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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:
April 05 - June 18, 2019
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:
1992
Deviations:
no
Remarks:
In accordance with the test guidelines the test was prolonged to 35 days since the biodegradation curve of the test item showed that biodegradation had started but the plateau had not been reached by Exposure Day 28.
Qualifier:
according to
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Version / remarks:
2008
Qualifier:
according to
Guideline:
EPA OPPTS 835.3110 (Ready Biodegradability)
Version / remarks:
1998
GLP compliance:
yes (incl. certificate)
Remarks:
Swiss Federal Office of Public Health, Consumer protection directorate, Notification authority for chemicals, Bern, Switzerland
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Duration of test (contact time):
> 28 - <= 35 d
Initial conc.:
100 mg/L
Based on:
test mat.
Initial conc.:
266 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: according to guideline, prepared in purified water
- Test temperature: 23 °C in a thermostatic cabinet
- pH: 7.4 (test start), 7.3 - 7.8 (test end)
- pH adjusted: The pH of the test medium was adjusted from 7.7 to 7.4 with a diluted hydrochloric acid solution.
- Suspended solids concentration: 30 mg/L
- Continuous darkness: no, diffuse lighting

TEST SYSTEM
- Culturing apparatus: laboratory glass bottles GL45 (nominal volume: 500 mL; fill volume: 164 mL), air-tight closed with OxiTop measuring heads.
- Number of culture flasks/concentration: 2
- Measuring equipment: OxiTop Control system consisting of pressure measuring heads, test bottles, inductive stirring system and the OxiTop® OC 110 Controller
- Test performed in closed vessels: yes
- Details of trap for CO2 and volatile organics if used: CO2 was absorbed by an alkali trap which caused a net reduction in gas pressure within the test vessel.

SAMPLING
- Sampling frequency: BOD values were recoreded automatically every four hours.
- Sampling method: No sampling was necessary since the pressure reduction was continuously detected.
- Sterility check if applicable: no

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, two replicates
- Abiotic sterile control: no
- Toxicity control: yes, 1 replicate
- Other: procedure control: yes, 2 bottles
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
30
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
33
Sampling time:
35 d
Results with reference substance:
The biodegradation of the reference item reached values of 60 % and 89 % by Day 3 and Day 14, respectively. After 28 days and at the end of the test (Day 35), the average biodegradation was 95 %.

Table 1: % degradation of the test item

 

Percentage Biodegradation

 

Test Item

Procedure Control

Toxicity Control

Time

Replicate No.

Replicate No.

Replicate No.

[Days]

1

2

1

2

1

0

0

0

0

0

0

1

2

2

22

19

10

2

4

3

46

49

19

3

4

5

60

60

27

4

5

5

71

70

30

5

5

6

74

74

31

6

6

8

78

80

33

7

8

9

79

83

34

8

11

10

82

84

35

9

12

11

81

85

35

10

15

12

84

88

36

11

16

13

86

90

37

12

16

13

86

91

38

13

16

15

85

90

38

14

17

15

87

91

39

15

17

15

86

91

40

16

17

15

87

92

40

17

19

16

88

92

41

18

19

16

89

94

41

19

19

17

89

93

41

20

19

19

91

95

42

21

20

23

89

94

41

22

21

28

90

95

42

23

21

32

91

95

42

24

21

34

90

94

43

25

22

35

92

96

43

26

22

36

93

96

43

27

22

36

93

96

43

28

23

38

93

97

44

29

23

39

93

96

43

30

23

38

94

98

44

31

24

39

94

97

43

32

23

40

94

97

44

33

23

40

93

97

43

34

24

42

93

97

44

35

25

42

93

96

43

Mean (Day 35)

33

95

not applicable

Validity of the test:

The test is considered to be valid, since the following criteria were met:

-       The difference between extremes of replicate values of the degradation of the test item at the end of the 10-day window is less than 20 %.

-       The percentage degradation of the reference item reached with 60 % by Exposure Day 3 the pass level for ready biodegradability (criterion: at least 60 % in a 10-day window by Day 14).

-       The test item is considered to be non-inhibitory, since the toxicity control attained 39 % degradation by Day 14 (criterion: >= 25 % degradation by Day 14).

-       The mean BOD of the inoculated mineral medium (control) was 23 mg O2/L after 28 days (criterion: normally 20-30 mg O2/L, but not greater than 60 mg O2/L after 28 days).

-       The pH was in the range of 7.3 to 7.8 in all test vessels after 35 days of exposure (criterion for the test item vessels: not outside the range 6.0 – 8.5).

Validity criteria fulfilled:
yes
Interpretation of results:
inherently biodegradable
Conclusions:
The test item was found to be not readily biodegradable after 28 days of exposure to activated sludge under the conditions of the conducted Manometric Respirometry Test. However, the obtained biodegradation values of 25 % and 42 % calculated for the two test item replicates after 35 days of incubation can be used to indicate inherent, primary biodegradability, based on the “Revised Introduction to the OECD Guidelines for Testing of Chemicals, Section 3” (2006).

Description of key information

Not readily biodegradable: 30 % after 28 d (O2 consumption, OECD 301F)

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

One experimental study is available investigating the biodegradation of the test item. The test item was investigated for its ready biodegradability in a manometric respirometry test according to OECD 301 F (1992) and GLP using activated sludge from a domestic sewage treatment plant (non-adapted). 100 mg/L (266 mg/L based on ThOD) of the test item was tested and the O2 consumption was measured automatically every 4 h for 35 days.

In accordance with the test guidelines the test was prolonged to 35 days since the biodegradation curve of the test item showed that biodegradation had started but the plateau had not been reached by Exposure Day 28.  The 10-Day window started on Day 8 and ended on Day 18 with a mean biodegradation value of 17 %. Therefore, the pass level for ready biodegradability, i.e. biodegradation of at least 60 % of the ThOD in a 10-Day window within a 28-day period of the test, was not reached. In conclusion, the test item was not readily biodegradable under the test conditions within 28 days. However, the obtained biodegradation values of 25 % and 42 % calculated for the two test item replicates after 35 days of incubation can be used to indicate inherent, primary biodegradability, based on the “Revised Introduction to the OECD Guidelines for Testing of Chemicals, Section 3” (2006). In addition a toxicity control was prepared containing test item and reference substance (benzoic acid, sodium salt) in order to assess possible toxic effects of the test item to the inoculum. In the toxicity control a biodegradation of 39 % by Day 14 and 43 % at the end of the test period (Day 35) was recorded indicating that the test item had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration of 101 mg/L.