Caesium fluoride

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

The Ames assay in vitro was waived for cesium fluoride because bacterial mutagenesis assays of inorganic metal compounds are frequently negative. Bacterial reverse mutation assays in vitro with sodium fluoride and cesium hydroxide provided negative results. An in vitro chromosome aberration assay was waived because suitable in vivo data is available. Mammalian cell gene mutation tests in vitro with the source substances cesium hydroxide monohydrate and sodium fluoride did not show mutagenic properties.

Link to relevant study records

Reference

Reference 1

Endpoint:

in vitro cytogenicity / chromosome aberration study in mammalian cells

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

an in vitro cytogenicity study in mammalian cells or in vitro micronucleus study does not need to be conducted because adequate data from an in vivo cytogenicity test are available

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
No study data is available for chromosome aberration in vitro with cesium fluoride. Therefore in vivo study data has been used to address this endpoint. Available in vitro studies with different source substances (Cs2CO3, CsOH, CsCl, NaF not included in the data set) all showed a positive response. The biological relevance is however questionable, because the positive in vitro results were not confirmed in respective in vivo studies with the above substances.

Reference 2

Endpoint:

in vitro gene mutation study in mammalian cells

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

Please refer to read-across justification attached to IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

Key result

Species / strain:

Chinese hamster Ovary (CHO)

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

results with CsOH

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

True negative controls validity:

not examined

Positive controls validity:

valid

Reference 3

Endpoint:

in vitro gene mutation study in mammalian cells

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

Please refer to read-across justification attached to IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

Key result

Species / strain:

hepatocytes: ARL 18

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

results with NaF

Cytotoxicity / choice of top concentrations:

cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

True negative controls validity:

not examined

Positive controls validity:

valid

Reference 4

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

Please refer to read-across justification attached to IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Key result

Species / strain:

other: TA 98, 100, 1535, 1537, E.coli WP2 uvr A

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

Hita, 1994

Cytotoxicity / choice of top concentrations:

cytotoxicity

Untreated negative controls validity:

valid

Positive controls validity:

valid

Key result

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

Tong, 1988

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Positive controls validity:

valid

Key result

Species / strain:

S. typhimurium TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

Tong, 1988

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Positive controls validity:

valid

Key result

Species / strain:

S. typhimurium TA 1535

Remarks:

Li, 1987

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

Tong, 1988

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Positive controls validity:

valid

Key result

Species / strain:

S. typhimurium TA 1537

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

Tong, 1988

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Positive controls validity:

valid

Key result

Species / strain:

S. typhimurium TA 1538

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

Tong 1988

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

not examined

True negative controls validity:

not examined

Positive controls validity:

valid

Key result

Species / strain:

S. typhimurium, other: TA97a, TA98, TA100, TA102 and TA1535

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

Li 1987

Cytotoxicity / choice of top concentrations:

no cytotoxicity

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

True negative controls validity:

not examined

Positive controls validity:

valid

Reference 5

Endpoint:

in vitro gene mutation study in bacteria

Data waiving:

study scientifically not necessary / other information available

Justification for data waiving:

other:

Justification for type of information:

JUSTIFICATION FOR DATA WAIVING
According to the Endpoint specific Guidance (Chapter R.7a, version 4.1, October 2015) bacterial mutagenesis assays of inorganic metal compounds are frequently negative due to limited capacity for uptake of metal ions and/or the induction of large DNA deletions by metals in bacteria potentially leading to an increased death rate in mutants. The high prevalence of false negatives for metal compounds might suggest that mutagenesis assays with mammalian cells, as opposed to bacterial cells, would be the preferred starting point for testing for this class of Annex VII substances. Therefore, mutagenicity data in mammalian cells is provided instead for the alkali metal part of the molecule.

Based on physico-chemical properties of the cesium salts and the fact that they readily dissociate into the cesium cation and the respective anion once in contact with an aqueous solution, their toxicokinetic profile is comparable. Following oral administration, the cesium ion will become systemically available and is readily distributed throughout the body via the blood stream. Within the body, the cesium cations behave in a similar manner as physiological potassium cations (Rundo 1964; Rundo et al., 1963). Bioaccumulation to a particular body tissue is unlikely while urinary excretion is the major route of elimination of unchanged cesium from the human body (Boecker, 1969; Henrichs et al., 1989; Richmond et al., 1962).

