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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:
April 14, 1994
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:
yes
Remarks:
- Deion. water instead of dest. water for the stock solution. - Preparation of the inoculum : higher sludge weight after the washing procedure (Sludge concentrations in the test according to the guidelines) - 4 instead of 5 test concentrations
Principles of method if other than guideline:
SAV: 05 000 02
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
- Test concentrations : 320,100, 32 and 10 mg/l of the test substance
Vehicle:
no
Details on test solutions:
- 0.5 g/l test substance was treated for 10 min. in a ultrasonic bath for dissolving.
- Sludge dry weight: 1.50 g/l
Test organisms (species):
other: Activated sludge of a communal sewage treatment plant (ARA - Birs 1 Reinach)
Details on inoculum:
Sludge pretreatment : 3 times washing with tap water and addition of synthetic sewage (a day before the main test)
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
21.1 °C
pH:
pH of sludge: 7.9 before the test beginning
pH of test substance after 3 h:
- 7.5 (320 mg/l of test substance)
- 7.8 (100 mg/l of test substance)
- 7.9 (32 mg/l of test substance)
- 7.9 (10 mg/l of test substance)
- 7.5 (320 mg/l of test substance)
Nominal and measured concentrations:
Nominal concentrations:
- 320,100, 32 and 10 mg/l of the test substance
Details on test conditions:
TEST SYSTEM
- Aeration: 0.1 - 0.2 l/min by pasteur-pipette
- Test volume: 100 ml

Reference substance (positive control):
yes
Remarks:
3,5 dichlorophenol
Duration:
3 h
Dose descriptor:
IC50
Effect conc.:
> 320 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.:
ca. 18.5 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):
IC50 (3h): 12.5 mg/l

To calculate the inhibitory effect of the test substance, its respiration rate is expressed as a percentage of the mean of two control respiration rates:

[(C1+C2)/2]-Zs

x100

[(C1+C2)/2]

S = Test substance; Z = O2 -consumption; C1 = Control 1; C2 = Control 2

IC50

The respiration rate of each test concentration was calculated as a percentage of the mean of the two control respiration rates. The results were plotted on a logarithmic (concentration)/normal (% inhibition) graph, where the IC50 can be evaluated.

Validity criteria fulfilled:
yes
Conclusions:
IC50 (3h) > 320 mg/l
Executive summary:

Method:

The toxicity to microorganisms was determined by the OECD Guideline n. 209.

Results:

IC50 (3h) > 320 mg/l

Description of key information

IC50 > 320 mg/l

Key value for chemical safety assessment

EC50 for microorganisms:
320 mg/L

Additional information

The toxicity to microorganisms was determined by the OECD guideline n.209. The substance was tested at four concentrations : 320,100, 32 and 10 mg/l. The resulting IC50 after 3 hours was > 320 mg/l.

All the existing studies, showed consistent results summarized in the attachement.

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