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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:
2015
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reference:
Composition 0
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Test material information:
Composition 1
Specific details on test material used for the study:
None.
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
The inoculum was obtained on 13 October 2015 from the activated sludge of the biological wastewater treatment plant from Mourenx (France, 64) which handles predominantly domestic sewage. On arrival at the laboratory, the sludge (around 2 L) was centrifuged at approximately 20°C for 10 min at 1000 g; the solid sewage inoculant portion was re-suspended in dilution water in order to keep the concentration unchanged with respect to the sample. The inoculum was preconditioned 48 hours (aeration) until the flasks were inoculated. Sub-samples of the homogenisedhomogenized sludge were dried in an oven at approximately 105°C and the suspended solids content determined to be 3.47 g/L. The inoculum was not adapted to the test item before the biodegradation test.
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
The test was conducted in the respirometer BSBdigi Selutec® where the temperature was monitored over the duration of the test using a digital maximum/minimum calibrated thermometer. A total of 7 bioreactors were used; 2 each for test item, blank control, reference item control and one for toxicity control. Recorded test temperatures were between 21.9 and 22.5°C. pH ranged between 7.1 and 7.4 among flasks during the test
Reference substance:
benzoic acid, sodium salt
Preliminary study:
None.
Test performance:
All validity criteria were met.
Key result
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Details on results:
Under test conditions, no biodegradation of 1,3-dibutylethylthiourea was observed. DBTU showed no toxicity to the inoculum, as the toxicity control (containing both DBTU and sodium benzoate) did show biodegradation of sodium benzoate higher than 25% after 28 days.
Results with reference substance:
Biodegradation of sodium benzoate was 96% after 14 days.

Table 2: Biodegradation (%) calculated in each reactor.

Day

Fc1

Fc2

Average Fc

Ft1

Ft2

Average Ft

Fi

0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

1

24.3

22.5

23.4

0.0

0.0

0.0

9.6

2

40.2

38.2

39.2

0.0

0.0

0.0

15.6

3

59.1

55.1

57.1

0.0

0.0

0.0

19.5

4

77.3

74.8

76.1

0.0

0.0

0.0

31.6

5

83.3

79.9

81.6

0.0

0.0

0.0

33.1

6

86.6

83.7

85.1

0.0

0.0

0.0

34.3

7

89.6

86.7

88.1

0.0

0.0

0.0

35.3

8

91.2

88.7

89.9

-0.4

-0.4

-0.4

35.8

9

92.1

90.1

91.1

-1.1

-1.1

-1.1

36.0

10

93.3

91.9

92.6

-1.6

-1.6

-1.6

36.2

11

94.2

93.2

93.7

-2.3

-2.3

-2.3

36.0

12

95.0

94.5

94.7

-2.9

-2.9

-2.9

36.1

13

95.6

95.3

95.5

-3.5

-3.5

-3.5

35.7

14

96.2

95.8

96.0

-4.1

-4.1

-4.1

35.6

15

96.9

96.2

96.6

-4.6

-4.6

-4.6

35.4

16

97.5

96.6

97.0

-5.0

-5.0

-5.0

35.4

17

97.7

96.8

97.3

-5.3

-5.5

-5.4

35.2

18

98.3

97.2

97.7

-4.9

-5.7

-5.3

35.2

19

98.3

97.7

98.0

-5.3

-6.1

-5.7

35.1

20

98.5

98.2

98.3

-5.3

-6.3

-5.8

35.2

21

98.7

98.8

98.7

-5.5

-6.5

-6.0

35.2

22

98.9

99.2

99.1

-5.7

-6.7

-6.2

35.1

23

99.0

99.5

99.2

-5.5

-6.8

-6.1

35.1

24

99.1

99.8

99.4

-5.5

-6.9

-6.2

35.1

25

99.2

99.8

99.5

-5.7

-7.0

-6.3

35.2

26

99.2

99.9

99.6

-4.9

-6.5

-5.7

35.2

27

99.4

99.9

99.7

-5.1

-6.7

-5.9

35.1

28

99.5

100.2

99.8

-5.1

-6.7

-5.9

35.2

Ft: Test item

Fc: Reference control

Fi: Toxicity control

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
1,3-dibutylthiourea is not readily biodegradable.
Executive summary:

The study was conducted in accordance with procedures outlined in OECD Guideline 301F (1992). The ready biodegradability of 1,3 -dibutylthiourea was investigated over a 28 days period. The test was conducted at a nominal loading rate of 100 mg/L. A total of 7 bioreactors were used; 2 each for test item, blank control, reference item control and one for toxicity control.

 

The results of the test were as follows:

- The test item was not readily biodegradable under the conditions of the test as it failed to achieve a transition from 10% to 60% degradation in a 10-day window during the 28 days test.

- The test item was not considered to be inhibitory to the microbial inoculum since the biodegradation observed in the toxicity control bioreactor was not less than 25% after 14 days.

- Under test conditions, no biodegradation of 1,3 -dibutythiourea was observed.

The validity criteria were met:

- The percentage degradation of the reference compound has reached the pass levels by day 14: 96.0%

- The biodegradation observed in the toxicity control bioreactor was not less than 25% after 14 days: 35.6%

- The oxygen uptake of the inoculum blank was not greater than 60 mg/l in 28 days: 18.0 mg/L

- 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 pH value was not outside the range 6-8.5: min 7.4, max 8.1

Description of key information

The key study showed that 1,3 -dibutylthiourea is not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information