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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:
19 July - 17 Aug 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)
Version / remarks:
26 Sep 2014
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.29 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test))
Version / remarks:
24 January 2014
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Remarks:
Swiss Federal Office for the Environment
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: aerobic activated sewage sludge from the aeration stage of the local wastewater treatment plant, which treats predominantly domestic sewage.
- Preparation of inoculum for exposure: The aerobic activated sewage sludge was washed twice by centrifugation, decantation of the supernatant liquid phase and resuspension of the solid material in tap water and finally in mineral medium
- Storage conditions: sludge was aerated with CO2-free air at room temperature
- Storage length: two days prior to use
- Pretreatment: dry weight of the sludge was determined and the sludge was diluted 1:1 with mineral medium
- Concentration of sludge: 4 mg dry material per liter
Duration of test (contact time):
28 d
Initial conc.:
19.1 mg/L
Based on:
TOC
Initial conc.:
25.7 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
inorg. C analysis
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: according to testing guidelines
- Test temperature: 20 ± 1 °C
- pH: 6.8 (test item bottle), 7.3 (inoculum control bottle)
- pH adjusted: yes, from 7.7 to 7.4
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 125 mL Wheaton glass serum bottles, with a total volume of around 160 mL, sealed with aluminum crimp caps with Teflon lined chlorobutyl septa
- Number of culture flasks/concentration: 30
- Method used to create aerobic conditions: sealed bottles with a headspace of air, which provides a reservoir of oxygen for aerobic biodegradation
- Measuring equipment: IC analyses were performed using TOC infrared gas analyzer (vario TOC cube, Elementar Analysensysteme GmbH, Germany, equipped with an automatic sampler)

SAMPLING
- Sampling frequency: Test item and inoculum control: Exposure Day 0, 2, 5, 7, 9, 14, 21 and 28; Procedure control (reference item): Exposure Day 0, 2, 7, 14 and 28; Toxicity control (test item + reference item): Exposure Day 0, 14 and 28.
- Sampling method: Triplicate bottles were measured on each sampling occasion throughout the test. Five bottles from each series (except the toxicity control) were analyzed at the end of the test

CONTROL AND BLANK SYSTEM
- Toxicity control: 1-octanol and test item
Reference substance:
other: 1-octanol
Test performance:
solubility pre-experiment: Test item was not soluble at 2950 μL/L (corresponding to 2.6 mg/L) in mineral medium. Therefore, no stock solution could be prepared.
Key result
Parameter:
% degradation (inorg. C analysis)
Value:
87
St. dev.:
1
Sampling time:
28 d
Results with reference substance:
Biodegradation was calculated based on TOC of 0.738 mg C/mg.
Procedure control: reference item degraded by an average of 70 % (Exposure Day 7) and 77 % (Exposure Day 14) which confirms suitability of the activated sludge (> 60 % degradation by Exposure Day 14). At the end of the 28-day exposure period, the mean percentage biodegradation of the five procedure control bottles sampled was 94 % (95% CI ± 5.6 %).

Table 1: Inorganic Carbon Concentration (IC) in the Test Flasks

IC found in test flasks (IC in mg C/L)

Time

(days)

Test item1

Reference item1

Replicate No.

Replicate No.

1

2

3

4

5

mean

1

2

3

4

5

mean

0

-0.1*

0.0

0.1

--

--

0.0

0.0

0.0

-0.1*

--

--

0.0

2

2.6

3.2

2.8

--

--

2.9

7.5

6.7

6.2

--

--

6.8

5

9.6

9.9

10.2

--

--

9.9

--

--

--

--

--

n.a.

7

12.2

12.3

12.1

--

--

12.2

13.7

11.9

14.2

--

--

13.2

9

13.2

13.1

12.0

--

--

12.7

--

--

--

--

--

n.a.

14

14.4

14.8

15.5

--

--

14.9

15.2

13.3

14.6

--

--

14.4

21

15.5

16.1

16.7

--

--

16.1

--

--

--

--

--

n.a.

