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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:
other: A well performed guideline study. Certificate of analyses not included in the study report.
according to guideline
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
reference compound was exchange to a by the time availble compound (see section regarding ref compunds below)
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
Secondary activated sludge was collected from the RZWI Nieuwgraaf in Duiven (1989.11.8). This activated sludge plant predominantly treats domestic wastewater. Prior the use, the activated sludge was diluted with tap water (1.5 x) and homogenized for two minutes in a lab blender.
Test type:
Water media type:
Reference substance (positive control):
Key result
30 min
Dose descriptor:
Effect conc.:
11.1 mg/L
Nominal / measured:
Conc. based on:
act. ingr.
Basis for effect:
inhibition of total respiration
respiration rate
Details on results:
The respiration rates and the inhibition percentages and the results is reported as follows:
EC10 : 0.5 mg/L
EC20: 3.2 mg/L
EC80: 38.3 mg/L
Results with reference substance (positive control):

- Results with reference substance valid? YES
- Relevant effect levels: EC50 of the reference compound wihtin the acceptable range (5-30 mg/L)
- Other:

Respiration rate of the activated sludge (Rs) and inhibition percentage calculated at various concentration of the test compoun

 Concentration (mg/L)  pH start  Respiration rate (mg O2/L min)  Inhibition (%)
 Control Rcl 7.8 0.37 
 Control Rcl 7.8 0.37 
 2.8 7.8  0.31  16 
 5.7 7.8 0.25  32 
 11.3 7.8  0.17  54 
 22.7 7.8  0.11  70 
 45.4 7.8  0.07  81 
Validity criteria fulfilled:
The control respiration are wihtin 0 % of each other and the EC50 of the referenc compound wihin acceptable range.
Cyclohexanone peroxide at a concentration of 11.1 mg/L causes a 50% inhibition of the respiration in comparison to the control.
Executive summary:

The performed OECD 209 guideline study testing the toxicity of cyclohexanone peroxide shows that the substance has a EC50 of 11.1 mg/L. The EC10 was 0.5 mg/L.

Description of key information

This OECD 209 study performed under GLP condition showed an EC10 of 0.5 mg/L and a EC50 of 11.1 mg/L when activated sludge was exposed to cyclohexanone peroxide. 

Key value for chemical safety assessment

EC50 for microorganisms:
11.1 mg/L
EC10 or NOEC for microorganisms:
0.5 mg/L

Additional information

One study has been conducted to assess the toxicity of cyclohexanone peroxide to microorganisms. The performed guideline study, fulfilling validity criteria, give rise to the key values above used for the chemical safety assessment.