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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:
26 Sep 1995 to 25 Oct 1995
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Version / remarks:
17th July, 1992
Deviations:
yes
Remarks:
Only one CO2 scrubber used
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Activated sludge collected from a sewage treatment plant on 19/06/95.
- pH at collection: 8.0
- Preparation: The preparation was carried out according to the method described in the guideline.
Duration of test (contact time):
29 d
Initial conc.:
47.9 mg/L
Based on:
test mat.
Remarks:
replicate 1, corresponding to 15.8 mg ThOC/L
Initial conc.:
45 mg/L
Based on:
test mat.
Remarks:
replicate 2, corresponding to 14.8 mg ThOC/L
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Reconstituted water: The reconstituted water was prepared according to the method described in the guideline.
- Temperature: 22 ± 2 °C
- Aeration: Ca. 25 mL/min purified from carbon dioxide.

DESIGN
- Vessels: 2 L dark brown glass flasks equipped with gas inlet and a magnetic stirrer.
- CO2 scrubbers: Approximately 250 mL scrubbers with gas inlet tubes equipped with sintered glass tips containing 200 ml 0.05 N sodium hydroxide. Only one CO2 scrubber was used per test bottle. Theoretically, a solution of 0.05 M NaOH is sufficient to trap at least two times more CO2 than the maximum ThCO2 which can evolve in each test bottle (including CO2 possibly evolved from the bacteria e.g., endogenous respiration). Moreover, experimentally it was confirmed that no measurable CO2 carry over has ever occurred with the scrubbers used.

PREPARATIONS
The following test assays were prepared:
- 2 test substance treatment flasks (test substance and inoculum)
- 2 inoculum blank flasks
- 2 reference substance control flasks (procedure control)
- 1 toxicity control flask (reference substance, test substance and inoculum)


Reference substance:
benzoic acid, sodium salt
Remarks:
15 mg DOC/L
Preliminary study:
Not reported
Test performance:
Not reported
Key result
Parameter:
% degradation (CO2 evolution)
Value:
7
Sampling time:
29 d
Details on results:
Minor biodegradation was observed. Within the test substance treatments, CO2 evolution slowly increased over time, reaching an average of 13.6 mg C after 29 days, corresponding to a 7% biodegradation of the test substance. A detailed overview of the test results of the test substance and the controls is provided in 'Any other information on results incl. tables'.
Results with reference substance:
The degree of biodegradation of the reference substance after 21 days was 84% CO2/ThCO2. The degree of biodegradation of the reference substance with the test substance after 21 days was 88% CO2/ThCO2.

Table: CO2 evolution and biodegradation of the controls

CO2 evolution measured as mg C

Biodegradation

Day

Blank 1 [mg]

Blank 1 [mg]

Blank 1 [mg]

Ref 1 [mg]

Ref 1 [mg]

Ref 1 [mg]

Ref + TS [mg]

Reference [%]

Ref + TS [%]*

0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0

0

3

3.2

3.8

3.5

14.9

16.4

15.7

14.5

54

49

6

5.5

6.2

5.9

21.1

21.6

21.4

22.1

69

72

8

6.7

7.2

7.0

22.0

23.2

22.6

22.9

69

71

10

7.8

8.3

8.1

24.7

25.7

25.2

26.1

76

80

13

8.2

8.6

8.4

25.5

26.4

26.0

26.9

78

82

15

9.0

9.6

9.3

27.3

28.1

27.7

28.6

82

86

17

9.6

10.1

9.9

27.8

28.1

28.0

28.9

80

85

21

10.5

10.8

10.6

29.2

29.7

29.5

30.3

84

88

24

10.6

11.0

10.8

**

**

**

**

 

28

11.1

11.2

11.1

 

29

12.0

11.8

11.9

Ref = Reference substance

TS = Test substance

* The biodegradation of the "reference + test substance" control is calculated with the applied amount of the reference alone, i.e., 15 mg DOC/L.

** The controls of the reference and the reference + test substance together were stopped at day 21 since it met already the specifications of biodegradation criteria.

 

Table: CO2 evolution and biodegradation of the test substance

Day

CO2 evolution measured as mg C

Biodegradation % of the test substance

Replicate 1

Replicate 2

Replicate 1

Replicate 2

Mean

0

0.0

0.0

0

0

0

3

3.7

3.2

1

-0.1

0

6

6.5

6.1

2

1

2

8

7.8

7.5

3

2

3

10

9.2

9.0

5

4

4

13

9.5

9.3

5

4

4

15

10.8

10.5

6

5

6

17

11.3

11.0

6

5

6

21

12.4

12.2

7

7

7

24

12.3

12.3

7

7

7

28

12.8

13.0

7

8

8

29

13.5

13.7

7

8

7

Negative degradation values as obtained in this test are a consequence of the comparison of values obtained in the blank (endogenous respiration leading to a carbon dioxide evolution) and the low values obtained in the presence of the test substance.

Validity criteria fulfilled:
not specified
Interpretation of results:
not readily biodegradable
Conclusions:
The test substance is not readily biodegradable in this test. The biodegradation calculated as percentage of measured amount of inorganic carbon over the theory was 7 %.
Executive summary:

The biodegradation potential of the substance in water was determined in a screening study according to OECD TG 301B (CO2 -Evolution Test) and in compliance with GLP criteria. In this study, 14.8 and 15.8 mg/L TOC nominal (equivalent to 45.0 and 47.9 mg/L test substance) were inoculated with activated sludge from a predominantly domestic wastewater treatment plant for 29 days under aerobic conditions. During the incubation period the produced carbon dioxide (CO2) was measured and at the end of the test compared with the maximal theoretical CO2 production (ThCO2). Biodegradation was expressed as percentage of the measured CO2 (corrected for the blanc inoculum control) relative to the ThCO2. After the 29-day incubation period 7% of the substance was biodegraded. Based on these findings, the test substance is classified as not readily biodegradable.

Description of key information

Not readily biodegradable, OECD 301B (CO2-Evolution test), OECD 301B, Grade 1996

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

[Type of water: freshwater]