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Ecotoxicological information

Toxicity to microorganisms

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Reference
Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)
Version / remarks:
Commission Directive 87/302/EEC
Deviations:
not specified
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Version / remarks:
1984
Deviations:
not specified
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
no
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- based on pre-experiment, the substance was mixed into deionized water by ultrasonic treatment over 15 minutes and intensly stirred over 48 hours at room temperature in the dark. For all concentrations, the main part of the test substance was suspended in the test media, so that they were clearly above the water solubility limit of WS400572.

Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Name and location of sewage treatment plant where inoculum was collected: local wastewater treatment plant, Ergolz II, Füllinsdorf / Switzerland)
- Method of cultivation / Preparation of inoculum for exposure: The aerobic activated sewage sludge was washed two times by centrifugation, decantation of the supernatant liquid phase and resuspension of the solid material in tap water. The dry weight of the suspended solids was determined.
Based on the dry weight, a calculated amount of wet sludge was suspended in tap water to obtain a concentration equivalent to 3 g dry material per liter (mixed liquor suspended solids, MLSS). During the holding period of three days prior to use, the sludge was fed once with 50 mL synthetic sewage feed per liter and was kept at room temperature under continuous aeration until use. Before use, the dry weight of the activated sludge was measured again. The pH of the activated sludge inoculum was adjusted to pH 7.3 with sulfuric acid.
- Initial biomass concentration: 2.3 g/L dry weight (MLSS)
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20°C
pH:
7.4 - 8.5
Dissolved oxygen:
>= 7.2 mg/l
Nominal and measured concentrations:
nominal: 10, 32, 100, 320, 1000 mg/l
Details on test conditions:
TEST SYSTEM
- Test vessel: 1 L beakers, contents 500 mL
- Type (delete if not applicable): open
- Aeration: compressed air at a flow of approximately one liter per minute
- No. of vessels per concentration (replicates): 1
- No. of vessels per control (replicates): 2
- Sludge concentration (weight of dry solids per volume): 0.92 g/L (dry weight)

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

OTHER TEST CONDITIONS
- Adjustment of pH: no
EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : dissolved oxygen concentration after 3 hours contact time, continuously recorded for about 10 – 15 minutes.
Reference substance (positive control):
yes
Remarks:
3,5-dichlorophenol
Key result
Duration:
3 h
Dose descriptor:
other: EC20
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (total fraction)
Basis for effect:
inhibition of total respiration
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (total fraction)
Basis for effect:
inhibition of total respiration
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
>= 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat. (total fraction)
Basis for effect:
inhibition of total respiration
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: EC50 (3 h): 27 mg/L (within the guidelines-recommended range of 5 to 30 mg/L)
Validity criteria fulfilled:
yes
Remarks:
- two control respiration rates were within 15 per cent of each other (6.4%) ; - the EC50 (3 hours) of 3,5-dichlorophenol was in the accepted range 5 to 30 mg/L (27 mg/L)
Conclusions:
The results indicate that the test material is not toxic to activated sludge microorganisms up to the limits of its water solubility and a NOEC and thus a PNEC cannot be determined.
Executive summary:

As no effect on the respiration rate of activates sludge microorganisms was observed up to the limit of water solubility, the 3-hour EC20 (NOEC) and thus a PNEC cannot be determined.

Description of key information

Toxicity to microorganisms: not toxic to microorganisms: inhibition of respiration rates <10% (OECD 209, EU C.11)

Key value for chemical safety assessment

Additional information

EC10 >1000 mg/L for microorganisms.


The EC10 for the test material is much higher than its water solubility.