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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:
16 February 2016 to 15 March 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Ruhrverband Kläranlage, Sunthelle 6, 57392 Schmallenberg, Germany
- Storage conditions: samples were kept aerobic until use
- Storage length: samples were taken the day of test start
- Preparation of inoculum for exposure: The sludge was left for settlement for ca. one hour. Subsequently the supernatant was discarded and the concentration of suspended solids was measured in the remaining sludge.
- Concentration of sludge: 4.1 g/L
Duration of test (contact time):
28 d
Initial conc.:
80 mg/L
Based on:
test mat.
Initial conc.:
203.6 mg/L
Based on:
ThOD
Remarks:
NO3 (with nitrification)
Initial conc.:
52.8 mg/L
Based on:
ThOD
Remarks:
NH3 (without nitrification)
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral medium (please refer to "Any other information on materials and methods incl. tables")
- Test temperature: 22 °C, maintained by a built in thermostat
- pH: 7.2 at the start of test, 7.5 - 8.3 at the end of the test
- pH adjusted: No
- Aeration of dilution water: Yes (continuous stirring)
- Suspended solids concentration: 29.6 mg/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 500 mL reaction vessels
- Number of culture flasks/concentration: two replicates each for test item, inolculum control, procedure control, toxicity control and abiotic control.
- Measuring equipment: Sapromat respirometer (Voith Inc.)
- Details of trap for CO2 and volatile organics if used: soda lime to absorb CO2

SAMPLING
- Sampling frequency: Oxygen consumption was measured and recored contiinuously throughout the duration of the test.
- Sampling method: respirometer

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes
- Abiotic sterile control: Yes
- Toxicity control: Yes
Reference substance:
benzoic acid, sodium salt
Preliminary study:
Not performed
Test performance:
With a maximum of 9%, the difference of extremes of replicate values of the removal of the test item at the end of the test was less than 20%.
The percentage degradation of the reference item has exceeded the pass level of 60% by day 14. Biodegradation in the toxicity control was >25% by day 14.
The oxygen uptake of the inoculum blank is <60 mg/L in 28 days and the pH value was inside the range of 6.0 - 8.5.
Key result
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Details on results:
No biodegradation of the test item in the test media could be calculated since less oxygen was consumed in the test media than in the blank inoculum and a standard deviation of 6.4 % based on ThODNH3 and 1.7% based on ThOD NO3 were respectively observed after 28 days of incubation. No biodegradation within the 10-day-window could be calculated since the start criterion of the window (10 % degradation rate) was not reached within the 28 days of incubation.
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 (ThOD) In the procedural controls, the reference item was degraded by an average of 87 % by Exposure Day 14, thus confirming suitability of the activated sludge. At the end of the test (Day 28), the reference item was degraded by an average of 94 %.

The percentage biodegradation of test material and of the reference item sodium benzoate was calculated based on their biochemical oxygen demand (BOD) and theoretical oxygen demand (ThOD). Since the test item contains nitrogen, the percent biodegradation was calculated based on the ThODNH3 (considering that nitrification is absent) and ThODNO3 (considering that nitrification is complete). However, since the biodegradation rate – even considering the total lack of nitrification – was clearly below the threshold value for ready biodegradability, the effects of nitrification did not need to be considered.

The biodegradation of the test item and the reference item in the test over 28 days are presented in the table below:

Time

(days)

Percentage Biodegradation1

Test item based on

Procedure control based on

Toxicity control based on

ThODNH3

ThODNO3

ThOD

ThODNH3

ThODNO3

Flask No.

Flask No.

Flask No.

Flask No.

Flask No.

