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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
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test (Carbon and Ammonium Oxidation))
Deviations:
no
GLP compliance:
yes
Specific details on test material used for the study:
Batch no.: 3837
Purity: 25.5% in water
Solubility: soluble in water
Analytical monitoring:
not specified
Vehicle:
no
Details on test solutions:
deionized water
Test organisms (species):
activated sludge
Details on inoculum:
For the preparation of the inocula, a sample of aerobic mud was selected by the mixed treated plant of urban (about 66%) and industrial (about 34%) liquid sewage situated in San Rocco near Monza (MI).
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Test temperature:
20 +/- 2°C
Dissolved oxygen:
> 60-70% saturation
Nominal and measured concentrations:
Test substance: 1, 10 and 100 mg/L
Reference substance test: 1, 10, 50 mg/L
Details on test conditions:
Respiration rates were measured in an enclosed cell containing an oxygen electrode
Reference substance (positive control):
yes
Remarks:
3,5 dichlorophenol
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
act. ingr.
Basis for effect:
inhibition of total respiration
Details on results:
Mean percent of inhibition of the total respiration rate:
- Test substance: 14.31, 19.35, 20.25 for 1, 10 and 100 mg/L, respectively
Results with reference substance (positive control):
Mean percent of inhibition of the total respiration rate:
- Test reference: 29.47, 49.85, 89.89 for 1, 10 and 50 mg/L, respectively

Expression of results:

- Oxygen consumption rate (R) in mg/Lh: R = (Q1 -Q2)/Dt * 60 where;

Q1 is the O2 conc. at the beginning of the linear phase (mg/L)

Q2 is the O2 conc. at the end of the linear phase (mg/L)

Dt is the time interval between 2 measurements (min)

- Specific resrespiration ate (Rs) is expressed as the amount of oxygen consumed per g dry weight of sludges per hour (mg/gh): R/SS where; SS is the conc. of suspended solids in the mixture (g/L)

- Different indices of R which may be combined are: S (specific rate), T (total respiration rate), A (rate due to abiotic processes), and B (rate based on blank assays control (mean)).

- The percentage inhibition It (%) of total oxygen consumption at each concentration of the test substance:

It = (1 -(Rt-Rta)/Rtb) * 100

(Rta is equal to 0 if there will be no oxygen uptake in the preliminary test in the abiotic control of if the test substance does not have strong reducing properties).

Interpretation of results:

EC50 values including their associated 95% confidence limit were calculated by EPA Probit porgram Version 1.5.

Validity criteria fulfilled:
yes
Conclusions:
Under the study conditions, the 3 h EC50 of the substance in activated sludge microorganisms was determined to be >100 mg a.i./L.
Executive summary:

A study was conducted to determine the toxicity of the substance to activated sludge microorganisms according to OECD Guideline 209, in compliance with GLP. Activated sludge was exposed to the test substance at concentrations of 0, 1, 10 and 100 mg/L for 3 h. A reference substance (3, 5 - dichlorophenol) was included in this study at 1, 10 and 50 mg/L. The inhibition of the total respiration rate was measured and the mean percent of this parameter was calculated to be 14.31, 19.35, and 20.25% for 1, 10 and 100 mg/L of the test substance, respectively. Under the study conditions, the 3 h EC50 of the substance in activated sludge microorganisms was determined to be >100 mg a.i./L (Giarei, 2016).

Description of key information

Key value for chemical safety assessment

EC50 for microorganisms:
100 mg/L

Additional information

A study was conducted to determine the toxicity of the substance to activated sludge microorganisms according to OECD Guideline 209, in compliance with GLP. Activated sludge was exposed to the test substance at concentrations of 0, 1, 10 and 100 mg/L for 3 h. A reference substance (3, 5 - dichlorophenol) was included in this study at 1, 10 and 50 mg/L. The inhibition of the total respiration rate was measured and the mean percent of this parameter was calculated to be 14.31, 19.35, and 20.25% for 1, 10 and 100 mg/L of the test substance, respectively. Under the study conditions, the 3 h EC50 of the substance in activated sludge microorganisms was determined to be >100 mg a.i./L (Giarei, 2016).

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