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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:
2017-11-02 to 2018-01-09
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
adopted July 17, 1992
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
- Inoculum of the aqueous phase of non-adapted activated sludge from a municipal sewage treatment plant.

- Pretreatment: The activated sludge was washed twice with chlorine free tap water. After the second washing the settled sludge was resuspended in min-eral salts medium and was maintained in an aerobic condition by aera-tion for 2 hours. Thereafter the sludge was homogenized with a blender. After sedimentation the supernatant was decanted and maintained in an aerobic condition by aeration with CO2-free air for 7 days. 10 mL/L were used to initiate inoculation.

-Colony forming units in the test vessels: Approx. 10^7 - 10^8 CFU/L

Duration of test (contact time):
28 d
Initial conc.:
20 mg/L
Based on:
test mat.
Initial conc.:
51.4 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Preparation of the test vessels: Based on the calculated oxygen demand, the test concentration of 20 mg/L, corresponding to an oxygen demand of 51.4 mg O2/L in the vessel, was selected. The test solutions were prepared in measuring flasks and were placed in brown glass bottles as incubation vessels (inoculum control and functional control) or were prepared directly in brown glass bottles (test item and toxicity control).

Inoculum control: The inoculated test medium, consisting of the required volumes of mineral medium stock solutions, ultrapure water and inoculum, was prepared.
Functional control: The reference item was weighed out and transferred into a measuring flask, the required volumes of mineral medium stock solutions, ultrapure water and inoculum, were added.
Test Item: The test item was weighed out for each replicate and directly transferred into the test vessels with 250 mL of the inoculated test medium.
Toxicity control: The test item was weighed out and directly transferred into the test vessel with 250 mL of the reference item medium.

A rubber sleeve with soda lime was hung into the opening of the bottles to absorb evolved CO2. The bottles were closed with OxiTop measuring heads and the measuring system was activated.

Measurements: The temperature in the incubator was documented continuously throughout the test. At test start the pH-values of the prepared solutions in the measuring flasks (inoculum control and functional control) and the prepared solutions in the separate replicates (test item and toxicity control), were determined. At test end the pH-values of the test solutions in the brown glass bottles were determined. The oxygen consumption was determined in the incubation vessels by the OxiTop® measuring system at 360 measuring points (every 112 minutes) during the 28 d incubation period.
Reference substance:
benzoic acid, sodium salt
Test performance:
Results of the Functional Control:
The pass level for ready biodegradation (≥ 60% degradation) was reached within 3 days. The validity criterion that the degradation should be ≥ 60% after 14 d was fulfilled. Stages of Biodegradation: The adaptation phase changed to degradation phase within 2 days (degradation > 10%) and the biodegradation came to a maximum of 97% on day 26.

Results of the Toxicity Control:
In the toxicity control the biodegradation achieved 50% after 14 days. After 28 days the biodegradation came to 53%. The validity criterion that the test item should not inhibit the biodegradation of the reference item was fulfilled.
Key result
Parameter:
% degradation (O2 consumption)
Value:
4
Sampling time:
28 d
Details on results:
Both test item replicates did not reach the 10% level (beginning of biodegradation) within the 28-day-period of the study. The mean biodegradation on day 28 was 4%.
Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The test item is classified as not readily biodegradable within the 28 day period of the study.
Executive summary:

The test item is classified as not readily biodegradable within the 28 day period of the study.

Description of key information

The test item is not readily biodegradable within the 28 days of the study.

Key value for chemical safety assessment

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

Additional information