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Ecotoxicological information

Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From Mar. 20, 1990 to Apr. 17, 1990
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
equivalent or similar to
Guideline:
EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)
Deviations:
yes
Remarks:
Instead of centrifuged sludge a settled sludge was used. Due to the poor solubility of the test substance at test concentrations, no stock solution was prepared. The test substance was given directly into the medium.
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
no
Test organisms (species):
activated sludge
Details on inoculum:
Activated sludge collected from the sewage treatment plant of CH-4153 Reinach on 03/04/90.
The preparation was carried out according to the method described in the guideline. The sludge was separated from the aqueous layer by settling instead of centrifugation.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20 ± 2ºC
Nominal and measured concentrations:
nominal: 1.25, 4.35, 17.65, 35.50 and 102.45 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: 250 mL BOD flasks with gas inlet
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 2
- Biomass loading rate: sludge concentration was 1.7 g/L in the test bottles

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: dechlorinated drinking water
16 g peptone, 11g meat extract, 3.0 g urea, 0.7 g NaCl, 0.4 g CaCl2.2H2O, 0.2 g MgSO4.7H2O, 2.8 g K2HPO4 per liter dechlorinated drinking water.

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Photoperiod: continuous
- Temperature: 20+/-2°C

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : oxygen consumption per hour in mg/L after 3 hours exposure
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenole (3.2, 10 and 32 mg/L)
Duration:
3 h
Dose descriptor:
EC10
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
other: EC20
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Duration:
3 h
Dose descriptor:
other: EC80
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
No effect on the bacteria was observed. The maximum respiration inhibition degree was 6% at maximum. Therefore, it is deemed justified to state the EC10 for the inhibitory effect on activated sludge as being > 100 mg/L
Results with reference substance (positive control):
- Results with reference substance valid: Yes
- Relevant effect levels: EC50 = 17.6 mg/L
Reported statistics and error estimates:
Results determined graphically for the test substance and the reference substance.
Validity criteria fulfilled:
yes
Conclusions:
Under the conditions of the study, the 3 hour EC50 of the test material to sewerage microorganisms was determined to be >100 mg/l. The inhibition of the degradation activity of activated sludge is not anticipated when introduced in appropriate low concentrations.
Executive summary:

In this guideline (EU C.11) study, the 3 hour EC50 of the test material to sewerage microorganisms was determined to be >100 mg/l. The test innoculum was sourced from a municipal sewerage treatment plant. Test concentrations ranged from 1.25 to 102.45 mg/l. Inhibition of sewerage microogranisms is not expected at low concentrations.

Description of key information

Study conducted to recognised testing guideline.

Key value for chemical safety assessment

EC50 for microorganisms:
100 mg/L

Additional information

In the key study on the toxicity of the test substance on activated sludge (CIBA-GEIGy Ltd. 1990) an EC20 of > 100 mg/L, the highest tested concentration, was reported. The test was conducted under GLP regulations and according to OECD test guideline 209. The respiration inhibition was determined in activated sludge obtained from a municipal sewage treatment plant. The effect concentrations were derived after a test duration of 180 minutes. However, since no effect on the bacteria was observed and the maximum respiration inhibition degree was 6% at maximum, therefore, it is deemed justified to state the EC10 for the inhibitory effect on activated sludge as being > 100 mg/L.