Registration Dossier

Administrative data

Description of key information

- Oral route (rat, 37 to 45 days): no relevant signs of toxicity up to the limit dose of 1000 mg/kg bw

- Inhalation (rat, 90 days): "lung overload" inflammatory response syndrome ("portal-of-entry" effects) with a LOAEC at 50.5 mg/m3

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records
Reference
Endpoint:
short-term repeated dose toxicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Study period:
April 2008 - August 2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose:
reference to same study
Reason / purpose:
reference to same study
Qualifier:
according to
Guideline:
OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Limit test:
no
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- 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

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

IN-LIFE DATES: From 14 May 2008 To 14 July 2008
Route of administration:
oral: gavage
Vehicle:
methylcellulose
Remarks:
0.5% solution
Details on oral exposure:
PREPARATION OF DOSING SOLUTIONS:
- 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

VEHICLE
- 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:
yes
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
Dose / conc.:
0 mg/kg bw/day (nominal)
Dose / conc.:
168 mg/kg bw/day (nominal)
Remarks:
nominal up until day 3, due to an error of density measurement
Dose / conc.:
509 mg/kg bw/day (nominal)
Remarks:
nominal up until day 3, due to an error of density measurement
Dose / conc.:
1 150 mg/kg bw/day (nominal)
Remarks:
nominal up until day 3, due to an error of density measurement
Dose / conc.:
150 mg/kg bw/day (nominal)
Remarks:
nominal from day 4 up to the end of the study
Dose / conc.:
450 mg/kg bw/day (nominal)
Remarks:
nominal from day 4 up to the end of the study
Dose / conc.:
1 000 mg/kg bw/day (nominal)
Remarks:
nominal from day 4 up to the end of the study
No. of animals per sex per dose:
10
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:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: at least twice daily (morbidity and mortality) or once daily (clinical signs)

DETAILED CLINICAL OBSERVATIONS: Yes
- 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.

BODY WEIGHT: Yes
- 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

FOOD CONSUMPTION: Yes
- 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

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- 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

CLINICAL CHEMISTRY: Yes
- 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

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: Yes
- 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

Details:
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:
GROSS PATHOLOGY: Yes
- Organ weights (F0 generation, see table below)
- Macroscopic post-mortem examination (F0 generation)

HISTOPATHOLOGY: Yes
On all tissues specified (see table below), macroscopic lesions and females sacrificed because of absence of delivery to investigate possible causes
Statistics:
- 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
Clinical signs:
no effects observed
Description (incidence and severity):
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.
Mortality:
no mortality observed
Description (incidence):
There were no unscheduled deaths during the study.
Body weight and weight changes:
no effects observed
Description (incidence and severity):
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.
Food consumption and compound intake (if feeding study):
no effects observed
Description (incidence and severity):
There were no effects of treatment with the test item on mean male or female food consumption.
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
no effects observed
Description (incidence and severity):
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.
Clinical biochemistry findings:
no effects observed
Description (incidence and severity):
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.
Urinalysis findings:
not examined
Behaviour (functional findings):
no effects observed
Description (incidence and severity):
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.
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
no effects observed
Description (incidence and severity):
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.
Gross pathological findings:
no effects observed
Description (incidence and severity):
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 to xicological 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.
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
no effects observed
Description (incidence and severity):
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.
Histopathological findings: neoplastic:
no effects observed
Key result
Dose descriptor:
NOEL
Remarks:
parental toxicity
Effect level:
1 000 mg/kg bw/day (nominal)
Sex:
male/female
Basis for effect level:
other: No relevant effects up to highest dose tested
Critical effects observed:
not specified
Conclusions:
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 Oxide 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.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEL
1 000 mg/kg bw/day
Study duration:
subacute
Species:
rat

