Octanoic acid, 2-phenoxyethyl ester

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:

10 Dec 2008 - 8 Jan 2009

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge: Activated sludge was obtained from the municipal sewage treatment plant "Waterschap de Maaskant", ('s-Hertogenbosch, The Netherlands), which received predominantely domestic sewage.
- Storage conditions: The activated sludge was kept under continuous aeration until further treatment.
- Preparation of inoculum for exposure: Before use, the sludge was allowed to settle (34 min.) and the liquid was decanted for use as inoculum.
- Water filtered: yes
- Type and size of filter used, if any: Tap-water was purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon and ion-exchange cartridges (Milli-Q)

Duration of test (contact time):

28 d

Initial conc.:

12 mg/L

Based on:

other: TOC

Initial conc.:

16.5 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: as recommended in guideline
- Test temperature: 21.5 - 22.2 °C
- pH: 7.6 - 7.9
- pH adjusted: no
- Aeration of dilution water: continuously
- Suspended solids concentration: 4.1 g/L
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 2 L all-glass brown coloured bottles
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: CO2-free air was passed through the test vessel at a rate of ~ 1-2 bubbles per second (~ 30-100 mL/min.).
- Measuring equipment: The amount of CO2 produced was determined by titrating the remaining Ba(OH)2 with 0.05 M standardized HCl.
- Details of trap for CO2 and volatile organics if used: Three CO2 absorbers (bottles filled with 100 mL 0.0125 M Ba(OH)2) were connectedin series to the exit air line of each test bottle.

SAMPLING
- Sampling frequency: On days 2, 5, 7, 9, 14, 19, 23, 27 and 29.
- Sampling method: The CO2-absorber nearest to the test bootle was removed for titration (each of the remaining two absorbers was moved one position in the direction of the test vessel and a new one was placed at the end of the series).

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2
- Positive control: 1
- Toxicity control: 1

Reference substance:

benzoic acid, sodium salt

Remarks:

12 mg/L TOC

Parameter:

% degradation (CO2 evolution)

Value:

81

Sampling time:

28 d

Remarks on result:

other: average of two replicates: 86%, 77%

Details on results:

The test substance reached a biodegradation of > 60% within 28 days, but the 10 day-window criterion was not met. Thus, the test substance is readily biodegradable but failing the ten day window according to OECD criteria. Based on the permanently increasing degradation curve during the test period and the high biodegradation rate of 81% achieved within 28 days, the test substance can be considered as biodegradable.

Results with reference substance:

The reference substance was degraded to 64% in 28 days.

In the toxicity control more than 25% biodegradation occurred within 14 days (51% based on hCO2). Therefore, the test substance was assumed not to inhibit microbial activity.

Table 1: Biodegradation of blank and test substance (bottle 1 and 2)

Day	Cumulative CO2 [mg]			Biodegradation [%]
	Blank	Bottle 1	Bottle 2	Bottle 1	Bottle 2
2	2.1	0.0	0.3	0	0
5	5.8	11.6	9.7	13	11
7	8.3	18.2	15.4	21	17
9	11.5	24.5	19.8	28	22
14	16.9	38.0	33.7	43	38
19	22.7	59.8	55.2	68	62
23	29.5	68.3	63.1	78	71
27	35.6	73.0	66.8	83	75
29	45.5	75.5	67.9	86	77

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable, but failing 10-day window

Description of key information

Readily biodegradable but failing 10-day window: 81% in 28 days (OECD 301B)

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

The biodegradability of 2-Phenoxyethyl octanoate (CAS 23511-73-1) was tested according to OECD guideline 301B. The initial test substance concentration was 16.5 mg/L (12mg/L based on TOC) Non-adapted effluent obtained from a STP predominately treating domestic sewage was used as inoculum. Based on the CO2 evolution a mean degradation rate of 81% was observed after 28 days (mean of two replicates with 86% and 77%). The degradation rate did not reach the pass level of 60% removal of DOC within the 10-day window. Therefore, the substance is considered readily biodegradable but failing 10-day window.