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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:
Experimental Phase: 01 May 2018 to 29 May 2018. Report Issued: 01 October 2018.
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to guideline
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
One deviation occured but it was considered to have had no adverse effect on the integrity of the study given that all validation criteria were met for the study.
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
A mixed population of sewage treatment micro-organisms was obtained on 01 May 2018 from the final effluent stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK, which treats predominantly domestic sewage.

The sample of effluent was filtered through coarse filter paper (first approximate 200 mL discarded) and the filtrate maintained on continuous aeration in a temperature controlled room at approximately 21°C prior to use.
Duration of test (contact time):
28 d
Initial conc.:
33 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
- Composition of medium: Acitivated Sludge
- Test temperature: 21°C
- pH: 7.4 - 7.5 (at start on the test)
- pH adjusted: yes
- Aeration of dilution water: No
- Continuous darkness: Yes

- Culturing apparatus: 250 mL BOD bottles (darkened glass) with ground glass stoppers.
- Number of culture flasks/concentration: Sufficient bottles were prepared to allow a single oxygen determination per bottle with duplicate bottles for each test preparation at each sampling occasion.
- Measuring equipment: YSI 54A dissolved oxygen meter and BOD Probe
- Test performed in open system: No bottles were firmly stoppered.

- Mineral Medium used: The mineral medium used in the study was that recommended in the OECD Guideline.

- Sampling frequency: Dissolved oxygen concentrations in duplicate samples from the control, reference and test item series were determined, on Days 0, 3, 5, 7, 10, 14, 21 and 28 by means of a YSI 54A. Dissolved oxygen meter and BOD Probe. Dissolved oxygen concentrations in duplicate samples from the toxicity control series were determined on Days 0, 14 and 28 only.

- Inoculum blank: Yes
- Abiotic sterile control: Yes
- Toxicity control: Yes
Reference substance:
benzoic acid, sodium salt
Concentration used: 3.0 mg/L
Key result
% degradation (O2 consumption)
Sampling time:
28 d
Results with reference substance:
The reference item (sodium benzoate), attained 64% biodegradation after 14 days with greater than 60% degradation being attained in a 10-Day window. After 28 days 71% biodegradation was attained. These results confirmed the suitability of the inoculum and test conditions and satisfied the validation criterion given in the OECD Test Guidelines.
Validity criteria fulfilled:
Interpretation of results:
not readily biodegradable
The test item attained 6% biodegradation after 28 days and therefore cannot be considered to be readily biodegradable under the terms and conditions of OECD Guideline No 301D.
Executive summary:


A study was performed to assess the ready biodegradability of the test item in an aerobic aqueous medium. The method was designed to be compatible with the OECD Guidelines for Testing of Chemicals (1992) No. 301D, "Ready Biodegradability; Closed Bottle Test”



The test item, at a concentration of 33 mg/L, was exposed to sewage treatment micro-organisms with mineral medium in sealed culture vessels in the dark at approximately 21°C for 28 days. The degradation of the test item was assessed by the determination of the amount of oxygen consumed. Control solutions with inoculum and the reference item, sodium benzoate, together with a toxicity control were used for validation purposes.


Result and Conclusion

The test item attained 6% biodegradation after 28 days and therefore cannot be considered to be readily biodegradable under the terms and conditions of OECD Guideline No 301D.

Description of key information

Ready biodegradability of the Test Substance.

Key value for chemical safety assessment

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

Additional information