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Endpoint:
activated sludge respiration inhibition testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
08 January 2013 to 31 January 2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
Read-across performed with structurally similar substance.
Reason / purpose for cross-reference:
other: read-across target
Qualifier:
according to guideline
Guideline:
OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test
Deviations:
no
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)
PRE-TEST
- Test material was soluble at a concentration of 8 g test material per litre deionised water before and after pH adjustment from 5.0 to 7.4.
- Test material precipitated and the pH decreased to pH 4.5 after stirring the solution overnight at room temperature.

RANGE FINDER and DEFINITIVE TEST
- To avoid a possible precipitation process, no test material stock solution was used for the test (i.e., direct addition to test water).
- No emulsifiers or solvents were used.
- At the start of the test, appropriate amounts of test material were weighed and added to 234 mL of dilution water. After a short stirring period the pH in each test vessel was adjusted with diluted NaOH solution. Then, 16 mL synthetic sewage and 250 mL activated sludge inoculum was added (sludge concentration 3 g/L).
Test organisms (species):
activated sludge of a predominantly domestic sewage
Details on inoculum:
- Laboratory culture: Aerobic activated sludge from a wastewater treatment plant (ARA Ergolz II, Füllinsdorf / Switzerland) treating predominantly domestic wastewater.
- Method of cultivation: Following the recommendations of OECD Guideline No 209 (2010). Sludge was washed three times with chlorine free tap water by centrifugation and the supernatant liquid phase was decanted. Wet to dry weight ratio was determined. Based on this ratio a calculated amount of wet sludge was resuspended in tap water to obtain a concentration equivalent to 3 g dry material per L. During holding period of 2 days prior to use, sludge was fed daily with 50 mL synthetic sewage feed per L and kept at room temperature under continuous aeration.
- Preparation of inoculum for exposure: Again, dry weight was determined and readjusted to 3 g dw/L in the inoculum used for the test (equivalent to 1.5 g/L in the final incubation mixture). pH of inoculum was adjusted from 7.0 to 7.5 using NaOH solution.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
3 h
Hardness:
not reported
Test temperature:
20°C
pH:
Start: 7.2 - 7.6
End: 7.4 - 7.8
Dissolved oxygen:
Just before measurement of respiration rates, at the end of the incubation period, dissolved oxygen concentrations were at least 7.1 mg/L.
Salinity:
not applicable
Nominal and measured concentrations:
Nominal concentrations tested:
Control + 25.6, 64, 160, 400 and 1000 mg CeCl3 anhydrous per litre
Details on test conditions:
TEST SYSTEM
- Test vessel: 2000 mL glass beakers containing 500 mL of incubation mixture
- No. of vessels per concentration (replicates): 3
- No. of vessels per blank control (replicates): 6
- Dry matter in the test: 3 g suspended solids/L

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: distilled or deionized water < 1 mg/L DOC

OTHER TEST CONDITIONS
- Adjustment of pH: yes, see above
- Photoperiod: normal laboratory lighting

EFFECT PARAMETERS MEASURED (with observation intervals if applicable):
- After 3 h, a well-mixed sample of each test medium was poured into a BOD flask and not further aerated.
- Dissolved oxygen concentration measured using an oxygen electrode (WTW TriOxmatic 300) and an oxygen meter (WTW Oxi 539, Wissenschaftlich-Technische Werkstaetten WTW, Weilheim/Germany).

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 2.5
- Range finding study: yes, control + 10, 100 and 1000 mg CeCl3/L
- Results used to determine the conditions for the definitive study: 50 % inhibition falls between 100 and 1000 mg CeCl3/L


Reference substance (positive control):
yes
Remarks:
3,5-Dichlorophenole (CAS No. 591-35-5)
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
436 mg/L
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
Ce
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Remarks on result:
other: 95% CL = 407-466
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
91 mg/L
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
Ce
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
767 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
anhydrous
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Remarks on result:
other: 95% CL = 716-819
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
160 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
anhydrous
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Details on results:
Further results based on element:
3-h EC10 = 192 mg Ce/L
3-h EC20 = 254 mg Ce/L
3-h EC80 = 746 mg Ce/L

Results based on test material (CeCl3, anhydrous):
3-h EC10 = 337 mg/L
3-h EC20 = 447 mg/L
3-h EC80 = 1313 mg/L

