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activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
guideline study (no GLP) - Documentation of the older study falls short of today´s requirements, but corresponds to the standards at the time they were conducted; the quality of the study performance is nevertheless not influenced. Sufficient data suitable for assessment.
according to
ISO 8192 (Water quality - Test for inhibition of oxygen consumption by activated sludge for carbonaceous and ammonium oxidation)
GLP compliance:
Analytical monitoring:
Details on test solutions:
- Method: Stock solution has been prepared; concentration: 1.25 g/L. Dilution series from stock solutions was prepared.
Test organisms (species):
activated sludge, domestic
Details on inoculum:
- Activated sludge from the municipal wastewater treatment plant of Edenkoben/Rheinland-Pfalz, Germany from 1990-02-13.
- Preparation of inoculum for exposure: The inoculum was washed twice.
- Biomass concentration: 1.5 g/L dry weight
Test type:
Water media type:
Limit test:
Total exposure duration:
180 min
Nominal and measured concentrations:
- Dilution series from a stock solution (1.25 g/L nominal) resulted in the following concentrations: 0, 0.02, 0.05, 0.2, 0.5, 1.0 g/L (nominal).
Reference substance (positive control):
180 min
Dose descriptor:
other: EC20
Effect conc.:
> 1 000 mg/L
Nominal / measured:
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
respiration rate
Details on results:
Expert judgement: The originally calculated EC20 (180 min) of 250 mg/L was corrected
- Inhibition effects (per cent inhibition) were calculated by using the mean of the two values determined for the controls (35.6 and 31.5 mg O2/[L h])
- The resulting inhibition effects [%] were: -17, -17, -12, -22, -12 for nominal concentrations of 0.02, 0.05, 0.2, 0.5, 1.0 g/L, respectively.
- Hence with the highest concentration of 1 g/L an inhibition effect of -12% was determined and only in one case the threshold of 20% was exceeded insignificantly.
Results with reference substance (positive control):
- Results with reference substance valid? Yes.
- Relevant effect levels: EC50 (180 min) between 5 and 30 mg/L
Validity criteria fulfilled:
The control respiration rates (blanc) are within 15 % of each other. The EC50 (180 min) of the reference control is in the accepted range 5 to 30 mg/L .
3-hour EC20: >1000 mg/L
Executive summary:

The toxicity of the test substance to microorganisms was studied in accordance with ISO 8192. The respiration rate of activated sludge was exposed to the test substance at concentrations of 0.02, 0.05, 0.2, 0.5, and 1.0 g/L. The 180-minute EC20 was >1000 mg/L.

Description of key information

3-hour EC20 (activated sludge, domestic): >1000 mg/L; ISO 8192; Reliability = 2

Key value for chemical safety assessment

Additional information

EC20 for microorganisms: 1000 mg/L