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records
Reference
Endpoint:
sub-chronic toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
August 1993 - December 1993
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)
GLP compliance:
yes
Limit test:
no
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Canada Inc., St Constant, Quebec, Canada
- Age at study initiation: 7 weeks old
- Weight at study initiation: 206 - 270 g (males) / 135 - 179 g (females)
- Fasting period before study: no
- Housing: individually in stainless-steel wire mesh-bottomed cages
- Diet: ad libitum (except during exposure, urinalysis, prior to bleeding and prior to necropsy)
- Water: ad libitum
- Acclimation period: 2 (males) or 3 (females) weeks

ENVIRONMENTAL CONDITIONS
- Temperature: 22 ± 3°C
- Humidity: 50 ± 20%
- Air changes: 12 - 15 per hr
- Photoperiod: 12 hrs dark / 12 hrs light

IN-LIFE DATES: From August 31, 1993 To December 20, 1993
Route of administration:
inhalation: aerosol
Type of inhalation exposure:
nose only
Vehicle:
other: unchanged (no vehicle)
Remarks on MMAD:
MMAD / GSD: Mass Median Aerodynamic Diameter (MMAD) ± Gravimetric Standard Deviation (GSD):
- Males at 0.0050 mg/L = 1.9 ± 1.9
- Females at 0.0050 mg/L = 1.8 ± 1.9
- Males at 0.0505 mg/L = 2.0 ± 1.9
- Females at 0.0505 mg/L = 2.0 ± 1.9
- Males at 0.5082 mg/L = 2.2 ± 1.8
- Females at 0.5068 mg/ L = 2.2 ± 1.8
Details on inhalation exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Four standard stainless-steel cylindrical "flow-through" nose-only inhalation chambers (approx. 80.6 L per chamber)
- Method of holding animals in test chamber: polycarbonate restraint cones
- Source and rate of air: laboratory compressed air supply
- Method of conditioning air: pre-dried compressed air
- System of generating particulates/aerosols: Venturi T-section (connected to powder feed nozzle and compressed air system)
- Temperature, humidity, pressure in air chamber: 20-24°C, 30-70% relative humidity, at least 19% O2
- Air flow rate: set at a level determined in preliminary work to be adequate to maintain chamber environment conditions
- Air change rate: at least 10 per hour
- Method of particle size determination: Andersen 1 ACFM cascade impactor operated at a flow rate of 28.3 L/min
- Treatment of exhaust air: purifying system

TEST ATMOSPHERE
- Brief description of analytical method used: Gravimetric aerosol concentrations measured hourly using vertically oriented open-faced glass fiber filters. Test atmosphere continually monitored throughout exposure period by a precalibrated real-time aerosol monitor.
- Samples taken from breathing zone: yes

VEHICLE
Not applicable
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Filters from 2nd day of exposure and monthly thereafter used for chemical analysis by Sponsor.
Duration of treatment / exposure:
13 weeks
Frequency of treatment:
6 hours a day, 5 days a week
Dose / conc.:
0.005 mg/L air
Remarks:
Basis: mean achieved chamber concentrations
Dose / conc.:
0.051 mg/L air
Remarks:
Basis: mean achieved chamber concentrations
Dose / conc.:
0.507 mg/L air
Remarks:
Basis: mean achieved chamber concentrations
Dose / conc.:
5 mg/m³ air
Remarks:
Basis: mean achieved chamber concentrations
Dose / conc.:
50.5 mg/m³ air
Remarks:
Basis: mean achieved chamber concentrations
Dose / conc.:
507.5 mg/m³ air
Remarks:
Basis: mean achieved chamber concentrations
No. of animals per sex per dose:
15
Control animals:
yes
Details on study design:
- Dose selection rationale: Existing toxicity data, limitations imposed by the exposure apparatus and procedure as well as the stability of the experimental atmosphere and based on a TLV of 5 mg/m3 for respirable nuisance dust.
- Rationale for animal assignment (if not random): computer-based randomization procedure based on bodyweight (males and females separately)
- Rationale for selecting satellite groups: Not applicable
- Post-exposure recovery period in satellite groups: Not applicable
Positive control:
Not applicable
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily (within the cage) and immediately before, during (hourly) and after exposure (outside the cage)

