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activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to guideline
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
GLP compliance:
Specific details on test material used for the study:
- Name of test material (as cited in study report): N-Hexyldiglykol roh
- Physical state: colourless liquid
- Analytical purity: not reported
- Batch No.: taken from continuous production process
- Storage condition of test material: at room temperature
Test organisms (species):
activated sludge, domestic
Details on inoculum:
- Activated sludge from Iaboratory wastewater plants treating municipal and synthetic sewage.
- Initial biomass concentration: 1 g/L dw
- Preparation of inoculum for exposure: The inoculum was washed, brought to a concentration of 5 g/L dry substance and aerated for 24 hours. 50 ml were added to a total volume of 250 ml to obtain a concentration of 1 g/L dry substance in the test.
Test type:
Water media type:
Limit test:
Total exposure duration:
30 min
Test temperature:
20 ± 2 °C
7.2 - 7.4
Nominal and measured concentrations:
Nominal concentration: 1000 mg/L
Details on test conditions:
- Test vessel: Erlenmeyer-vessel (nominal volume 250 mL)
- Synthetic medium: 8 mL/vessel 100-fold concentrated OECD medium

Reference substance (positive control):
Key result
30 min
Dose descriptor:
Effect conc.:
1 000 mg/L
Nominal / measured:
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
respiration rate
Results with reference substance (positive control):
Effective concentrations:
EC20= 1.6 mg/L
EC50= 9 mg/L
EC80= 63 mg/L

Description of key information

The inhibition of the degradation activity of activated sludge is not anticipated when DGHE is introduced in appropriate low concentrations.

The NOEC value is ≥1000 mg/L as observed in a respiration inhibition study with activated sludge of a predominantly domestic sewage.

Key value for chemical safety assessment

Additional information

The toxicity of the substance to microorganisms was investigated in an activated sludge respiration inhibition study according to OECD TG 209 and in compliance with GLP criteria (BASFSE, 1999). In this study activated sludge from domestic sewage was exposed in a limit test to 1000 mg/L test substance for 30 minutes. The effects on microorganisms was determined by measuring total respiration rates and comparing these to an unexposed control. Inhibition of respiration rates was not observed. Based on these findings, the NOEC value was determined at 1000 mg/L.

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