Cerium dioxide

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

No indication of genetic toxicity based on in vitro test results (Ames test and gene mutation assay in mammalian cells).

Link to relevant study records

Reference

Reference 1

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

January 2007 - March 2007

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

(without concentration, stability and homogeneity analytical determinations based on the high stability of the test substance)

Qualifier:

according to guideline

Guideline:

OECD Guideline 471 (Bacterial Reverse Mutation Assay)

Deviations:

yes

Remarks:

no concentration, stability and homogeneity analytical determinations included based on the high stability of the test substance

GLP compliance:

yes

Type of assay:

bacterial reverse mutation assay

Species / strain / cell type:

S. typhimurium TA 1535, TA 1537, TA 98 and TA 100

Species / strain / cell type:

E. coli WP2 uvr A

Metabolic activation:

with and without

Metabolic activation system:

Phenobarbital/5,6-benzoflavone-pretreated male Sprague-Dawley rat liver S9 fraction

Test concentrations with justification for top dose:

0 (vehicle), 1.58, 5, 15.8, 50, 158, 500, 1581 or 5000 µg/plate (5 highest concentrations were analyzed)

Vehicle / solvent:

- Vehicle(s)/solvent(s) used: aqueous 1% w/v methylcellulose (suspension)
- Justification for choice of solvent/vehicle: limited solubility in water and dimethyl formamide

Untreated negative controls:

yes

Negative solvent / vehicle controls:

yes

True negative controls:

no

Positive controls:

yes

Positive control substance:

4-nitroquinoline-N-oxide

9-aminoacridine

2-nitrofluorene

sodium azide

benzo(a)pyrene

other: 2-aminoanthracene

Details on test system and experimental conditions:

METHOD OF APPLICATION: in agar (plate incorporation) + preincubation

DURATION
- Preincubation period: 30 minutes
- Selection time (if incubation with a selection agent): 48 to 72 hours

SELECTION AGENT: tryptophan

NUMBER OF REPLICATIONS: 3 per concentration and per condition (+/-S9)

Evaluation criteria:

- Positive: if treatment produced a dose-related increase in revertant colony numbers of at least 2-fold (1.5-fold for strain TA100) the concurrent vehicle control either in the presence or absence of S9 mix
- Negative: if treatment did not produce a dose-related increase in revertant colony numbers of at least 2-fold (1.5-fold for strain TA100) the concurrent vehicle control either in the presence or absence of S9 mix
- Equivocal: if results obtained failed to satisfy the criteria for a clear "positive" or "negative" response

Statistics:

Mean comparison of numbers of revertant colonies between treatment groups and concurrent vehicle control group

Key result

Species / strain:

S. typhimurium TA 1535, TA 1537, TA 98 and TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity nor precipitates, but tested up to recommended limit concentrations

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Key result

Species / strain:

E. coli WP2 uvr A

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity nor precipitates, but tested up to recommended limit concentrations

Vehicle controls validity:

valid

Untreated negative controls validity:

not applicable

Positive controls validity:

valid

Summary tables of mutagenicity assay results:

 

Plate incorporation assay:

Dose (µg/plate)

Number of revertant colonies per plate (Mean ± SD)

