Cesium formate

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

2011-04-27 to 2011-09-21

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Once taken up by the organism, cesium formate dissociates into the cesium cation (Cs) and the formate anion (HCO2 -). Toxicity is caused by the cesium cation, therefore conducting a study on cesium chloride as a surrogate for cesium formate is justified.

Reason / purpose for cross-reference:

read-across source

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Version / remarks:

adopted July 22, 2010

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.11 (Biodegradation: Activated Sludge Respiration Inhibition Test)

Version / remarks:

dated May 30, 2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

not required

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: Based on the results of a performed preliminary informatory range-finding test the test item was investigated at the concentration level of 1000 mg/L. Based on the solubility properties of the test item (based on the MSDS information) the adequate amounts of the test item were weighted in a small inert plastic dish (“plate”: to allow the contact between the inoculum and the whole test item amount) and this plastic dish containing the adequate test item amount was thrown into each test flask. Thereafter a pH measurement, adjustment was carried out (from ~pH 12 as close as practically possible to the range of pH 7.5 ± 0.5) and finally the test item solutions were inoculated.
The test item concentration of 1000 mg/L was examined with five replicates. Concentrations in excess of nominal 1000 mg test item/L were not tested.
Because of the test item water solubility limit (ca 1.910 g/L at 20°C, based on the MSDS) a concentrated stock solution (with a concentration of > 1.910 g/L) was not prepared buta defined amount (300 mg to 300 mL test mixture) of the test item was directly added to each test mixture. An analytical estimation of the test substance concentration in the test vessels was therefore considered as not necessary, and the subsequent calculations referred to the nominal test item concentration. The test item fully dissolved in the test mixture, no precipitation occurred.

Test organisms (species):

activated sludge, domestic

Details on inoculum:

- Preparation of inoculum for exposure: The coarse particles were removed by settling for 10 minutes, and the upper layer of finer solids was decanted. The activated sludge used for this study was washed by centrifugation and the supernatant liquid phase was decanted. The solid material was re-suspended in isotonic saline solution with shaking and again centrifuged. This procedure was repeated twice. An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge to dry weight determined. Based on this ratio, calculated amount of wet sludge was suspended in isotonic saline solution to yield a concentration equivalent to 3 g per litre (on dry weight basis).
The activated sludge was not used on the day of the collection but continuously aerated (2L/minute) at the test temperature for about 24 hours (1 day) and was fed once with 50 mL synthetic sewage/L activated sludge.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

3 h

Test temperature:

20 ± 2 °C, The temperature in the test mixtures during the measurements was in average: 21.6 °C.
The noticed temperatures in the environmental room varied between: 20.3-19.6 °C.

pH:

7.01 - 8.15

Nominal and measured concentrations:

1000 mg/L (nominal)

Details on test conditions:

TEST SYSTEM
- Test vessel: Erlenmeyer bottles of approximately 300 mL volume
- Aeration: With compressed air (0.5 litre per minute)
- No. of vessels per concentration (replicates): five
- No. of vessels per control (replicates): six replicates
- No. of vessels per reference control (replicates): three concentrations with three replicates
- No. of vessels per nitrification control (replicates): three replicates

TEST MEDIUM / WATER PARAMETERS
- in accordance to the guideline

OTHER TEST CONDITIONS
- Adjustment of pH: the tst was performed without pH adjustment

TEST CONCENTRATIONS
- Range finding study:
Pre-experiments were performed to determine the solubility of the test item in the used aqueous system, to investigate the test item effect on the pH within the test system and to select suitable methods for the preparation of a stock solution and for the dosage of the test item in the test medium.
The preliminary range-finding test one test container from the concentration of 10 mg/L, one container from the concentration of 100 mg/L, triplicates at the highest test item concentration (1000 mg/L), blank, abiotic (three abiotic controls with the highest concentration of the test substance: 1000 mg/L) and reference controls were included.
In the preliminary experiment one series of the test containers was investigated without pH adjustment and one series with adjusted (to the range of pH 6-8) pH. (In the preliminary experiment two test item stock solutions were prepared with a concentration of 30 mg/mL (clear solutions) one with adjusted pH and one without pH adjustment.)
The nitrification potential of sludge was examined with additional control mixture that contained N-allylthiourea at 11.6 mg/L.
In the preliminary range-finding test the test item did not show any inhibitory effect up to and including the concentration level of 1000 mg/L when pH adjustment was performed and slight inhibition (~22 %) was noticed at the concentration of 1000 mg/L, without pH adjustment and therefore pH relevant effects cannot be excluded.
The abiotic control group did not show significant oxygen uptake (some oxygen uptake was detected in the range of the biological variability of the test system), therefore in the main test the abiotic control was not repeated.
In the preliminary test the nitrification respiration was insignificant and it was assumed that the heterotrophic oxygen uptake equals the total uptake and no significant nitrification is occurring. Therefore the main test was performed in one set of test vessels, without ATU addition.
In the main test (for informative reason) a nitrification control group (containing N-allylthiourea) was investigated with three parallels.

