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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:
1989-05-30 to 1989-06-20
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Non-GLP study according to guideline 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 a centrifuged sludge a settled sludge was used. Due to the poor solubility of the test substance at test conditions, direct weighted amounts were added to the test medium instead of a stock solution.
GLP compliance:
no
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: 0.54, 1.06, 2.69, 7.41 and 20.46 mg of the test substance were weighted 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:
- Initial biomass concentration: 1.5 g/L (sludge concentration)
- Source: Sludge collected from the sewage treatment plant of CH-4106 Therwil on 1989-05-29
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20 ± 2°C
Nominal and measured concentrations:
Nominal: 2.7, 5.3, 13.4, 37.0, 102.3
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: 1.5 g/L
- Aeration: 3 hours during test procedure

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

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

Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
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:
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: IC80
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: IC50 = 14 mg/L (rates tested: 3.3, 10.2 and 32.5 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 micro-organisms were exposed to the test item at nominal concentrations of 2.7, 5.3, 13.4, 37.0 and 102.3 mg/L in accordance with OECD 209. The IC50 value based on respiration rate after 3 hours was greater than 100 mg/L.

This toxicity study is classified as acceptable and satisfies the guideline requirements for OECD 209 toxicity study.