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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:
2008-12-08 to 2009-01-08
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
This study was performed according to OECD Guideline 301 F with GLP statement. All validity criteria were fulfilled and no deviations were observed.
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
no
Principles of method if other than guideline:
Not applicable
GLP compliance:
yes (incl. certificate)
Remarks:
inspected on 05-09 and 26-30 November 2007 / signed on 12 November 2008
Specific details on test material used for the study:
No additional information
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge: Study was performed with aerobic activated sludge from a wastewater treatment plant (ARA Ergolz II, Füllinsdorf, Switzerland) treating predominantly domestic wastewater.
- The sludge was washed twice with tap water by centrifugation and the supernatant liquid phase was decanted. A homogenized aliquot of the final sludge suspension was weighed, thereafter dried and the ratio of wet to dry weight was calculated.
- Based on this ratio, calculated amounts of wet sludge were suspended in test water to obtain a concentration equivalent to 4 g (±10%) dry material per liter. During the holding period of three days prior to use, the sludge was aerated at room temperature. Prior to use, the sludge was first thoroughly mixed and then diluted with test water to a concentration of 1 g per liter (dry weight basis). Based on the determined dry weight of this diluted activated sludge defined amounts were added to test water to obtain a final concentration of 30 mg dry material per liter.
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Test water according to OECD 301 F
- Source/preparation of dilution water: Purified water
- Test temperature: 22 °C, maintained with a built-in thermostat and checked once per week
- pH: pH measured in all flasks at the start of the test was in the range 7.5 – 7.6. At the end of exposure (Day 28), pH values of 7.4 – 8.4 were measured.
- pH adjusted: Yes; pH was adjusted from 7.6 to 7.4 with a diluted hydrochloric acid solution.
- Suspended solids concentration:
- Continuous darkness: Yes
- Test volume: 250 mL per flask

TEST SYSTEM
- Culturing apparatus: Flasks (500 mL)
- Number of culture flasks/concentration: Two for test item, inoculum and procedure control and one for toxicity control
- Measuring equipment: Test flasks were incubated under SAPROMAT D12 (Voith GmbH, Heidenheim, Germany)
- Details of trap for CO2: Evolved CO2 was absorbed by soda lime

SAMPLING
- Sampling frequency: Oxygen consumption was recorded manually by taking a daily reading at least on each working day. The pH was measured in each test flask before the addition of the activated sludge inoculum and at the end of incubation.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes; containing inoculum only
- Procedure control: Yes; containing reference substance (sodium benzoate) with inoculated medium
- Toxicity control: Yes; containing test material and reference substance (sodium benzoate) with inoculated medium
Reference substance:
benzoic acid, sodium salt
Remarks:
100 mg/L
Preliminary study:
None
Test performance:
No data
Key result
Parameter:
% degradation (O2 consumption)
Value:
80
Sampling time:
28 d
Remarks on result:
other: within the 10d window
Details on results:
The percent biodegradation of the test item was calculated based on the theoretical oxygen demand (ThOD) of 3.09 mg O2/mg test item.

The biochemical oxygen demand (BOD) of ST 17 C 08 in the test media significantly increased between Exposure Day 1 and 4 until test termination after 28 days. At the end of the 28-day exposure period, the mean biodegradation of the test substance amounted to 80%. Consequently, the test substance was found to be biodegradable under the test conditions within 28 days.

Moreover, the pass level for ready biodegradability, i.e. biodegradation of at least 60% of the ThOD in a 10-day window within the 28-day period of the test, was reached. Therefore, the test substance can be classified as readily biodegradable under the test conditions within 28 days.

In the toxicity control, the course of biodegradation over the 28-day exposure period was similar to the two procedure controls (containing only the reference item) during the first 8 days of exposure. Thereafter until the end of the test, the run of the curve of the oxygen consumption was significantly higher than the one of the two procedure controls. Within 14 days of exposure, biodegradation amounted to 41%. Thus, according to the test guidelines, the test item had no inhibitory effect on activated sludge microorganisms at the tested concentration of 100 mg/L because biodegradation in the toxicity control was >25% within 14 days.
Results with reference substance:
The percent biodegradation of the reference item sodium benzoate was calculated based on the theoretical oxygen demand of 1.67 mg O2/mg.
In the procedure controls, the reference item sodium benzoate was degraded by an average of 85% by Exposure Day 14, and reached an average biodegradation of 88% by the end of the test (Day 28), thus confirming suitability of the activated sludge.

