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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:
supporting study
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:
yes (incl. QA statement)
Oxygen conditions:
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
Activated sludge from laboratory wastewater plant treating municipal sewage.
Concentration of activated sludge in the test assay: 30 mg/L dry substance
Duration of test (contact time):
28 d
Initial conc.:
37 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Reference substance:
Key result
% degradation (CO2 evolution)
70 - 80
Sampling time:
28 d
Details on results:
- Duration of adaptation phase: 8 days
- Duration of degradation phase: 20 days
- Degradation degree of DOC at the end of the test, mean value: 90-100 %
Results with reference substance:
- Degradation degree of the reference substance after 14 days: 80-90 %
- Degradation degree in the inhibition control after 14 days: 70-80 %
Validity criteria fulfilled:
Interpretation of results:
readily biodegradable, but failing 10-day window

Description of key information

Readily biodegradable: 79-82% in 28 days (OECD 301B)

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:

Additional information

Two studies investigating the ready biodegradability of Triisobutyl phosphate (TiBP) are available. The key study was conducted according to GLP and OECD guideline 301B using non-adapted activated sludge from a domestic STP as inoculum (BASF 2019). After 28 days 79-82% degradation of TiBP was observed and the 10d-window was passed. Thus, the substance was classified as readily biodegradable. This was confirmed by a second study also conducted to GLP and OECD guideline 301B, which just missed to fulfill the 10d-window criterion.