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Administrative data

short-term repeated dose toxicity: oral
Type of information:
migrated information: read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Study period:
April 2008 - 2010
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: GLP OECD TG 422 compliant study, using a main constituent of the reaction mass for a read-across purpose
Reason / purpose for cross-reference:
reference to same study

Data source

Reference Type:
study report
Report date:

Materials and methods

Test guideline
according to guideline
OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)
GLP compliance:
yes (incl. QA statement)
Limit test:

Test material

Constituent 1
Chemical structure
Reference substance name:
Cerium dioxide
EC Number:
EC Name:
Cerium dioxide
Cas Number:
Molecular formula:

Test animals

Details on test animals or test system and environmental conditions:
- Source: Janvier, Le Genest-Saint-Isle, France
- Age at study initiation: 10 weeks old
- Weight at study initiation: 402 - 454 g (males) / 244 - 285 g (females)
- Fasting period before study: no
- Housing: individual (except during pairing), in wire-mesh cages (43 x 21.5 x 18 cm) or polycarbonate cages (43 x 21.5 x 20 cm) for females during lactation
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 6 days

- Temperature (°C): 22 +/- 2
- Humidity (%): 50 +/- 20
- Air changes (per hr): about 12
- Photoperiod (hrs dark / hrs light): 12 / 12 (7.00 am - 7.00 pm)

IN-LIFE DATES: From: 14 May 2008 To: 14 July 2008

Administration / exposure

Route of administration:
oral: gavage
other: 0.5% methylcellulose solution
Details on oral exposure:
- Test item ground to fine powder using mortar and pestle, suspended in vehicle and homogenized by magnetic stirrer
- Dosing solutions prepared for use for up to 12 days and stored in brown flasks at +4°C, protected from light, prior to use

- Justification for use and choice of vehicle (if other than water): appropriate for oral suspensions
- Concentration in vehicle: 30, 90 or 200 mg/mL
- Amount of vehicle (if gavage): 5 mL/kg
- Lot/batch no. (if required): Sigma batches 017K0052 and 066K0129 (methylcellulose)
- Concentration: 0.5% in water
Analytical verification of doses or concentrations:
Details on analytical verification of doses or concentrations:
During the pre-study period, the homogeneity, stability and concentration of two dosage forms prepared at low and high concentrations (33.6 and 230 mg/mL) were checked using ICP-OES (Inductively Coupled Plasma-Optical Emission Spectrometry) after validation of the analytical method. The results showed acceptable homogeneity and stability of both concentrations over 12 days of storage at +4°C protected from light.

During the study, the concentration of the test item (0, 33.6, 101.7 and 230 mg/mL in week 1 and 0, 30, 90 and 200 mg/mL in week 6) and homogeneity of the dosage forms were determined in samples of each control and test item dosage form prepared for use in weeks 1 and 6. The results showed acceptable homogeneity and concentration of all dosage forms analyzed. Precision (RSD =< 10%) and accuracy (100 +/- 10%) of the method were found to be satisfactory. The homogeneity of the dosage form prepared for week 6 at 200 mg/mL was slightly outside the acceptance criteria with a RSD of 12.8% but this was considered to have no impact on the validity of the study.
Duration of treatment / exposure:
- Males: 15 days before mating, during mating (up to 3 weeks), until euthanasia (4 weeks total)
- Females: 15 days before mating, during mating (up to 3 weeks), during pregnancy, during lactation, until day 5 post partum inclusive
Frequency of treatment:
Once daily, 7 days a week
Doses / concentrationsopen allclose all
Doses / Concentrations:
0, 168, 509 or 1150 mg/kg bw
other: nominal (up until day 3, due to an error of density measurement)
Doses / Concentrations:
0, 150, 450 or 1000 mg/kg bw
other: nominal (from day 4 up to the end of the study)
No. of animals per sex per dose:
Control animals:
yes, concurrent vehicle
Details on study design:
- Dose selection rationale: on the basis of a previous 10-day dose-range finding study (CIT No. 33178 TSR) at the same dose levels which elicited no treatment-related effects
- Rationale for animal assignment (if not random): computerized stratification procedure so that the average body weight of each group was similar
Positive control:
Not included


Observations and examinations performed and frequency:
- Time schedule: at least twice daily (morbidity and mortality) or once daily (clinical signs)

- Time schedule: once before beginning of treatment period and once weekly during treatment period
Observations included (but were not limited to) changes in the skin, fur, eyes, mucous membranes, occurrence of secretions and excretions and autonomic activity (e.g. lachrymation, piloerection, pupil size, unusual respiratory pattern). Changes in gait, posture and response to handling as well as the presence of clonic or tonic movements, stereotypes (e.g. excessive grooming, repetitive circling) or bizarre behavior (e.g. self-mutilation, walking backwards) were also recorded.

