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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:
2011-01-03 to 2011-02-03
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:
1992
Deviations:
no
GLP compliance:
yes
Test material information:
Composition 1
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: ARA Ergolz II, Füllinsdorf, Switzerland
- Preparation of inoculum for exposure: washed twice with tap water by centrifugation. Supernatant was decanted. The sludge suspension was dried.
- Pretreatment: During 2 days before the use, the sludge was aerated to room temperature.
- Concentration of sludge: 4g dry matter per L (+/- 10%). Prior use, a dilution to 1g/L (dry weight basis).
- Initial cell/biomass concentration: Additions to the test water to obtain final concentration 30 mg dry material/L
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Remarks:
This corresponds to roughly 300 ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Remarks:
cumulative oxygen consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: test water prepared according to the guideline.
- Test temperature: 22°C
- pH: from 7.8 to 7.4
- pH adjusted: yes at start
- Suspended solids concentration: 30 mg dry matter/L
- Continuous darkness: yes
- Continuous stirring: yes

TEST SYSTEM
- Culturing apparatus: SAPROMAT D12 (Voith GmbH, Heidenheim, Germany)
- Number of culture flasks: 7, 2 with test item, 2 inoculum controls, 2 with reference substance, and 1 toxicity control.
- Method used to create aerobic conditions: cosumed oxygen is replaced by electrolytically generated oxygen from a copper sulfate solution.
- Measuring equipment: Pressure drop due to CO2 adsoprtion on soda lime
- Test performed in closed system: yes
- Details of trap for CO2: soda lime


SAMPLING
- Sampling frequency: daily measurement of O2 consumption

CONTROL AND BLANK SYSTEM
- inoculum blank: 2 replicates containing only the reference substance sodium benzoate
- Toxicity control: yes 1 replicate, 100 mg/L (300 ThOD) test item and 100 mg/L (167 ThOD) reference substance


STATISTICAL METHODS: None
Reference substance:
benzoic acid, sodium salt
Preliminary study:
None performed
Key result
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Remarks on result:
other: negative value (-2%) was observed due to higher oxygen consumption in the inoculum controls than in the test flasks with test item
Details on results:
The pH varied from 7.4 at the start of the experiment to maximally 7.8.

Percentage Biodegradation (corrected for the mean oxygen uptake of the inoculum controls):

Time (days) Test item Procedure control Toxicity control
Rep 1 Rep 2 Rep 1 Rep 2 Rep 1
0 0 0   0 0
2 0 0 58 57 14
6 -3 -3 78 76 27
9 -3 -3 84 81 29
14 -3 -3 91 86 30
18 -3 -2 95 89 30
24 -3 -2 98 90 31
28 -3 -2 100 90 31
Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
The test item was investigated for its ready biodegradability in a manometric respirometry test, according to OECD 301F. After 28 days exposure, the % ultimate biodegradation was 0%, hence it must be concluded that the test item is not biodegradable under the test conditions.
Executive summary:

The test item was investigated for its ready biodegradability in a manometric respirometry test over 28 days according to OECD 301 F.

The biochemical oxygen demand (BOD) of the test item in the test media was in the normal range found for the inoculum controls. Consequently, the test item was not biodegradable under the test conditions within 28 days.

In the toxicity control, containing both the test item and the reference item sodium benzoate, the substance had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration of 100 mg/L.

The degradation in the toxicity control was 30 % within 14 days of exposure and 31% by day 28.

The reference item sodium benzoate was degraded by an average of 88% by Exposure Day 14, and reached an average biodegradation of 95% by the end of the test (Day 28), thus confirming suitability of the activated sludge.

Description of key information

For this endpoint, one study assessing the readily biodegradability of the substance in a manometric respirometry test according to OECD 301F is available. After 28 days exposure, the ultimate biodegradation of the test item was 0%. It was concluded that the test item is not biodegradable under the test conditions within 28 days.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The reference substance sodium benzoate was degraded up to 95 % by the end of the test (day 28), confirming the suitability of the activated sludge. The degradation in the toxicity control was 30 % within 14 days of exposure and 31% by day 28. This result confirms that the test substance had no inhibitory effect on the activity of the activated sludge as the degradation was above 25% by day 14.