicate bottles at each sampling time). Bottles were incubated in water bath at 20 ± 1°C.

Dissolved oxygen concentrations for each test medium were determined, in duplicate, at 0, 5, 15 and 28 days by means of lead/silver galvanic cell probe.

Percentage biodegradation after 28 days for the test substance was 22%. The test substance was not considered readily biodegradable under the test conditions employed. Sodium benzoate attained 100% degradation after 28 days.

Oxygen depletions in the inoculated and non-inoculated control series were within the prescribed limits.

Description of key information

Study Type

 Study Details Value  Guideline Reliability 
Ready Biodegradation Study

Closed bottle test

Not Readily Biodegradable


Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information