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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:
1988-11-30
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Non-GLP guideline study (OECD 209). Deviations to the updated OECD Guideline (adopted 2010) The coefficient of analysis of the control was not reported and a reduced number of replicates in the treatment groups were used.
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
yes
Remarks:
, instead of a centrifuged sludge a settled sludge was used. Substance was tested at 1 concentration in duplicate samples. Substance was not dissolved but distributed in test medium. Sludge concentration 2 g/L instead of 1.4 - 1.8 g/L.
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: 20.1 rsp.20.0 mg of the test substance were weighed and added to the test medium. The volume was adjusted to 200 mL with bidistilled water and aerated for 3 hours.
Test organisms (species):
activated sludge, domestic
Details on inoculum:
- Preparation of inoculum for exposure: Instead a centrifuged sludge a settled sludge was used.
- Initial biomass concentration: 2 g/L
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Test temperature:
20 ± 2 °C
Nominal and measured concentrations:
nominal: 100 mg/L
weighed: 100 and 100.5 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: BOD flasks with gas inlet
- Material, size, headspace, fill volume: 250 mL (size)
- Aeration: none during the test
- No. of vessels per concentration: 1
- No. of vessels per control: 1
- Biomass loading rate: 2 g/L

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: dechlorinated drinking water
- Nutrient solution: in accordance to the guideline

OTHER TEST CONDITIONS
- Adjustment of pH: none

EFFECT PARAMETERS MEASURED: Oxygen consumption per hour in mg/L

TEST CONCENTRATIONS
- Justification for using less concentrations than requested by guideline: expected low toxicity of the test substance
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol at 32, 10, and 3.2 mg/L
Duration:
3 h
Dose descriptor:
IC50
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: IC20
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: IC80
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:
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: The substance was not dissolved but distributed in the test medium
- Effect concentrations exceeding solubility of substance in test medium: none reported
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: IC50 12 mg/L

Description of key information

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

Key value for chemical safety assessment

Additional information

The study was performed according to OECD guideline no. 209 (1984). The EC50 (3h) was determined to be > 100 mg/L, based on nominal concentrations. The test compound was added to the water without any suspension aid. No effect on the bacteria was observed.