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Toxicity to microorganisms

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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
according to
other: Respiration inhibition test, ETAD ecological method no. 103
GLP compliance:
Analytical monitoring:
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
Source: ARA rhein, Pratteln, Switzerland
Treatment: the sludge is centrifuged and washed 3 times with drinking water, then suspended in water with a solids content of 4 g/l and, after the addition of 50 ml synthetic sewage, aerated overnight at 20 °C.
Water media type:
Limit test:
Total exposure duration:
3 h
180 mg CaCO3/l
Test temperature:
20 ± 2 °C
7.6 - 8.0
Details on test conditions:
- Test vessel: 1000 ml glass beaker with 500 ml test solution
- Aeration: 0.5 to 1 l/min
- No. of vessels per concentration: 1
- Sludge concentration: 1.6 g/l

EFFECT PARAMETERS MEASURED: inhibition of respiration

- Test concentrations: 100, 180, 320, 560, 1000 mg/l, control 1 and control 2
Reference substance (positive control):
3 h
Dose descriptor:
Effect conc.:
950 mg/L
Nominal / measured:
Conc. based on:
test mat.
Basis for effect:
other: inhibition of respiration - oxygen consumption
Details on results:
conc. mg/l oxygen consumption (mg O2/min/g) inhibition %
control 1 0.719 -
control 2 0.792 -
control, mean 0.756 0
100 0.702 7.1
180 0.746 1.3
320 0.625 17.3
560 0.537 29
1000 0.347 54.1
Estimated IC50 = 950 mg/l
Executive summary:

Test on toxicity to microorganisms according to ETAD ecological method no. 103.

Concentrations of 100, 180, 320, 560 and 1000 mg/l were tested; 2 controls were run. Inhibition of respiration, based on oxygen consumption, was assessed 3 hours after start of exposure.

An IC50 (3h) value of 950 mg/l was estimated.

Description of key information

IC50 (3h) = 950 mg/l

Key value for chemical safety assessment

EC50 for microorganisms:
950 mg/L

Additional information

The toxicity to microorganisms was investigated following the procedures outlined into the ETAD ecological method no. 103. Two studies were available, on different test samples.

In the key study, a test sample of high dyestuff content (ca. 94 %) was used. The experiment was run at the following nominal concentrations: 100, 180, 320, 560 and 1000 mg/l. During the exposure period of 3 hours, respiration inhibition based on oxygen consumption was measured.

The IC50 value was determined to be 950 mg/l.

In the supporting study, a liquid test sample was used, with a dyestuff content of 17 %. Test concentrations were 560, 1000,1800, 3200, 5600 mg/l. The IC50 value was determined to be 4800 mg/l, equivalent to 816 mg/l as active ingredient.

Overall, both data are indicative of the same toxicity profile.