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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:
18 Jan - 15 Feb 2011
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
The oxygen depletion in blank was 2.31 mg O2/L (slightly higher than specified in guideline 1.5 mg/L, but seemed to be acceptable).
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Version / remarks:
1992
GLP compliance:
yes (incl. certificate)
Remarks:
Niedersächsisches Umweltministerium, Hannover, 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
- Pretreatment: filtered with folded filter. First 200 mL of the filtrate were disposed. The second filtrate was used for inoculation
- Colony forming units in test vessels: 10^4 - 10^6 CFU/L
- Water filtered: yes
Duration of test (contact time):
28 d
Initial conc.:
3 mg/L
Initial conc.:
8.01 other: mg O2/L
Based on:
ThOD/L
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: mineral nutrient solution according to OECD 301 D
- Test temperature: 20 - 21 °C
- O2 of demineralized water after aeration: 9.09 mg/L
- pH: 6.93 - 7.44
- Aeration of dilution water: yes

TEST SYSTEM
- Culturing apparatus: BOD bottles with glass stoppers (volume 300 mL)
- Number of culture flasks/concentration: 10
- Method used to create aerobic conditions: 1 day before test start, demineralized water for the test medium was aerated until oxygen saturation and then left at room temperature for at least 20 h.
- Measuring equipment: pH: pH-Meter, "CORNING" pH 240, Oxygen concentration: Oximeter, "WTW" Oxi 530

SAMPLING
- Sampling frequency: the oxygen concentration was measured in the vessels on day 0, 8, 14, 21 and 28
- Other: temperature in the incubator was recorded once every working day. The pH value of the solutions was determined at the beginning and at the end of the test.

CONTROL AND BLANK SYSTEM
- Inoculum control: 10
- Reference control: 10
- Toxicity control: 10 (1.5 mg/L test item + 5.0 mg/L reference substance)
- Other: test series was accompanied by a complete parallel series for the determination of O2 demand of the inoculated control medium (C1, C2)

Reference substance:
acetic acid, sodium salt
Remarks:
10 mg/L (ThOD: 0.78 mg O2/mg)
Key result
Parameter:
% degradation (O2 consumption)
Value:
62
Sampling time:
28 d
Details on results:
10-day window criterion fulfilled.
Results with reference substance:
71% degradation after 28 d.

The oxygen demand in the inoculum control reached a maximum of 2.31 mg O2/L after 28 days.

The biodegradation rate of the toxicity control reached 65% after 14 days. The test item did not inhibit the biodegradation of the reference substance.

Table 1: Oxygen determination at each sampling point and % biodegradation.

Sampling date [d] Test item Toxicity control Reference control
O2 mg/L BOD mg/L % degr. O2 mg/L BOD mg/L % degr. O2 mg/L BOD mg/L % degr.
0 9.41  -  - 9.38  -   -  9.56  -   - 
8 3.23 4.93 61 3.78 4.35 55 2.96 5.35 69
14 2.91 4.97 62 2.71 5.14 65 2.21 5.82 74
21 1.94 5.52 69 2.36 5.07 64 2.06 5.55 72
28 2.13 4.97 62 2.59 4.48 57 1.76 5.49 71
Validity criteria fulfilled:
yes
Remarks:
The oxygen depletion in blank was 2.31 mg O2/L (slightly higher than specified in guideline 1.5 mg/L, but seemed to be acceptable).
Interpretation of results:
readily biodegradable
Conclusions:
This study indicates that the substance is readily biodegradable (62% after 28 d (O2 consumption), OECD 301 D). Furthermore the test showed that the substance is not inhibitory ot microorganisms at the tested concentration of 1.5 mg/L.

Description of key information

Readily biodegradable (62% in 28 d, 14-d window passed, OECD 301 D)

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

There is one GLP study available investigating the biodegradability of the substance in an aerobic, aqueous medium according to the OECD guideline 301 D.

In a closed bottle test a nominal concentration of 3.0 mg/L (8.01 mg O2/L) test substance was inoculated with non-adapted activated domestic sludge for 28 d under controlled conditions. A functional, toxicity, and inoculum control were run in parallel. Degradation was followed by measuring the oxygen concentrations in regular intervals. % biodegradation was expressed in terms of theoretical oxygen demand (ThOD) and biological oxygen demand (BOD).

The test substance reached the 10% level (begin of degradation) after 2 d. In the 10-d window a mean biodegradation rate of 62% was reached. The biodegradation reached the pass level of > 60% after 8 d and came to a maximum of 69% after 21 d. The toxicity control containing both test and reference item reached a maximum degradation rate of 65% within 14 d. The degradation of the reference item was not inhibited by the test substance. The oxygen depletion in blank was 2.31 mg O2/L, it is slightly higher than specified in guideline 1.5 mg/L, but seemed to be acceptable.