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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:
Jan 10, 2002 - Apr 08, 2002
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))
Version / remarks:
July, 2010
Deviations:
no
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
Batch: E 01031354
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
The test substance was insufficiently soluble to permit addition via aqueous solution. Individually weighed quantities of test substance were added directly to the appropriate test vessels.
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
Activated sludge, micro organisms from a domestic waste water treatment plant was supplied by the sewage plant Groß-Zimmern, Germany.

Preparation and Maintenance
The sludge was washed by centrifugation and the supematant liquid phase was decanted. The solid material was resuspended in tap water and again centrifuged. The latter procedure was repeated twice. An aliquot of the final sludge suspension was
weighed, dried and the ratio of wet sludge (g) to its dry weight (g) determined. Based on this ratio, calculated aliquots of washed sludge suspension, corresponding to 3 g dry material per litre, were made up with tap water. The pH of the activated sludge was determined to be 7.9. The activated sludge was used directly after adjustment without storage.
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
3 h
Test temperature:
20 ± 2°C
pH:
7.01 - 7.25
Dissolved oxygen:
saturated
Nominal and measured concentrations:
10, 32, 100, 320, and 1000 mg/L (nominal)
Details on test conditions:
TEST SYSTEM
- Test vessel: ca 250 mL glass conical flask
- Type (delete if not applicable): open
- Aeration:compressed air supply
- No. of vessels per control (replicates): 1
- Sludge concentration (weight of dry solids per volume): 3 g/L
- Nutrients provided for bacteria: no
- Biomass loading rate:

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: dechlorinated tap water
- Particulate matter:
OTHER TEST CONDITIONS
- Adjustment of pH: yes

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
TEST CONCENTRATIONS
- Spacing factor for test concentrations: 3.2
- Justification for using fewer concentrations than requested by guideline: n.a.
- Range finding study no
- Test concentrations: 10, 32, 100, 320, and 1000 mg/L
Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenol
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
1 000 mg/L
Nominal / measured:
meas. (initial)
Conc. based on:
test mat.
Basis for effect:
inhibition of total respiration
Results with reference substance (positive control):
3,5-DCP:
Total Respiration: 8.2 mg/L
Validity criteria fulfilled:
yes
Conclusions:
Based on measured inhibition rates, the 3-hour EC 20 and EC 50 could not be quantified because up to the highest nominal test concentration of 1000 mg/L less than 20 % inhibition was noted after three hours incubation. Nevertheless, the 3-hour EC 20 and EC 50 are clearly higher than 1000 mg/L under the present test conditions.
Executive summary:

The informtion for this endpoint study record was obtained from an experimental study. The OECD GLP criteria were met and the methods applied are fully compliant with OECD TG 209.

Based on measured inhibition rates, the 3-hour EC 20 and EC 50 could not be quantified because up to the highest nominal test concentration of 1000 mg/L less than 20 % inhibition was noted after

three hours incubation. Nevertheless, the 3-hour EC 20 and EC 50 are clearly higher than 1000 mg/L under the present test conditions.

Description of key information

OECD 209 study (Reliability 1): EC20 > 1000 mg/L,  EC50 > 1000 mg/L

Key value for chemical safety assessment

EC50 for microorganisms:
1 000 mg/L
EC10 or NOEC for microorganisms:
1 000 mg/L

Additional information