Dioctanoyl peroxide

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Experimental starting date 10-07-2013 Experimental completion date 08-08-2013

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.4-E (Determination of the "Ready" Biodegradability - Closed Bottle Test)

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)

Qualifier:

according to guideline

Guideline:

ISO 10707 Water quality - Evaluation in an aqueous medium of the "ultimate" aerobic biodegradability of organic compounds - Method by analysis of biochemical oxygen demand (closed bottle test)

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Batch/lot No. 1204350050
Purity 99.2%
Solubility in water insoluble
Stability not relevant
Storage >-10°C in the dark

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

Secondary activated sludge (04-07-2013) was obtained from the wastewater treatment plant Nieuwgraaf in Duiven, The Netherlands. This plant is an activated sludge plant treating predominantly domestic wastewater. The activated sludge was preconditioned to reduce the endogenous respiration rates. To this end, 400 mg Dry Weight (DW)/L of activated sludge was aerated for one week. The sludge was diluted in the BOD bottles (van Ginkel and Stroo, 1992).

Duration of test (contact time):

28 d

Initial conc.:

2 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

Deionized water
Deionized water containing no more than 0.01 mg/L Cu (Sterlab certified; non-GLP analysis) was prepared in a water purification system.

Test bottles
The test was performed in 0.30 L BOD (biological oxygen demand) bottles with glass stoppers.

Nutrients, stocks and administration
The nutrient medium of the Closed Bottle test contained per liter of deionized water; 8.5 mg KH2PO4, 21.75 mg K2HPO4, 33.3 mg Na2HPO4·2H2O, 22.5 mg MgSO4·7H2O, 27.5 mg CaCl2, 0.25 mg FeCl3·6H2O. Ammonium chloride was
omitted from the medium to prevent nitrification.
Accurate administration of the water-insoluble test substance was accomplished by preparing a stock solution of 1.0 g/L in DCM. The test substance in DCM (0.6 mL) was added to the bottles. The solvent was allowed to evaporate overnight in a ventilated hood. Sodium acetate was added to the bottles using a stock solution of 1.0 g/L in water.

Test procedures
The Closed Bottle test was performed according to the study plan. The study plan was developed from ISO Test Guidelines (1994). Use was made of 10 bottles containing only inoculum, 10 bottles containing only inoculum in bottle treated with DCM (added and evaporated), 10 bottles containing inoculum and test substance, and 6 bottles containing sodium acetate and inoculums. The concentrations of the test substance, and sodium acetate in the bottles were 2.0 and 6.7 mg/L, respectively. Each of the prepared solutions was dispensed into the respective group of BOD bottles so that all bottles were completely filled without air bubbles. The zero time bottles were immediately analyzed for dissolved oxygen using an oxygen electrode. The remaining bottles were closed and incubated in the dark. Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28.

Calculation of endogenous respiration
The endogenous respiration (oxygen depletion in the control) was calculated as
follows:
Oxygen depletion (endogenous respiration) (mg/L) = Mc (day 0) - Mc (day 28)
Mc is the mean oxygen level in the control bottles.

Calculation of the theoretical oxygen demand (ThOD)
The ThODs of dioctanoyl peroxide, and sodium acetate were calculated from their molecular formulae and molecular weights as follows.

ThOD_NH3 (mgO2/mg) = (16(2C+0.5(H-Cl-3N)+3S+2.5P+0.5Na-O)/MW

Calculation of the biochemical oxygen demand (BOD)
Provided that the oxygen concentrations in all bottles at the start of the test were equal, the amounts of oxygen consumed in test and reference compound bottles were calculated as follows:
Oxygen consumptionn (mg/L) by test substance = Mcs - Mt
Oxygen consumptionn (mg/L) by reference compound = Mc - Ma
Mc or cs is the mean oxygen level in the control bottles (C) and control bottles treated with DCM (added and evaporated) (Css) n-days after the start of the test.
Mt or a is the mean oxygen concentration in the bottles containing the test substance (t) or the reference compound, sodium acetate (a), n-days after the start of the test.
The biological oxygen demand (BOD) mg/mg of the test substance and sodium acetate was calculated by dividing the oxygen consumption by the concentration of the test substance and sodium acetate in the closed bottle, respectively.

Calculation of the biodegradation percentages
The biodegradation was calculated as the ratio of the biochemical oxygen demand (BOD) to the theoretical oxygen demand (ThOD).

Reference substance:

acetic acid, sodium salt

Test performance:

Toxicity
Inhibition of the degradation of a well-degradable compound, e.g. sodium acetate by the test substance in the Closed Bottle test was not determined because possible toxicity of dioctanoyl peroxide to microorganisms degrading acetate is not relevant. Inhibition of the endogenous respiration of the inoculum by the test substance at day 7 was not detected. Therefore, no inhibition of the biodegradation due to the "high" initial test substance concentration is expected.

