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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
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:
2010
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
Batch number: TROD7BB06
Analytical monitoring:
no
Vehicle:
no
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
The sludge used was collected at the domestic sewage treatment plant of Piracicaba, Águas do Mirante. It was collected and used on the same day of the test.
pH of sludge: 7.01
dry matter of sludge: 3.0 g suspended solids/L
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20 ± 2°C
pH:
7.6-8.0
Nominal and measured concentrations:
nominal: 0, 10, 100 and 1000 mg/L.
Details on test conditions:
Duration Three hours
Replicates One replicate/treatment (positive control)
One replicate for concentration (10 mg L-1)
One replicate for concentration (100 mg L-1)
Three replicates for concentration (1000 mg L-1)
Water Tap water
Feeding Nutrient solution, 16 mL vessel-1
Temperature 20 ± 2ºC

The study was performed in a closed system with aeration. In the control vessels, 16 mL of nutrient solution was mixed with 234 mL of water. The positive control and the test vessels were prepared by adding the appropriate amount of positive control solution respectively test item into the test vessel, adding 16 mL nutrient solution and water to give 250 mL. Then, 250 mL inoculum was added in ten minutes intervals. After addition of the inoculums, the flasks were closed immediately and the mixtures were stirred with aeration.
After three hours the contents were poured into a tube of approximately 50 mL and the respiration rate was determined by measuring the O2 concentration over a ten minutes period. The following vials were measured equally at ten minutes intervals.
Reference substance (positive control):
yes
Remarks:
For the positive control, copper sulfate pent hydrate was used in three concentrations (58 mg L-1, 100 mg L-1 and 180 mg L-1). The substance was weighed directly into the bottles (29-50-90 mg for 500 mL total volume)
Key result
Duration:
3 h
Dose descriptor:
EC10
Effect conc.:
>= 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: oxygen consumption
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
>= 1 000 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
other: oxygen consumption
Details on results:
O2-Consumption, Inhibition - test substance.
Test Concentration pH Consumption (mg L-1 h) Inhibition (%) Variation in DO consumption of controls (%)
Control C1 8.00 37.24 -
F1 – 1% 8.00 47.31 0.00
F2 – 10% 7.78 38.57 0.00
F3 – 100% 7.75 42.94 0.00
F3 – 100% 8.00 43.09 0.00
F3 – 100% 7.93 43.05 0.00
Abiotic control 7.06 0.00 -
Control C2 7.57 39.90 -
Validity criteria fulfilled:
yes
Conclusions:
A preliminary test was conducted to evaluate the inhibition of oxygen consumption. Three concentrations of the test substance (10, 100 and 1000 mg/L) were used, and the third concentration was done in triplicate. The sludge used had a concentration of 3.0 g/L solids.
As there was an absence of inhibition of oxygen consumption by the test substance, the definitive test becomes unnecessary.
Executive summary:

The effects on microorganisms from activated sludge were determined by measuring their respiration rate under defined conditions in the presence of different concentrations of the test substance. The respiration rates of samples of activated sludge fed with synthetic sewage were measured in an enclosed cell containing an oxygen electrode after a contact time of three hours.

Three concentrations of the test substance (10, 100 and 1000 mg/L) were used, and the third concentration was done in triplicate. The sludge used had a concentration of 3.0 g/L solids. There was an no inhibition of oxygen consumption by the test substance.

Description of key information

The effects on microorganisms from activated sludge were determined by measuring their respiration rate under defined conditions in the presence of different concentrations of the test substance. The respiration rates of samples of activated sludge fed with synthetic sewage were measured in an enclosed cell containing an oxygen electrode after a contact time of three hours.

Three concentrations of the test substance (10, 100 and 1000 mg/L) were used, and the third concentration was done in triplicate. The sludge used had a concentration of 3.0 g/L solids. There was an no inhibition of oxygen consumption by the test substance.

Key value for chemical safety assessment

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

Additional information