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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:
2020
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)
Version / remarks:
17 July 1992
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: Beijing Xiaojiahe Sewage Treatment Work

- Pretreatment: The activated sludge was washed 3 times in the mineral medium through centrifugation (at 1100 g for 10 minutes). Thereafter the sludge was aerated before using. The aerated sludge was kept under test condition for about 5 days. After the pre-conditioning of inoculum, the sample was withdrawn just before using to measure the dry weight of the suspended solid.
Duration of test (contact time):
28 d
Initial conc.:
21.1 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Test temperature: 21.1 – 22.8℃
- pH: 7.42 – 7.52
- pH adjusted: no
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: BOD bottle (volume: approx. 500 mL)
- Number of culture flasks/concentration: 2
- Measuring equipment: BOD meter
- Test performed in closed vessels: yes

SAMPLING
- Sampling frequency: data on oxygen uptake was collected every 24 hours. During the test, the temperature of incubator was supervised daily and recorded. At the start and end of test, the pH of the contents of the bottles was measured.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Procedure control: yes
- Toxicity control: yes
- Test suspension: yes

STATISTICAL METHODS: Data was summarized in tabular form, showing percentage biodegradation of test group and procedure control. The difference of extremes of replicate values of the percentage degradation of test substance at the end of the test and the percentage degradation in 14 days of toxicity control were calculated using Excel.
Reference substance:
benzoic acid, sodium salt
Preliminary study:
no
Test performance:
164 mL inoculum blank / test suspension / procedure control / toxicity control solution was put into the test bottle, and the BOD equipment was assemble, the equipment check if it was air-tight, the stirrer was started, and the measurement of oxygen uptake was started. The developed CO2 was captured using excess NaOH. The test bottles were placed in incubator and kept in the dark except during observation for 28 days. Oxygen uptake and temperature was measured daily. At the start and end of test, the pH of the contents of the bottles was measured.
Key result
Parameter:
% degradation (O2 consumption)
Value:
82.74
Sampling time:
28 d
Details on results:
The average biodegradation on the 1st day was 32.31%, which was over 10%, so the 10-d window was fulfilled between 1-11 days. The percentage biodegradation of the test substance was 80.10% on day 11. It has reached the pass level of ready biodegradation (60% ThOD). On the 28th day, the average percentage biodegradation reached to 82.74%.

The details of percentage biodegradation are presented in Table 1 in the section “Any other information on results incl. tables”.
Results with reference substance:
The average biodegradation at the 1st day after exposure was 53.52 %, which was over 10%, so it has entered the 10-day window period. The average biodegradation increased to 87.28 % on day 14, it meant it reached pass level of ready biodegradation (60 %ThOD). On the 28th day after exposure, the average biodegradation reached to 87.13 %.

Table 1: The Determination of oxygen consumption and percentage biodegradation

Group

Beaker No.

Day

1

2

3

4

5

6

7

8

9

10

11

12

13

14

BOD (mg/L)

TB

(inoculum blank)

1

0.0

0.0

0.0

0.0

0.0

0.0

0.0

2.8

5.6

2.8

8.4

8.4

8.4

11.3

2

0.0

0.0

0.0

0.0

0.0

0.0

0.0

2.8

5.6

5.6

5.6

5.6

8.4

8.4

TS

(test suspension)

3

33.8

50.6

59.1

61.9

67.5

73.2

76.0

78.8

81.6

84.4

87.2

90.0

92.8

92.8

4

30.9

50.6

56.3

64.7

67.5

73.2

76.0

78.8

81.6

84.4

87.2

90.0

90.0

90.0

Biodegradation

(%)

32.31

50.54

57.63

63.22

67.41

73.11

75.90

75.90

75.90

80.10

80.10

82.89

82.89

81.45

PC

(procedure control)

5

53.5

64.7

67.5

70.3

73.2

78.8

81.6

84.4

87.2

87.2

90.0

92.8

95.7

95.7

6

53.5

61.9

67.5

70.3

73.2

78.8

81.6

84.4

87.2

90.0

92.8

95.7

95.7

98.5

Biodegradation

(%)

53.52

63.32

67.52

70.33

73.23

78.83

81.63

81.63

81.63

84.43

84.43

87.28

87.33

87.28

TC

(toxicity control)

7

50.6

95.7

110

118

127

132

138

143

149

152

155

160

163

166

Biodegradation

(%)

-

-

-

-

-

-

-

-

-

-

-

-

-

78.04

Continued from Table 1:

 

Group

Beaker No.