Table 5.2.1/2: Biodegradation in the test flasks

Time (days)

Percentage Biodegradation1

Test item

Procedure control

Toxicity control

Replicate No.

Replicate No.

Replicate No.

1

2

1

2

1

0

0

0

0

0

0

1

0

0

11

10

7

2

-

-

-

-

-

3

-

-

-

-

-

4

7

7

68

69

23

5

12

13

72

74

25

6

17

18

75

76

26

7

23

24

77

78

27

8

30

31

79

80

29

9

-

-

-

-

-

10

-

-

-

-

-

11

49

52

83

83

34

12

54

58

85

84

36

13

57

62

86

84

38

14

59

65

86

84

41

15

61

67

87

86

44

16

-

-

-

-

-

17

-

-

-

-

-

18

66

72

89

85

52

19

68

74

89

86

55

20

69

75

90

85

58

21

70

76

90

85

61

22

70

77

90

85

63

23

-

-

-

-

-

24

-

-

-

-

-

25

73

80

91

85

70

26

74

81

92

85

72

27

75

81

92

85

73

28

77

83

92

85

75

Mean (Day 28)

80

88

not applicable

 

1 Corrected for the mean oxygen uptake of the inoculum controls

-- Not determined

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
At the end of the 28-day exposure period, the mean biodegradation of the test substance amounted to 80%. Moreover, the pass level for ready biodegradability, i.e. biodegradation of at least 60% of the ThOD in a 10-day window within the 28-day period of the test, was reached. Therefore, the test substance can be classified as readily biodegradable under the test conditions within 28 days.
Executive summary:

In a ready biodegradation study performed according to OECD Guideline 301 F and GLP, test substance was tested at a concentration of 100 mg/L and the inoculum was activated sewage sludge, domestic. The degradation of the test material was assessed by the determination of the oxygen consumption. The test treatments, inoculum blank and procedure control were measured in duplicates and one vessel was used for toxicity control.

The percent biodegradation of the test item was calculated based on the theoretical oxygen demand (ThOD) of 3.09 mg O2/mg test item. The biochemical oxygen demand (BOD) of the test substance in the test media significantly increased between Exposure Day 1 and 4 until test termination after 28 days. At the end of the 28-day exposure period, the mean biodegradation of the test substance amounted to 80%. Consequently, the test substance was found to be biodegradable under the test conditions within 28 days. Moreover, the pass level for ready biodegradability, i.e. biodegradation of at least 60% of the ThOD in a 10-day window within the 28-day period of the test, was reached.

In the toxicity control, containing both the test substance and the reference item sodium benzoate, the test substance had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration of 100 mg/L. In the procedure controls, the reference item sodium benzoate was degraded by an average of 85% by Exposure Day 14, and reached an average biodegradation of 88% by the end of the test (Day 28), thus confirming suitability of the activated sludge.

Therefore, the test substance can be classified as readily biodegradable under the test conditions within 28 days.

Description of key information

OECD Guideline 301F, GLP, key study, validity 1:

80% biodegradation after 28 days within the 10-day window.

Readily biodegradable.

Non-toxic to microorganisms up to 100 mg/L.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

One valid key study is available (Harlan, 2009), to assess the readily biodegradation of the registered substance.

This study was performed on the registered substance according to OECD Guideline 301F and GLP. The test substance at 100 mg/L was inoculated with activated sludge from a wastewater treatment plant, treating predomantly domestic wastewater. The degradation of the test substance was assessed by the determination of the oxygen consumption. At the end of the 28-day exposure period, the mean biodegradation of the test substance amounted to 80% within the 10 -day window. Therefore, the test substance is considered readily biodegradable. In the toxicity control, containing both the test substance and the reference substance (sodium benzoate), the test substance had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration of 100 mg/L. In the procedure controls, the reference substance was degraded by an average of 85% by Exposure Day 14, and reached an average biodegradation of 88% by the end of the test (Day 28), thus confirming suitability of the activated sludge.