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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:
13 Dec 2010 - 12 Jan 2011
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
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)
GLP compliance:
yes (incl. certificate)
Remarks:
Swiss Federal Office of Public Health, Consumer protection directorate, Bern, Switzerland
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Wastewater treatment plant ARA Ergolz II, Füllinsdorf, Switzerland
- Storage conditions: aerated at room temperature
- Storage length: 2 d
- Pretreatment: Sludge was washed twice with tap water by centrifugation and the supernatant liquid phase was decanted.
- Initial cell/biomass concentration: 4 g (± 10%) dry material/L
- Water filtered: no
Duration of test (contact time):
28 d
Initial conc.:
3 mg/L
Based on:
test mat.
Initial conc.:
7.6 mg/L
Based on:
ThOD/L
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: according to guideline
- Test temperature: 23 - 24 °C
- pH: 7.2 - 7.4
- pH adjusted: yes, with a diluted hydrochloric acid
- Aeration of dilution water: The test water was aerated for at least 20 min and allowed to stand for about 20 h at the test temperature.
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: Wide-necked reagent bottles (with conical shoulder, 250 mL). The bottles were cleaned with 5-10 mL of a wash liquid (2.5 g iodine and 12.5 g potassium iodide/L of 1% w/v sulfuric acid)
- Number of culture flasks/concentration: 18
- Measuring equipment: O2-electrode (under constant stirring at about 500 rpm) using a WTW OXI 539 meter
- Test performed in closed vessels due to significant volatility of test substance: closed bottle test, flasks were tightly stoppered

SAMPLING
- Sampling frequency: On day 0, 2, 5, 7, 9, 14, 21 and 28 (test item and inoculum control); On day 0, 2, 7, 14 and 28 (procedure control); On day 0, 7, 14 and 28 (toxicity control)
- Sampling method: The oxygen concentration in the test flasks was measured in two separate test flasks per treatment and sampling day in an airtight system.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, 18 flasks
- Toxicity control: yes, 10 flasks
- Other: Procedure control: yes, 12 flasks
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (O2 consumption)
Value:
48
Sampling time:
28 d
Results with reference substance:
The reference substance was degraded to 108% after 28 d, pass level was reached.

The toxicity control attained 52% degradation after 14 days of incubation. “If in a toxicity test, containing both the test and reference substance, less than 35% degradation (based on total DOC) or less than 25% (based on total ThOD or ThCO2) occurred within 14 days, the test substance can be assumed to be inhibitory.” (OECD guideline 301). Since more than 25% degradation occurred in the toxicity control, the substance is with high probability not toxic to aquatic microorganisms.

Table 1: Biodegradation [%] of test substance, reference substance and toxicity control at different time intervals

 

Nominal concentration [mg/L]

Replicate

% biodegradation after x days

2

5

7

9

14

21

28

Test item

3.0

A

-3

1

36

36

48

48

48

3.0

B

-2

1

37

44

48

49

47

 

mean

-2

1

36

40

48

48

48

Procedure control

3.0

A

78

n.d.

103

n.d.

105

n.d.

108

3.0

B

78

n.d.

105

n.d.

109

n.d.

108

 

mean

78

n.a.

104

n.a.

107

n.a.

108

Toxicity control*

6.6

A

n.d.

n.d.

38

n.d.

52

n.d.

47

6.6

B

n.d.

n.d.

38

n.d.

52

n.d.

47

 

mean

n.a.

n.a.

38

n.a.

52

n.a.

47

* Containing 3.6 mg/L test item and 3.0 mg/L sodium benzoate

 

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The test item is not readily biodegradable according to OECD 301D.
Executive summary:

The study was performed according to OECD guideline 301D (GLP) with a test substance concentration of 3 mg/L (7.6 mg/L based on ThOD/L). Duplicate test vessels were incubated at 23 - 24°C in the dark with activated sludge from a domestic sewage treatment plant as inoculum. After 28 d, 48% degradation of the test substance was recorded based on O2-consumption. The positive control resulted in complete degradation after 28 d. A toxicity control containing both, reference substance and test substance, did not indicate inhibitory effects to the inoculum (47% degradation after 14 d; trigger value of 25% biodegradation in the toxicity control was reached). All validity criteria were met. In conclusion, the substance is not readily biodegradable according to the OECD criteria.

Description of key information

Not readily biodegradable: 48% after 28 d (O2 consumption, OECD 301D)

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, not fulfilling specific criteria

Additional information

One experimental study is available investigating the ready biodegradability of the substance. The study was performed according to OECD guideline 301D (GLP) with a test substance concentration of 3 mg/L (7.6 mg/L based on ThOD/L). Duplicate test vessels were incubated at 23 - 24 °C in the dark with activated sludge from a domestic sewage treatment plant as inoculum.
After 28 d, 48% degradation of the test substance was recorded based on O2-consumption. The positive control resulted in complete degradation after 28 d. A toxicity control containing both, reference substance and test substance, did not indicate inhibitory effects to the inoculum (47% degradation after 14 d; trigger value of 25% biodegradation in the toxicity control was reached). All validity criteria were met. In conclusion, the substance is not readily biodegradable according to the OECD criteria.