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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:
2016-05-23 to 2016-07-13
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Aerobic activated sludge (microorganisms from a domestic waste¬water treatment plant)
- supplied by the sewage treatment plant of Rossdorf, Germany.- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure):
- 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 deter-mined. Based on this ratio, calculated aliquots of washed sludge suspension, corresponding to 3.5 g dry material per litre were mixed with test water (see 6.5) and aerated overnight. This suspension was used for the experiment.
- Concentration of sludge: 3.5 g dry material per litre

Duration of test (contact time):
28 d
Initial conc.:
102.7 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium:
Analytical grade salts were added to pure water to prepare the following stock solutions:
a) 8.5 g KH2PO4, 21.75 g K2HPO4, 33.4 g Na2HPO4 x 2 H2O, 0.5 g NH4Cl filled up with pure water to 1000 mL volume; The pH-value was 7.4.
b) 11.25 g MgSO4 x 7 H2O filled up with pure water to 500 mL volume
c) 18.2 g CaCl2 x 2 H2O filled up with pure water to 500 mL volume
d) 0.125 g FeCl3 x 6 H2O filled up with pure water to 500 mL volume
In order to avoid precipitation of iron hydroxide in the stock solution d), one drop of concentrated HCl per litre was added before storage.
50 mL of stock solution a) and 5 mL of the stock solutions b) to d) were combined and filled up to a final volume of 5000 mL with pure water.

- Test temperature: 22°C ± 1°C
- pH: 7.6 (measured at the start of the test); 7.6 to 8.4 (measured at the end of the test)
- pH adjusted: no
- Aeration of dilution water:
- Suspended solids concentration: 3.5 g/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: Manometric Test System with test flasks containing a volume of approximately 500 mL,.BSB/BOD-Sensor-System, Aqualytic Dortmund, Germany, positioned in climatic chamber. The amounts of test item and reference item were directly weighed into the test flasks.
- Number of culture flasks/concentration: 2
- Measuring equipment: The consumption of oxygen was determined by measuring the change of pressure in the flasks. Evolved carbon dioxide was absorbed in an aqueous solution (45%) of potassium hydroxide.

SAMPLING
- Sampling frequency and method: The change of pressure in the test flasks was meas-ured by means of a manometric method (BSB/BOD-Sensor-System, Aqualytic Dortmund, Germany) each day.

CONTROL AND BLANK SYSTEM
- Inoculum blank: see below table
- Abiotic sterile control: see below table
- Toxicity control: see below table

STATISTICAL METHODS:
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Details on results:
Toxicity control: 32% biodegradation was noted after 14 and 28 days of incubation based on ThODNH4. Hence, the test item can be assumed to be not inhibitory to the aerobic activated sludge microorganisms be-cause degradation was >25% within 14 days.
Results with reference substance:
The reference item sodium benzoate was sufficiently degraded to 88% after 14 days and after 28 days of incubation. The percentage biodegradation of the reference item confirms the suitability of the used aerobic activated sludge inoculum.

Table3. Percentage Biodegradation of Test Item and of the Toxicity Control based on ThODNO3, and of Sodium Benzoatebased on ThODNH4

Time

Percentage Biodegradation1

(Days)

Test Item1

Sodium Benzoate2

Toxicity
control1, 2

 

Flask 1 [%]

Flask 2 [%]

Flask 5 [%]

Flask 7 [%]

1

0

0

12

4

2

0

0

21

7

3

0

0

26

10

4

0

2

44

16

5

0

2

56

19

6

1

1

66

22

7

0

0

76

25

8

0

0

79

26

9

0

0

82

27

10

1

0

81

27

11

0

0

82

27

12

0

0

85

28

13

2

0

85

28

14

2

2

88

29

15

1

1

87

29

16

2

0

88

29

17

2

2

88

29

18

2

2

88

29

19

2

1

87

30

20

2

0

88

29

21

2

0

88

29

22

0

0

85

28

23

0

0

88

28

24

1

0

87

29

25

0

0

88

28

26

0

0

88

28

27

0

0

88

29

28

0

0

88

29

            1ThODNO3of Isophorone amino alcohol (IPAA): 2.989 mg O2/mg test item
            2ThODNH4of sodium benzoate: 1.666 mg O2/mg reference item

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
The test item is considered to be not readily biodegradable.
Executive summary:

The ready biodegradability of the test item was determined with non-adapted activated sludge in the Manometric Respirometry Test for a period of 28 days. The study was conducted according to OECD guideline 301 F and regulation 440/2008/EC C.4-D at IBACON GmbH, Rossdorf, Germany.

The oxygen was depleted by the respiration of bacteria and the degradation was followed by measuring the oxygen. The test item concentration selected as appropriate was 102.7 mg/L, corresponding to269.1 mg/L(ThODNH4). The biodegradation rate is expressed as the percentage BOD (biological oxygen demand) and was calculated for each study day.

The mean biodegradation at test end of the test af-ter 28 days was 0% (ThODNH4, ThODNO3). Therefore, the test item is considered to be not readily biodegradable. The validity criteria of the guideline are fulfilled.

Description of key information

The ready biodegradability of the test item was determined with non-adapted activated sludge in the Manometric Respirometry Test for a period of 28 days. The study was conducted according to OECD guideline 301 F and regulation 440/2008/EC C.4-D at IBACON GmbH, Rossdorf, Germany.

The mean biodegradation at test end of the test af-ter 28 days was 0% (ThODNH4, ThODNO3). Therefore, the test item is considered to be not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information