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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:
14 Dec 2010 - 11 Jan 2011
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
GLP compliance:
yes (incl. QA statement)
Remarks:
Landesanstalt für Umwelt, Messungen und Naturschutz Baden-Württemberg, Karlsruhe, Germany
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Sewage treatment plant Breisgauer Bucht, Germany
- Laboratory culture: no
- Pretreatment: Sludge was washed twice using tap water.
- Concentration of sludge: 5 g/L (dry substance)
- Initial cell/biomass concentration: 30 mg/L
- Water filtered: no
Duration of test (contact time):
29 d
Initial conc.:
20 mg/L
Based on:
other: TOC
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: According to guideline OECD 301B
- Test temperature: 21-22 °C
- Aeration of dilution water: yes, using CO2-free air
- Continuous darkness: no (diffuse light)

TEST SYSTEM
- Culturing apparatus: 2 L gas-washing bottles with a septum-closed opening sideways
- Number of culture flasks/concentration: 3
- Method used to create aerobic conditions: The medium was continually sparged with a supply of CO2-free air and agitated with a magnetic stirrer.
- Measuring equipment: TOC analyser TOC-5050A Shimadzu with autosampler ASI 5000A
- Test performed in closed vessels: yes
- Test performed in open system: no
- Details of trap for CO2 and volatile organics if used: 2 absorber flasks with 0.2 M NaOH solution.

SAMPLING
- Sampling frequency: Sampling was performed on day 3, 6, 9, 14, 21 and 28.
- Sampling method: 4 mL NaOH solution was collected from the absorber flasks and the inorganic carbon (IC) was determined. Samples were closed using parafilm to avoid CO2 absorption from the air. 2 mL of a 4 M HCl solution were added to the test vessels on day 28 to outgas CO2 from the water phase and to stop the degradation process.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, 3 flasks
- Other: Positive control: sodium benzoate, 3 bottles
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (CO2 evolution)
Value:
89.9
Sampling time:
29 d
Remarks on result:
other: after adding of 4 M HCl solution
Details on results:
Within the 10-day window the 60% level was passed. Therefore, the test substance is regarded as readily biodegradable.
Results with reference substance:
The reference substance was degradad to 86.9% after 28 days. The 60% pass-level was reached.

VALIDITY CRITERIA

The study fulfilled the validity criteria of the guideline (Table 1).

Table 1: Validity criteria for OECD 301 B.

Criterion from the guideline

Outcome

Validity criterion fulfilled

Difference of extremes of replicate values of the removal of the test chemical at the plateau, at the end of the test or at the end of the 10-d window, as appropriate, is less than 20%.

Differences of extremes or replicate values were < 20%.

Yes

Percentage degradation of the reference compound has reached the pass levels by day 14.

Degradation of the reference substance was ≥ 60% (ThCO2) after 6 d.

Yes

The IC content of the test substance suspension in the mineral medium at the beginning of the test must be less than 5% of the TC.

The IC content of the test substance at test start was < 5%.

Yes

The total CO2 evolution in the inoculum blank at the end of the test should not normally exceed 40 mg/L medium.

The maximum CO2 content in the inoculum blank was < 40 mg/L.

Yes

 

RESULTS

Table 2: Degradation of the test substance [% ThCO2]

Replicate

day

0

3

6

9

14

21

28

29

1

0

30.2

60.1

68.3

77.5

75.3

79.1

82.4

2

0

40.4

74.1

80.1

88.9

86.7

94.0

99.0

3

0

34.2

65.9

73.5

81.1

81.4

84.1

88.2

Validity criteria fulfilled:
yes
Remarks:
For further details please refer to “Any other information on results incl. tables”.
Interpretation of results:
readily biodegradable

Description of key information

Readily biodegradable (89.9% in 28 d, OECD 301 B); read-across

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information

One experimental study is available, in which the biodegradation ofFatty acids, C16, C18 and C18-unsaturated, C12-15 alcohol (linear and branched), esters in water was assessed according to OECD guideline 301 B and GLP.

In this test, a test item concentration of 20 mg/L (TOC) was inoculated with 30 mg/L non-adapted activated sludge for 28 d under aerobic conditions. Degradation was assessed by measuring CO2 evolution. After 28 d, the degradation of the test item had reached 89.9% and the 10-d window was passed. Therefore, Fatty acids, C16, C18 and C18-unsaturated, C12-15 alcohol (linear and branched), esters is readily biodegradable according to OECD guideline criteria.

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