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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:
2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
Physical state/Appearance: white solid
Batch: 08262015
Purity: >98%
Expiry Date: 20 June 2017
Storage Conditions: room temperature in the dark
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge (adaptation not specified)
Details on inoculum:
A mixed population of activated sewage sludge micro-organisms was obtained on from the aeration stage of the Severn Trent Water Plc sewage treatment plant, which treats predominantly domestic sewage.

The activated sewage sludge sample was washed twice by settlement and re-suspension in mineral medium to remove any excessive amounts of dissolved organic carbon (DOC) that may have been present. The washed sample was then maintained on continuous aeration in the laboratory at a temperature of approximately 21 ºC and used on the day of collection. Determination of the suspended solids level of the activated sewage sludge was carried out by filtering a sample (100 mL) of the washed activated sewage sludge by suction through pre-weighed GF/A filter paper using a Buchner funnel. Filtration was then continued for a further 3 minutes after rinsing the filter three successive times with 10 mL of deionized reverse osmosis water. The filter paper was then dried in an oven at approximately 105 ºC for at least 1 hour and allowed to cool before weighing. This process was repeated until a constant weight was attained. The suspended solids concentration was equal to 3.0 g/L prior to use.
Duration of test (contact time):
28 d
Initial conc.:
14.3 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
Preliminary Solubility Work
Information provided by the Sponsor indicated that the solubility of the test item in water was 0.028 g/mL. Therefore preliminary solubility/dispersibility work was performed in order to determine the most suitable method of preparation.

Preparation of Test System
The following test preparations were prepared and inoculated in 5 liter test culture vessels each containing 3 liters of solution:

a) An inoculated control, in duplicate, consisting of inoculated mineral medium.
b) The procedure control containing the reference item (sodium benzoate), in duplicate, in inoculated mineral medium to give a final concentration of 10 mg carbon/L.
c) The test item, in duplicate, in inoculated mineral medium to give a final concentration of 10 mg carbon/L.
d) The test item plus the reference item in inoculated mineral medium to give a final concentration of 20 mg carbon/L to act as a toxicity control (one vessel only).
Data from the inoculum control and procedure control vessels was shared with similar concurrent studies.

Each test vessel was inoculated with the prepared inoculum at a final concentration of 30 mg suspended solids (ss)/L. The test was carried out in a temperature controlled room at temperatures of between 22 and 24C, in darkness.

Approximately 24 hours prior to addition of the test and reference items the vessels were filled with 2400 mL of mineral medium and 30 mL of inoculum and aerated overnight. On Day 0 the test and reference items were added and the pH of all vessels measured using a Hach HQ40d Flexi handheld meter. The pH was adjusted to pH 7.4 ± 0.2 using diluted hydrochloric acid or sodium hydroxide solution prior to the volume in all the vessels being adjusted to 3 liters by the addition of mineral medium which had been purged overnight with CO2 free air.

The test vessels were sealed and CO2-free air bubbled through the solution at a rate of 30 to 100 mL/min per vessel and stirred continuously by magnetic stirrer.

The CO2-free air was produced by passing compressed air through a glass column containing self-indicating soda lime (Carbosorb®) granules.

The CO2 produced by degradation was collected in two 500 mL Dreschel bottles containing 350 mL of 0.05 M NaOH. The CO2 absorbing solutions were prepared using purified water.
Key result
Parameter:
% degradation (CO2 evolution)
Value:
70
Sampling time:
28 d
Details on results:
The test item attained 70% biodegradation after 28 days. Under the strict terms and conditions of OECD Guideline No. 301B the test item cannot be considered to be readily biodegradable as the test item failed to satisfy the 10-Day window validation criterion, whereby 60% biodegradation must be attained within 10 days of the biodegradation exceeding 10%. However, the test item has exhibited the potential for rapid biodegradation.

The toxicity control attained 48% biodegradation after 14 days and 76% biodegradation after 28 days thereby confirming that the test item did not exhibit an inhibitory effect on the sewage treatment micro-organisms used in the test.

Results with reference substance:
Sodium benzoate attained 70% biodegradation after 14 days and 79% biodegradation after 28 days thereby confirming the suitability of the inoculum and test conditions.

Percentage Biodegradation Values

Day

% Biodegradation

Procedure Control

Test Item

Toxicity Control

0

0

0

0

2

55

0

28

6

60

6

31

8

78

17

41

10

78

27

46

14

70

32

48

21

83

54

63

28

79

70

76

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable, but failing 10-day window
Conclusions:
2-Propenoic acid, 2-[[(octadecylamino)carbonyl]oxy]ethyl ester attained 70% biodegradation after 28 days. Under the strict terms and conditions of OECD Guideline No. 301B the test item cannot be considered to be readily biodegradable as the test item failed to satisfy the 10-Day window validation criterion, whereby 60% biodegradation must be attained within 10 days of the biodegradation exceeding 10%.

Description of key information

In an OECD 301B study, under GLP conditions, 2-Propenoic acid, 2-[[(octadecylamino)carbonyl]oxy]ethyl ester degraded 70% after 28 days, however it failed to reach 60% degradation after 10 days and therefore failed to meet the 10 day window. 2-Propenoic acid, 2-[[(octadecylamino)carbonyl]oxy]ethyl ester is, therefore, considered to be not readily biodegradable (Envigo, 2016e).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable but failing 10-day window
Type of water:
freshwater

Additional information