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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:
25 Oct - 22 Nov 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
17 Jul 1992
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
Staatliches Gewerbeaufsichtsamt Hildesheim, Germany
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Municipal sewage treatment plant, Hildesheim, Germany
- Storage conditions: aerobic (aeration with CO2-free air)
- Storage length: 6 d
- Preparation of inoculum for exposure: aqueous phase of non-adapted activated sludge
- Pretreatment: The activated sludge was washed twice with chlorine free tap water. After the second washing the settled sludge was resuspended in mineral salts medium and was maintained in aerobic conditions by aeration during 2.5 h. Thereafter, the sludge was homogenized with a blender. After sedimentation the supernatant was decanted and maintained in an aerobic condition by aeration with CO2-free air for 6 d.
- Initial cell/biomass concentration of the inoculum: 1.18E+09 colony forming units/L (standard dilution plate count)
Duration of test (contact time):
28 d
Initial conc.:
51.3 mg/L
Based on:
ThOD
Initial conc.:
38 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral salts medium according to OECD 301 F.
- Test temperature: 20.5 - 21.1°C
- pH: 7.68 - 7.78 (at test start), 7.66 - 8.07 (at test end)
- Colony forming units (CFU) in the test vessels: approximately 1.18E+07 CFU/L
- Continuous darkness: Yes, in an incubator.
- Other: Continuous stirring

TEST SYSTEM
- Culturing apparatus: brown glass bottles (500 mL)
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: Aeration with CO2-free air.
- Measuring equipment: OxiTop measuring heads, WTW
- Test performed in open system: No, the bottles were closed with OxiTop measuring heads.
- Details of trap for CO2 and volatile organics if used: A rubber sleeve with soda lime was hung into the bottles to absorb evolved CO2.
- Other: Test volume: 250 mL

SAMPLING
- Sampling frequency: The oxygen consumption was determined in the incubation vessels by the OxiTop measuring system every 112 min during the 28 d incubation period (360 measuring points).

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2 replicates containing mineral medium stock solutions, ultrapure water and inoculum.
- Functional control: 1 replicate containing reference item (45 mg/L = 75.2 mg O2/L) dissolved in mineral medium stock solutions, ultrapure water and inoculum.
- Toxicity control: 1 replicate containing the test item and reference item dissolved in mineral medium stock solutions, ultrapure water and inoculum.
- Other: Separate replicates of the test item and toxicity control were prepared for measurement of the pH-value at test start.
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
70
Sampling time:
28 d
Remarks on result:
other: mean of replicates
Results with reference substance:
The pass level for ready biodegradation (> 60% degradation) was reached on Day 3. The validity criterion that the devgradation should by > 60% after 14 d was fulfilled.
Stages of Biodegradation: The adaptation phase changed to degradation phase within 2 d (degradation > 10%) and the biodegradation reached a maximum of 92% on Day 23.

Both test item replicates reached the 10% level (beginning of biodegradation) on Day 6. The mean of replicates reached the 60% pass level on Day 13. The mean biodegradation on Day 28 was 70%.

In the toxicity control the biodegradation achieved 84% after 14 d and 92% after 28 d. The validity criterion that the test item should not inhibit the biodegradation of the reference item was fulfilled.

Table 1. Biodegradation [%] of the Test Item in Comparison to the Functional Control and Toxicity Control.

Date

 

Functional Control

 

Biodegradation [%]

 

Toxicity Control: Test Item + Reference Item

 

[d]

R1

P1

P2

T1

2016-10-26

1

7

0

0

5

2016-10-27

2

52

0

3

36

2016-10-28

3

65

0

4

42

2016-10-29

4

75

0

6

49

2016-10-30

5

79

4

7

51

2016-10-31

6

81

32

21

53

2016-11-01

7

83

47

46

61

2016-11-02

8

84

52

52

73

2016-11-03

9

86

54

54

77

2016-11-04

10

86

56

57

79

2016-11-05

11

87

57

59

81

2016-11-06

12

88

59

60

82

2016-11-07

13

88

61

62

83

2016-11-08

14

89

61

63

84

2016-11-09

15

90

64

65

86

2016-11-10

16

86

60

62

84

2016-11-11

17

87

60

61

85

2016-11-12

18

89

60

62

86

2016-11-13

19

88

63

63

87

2016-11-14

20

87

64

64

87

2016-11-15

21

89

63

65

87

2016-11-16

22

88

63

67

88

2016-11-17

23

92

67

70

91

2016-11-18

24

92

68

71

92

2016-11-19

25

91

68

71

91

2016-11-20

26

90

67

70

91

2016-11-21

27

91

67

72

92

2016-11-22

28

91

67

72

92


 

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
After a test period of 28 d, the test item is classified as readily biodegradable within the 10 d window and within the 28 d period of the study.

Description of key information

Readily biodegradable within the 10 d-window (70% after 28 d, OECD 301 F).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

There is one GLP study available investigating the ready biodegradability of the substance according to the OECD guideline 301 F.

In the Manometric Respirometry Test, a nominal concentration of 38 mg/L test item (equivalent to 51.3 mg ThO2/L) was inoculated with 1.18 1E7 colony forming units/L non-adapted, activated sludge over a period of 28 d. Degradation was followed by continuously measuring oxygen concentration in the test bottles. Inoculum, functional and toxicity controls were run in parallel. The percentage biodegradation was expressed in terms of biological oxygen demand.

On Day 28 the mean biodegradation of the test item was 70%. Both test item replicates reached the 10% level on Day 6 and the 60% pass level on Day13, thereby fulfilling the 10-d window. The toxicity control achieved 84% degradation within 14 d indicating no inhibitory effect of the test item on the metabolic activity of the inoculum. Therefore, the test item is classified as readily biodegradable.