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: weekly

BODY WEIGHT: Yes
- Time schedule for examinations: weekly, commencing on the day of randomization and extending through the treatment period (+ on days of behavioral testing and immediately before sacrifice)

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: during acclimation and at study termination
- Dose groups that were examined: low and high dose-groups

HAEMATOLOGY: Yes
- Time schedule for collection of blood: in week 6 and at study termination
- Anaesthetic used for blood collection: No
- Animals fasted: Yes (overnight)
- How many animals: all surviving animals
- Parameters examined: red blood cell count, hemoglobin, hematocrit, erythrocyte indices, platelet count, mean platelet volume, white blood cell count (total and differential), prothrombin time, blood cell morphology

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: in week 6 and at study termination
- Animals fasted: Yes (overnight)
- How many animals: all surviving animals
- Parameters examined: Alkaline Phosphatase (ALP), Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST), total bilirubin, cholesterol, triglycerides, glucose, blood urea nitrogen, creatinine, total proteins, albumin, globulin, albumin/globulin ratio, sodium, chloride, potassium, calcium, inorganic phosphorus

URINALYSIS: Yes
- Time schedule for collection of urine: in week 6 and at study termination
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes (overnight)
- Parameters examined: color and appearance, pH, glucose, ketones, hemoglobin, volume, specific gravity, bilirubin, urobilinogen, proteins, nitrite, microscopy of centrifuged deposit

