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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2008
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
yes
Remarks:
Temperature in the limit test and main test deviated from the guideline
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Vehicle:
no
Test organisms (species):
activated sludge of a predominantly domestic sewage
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Details on test conditions:
Test duration: 17 hours.
Test temperature: 20 °C.
Test culture: 10 ml.
pH values during the test: 5.8 - 7.2
Test concentrations: 625, 1250, 2500, 5000, 7500 and 10000 mg/l (nominal).
Reference substance (positive control):
no
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
125 mg/L
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 2 000 mg/L
Duration:
3 h
Dose descriptor:
other: EC20
Effect conc.:
163 mg/L

The following inhibitions of the respiration rate of the activated sludge were detected:

at 2,000 mg/L  42 %

at 1,000 mg/L  44 %

at 500 mg/L      42 %

at 250 mg/L      34 %

at 125 mg/L      13 %

The test item showed inhibition values which were not correlated to its concentration: at concentrations 2,000, 1,000, and 500 mg/L approximately the same inhibition was found. It is believed that the test system, consisting of a wide variety of micro-organisms, is not uniformly affected by the test item.

Validity criteria fulfilled:
yes
Conclusions:
NOEC = 125 mg/L
Executive summary:

All validity criteria were met. The respiration rate of the activated sludge lay within the normal range of 0.5 – 0.9 mg/(L*min). Therefore, the result of the test can be considered valid.

Description of key information

The following inhibitions of the respiration rate of the activated sludge were detected:
at 2,000 mg/L 42 %
at 1,000 mg/L 44 %
at 500 mg/L 42 %
at 250 mg/L 34 %
at 125 mg/L 13 %

Key value for chemical safety assessment

EC50 for microorganisms:
2 000 mg/L
EC10 or NOEC for microorganisms:
125 mg/L

Additional information

The test item showed inhibition values which were not correlated to its concentration: at concentrations 2,000, 1,000, and 500 mg/L approximately the same inhibition was found. It is believed that the test system, consisting of a wide variety of micro-organisms, is not uniformly affected by the test item.