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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:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to guideline
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
GLP compliance:
Oxygen conditions:
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Type: Mixed population of aquatic microorganisms
- Origin: Well-operated municipal sewage treatment plant (Kläranlage Berlin-Ruhleben, Germany), predominantly dealing with domestic sewage
- Pretreatment: Stirred and aerated for approx. 4.5 hours; homogenised in ablender; allowed to settled for approx. 30 minutes
- Concentration: 90 mg suspendid solids from the supernatant for each test vessel
Duration of test (contact time):
30 d
Initial conc.:
10 mg/L
Based on:
IC (inorganic carbon)
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
- Addition of inoculum: 19 mL of the inoculum from the activated sludge were added to the nutrient solutions in each of the test vessels; aerated with C02-free air for about 24 hours
- Stock solution of the reference substance: 1.0 g sodium acetate was dissolved in 1 L demineralized water; 102 mL of this stock solution were added to the reference test
bottle and into the bottle for the toxicity control
- Preparation of the reference and test compound solutions: The test material was dispersed in vessels containing approx. 1-2 mL water and added directly at amounts of 37.3 mg test item to each of three test bottles and one bottle for the toxicity control; finally the vessels were rinsed with 2-3 mL demineralized water; finally, each test vessel was filled up with demineralized water to a volume of 3000 ml
- Concentrations (based on carbon): Test substance (10 mg/L); Reference substance (10 mg/L); Toxicity control (10 mg/L (test item) + 10 mg/L (reference substance))
- Blank control: Three test bottles containing nutrient reagents and inoculum

- Temperature: 19 to 21 °C
- Exposure time: 30 days
- Aeration: with filtered C02-free aeration (1.5 to 6.5 L air per hour for each test vessel)
- pH-value of the test solutions and the toxicity control on day 29: 7.8 to 8.2
- Converting dissolved inorganic carbon into C02: 1 mL of concentrated HCI was added to each test vessel on day 29
Reference substance:
acetic acid, sodium salt
(Merck; Batch No. TA 662668502/Purity not specified)
Key result
% degradation (CO2 evolution)
<= 0
Sampling time:
4 d
Remarks on result:
other: also on day 7, 11, 14, 17, 23, 28, 30
Details on results:
No degradation was observed for norethisterone.
Results with reference substance:
The reference substance was degraded to 74% at day 14, while the activity of the microorganisms in the toxicity control was not affected by the test compound.
Validity criteria fulfilled:
Interpretation of results:
under test conditions no biodegradation observed
Norethisterone was neither toxic nor ready biodegradable under the test conditions.
Executive summary:

The biodegradability was studied in a CO2 evolution test according to OECD 301B. The test compound was incubated over a period of 28 days at a concentration of 10 mg/L as carbon. Additionally, a reference substance (sodium acetate) was incubated under the same conditions, and a toxicity control containing both compounds. No degradation was observed for norethisterone. The reference substance was degraded to 74% at day 14, while the activity of the microorganisms in the toxicity control was not affected by the test compound. Therefore, norethisterone can be classified as not ready biodegradable.

Description of key information

No degradation was observed for norethisteron after 28 days of incubation. The reference compound was degraded to 69% after 10 days of incubation, while the activity of the microorganisms in the toxicity control was not affected by the test compound. Therefore norethisterone is considered to be "Not readily Biodegradable".

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information