NEUROBEHAVIOURAL EXAMINATION: Yes (Functional Observational Battery)
- Time schedule for examinations: during acclimation, on day 1 (post dosing) and once during each of weeks 4, 8 and 13
- Dose groups that were examined: all animals
- Battery of functions tested:
* Sensory activity: observations in home cage (body position, tremors, twitches, convulsions, bizarre/stereotypic behavior), removal from home cage (ease of removal, vocalization), observations in arena (rearing, ataxic, hypotonic and impaired gait, overall gait incapacity, bizarre/stereotypic behavior, palpebral closure, tremors, twitches, convulsions, piloerection, respiratory rate/pattern, locomotor activity level, arousal, grooming, defecation, urination, olfactory response), handling observations (lacrimation, pupil size, salivation, urinary staining, diarrhea, body and abdominal tones, extensor thrust, corneal reflex, pinna reflex, toe and tail pinch, visual placing), on surface (auricular startle, air righting reflex), on top of box (positional passivity)
* Grip strength: forelimb, hindlimb, hindlimb splay
* Motor activity: activity counts recorded by microcomputer in 6 successive 10-minute sessions
* Other: body temperature
Sacrifice and pathology:
GROSS PATHOLOGY: Yes (external examination, including identification of all clinically recorded lesions, and detailed internal examination)
ORGAN WEIGHTS: Yes (adrenals, brain, heart, kidneys, liver, lungs, ovaries or testes, pituitary, prostate, spleen, thymus, thyroid, uterus)
HISTOPATHOLOGY: Yes (following standard list of tissues + abnormalities): adrenal, aorta, bone marrow, sternum, brain, bronchus, nasal cavity, cecum, colon, duodenum, epididymis, esophagus, eye, heart, ileum, jejunum, kidney, larynx, liver, lung, mandibular lymph node, mesenteric lymph node, mammary gland (M&F), skeletal muscle , optic nerve, sciatic nerve, pancreas, parathyroid, pharynx, pituitary gland, prostate, salivary gland, seminal vesicle, skin, cervical spinal cord, spleen, stomach, testis, thymus, thyroid, tongue, trachea, urinary bladder, bronchial lymph node, mediastinal lymph node, pancreatic lymph node, ovary, uterus.
Other examinations:
Not applicable
Statistics:
- Group mean values (with standard deviations) analyzed for homogeneity of variance using Bartlett's test
- Homogeneous data analyzed using Analysis of Variance and differences from controls assessed using Dunnett's 't' test
- Heterogeneous data analyzed using Kruskal-Wallis test and differences from controls assessed using Dunn's test
- Frequency data, gross pathology and histopathology findings analyzed using Fisher's exact probability test
Clinical signs:
no effects observed
Description (incidence and severity):
No relevant (treatment-related) effects were observed.
Mortality:
no mortality observed
Description (incidence):
No relevant (treatment-related) effects were observed.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
- No relevant changes in females
- Statistically significantly lower mean body weight gains in high-dose males when compared to controls in weeks 2 and 8
- Overall body weight gain of high-dose males marginally inferior to that of controls, although not statistically significant
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
- No relevant changes in females
- Food consumption of high-dose males marginally lower than that of controls although without statistical significance
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
no effects observed
Description (incidence and severity):
No relevant (treatment-related) effects were observed.
Haematological findings:
effects observed, treatment-related
Description (incidence and severity):
- No relevant changes in red blood cell count, hemoglobin, hematocrit, erythrocyte indices, platelet count, mean platelet volume, total or differential white blood cell counts except neutrophil counts, prothrombin time, blood cell morphology
- Statistically significantly elevated segmented neutrophil counts (when expressed as percentages of white blood cells) in low-dose and mid-dose females and high-dose males and females at weeks 6 and/or 13 compared to controls
- When expressed in absolute terms, segmented neutrophil counts in low-dose females and mid-dose and high-dose males and females elevated at weeks 6 and 13 compared to controls
Clinical biochemistry findings:
no effects observed
Description (incidence and severity):
No relevant (treatment-related) effects were observed.
Urinalysis findings:
no effects observed
Description (incidence and severity):
No relevant (treatment-related) effects were observed.
Behaviour (functional findings):
no effects observed
Description (incidence and severity):
No relevant (treatment-related) effects were observed.
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
- No relevant changes in adrenals, brain, heart, kidneys, liver, ovaries or testes, pituitary, prostate, spleen (females), thymus, thyroid or uterus weights
- Statistically significant higher lung (absolute and relative) weights in mid-dose and high-dose groups compared to controls
- Change in lung weight seen in all treated groups, although not always statistically significant
- Statistically significantly higher spleen (relative) weights and higher spleen (absolute) weights in high-dose males compared to controls
Gross pathological findings:
effects observed, treatment-related
Description (incidence and severity):
- No relevant findings at external examination, including identification of all clinically recorded lesions, and at detailed internal examination, except for lungs and lymph nodes
- Lungs: discoloration or pale areas (30 rats each in mid-dose and high-dose groups), pale foci (4 rats in low-dose group), uncollapsed parenchyma (2 rats in mid-dose group and 30 in high-dose group)
- Lymph nodes: enlargement and/or pale discoloration of the bronchial lymph nodes (28 rats in low-dose group, 30 each in mid-dose and high-dose groups), mediastinal lymph nodes (1 rat in control group, 12 in low-dose group, 18 in mid-dose group and 20 in high-dose group), pancreatic lymph nodes (3 rats in control group, 1 each in mid-dose and high-dose groups)
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
- No relevant findings in adrenals, aorta, bone marrow, sternum, brain, cecum, colon, duodenum, epididymis, esophagus, eye, heart, ileum, jejunum, kidney, mesenteric lymph node, mammary gland, skeletal muscle , optic nerve, sciatic nerve, pancreas, parathyroid, pharynx, pituitary gland, prostate, salivary gland, seminal vesicle, skin, cervical spinal cord, stomach, testis, thymus, thyroid, tongue, urinary bladder, ovary, uterus
- Pigment accumulation and/or alveolar epithelial/lymphoid hyperplasia in the lungs (in low-dose, mid-dose and high-dose groups)
- Lymphoid hyperplasia of the bronchial or mediastinal (in low-dose, mid-dose and high-dose groups) and pancreatic (in mid-dose group) lymph nodes
- Metaplasia and/or pigment accumulation in larynx (in low-dose, mid-dose and high-dose groups)
- Pigment accumulation in bronchial or mediastinal lymph nodes, nasal cavity and bronchi (in low-dose, mid-dose and high-dose groups), in trachea and pancreatic lymph nodes (in mid-dose and high-dose groups), and in liver, mandibular lymph nodes and spleen (high-dose group only)
Histopathological findings: neoplastic:
no effects observed
Dose descriptor:
NOEC
Effect level:
0.507 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
male/female
Basis for effect level:
clinical signs
mortality
ophthalmological examination
clinical biochemistry
urinalysis
behaviour (functional findings)
Dose descriptor:
NOEC
Effect level:
0.507 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
female
Basis for effect level:
body weight and weight gain
food consumption and compound intake
Dose descriptor:
NOEC
Effect level:
0.051 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
male
Basis for effect level:
body weight and weight gain
food consumption and compound intake
Dose descriptor:
NOEC
Effect level:
0.005 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
male
Basis for effect level:
haematology
Dose descriptor:
LOAEC
Effect level:
0.005 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
female
Basis for effect level:
haematology
Dose descriptor:
NOAEC
Effect level:
0.005 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
male/female
Basis for effect level:
organ weights and organ / body weight ratios
Dose descriptor:
LOAEC
Effect level:
0.005 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
male/female
Basis for effect level:
gross pathology
histopathology: non-neoplastic
Dose descriptor:
LOAEC
Effect level:
0.051 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
male/female
Basis for effect level:
histopathology: non-neoplastic
Critical effects observed:
not specified