28

16.7

16.2

16.6

16.4

16.7

16.6

17.3

16.1

18.1

19.3

17.1

17.6

Table 1 (continued): Inorganic Carbon Concentration (IC) in the Test Flasks

IC found in test flasks (IC in mg C/L)

Time

(days)

Inoculum Control

Toxicity Control1

Replicate No.

Replicate No.

1

2

3

4

5

mean

1

2

3

mean

0

0.8

0.8

0.8

--

--

0.8

0.3

0.3

0.8

0.5

2

0.8

0.8

0.7

--

--

0.8

--

--

--

n.a.

5

0.8

1.0

0.8

--

--

0.9

--

--

--

n.a.

7

0.8

0.8

0.9

--

--

0.8

--

--

--

n.a.

9

0.8

0.7

0.7

--

--

0.7

--

--

--

n.a.

14

0.7

0.9

0.7

--

--

0.8

14.5

15.9

14.4

15.0

21

0.9

0.8

0.8

--

--

0.8

--

--

--

n.a.

28

0.9

0.8

0.9

0.9

0.8

0.9

18.0

17.4

19.2

18.2

1: Corrected for the mean inoculum control.

--: No samples taken.

n.a.: Not applicable.

* Negative value due to slightly higher inorganic carbon concentration measured the inoculum controls than in the vessels with test item or reference item.

Table 2: Percentage Biodegradation of the Test Item CITRONELLYL BUTYRATE and the Reference Item 1-Octanol during the Incubation Period

Time

(days)

 

% Degradation

Test item

Reference item

Replicate No.

Replicate No.

1

2

3

4

5

mean

1

2

3

4

5

mean

0

-0.5*

0.0

0.5

--

--

0.0

0.0

0.0

-0.5*

--

--

-0.2*

2

13.8

16.9

14.8

--

--

15.2

40.1

35.9

33.2

--

--

36.4

5

50.4

52.0

53.5

--

--

52.0

--

--

--

--

--

n.a.

7

63.6

64.2

63.1

--

--

63.6

72.8

63.2

75.5

--

--

70.5

9

68.9

68.3

62.6

--

--

66.6

--

--

--

--

--

n.a.

14

75.5

77.6

81.2

--

--

78.1

81.1

71.0

77.9

--

--

76.7

21

80.9

84.0

87.2

--

--

84.0

--

--

--

--

--

n.a.

28

87.6

84.9

87.0

86.0

87.6

86.6

92.4

86.0

96.6

103.0

91.3

93.8

Table 2 (continued):

Time

(days)

 

% Degradation

Toxicity control1

Replicate No.

1

2

3

mean

0

1.6

1.6

4.3

2.5

2

--

--

--

n.a.

5

--

--

--

n.a.

7

--

--

--

n.a.

9

--

--

--

n.a.

14

77.4

84.9

76.9

79.7

21

--

--

--

n.a.

28

96.1

92.9

102.5

97.2

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The test item was found to be readily biodegradable under the test conditions, with a mean percentage biodegradation of 87 % (95 % CI of ± 1.0 %) at the end of the 28-day exposure period.
The pass level for ready biodegradability (IC production of at least 60 % of ThIC in a 10-day window within the 28-day test period) was reached on Exposure Day 7 (64 %).
The test item had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration of 25.7 mg/L.

Description of key information

Readily biodegradable according to OECD criteria (87 % degradation after 28 d, OECD 310).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

One experimental study is available investigating the biodegradability of the substance. The study was performed according to OECD 310 (GLP). Non-adapted, domestic activated sludge from a sewage treatment plant was used as inoculum. The test item was found to be readily biodegradable under the test conditions, with a mean percentage of 87 % degradation at the end of the 28-day exposure period. The pass level for ready biodegradability (IC production of at least 60 % of ThIC) was reached after 7 days of exposure. Thus, the test substance is considered to be “readily biodegradable” according to the OECD criteria. A toxicity control, containing both the reference substance and the test substance, had no inhibitory effect on the activity of activated sludge microorganisms (80% degradation by Exposure Day 14) at the tested concentration of 25.7 mg/L. All validity criteria of the study were met.

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