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Biodegradation in water: screening tests

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biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
24 Aug - 21 Sep 2000
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to guideline
EU Method C.4-E (Determination of the "Ready" Biodegradability - Closed Bottle Test)
equivalent or similar to guideline
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
GLP compliance:
Oxygen conditions:
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Kläranlage Odenthal, Germany
- Preparation of inoculum for exposure: aeration of mineral medium plus inoculum (filtrate) for 6 days (effluent concentration in reaction mixture 5 ml/L)
- Pretreatment: seperation of coarse particles by filtration

Duration of test (contact time):
28 d
Initial conc.:
2.5 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
- Composition of medium: mineral medium (no further specification)
- Test temperature: 20 ± 1 °C
- Continuous darkness: yes

- Culturing apparatus: closed bottles
- Number of culture flasks/concentration: 10

- Inoculum blank: 10 bottles
- Procedure control: 10 bottles
- Toxicity control: 10 replicates
Reference substance:
benzoic acid, sodium salt
2.9 mg/L
Key result
other: % degradation (dissolved oxygen)
Sampling time:
28 d
Details on results:
Theoretical oxygen demand: 2838 mg O2/g

Test item samples: 47, 59, 74 and 77% biodegradation was determined after 7, 14, 21 and 28 d, respectively

Toxicity control: 62, 64, 77 and 77% degradation was determined after 7, 14, 21 and 28 d
Results with reference substance:
Theoretical oxygen demand: 1665 mg O2/g

69, 79, 82 and 84% degradation was determined after 7, 14, 21 and 28 d.
Validity criteria fulfilled:
Interpretation of results:
readily biodegradable
The substance is readily biodegradable (77% degradation after 28 days).

Description of key information

Readily biodegradable: 77% within 28 d (EU Method C.4-E, activated sludge, domestic)

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

There is one GLP study available investigating the ready biodegradability of the test substance in an aerobic, aqueous medium, according to the Council Directive 92/69/EEC Method C.4-E.

In a closed bottle test a nominal concentration of 2.5 mg/L test substance was inoculated with 5 mL/L secondary effluent from a local, domestic sewage treatment plant for 28 d under aerobic conditions in completely full, closed bottles. A procedure and toxicity control as well as an inoculum blank were run in parallel. Biodegradation was followed by analysis of dissolved oxygen and was expressed as % of the theoretical oxygen demand (ThOD).

The biodegradation of the test substance was 47%, 59%, 74% and 77% after 7, 14, 21, and 28 d. Therefore, the test substance is classified as readily biodegradable (77% within 28 d, 14-d window passed). The toxicity control indicated that the test substance did not inhibit the biodegradation of the reference substance.