Octanoic acid, 2-phenoxyethyl ester

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

02 Dec 2011

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: GLP Guideline study with acceptable restrictions: No test substance monitoring was performed. The pH in some test vessels was slightly higher (pH 8.2) than recommended by the guideline. No analytical purity is given.

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Version / remarks:

adopted 22 July 2010

Deviations:

no

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Preparation was as much as possible performed under yellow light and/or low light conditions. The test substance was not completely soluble in test medium at the loading rates initially prepared. Therefore, 1 L test bottles were filled with 200 mL of test substance mixtures in Milli-RO water with initial loading rates of 2.5 times the final loading rate. These mixtures were stirred in closed dark brown bottles for approx. 24 hours. The appearance of these mixtures varied from clear to opalescent, with test substance at the surface of the medium. Subsequently, 16 mL synthetic sewage feed, 250 mL sludge and Milli-RO water up to 500 mL were added resulting in the required loading rates.

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Preparation of inoculum for exposure: Activated sludge were obtained from the municipal sewage treatment plant Watershap Aa en Maas ('s-Hertogenbosch, The Netherlands), which predominantely treats domestic sewage. The sludge was coarsely sieved, washed and diluted with ISO-medium. A small amount of the sludge was weighed and dried overnight at ca. 105 °C to determine the amount of suspended solids (3.0 g/L). The pH was 7.7 on day of testing. The batch of sludge was used one day after collection; therefore 50 mL of synthetic sewage feed (prepared according to guideline) was added per litre of activated sludge at the end of the collection day. The sludge was kept aerated at test temperature until use.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

20 - 21.2 °C

pH:

7..7 - 7.8 (test start)
7.5 - 8.2 (test end)

Dissolved oxygen:

7.8 - 9.0 mg O2/L (test start)

Nominal and measured concentrations:

Nominal: 10, 100 and 1000 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: beakers
- Material: glass; size: 1 L; fill volume: 500 mL
- Aeration: The aeration with clean, oil-free air was adjusted in such a way that the dissolved oxygen concentration at the start was above 60-70% saturation (60% of air saturation is > 5 mg/L at 20 °C) and to maintain the sludge flocs in suspension.
- No. of vessels per concentration: 1 (10 and 100 mg/L ); 3 (1000 mg/L); 1 (1000 mg/L with nitrification inhibitor)
- No. of vessels per control: 6 (blank control); 1 (nitrification control); 1 (abiotic control);

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: tap-water purified by reverse osmosis (Milli-RO) and subsequently passed over activated carbon and ion-exchange cartridges (Milli-Q)
- Test medium: adjusted ISO medium, formulated using RO-water with the following composition: 211.5 mg/L CaCl2 x 2H2O + 88.8 mg/L MgSO4 x 7 H2O + 46.7 mg/L NaHCO3 + 4.2 mg/L KCl
- Intervals of water quality measurement: Oxygen concentration was measured in all controls and test concentrations at the start of the test and pH was measured ain all controls and test concentrations at the start and the end of the test. Temperature was measured at the end of the test period.

EFFECT PARAMETERS MEASURED: Oxygen consumption was recorded for a period of 10 minutes after 3 h test duration using oxygen probes connected to a BlueBox, a multichannel measuring and controlling system.

TEST CONCENTRATIONS
- Range finding study: A combined limit/range finding test was performed.

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Remarks:

respiration rate

Details on results:

No statistical significant inhibition of the respiration rate of the sludge was recorded at a loading rate of 1000 mg/L. Furthermore, there was no oxygen uptake from abiotic processes and no heterotrophic inhibition at 1000 mg/L after exposure with a nitrification inhibitor.

Results with reference substance (positive control):

- Results with reference substance valid? yes
- Relevant effect levels: The EC50 of the reference substance is with 8.1 mg/L within the acceptable range of 2 to 25 mg/L for total respiration.

Reported statistics and error estimates:

Statistical significance of inhibition of the respiration rate was calculated at a loading rate of 1000 mg/L using a chi-square test for normality, the F-test for equality of variances and a two sample t-test (Toxstat).

The effect at a loading rate of 1000 mg/L is statistically significant. However, this effect was stimulation instead of inhibition of the respiration rate and therefore considered as not significant for the test.

Table 1: Study results

Flask	Conc./loading rate [mg/L]	Respiration rate [mg O2/L h]	Respiration rate [mg O2/g h]*	Inhibition respiration related to the control (mean value)
Control 1	0	38	25
Control 2	0	39	26
Control 3	0	36	24
Control 4	0	33	22
Control 5	0	34	23
Control 6	0	37	25
Mean		36	24
SD		2	2
CV (%)		6	6
CN (with ATU)	0	21	14
Reference 1	5.0	23	15	36
Reference 2	12	13	9	64
Reference 3	30	7	5	81
Treatment 1	10	41	27	-13
Treatment 2	100	41	27	-13
Treatment 3a	1000	46	31	-27
Treatment 3b	1000	43	29	-19
Treatment 3c	1000	41	27	-13
Treatment 3 (mean)		43	29	-20
TA (abiotic)	1000	1	1	97
TN (with ATU)	1000	30	20	-43**

CN: nitrification control

CV: coefficient of variance

ATU: N-allylthiourea

*: The amount of suspended solids in the final test mixture was 1.5 mg/L.

**: relative to CN

Description of key information

Not toxic to microorganisms, EC10 >1000 mg/L

Additional information

The effect of 2-Phenoxyethyl octanoate (CAS 23511-73-1) on the respiration of activated sludge was investigated according to OECD guideline 209. Non-adapted activated sludge taken from a municipal sewage treatment plant was exposed to test substance concentrations of 10, 100 and 1000 mg/L. The respiration rate of the activated sludge was recorded for 3 hours. A significant reduction of the respiration rate compared to the control was not observed. The reported EC10 is > 1000 mg/L (nominal).