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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:
25 Feb - 25 Mar 2011
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)
Version / remarks:
17 Jul 1992
Deviations:
no
GLP compliance:
yes (incl. certificate)
Remarks:
Staatliches Gewerbeaufsichtsamt Hildesheim, Germany (20 Oct 2010)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Municipal sewage treatment plant, Hildesheim, Germany
- Pretreatment: The activated sludge was washed twice with autoclaved tap water. After the second washing the settled sludge was filled up with mineral salts medium and was maintained in an aerobic condition by aeration for 4 h. Thereafter the sludge was homogenized with a blender. The supernatant was decanted and maintained in an aerobic condition by aeration with CO2-free air for 6 d. 10 mL/L were used to initiate inoculation.
- Concentration of sludge: 1E07 - 1E08 CFU/L
- Initial cell/biomass concentration: 4.3E09 CFU/L
Duration of test (contact time):
28 d
Initial conc.:
25 mg/L
Based on:
test mat.
Initial conc.:
55 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral salts medium according to OECD 301 F
- Test temperature: 21.0 - 22.0 °C
- pH: 7.52 - 7.58 (test start), 7.66 - 7.99 (test end)
- Continuous darkness: Yes, in an incubator
- Dispersion treatment: Continuous stirring

TEST SYSTEM
- Culturing apparatus: Brown glass bottles (500 mL) with OxiTop measuring heads
- Number of culture flasks/concentration: 2
- Measuring equipment: OxiTop measuring heads, WTW
- Details of trap for CO2 and volatile organics if used: A rubber sleeve with soda lime was hung into the opening of the bottles to absorb evolved CO2.

SAMPLING
- Sampling frequency: Temperature in the incubator was recorded continuously by a hygrothermograph. pH-values were measured at test start and end. The oxygen consumption was determined continuously from the pressure in the incubation vessels by OxiTop measuring system at 360 measuring points (every 112 minutes) during the 28 d incubation period.
- Sampling method: Separate replicates of test item and toxicity control were prepared for measurement of the pH-value at test start.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Test medium without test and/or reference item (two replicates)
- Toxicity control: Test item and reference item in test concentration (1 replicate)
- Functional control: Sodium benzoate in test medium (1 replicate)

STATISTICAL METHODS:
Excel, Microsoft Corporation
SigmaPlot (Windows), SPSS Corporation
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
75
Sampling time:
28 d

BIODEGRADATION OF THE TEST ITEM

The test item replicate 1 reached the 10% level (beginning of biodegradation) after 14 d, test item replicate 2 after 15 d. The pass level of 60% was reached within the 10 -d window after 21 d. After 28 d the mean biodegradation was 75% (Table 1).

Table 1. Biodegradation [%] of the test item in comparison to the functional control and toxicity control.

 

 

Date

 

 

[d]

Biodegradation [%]

 

Functional control

45 mg/L

 

Test item

25 mg/L

Toxicity control

25 mg/L test item +

45 mg/L reference item

 

 

R1

P1

P2

T1

2011-02-25

0

0

0

0

0

2011-02-26

1

36

0

0

0

2011-02-27

2

58

0

0

0

2011-02-28

3

69

0

0

2

2011-03-01

4

74

0

0

21

2011-03-02

5

77

0

0

28

2011-03-03

6

80

0

0

31

2011-03-04

7

82

0

0

37

2011-03-05

8

83

0

0

39

2011-03-06

9

84

0

0

42

2011-03-07

10

86

0

0

44

2011-03-08

11

87

0

0

45

2011-03-09

12

90

0

0

47

2011-03-10

13

90

0

0

47

2011-03-11

14

90

18

0

47

2011-03-12

15

91

42

12

47

2011-03-13

16

92

51

26

47

2011-03-14

17

93

58

37

48

2011-03-15

18

95

63

47

49

2011-03-16

19

95

65

53

50

2011-03-17

20

95

65

53

50

2011-03-18

21

95

68

58

51

2011-03-19

22

93

71

55

50

2011-03-20

23

95

71

60

50

2011-03-21

24

95

73

60

50

20·1·1-03-22

25

94

77

62

51

2011-03-23

26

96

79

64

51

2011-03-24

27

96

79

64

52

2011-03-25

28

95

81

68

52

 

FUNCTIONAL CONTROL

The adaptation phase changed to degradation phase after 1 d (degradation > 10%). The pass level > 60% was reached after 3 d. The biodegradation rate came to a maximum of 96% on day 26.

TOXICITY CONTROL

In the toxicity control biodegradation achieved 47% after 14 d and 52% after 28 d. The validity criterion that the test item should not inhibit the biodegradation of the reference item was fulfilled.

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The test item is readily biodegradable within 28 d and the 10-d window criterion was fulfilled.

Description of key information

Readily biodegradable: 75% in 28 d (OECD 301 F)

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

There is one GLP study available, in which the ready biodegradability of the substance was determined in a Manometric Respirometry Test according to OECD guideline 301 F.

25 mg/L test item, corresponding to a ThOD of 55.0 mg O2/L per test vessel, was inoculated with 4.3 *10^9 CFU/L non-adapted, activated sludge from a municipal sewage treatment plant for 28 d. The test bottles were closed with OxiTop measuring heads and oxygen consumption was determined continuously from the pressure in the incubation vessels. A functional and toxicity control was run in parallel.

The test item replicate 1 reached the 10% biodegradation after 14 d and test item replicate 2 after 15 d. The pass level was reached within the 10-d window after 21 d. After 28 d, the mean biodegradation was 75%. Therefore, the test item is classified as readily biodegradable according to the guideline criteria. The toxicity control achieved 47% biodegradation of the reference item potassium dichromate after 14 d, and 52% after 28 d, indicating that the substance is not inhibitory to activated sludge microorganisms.