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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:
November 2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP study following OECD guideline, well described.
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
yes
Remarks:
ammonium chloride was omitted from the medium to prevent oxygen consumption due to nitrification (omission does not result in nitrogen limitation as shown by the biodegradation of the reference compound).
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
Secondary activated sludge (15-08-2013) was obtained from the wastewater treatment plant Nieuwgraaf in Duiven, The Ne¬therlands. 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):
60 d
Initial conc.:
2 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Parameter:
% degradation (O2 consumption)
Value:
32
Sampling time:
7 d
Remarks on result:
other: % degradation after 28 days
Parameter:
% degradation (O2 consumption)
Value:
82
Sampling time:
7 d
Remarks on result:
other: % degradation after 60 days
Results with reference substance:
The biodegradation percentage of the reference compound, sodium acetate, at day 14 was 78. Final¬ly, the validity of the test is shown by oxygen concentrations >0.5 mg/L in all bottles during the test period.

 

Theoretical oxygen demand (ThOD)

The calculated theoretical oxygen demand (ThOD) of test substance tert-pentyl peroxypivalate, (75% active material and 25% isododecane) is 2.6 mg/mg. The ThOD of isododecane is 3.5 mg/mg. The ThOD of the active material is 2.3 mg/mg. The ThOD of sodium acetate is 0. 8 mg/mg

 

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 the test substance 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 (Table I). 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 7.1 (controls and isododecane) and 7.2 (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  0.7 mg/L at day 28 (Ta­ble I). 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.

 

Biodegradability

The biodegradability of the test substance was 21 and 52% at day 28 and 60, respectively. Isododecane was not biodegraded in the prolonged Closed Bottle tests (Table II). Lack of biodegradation does not mean that isododecane is recalcitrant in nature. The stringency of the test procedures could account for the recalcitrance of isododecane in the Closed Bottle test. Tert-pentyl peroxypivalate (active material) is biodegraded 32% at day 28 in the Closed Bottle test (Figure and Table II). The tert-pentyl peroxypivalate is biodegraded 82% at day 60 in the prolonged Closed Bottle test. Tert-pentyl peroxypivalate (active material) should therefore be clas­sified as inherently biodegradable and not persistent.

Validity criteria fulfilled:
yes
Remarks:
Endogenous respiration of 0.7 mg/L at day 28. Furthermore, the differences of the replicate values at day 28 were less than 20%
Interpretation of results:
inherently biodegradable
Conclusions:
Under the conditions of the test, is inherently biodegradable
Executive summary:

ABSTRACT

 

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 tert-pentyl peroxypivalate did not cause a reduction in the endogenous respiration. The test substance is therefore con­sidered to be non-inhibitory to the inoculum.

Tert-pentyl peroxypivalate was biodegraded 32% at day 28 in the Closed Bottle test. In the prolonged Closed Bottle test this substance was biodegraded 82% at day 60. Although tert-pentyl peroxypivalate (active material) cannot be classified as readily biodegradable, the biodegradation reached at the last day of the test demonstrates that this substance is inherently biodegradable and not persistent

The test is valid as shown by an endogenous respiration of 0.7 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

One OECD 301D test is available where tert-pentyl peroxypivalate is biodegraded 82% after extending test to 60 days.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable, fulfilling specific criteria

Additional information

Tert-pentyl peroxypivalate (active material) is biodegraded 32% at day 28 in the Closed Bottle test. The tert-pentyl peroxypivalate is biodegraded 82% at day 60 in the prolonged Closed Bottle test. Tert-pentyl peroxypivalate (active material) should therefore be classified as inherently biodegradable and not persistent.