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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:
11 Oct - 09 Nov 2016
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)
Version / remarks:
17 Jul 1992
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Remarks:
Staatliches Gewerbeaufsichtsamt Hildesheim, Germany
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Municipal sewage treatment plant, Hildesheim, Germany (04 Oct 2016)
- Storage conditions: In aerobic conditions by aeration with CO2-free air.
- Storage length: 7 d
- Pretreatment: The activated sludge was washed twice with chlorine-free tap water. After the second washing the settled sludge was resuspended in mineral salts medium and was maintained in an aerobic condition by aeration for 3 h. Thereafter, the sludge was homogenized with a blender. After sedimentaiton the supernatant was decanted and maintained in a aerobic conditions by aeration with CO2-free air for 7 d.
- Concentration of inoculum: 10 mL/L were used to initiate inoculation (1.11E+09 colony forming units/L)
- Initial cell/biomass concentration: 1.11E+07 colony forming units/L (final test solution)
Duration of test (contact time):
28 d
Initial conc.:
19.9 mg/L
Based on:
test mat.
Initial conc.:
60 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral medium stock solutions diluted in ultrapure water, according to guideline.
- Test temperature: 20.4 - 21.0 °C
- pH: 7.70 - 7.73 at test start and 7.70 - 7.96 (at test end)
- pH adjusted: No
- Continuous darkness: Yes

TEST SYSTEM
- Culturing apparatus: Brown glass bottles (500 mL)
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: Aeration with CO2-free air
- Measuring equipment: OxiTop measuring heads
- Test performed in open system: No
- Details of trap for CO2: A rubber sleeve with soda lime was hung into the opening of the bottles to absorb evolved CO2.
- Other: The test solutions were continuously stirred during the test.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes, 250 mL test medium (mineral medium stock solutions and inoculum in ultrapure water) without test and/or reference item (2 replicates).
- Abiotic sterile control: No.
- Toxicity control: Yes, reference item and test item in 250 mL reference item medium (reference item and inoculum in mineral medium stock solutions and ultrapure water) (1 replicate).
- Functional control: 250 mL reference item medium (reference item and inoculum in mineral medium stock solutions and ultrapure water) (1 replicate).
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
4
Sampling time:
28 d
Remarks on result:
other: mean value

The biodegradation in % was calculated based on a ThOD of 3.02 mg O2/mg test item.

FUNCTIONAL CONTROL

The pass level for ready biodegradability (> 60%) was reached on Day 3. The validity criterion that the degradation should be > 60% after 14 d was fulfilled.

TOXICITY CONTROL

In the toxicity control the biodegradation was 47% after 14 d. After 28 d the biodegradation reached 57%. The validity criterion that the test item should not inhibit the biodegradation of the reference item was fulfilled.

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The test item is classified as not readily biodegradable within the 28 d period of the study.
The degradation of the reference item was not inhibited by the test item.
Executive summary:

The ready biodegradability of the test item was determined with non-adapted activated sludge in a manometric respirometry test for a period of 28 d according to OECD guideline 301 F. The test item concentration was 19.9 mg/L (60.0 mg O2/L). Both test item replicates did not reach the 10% level (begin biodegradation phase) within the 28 d period. The mean biodegradation on Day 28 was 4%.

Description of key information

Not readily biodegradable: 4% in 28 d (activated sludge, domestic, non-adapted, OECD 301 F)

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

There is one GLP study available investigating the ready biodegradability of the test substance according to the OECD guideline 301 F.

In a Manometric Respirometry Test, a test medium with 19.9 mg/L test item (nominal, 60.0 mg O2/L) was inoculated with 1.11E+07 colony forming units/L non-adapted activated sludge from a local, municipal sewage treatment plant and incubated for 28 d. A functional, inoculum, as well as a toxicity control were run in parallel. Oxygen depletion by the respiration of bacteria was monitored using the OxiTop system. The percentage biodegradation was expressed in terms of biological oxygen demand (BOD) and theoretical oxygen demand (ThOD).

The functional control reached the pass level (> 60%) on Day 3 and maximum biodegradation (100%) on Day 25. In the toxicity control 47% degradation occurred by Day 14 and 57% by Day 28. Therefore, the degradation of the reference item was not inhibited by the test item.

Both replicates of the test item did not reach the 10% level (end of adaptation, begin of biodegradation phase) within the 28 d period of the test. The mean biodegradation of the test substance on Day 28 was 4%. Hence, the test item is classified as not readily biodegradable within the 28 d period of the study.