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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:
1988/10/07 to 1988/11/08
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study, not performed under GLP. Deviations from the updated OECD-guideline (adopted 2010): A settled sludge was used instead of a centrifuged sludge; A limit test at 100 mg/L was performed
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
yes
Remarks:
Guideline study, not performed under GLP. Deviations from the updated OECD-guideline (adopted 2010): A settled sludge was used instead of a centrifuged sludge; A limit test at 100 mg/L was performed
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: 21.8 rsp. 20.8 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: According to guideline, except settling instead of centrifuging
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Test temperature:
20+/-2 deg C
Nominal and measured concentrations:
100 mg/L (nominal); 109 and 104 mg/L used in test 1 and 2, respectively.
Details on test conditions:
TEST SYSTEM
- Type : 250 mL BOD flasks with gas inlet.
- Aeration: yes

- No. of vessels per concentration (replicates): 2
- No. of vessels per control (replicates): 1
- No. of vessels per vehicle control (replicates): 2
- Biomass loading rate: sludge concentration = 1.8 g/L

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Distilled water

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Oxygen consumption

TEST CONCENTRATIONS
- Justification for using less concentrations than requested by guideline: test performed as a limit test due to the expected low toxicity of the test material
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:
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:
- Effect concentrations exceeding solubility of substance in test medium: yes
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: IC50 = 8 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 100 mg/L in accordance with OECD 209. The IC50 value based on respiration rate after was 100 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.