Day

15

16

17

18

19

20

21

22

23

24

25

26

27

28

BOD (mg/L)

TB

(inoculum blank)

1

11.3

11.3

11.3

14.1

11.3

14.1

14.1

14.1

14.1

16.9

16.9

16.9

16.9

16.9

2

8.4

8.4

11.3

11.3

11.3

11.3

11.3

14.1

14.1

14.1

14.1

14.1

16.9

16.9

TS

(test suspension)

3

92.8

92.8

92.8

95.7

95.7

95.7

95.7

95.7

98.5

98.5

98.5

98.5

98.5

98.5

4

92.8

92.8

92.8

95.7

95.7

95.7

98.5

98.5

98.5

98.5

98.5

101

98.5

101

Biodegradation

(%)

82.84

82.84

81.40

82.89

84.29

82.89

84.29

82.89

84.29

82.89

82.89

84.14

81.50

82.74

PC

(procedure control)

5

95.7

95.7

98.5

98.5

98.5

98.5

98.5

98.5

98.5

101

101

101

101

104

6

98.5

98.5

101

101

101

101

98.5

101

101

101

104

104

104

104

Biodegradation

(%)

87.28

87.28

88.48

87.08

88.48

87.08

85.83

85.68

85.68

85.53

87.03

87.03

85.63

87.13

TC

(toxicity control)

7

166

169

169

172

172

174

177

177

177

174

174

174

180

180

Biodegradation

(%)

-

-

-

-

-

-

-

-

-

-

-

-

-

-

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
In a study according OECD 301F, the result showed that the percentage biodegradation of the test item was 80.10 % at the end of the 10-d window, so the test item is regarded as readily biodegradable.
Executive summary:

The ready biodegradability of the test item was determined by measuring the percentage biodegradation of inoculum to the test item over a period of 28 days in a study according to  OECD Test Guideline 301 (F), Ready Biodegradability-Manometric Respirometry Test, 17 July 1992 and The Guidelines for the Testing of Chemicals-degradation and accumulation(second) 301. The activated sludge was washed 3 times in the mineral medium through centrifugation (at 1100 g for 10 minutes). Thereafter the sludge was aerated before using. The aerated sludge was kept under test condition for about 5 days. After the pre-conditioning of inoculum, the sample was withdrawn just before using to measure the dry weight of the suspended solid. This test was set in one treatment group at the concentration of 21.10 mg test item /L (corresponding to a ThODNH3 of 100 mg O2/L) with 2 replications, blank control group with 2 replications and procedure control group at the concentration of 60.02 mg reference item /L (corresponding to a ThOD of 100 mg O2/L) with 2 replications, the toxicity control group at the concentration of 21.10 mg test item /L(corresponding to a ThODNH3 of 100 mg O2/L) and 60.02 mg reference item /L (corresponding to a ThOD of 100 mg O2/L) without repeat and tested in BOD-bottles at the test condition for 28 days. All validity criteria were met. The maximum oxygen uptake of the inoculum blank was 16.9 mg/L in 28 days that wasn’t greater than 60 mg/L. For the procedure control, the average biodegradation increased to 87.28% on day 14, which means it reached pass level of ready biodegradation (60%ThOD). For the toxicity control test, the result showed that the biodegradation increased to 78.04% (more than 25%) on the 14th day, so the test substance can’t be assumed to be inhibitory. The result showed that the percentage biodegradation of the test item was 80.10 % at the end of 10-d window (1 day – 11 day) and 82.74 % at the end of the test (28 day), thus the test item is regarded as readily biodegradable.

Description of key information

The percentage biodegradation of the test item was 80.10 % at the end of the 10-d window, so the test item is regarded as readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information

The ready biodegradability of the test item was determined by measuring the percentage biodegradation of inoculum to the test item over a period of 28 days in a study according to  OECD Test Guideline 301 (F), Ready Biodegradability-Manometric Respirometry Test, 17 July 1992 and The Guidelines for the Testing of Chemicals-degradation and accumulation (second) 301. The activated sludge was washed 3 times in the mineral medium through centrifugation (at 1100 g for 10 minutes). Thereafter the sludge was aerated before using. The aerated sludge was kept under test condition for about 5 days. After the pre-conditioning of inoculum, the sample was withdrawn just before using to measure the dry weight of the suspended solid. This test was set in one treatment group at the concentration of 21.10 mg test item /L (corresponding to a ThODNH3 of 100 mg O2/L) with 2 replications, blank control group with 2 replications and procedure control group at the concentration of 60.02 mg reference item /L (corresponding to a ThOD of 100 mg O2/L) with 2 replications, the toxicity control group at the concentration of 21.10 mg test item /L(corresponding to a ThODNH3 of 100 mg O2/L) and 60.02 mg reference item /L (corresponding to a ThOD of 100 mg O2/L) without repeat and tested in BOD-bottles at the test condition for 28 days.

All validity criteria were met. The maximum oxygen uptake of the inoculum blank was 16.9 mg/L in 28 days that wasn’t greater than 60 mg/L. For the procedure control, the average biodegradation increased to 87.28% on day 14, which means it reached pass level of ready biodegradation (60% ThOD). For the toxicity control test, the result showed that the biodegradation increased to 78.04% (more than 25%) on the 14th day, so the test substance can’t be assumed to be inhibitory. The result showed that the percentage biodegradation of the test item was 80.10 % at the end of 10-d window (1 day – 11 day) and 82.74 % at the end of the test (28 day), thus the test item is regarded as readily biodegradable.

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