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activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1 (reliable without restriction)
according to guideline
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
GLP compliance:
yes (incl. QA statement)
Test organisms (species):
activated sludge of a predominantly domestic sewage
Total exposure duration:
3 h
Remarks on exposure duration:
contact time 3 hours, during which aeration takes place
Test temperature:
20 ± 2°C
Details on test conditions:
Duration: contact time 3 hours, during which aeration takes place
Air supply: clean, oil-free air. Air flow 0.5 to 1 litre/minute
Nutrient solution: synthetic sewage feed
Test item concentrations:: 0.10, 1.0, 10.0, 100.0 and 1000.0 mg/l
Reference item concentrations: 0.01 , 0.1, 1.0 , 10.0 and 100.0 mg/l
Blank controls: Inoculated sample without test substance
Temperature: 20 ± 2°C
Test item stock solutions 10 g/l (at pH = 7.0) (no undissolved particles were
Reference substance stock solutions 1 g/l
Synthetic medium stock solution: See p. 3.1.4
Activated sludge stock suspension: 3 g/l of suspended solids
Activated sludge suspension in test vessels 1.5 g/l of suspended solids
ATU stock solution 2.32 g/l
3 h
Dose descriptor:
Effect conc.:
109 mg/L
Basis for effect:
inhibition of total respiration
3 h
Dose descriptor:
Effect conc.:
158.6 mg/L
Basis for effect:
inhibition of heterotrophic respiration
3 h
Dose descriptor:
Effect conc.:
57.3 mg/L
Basis for effect:
inhibition of nitrification rate
Details on results:
The following test item end points ECX (mg/l) were calculated (eq. for total, heterotrophic and
nitrification inhibition.
ECx, mg/l
Inhibition, % EC20 EC50 EC90
Total 75.1 109.0 175.6
Heterotrophic 123.6 158.6 282.8
Nitrification < 0.1 57.3 247.3
The lowest tested concentration that causes the observed respiration inhibition is equal to 0.1 mg/l.
Validity criteria fulfilled:
calculated values of the end points EC50 for the test item were found to be:
1. Total respiration inhibition: 109.0 mg/l.
2. Heterotrophic respiration inhibition: 158.6 mg/l.
3. Nitrification inhibition: 57.3 mg/l .

Description of key information

Key value for chemical safety assessment

EC50 for microorganisms:
109 mg/L

Additional information