For the present cesium salt, the absence of a mutagenic potential was demonstrated in several Ames assays conducted with salts containing either cesium or fluoride ion. Moreover, various in vitro or in vivo mutagenicity tests in mammalian cells or in mammals respectively with these cesium salts are available and were used in read-across and weight of evidence approaches. In the case of cesium fluoride, read-across strategy was used with cesium salts such as CsOH and the respective salts to figure out the anion effect, i.e. NaF. For all, no positive effect was recorded therefore, it has been extrapolated that cesium fluoride is not mutagenic.

References

Boecker BB. (1969) The metabolism of 137Cs inhaled as 137CsCl by the beagle dog. Proceedings of the Society Experimental Biology and Medicine 130(3):966-971.
Richmond CR., Furchner JE., Langham WH. (1962) Long-term retention of radiocesium by man. Health Physics 8:201-205.
Rundo J. (1964) A survey of the metabolism of caesium in man. British Journal of Radiology 37:108-114.
Rundo J., Mason JI., Newton D., Taylor BT. (1963) Biological half-life of caesium in man in acute chronic exposure. Nature 200:188-189.
Henrichs K., Paretzke HG., Voigt G., Berg D. (1989) Measurements of Cs absorption and retention in man. Health Physics 57(4):571-578.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Description of key information

Cytogenicity in vivo was assessed with the source substances cesium hydroxide monohydrate, cesium carbonate, cesium chloride and sodium fluoride. Both the micronucleus assays with sodium fluoride and cesium chloride and the chromosome aberration assays with cesium hydroxide monohydrate and cesium carbonate were negative.

Link to relevant study records

Reference

Reference 1

Endpoint:

in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

Please refer to read-across statement attached to IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Key result

Sex:

male/female

Genotoxicity:

negative

Toxicity:

yes

Vehicle controls validity:

valid

Negative controls validity:

not examined

Positive controls validity:

valid

Remarks on result:

other: Based on CsCl

Key result

Sex:

male

Genotoxicity:

negative

Toxicity:

yes

Vehicle controls validity:

valid

Negative controls validity:

not examined

Positive controls validity:

valid

Remarks on result:

other: based on NaF

Reference 2

Endpoint:

in vivo mammalian somatic cell study: cytogenicity / bone marrow chromosome aberration

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

Please refer to read-across statement attached to IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Key result

Sex:

male/female

Genotoxicity:

negative

Toxicity:

no effects

Vehicle controls validity:

valid

Negative controls validity:

not examined

Positive controls validity:

valid

Remarks on result:

other: Based on Cs2CO3

Key result

Sex:

male

Genotoxicity:

negative

Toxicity:

yes

Remarks:

Dose dependent toxicity was observed from 400 to 1000 mg/kg bw

Vehicle controls validity:

valid

Negative controls validity:

not examined

Positive controls validity:

valid

Remarks on result:

other: based on CsOH monohydrate

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

No data is available for mutagenicity of the target substance in vitro and in vivo. Consequently, data from the source substances CsOH monohydrate and sodium fluoride in vivo were used. Please refer to IUCLID section 13 for further information on read across.

 

in vitro tests

Bacterial reverse mutation

According to the Endpoint specific Guidance (Chapter R.7a, version 4.1, October 2015) bacterial mutagenesis assays of inorganic metal compounds are frequently negative due to limited capacity for uptake of metal ions and/or the induction of large DNA deletions by metals in bacteria potentially leading to an increased death rate in mutants. The high prevalence of false negatives for metal compounds might suggest that mutagenesis assays with mammalian cells, as opposed to bacterial cells, would be the preferred starting point for testing for this class of Annex VII substances. Therefore, mutagenicity data in mammalian cells is provided instead (Please see further below).

Bacterial mutagenesis assays are available for the counter ion fluoride. The endpoint is therefore covered using two negative Ames tests with sodium fluoride.

