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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From December 14 to December 15, 2020
Reliability:
1 (reliable without restriction)
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))
Version / remarks:
22 July 2010
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
no
Vehicle:
yes
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: To prepare test item mixtures, the test item was directly weighed into the test vessel and distilled water was added.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Laboratory culture:
- Name and location of sewage treatment plant where inoculum was collected: A fresh sample of activated sludge was collected from the aeration tank of Shenyang North Sewage Treatment Plant 1 day before the test was started.
- Method of cultivation: The activated sludge was fed with the synthetic sewage feed (50 mL synthetic sewage feed/L activated sludge) and continuously aerated at the test temperature (preliminary test: 19.9~20.5°C) overnight prior to use in the test.
- Preparation of inoculum for exposure:
- Pretreatment: Before the activated sludge was used as the inoculum, the concentration of the sludge was determined again by the drying method, and the concentration was adjusted to be 3 g/L.
- Initial biomass concentration:
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20±2°C
pH:
7.0
Dissolved oxygen:
above 60 – 70% saturation
Nominal and measured concentrations:
10, 100, 300 and 1000 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel:
- Type (delete if not applicable): open
- Material, size, headspace, fill volume:
- Aeration: Test mixtures, reference mixtures and the blank controls were incubated at the test temperature under conditions of forced aeration (0.5 to 1 L/min) to keep the dissolved oxygen concentration above 60 – 70% saturation and to maintain the sludge flocs in suspension.
- No. of vessels per concentration (replicates): The test concentrations of 10, 100 and 300 mg/L were tested with 1 replicate, and 1000 mg/L was tested with triplicate.
- No. of vessels per control (replicates):
- No. of vessels per vehicle control (replicates):
- No. of vessels per abiotic control (replicates): 1 abiotic control at concentration of 1000 mg/L was performed.
- Sludge concentration (weight of dry solids per volume): 3 g/L
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol (3,5-DCP)
Key result
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:
In preliminary test, the specific oxygen uptake rate of the blank controls (without the test item or reference item) was 20.8 mg/(g·h SS) oxygen. The coefficient of variation of oxygen uptake rate in control replicates was 2.8% at the end of the test. The validity criteria have therefore been satisfied.
Based on the preliminary test results of the test item test, there was no oxygen uptake in the abiotic control. In the test item mixture, the average percentage inhibition was 11.4% at the concentration of 1000 mg/L and the test item had slight inhibition effect in 1000 mg/L.
Due to the absence of significant inhibition of oxygen consumption by the test item in a preliminary test a definitive test is unnecessary.
Results with reference substance (positive control):
The EC50 (3 hours) of 3,5-dichlorophenol for total respiration is 5.9 mg/L.
Validity criteria fulfilled:
yes
Conclusions:
The EC50 (3 hours) of the test item for total respiration was greater than 1000 mg/L under the conditions of the study.
Executive summary:

The study was conducted according to OECD Guideline 209 under GLP, to determine the inhibition effect of the test item on micro-organisms from activated sludge (largely bacteria) by measuring their total respiration rate. The contact time for exposure was 3 hours.


Based on the preliminary test results of the test item test, there was no oxygen uptake in the abiotic control. In the test item mixture, the average percentage inhibition was 11.4% at the concentration of 1000 mg/L and the test item had slight inhibition effect in 1000 mg/L.


Due to the absence of significant inhibition of oxygen consumption by the test item in a preliminary test a definitive test is unnecessary.


Therefore, the EC50 (3 hours) of the test item for total respiration was greater than 1000 mg/L under the conditions of the study.

Description of key information

The EC50 (3 hours) of the test item for total respiration was greater than 1000 mg/L under the conditions of the study.

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L

Additional information

The study was conducted according to OECD Guideline 209 under GLP, to determine the inhibition effect of the test item on micro-organisms from activated sludge (largely bacteria) by measuring their total respiration rate. The contact time for exposure was 3 hours.


Based on the preliminary test results of the test item test, there was no oxygen uptake in the abiotic control. In the test item mixture, the average percentage inhibition was 11.4% at the concentration of 1000 mg/L and the test item had slight inhibition effect in 1000 mg/L.


Due to the absence of significant inhibition of oxygen consumption by the test item in a preliminary test a definitive test is unnecessary.


Therefore, the EC50 (3 hours) of the test item for total respiration was greater than 1000 mg/L under the conditions of the study.