Reference substance (positive control):

yes

Remarks:

3,5-Dichlorophenol

Key result

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

CsOH monohydrate

Basis for effect:

inhibition of total respiration

Remarks on result:

other: respiration rate

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

CsOH monohydrate

Basis for effect:

inhibition of total respiration

Remarks on result:

other: Respiration rate

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

CsOH monohydrate

Basis for effect:

inhibition of total respiration

Remarks on result:

other: Respiration rate

Key result

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

> 892.8 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

calculated for CsOH anhydrous

Basis for effect:

inhibition of total respiration

Remarks on result:

other: Respiration rate

Key result

Duration:

3 h

Dose descriptor:

EC50

Effect conc.:

> 892.8 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

calculated for CsOH anhydrous

Basis for effect:

inhibition of total respiration

Remarks on result:

other: Respiration rate

Key result

Duration:

3 h

Dose descriptor:

NOEC

Effect conc.:

892.8 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

calculated for CsOH anhydrous

Basis for effect:

inhibition of total respiration

Remarks on result:

other: Respiration rate

Details on results:

Inhibition of Respiration Rate:
An additional nitrification control was examined in the main test with three parallels to check the possible nitrification potential of the applied activated sludge batch. With the applying of the nitrification control the differentiation between the total, heterotrophic and nitrification respiration was possible. The total respiration (RT) was 68.98 mg/Lh, the heterotrophic respiration (RH) was 73.08 mg/Lh, the nitrification respiration (RN): -4.1 mg/Lh was calculated according to the following equation: RN= RT-RH. The obtained -4.1 mg/Lh was was considered rather as 0.0 mg/Lh difference [not significant difference within a biological variability range of the applied test system, that lower than the 5 % of RT (3.45 mg/Lh) in blank controls]. According to the above calculations it was assumed that the heterotrophic oxygen uptake equals the total uptake.

Results with reference substance (positive control):

- Results with reference substance valid? yes
- Relevant effect levels: The 3-hour EC50 of 3,5-Dichlorophenol was calculated to be 12.63 mg/L, (95 % confidence limits: 11.11-14.15).
- Other: The following concentrations of the positive reference control 3,5-Dichlorophenol were tested on the same activated sludge and under identical conditions as the test item: 2, 7 and 24.5 mg/L. Each concentration of the 3,5-Dichlorophenol reference item was tested in three parallels. In comparison to the blank controls the specific respiration rate of the activated sludge was not inhibited at the lowest concentration of 2 mg/L, at the nominal concentrations of 7 and 24.5 mg/L, the respiration rate was inhibited by 37.48 % and 91.68 %, respectively.

Reported statistics and error estimates:

The EC50 value of the reference item and its confidence limits were calculated using Probit analysis. The analysis was done using the TOXSTAT statistical software program.
Since one concentration (as a limit concentration) of the test item was tested, this concentration level of the test item was compared to the blank control using the 2 Sample t-Test (α=0.05).

Validity criteria fulfilled:

yes

Conclusions:

Under the conditions of the performed activated sludge respiration inhibition test, the EC10 and EC50 values of cesium hydroxide monohydrate were determined as higher than 1000 mg/L. Based on the statistical evaluation in this test the NOEC was 1000 mg/L for cesium hydroxide monohydrate. Based on these data, the calculated EC10 and EC50 values of cesium hydroxide anhydrous were greater than 892.8 mg/L and the NOEC was 892.8 mg/L.

Executive summary:

The purpose of the 3 h test was to evaluate the influence of the read across substance cesium hydroxide monohydrate on the activity of activated sludge by measuring the respiration rate under defined conditions. The respiration rates (total, heterotrophic and nitrification oxygen uptake 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 3 hours. The test item was investigated at one (limit) concentration level of 1000 mg/L. The observed oxygen consumption rates consequently the specific respiration rates were in the range of the blank controls, no inhibitory effect of the test item was observed. Based on measured oxygen consumption values and calculated specific respiration rates it can be stated that the 3-hour EC10 and EC50 values of the test item are higher than 1000 mg/L. Based on these data, the calculated EC10 and EC50 values of cesium hydroxide anhydrous were greater than 892.8 mg/L and the NOEC was 892.8 mg/L (ToxiCoop, 2011).

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

892.8 mg/L

Additional information

The purpose of the 3 h test was to evaluate the influence of the read across substance cesium hydroxide monohydrate on the activity of activated sludge by measuring the respiration rate under defined conditions. The respiration rates (total, heterotrophic and nitrification oxygen uptake 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 3 hours. The test item was investigated at one (limit) concentration level of 1000 mg/L. The observed oxygen consumption rates consequently the specific respiration rates were in the range of the blank controls, no inhibitory effect of the test item was observed. Based on measured oxygen consumption values and calculated specific respiration rates it can be stated that the 3-hour EC10 and EC50 values of the test item are higher than 1000 mg/L.Based on these data, the calculated EC10 and EC50 values of cesium hydroxide anhydrous were greater than 892.8 mg/L and the NOEC was 892.8 mg/L (ToxiCoop, 2011).