TA1535

TA1537

TA98

TA100

WP2 uvrA

-S9

+S9

-S9

+S9

-S9

+S9

-S9

+S9

-S9

+S9

Negative controls

1% methylcellulose

0

22 ± 5

23 ± 6

9 ± 2

20 ± 5

25 ± 1

39 ± 2

159 ± 18

161 ± 5

52 ± 9

64 ± 12

Positive controls

NaAZ 9AC 2NF NQO 2AA BaP

0.5 50 1 0.5 5 5

311 ± 17 nt nt nt nt nt

nt nt nt nt 385 ± 9 nt

nt 574 ± 119 nt nt nt nt

nt nt nt nt nt 117 ± 9

nt nt 147 ± 20 nt nt nt

nt nt nt nt nt 451 ± 37

546 ± 26 nt nt nt nt nt

nt nt nt nt nt 1145 ± 25

nt nt nt 222 ± 8 nt nt

nt nt nt nt 294 ± 19 nt

Test substance

Cerium Oxide

50 158 500 1581 5000

21 ± 3 19 ± 1 17 ± 3 25 ± 2 22 ± 3

26 ± 1 19 ± 3 17 ± 7 24 ± 5 19 ± 6

17 ± 6 16 ± 2 14 ± 6 19* ± 2 14 ± 3

16 ± 6 17 ± 2 13 ± 2 17 ± 2 11 ± 4

28 ± 7 28 ± 2 23 ± 6 27 ± 2 25 ± 7

37 ± 4 39 ± 6 30 ± 3 35 ± 8 42 ± 7

140 ± 6 166 ± 4 182 ± 11 148 ± 12 135 ± 4

151 ± 16 172 ± 11 148 ± 9 166 ± 9 150 ± 11

41 ± 2 45 ± 6 55 ± 1 47 ± 11 45 ± 10

44 ± 4 69 ± 17 54 ± 5 49 ± 8 57 ± 4

NaAZ: Sodium azide

9AC: 9-aminoacridine

2NF: 2-nitrofluorene

NQO: 4-nitroquinoline N-oxide

2AA: 2-aminoanthracene

BaP: Benzo[a]pyrene

nt: not tested

* Apparent increase considered to be normal variation since colony counts were within historical control range

 

Pre-incubation assay:

Dose (µg/plate)

Number of revertant colonies per plate (Mean ± SD)

TA1535

TA1537

TA98

TA100

WP2 uvrA

-S9

+S9

-S9

+S9

-S9

+S9

-S9

+S9

-S9

+S9

Negative controls

1% methylcellulose

0

18 ± 2

21 ± 7

12 ± 3

15 ± 5

20 ± 4

38 ± 11

133 ± 7

173 ± 13

52 ± 7

52 ± 7

Positive controls

NaAZ 9AC 2NF NQO 2AA BaP

0.5 50 1 0.5 5 5

280 ± 19 nt nt nt nt nt

nt nt nt nt 321 ± 17 nt

nt 778 ± 111 nt nt nt nt

nt nt nt nt nt 103 ± 6

nt nt 80 ± 15 nt nt nt

nt nt nt nt nt 353 ± 23

511 ± 39 nt nt nt nt nt

nt nt nt nt nt 991 ± 58

nt nt nt 1458 ± 51 nt nt

nt nt nt nt 560 ± 53 nt

Test substance

Cerium Oxide

50 158 500 1581 5000

17 ± 1 23 ± 2 18 ± 7 19 ± 2 23 ± 2

18 ± 4 16 ± 4 25 ± 7 17 ± 1 23 ± 4

14 ± 4 17 ± 2 13 ± 3 16 ± 8 16 ± 2

19 ± 8 14 ± 6 15 ± 1 18 ± 4 15 ± 3

25 ± 3 31 ± 3 28 ± 3 30 ± 11 27 ± 11

46 ± 8 39 ± 3 37 ± 2 42 ± 10 42 ± 5

136 ± 14 120 ± 19 123 ± 38 147 ± 13 125 ± 4

159 ± 18 167 ± 26 165 ± 14 172 ± 6 175 ± 17

41 ± 1 43 ± 3 42 ± 7 56 ± 4 45 ± 6

50 ± 9 59 ± 9 60 ± 2 55 ± 5 61 ± 8

NaAZ: Sodium azide

9AC: 9-aminoacridine

2NF: 2-nitrofluorene

NQO: 4-nitroquinoline N-oxide

2AA: 2-aminoanthracene

BaP: Benzo[a]pyrene

nt: not tested

Conclusions:

No mutagenic activity was observed with the test substance in this Ames test up to the limit concentration of 5000 µg/plate with or without metabolic activation.

Executive summary:

The mutagenic potential of Cerium Oxide was tested in a bacterial reverse mutation (Ames) test. The test substance was applied on four strains ofSalmonella typhimurium(TA1535, TA1537, TA98 and TA100) and one strain ofEscherichia coli(WP2uvrA), using both plate incorpoation and preincubation methods, at concentrations of 0 (1% aqueous methylcellulose), 1.58, 5, 15.8, 50, 158, 500, 1581 or 5000 µg/plate, with or without metabolic activation. The appropriate positive controls were included and responded adequately.

 

Whatever the test concentration and the presence or absence or metabolic activation, no significant increase in the number of revertant colonies per plate over controls occurred.

 

Therefore Cerium Oxide showed no mutagenic activity in this bacterial reverse mutation (Ames) test using the plate incorporation and preincubation methods up to the limit concentration of 5000 µg/plate with or without metabolic activation.

