Oligo

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:

18 Oct 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))

Version / remarks:

Adopted 22 July 2010

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: The test sample (250 mg), synthetic sewage (8 mL), purified water (117 mL) and the activated sludge (125 mL) were added to each test vessel. The test sample was accurately weighed with an electric analytical balance and added.
- Eluate: no
- Differential loading: yes
- Controls: yes, test medium control

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Name and location of sewage treatment plant where inoculum was collected: Kurume central sewage treatment center (Kurume-shi, Fukuoka, Japan); Sampled on: 17 Oct 2017
- Method of cultivation: The activated sludge (4 L) was fed with 200 mL synthetic sewage and cultivated for 22.5 h at 20 ± 2 °C under aerobic condition in order to acclimate to the test temperature. Acclimation to the test item was not performed.
- Suspended solids: 2420 mg/L

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

20 ± 2 °C

pH:

7.5 ± 0.5

Nominal and measured concentrations:

nominal: control, 1000 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 300 mL glass vessel (102 mL measurement bottle)
- Aeration: yes (flow rate: 0.5 - 1 L/min)
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 6
- No. of vessels per positive control: 1
- Nutrients provided for bacteria: synthetic sewage according to guideline

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: purified water according to guideline

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Details on termination of incubation: After 3 h of exposure, the measurement bottle was filled with the test solution promptly and softly with attention to avoid foaming. Afterwards, the concentration of dissolved oxygen (DO) was measured.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable)
- Respiration rate was measured after 3 h of exposure

TEST CONCENTRATIONS
- Justification for using fewer concentrations than requested by guideline:
- Range finding study
- Test concentrations: 10, 100 and 1000 mg/L
- Results used to determine the conditions for the definitive study: An inhibition of -1%, -2% and 0%, respectively was found after 3 h of exposure.

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Details on results:

- Blank controls oxygen uptake rate: 76.7 mg O2/g/h
- Coefficient of variation of oxygen uptake rate in control replicates: 1.3%

Results with reference substance (positive control):

- Results with reference substance valid? yes
- Relevant effect levels: EC50 (3 h): 11 mg/L

Table 1: Oxygen consumption rate and percentage inhibition of respiration after 3 h of exposure

Test solution	Nominal concentration (mg/L)	Oxygen consumption rate (mg O2/L/h)	Percentage inhibition of respiration (%)	Average percentage inhibition of respiration (%)
Test mixture	1000	83.4	10	8
	1000	86.4	7
	1000	87.6	6
Reference mixture	4.0	84.7	9	-
	8.0	64.4	31	-
	16	20.5	78	-
	32	8.08	9.1	-
Blank control	-	At the beginning: 89.0, 92.6, 94.3 At the end: 93.9, 92.8, 94.4	-	-

Average oxygen consumption rate in blank control: 92.8 mg O2/L/h

Table 2: Validity criteria for OECD 209.

Criterion from the guideline	Outcome	Validity criterion fulfilled
The blank controls (without the test substance or reference substance) oxygen uptake rate should not be less than 20 mg oxygen per one gram of activated sludge (dry weight of suspended solids) in an hour.	76.7 mg O2/g/h	yes
The coefficient of variation of oxygen uptake rate in control replicates should not be more than 30% at the end of definitive test.	1.3%	yes

 

Validity criteria fulfilled:

yes

Remarks:

For further details please refer to “Any other information on results incl. tables”.

Description of key information

EC50 (3 h) > 1000 mg/L (OECD 209, inhibition of respiration)

Additional information

One experimental study according to OECD 209 (GLP) is available investigating the effects of Fatty acids C16-18 (even numbered), oligoesters with sucrose on the respiration of activated sludge microorganisms. Activated sludge from a municipal sewage treatment plant was used as inoculum and exposed for 3 h. The respiration rate was measured after 3 h of exposure. An inhibition of 8% (mean of three replicates) was calculated resulting in an EC50 (3 h) > 1000 mg/L.