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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
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
Qualifier:
according to guideline
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Worlingworth sewage treatment works (Suffolk, UK)
- Method of cultivation / Preparation of inoculum for exposure: At the time of collection, the sludge was sieved (1 mm²) then transported to the laboratory and left stand for approximately 30 minutes to allow the sewage solids to settle. A portion of the supernatant was removed and the sludge aerated until required.
Duration of test (contact time):
28 d
Initial conc.:
50 mg/L
Based on:
COD
Initial conc.:
15 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 (MSM) according to guideline, prepared using tap-water that had been softened and treated by reverse osmosis and then purified; nominal resistivity ≥ 18 MegOhm.cm. The pH wasadjusted to 7.4 ± 0.2 with 5M HCl. This water complies with the relevant standards (British Standard (BS) 3978, 1987; American Society for Testing and Materials (ASTM) D 1193-06) for classification as Grade 1 or Type 1 water for laboratory use.
- Test temperature: 20 to 22°C.
- pH: 7.3 to 7.5 at the start of the test and 7.4 to 7.5 at the end
- pH adjusted: not necessary
- Suspended solids concentration: 30 mg/L
- Continuous darkness: not reported; amber glass bottles were used
- Other: The inoculum was added to the culture bottles 1 day before test initiation to allow a period of ageing.

TEST SYSTEM
- Culturing apparatus: amber glass culture bottles in a temperature controlled water bath
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: internal oxygen generating process
- Measuring equipment: Co-ordinated Environmental Services (CES) Ltd automated respirometer

SAMPLING
- Sampling frequency: continuous monitoring of the cumulative amount of oxygen consumed; the cumulative oxygen demand made by each cell was printed at, typically, hourly intervals

CONTROL AND BLANK SYSTEM
- Inoculum blank (2 flasks): inoculated mineral salts medium (MSM)
- Reference (1 flask): inoculated MSM + sodium benzoate (50 mg O₂/L)
- Toxicity control (1 flask): inoculated MSM + test material (50 mg O₂/L) + sodium benzoate (50 mg O₂/L)
- Nitrification test (1 flask): inoculated MSM + test material (50 mg O₂/L) + Allylthiourea (ATU, 11.6 mg/L)
- Nitrification control (1 flask): inoculated MSM + ATU (11.6 mg/L)

Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
23
Sampling time:
28 d
Details on results:
Mean oxygen consumption in biotic mixtures containing the test material was equivalent to 10% of the COD value after approximately 5 days and 23% at the end of the test (Day 28). A biodegradation plateau was observed from approximately Day 9.
In the nitrification controls (ATU inhibited) oxygen consumption was about twice as high as in uninhibited cultures (45% of COD at test end). This finding was not discussed in the report. However, it is regarded as not relevant for the outcome of the study.
In the presence of test material the degradation of sodium benzoate achieved 64% after 2 days indicating that the test substance was not inhibitory to the microbial inoculum.
Results with reference substance:
The reference substance sodium benzoate had achieved 61% of the ThOD after 2 days of incubation and 107% by Day 28.

Table 1: Biodegradation of the test and reference substances

 

% Biodegradation

Day

Test material

Test material

in the presence of ATU

Sodium Benzoate

Sodium Benzoate

in the inhibition mixture

Test 1

Test 2

Mean

1

1

1

1

1

2

0

2

3

4

3

8

61

64

3

5

6

5

15

63

-

4

7

7

7

17

67

-

5

10

10

10

20

70

-

6

13

15

14

23

73

-

7

17

17

17

26

77

-

8

18

19

19

28

81

-

9

20

20

20

30

86

-

10

21

22

21

32

90

-

11

21

22

22

33

93

-

12

22

23

22

33

96

-

13

22

23

23

34

99

-

14

23

24

23

35

101

-

15

23

24

23

35

103

-

16

23

24

24

36

104

-

17

23

24

24

36

104

-

18

23

23

23

36

104

-

19

23

23

23

37

105

-

20

23

23

23

38

105

-

21

23

22

22

39

105

-

22

23

22

22

40

105

-

23

23

21

22

41

106

-

24

23

21

22

42

106

-

25

23

21

22

43

107

-

26

24

20

22

44

107

-

27

24

20

22

44

107

-

28

25

21

23

45

107

-

 

Validity criteria fulfilled:
yes
Remarks:
the reference compound reached the pass level by day 2, the cumulative amount of oxygen consumed by the control mixtures was 34 and 36 mg O₂/L, difference between replicates of <20% (considered relevant only if the substance is readily biodegradable)
Interpretation of results:
inherently biodegradable
Conclusions:
The substance can be at least partially biodegraded (inherent, primary, biodegradability).

Description of key information

Biodegradation in water: screening tests: biodegradation 23% (COD) in 28 days (OECD 301F, EU C.4-D)

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable
Type of water:
freshwater

Additional information

Mean oxygen consumption in biotic mixtures containing the test material was equivalent to 10% of the COD value after approximately 5 days and 23% at the end of the test (Day 28). A biodegradation plateau was observed from approximately Day 9.


The results clearly show that the substance can be at least partially biodegraded (inherent, primary, biodegradability).