Tissue/Lesion

Incidence of microscopic findings

(/No. of animals examined)

 

 

 

 

 

 

 

 

Males - 0 mg/L

Females - 0 mg/L

Males - 0.005 mg/L

Females - 0.005 mg/L

Males - 0.0505 mg/L

Females - 0.0505 mg/L

Males - 0.5075 mg/L

Females - 0.5075 mg/L

Bronchi

pigment accumulation

0/15

0/15

1/15

0/15

5/15*

4/15*

15/15*

15/15*

Nasal cavity:

 

 

 

 

 

 

 

 

- Goblet cell hypertrophy and/or hyperplasia

0/15

0/15

0/15

1/15

0/15

0/15

1/15

2/15

- Pigment accumulation

0/15

0/15

12/15*

3/15

15/15*

11/15*

15/15*

15/15*

Larynx:

 

 

 

 

 

 

 

 

- Metaplasia

0/15

0/15

3/15

3/15

9/15*

6/15*

13/15*

9/15*

- Pigment accumulation

0/15

0/15

6/15*

0/15

9/15*

7/15*

12/15*

9/15*

Liver

pigment accumulation

0/15

0/15

0/9

0/1

0/7

0/5

6/15*

5/15*

Lungs:

 

 

 

 

 

 

 

 

- Pigment accumulation

0/15

0/15

15/15*

15/15*

15/15*

15/15*

15/15*

15/15*

- Alveolar epithelial hyperplasia (with severity)

0/15

0/15

1/15(+)

0/15

11/15* (+ to ++)

5/15* (+ to ++)

14/15* (+ to +++)

15/15* (+ to ++)

- Lymphoid hyperplasia

0/15

0/15

0/15

0/15

0/15

1/15

12/15*

7/15*

Mandibular lymph nodes:

pigment accumulation

0/15

0/15

0/3

0/5

0/5

0/3

6/15*

6/15*

Spleen:

pigment accumulation

0/15

0/15

0/1

0/0

0/0

0/0

6/15*

3/15

Trachea:

pigment accumulation

0/15

0/15

0/15

0/15

1/15

1/15

14/15*

14/15*

Bronchial lymph nodes:

 

 

 

 

