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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:
5 Nov - 3 Dec 2014
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to guideline
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
according to guideline
EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)
GLP compliance:
yes (incl. QA statement)
Landesamt für Wasserwirtschaft und Gewerbeaufsicht, Kaiser-Friedrich-Straße 7, 55116 Mainz, Germany
Oxygen conditions:
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: wastewater treatment plant of Mannheim, Germany, collected on 3 Nov 2014 from the aeration tank of the plant.
- Storage conditions: A suitable aliquot of the activated sludge suspension was sieved by a finely woven mesh with a mesh size about 1 mm. To reduce the content of inorganic carbon in the blank controls the activated sludge was aerated with carbon dioxide free air for about 48 hours at 22 ± 2 °C.
- Preparation of inoculum for exposure: e suspension was washed one time with drinking water. Subsequently the aeration was stopped and the sludge was allowed to settle. After settling the supernatant was discarded and the remaining sludge suspension was filled up
with drinking water
- Concentration of sludge: 6.0 g/L d.w.
- Initial cell/biomass concentration:
Duration of test (contact time):
28 d
Initial conc.:
20 mg/L
Based on:
other: TOC
Initial conc.:
69 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
- Composition of medium: mineral medium compliant with the test guideline OECD 301B
- Test temperature: 19.4 - 22.4°C
- pH: 7.4 ± 0.2
- pH adjusted: yes
- Aeration of dilution water: no
- Suspended solids concentration: 30 mg/L d.w.

- Culturing apparatus: 2 L incubation bottles filled up to a volume of 1.5 L. The bottles were connected to two serial scrubbing bottles (total volume 250 mL) filled with 100 mL 0.05 mol sodium hydroxide solution for the adsorption of carbon dioxide from biodegradation processes.
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: the test vessels were connected with an aeration unit and the bubble aeration with carbon dioxide free air. Air flow: ca. 800 mL/h.
- Measuring equipment: CO2 traps

Twice a week the Total Inorganic Carbon (TIC) values of the adsorption solutions of the first trap were determined and used for the calculation of the produced carbon dioxide. After each sampling the second trap was moved forward and the new trap with fresh sodium hydroxide solution was placed into the second position. Each trap was analyzed separately.

- Inoculum blank: yes, 2 blank control assays
- Toxicity control: yes, 1 inhibition control assay
Reference substance:
Key result
% degradation (CO2 evolution)
> 90 - < 100
Sampling time:
28 d
Details on results:
The degree of biodegradation after an exposure period of 28 days was 90-100 % CO2/ThCO2 (mean value). Since the test substance is a mixture of structure similar compounds, the 10-day window does not apply.
Results with reference substance:
90% after 28 days
Validity criteria fulfilled:
Interpretation of results:
readily biodegradable

Description of key information

Readily biodegradable according to OECD criteria: 90-100% after 28 days based on CO2 evolution (OECD 301 B)

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

A GLP-study assessing ready biodegradation of C16-20AS Na (CAS 91648-55-4) was performed according to OECD 301 B guideline (BASF, 2015). Effluent of the sewage treatment plant handling predominantly domestic sewage was used as inoculum. The initial concentration of the test substance was 69 mg/L (20 mg/L as TOC). Biodegradation of 90-100% was determined after 28 days based on CO2 evolution. Since the test substance is a mixture of similar compounds, the 10-day window does not apply. Based on this result it can be concluded that C16-20AS Na (CAS 91648-55-4) is is readily biodegradable according to OECD criteria.