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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 Sep - 27 Oct 2000
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Version / remarks:
adopted 1992
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Remarks:
Niedersächsisches Umweltministerium, Hannover, Germany
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
- Preparation of inoculum for exposure: The activated sludge was filtered with folded filter. The first 200 mL of the filtrate are not used. The second filtrate effluent from the domestic waste water is used to initiate inoculation.
- Concentration of sludge: 10 E+04 to 10 E+06 cfu/L per test vessel
- Initial cell/biomass concentration: 0.2 ml of the inoculum was given in each BOD bottle
Duration of test (contact time):
28 d
Initial conc.:
3 mg/L
Based on:
test mat.
Initial conc.:
7.29 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: according to the guideline 301 D
- Test temperature: 20 °C
- pH: 7.39 (stock solution)
- Aeration of dilution water: One day before the test started the demineralized water for the test medium was aerated until oxygen saturation and then left at room temperature for at least 20 h.
- Other: Detailes of parameters of the test media are listed in Table 1 and 2 in the section "Any other information on material and methods incl. tables".

TEST SYSTEM
- Culturing apparatus: BOD bottles with glass stoppers (300 mL)
- Number of culture flasks/concentration: 5 x 2 per test item
- Method used to create aerobic conditions: One day before the test started the demineralized water for the test medium was aerated until oxygen saturation and then left at room temperature for at least 20 h. The stock solutions were filled to the BOD bottles with a siphon. The incubation vessels were closed without air bladders.
- Measuring equipment: respirometer recording O2 consumption
- Test performed in closed vessels due to significant volatility of test substance: closed system

SAMPLING
- Sampling frequency: 0, 7, 14, 21 and 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:
acetic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
79
Sampling time:
28 d
Details on results:
The biodegradation came to 73% after 14 days and to a maximum of 81% after 21 days. At this point of time the plateau was reached. Since the 10-day window was met the substance is considered to be readily biodegradable according to the OECD criteria. Results are reported in detail in Table 1 to 3 in "Any other information on results incl. tables".
Results with reference substance:
The reference control reached the pass level > 60% after 5 days. After 14 days a biodegradation rate of 96% was reached.

Validity criteria:

The percentage degradation of the functional control reached the pass level of > 60% after 14 days. The oxygen depletion in the inoculum control did not exceed 1.5 mg dissolved oxygen/L after 28 d. The depletion came to a maximum of 1.60 mg O2/L after 21 days. This has no impact an integrity and quality of the study. The residual concentration of oxygen in the test bottles did not fall below 0.5 mg/L. The residual concentration of oxygen in the functional control bottles was less than 0.5 mg O2/L after 14 days. The residual concentration of oxygen in one toxicity control bottle was less than 0.5 mg O2/L after 21 days. The difference of extremes of replicate values of removal of the test item at the end of the test was less than 20%.

Table 1: Biodegradation of the test item in comparison to the reference control and the toxicity control

 

biodegradation [%]

study day [d]

7

14

21

28

Test Item 3 mg/L

70

73

81

79

Reference Control 10 mg/L

88

96

94

94

Toxicity Control 1.5 + 5 mg/L

84

88

92

92

Table 2: Oxygen determination of the inoculum control and functional control

Study day

inoculum control

functional control 10 mg/L

ThOD 0.78 mg O2/mg

[d]

O2 [ mg/L]

O2 [mg/L]

BOD

degr.

 

C1

C2

mv

O2-depl.

R1

R2

mv

[mg O2/L]

[mg O2/mg]

[%]

0

9.04

8.98

9.01

-

9.00

8.94

8.97

-

-

-

7

8.12

7.94

8.03

0.98

1.09

1.19

1.14

6.85

0.69

88

14

7.79

7.73

7.76

1.25

0.23

0.20

0.22

7.50

0.75

96

21

6.86

7.95

7.41

1.60

0.12

0.10

0.11

7.26

0.73

94

28

7.59

7.74

7.67

1.34

0.31

0.45

0.38

7.25

0.73

94

 

Table 3: Oxygen determination of the test item and the toxicity control

Study day

test item 3 mg/L

toxicity control

1.5 mg/L test item

+ 5 mg/L reference item

 

ThOD 2.43 mg/L

ThOD 1.16 mg O2/mg

[d]

O2 [ mg/L]

BOD

Degr. [%]

O2 [ mg/L]

BOD

Degr. [%]

 

P1

P2

mv

[mg O2/L]

[mg O2/mg]

[%]

T1

T2

mv

[mg O2/L]

[mg O2/mg]

[%]

0

8.99

8.90

8.95

-

-

-

8.95

9.04

9.00

-

-

-

7

2.87

2.93

2.90

5.07

1.69

70

1.78

1.62

1.70

6.32

0.97

84

14

2.20

2.49

2.35

5.35

1.78

73

1.12

1.11

1.12

6.63

1.02

88

21

1.19

1.74

1.47

5.88

1.96

81

0.56

0.30

0.43

6.97

1.07

92

28

1.90

1.84

1.87

5.74

1.91

79

011

0.65

0.68

6.98

1.07

92

mv = mean value BOD = biological oxygen demand

degr. = degradation

O2-depl. = Oxygen depletion

ThOD= Theoretical oxygen demand

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The biodegradation came to 73% after 14 days and to a maximum of 81% after 21 days. At this point of time the plateau was reached. After 28 d the biodegradation was 79%. Since the 10-day window was met the substance is considered to be readily biodegradable according to the OECD criteria.

Description of key information

Readily biodegradable: 79% degradation after 28 d, OECD 301D

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 301 D (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. The biodegradation came to 73% after 14 days and to a maximum of 81% after 21 days. After 28 d the biodegradation was 79%. At this point of time the plateau was reached. The pass level for ready biodegradability was reached after 7 days of exposure, therefore the test substance is considered to be “readily biodegradable” according to the OECD criteria. A toxicity control containing both, reference substance and test substance, did not indicate inhibitory effects to the inoculum (73% degradation after 14 d). All validity criteria of the study were met.