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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:
15 September 2006 - 20 October 2006
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EPA OPPTS 835.3110 (Ready Biodegradability)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): the aeration stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK

The activated sewage sludge sample was washed three times by settlement and resuspension in culture medium to remove any excessive amounts of dissolved organic carbon (DOC) that may have been present. The washed sample was then maintained on continuous aeration in the laboratory at a temperature of approximately 21ºC and used on the day of collection.
The suspended solids were equal to 3.0 g/l prior to use.
Duration of test (contact time):
29 d
Initial conc.:
16.1 mg/L
Based on:
test mat.
Initial conc.:
10 mg/L
Based on:
other: carbon
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: according to OECD guideline
- Test temperature: 21°C
- pH: 7.6-7.8
- pH adjusted: no
- Aeration of dilution water: yes
- Suspended solids concentration: 30 mg/l
- Continuous darkness: yes


TEST SYSTEM
- Culturing apparatus: 5 litre glass culture vessels
- Number of culture flasks/concentration:
inoculum: duplicate
reference substance + inoculum: duplicate
test material + inoculum: duplicate
test material + reference substance + inoculum: single

- Method used to create aerobic conditions: CO2-free air bubbled through the solution at a rate of approximately 40 ml/minute and stirred continuously by magnetic stirrer.
- Test performed in closed vessels due to significant volatility of test substance: no
- Test performed in open system: no
- Details of trap for CO2 and volatile organics if used: The CO2 produced by degradation was collected in two 500 ml Dreschel bottles containing 350 ml of 0.05 M NaOH.

SAMPLING
See details on analytical methods

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Abiotic sterile control: no
- Toxicity control: yes
Reference substance:
benzoic acid, sodium salt
Preliminary study:
Results obtained from the samples taken for DOC analysis from the preliminary investigational work indicated that the test material did not adsorb to filter matrices or activated sewage sludge.
Test performance:
The total CO2 evolution in the control vessels on Day 28 was 19.35 mg/l and therefore satisfied the validation criterion given in the OECD Test Guidelines. The IC/TC ratio of the test material suspension in the mineral medium at the start of the test was below 5% and hence satisfied the validation criterion given in the OECD Test Guidelines. The difference between the values for CO2 production at the end of the test for the replicate vessels was <20% and hence satisfied the validation criterion given in the OECD Test Guidelines.
Key result
Parameter:
% degradation (CO2 evolution)
Value:
100
Sampling time:
28 d
Details on results:
The test material attained 100% degradation after 28 days and satisfied the 10-Day window validation criterion, whereby 60% degradation must be attained within 10 days of the degradation rate exceeding 10%. The test material can therefore be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No 301B.
Results with reference substance:
The toxicity control attained 41% degradation after 14 days and 98% degradation after 28 days thereby confirming that the test material was not toxic to the sewage treatment micro-organisms used in the test.
Sodium benzoate attained 92% degradation after 14 days and 105% degradation after 28 days thereby confirming the suitability of the inoculum and test conditions.
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
A ready biodegradation study was perormed according to OECD/EC guidelines and GLP principles. The test substance attained 100% degradation after 28 days and can therefore be considered to be readily biodegradable.

Description of key information

A ready biodegradation study was perormed according to OECD/EC guidelines and GLP principles. The test substance attained 100% degradation after 28 days and can therefore be considered to be readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

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