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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:
03 January 2018 - 15 February 2018
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reference:
Composition 0
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
17 July 1992
Deviations:
no
GLP compliance:
yes
Test material information:
Composition 1
Specific details on test material used for the study:
Solubility in water: 167.13 g/L (20°C)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: 'Waterschap Aa en Maas', 's-Hertogenbosch, The Netherlands,
- Pretreatment: The freshly obtained sludge was coarsely sieved (1 mm) washed with mineral medium and kept under continuous aeration until further treatment.
- Concentration of suspended solids: 3.0 g/L
Duration of test (contact time):
28 d
Initial conc.:
48 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST ITEM PREPARATION
Since the test item was easily soluble in water, the test media were prepared using a stock solution of 1 g/L in mineral medium. A weighed amount of 251.64 mg of test item was dissolved in mineral medium and made up to 250 mL. After stirring for 19 minutes, the final stock solution was clear and colourless. Aliquots of 17 mL of the stock solution were added to test item bottles A and B, and a 12 mL aliquot was added to the toxicity control. The test solutions were continuously stirred during the test, to ensure optimal contact between the test item and the test organisms.

TEST CONDITIONS
- Composition of medium: according to OECD guideline 301
- Test temperature: 22 - 24°C.
- pH: between 7.8 on day 0 and ranging from 7.5-8.7 on day 28, in all test bottles.
- pH adjusted: no
- Suspended solids concentration: 9 mg/L
- Continuous darkness: yes


TEST SYSTEM
- Culturing apparatus: 500 mL brown colored glass bottles, fill volume: 360 or 244 mL (depending on headspace-to-volume ratio)
- Number of culture flasks/concentration: 2 bottles for the test item and the inoculum blank, 1 bottle for the procedure control and the toxicity control
- Measuring equipment: the respirometer used was a Lovibond BD600-GLP manometric respirometry system, equipped with an inductive stirring system.
- Details of trap for CO2 and volatile organics if used: two pellets of sodium hydroxide were placed in rubber gaskets and used as CO2 absorbent

SAMPLING
- Sampling frequency: on day 0, 4, 7, 11, 14, 18, 21, 25, 28
- Sampling method: recording of measurements in air pressure decrease by respirometer heads which automatically converts data into oxygen consumption (mg O2/L).
- Other: pH was measured at day 0 and day 28, temperature was measured continuously

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, containing inoculum only
- Abiotic sterile control: no
- Toxicity control: yes, containing inoculum, test item and reference item
- Other: procedure control, containing inoculum and reference item

STATISTICAL METHODS: no statistical analysis was performed
Reference substance:
acetic acid, sodium salt
Remarks:
Purity: 99.5%; ThOD: 0.78 mg O2/mg
Key result
Parameter:
% degradation (O2 consumption)
Value:
94
Sampling time:
28 d
Remarks on result:
other: for duplicate bottles tested
Details on results:
- The ThOD of the test item was calculated to be 1.67 mg O2/mg.
- The relative biodegradation values calculated from the measurements performed during the test period revealed 94% for both bottle A and B (based on ThOD). Furthermore, biodegradation of Bicine of at least 60% was reached within a 10-day window.
- In the toxicity control, more than 25% biodegradation occurred within 14 days (92%, based on ThOD). Therefore, the test item was assumed not to inhibit microbial activity.
- The test conditions (temperature and pH) were within the presciribed limits during the exposure period.

Table 1 O2 Consumption and Percentage Biodegradation of the Test Item (Bottle A)

Day

Oxygen consumption (mg O2/L)

BOD
(mg O2/L)

Biodegradation*)

(%)

Blank

(mean)

Bottle A

0

2

1

0

0

4

8

8

0

0

7

11

15

5

6

11

14

64

51

64

14

14

75

62

77

18

15

83

69

86

21

16

87

72

90

25

16

90

75

94

28

16

   90#)

75

94

*): Calculated as the ratio between BOD and ThOD of test item added: 79.4 mg O2/L.

#): Value was >90 and was outside the programmed measurement range.

 

Table 2 O2 Consumption and Percentage Biodegradation of the Test Item (Bottle B)

Day

Oxygen consumption (mg O2/L)

BOD
(mg O2/L)

Biodegradation*)

(%)

Blank

(mean)

Bottle B

0

2

1

0

0

4

8

10

2

3

7

11

16

6

7

11

14

61

48

60

14

14

70

57

71

18

15

81

67

84

21

16

87

72

90

25

16

   90#)

75

94

28

16

   90#)

75

94

*): Calculated as the ratio between BOD and ThOD of test item added: 79.4 mg O2/L.

#): Value was >90 and was outside the programmed measurement range.

 

Validity criteria fulfilled:
yes
Remarks:
see 'overall remarks'
Interpretation of results:
readily biodegradable
Conclusions:
Under the conditions of the Manometric Respirometry Test, performed according to OECD 301F and GLP principles, the substance was determined to be readily biodegradable (94%).

Description of key information

Under the conditions of the Headspace Test, performed according to OECD 310 and GLP principles, the test item biodegraded for 64% but did not fulfill the 10-day window criterion. Therefore, the substance was determined to be not readily biodegradable. However, under the conditions of the Manometric Respirometry Test, performed according to OECD 301F and GLP principles, the substance was determined to be readily biodegradable (94%). The latter test overrules the first one according to OECD test guideline 310, and therefore the test substance is considered to be readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information