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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:
1994-04-12 to 1994-05-12
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Version / remarks:
(1992)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)
Version / remarks:
(1992)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Remarks:
signed 1994-03-16
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
- Method of cultivation: aerobic
- Pretreatment: The activated sludge was maintained on aeration at 21 °C and the sludge was washed 3 times in culture medium by settlement and resuspended prior to use
- Concentration of sludge: 30 mg suspended solids/L
Duration of test (contact time):
28 d
Initial conc.:
16 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral nutrient solution acc. to OECD 301
- Test temperature: 21 °C
- Suspended solids concentration: 30 mg/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 5 L-glass culture vessels containing 3 L
- Number of culture flasks/concentration: 2 bottles for test item, inoculum blank, and procedure control each, and 1 bottle for abiotic control
- Method used to create aerobic conditions: culture vessels were sealed and CO2-free air bubbled through the solution at a rate of 30 - 50 mL/min.
- Measuring equipment: Ionics 555 TOC Analyser
- Details of trap for CO2: 2 x 500 mL Dreschel bottles filled with 350 mL 0.05 M NaOH.


SAMPLING
- Sampling frequency: Samples (2 mL) were taken from the first CO2 absorber vessles on days 0, 1, 2, 3, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 27, 28, and 29. The second absorber vessel was sampled on days 0 and 29.
- Sampling method: direct analysis of evolved CO2 by TOC Analyser

CONTROL AND BLANK SYSTEM
- Inoculum blank: culture medium and inoculum
- Abiotic sterile control: culture medium, inoculum and test item poisoned by additionof 10 mL of 10 g/L mercuric chloride solution

STATISTICAL METHODS:
The percentage degradation or percentage of Theoretical Amount of Carbon Dioxide (ThCO2) produced was calculated as given in the OECD 301B (1992).
Reference substance:
benzoic acid, sodium salt
Test performance:
No unusual observations during test.
Key result
Parameter:
% degradation (CO2 evolution)
Value:
86
Sampling time:
28 d
Remarks on result:
other: 10-d window was passed
Details on results:
The results of the inorganic carbon analysis of both absorber vessels confirmed that no significant amounts of CO2 were present in solution in the culture vessels as inorganic carbonate.
Analysis of the test media from the test material culture vessels on days 0 and 29 for total organic carbon (TOC) gave a percentage degradation value of 100% for both replicates R1 and R2 respectively. Analysis of the test media from the abiotic control vessel showed a 58% loss of TOC after 29 days. The higher degradation value calculated from TOC analysis as compared to that calculated from the production of carbon dioxide is considered to be due to adsorption of the test material to the glassware and/or incorporation into cellular material. The result of the TOC analysis of the abiotic control i.e. a 58% loss of TOC after 29 days, suggests the test material adsorbs to the glassware used in the study.
Results with reference substance:
- Biodegradation of reference item sodium benzoate: > 60 % after 6 days; 80 % after 14 days
-Validity: degradation of reference item reached pass level (> 60 % after 14 days)

Percentage biodegradation

Day

% Degradation

Sodium Benzoate

% Degradation

Test item

% Abiotic

Degradation

Test item

Abiotic Control

1

2

3

6

8

10

12

14

16

18

20

22

24

27

28

29*

4

18

37

65

77

78

78

80

82

81

89

87

86

89

83

81

0

2

8

43

53

49

61

61

69

74

86

86

84

91

86

87

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

*Day 29 values corrected to include any carry-over of C02detected in absorber 2 on day 29.

 

Total organic Carbon values in culture vessels

 

 

Test Material

T0C* Concentration in culture vessel (mg/L)

Day 0

Day 29

mg C/L

% of nominal carbon content

mg C/L

% of initial carbon concentration

% degradation

Test item

mg C/L 

R1

 

9.12

91

0.00

 

0

100

Test item

mg C/L 

R2

 

9.52

95

0.00

0

100

Test item

Abiotic Control

mg C/L

11.93

119

5.06

42

50

R1 – R2 = Replicates 1 and 2

*Corrected for control values

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The test item is readily biodegradable since a 86% degradation was observed after 28 days (10-day window passed).
Executive summary:

The biodegradability of the test item was initiated according to OECD 301 B (1992) at a concentration of 16.0 mg/L corresponding to 10 mg C/L. The substance is considered to be readily biodegradable under the test conditions; the biodegradation amounted to 86 % after 28 days and the 10-d window was passed. A toxicity control was not performed.

Description of key information

readily biodegradable (86 % after 28 days; 10-d window passed)

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The biodegradability of the test item was initiated according to OECD 301 B (1992) at a concentration of 16.0 mg/L corresponding to 10 mg C/L. The substance is considered to be readily biodegradable under the test conditions; the biodegradation amounted to 86 % after 28 days and the 10-d window was passed. A toxicity control was not performed.