 

This study is classified as acceptable. It is compliant with the OECD 471 guideline requirements on bacterial reverse mutation test.

Reference 2

Endpoint:

in vitro gene mutation study in mammalian cells

Type of information:

experimental study

Adequacy of study:

key study

Study period:

08 November 2005 - 03 January 2006

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 476 (In Vitro Mammalian Cell Gene Mutation Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of assay:

in vitro mammalian cell gene mutation test using the Hprt and xprt genes

Target gene:

HPRT locus of V79 Chinese Hamster cells

Species / strain / cell type:

Chinese hamster lung fibroblasts (V79)

Details on mammalian cell type (if applicable):

MEDIA USED
- Type and identity of media: Minimal Essential Medium supplemented with 10% fetal calf serum
- Properly maintained: yes
- Periodically checked for Mycoplasma contamination: yes
- Periodically checked for karyotype stability: yes
- Periodically "cleansed" against high spontaneous background: yes

Metabolic activation:

with and without

Metabolic activation system:

Phenobarbital/beta-Naphtoflavone-induced rat liver S9 fraction

Test concentrations with justification for top dose:

Experiment I:
- 4 hours without S9: 28.1, 56.3, 112.5, 225, 450 and 1800 µg/mL
- 4 hours wIth S9: 28.1, 56.3, 112.5, 225, 450 and 1800 µg/mL

Experiment II:
- 24 hours without S9: 28.1, 56.3, 112.5, 225, 450 and 1800 µg/mL
- 4 hours with S9: 14.1, 28.1, 56.3, 112.5, 225 and 1800 µg/mL

Vehicle / solvent:

- Solvent used: deionized water

Untreated negative controls:

yes

Remarks:

culture medium

Negative solvent / vehicle controls:

yes

Remarks:

deionized water

True negative controls:

yes

Remarks:

untreated cells

Positive controls:

yes

Positive control substance:

ethylmethanesulphonate

Untreated negative controls:

yes

Remarks:

culture medium

Negative solvent / vehicle controls:

yes

Remarks:

deionized water

True negative controls:

yes

Remarks:

untreated cells

Positive controls:

yes

Positive control substance:

7,12-dimethylbenzanthracene

Details on test system and experimental conditions:

METHOD OF APPLICATION: in medium


DURATION
- Preincubation period: not applicable
- Exposure duration: 4 or 24 hours
- Expression time (cells in growth medium): approx. 7 days
- Selection time (if incubation with a selection agent): not specified
- Fixation time (start of exposure up to fixation or harvest of cells): not specified


SELECTION AGENT (mutation assays): 6-thioguanine
STAIN (for cytogenetic assays): 10% methylene blue in 0.01% KOH solution


NUMBER OF REPLICATIONS: duplicate cultures in 2 independent experiments


NUMBER OF CELLS EVALUATED: 5x10E2 (cytotoxicity, cloning efficiency I) - 1.5x10E6 (mutant frequency)


DETERMINATION OF CYTOTOXICITY
- Method: cloning efficiency I (cytotoxicity); cloning efficiency II (cell viability)


OTHER EXAMINATIONS:
- Mutant colonies per 10E6 cells = mean number of mutant colonies per flask found after plating in 6-thioguanine containing medium x 10E6 divided by the number of cells survived
- Induction factor = mutant colonies per 10E6 cells / mutant colonies per 10E6 cells of the corresponding solvent control

Evaluation criteria:

The assay is considered acceptable if:
- the numbers of mutant colonies per 10E6 cells in negative and/or solvent controls fall with the test facility historical data range
- the positive control substances produce a significant increase in mutant colony frequencies
- the cloning efficiency II value of the negative and/or solvent controls exceed 0.5

A test substance is considered as positive if it induces either a concentration-related increase in the mutation frequency or a reproducible and positive response at one of the test points (at least three times above the spontaneous mutation frequency).

Statistics:

Since the distribution of mutant cells does not follow known statistical models, no adequate statistical method was available

Key result

Species / strain:

Chinese hamster lung fibroblasts (V79)

Metabolic activation:

with and without

Genotoxicity:

negative

Cytotoxicity / choice of top concentrations:

no cytotoxicity, but tested up to precipitating concentrations

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

TEST-SPECIFIC CONFOUNDING FACTORS
Precipitation was observed by the naked eye in all parts of pre-experiment at 112.5 µg/mL and above. In the first main experiment (4-hour exposure), precipitation was seen at 225 µg/mL and above with or without S9. In the second main experiment, precipitation was observed at 225 µg/mL and above in the absence of S9 (24-hour exposure) and at 112.5 µg/mL and above in the presence of S9 (4-hour exposure).