Li et al. (1987) investigated the mutagenicity of fluoride (as sodium fluoride, NaF) with Ames Salmonella/microsome assays in strains of TA97a, TA98, TA100, TA102 and TA1535. The concentrations of NaF tested ranged from 0.44 to 4421 µg/plate (0.1 to 1000 ppm F), both with and without microsome activation. In addition, the suggested antimutagenic effect of fluoride was evaluated with known mutagens at various concentrations of NaF (0.44-442.2 µg/plate, 0.1-100 ppm F). The data showed that NaF, in amounts from 0.44 to 442.2 µg/plate (0.1-100 ppm F), failed to significantly increase the number of the revertants over the number observed in the solvent (distilled deionized water) controls. Increases of NaF to, and beyond, 1100 µg/plate (250 ppm F) resulted in a toxic effect and a reduction of the revertants to various degrees among the strains. NaF in the presence of known mutagens did not significantly decrease the number of the revertants. The results of this study indicate that NaF does not have mutagenic or antimutagenic effects in the strains tested with Ames Salmonella assays.

Tong et al. (1988) investigated the mutagenic potential of sodium fluoride in five bacterial strains: Salmonella typhimurium (TA 98, TA 100, TA 1535, TA1537 and TA1538), according to Shimada et al (1985) in an Ames assay with and without metabolic activation. A cytotoxicity assay (Shimada et al., 1985) was run in parallel in the actual assay. The test concentrations were 10, 20, 40, 80, 160 and 320 µg/plate. At 80 to 320 µg/plate slight cytotoxicity was observed. There was no significant increase in revertants either in the absence or presence of Aroclor-induced rat S9 preparation at all the doses tested. Negative and the strain-specific positive control values indicate that test conditions were adequate. Based on the results, sodium fluoride is considered to be non-mutagenic.

 

Chromosome aberration

No data on chromosome aberration is available for the target substance in vitro. Consequently, cytogenicity data from the source substances CsOH monohydrate and sodium fluoride in vivo were used. Please refer to IUCLID section 7.6.2 for further information.

 

Mammalian cell gene mutation

No data on mammalian cell gene mutation is available for the target substance. Consequently, data from the source substances CsOH monohydrate and sodium fluoride were used to cover this endpoint.

CsOH was tested in a HPRT Mammalian Gene Mutation Test in CHO-K1 cells according to OECD guideline 476 and EU method B.17.

The test item was dissolved in Ham's F12 medium and the following concentrations and intervals (without and with metabolic activation using S9 mix) were tested in two independent experiments (both run in duplicate):

Experiment 1, 5-hour treatment period without and with S9 mix:

625, 1250, 2500, 3125, 3750, 4200, 4600*, and 5000*µg/mL

Experiment 2, 20-hour treatment period without S9 mix:

625, 1250, 2500, 3125, 3750, 4000, 4200*, 4600*, and 5000*µg/mL

Experiment 2, 5-hour treatment period with S9 mix:

625, 1250, 2500, 3125, 3750, 4000, 4200, 4600*, and 5000*µg/mL

*These concentrations were very toxic when cesium hydroxide monohydrate were applied and there was not enough cells to start the phenotypic expression period after the treatment.

In Experiment 1, there were no biologically or statistically significant increases in mutation frequency at any concentration tested, either in the absence or in the presence of metabolic activation. There were no statistical differences between treatment and control groups and no dose-response relationships were noted.

In Experiment 2, the mutant frequency of the cells did not show significant alterations compared to the concurrent control, when the test item was tested without S9 mix over a prolonged treatment period (20 hours). Furthermore, a five-hour treatment with in the presence of S9 mix did not cause significant increases in mutant frequency, further indicating that the findings in Experiment 1 were within the normal biological variation.

As in Experiment 1, in Experiment 2 no statistical differences between treatment and solvent control groups and no dose response relationships were noted. The sensitivity of the test and the efficacy of the S9 mix were demonstrated by large increases in mutation frequency in the positive control cultures.

Cesium hydroxide monohydrate tested both without and with metabolic activation (S9 mix), did not induce increases in mutant frequency in this test in Chinese hamster ovary cells. The source substance was not mutagenic in this in vitro mammalian cell gene mutation test performed with CHO-K1 cells. It is concluded that cesium carbonate has no mutagenic effects on mammalian cell genes.

In a mammalian cell gene mutation assay (HGPRT), rat liver epithelial cell line ARL 18 cultured in vitro was exposed to sodium fluoride at concentrations of 2, 10, 20, 40, 80 and 160 µg/mL in the presence and absence of metabolic activation (Tong et al. 1988). Positive controls (with Benz(a)pyrene and potassium chromate) and one solvent control (DMSO) were run in parallel.

