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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:
2011-02-25 to 2011-03-25
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Municipal sewage treatment plant, D-31137 Hildesheim
- Pretreatment: the activated sludge was washed twice with autoclaved tap water. After the washing the settled sludge was filled up with mineral salts medium and maintained in an aerobic condition by aeration for 4 hours. Thereafter, the sludge was homogenized with a blender. The supernatant was decanted and maintained in an aerobic condition by aeration with CO2-free air for 6 days. 10mL/L were used to initiate inoculation.
- Colony forming units in the test vessels: 10E7 - 10E8 CFU/L
Duration of test (contact time):
28 d
Initial conc.:
25 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral salts medium according to OECD 301F
- Test temperature: 21 - 22°C
- pH: 7.68
- Dispersion treatment: continuous stirring
- ThOD in test vessel: 60.5 mg O2/L
- Photoperiod: dark, in an incubator
- Other: application: once at the start, the test item (6.0µL/test vessel) was injected directly into the test solution.

TEST SYSTEM
- Test vessels: brown glass bottles (500 mL)
- Test volume: 250 mL
- Number of culture flasks/concentration: 2 for the test item (P1, P2); 1 for functional control (R1); 1 for toxicity control (T1); 2 for inoculum control (C1, C2)
- Test performed in closed vessels: bottles were closed with OxiTop measuring heads
- Details of trap for CO2 and volatile organics if used: a rubber sleeve with soda lime was hung into the opening of the bottles to absorb evolved CO2
- Test concentration: 25 mg/L test item

CONTROL AND BLANK SYSTEM
- Inoculum blank: test medium without test and/or reference item
- Toxicity control: test item (25 mg/L) and reference item (45 mg/L)
- Functional control: 45 mg/L reference item

STATISTICAL METHODS: Calculation of the ThOD. The oxygen depletion of the test and reference item were calculated. The biodegradation of the test and reference item was calculated out of the BOD in relation to the ThOD.
Reference substance:
benzoic acid, sodium salt
Remarks:
purity: 100 %
Test performance:
The pass level of biodegradation of the functional control was >60% after 3 days. The biodegradation rate came to a maximum of 96% on day 26. The validity criterion (> 60% after 14 days) was fulfilled.
The toxicity control achieved 87% biodegradation after 14 days. After 28 days the biodegradation came to 93%. The validation criteria that the test item should not inhibit the biodegradation of the reference item was fulfilled.
Key result
Parameter:
% degradation (O2 consumption)
Value:
100
Sampling time:
28 d
Details on results:
The CFU of the inoculum was determined at the start by standard dilution plate count: 4.3 x 10 e9 CFU/L.
The biodegradation of the test item was 100% after 28 days. The replicates reached the 10% level (beginning of biodegradation) after 3 days, and the pass level of 60% was reached within the 10-d-window on day 5.

The biodegradation is described here:

  Concentration Replicate Biodegradation (%)
day 7 day 14 day 21 day 28
Test item 25 mg/L 1 81 91 97 100
2 88 98 100 100
Functional control 45 mg/L 1 82 90 98 95
Toxicity control 25 mg/L test item + 45 mg/L reference item 1 74 87 91 93
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The test item is found to be readily biodegradable in the 10-d-window and after 28 days (100%).
Executive summary:

The ready biodegradability of the test item was determined with a non adapted activated sludge in the Manometric Respirometry Test for a period of 28 days, according to the OECD test guideline 301F. The test item concentration was 25 mg/L, corresponding to a ThOD of 60.5 mg O2/ test vessel. The oxygen was depleted by the respiration of bacteria and the degradation was followed by measuring the oxygen concentration. The biodegradation rate is therefore expressed as the percentage BOD (biological oxygen demand) and was calculated for each study day.

The mean oxygen deletion in the inoculum was 7.8 mg O2/L on day 28.

In order to check the activity of the test system sodium benzoate was used as functional control. The pass level >60% was reached after 3 days. The biodegradation rate came to a maximum of 96% on day 26.

In the toxicity control containing both test and reference item 87% degradation occurred within 14 days. After 28 days the biodegradation came to 93%. The degradation of the reference item was not inhibited by the test item.

For the test item, the replicates reached the 10% level after 3 days, and the pass level of 60% was reached within the 10-d-window on day 5. After 28 days the mean biodegradation was 100%.

The test item is found to be readily biodegradable in the 10-d-window and after 28 days.

Description of key information

The ready biodegradability of the test item was determined for a period of 28 days, according to the OECD test guideline 301F.  The test item is found to be readily biodegradable in the 10-d-window and after 28 days.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The ready biodegradability of the test item was determined with a non adapted activated sludge in the Manometric Respirometry Test for a period of 28 days, according to the OECD test guideline 301F. The 10% level was reached after 3 days and the pass level of 60% was reached within the 10-d window, i.e. on day 5. After 28 days the mean biodegradation was 100%. The test item is classified as readily biodegradable fulfilling the 10-d window. Moreover, in the toxicity control, the degradation of the reference item was not inhibited by the test item.