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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:
From 10 December 2002 to 08 January 2003
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
GLP compliance:
yes
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): From the aeration stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK, which treats predominantly domestic sewage.

- Storage conditions: The sample of activated sewage sludge was maintained on continuous aeration upon receipt.

- Pretreatment: A sample of the activated sewage sludge was washed three times by settlement and resuspension in culture medium to remove any excessive amounts of dossolved organic carbon (DOC) that may have been present.

- Concentration of sludge: 3.2 g/L

- Water filtered: yes

- Type and size of filter used, if any: A piece of pre-weighed GF/A filter paper.
Duration of test (contact time):
28 d
Initial conc.:
10 mg/L
Based on:
DOC
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: KH2PO4 8.50 g/L, K2HPO4 21.75 g/L, Na2HPO4.2H2O 33.40 g/L, NH4Cl 0.50 g/L; CaCl2 27.50 g/L, MgSO4.7H2O 22.50 g/L, FeCl3.6H2O 0.25 g/L

- Test temperature: 21 deg. C

- pH: 7.5-7.7

- Suspended solids concentration: Each test vessel was inoculated with the prepared inoculum at a final concentration of 30 mg suspended solids (ss)/L.

- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 5 litre glass culture vessels

- Number of culture flasks/concentration: 2 flasks

- Method used to create aerobic conditions: The CO2-free air was produced by passing compressed air through a glass column containing self-indicating soda lime granules.

- 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 0.5 M NaOH. The CO2 absorbing solutions were prepared using purified de-gassed water.

SAMPLING
- Sampling frequency: CO2 analysis: on Days 0, 1, 2, 3, 6, 8, 12, 14, 17, 20, 22, 24, 27, 28 and 29; DOC analysis: on Days 0 and 28.

- Sample storage before analysis: CO2 analysis: The samples taken on Days 12 and 22 were stored deep frozen at approximately -20 deg.C.

CONTROL AND BLANK SYSTEM
- Inoculum blank: A control, in duplicate, consisting of inoculated culture medium.

- Toxicity control: The test material plus the standard material in inoculated culture medium to give a final concentration of 20 mg carbon/L to act as a toxicity control (one vessel only).
Reference substance:
benzoic acid, sodium salt
Preliminary study:
No information provided
Test performance:
No information provided
Parameter:
% degradation (CO2 evolution)
Value:
21
Sampling time:
28 d
Details on results:
The total CO2 evolution in the control vessels on Day 28 was 22.29 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.

The test material attained 21% degradation after 28 days and therefore cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No 301B.
Results with reference substance:
Sodium benzoate attained 98% degradation after 28 days thereby confirming the suitability of the inoculum and test conditions. The increase in inorganic carbon in the first absorber vessels on Day 29 resulted in an increase in the percentage degradation value for the standard material from 98% on Day 28 to 99% on Day 29.
Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The test item attained 21% degradation after 28 days and therefore cannot be considered to be readily biodegradable.

Description of key information

The test item attained 21% degradation after 28 days and therefore cannot be considered to be readily biodegradable (Safepharm Laboratories Limited, 2004).

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information