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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:
29 Jun - 27 Jul 1999
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)
Qualifier:
according to
Guideline:
EU Method C.4-E (Determination of the "Ready" Biodegradability - Closed Bottle Test)
Deviations:
no
GLP compliance:
yes
Test material information:
Composition 1
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: activated sludge from secondary effluent of a domestic sewage treatment plant (waste water treatment plant Odenthal, Germany); Date of collection: 25 Jun 1999
- Storage conditions: aerated
- Storage length: 4 d
- Pretreatment: separation of coarse particles by filtration
- Concentration of sludge: 5 mL/L (concentration of effluent in reaction mixture)
Duration of test (contact time):
28 d
Initial conc.:
2.9 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Test temperature: 20 ± 1 °C
- Aeration of dilution water: yes
- Suspended solids concentration: 5 mL/L concentration of effluents in reaction mixture
- Continuous darkness: yes

TEST SYSTEM
- Number of culture flasks/concentration: 2
- Method used to create anaerobic conditions: the activated sludge was maintained in an aerobic condition by aeration for 4 h

SAMPLING
- Sampling frequency: 7, 14, 21, 28 days
- Sampling method: oxygen concentration was measured

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, 2 bottles per sampling
- Toxicity control: yes, 2 bottles per sampling
- Other: Reference control: yes, 2 bottles per sampling
- Abiotic sterile control: no

Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Details on results:
Within the test period of 28 days, a degradation of 0% was determined for the test item. Thus, the test item is not readily biodegradable according to the OECD criteria.
Results with reference substance:
The reference control achieved a degradation of 71% after 14 days.

Biological Results:

Table 1: Results - DO depletion: % Degradation of test substance

Test substance

Test concentration: 2.9 mg/L

ThOD: 2409 mg/g

COD : --- mg/g

DO depletion after n days [mg/L]

7 d

14 d

21 d

28 d

No.1: (mt0 - mtx) - (mb0 - mbx)

0.00

0.00

0.00

0.00

No.2: (mt0 - mtx) - (mb0 - mbx)

0.00

0.00

0.00

0.00

Dl: % Degradation

0

0

0

0

D2: % Degradation

0

0

0

0

D, Mean

0

0

0

0

 

Table 2: Results - DO depletion: % Degradation of the reference item

Reference substance

Test concentration: 2.9 mg/1

ThOD: 1665 mg/g

COD : --- mg/g

DO depletion after n days [mg/L]

7 d

14 d

21 d

28 d

No.1: (mt0 - mtx) - (mb0 - mbx)

3.30

3.40

3.69

3.71

No.2: (mt0 - mtx) - (mb0 - mbx)

3.20

3.50

3.48

3.78

Dl: % Degradation

68

70

76

77

D2: % Degradation

66

72

72

78

D, Mean

67

71

74

78

 

Table 3: Results - DO depletion: % Degradation of toxicity control

*Toxicity control

DO depletion after n days [mg/L]

7 d

14 d

21 d

28 d

No.1: (mt0 - mtx) - (mb0 - mbx)

3.14

3.57

4.10

3.94

No.2: (mt0 - mtx) - (mb0 - mbx)

3.16

3.85

4.60

4.01

Dl: % Degradation

27

30

35

33

D2: % Degradation

27

33

39

34

D, Mean

27

32

37

34

* In the toxicity control 2.9 mg/L test substance and 2.9 mg/L reference substance were used. The ThOD values respectively COD values of these substances are shown in the tables above.

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
The derived 28 d degradation rate was 0% for the test substance and 34% for the toxicity control. Since the test substance did not show any biodegradability within 28 d it is not considered to be readily biodegradable according to the OECD criteria. Due to the fact that the degradation rate of the toxicity control was > 25% after 14 d, toxic effects of the test substance to the inoculum can be excluded.

Description of key information

Not readily biodegradable: 0% within 28 d (OECD 301D)

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

One GLP guideline study according to OECD 301D is available investigating the ready biodegradability of the substance. A mixed microbial population of the activated sludge of a local municipal STP was inoculated with a nominal concentration of 2.9 mg/L test substance and incubated for 28 d under controlled conditions in the dark. Degradation was followed by the determination of dissolved oxygen content after 0 h, 7, 14, 21 and 28 d. An inoculum blank, a reference control and a toxicity control were run in parallel. The derived 28 d degradation rate was 0% for the test substance and 34% for the toxicity control. Since the test substance did not show any biodegradability within 28 d it is not considered to be readily biodegradable according to the OECD criteria. Due to the fact that the degradation rate of the toxicity control was >25% after 14 d, toxic effects of the test substance to the inoculum can be excluded.