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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:
1989-04-18
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Non-GLP guideline study.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:
: settled sludge used; no stock solution
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: 20.56, 6.58, 2.26, 0.63 rsp. 0.29 mg of the test substance were weighed and added to the test medium. The volume was adjusted to 200 ml with water and aerated for 3 hours.
Test organisms (species):
activated sludge, domestic
Details on inoculum:
- Source:
Activated sludge produced in the test apparatus from a mixed inoculum obtained from:
- Bacteria collected from the secondary effluent of the sewage treatment plant of CH-4153 Reinach
- Water from the Rhine collected in CH-4000 Basle.
- A suspension of garden soil collected in CH-4000 Basle
- Preparation: according to the guideline
- Initial biomass concentration: 1.7 g/L
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 +- 2 °C
Nominal and measured concentrations:
102.8, 32.9, 11.3, 3.1, 1.4 mg/L (nominal)
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
- No. of vessels per reference substance (replicates): 1
- Reference substance: 3,5-Dichlorophenol (32, 10, 3.2 mg/L)

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

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- oxygen consumption per hour in mg/L with a ORION - Electrode Type 97-08, ORION Microprocessor lonalizer 901 and plotted on a recorder

TEST CONCENTRATIONS
- Test concentrations: 102.8, 32.9, 11.3, 3.1, 1.4 mg/L (nominal)
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
Duration:
3 h
Dose descriptor:
IC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth inhibition
Duration:
3 h
Dose descriptor:
other: IC20
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth inhibition
Duration:
3 h
Dose descriptor:
other: IC80
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
growth inhibition
Details on results:
- Any observations (e.g. precipitation) that might cause a difference between measured and nominal values: none
- Effect concentrations exceeding solubility of substance in test medium: yes
Results with reference substance (positive control):
- Results with reference substance valid? yes
- IC50 = 14 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

In a 3-hr acute toxicity study sewage sludge microorganisms were exposed to the test item at nominal concentrations of 102.8, 32.9, 11.3, 3.1 and 1.4 mg/L in accordance with OECD 209. The IC50 value based on respiration rate was bigger than 102.8 mg/L after a 3 h contact time. This toxicity study is classified as acceptable and satisfies the guideline requirements for OECD 209 toxicity study.