Sodium fluoride was tested up to cytotoxic concentrations. Toxic effects were observed in the two highest doses (80, 160 µg/mL). The positive controls did induce the appropriate response. There was no evidence of induced mutant colonies over background in the non toxic concentrations.

 

in vivo tests

No data on cytogenicity in vivo is available for the target substance. Consequently, data from the source substances cesium carbonate and CsOH monohydrate (chromosome aberration assay) and sodium fluoride and cesium chloride (micronucleus assay) were used to cover this endpoint.

 

Micronucleus assays

In a Wistar rat bone marrow micronucleus assay equivalent to OECD guideline 474, 5 male rats /group/sampling time were treated orally with sodium fluoride at doses of 0, 500 and 1000 mg/kg bw (Albanese, 1987). Bone marrow cells were harvested at 24 and 48 hours post treatment. The vehicle was distilled water. The test substance was applied by gavage as a single dose.

4 out of 5 animals died before the second harvest point (48 hours). No signs of abnormal behaviour were observed in the remaining animals. As the ratio between normochromatic and polychromatic erythrocytes was nearly 1:1 in the control and treated animals, cytotoxicity for sodium fluoride was excluded. There was no a significant increase in the frequency of micronucleated polychromatic erythrocytes in bone marrow after any treatment time.

Potential mutagenic activity of cesium chloride was examined in bone marrow of male and female NMRI BR mice according to OECD 474. Animals were treated intraperitoneal on two occasions, 24 hrs apart using 250 mg/kg bw/d, 500 mg/kg bw/day and 1000 mg/kg bw/d.

The intraperitoneal administration on two occasions did not induce any biologically relevant increase in the frequency of MPCEs in male or female mice at 24 hours after the last treatment compared to the vehicle control.

The percentage of PCE among total (polychromatic and normachromatic) erythrocytes in 1000 mg/kg bw/day dose groups of male was slightly lower than the concurrent negative control value, but there was no clear evidence for test item induced bone marrow toxicity.

Under the conditions of this assay, cesium chloride did not induce any biologically relevant increase in the number of micronucleated polychromatic erythrocytes at dose levels of 250, 500 and 1000 mg/kg body weight after intraperitoneal administration on two occasions, 24 hrs apart in NMRI BR mice. Cesium chloride did not show any genotoxic activity in this Mouse Micronucleus Test.

 

Chromosome aberration assays

The assay performed with the source substance cesium hydroxide monohydrate investigated the potential to induce chromosome aberrations in vivo according to OECD guideline No. 475 and EU method B.11. The single oral administration of the source substance did not induce statistically or biologically significant increases in the number of bone marrow cells showing structural chromosome aberrations compared to concurrent controls with harvest at 18 or 42 hours following treatment start. No statistically significant decreases in the number of mitotic cells compared to concurrent controls were induced. Therefore, according to the results achieved in this in vivo mammalian bone marrow chromosome aberration test cesium hydroxide monohydrate is not considered to be clastogenic.

The study was performed to investigate the potential of Cesium carbonate to induce chromosome aberrations in bone marrow cells of the rat according to OECD Guideline 475 (1997) and US EPA OPPTS 870.5385. The test item was formulated in deionised water. The volume administered orally was 10 mL/kg bw. Rats were treated once with 437.5 mg/kg or 875 mg/kg or 1750 mg/kg. After 24 and 48 hours (only the high dose group) spindle inhibitor colcemide was injected intraperitoneal, bone marrow cells were collected for chromosome aberration analysis and 10 animals (5 males/5 females) per test group were evaluated for occurrence of cytogenetic damage. No relevant reduction of mitotic indices could be observed. Therefore cesium carbonate was not cytotoxic in the bone marrow. No statistically significant increase in the frequency of aberrant cells occurred. Results are comparable to vehicle control. In addition positive control showed a significant increase of induced aberration frequency. Cesium carbonate is not considered clastogenic.

 

Conclusion

Based on the above study data with both ions of concern (Cs and F) it can be concluded that neither of them indicate a genotoxic potential. Thus, the same can be assumed for the target substance cesium fluoride.

Justification for classification or non-classification

Based on the results obtained in in vitro and in vivo studies cesium fluoride is not considered to be genotoxic/mutagenic or clastogenic and thus has not to be classified according to Regulation (EC) No 1272/2008.