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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
Study period:
September 04, 2017 - November 01, 2017
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to guideline
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
adopted July 17, 1992
according to guideline
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Version / remarks:
May 30, 2008
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
Aerobic activated sludge, microorganisms from a domestic waste water treatment plant. The aerobic activated sludge used for this study was sedimented for 30 minutes, washed by centrifugation and the supernatant liquid phase was decanted. The solid material was re-suspended in test water and centrifuged again. This procedure was done three times. An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge to its dry weight was determined. Based on this ratio, calculated aliquots of washed sludge suspension, corresponding to 3.5 g dry material per litre were mixed with test water and aerated overnight. This suspension was used for the experiment.
Duration of test (contact time):
28 d
Initial conc.:
101.2 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Temperature: 22 +/-1°C
Light conditions: darkness
pH: 7.6 (start), 7.6 (end)

The amounts of test item and reference item were directly weighed into the test flasks. No emulsifiers or solvents were used.The closed test flasks were incubated in a climatised chamber under continuous stirring.
Reference substance:
benzoic acid, sodium salt
Key result
% degradation (O2 consumption)
Sampling time:
28 d
Details on results:
The mean biodegradation of the test item at test end after 28 days was 0% (ThOD-NH4).
Results with reference substance:
The reference item sodium benzoate was sufficiently degraded to 80% after 14 days and to 83% after 28 days of incubation. The percentage biodegradation of the reference item confirms the suitability of the used aerobic activated sludge inoculum.
Validity criteria fulfilled:
Interpretation of results:
not readily biodegradable
The test item is considered to be not readily biodegradable.
Executive summary:

The test item was investigated for its ready biodegradability in a manometric respirometry test over a period of 28 days. The biodegradation was followed by the oxygen uptake of the microorganisms during exposure. As a reference item sodium benzoate was tested simultaneously under the same conditions as the test item, and functioned as a procedure

control. The GLP study was performed according to OECD TG 301F.

Biodegradation of test item

The test item did not reach a mean biodegradation of 10% during the incubation time of 28 days. The mean biodegradation at test end after 28 days was 0% (ThOD-NH4). Therefore, the test item is considered to be not readily biodegradable based on ThOD-NH4.

Biodegradation of Sodium Benzoate

The reference item sodium benzoate was sufficiently degraded to 80% after 14 days and to 83% after 28 days of incubation, thus confirming the suitability of the aerobic activated sludge inoculum used.

Biodegradation in the Toxicity Control

In the toxicity control containing both, the test item and the reference item sodium benzoate, 31% biodegradation was noted within 14 days and 33% biodegradation after 28 days of incubation. According to the test guidelines, the test item can be assumed to be not inhibitory to the aerobic activated sludge microorganisms because degradation was >25% within 14 days.

The test item is considered to be not readily biodegradable.

Description of key information

OECD 301F not readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:

Additional information