 

 

 

 

- Pigment accumulation

0/15

0/15

13/13*

14/15*

15/15*

15/15*

15/15*

15/15*

- Lymphoid hyperplasia

0/15

0/15

11/13*

13/15*

15/15*

15/15*

15/15*

15/15*

Mediastinal lymph nodes:

 

 

 

 

 

 

 

 

- Pigment accumulation

0/0

0/1

2/2

10/10

8/10

9/9

9/9

9/10

- Lymphoid hyperplasia

0/0

0/1

2/2

10/10

9/10

9/9

9/9

9/10

Pancreatic lymph nodes:

 

 

 

 

 

 

 

 

- Pigment accumulation

-

0/2

-

0/0

-

1/1

-

1/1

- Lymphoid hyperplasia

-

0/2

-

0/0

-

1/1

-

0/1

* p < 0.05

+: slight

++: mild

+++: moderate

Conclusions:
An overall NOEC was not established in the study report based on changes in hematology (females only), macroscopic observations at necropsy and histopathology at the lowest concentration tested, i.e. 0.005 mg/L. However, considering that lymphoid hyperplasia in the bronchial lymph nodes may not represent a specific toxic effect, but rather a non-specific adaptive response to the overloading of pulmonary alveolar macrophages by inorganic poorly soluble particles, and considering that alveolar epithelial hyperplasia in the lungs represents a more sensitive indication of adverse effects in the rat following inhalatory exposure to very high particulate concentrations, the LOAEC can be set at 0.0505 mg/l (50.5 mg/m3) based on the incidence and severity of alveolar epithelial hyperplasia in the lungs.
Executive summary:

In an OECD TG 413 compliant study, the potential general toxicity of Cerium Oxide was tested following repeated nose-only inhalation of a dry powder aerosol of cerium dioxide (mass median aerodynamic diameter = 1.8-2.2 µm, geometric standard deviation = 1.8-1.9) to 7-week old Sprague-Dawley rats (15/ sex) for 6 hours a day, 5 days a week, for 13 weeks, at the gravimetric concentrations of 0 (air), 0.005, 0.0505 or 0.5075 mg/L (0, 5, 50.5 or 507.5 mg/m3, respectively). Observations and measurements included mortality, clinical signs, body weight, food consumption, Functional Observational Battery, motor activity, hematology, clinical biochemistry, urinalysis, ophthalmological examination, gross pathological examination, organ weights and histopathological examination of selected tissues.

 

No treatment-related deaths or clinical signs occurred during the study. There were no effects on ophthalmology, clinical chemistry, urinalysis at any dose level. No behavioural changes following either acute or subchronic exposure and no significant differences in motor activity were observed in treated groups in the Functional Observational Battery assessment.

 

Treatment-related changes included changes in hematology, lung and spleen weights, macroscopic observations at necropsy and histopathology of the respiratory tract and lymphoreticular system.

 

Statistically significant increases in absolute and differential segmented neutrophil counts were observed at weeks 6 and 13 in females at 0.005 mg/L and above and in males at 0.0505 mg/L and above. Statistically significant increases in the absolute and relative weight of the lungs were noted for both males and females exposed to 0.0505 mg/L and above. Male rats exposed to 0.5075 mg/L also had a statistically significantly increase in the relative spleen weight. At necropsy, discoloration or pale areas and uncollapsed parenchyma in the lungs were observed in males and females at 0.0505 mg/L and above, and pale foci in females at 0.005 mg/L. Enlargement or pale discoloration of the bronchial, mediastinal and pancreatic lymph nodes were also observed in all treated groups.

 

Microscopically, pigmented material accumulation in the lungs, bronchial, mandibular and mediastinal or pancreatic lymph nodes, trachea, bronchi, larynx, nasal cavity, liver and spleen, as well as alveolar epithelial hyperplasia in the lungs, metaplasia in larynx, and lymphoid hyperplasia in lymph nodes and lungs, correlating with the presence of pigment in these tissues, were seen in all treated groups with a clear dose-response relationship.

