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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:
1992-06-15 to 1992-06-17
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:
no
GLP compliance:
yes
Analytical monitoring:
no
Details on sampling:
not applicable
Vehicle:
no
Test organisms (species):
activated sludge
Details on inoculum:
- Source: Activated sludge from a laboratory wastewater treatment plant
- Preparation of inoculum for exposure: not reported
- Pretreatment: no pretreatment
- Initial biomass concentration: 6 g dry matter/L
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Post exposure observation period:
not applicable
Hardness:
not reported
Test temperature:
not reported
pH:
not reported
Dissolved oxygen:
not reported
Salinity:
not applicable
Nominal and measured concentrations:
Nominal: 560, 1000, 1800, 3200, 5600 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: not reported
- Type (delete if not applicable): not reported
- Material, size, headspace, fill volume: not reported
- Aeration: not reported

- No. of vessels per concentration (replicates): not reported
- No. of vessels per control (replicates): not reported

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: not reported
- Total organic carbon: not reported
- Particulate matter: not reported
- Metals: not reported
- Pesticides: not reported
- Chlorine: not reported
- Alkalinity: not reported
- Ca/mg ratio: not reported
- Conductivity: not reported
- Culture medium different from test medium: not reported

OTHER TEST CONDITIONS
- Adjustment of pH: not reported
- Photoperiod: not reported
- Light intensity: not reported

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : respiration rate of sewage sludge
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
815 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
The inhibition of the respiration of the sludge was between 30% at the lowest test concentration of 560 mg/L and 92.3% at the highest test concentration of 5600 mg/L
Results with reference substance (positive control):
The study results with the reference substance are not reported.
Validity criteria fulfilled:
yes
Conclusions:
The substance inhibited the microbial activity of sewage sludge and the EC50 value was 815 mg/L after 3 hours.
Executive summary:

The toxicity of the substance methyl benzoate to bacteria in sewage sludge was tested under GLP conditions in a static system in accordance with OECD guideline No 209. The respiration rate of activated sludge from a laboratory wastewater treatment plant was determined at a sludge concentration of 6 g dry matter/L in the absence of test substance. Then the corresponding respiration rate of the sludge exposed to nominal test concentrations of 560, 1000, 1800, 3200 and 5600 mg/L for 3 hours was determined and compared to the respiration rate of untreated sludge. The microbial activity of the sludge was inhibited at all test concentrations and reduced by 30% to 92.3%. The EC50 value for inhibition was 815 mg/L after 3 hours. The sensitivity of the activated sludge was tested and confirmed with the reference substance 3,5 -dichlorophenole.

Description of key information

The 3-hour EC50 value for inhibition of respiration of activated sludge was 815 mg/L.

Key value for chemical safety assessment

EC50 for microorganisms:
815 mg/L

Additional information

The inhibition of respiration of activated sludge following three hours of exposure to methyl benzoate at a series of test concentrations was determined in a valid study in accordance with OECD TG 209. Activated sludge was taken from a laboratory sewage treatment plant according to OECD. The EC50 value for inhibition of the respiration rate of activated sludge was 815 mg/L after 3 hours of exposure.