RANGE-FINDING/SCREENING STUDIES:
A pre-test was performed in order to determine the concentration range for the mutagenicity experiments, using same experimental conditions as described for the main experiments. In the pre-test, the colony forming ability of approximately 500 single cells after exposure to the test substance was observed and compared to the controls.
The highest concentration used in the pre-test was chosen with regard to the purity (99.8 %) and the molecular weight of the test item (172.12 g/mol). Test item concentrations between 14.1 and 1800 µg/mL (approximately 10 mM) were used to evaluate toxicity in the presence (4 h treatment) and absence (4 h and 24 h treatment) of metabolic activation. No relevant toxic effect (relative cloning efficiency at or below 50 %) occurred up to the high-est concentration of both treatment periods with and without metabolic activation. Precipitation was noted at 112.5 µg/mL and above in the absence and presence of metabolic activation at both treatment intervals (4 and 24 hours). There was no relevant shift of osmolarity and pH values of the medium even at the maximum concentration of the test item.

COMPARISON WITH HISTORICAL CONTROL DATA:
In both experiments (with or without S9), the range of the negative and solvent controls was from 2.1 to 12.3 mutants per 10E6 cells. The range of the cells exposed to the test substance was from 0.9 to 26.3 mutants per 10E6 cells. However all experimental points remained within the historical control data range.

Summary result table:

	Concentration (µg/mL)	S9 mix	Relative cloning efficiency I (%)	Relative cloning efficiency II (%)	Mutant colonies per 10E6 cells	Induction factor	Relative cloning efficiency I (%)	Relative cloning efficiency II (%)	Mutant colonies per 10E6 cells	Induction fact
Experiment I / 4-h treatment			Culture I				Culture II
Negative control	0	-	100.0	100.0	5.7	-	100.0	100.0	7.2	-
Solvent control (water)	0	-	100.0	100.0	12.3	1.0	100.0	100.0	7.7	1.0
Positive control (EMS)	300.0	-	30.2	80.2	137.5	24.0	30.1	86.9	67.3	9.4
Test item	28.1 56.3 112.5 225.0 (p) 450.0 (p) 1800.0 (p)	- - - - - -	103.6 105.2 89.3 101.4 94.2 103.0	culture discontinued* 97.7 89.3 82.1 102.0 84.9	culture discontinued* 3.7 5.4 7.2 5.6 5.4	culture discontinued* 0.3 0.4 0.6 0.5 0.4	95.8 102.7 91.4 97.5 83.6 100.6	culture discontinued* 98.1 95.8 92.3 98.5 98.8	culture discontinued* 6.7 6.9 10.6 7.9 7.1	culture discontinued* 0.9 0.9 1.4 1.0 0.9
Experiment II / 24-h treatment			Culture I				Culture II
Negative control	0	+	100.0	100.0	5.7	-	100.0	100.0	8.4	-
Solvent control (water)	0	+	100.0	100.0	3.0	1.0	100.0	100.0	5.2	1.0
Positive control (DMBA)	2.0	+	24.1	80.2	510.3	172.2	77.8	55.8	1034.3	200.6
Test item	14.1 28.1 56.3 112.5 (p) 225.0 (p) 1800.0 (p)	+ + + + + +	96.4 93.4 91.5 102.4 112.2 107.5	64.3 73.2 73.6 74.1 32.9 culture discontinued*	8.1 4.5 3.1 6.8 15.7 culture discontinued*	2.7 1.5 1.1 2.3 5.3 culture discontinued*	89.0 88.9 82.2 85.2 88.6 76.0	66.1 72.8 81.6 74.2 95.4 culture discontinued*	3.4 8.5 5.5 2.3 4.1 culture discontinued*	0.7 1.7 1.1 0.4 0.8 culture discontinued*

(p) Precipitation visible to unaided eye

* Since a minimum of 4 analyzable concentrations is required

Conclusions:

No evidence of gene mutations at the HPRT locus in V79 cells up to the concentration of 1800 µg/mL of the test subsatnce with or without S9.