 

Based on the findings at 0.005 mg/L, no NOEC was established in this study. The concentration of 0.005 mg/L (5 mg/m3) was a LOAEC in the study, based on the increased incidence of lymphoid hyperplasia in the bronchial lymph nodes of rats of both genders.

 

However, considering that lymphoid hyperplasia in the bronchial lymph nodes may not represent a specific toxic effect, but rather a non-specific adaptive response to the overloading of pulmonary alveolar macrophages by inorganic poorly soluble particles, and considering that alveolar epithelial hyperplasia in the lungs represents a more sensitive indication of adverse effects in the rat following inhalatory exposure to very high particulate concentrations, the concentration of 0.0505 mg/l (50.5 mg/m3) can be considered as a LOAEC based on the incidence and severity of alveolar epithelial hyperplasia in the lungs.

 

Based on the classification criteria of Annex VI Directive 67/548/EEC or UN/EU GHS and considering the interspecies differences between rats and non-rodent mammals regarding location of the inhaled particles during chronic exposure, no significant effect of relevance to human health were observed in this study. No systemic toxic effects specific to cerium dioxide as such were observed. The observed effects were rather consistent with a species-specific phenomenon of "lung overload" inflammatory response in the rat following inhalation of poorly soluble particles of low toxicity and resulting "portal-of- entry" effects, with a limited relevance to the human occupational situation given the levels of exposure. Therefore no classification is warranted for this endpoint.

 

This study is classified as acceptable. It satisfies the OECD 413 guideline requirements on subchronic inhalation toxicity.
Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
LOAEC
50.5 mg/m³
Study duration:
subchronic
Species:
rat
Organ:
lungs

Repeated dose toxicity: inhalation - local effects

Link to relevant study records
Reference
Endpoint:
sub-chronic toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
August 1993 - December 1993
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)
GLP compliance:
yes
Limit test:
no
Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Canada Inc., St Constant, Quebec, Canada
- Age at study initiation: 7 weeks old
- Weight at study initiation: 206 - 270 g (males) / 135 - 179 g (females)
- Fasting period before study: no
- Housing: individually in stainless-steel wire mesh-bottomed cages
- Diet: ad libitum (except during exposure, urinalysis, prior to bleeding and prior to necropsy)
- Water: ad libitum
- Acclimation period: 2 (males) or 3 (females) weeks

ENVIRONMENTAL CONDITIONS
- Temperature: 22 ± 3°C
- Humidity: 50 ± 20%
- Air changes: 12 - 15 per hr
- Photoperiod: 12 hrs dark / 12 hrs light

IN-LIFE DATES: From August 31, 1993 To December 20, 1993
Route of administration:
inhalation: aerosol
Type of inhalation exposure:
nose only
Vehicle:
other: unchanged (no vehicle)
Remarks on MMAD:
MMAD / GSD: Mass Median Aerodynamic Diameter (MMAD) ± Gravimetric Standard Deviation (GSD):
- Males at 0.0050 mg/L = 1.9 ± 1.9
- Females at 0.0050 mg/L = 1.8 ± 1.9
- Males at 0.0505 mg/L = 2.0 ± 1.9
- Females at 0.0505 mg/L = 2.0 ± 1.9
- Males at 0.5082 mg/L = 2.2 ± 1.8
- Females at 0.5068 mg/ L = 2.2 ± 1.8
Details on inhalation exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Four standard stainless-steel cylindrical "flow-through" nose-only inhalation chambers (approx. 80.6 L per chamber)
- Method of holding animals in test chamber: polycarbonate restraint cones
- Source and rate of air: laboratory compressed air supply
- Method of conditioning air: pre-dried compressed air
- System of generating particulates/aerosols: Venturi T-section (connected to powder feed nozzle and compressed air system)
- Temperature, humidity, pressure in air chamber: 20-24°C, 30-70% relative humidity, at least 19% O2
- Air flow rate: set at a level determined in preliminary work to be adequate to maintain chamber environment conditions
- Air change rate: at least 10 per hour
- Method of particle size determination: Andersen 1 ACFM cascade impactor operated at a flow rate of 28.3 L/min
- Treatment of exhaust air: purifying system

