2-ethylhexanoic acid, cerium salt

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

8 Jan 2013 - 31 Jan 2013

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

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 item was soluble at a concentration of 8 g test item per liter deionized water before and after pH adjustment from 5.0 to 7.4.
- Test item 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 item 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 item 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, DO 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 liter

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.
- DO 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

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

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

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

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 substance (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 liter 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 item 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 item per liter the test item 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.

Description of key information

The key study (Eisner, 2013) was an activated sludge respiration inhibition test performed with CeCl3 and yielding a 3-h EC50 and NOEC value of 436 and 91 mg Ce/L, respectively.

Key value for chemical safety assessment

EC50 for microorganisms:

436 mg/L

EC10 or NOEC for microorganisms:

91 mg/L

Additional information

The key study (Eisner, 2013) was an activated sludge respiration inhibition study with CeCl3 yielding a 3-h NOEC and EC50 of 91 and 436 mg Ce/L, respectively.