Executive summary:

The potential of Cerium Oxide to induce gene mutations at the HPRT locus in Chinese Hamster V79 cells was tested. The assay was performed in two independent experiments, each using duplicate cultures. In the first experiment, the cells were exposed to the test substance suspended in deionized water at concentrations ranging from 28.1 to 1800 µg/mL (equivalent to10 mM) for 4 hours with or without metabolic activation (S9). In the second experiment, cell exposure was 24 hours at concentrations ranging from 28.1 to 1800 µg/mL in the absence of S9 and 4 hours at concentrations ranging from 14.1 to 1800 µg/mL in the presence of S9. The cells were evaluated for mutant frequency at selected test concentrations. Positive controls consisted of 1.2 or 2.4 mM ethylmethane sulfonate and 7.7 µM 7,12-dimethylbenz(a)anthracene without and with S9, respectively.

 

Precipitation was observed from 225 µg/mL up to the maximum concentration with and without S9 (4 h treatment) in the first main experiment and without S9 mix in the second experiment (24 h treatment). It was also observed from 112.5 µg/mL up to the maximum concentration in the second experiment with S9 (4 h treatment). No relevant cytotoxic effects indicated by relative cloning efficiency lower than 50% were observed up to 1800 µg/mL in both main assays with or without S9. No significant and reproducible dose-dependent increases in the mutation frequency were observed in both main experiments.

 

Appropriate reference mutagens used as positive controls showed a distinct increase in induced mutant colonies, indicating that the tests were sensitive and valid.

 

Therefore, Cerium Oxide did not induce gene mutations at the HPRT locus in V79 cells up to the concentration of 1800 µg/mL with or without S9.

 

This study is classified as acceptable. It satisfies the OECD 476 guideline requirements on In vitro Mammalian Cell Gene Mutation Test.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Genetic toxicity in vivo

Description of key information

No indication of genetic toxicity based on in vivo test results (mouse bone marrow micronucleus assay).

Link to relevant study records

Reference

Endpoint:

in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 26/05/1992 to 04/06/1993

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

Deviations:

no

GLP compliance:

yes

Type of assay:

micronucleus assay

Species:

mouse

Strain:

Swiss

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Iffa Credo, 69210 L'Arbresle France
- Age at study initiation: 5 weeks old
- Weight on day of dosing: 30 - 34 g (males) / 23 - 29 g (females)
- Housing: by groups of 5 of the same sex in polycarbonate cages with stainless steel lid
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 5 days

ENVIRONMENTAL CONDITIONS
- Temperature: 21 ± 2°C
- Humidity: 50 ± 20%
- Air changes (per hr): filtered and non-recycled fresh air
- Photoperiod: 12 hrs dark / 12 hrs light

IN-LIFE DATES: Not specified

Route of administration:

oral: gavage

Vehicle:

- Vehicle used: 1% carboxymethylcellulose solution
- Justification for choice of solvent/vehicle: appropriate to oral suspensions
- Concentration of test material in vehicle: 100 mg/mL
- Amount of vehicle: 20 mL/kg bw
- Lot/batch no. (if required): Sigma 58C-0156

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Immediately before use, by putting the test substance in suspension

Duration of treatment / exposure:

Single administration

Frequency of treatment:

Single administration

Post exposure period:

24 hours (test substance, negative control, positive control) and 48 hours (test substance, negative control)

Dose / conc.:

2 000 mg/kg bw (total dose)

Remarks:

Basis: nominal

No. of animals per sex per dose:

5

Control animals:

yes, concurrent vehicle

Positive control(s):

- Nature: cyclophosphamide
- Justification for choice of positive control: not provided
- Route of administration: Oral (gavage)
- Dose: 50 mg/kg bw

Tissues and cell types examined:

Femur bone marrow erythrocytes

Details of tissue and slide preparation:

- Femur bone marrow eluted out with fetal calf serum and cell suspension centrifuged
- Supernatant removed and cells in sediment resuspended by shaking
- One drop of cell suspension spread on a coded slide
- Slides air-dried and stained by May-Grünwald Giemsa
- Two slides prepared per animal but only one used for scoring

Evaluation criteria:

- 2000 polychromatic erythrocytes scored for micronuclei per animal
- Ratio between polychromatic and normochromatic erythrocytes (PE/NE ratio) calculated by scoring 1000 erythrocytes per animal
- Substance considered clastogenic if statistical increase in mean number of micronucleated polychromatic erythrocytes for at least one of the sampling time compared to negative controls and this increase doubles the number of micronucleated polychromatic erythrocytes in the test facility's historical data (1.4 +/- 0.6 per thousand)

Statistics:

- Intergroup comparison of mean numbers of micronucleated polychromatic erythrocytes using Kastenbaum and Bowman's test (5% significance level)
- Intergroup comparison of PE/NE ratios using Student's t test

Key result

Sex:

male/female

Genotoxicity:

negative

Remarks:

at 2000 mg/kg bw (nominal)

Toxicity:

no effects

Vehicle controls validity:

valid

Negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

RESULTS OF RANGE-FINDING STUDY
No clinical signs in 3 males and 3 females given a single oral dose of 2000 mg/kg bw.

