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activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
7 June 2005 - 8 June 2005
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to guideline
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
according to guideline
EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
Lot number: 52834
Expiry date: December 2006
Purity/Composition: >98%
Appearance: Clear, colourless liquid
Storage conditions: Room temperature in the dark
Analytical monitoring:
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Laboratory culture: no
- Name and location of sewage treatment plant where inoculum was collected: domestic treatment plant
- Preparation of inoculum for exposure: maintained under aerobic conditions
- Pretreatment: dried, mixed with synthetic sewage then the mixture was aerated overnight
- Initial biomass concentration:
Test type:
other: aerobic
Limit test:
Total exposure duration:
3 h
200 - 250 mg/l CaCO3
Test temperature:
20 ± 2°C
7.3 - 8.0
Nominal and measured concentrations:
Nominal concentrations: 1, 10 and 100 mg/l
Details on test conditions:
- Test vessel: beakers
- Type (delete if not applicable): closed
- Material, size, headspace, fill volume: glass
- Aeration: yes
- No. of vessels per concentration (replicates): 1 for 1 and 10 mg/l and 3 for 100 mg/l
- No. of vessels per control (replicates): 1
- No. of vessels per positive control (replicates): 1
- Sludge concentration (weight of dry solids per volume): 4g/l
- Adjustment of pH: no
- Source/preparation of dilution water: dechlorinated tap water
EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : oxygen consumption
Reference substance (positive control):
Key result
3 h
Dose descriptor:
Effect conc.:
> 100 mg/L
Nominal / measured:
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks on result:
not determinable
Details on results:
The specific respiration rate of the contro culture established at the end of the test (21.4 mgO2/g/h) was 99% of the rate of the established at the start (21.7 mgO2/g/h).
The test was valid and the sample of activated sludge employed was sensitive to inhibition.
The test item was considered to have had no biologically significant inhibitory effect on the respiration rate of activated sludge at any of the concentrations employed in the test. The sludge respiration rate was decreased by 6% in two of the replicates at a concentration of 100 mg/l and by 11% in the third replicate.
Results with reference substance (positive control):
Sludge respiration rates were progressively reduced in the presence of increasing concentrations of 3,5-DCP. The three-hour 50% effect concentration (EC50) for 3,5-DCP was calculated to be 7.0 mg/l (95% confidence limits 5.1 - 9.4 mg/l).
Validity criteria fulfilled:
The test, item was considered to have had no biologically significant inhibitory effect on the respiration rate of activated sludge at any of the concentrations emplyed in the test. The EC20, EC50 and EC80 of the test substance could not, therefore, be calculated but these must be greater than 100mg/l,the highest level tested.

Description of key information

Activated Sludge Respiration inhibition test:

The EC20, EC50 and EC80 of the test substance could not be calculated but these must be greater than 100 mg/l, the highest level tested.

Key value for chemical safety assessment

EC50 for microorganisms:
100 mg/L

Additional information