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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:
from 2002-09-04 to 2002-10-08
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Municipal sewage treatment plant, D-31137 Hildesheim, Germany
- Pretreatment: Filtered through folded filter. The second effluent was used for initiation of inocilation.
- Initial cell/biomass concentration: 10^4 - 10^6 CFU/L
Duration of test (contact time):
28 d
Initial conc.:
3.5 mg/L
Based on:
ThOD
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
- pH: 7.49 - 7.56
- Aeration of dilution water: till 20 h before the start of the test
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: BOD bottles with glass stoppers (volume 300 mL)
- Number of culture flasks/concentration:
10 bottles containing test item and inoculum (test suspension);
10 bottles containing only inoculum (inoculum control);
10 bottles containing reference item and inoculum (functional control);
10 bottles containing test item and reference item and inoculum (toxicity control);

CONTROL AND BLANK SYSTEM
- Inoculum blank: Nutrient solution and inoculum
- Toxicity control: 1.75 mg/L test item + 5.0 mg/L reference item + nutrient solution and inoculum
Reference substance:
acetic acid, sodium salt
Preliminary study:
The ThOD of 2.095 mg O2 / mg test item was used for caiculation of BOD and biodegradation in %.
Key result
Parameter:
% degradation (O2 consumption)
Value:
7
Sampling time:
28 d
Details on results:
The test item did not reach the 10 % level (begin of degradation). The pass level of a biodegradation of > 60 % was not reached neither in the 10-d window nor after 28 days.
Results with reference substance:
The pass level of a biodegradation > 60 % was reached after 4 days. The validity criterion that the degradation should be > 60 % after 14 d was fulfilled. After 14 days the biodegradation was determined to 97 %.

In the case of the functional control, the adaptation phase transformed to a degradation phase after 1 day (degradation > 10 %). The pass level > 60 % was reached after 6 days. After 21 days the biodegradation came to 100 % and the plateau was reached.

The biodegradation rate of the toxicity control came to 48 % after 14 days and to a maximum of 54 % after 21 days.

The test item did not reach the 10 % level (begin of degradation). The pass level of a biodegradation of > 60 % was not reached neither in the 10 - d - window nor after 28 days.

Table 1. Oxygen Determination of the Test Item and the Toxicity Control

Study day [d]

Test item 3.5 mg/L

ThOD 2.095 mg O2/mg

Toxicity control

1.75 mg/L test item

+ 5 mg/L reference item

ThOD 1.12 mg O2/mg

O2[mg/L]

BOD

degr.

 

P1

P2

mv

[mg O2/L]

[mg O2/mg]

[%]

O2[mg/L]

BOD

degr.

T1

T2

mv

[mg O2/L]

[mg O2/mg]

[%]

0

7

14

21

28

10.68

9.01

8.77

8.44

8.68

11.11

9.09

8.61

8.39

8.33

10.90

8.05

8.69

7.42

8.51

-

0.47

0.45

0.68

0.50

-

0.13

0.13

0.19

0.14

-

6

6

9

7

11.10

5.70

5.38

5.10

5.94

10.95

5.66

5.84

5.28

5.36

11.03

5.68

5.61

5.19

5.65

-

3.97

3.66

4.04

3.49

-

0.59

0.54

0.60

0.52

-

53

48

54

46

 

Table 2. Oxygen Determination of the Inoculum Control and Functional Control

Study day [d]

Inocolum control

O2[mg/L]

Functional control 10 mg/L

ThOD 0.78 mg O2/mg

C1

C2

mv

O2-depl.

O2[mg/L]

BOD

Degr.

R1

R2

mv

[mg O2/L]

[mg O2/mg]

[%]

0

7

14

21

28

9.76

8.36

8.15

8.10

8.05

10.11

8.75

8.20

8.18

8.05

9.94

8.56

8.18

8.14

8.05

-

1.38

1.76

1.80

1.89

11.00

2.15

1.93

1.58

1.57

11.19

2.20

1.58

1.24

1.48

11.10

2.18

1.76

1.41

1.53

-

7.54

7.58

7.89

7.68

-

0.75

0.76

0.79

0.77

-

96

97

101

99

 

mv = mean value

BOD = Biological oxygen demand

degr. = degradation

O2- depl. = Oxygen depletion

ThOD = Theoretical oxygen demand

 

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
The ready biodegradability of the test substance was investigated according to the OECD guideline 301 D: Ready Biodegradability: Closed bottle test (1992). Under the test conditions, the test substance was found to be not readily biodegradable over the test period of 28 days. Furthermore, the test substance showed no inhibitory effect on the microorganisms. At the end of the test, the test substance did not reach the 10 % level of degradation.
Executive summary:

The ready biodegradability of the test substance was investigated in accordance with the OECD guideline 301 D: Ready Biodegradability: Closed bottle test (1992). The biodegradation of the test substance was followed by exposing it to microorganisms from the secondary effluent of a domestic activated sludge over 28 days. The method assesses the ready biodegradability of a test substance under aerobic conditions at 20 ± 1°C in the dark. During this period the biodegradation was determined on the basis of the reduction of dissolved oxygen. The degree of biodegradation was calculated by the amount of oxygen taken up by the test substance (corrected for that in the blank inoculum control) as a percentage of ThOD or COD. As a reference compound (functional control control), 10 mg/L of sodium acetate was tested simultaneously under the same conditions. In the toxicity control, the test substance showed no inhibitory effect on the microorganisms at the test concentration of 1.75 mg/L. In the functional controls, the reference compound sodium acetate was readily biodegraded by an average of 99 % after 28 days of exposure. At the end of the test (28 days), the test substance was biodegraded by an average of 7 %. Therefore, for the test substance no biodegradation was observed under the test conditions.

Description of key information

The ready biodegradability of the test substance was investigated according to the OECD guideline 301 D: Ready Biodegradability: Closed bottle test (1992). Under the test conditions, the test substance was found to be not readily biodegradable over the test period of 28 days. Furthermore, the test substance showed no inhibitory effect on the microorganisms. At the end of the test, the test substance did not reach the 10 % level of degradation.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The ready biodegradability of the test substance was investigated in accordance with the OECD guideline 301 D: Ready Biodegradability: Closed bottle test (1992). The biodegradation of the test substance was followed by exposing it to microorganisms from the secondary effluent of a domestic activated sludge over 28 days. The method assesses the ready biodegradability of a test substance under aerobic conditions at 20 ± 1°C in the dark. During this period the biodegradation was determined on the basis of the reduction of dissolved oxygen. The degree of biodegradation was calculated by the amount of oxygen taken up by the test substance (corrected for that in the blank inoculum control) as a percentage of ThOD or COD. As a reference compound (functional control control), 10 mg/L of sodium acetate was tested simultaneously under the same conditions. In the toxicity control, the test substance showed no inhibitory effect on the microorganisms at the test concentration of 1.75 mg/L. In the functional controls, the reference compound sodium acetate was readily biodegraded by an average of 99 % after 28 days of exposure. At the end of the test (28 days), the test substance was biodegraded by an average of 7 %. Therefore, for the test substance no biodegradation was observed under the test conditions.