RESULTS OF DEFINITIVE STUDY
See summary table below.

Mean number of micronucleated polychromatic erythrocytes and PE/NE ratio:

Time of sacrifice (hours post-dosing)	Group	Number of polychromatic erythrocytes / 1000 polychromatic erythrocytes (mean ± standard deviation)	PE/NE ratio (mean ± standard deviation)
24
	Vehicle	1.9 ± 1.0	1.0 ± 0.2
	Test substance	2.4 ± 1.3	1.1 ± 0.2
	Cyclophosphamide	56.6 ± 10.4***	0.8 ± 0.1*
48
	Vehicle	1.7 ± 1.6	1.0 ± 0.2
	Test substance	2.9 ± 1.3	1.1 ± 0.3

*** p < 0.001       * p < 0.05

Conclusions:

No evidence of clastogenicity in this mouse bone marrow micronucleus assay at the limit dose of 2000 mg/kg.

Executive summary:

The clastogenic potential of Cerium Oxide was tested in an oral mouse bone marrow micronucleus assay. Swiss OF1 5-week old mice (5/sex per group) were given a single oral administration of 2000 mg/kg Cerium Oxide by gavage. Two test substance-treated groups, two vehicle (1% carboxymethylcellulose)-treated control groups and one positive control (cyclophosphamide) group were used. Euthanasia was performed 24 and 48 hours after dosing for substance-treated and negative control groups. Positive controls were euthanasied 24 hours after dosing. For each animal, 2000 polychromatic erythrocytes from femur bone marrow were microscopically examined for micronuclei. The polychromatic to normochromatic erythrocytes (PE/NE) ratio was determined from 1000 erythrocytes per mouse.

At both sampling times, there were no statistical differences from negative control values in the number of micronucleated polychromatic erythrocytes and the PE/NE ratio from substance-treated animals.

An appropriate reference mutagen used as positive control showed a significant increase in micronucleated polychromatic erythrocytes together with a significant decrease in the PE/NE ratio, indicating that the test was sensitive and valid.

Therefore, Cerium Oxide did not induce cytogenetic damage in this micronucleus test in mice treated by the oral route at the limit dose of 2000 mg/kg.

This study is classified as acceptable. It satisfies the OECD 474 guideline requirements on Mammalian Erythrocyte Micronucleus Test.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed (negative)

Additional information

The ability of bulk cerium dioxide to induce genetic damage was assessed both in vitro and in vivo.

In vitro, three bacterial reverse mutation assays (Ames test) are available. A GLP-compliant Ames test (of reliability 1 according to Klimisch cotation criteria) was selected as the key study (Charles River Laboratories, 2007). A second Ames test using an additional Salmonella strain (also of reliability 1 according to Klimisch cotation criteria) was used as a supporting study. The reliability of the third Ames test was not assessable due to the lack of details on the test method. All Ames tests gave negative results up to the limit concentration of 5000 µg/plate of cerium dioxide with or without exogenous metabolic activation. In a gene mutation assay at the hprt locus of V79 cells (RCC-CCR, 2006; reliability 1 according to Klimisch cotation criteria), cerium dioxide also induced no mutations up to 1800µg/mL with or without metabolic activation.

In vivo, cerium dioxide was tested in a mouse bone marrow micronucleus assay (CIT, 1993; reliability 1 according to Klimisch cotation criteria). There was no indication of clastogenic effects at 24 h or 48 h following a single administration of a limit dose level of 2000 mg/kg bw.

Therefore, cerium dioxide is considered to be devoid of genetic toxicity.

Justification for classification or non-classification

Based on the classification criteria of Annex VI Directive 67/548/CEE or UN/EU GHS, and considering the negative results in all in vitro and in vivo genetic toxicity tests using cerium dioxide, no classification for mutagenicity is required.