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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:
06 May - 03 Jun 2016
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:
1992
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Version / remarks:
2008
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: Sewage treatment plant Rossdorf, Germany
- Laboratory culture: no
- Preparation of inoculum for exposure: The aerobic activated sludge used for this study was washed by centrifugation and the supernatant liquid phase was decanted. The solid material was re-suspended in tap water and centrifuged again. This procedure was done three times. An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge to its dry weight was determined. Based on this ratio, calculated aliquots of washed sludge suspension, corresponding to 3.5 g dry material per litre were mixed with test water and aerated for two days. This suspension was used for the experiment.
Duration of test (contact time):
28 d
Initial conc.:
103.7 mg/L
Based on:
test mat.
Initial conc.:
254.6 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: according to guideline
- Test temperature: 22 ± 1 °C
- pH (end): 7.2 - 7.4 (test material), 7.5 (inoculum control), 7.6 (reference substance)
- pH (start): 7.6
- pH adjusted: no
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: Manometric Test System with test flasks volume of approx. 500 mL
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: continuous stirring
- Measuring equipment: BSD/BOD sensor system
- Test performed in open system: no, gas-tight closed bottles
- Details of trap for CO2 and volatile organics if used: 45% potassium hydroxide solution was used for trapping of CO2.
- Other: The amounts of test item and reference item were directly weighed into the test flasks. No emulsifiers or solvents were used.

SAMPLING
- Sampling frequency: continuous measurement of of O2 consumption
- Sampling method: BSD/BOD sensor system
- Sample storage before analysis: no storage, continuous analysis

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, 2 bottles
- Abiotic sterile control: yes, 1 bottle
- Toxicity control: yes, 1 bottle
- Other: procedure control: yes, 1 bottle
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (O2 consumption)
Value:
64
Sampling time:
28 d
Remarks on result:
other: Mean value of two replicates.
Details on results:
No degradation was recorded in the abiotic sterile control.
Results with reference substance:
The reference substance was degraded to 83% after 14 d and 88% after 28 d confirming the suitability of the inoculum.

The test substance is not expected to be inhibitory/toxic to the inoculum since 38% degradation was recorded in the toxicity control after 14 d and 53% after 28 d.

Table 2: Percent degradation of the test substance

Time [d]

Percentage degradation

Flask 1

Flask 2

1

0

0

2

4

2

3

4

2

4

12

6

5

16

8

6

20

12

7

22

14

8

25

18

9

26

21

10

28

21

11

30

25

12

34

29

13

37

34

14

40

36

15

44

40

16

47

41

17

49

41

18

49

45

19

51

47

20

53

51

21

55

53

22

57

55

23

57

55

24

59

57

25

61

59

26

63

59

27

65

61

28

67

61

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
Since Tetraesters of pentaerythritol with heptanoic acid and 3,5,5-trimethylhexanoic acid is a UVCB substance and consists of structurally similar constituents with [e.g. different chain-lengths, degree and/or site of branching or stereo-isomers], sequential (instead of concurrent) biodegradation of the individual structures can take place, but all can be considered as readily biodegradable. Thus, referring to Annex I to the OECD Guideline for Testing of Chemicals ‘Revised introduction to the OECD guidelines for testing of chemicals, section 3’ (OECD, March 2006), the 10-day window should not be considered for this UVCB substance and due to a degradation of >60 % within 28 days the substance can be regarded as readily biodegradable.

Description of key information

Readily biodegradable: 64% after 28 d (O2 consumption; 10-day window not applicable)

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

One experimental study is available investigating the ready biodegradability of Tetraesters of pentaerythritol with heptanoic acid and 3,5,5-trimethylhexanoic acid (List number 805-289-4; Hammesfahr, 2016). The study was conducted according to OECD 301F using non-adapted activated sludge from a municipal sewage treatment plant. After 28 d a biodegradation of 64% (O2 consumption) was recorded. Since Tetraesters of pentaerythritol with heptanoic acid and 3,5,5-trimethylhexanoic acid is a UVCB substance and consists of structurally similar constituents with [e.g. different chain-lengths, degree and/or site of branching or stereo-isomers], sequential (instead of concurrent) biodegradation of the individual structures can take place, but all can be considered as readily biodegradable. Thus, referring to Annex I to the OECD Guideline for Testing of Chemicals ‘Revised introduction to the OECD guidelines for testing of chemicals, section 3’ (OECD, March 2006), the 10-day window should not be considered for this UVCB substance and due to a degradation of >60 % within 28 days the substance can be regarded as readily biodegradable.