- Time schedule for examinations:
Males: on first day of treatment and then once weekly
Females: on first day of treatment and then once weekly until mated, and on days 0, 7, 14 and 20 post coitum and days 1 and 5 post partum

- Time schedule for examinations:
Males: once weekly over 7-day periods from first day of dosing
Females: once weekly over 7-day periods from first day of dosing through gestation and lactation
Not recorded during pairing period



- Time schedule for collection of blood: just before necropsy
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: Yes (overnight for at least 14 hours)
- How many animals: first 5 males and 5 females to deliver in each group
- Parameters examined: erythrocytes, hemoglobin, mean cell volume, packed cell volume, mean cell hemoglobin concentration, mean cell hemoglobin, thrombocytes, leucocytes, differential white cell count with cell morphology, reticulocytes, prothrombin time, activated partial thromboplastin time, fibrinogen

- Time schedule for collection of blood: just before necropsy
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: Yes (overnight for at least 14 hours)
- How many animals: first 5 males and 5 females to deliver in each group
- Parameters examined: sodium, potassium, chloride, calcium, inorganic phosphorus, glucose, urea, creatinine, total bilirubin, total proteins, albumin, albumin/globulin ratio, total cholesterol, triglycerides, alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase, bile acid


- Time schedule for examinations: once at the end of treatment period (day 5 post partum for females)
- Dose groups that were examined: all groups (first 5 males and 5 females to deliver)
- Battery of functions tested: sensory activity / grip strength / motor activity / other: standard reflexes and responses, rectal temperature

The FOB included a detailed clinical examination, measurement of reactivity to manipulation or to different stimuli and motor activity. The animals were randomized in order to ensure "blind" evaluation. All animals were observed in the cage, in the hand and in the standard arena.
The following parameters were assessed and graded:
- "touch escape" or ease of removal from the cage,
- in the hand: fur appearance, salivation, lachrymation, piloerection, exophthalmos, reactivity to handling, pupil size (presence of myosis or mydriasis),
- in the standard arena (2-minute recording): grooming, palpebral closure, defecation, urination, tremors, twitches, tonic and clonic convulsions, gait, arousal (hypo- and hyper-activity), posture, stereotypy, behavior, breathing, ataxia and hypotonia.
Then, the following parameter measurements, reflexes and responses were recorded:
- touch response,
- forelimb grip strength,
- pupillary reflex,
- visual stimulus response,
- auditory startle reflex,
- tail pinch response,
- righting reflex,
- landing foot splay,
- at the end of observation: rectal temperature.
Finally, motor activity of all animals was measured once by automated infra-red sensor equipment over a 60-minute period.

OTHER: No other general toxicity parameter
Sacrifice and pathology:
- Organ weights (F0 generation, see table below)
- Macroscopic post-mortem examination (F0 generation)

On all tissues specified (see table below), macroscopic lesions and females sacrified because of absence of delivery to investigate possible causes
- Comparison of mean values by one-way variance analysis and Dunnett's test
- Percentage values compared by Fisher's exact probability test
- Specific sequences of tests used for clinical chemistry and organ weight data

Results and discussion

Results of examinations

Clinical signs:
no effects observed
no mortality observed
Body weight and weight changes:
no effects observed
Food consumption and compound intake (if feeding study):
no effects observed
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
no effects observed
Clinical biochemistry findings:
no effects observed
Urinalysis findings:
not examined
Behaviour (functional findings):
no effects observed
Organ weight findings including organ / body weight ratios:
no effects observed
Gross pathological findings:
no effects observed
Histopathological findings: non-neoplastic:
no effects observed
Histopathological findings: neoplastic:
no effects observed
Details on results:
There were no unscheduled deaths during the study.
Isolated and non-dose-related incidences of soft feces, loud breathing, chromorhinorrhea and reflux at dosing were observed in all groups treated with Cerium oxide. Generally only one animal was affected and the signs were short-lived. It was considered that none of these represented signs of toxicity of the test item.
In addition, hairloss and cutaneous lesions were observed in the control group and the groups treated at 150 or 450 mg/kg/day. These signs are commonly observed in laboratory rats of this strain and are considered not to be related to treatment with the test item.

There were no effects of treatment with the test item on mean male or female body weight or body weight gains during the premating, gestation or lactation phases.
The female group treated at 450 mg/kg/day had a slightly lower mean body weight gain over the gestation period when compared with the controls but the difference was mainly due to one female with a low body weight gain which skewed the group mean.

There were no effects of treatment with the test item on mean male or female food consumption.

The males treated at 450 mg/kg/day showed increases when compared with the controls for red blood cell count, hemoglobin level and hematocrit. These differences were not statistically significant and were not observed at 150 or 1000 mg/kg/day. It was considered that the differences did not represent an effect of treatment with the test item.
The female group treated at 1000 mg/kg/day showed a statistically significant increase in hemoglobin concentration and monocyte count. Neither was observed in the males treated at the same dose-level and no related parameters were affected. It was considered that these differences were not treatment-related.

