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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
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): WWTP Mannheim, Germany (collection date 10.02.14)
- Laboratory culture:
- Method of cultivation:
- Storage conditions:
- Storage length: 24 hours
- Preparation of inoculum for exposure: inoculum was aerated the CO2-free air for 24 hours at 22±2 °C
- Pretreatment: washing with tap water
- Concentration of sludge: 30 mg/L dry wight
- Initial cell/biomass concentration:
- Water filtered: yes/no
- Type and size of filter used, if any: woven mesh (size 1 mm)
Duration of test (contact time):
28 d
Initial conc.:
20 mg/L
Based on:
other: TOC
Initial conc.:
ca. 45 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
- Composition of medium: mineral medium according OECD 301A/B
- Additional substrate:
- Solubilising agent (type and concentration if used):
- Test temperature: 22±2 °C
- pH: 7.4±0.2
- pH adjusted: yes, if necessary
- CEC (meq/100 g):
- Aeration of dilution water:
- Suspended solids concentration:
- Continuous darkness: yes/no
- Other:

- Culturing apparatus: 2L incubation bottles
- Number of culture flasks/concentration: 2 flasks/ 1 concentration
- Method used to create aerobic conditions: approx. 800 mL/h CO2-free air
- Method used to create anaerobic conditions: -
- Measuring equipment:
- Test performed in closed vessels due to significant volatility of test substance:
- Test performed in open system:
- Details of trap for CO2 and volatile organics if used: two serial 250 mL scrubbing bottles filled with 100 mL 0.05 mol sodium hydroxide solution
- Other:

- Sampling frequency: twice a week TIC determination using the first CO2 trap; after exposure residual CO2 was stripped by acidifying the test medium with HCl
- Sampling method:
- Sterility check if applicable:
- Sample storage before analysis:
- Other:

- Inoculum blank: 2 control assays
- Abiotic sterile control:
- Toxicity control: 1 inhibition control
- Other:

Reference substance:
% degradation (CO2 evolution)
20 - 30
Sampling time:
28 d
Remarks on result:
other: mean value from two tests
Results with reference substance:
73% CO2/ThCO2 after 14 days
Validity criteria fulfilled:
Interpretation of results:
inherently biodegradable, not fulfilling specific criteria
The test substance was not readily biodegradable under test conditions. Based on the observations in the study the substance is considered to be inherently biodegradable, not fulfilling specific criteria.
Executive summary:

The conclusion that Azo Initiator 2,2’-[azobis(1-methylethylidene)]bis[4,5-dihydro-1H-imidazole dihydrochloride was not readily biodegradable in this carbon dioxide evolution test based on the quantitative determination of the formed carbon dioxide in ther test substance assay by comparison with the calculated maximal theoretical carbon dioxide production.

The required pass level for ready biodegradation after exposure period of 28 days was 20 -30 % CO2/ThCO2 in this test.

The degree of biodegradation was calculated as mean of the values from two test assays at the end of exposure.

Based on the rate of biodegradation of 20 -30 % CO2/ThCO2 at the end of exposure the test substance can be evaluated as partly or moderately biodegradable in this test.

The results in this study are consistent with all validity criteria and the test is valid according to the test guideline on this study. No deviations from the test guidelines or other incidents occured during the course of the reported test, which may have influenced the results.

Description of key information

Based on the observations in the available screening study the substance is considered as inherently biodegradable, not fulfilling specific criteria.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria

Additional information