Test conditions
The pH of the media was 7.3 at the start of the test. The pH of the medium at day 28 was 7.2 (controls) and 7.1 (test). Temperatures were within the prescribed temperature range of 22 to 24°C.

Validity of the test
The validity of the test is demonstrated by an endogenous respiration of 0.9 mg/L at day 28. Furthermore, the differences of the replicate values at day 28 were less than 20%. The biodegradation percentage of the reference
compound, sodium acetate, at day 14 was 78. Finally, the validity of the test is shown by oxygen concentrations >0.5 mg/L in all bottles during the test period.

Key result

Parameter:

% degradation (O2 consumption)

Value:

69

Sampling time:

28 d

Details on results:

Dioctanoyl peroxide is biodegraded by 69% at day 28 in the Closed Bottle test. The pass level of 60% was not reached within 14 days upon achieving 10% biodegradation. The reason for failing the 14-day window is probably the poor water solubility of the test substance. Poor water solubility of dioctanoyl peroxide is expected to affect biodegradation kinetics because slow desorption and dissolution rates of the test substance present at high concentrations may limit the biodegradation in ready biodegradability tests. The biodegradation curves of substances with a poor water solubility and limited bioavailability show a linear curve instead of the anticipated S-shaped curve. Poor water solubility is an important reason for not applying the time window (Battersby, 2000; Richterich and Steber, 2001). Dioctanoyl peroxide is therefore classified as readily biodegradable only based on the biodegradation percentage of 69% at day 28.

Key result

Parameter:

ThOD

Value:

2.4 other: mg O2/mg test. mat

Results with reference substance:

The ThOD of sodium acetate is 0.8 mg/mg

Dissolved oxygen concentrations (mg/L) in the closed bottles.

Time (days)	Oxygen concentration (mg/L)
	Ocs	Ot	Oc	Oa
0	8.8	8.8	8.8	8.8
	8.8	8.8	8.8	8.8
Mean (M)	8.8	8.8	8.8	8.8
7	8.1	6.6	8.2	4.4
	8.2	6.5	8.1	4.5
Mean (M)	8.2	6.6	8.2	4.5
14	8.0	5.6	8.0	3.8
	8.1	5.4	8.0	3.7
Mean (M)	8.1	5.5	8.0	3.8
21	8.0	5.1	8.1
	8.0	4.8	8.0
Mean (M)	8.0	5.0	8.1
28	7.9	4.4	7.9
	7.9	4.7	7.8
Mean (M)	7.9	4.6	7.9

 O_csMineral nutrient solution with only inoculums in bottles treated with DCM.

O_tMineral nutrient solution with test material (2.0 mg/L), and inoculum.

O_cMineral nutrient solution with only inoculum.

O_aMineral nutrient solution with sodium acetate (6.7 mg/L) and with inoculum.

Oxygen consumption (mg/L) and the percentages biodegradation of the test substance, dioctanoyl peroxide (BOD/ThOD) and sodium acetate (BOD/ThOD) in the Closed Bottle test.

 

Time (days)	Oxygen consumption (mg/L)		Biodegradation (%)
	Test substance	Acetate	Test substance	Acetate
0	0.0	0.0	0	0
7	1.6	3.7	33	69
14	2.6	4.2	54	78
21	3.0		63
28	3.3		69

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

The presence of dioctanoyl peroxide did not cause a reduction in the endogenous respiration. The test substance is therefore considered to be non-inhibitory to the inoculum. Dioctanoyl peroxide was biodegraded by 69% at day 28 in the Closed Bottle test. The test substance is therefore classified as readily biodegradable. The test is valid as shown by an endogenous respiration of 1.0 mg/L and by the total mineralization of the reference compound, sodium acetate. Sodium acetate was degraded by 78% 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.

Executive summary:

In order to assess the biotic degradation, a ready biodegradability test 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 slightly modified OECD, EU and ISO Test Guidelines, and in compliance with the OECD principles of Good Laboratory Practice.

The presence of dioctanoyl peroxide did not cause a reduction in the endogenous respiration. The test substance is therefore considered to be non-inhibitory to the inoculum. Dioctanoyl peroxide was biodegraded by 69% at day 28 in the Closed Bottle test. The test substance is therefore classified as readily biodegradable. The test is valid as shown by an endogenous respiration of 1.0 mg/L and by the total mineralization of the reference compound, sodium acetate. Sodium acetate was degraded by 78% 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 presence of dioctanoyl peroxide did not cause a reduction in the endogenous respiration. The test substance is therefore considered to be non-inhibitory to the inoculum. Dioctanoyl peroxide was biodegraded by 69% at day 28 in the Closed Bottle test. The test substance is therefore classified as readily biodegradable. The test is valid as shown by an endogenous respiration of 1.0 mg/L and by the total mineralization of the reference compound, sodium acetate. Sodium acetate was degraded by 78% 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.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable