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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:
2001-01-19 to 2001-06-15
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EU Method C.6 (Degradation: Chemical Oxygen Demand)
Version / remarks:
1984
Deviations:
no
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
no
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: WWTP Nieuwgraaf in Duiven, The Netherlands
- Laboratory culture: yes
- Pretreatment: The activated sludge was preconditioned to reduce the endogenous respiration rates.
- Concentration of sludge: 2 mg Dry Weight (DW)/L
- Initial cell/biomass concentration: 2 mg Dry Weight (DW)/L
Duration of test (contact time):
28 d
Initial conc.:
2.1 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: according to OECD guideline 301
- Test temperature: 19.0 to 21.2 °C
- pH: 7.0 to 7.3 at the start of the test; 6.7 to 7.2 at day 28
- Aeration of dilution water: yes


TEST SYSTEM
- Culturing apparatus: 250 to 300 mL BOD bottles with glass stoppers
- Number of culture flasks/concentration: 10 (containing only inoculum and evaporated silica gel, containg solvent and inoculum, test substance in solvent and inoculum, containing only inoculum) and 6 (containing sodium acetate and inoculum)
- Measuring equipment: electrochemically using an oxygen electrode (WTW Trioxmatic EO 200) and meter (WTW OXI 530)


CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Toxicity control: yes


STATISTICAL METHODS:
The validity of the test is demostrated by an endogenous respiration of 1.6 mg/L at day 28. Furthermore, the differences of the replicate values at day 28 was less than 20%. The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 83. Finally, the validity of the test is shown by oxygen concentrations > 0.5 mg/L in all bottles during the test period.
Reference substance:
acetic acid, sodium salt
Test performance:
The dissolved oxygen concentrations were determined electrochemically using an oxygen electrode and meter. The pH was measured using a Consort pH meter. The temperature was measured and recorded with a thermo couple connected to a data logger.
The dry weight (DW) of the inoculum was determined by filtrating 50 mL of the activated sludge over a preweighed 12 µm Schleier and Schüll filter.
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
7 d
Parameter:
% degradation (O2 consumption)
Value:
4
Sampling time:
14 d
Parameter:
% degradation (O2 consumption)
Value:
12
Sampling time:
21 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
26
Sampling time:
28 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
53
Sampling time:
140 d
Remarks on result:
other: conclusion: inherently biodegradable
Details on results:
The test item was biodegraded 26 % at day 28 in the Closed Bottle test. Since, in the prolonged Closed Bottle test the test compound is biodegraded 53 % at day 140, it should be classified as inherently biodegradable. The solvent present in the test substance was biodegraded 44% at day 140 in the Closed Bottle test. Hence, the solvent should be classfified as inherently biodegradable. The test item in solvent was tested in the Closed Bottle in the presence of silica gel. Silica gel was added to permit an accurate administration of the water insoluble test substance. The low water solubility of the test substance may be the reason of the inability to show ready biodegradability of the test substance. Water-insolbule compounds are known for their limited bioavalability. limited bioavailability often results in linear biodegradation curves as found for the solvent.
Results with reference substance:
The biodegradation percentage of the reference compound at day 14 was 83.
Validity criteria fulfilled:
yes
Interpretation of results:
inherently biodegradable
Conclusions:
The test item was biodegraded 26 % at day 28 in the Closed Bottle test. In the prolonged Closed Bottle test this compound was biodegraded 53 % at day 140. The biodegradation reached at the last day of the test demostrates that this test compound should be classified as inherently biodegradable.
Executive summary:

A ready biodegradability test of tert-butyl peroxyneodecanoate was performed which allows the biodegradability to be measured in an aerobic aqueous medium. The ready biodegradability was determined in the Closed Bottle test performed according to OECD guideline no. 301. The test was prolonged because the pass level was not reached at day 28.

Tert-butyl peroxyneodecanoate caused no reduction in the endogenous respiration. The test substance is therefore considered to be non-inhibitory to the inoculum.

The test item was biodegraded 26 % at day 28 in the Closed Bottle test. In the prolonged Closed Bottle test this compound was biodegraded 53 % at day 140. The biodegradation reached at the last day of the test demostrates that this test compound should be classified as inherently biodegradable.

The test is valid as shown by an endogenous respiration of 1.6 mg/L and by the total mineralization of the reference compound, sodium acetate. Sodium acetate was degraded 83 % of its theoretical oxygen demand after 14 days. Finally, the most important criterion was met by oxygen concentrations > 0.5 mg/L in all bottles during the test period.

Description of key information

The ready biodegradability of the test item was assessed according to OECD guideline 301 and EU-method C.6. The test item was biodegraded 26 % at day 28 in the Closed Bottle test. In the prolonged Closed Bottle test this compound was biodegraded 53 % at day 140. Therefore it can be concluded that the test item is not ready biodegradable, but inherently biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

A ready biodegradability test of tert-butyl peroxyneodecanoate was performed which allows the biodegradability to be measured in an aerobic aqueous medium. The ready biodegradability was determined in the Closed Bottle test performed according to OECD guideline no. 301. The test was prolonged because the pass level was not reached at day 28. Tert-butyl peroxyneodecanoate caused no reduction in the endogenous respiration. The test substance is therefore considered to be non-inhibitory to the inoculum. The test item was biodegraded 26 % at day 28 in the Closed Bottle test. In the prolonged Closed Bottle test this compound was biodegraded 53 % at day 140. The biodegradation reached at the last day of the test demostrates that this test compound should be classified as inherently biodegradable. The test is valid as shown by an endogenous respiration of 1.6 mg/L and by the total mineralization of the reference compound, sodium acetate. Sodium acetate was degraded 83 % of its theoretical oxygen demand after 14 days. Finally, the most important criterion was met by oxygen concentrations > 0.5 mg/L in all bottles during the test period.