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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:
20 June - 4 October 2006
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 (incl. certificate)
Remarks:
The study report included a current certificate of GLP compliance for the test facility.
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): Aeration tank at Worlingworth sewage treatment works (Suffolk, UK)
- Preparation of inoculum for exposure: aliquots (25 mL) of a homogenised sample were filtered through dried (approximately 105°C) and pre-weighed Whatman GF/C filter papers. Filters were dried and re-weighed. The solids in the sludge determined and an appropriate volume used to inoculate control and test vessels.
- Initial cell/biomass concentration: 30 mg/L
- Water filtered: yes
- Type and size of filter used, if any: Whatman GF/C
Duration of test (contact time):
29 d
Initial conc.:
10 mg/L
Based on:
ThIC
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: Composition of Mineral Salts Medium was consistant with the medium described in OECD test guideline 301 (301B).
- Test temperature: 20 to 24 °C
- pH: 7.4 ± 0.2
- pH adjusted: yes
- Aeration of dilution water: Inoculum was aerated prior to test initiation.
- Suspended solids concentration: 30 mg/L
- Continuous darkness: yes (test performed in amber glass bottles)

TEST SYSTEM
- Number of culture flasks/concentration: Duplicate test flasks used.
- Method used to create aerobic conditions: Vessels were continuously flushed with air (air has been treated before to remove carbon dioxide)
- Details of trap for CO2 and volatile organics if used: 3 Dreschel bottles in series, each containing 0.025N, nominal barium hydroxide (110 mL) were connected to the air outlet from each test vessel.

SAMPLING
- Sampling frequency: daily during the first week of the test and hereafter on day 10, 14, 21, 28 and 29
- Sampling method: 20 mL samples in duplicate were taken from the Dreschler bottle nearest to the test vessel, which was removed and replaced.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Abiotic sterile control: yes
- Toxicity control: yes
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (CO2 evolution)
Value:
ca. 10
Sampling time:
2 d
Parameter:
% degradation (CO2 evolution)
Value:
60
Sampling time:
7 d
Parameter:
% degradation (CO2 evolution)
Value:
102
Sampling time:
29 d
Results with reference substance:
The degradation of the reference substance had achieved 64% of its TCO2 after 6 days of incubation and 79% of its TCO2 after 29 days of incubation.
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The test substance was considered to be readily biodegradable under the conditions of this test. The test substance reached 102% degradation by the end of the 29-day test period.
Executive summary:

A ready biodegradability test (OECD test 301B, Modified Sturm Test) was performed to determine the biodegradability characteristics of the test substance.

The study was conducted according to OECD and EC test guidelines, and was performed in accordance with GLP.

The results obtained for the degradation of sodium benzoate (reference substance) and for cumulative CO2 production by the control mixtures (81.4 mg CO2 ) fulfil the validity criteria for this test.

The mean cumulative CO2 production by mixtures containing the test substance at 10 mg C/L was equivalent to appr. 10% of the TCO2 after 2 days, 60% on Day 7 and 102% by the end of the test on Day 29.

On this basis, the test substance was considered readily biodegradable under the conditions of the test.

Description of key information

The test substance was considered to be readily biodegradable under the conditions of ready biodegradability test (OECD test 301B). The test substance reached 102% degradation by the end of the 29-day test period.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

A ready biodegradability test (OECD test 301B, Modified Sturm Test) was performed to determine the biodegradability characteristics of the test substance. The study was conducted according to OECD and EC test guidelines, and was performed in accordance with GLP. The results obtained for the degradation of sodium benzoate (reference substance) and for cumulative CO2 production by the control mixtures (81.4 mg CO2) fulfil the validity criteria for this test. The mean cumulative CO2 production by mixtures containing the test substance at 10 mg C/L was equivalent to appr. 10% of the TCO2 after 2 days, 60% on Day 7 and 102% by the end of the test on Day 29. On this basis, the test substance was considered readily biodegradable under the conditions of the test.