- Inhibition of the respiration rates for all tested concentrations was in the range of -1.3 to 66.1% compared to the control, i.e. a marginal stimulatory effect was observed for some concentrations tested.
- No statistically significant inhibitory effect on the respiration rate of activated sludge up to and including the concentration of 160 mg CeCl3/L
- At a concentration of 400 mg CeCl3/L the inhibitory effect increased to 15.6 % and reached 66.1 % at the highest tested concentration (1000 mg CeCl3/L).
- Concentrations exceeding 1000 mg CeCl3 per litre were not tested.
Results with reference substance (positive control):
- Results with reference substance valid? yes
- Relevant effect levels: 3-h EC50 = 8 mg/L (95 % CI 2-25 mg/L)
Reported statistics and error estimates:
3-h EC10, EC20, EC50 and EC80 values and their 95% confidence limits were derived by Probit Analysis.
The 3-h EC50 for the reference substance was calculated by Weibull Analysis.
NOEC values were derived by per-vessel statistics using the Dunnett t-test.
Validity criteria fulfilled:
yes
Conclusions:
This activated sludge respiration inhibition test with cerium trichloride yielded a NOEC and EC50 of 160 and 767 mg CeCl3/L, respectively, corresponding to a NOEC and EC50 of 91 and 436 mg Ce/L.
Executive summary:

The inhibitory effect of the test material on the respiration rate of aerobic wastewater microorganisms in activated sludge was investigated in a 3-hour respiration inhibition test according to the OECD Guideline for Testing of Chemicals, No. 209, adopted 2010.

The inhibition of the respiration rates for all tested concentrations was in the range -1.3 to 66.1 % compared to the control. Up to and including the concentration of 242 mg test material per litre the test material had no statistically significant inhibitory effect on the respiration rate of activated sludge after the incubation period of 3 hours.

This activated sludge respiration inhibition test with cerium trichloride yielded a NOEC and EC50 of 160 and 767 mg CeCl3/L, respectively, corresponding to a NOEC and EC50 of 91 and 436 mg Ce/L.

Endpoint:
activated sludge respiration inhibition testing
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study conducted on read-across material
Justification for type of information:
Read-across performed with structurally similar substance.
Reason / purpose for cross-reference:
read-across source
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
436 mg/L
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
Ce
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Remarks on result:
other: 95% CL = 407- 466
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
91 mg/L
Nominal / measured:
nominal
Conc. based on:
element
Remarks:
Ce
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Key result
Duration:
3 h
Dose descriptor:
EC50
Effect conc.:
767 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
anhydrous
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate
Remarks on result:
other: 95% CL = 716 - 819
Key result
Duration:
3 h
Dose descriptor:
NOEC
Effect conc.:
160 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
anhydrous
Basis for effect:
inhibition of total respiration
Remarks:
respiration rate

Description of key information

Read-across performed with structurally similar substance.

This activated sludge respiration inhibition test with cerium trichloride yielded a NOEC and EC50 of 160 and 767 mg CeCl3/L, respectively, corresponding to a NOEC and EC50 of 91 and 436 mg Ce/L.

Performing a molecular weight correction, the NOEC and EC50 for the substance cerium acetate were 206 and 987 mg/L, respectively.

Key value for chemical safety assessment

EC50 for microorganisms:
987 mg/L
EC10 or NOEC for microorganisms:
206 mg/L

Additional information

Read-across performed with structurally similar substance

The inhibitory effect of the test material cerium trichloride on the respiration rate of aerobic wastewater microorganisms in activated sludge was investigated in a 3-hour respiration inhibition test according to the OECD Guideline for Testing of Chemicals, No. 209, adopted 2010.

The inhibition of the respiration rates for all tested concentrations was in the range -1.3 to 66.1 % compared to the control. Up to and including the concentration of 242 mg test material per litre the test material had no statistically significant inhibitory effect on the respiration rate of activated sludge after the incubation period of 3 hours.

This activated sludge respiration inhibition test with cerium trichloride yielded a NOEC and EC50 of 160 and 767 mg CeCl3/L, respectively, corresponding to a NOEC and EC50 of 91 and 436 mg Ce/L.