The male group treated at 1000 mg/kg/day had increased concentrations of creatinine and albumin (three or four of the males treated at 1000 mg/kg/day had values outside the control range). Related parameters (for example urea and total proteins) were not affected and the female group treated at the same dose-level did not show any differences to controls. It was considered that neither of these parameters had been affected by treatment with the test item.

The first five males and the first five delivered females of each group treated with Cerium oxide were assessed for Functional Observation Battery. All groups achieved normal scores compared to the controls for touch escape, reactivity to handling, touch response, fur appearance, pupil size, grooming, palpebral closure, gait, posture, breathing, defecation, urination, visual stimulus response, pupillary reflex, auditory startle reflex, tail pinch response, forelimb grip strength, righting reflex, landing foot splay and rectal temperature.
All animals had absence of salivation, lacrimation, piloerection, exophthalmos, tremors, twitches, clonic or tonic convulsions, hyperactivity, hypoactivity, ataxia, hypotonia, stereotypy and abnormal behavior.
There were no marked differences in the mean number of movements made by the assessed males or females of all test item-treated groups when compared with the controls. No dose-relationship was observed and the small increases and decreases observed in all test item-treated groups were considered not to represent an effect of treatment with the test item.

Organ weight changes (principally of adrenals, spleen and thymus) were considered not to be related to the test item as they were small in amplitude, had no gross or microscopic correlates, were not dose-related in magnitude, and/or were not consistent for the sexes.

In a few rats given the test item, intestinal distension with gas was described in the cecum (1/10 high-dose males), colon (2/10 high-dose and 1/10 low-dose males), and ileum (2/10 high dose and 1/10 low-dose males). In the absence of microscopic correlates, this finding was considered not to be of toxicological significance.
In one high-dose female there was a dilatation of the cervix associated with serous contents in the uterine horns. These findings were explained at microscopic examination by the presence of a congenital anomaly involving the cervix and distal vagina.
The other macroscopic findings had no histologic correlates or correlated with common histologic findings in control rats, and were considered to be incidental. One mid-dose female showed a thymic mass which correlated with a chronic abscess at microscopic examination.

A detailed, stage-aware qualitative evaluation of the testes was conducted in control and high dose males.
There were no microscopic findings related to the test item administration.
In the few low-, mid-, and high-dose females which were sacrificed because of no delivery, no estrous cycle abnormalities were found at microscopic examination of the genital organs. However, in one high-dose female, a congenital anomaly involving the cervix and distal vagina explained the absence of mating/pregnancy. Both the cervix and the distal vagina were dilated with presence of a large mucosal protrusion in the cavity.

Effect levels

Dose descriptor:
parental toxicity
Effect level:
> 1 000 mg/kg bw/day (nominal)
Basis for effect level:
other: No relevant effects up to highest dose tested

Target system / organ toxicity

Critical effects observed:
not specified

Applicant's summary and conclusion

No significant systemic toxicity was observed up to the highest tested dose, i.e. 1000 mg/kg b.w./d. The NOEL for parental toxicity is > 1000 mg/kg b.w./d.
Executive summary:

In an OECD TG 422-compliant study, the potential general and reproductive or developmental toxicity of Cerium dioxide were tested following daily oral administration by gavage to 10-week old Sprague-Dawley rats (10/sex) from 2 weeks before mating, through mating and, for the females, through gestation until day 5 post partum, at the dose levels of 0 (0.5% aqueous methylcellulose solution), 150, 450 or 1000 mg/kg (except for the first 3 days of dosing when an error in density measurements resulted in dose levels of slight overdosing at 168, 509 or 1150 mg/kg, respectively).

No unscheduled deaths or treatment-related clinical signs occurred during the study. There were no effects on body weight, body weight gain or food consumption at any dose level. The Functional Observational Battery assessment, hematology and blood chemistry parameters revealed no treatment-related effects. There were no relevant differences from controls for pairing, mating, fertility and delivery parameters. Pups showed no effects of treatment on survival or body weight performance. Macroscopic and microscopic examinations at necropsy did not reveal any treatment-related findings and there were no treatment-related changes in organ weights.

The NOELs for parental toxicity, for reproductive performance (mating and fertility) and for toxic effects on progeny were therefore all considered to be 1000 mg/kg.

No classification for repeat-dose toxicity or reproductive or developmental toxicity is warranted based on the absence of relevant effects in this study, according to the criteria of Annex VI Directive 67/548/EEC or UN/EU GHS.

This study is classified as acceptable. It satisfies the OECD 422 guideline requirements on repeated dose toxicity testing and reproduction/developmental toxicity screening.