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Environmental fate & pathways

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:
August 11 to September 12, 2005
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
This study was performed according to OECD Guideline 301F with GLP statement. All validity criteria were fulfilled.
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
Principles of method if other than guideline:
Not applicable
GLP compliance:
yes (incl. QA statement)
Remarks:
Swiss GLP compliance programme (inspected on March 31-April 01, 2005 / signed on June 2005)
Specific details on test material used for the study:
- Physical state: White crystals
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
Fresh activated sludge from a biological waste water treatment plant treating predominantly domestic sewage (City of Geneva, Peney-Dessous) was used.
The sludge is collected in the morning, washed three times in the mineral medium (by centrifuging at 1000 g for 10 minutes, discarding the supernatant and resuspending in mineral medium) and kept aerobic until being used on the same day.
Duration of test (contact time):
32 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral medium; compliant with recommendations of TG on mineral medium
The pH is measured and if necessary adjusted to 7.4 ± 0.2 with phosphoric acid or potassium hydroxide.
- Test temperature: 22 °C
- Dry weight of suspended solids: 4.76 g/L; To obtain a concentration of 30 mg/L (dry weight) in a 250 mL flask, 1.57 mL of sludge was added (inoculum).
- Continuous darkness: No data
- Water: The water used during this study is deionised water containing less than 10 mg/L dissolved organic carbon.

TEST SYSTEM
- Culturing apparatus: Test flasks of the Sapromat
- Number of culture flasks/concentration: 2
- Measuring equipment: The respirometers used during this study are SAPROMAT D 12, made by J. M. VOITH GmbH, Heidenheim, Germany.
- Test performed in closed vessels: Yes

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes
- Procedure control: Yes with the reference substance
- Toxicity control: Yes

TOXICITY OF THE TEST SUBSTANCE
The toxicity of the test substance for the inoculum was checked. A pair of flasks of the volumetric respirometer was filled with mineral medium + test substance (100 mg/I) + reference substance (100 mg/l) + inoculum and their respirations were recorded as for the other flasks. If they are lower than those of the flasks containing mineral medium + reference substance ( 100 mg/l) + inoculum, the test substance can be assumed to be inhibitory to the inoculum used.
Reference substance:
benzoic acid, sodium salt
Remarks:
100 mg/L
Preliminary study:
None
Test performance:
Everyday the oxygen consumption of each flask is recorded and correct temperature and stirring are checked. At the end of the test period (normally 28 days), the pH of each flask is measured again.
Key result
Parameter:
% degradation (O2 consumption)
Value:
7
Sampling time:
28 d
Parameter:
% degradation (O2 consumption)
Value:
7
Sampling time:
32 d
Details on results:
Oxygen uptakes, as read on the SAPROMAT meters, are corrected to account for the small differences between actual and nominal concentrations of test and reference substances.
The curves obtained with the reference substance alone and with the test substance + reference substance showed no toxic effect of the test substance to the micro-organisms at the test concentration (100 mg/L).
The test substance undergoes 7% biodegradation after 28 days (and 7% after 32 days) in the test conditions.
The repeatability validity criterion (not more than 20% difference between replicates) is fulfilled for the flasks containing test substance. Therefore, the test is considered valid.
Results with reference substance:
Degradation of sodium benzoate exceeded 40% after 7 days and 65% after 14 days: the activity of the inoculum was thus verified (validity criterion).

Table 5.2.1/2: Test substance - Biological Oxygen Demand (BOD, mg O2/L, adjusted to nominal concentrations)

 

Days:

7

14

21

28

32

BOD

sludge

1st flask

B1

11.0

17.0

25.0

28.0

28.0

2nd flask

B2

8.0

17.0

26.0

29.0

29.0

Mean

B

9.5

17.0

25.5

28.5

28.5

BOD

Test

Substance

1st flask

C1

30.7

33.0

50.5

52.5

52.5

2nd flask

C2

17.1

23.1

31.1

34.1

34.1

1st fl. corr

C1-B

21.2

16.0

25.0

24.0

24.0

 2nd fl. corr

C2-B

7.6

6.1

5.6

5.6

5.6

% biodegradation

of test

substance

1st flask

D1

11

8

13

12

12

2nd flask

D2

4

3

3

3

3

Mean

D

7

6

8

7

7

 

Calculations:

B1, B2, C1, C2 A1, A2: experimental O2uptake values

B = (B1 + B2) / 2

D1 = 100 * (C1 - B) / ThOD * [S]

D2 = 100 * (C2 - B) / ThOD * [S]

D = (DI + D2)/2

[S] : Initial test substance concentration (mg/L)

ThOD: 1.98 mg O2/mg

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
Under the test conditions, test substance should be regarded as not readily biodegradable according to this test.
Executive summary:

The ready biodegradability of the test substance has been determined by the Manometric Respirometry Test according to the OECD Guideline No. 301F, EU Method C.4 -D with GLP compliance.

A nominal concentration of test substance (100 mg/L) introduced in the system.

 

The curves obtained with the reference substance alone and with the test substance + reference substance show no toxic effect of the test substance to the micro-organisms at the test concentration (100 mg/L). The test substance undergoes 7% biodegradation after 28 days (and 7% after 32 days) in the test conditions. The repeatability validity criterion (not more than 20% difference between replicates) is fulfilled for the flasks containing test substance. Therefore, the test is considered valid.

 

Degradation of sodium benzoate exceeds 40 % after 7 days and 65 % after 14 days: the activity of the inoculum is thus verified.

 

Under the test conditions, test substance should be regarded as not readily biodegradable according to this test.

Description of key information

OECD Guideline 301F, EU Method C.4-D, GLP, key study, validity 1:

7% biodegradation after 28 days.

Not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

To assess the biodegradation of the registered substance, one valid experimental study is available.

This biodegradation study (Givaudan, 2005) was assessed as the key study and was performed on the registered substance according to the OECD Guideline No. 301F and EU Method C.4-D with GLP compliance. The test substance was exposed to activated sewage sludge micro-organisms at a concentration of 100 mg/L with culture medium at 22°C for 28 days. The degradation of the test substance was assessed by the measurement of oxygen consumption. Control solutions with inoculum and the standard material (aniline), together with a toxicity control were used for validation purposes. The curves obtained with the reference substance alone and with the test substance + reference substance shows no toxic effect of the test substance to the micro-organisms at the test concentration (100 mg/L). The test substance undergoes 7% biodegradation after 28 days (and 7% after 32 days) in the test conditions. The repeatability validity criterion (not more than 20% difference between replicates) is fulfilled for the flasks containing test substance. Therefore, the test is considered valid. Degradation of sodium benzoate exceeds 40 % after 7 days and 65 % after 14 days: the activity of the inoculum is thus verified. In conclusion, under the test conditions, test substance should be regarded as not readily biodegradable.