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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
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Reference:
Composition 0
Qualifier:
according to
Guideline:
other: BOD Test for Insoluble Substances (BODIS), preliminary guideline of the Bundesumweltamt Berlin (1990)
Qualifier:
equivalent or similar to
Guideline:
ISO 10708 Water quality - Evaluation in an aqueous medium of the ultimate aerobic biodegradability of organic compounds - Determination of biochemical oxygen demand in a two-phase closed bottle test
GLP compliance:
not specified
Test material information:
Composition 1
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge: Aeration tank of the municipal sewage treatment plant of Pforzheim, Germany
- Storage conditions: 2 L of mineral medium were prepared and inoculated with 20 mL of the activated sludge adjusted to 3.0 g/L. 9 test vessels containing magnetic stirrers were filled with 200 mL of this solution each, closed with glass stoppers and shaken without test substance for 1 week in the dark (100 rpm, 20 °C).
- Storage length: 1 week
- Pretreatment: The collected sludge was washed twice by centrifugation (10 min, 6000 rpm) with mineral medium. The remaining pellet was resuspended in mineral solution to a final concentration of 3.0 g/L.
- Initial suspended solids concentration (at test start): 30 mg/L
Duration of test (contact time):
28 d
Initial conc.:
20 mg/L
Based on:
ThOD
Initial conc.:
6.9 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Remarks:
biochemical oxygen demand (BOD)
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral medium containing the following compounds: 85 mg/L KH2PO4, 217.5 mg/L K2HPO4, 334 mg/L Na2HPO4 * 2 H2O, 5 mg/L NH4Cl, 36.42 mg/L CaCl2 * 2 H2O, 22.5 mg/L MgSO4 * 7 H2O, 0.25 mg/L FeCl3 * 6 H2O
- Test temperature: 20 °C
- pH: 6.97 - 7.66
- Aeration of dilution water: Prior to the test, the vessels with the test solutions were aerated for 15 min by a membrane air pump with tubes and Pasteur pipettes.
- Suspended solids concentration: 30 mg/L
- Continuous darkness: Yes
- Other: The closed bottles were incubated on a rotary shaker at 100 rpm to assure steady state oxygen partitioning between liquid and gas phase.

TEST SYSTEM
- Culturing apparatus: Closed glass bottles with glass stoppers
- Number of culture flasks/concentration: 3
- Method used to create aerobic conditions: Aeration with tubes and Pasteur pipettes
- Measuring equipment: Oximeter (WTW Oxi 191)
- Other: The test vessels were closed glass bottles with 2/3 of aqueous test mixture and 1/3 air.

SAMPLING
- Sampling frequency: 7, 15, 21, and 28 d after test start
- Sampling method: O2 concentrations were measured with an oximeter.
- Other: After the measurements, the test assays were aerated for 15 min, measured once more and then incubated once more for the remaining test period. the value measured after 15 min of aeration was used as Cs value (saturation value for dissolved oxygen at atmospheric pressure) and was usually < 9.2 mg/L.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Mineral medium without test item
- Procedural control (reference substance): 0.104 mg/L ThOD sodium benzoate
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
5.5
Sampling time:
28 d
Results with reference substance:
The reference substance sodium benzoate was degraded by 65.1% at the end of the test. The percentage degradation of the reference substance had reached 60% within 14 d.

VALIDITY CRITERIA

The test was considered valid because the percentage degradation of the reference substance had reached 60% within 14 d and the total oxygen uptake in the blanks after the first week of the test was lower than 3 mg O2/L and in the following week not ≥ 1 mg/L per week. The differences between extrems were lower than 20 % in the test vessels during the process.

BIOLOGICAL RESULTS

Table 1. Degradation rates after 28 days

Study Group

Oxygen content after 21 d

Ur

BOD

[mg O2]

% degradation

Cumul. BOD

Cumul. Degradation

[%]

T1

8.05

0.000

0.000

0.0

0.954

4.7

T2

7.70

0.024

0.715

3.5

2.085

10.2

T3

8.00

0.000

0.000

0.0

0.328

1.5

R1

8.00

0.000

0.000

0.0

13.261

63.5

R2

7.70

0.000

0.000

0.0

12.486

59.9

R3

8.00

0.000

0.000

0.0

15.019

72.0

Ur = relative uptake of oxygen in the water phase

T = Test substance

R = Reference substance

Validity criteria fulfilled:
yes
Remarks:
For further details please refer to “Any other information on results incl. tables”.
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
The test resulted in an average degradation rate of 5.5% after 28 d (BODIS test). Therefore, the substance is not readily biodegradable.
Executive summary:

The ready biodegradability of the substance was assessed according to the BODIS test (similar to ISO 10708). The test item (20 mg ThOD) was inoculated with activated sludge (30 mg suspended solids/L) in closed glass bottles for 28 d in the dark. Degradation was followed by weekly measurements of the biochemical oxygen demand (BOD). A procedural control (sodium benzoate) was run in parallel.

After 28 d the average degradation rate of the test item was 5.5%. The degradation rate of the reference substance sodium benzoate reached 65.1% at the end of the test, confirming the activity of the inoculum. Thus, the substance is not readily biodegradable according to guidance criteria.

Description of key information

Not readily biodegradable (5.5% within 28 d, BODIS test)

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

There is one study available, in which the ready biodegradability of the substance was assessed according to the BODIS test (similar to ISO 10708).

The test item (20 mg ThOD) was inoculated with activated sludge (30 mg suspended solids/L) in closed glass bottles for 28 d in the dark. Degradation was followed by weekly measurements of the biochemical oxygen demand (BOD). A procedural control (sodium benzoate) was run in parallel.

After 28 d the average degradation rate of the test item was 5.5%. The degradation rate of the reference substance sodium benzoate reached 65.1% at the end of the test, confirming the activity of the inoculum. Thus, the substance is not readily biodegradable according to guidance criteria.