1

2

1

2

1

2

1

2

1

2

0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

1

-8.5

-0.9

-2.2

-0.2

30.3

29.1

7.5

2.1

4.5

1.2

2

-13.6

-1.5

-3.5

-0.4

44.7

45.9

34.9

36.2

20.7

21.5

3

-16.7

-1.5

-4.3

-0.4

55.5

55.5

42.6

42.6

25.3

25.3

4

-22.7

-7.6

-5.9

-2.0

63.9

64.5

49.9

52.7

29.6

31.2

5

-22.7

-7.6

-5.9

-2.0

70.0

76.6

54.0

56.3

32.0

33.4

6

-19.7

-7.6

-5.1

-2.0

73.6

80.2

56.8

59.0

33.6

35.0

7

-16.7

-4.5

-4.3

-1.2

77.2

82.6

59.0

60.0

35.0

35.5

8

-18.2

-6.1

-4.7

-1.6

79.3

84.1

59.7

61.1

35.4

36.2

9

-18.2

-9.1

-4.7

-2.4

79.9

85.3

61.1

62.0

36.2

36.7

10

-18.2

-6.1

-4.7

-1.6

81.1

86.5

61.6

62.9

36.5

37.3

11

-18.2

-6.1

-4.7

-1.6

81.1

86.5

62.5

63.4

37.0

37.6

12

-18.2

-6.1

-4.7

-1.6

81.1

86.5

62.9

63.8

37.3

37.8

13

-22.7

-13.6

-5.9

-3.5

85.0

88.0

62.2

63.6

36.9

37.7

14

-22.7

-10.6

-5.9

-2.8

85.6

88.6

62.7

64.1

37.1

38.0

15

-19.7

-10.6

-5.1

-2.8

86.2

89.2

63.1

64.5

37.4

38.2

16

-19.7

-10.6

-5.1

-2.8

86.8

90.4

63.6

65.0

37.7

38.5

17

-19.7

-10.6

-5.1

-2.8

87.4

91.0

63.6

65.0

37.7

38.5

18

-21.2

-12.1

-5.5

-3.1

87.7

90.7

63.8

65.2

37.8

38.6

19

-18.2

-9.1

-4.7

-2.4

88.3

91.3

64.3

66.1

38.1

39.2

20

-18.2

-9.1

-4.7

-2.4

88.9

91.9

64.7

66.1

38.4

39.2

21

-18.2

-9.1

-4.7

-2.4

89.5

92.5

64.7

66.6

38.4

39.4

22

-18.2

-9.1

-4.7

-2.4

90.7

92.5

64.7

67.0

38.4

39.7

23

-19.7

-10.6

-5.1

-2.8

91.0

92.8

65.4

66.8

38.8

39.6

24

-19.7

-10.6

-5.1

-2.8

91.6

93.4

65.9

66.8

39.0

39.6

25

-16.7

-7.6

-4.3

-2.0

92.2

94.0

66.3

67.7

39.3

40.1

26

-16.7

-7.6

-4.3

-2.0

92.8

94.6

66.3

67.7

39.3

40.1

27

-18.2

-9.1

-4.7

-2.4

93.1

94.9

66.6

67.9

39.4

40.3

28

-18.2

-9.1

-4.7

-2.4

93.1

94.9

67.0

68.4

39.7

40.5

Mean (Day 28)

-13.6

-3.5

94.0

64.7

40.1

1 Corrected for the mean oxygen uptake of the inoculum

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The ready biodegradability of the test substance was investigated at a concentration of 80 mg/L in a valid manometric respirometry test according to the OECD guideline 301F, using domestic aerobic activated sewage sludge incubated at 22°C in the dark over 28 days under continuous stirring. The test item was not readily biodegradable under the conditions of the test.
Executive summary:

The ready biodegradability of the test substance was investigated at a concentration of 80 mg/L in a valid manometric respirometry test according to the OECD guideline 301F, using domestic aerobic activated sewage sludge incubated at 22°C in the dark over 28 days under continuous stirring. The biochemical oxygen demand (BOD) was measured daily and the percentage degradation was calculated from the theoretical oxygen demand (ThOD) after correcting for the BOD of inoculum controls.As a procedure control, the reference item sodium benzoate was tested. The toxicity control contained both test material and the reference item sodium benzoate. No biodegradation of the test item in the test media could be calculated since less oxygen was consumed in the test media than in the blank inoculum and a standard deviation of 6.4 % based on ThOD NH3 and 1.7% based on ThOD NO3 were respectively observed after 28 days of incubation.

The test item was found to be not readily biodegradable under the conditions of the test within 28 days.

Description of key information

The test substance was not readily biodegradable in a valid manometric respirometry test according to OECD 301F.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

No biodegradation of the test item in the test media could be calculated since less oxygen was consumed in the test media than in the blank inoculum and a standard deviation of 6.4% based on ThODNH3 and 1.7% based on ThODNO3 were respectively observed after 28 days of incubation. No biodegradation within the 10-day window could be calculated since the start criterion of the window (10% degradation rate) was not reached within the 28 days of incubation.