TEST ATMOSPHERE
- Brief description of analytical method used: Gravimetric aerosol concentrations measured hourly using vertically oriented open-faced glass fiber filters. Test atmosphere continually monitored throughout exposure period by a precalibrated real-time aerosol monitor.
- Samples taken from breathing zone: yes

VEHICLE
Not applicable
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Filters from 2nd day of exposure and monthly thereafter used for chemical analysis by Sponsor.
Duration of treatment / exposure:
13 weeks
Frequency of treatment:
6 hours a day, 5 days a week
Dose / conc.:
0.005 mg/L air
Remarks:
Basis: mean achieved chamber concentrations
Dose / conc.:
0.051 mg/L air
Remarks:
Basis: mean achieved chamber concentrations
Dose / conc.:
0.507 mg/L air
Remarks:
Basis: mean achieved chamber concentrations
Dose / conc.:
5 mg/m³ air
Remarks:
Basis: mean achieved chamber concentrations
Dose / conc.:
50.5 mg/m³ air
Remarks:
Basis: mean achieved chamber concentrations
Dose / conc.:
507.5 mg/m³ air
Remarks:
Basis: mean achieved chamber concentrations
No. of animals per sex per dose:
15
Control animals:
yes
Details on study design:
- Dose selection rationale: Existing toxicity data, limitations imposed by the exposure apparatus and procedure as well as the stability of the experimental atmosphere and based on a TLV of 5 mg/m3 for respirable nuisance dust.
- Rationale for animal assignment (if not random): computer-based randomization procedure based on bodyweight (males and females separately)
- Rationale for selecting satellite groups: Not applicable
- Post-exposure recovery period in satellite groups: Not applicable
Positive control:
Not applicable
Observations and examinations performed and frequency:
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily (within the cage) and immediately before, during (hourly) and after exposure (outside the cage)

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: weekly

BODY WEIGHT: Yes
- Time schedule for examinations: weekly, commencing on the day of randomization and extending through the treatment period (+ on days of behavioral testing and immediately before sacrifice)

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: during acclimation and at study termination
- Dose groups that were examined: low and high dose-groups

HAEMATOLOGY: Yes
- Time schedule for collection of blood: in week 6 and at study termination
- Anaesthetic used for blood collection: No
- Animals fasted: Yes (overnight)
- How many animals: all surviving animals
- Parameters examined: red blood cell count, hemoglobin, hematocrit, erythrocyte indices, platelet count, mean platelet volume, white blood cell count (total and differential), prothrombin time, blood cell morphology

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: in week 6 and at study termination
- Animals fasted: Yes (overnight)
- How many animals: all surviving animals
- Parameters examined: Alkaline Phosphatase (ALP), Alanine Aminotransferase (ALT), Aspartate Aminotransferase (AST), total bilirubin, cholesterol, triglycerides, glucose, blood urea nitrogen, creatinine, total proteins, albumin, globulin, albumin/globulin ratio, sodium, chloride, potassium, calcium, inorganic phosphorus

URINALYSIS: Yes
- Time schedule for collection of urine: in week 6 and at study termination
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes (overnight)
- Parameters examined: color and appearance, pH, glucose, ketones, hemoglobin, volume, specific gravity, bilirubin, urobilinogen, proteins, nitrite, microscopy of centrifuged deposit

NEUROBEHAVIOURAL EXAMINATION: Yes (Functional Observational Battery)
- Time schedule for examinations: during acclimation, on day 1 (post dosing) and once during each of weeks 4, 8 and 13
- Dose groups that were examined: all animals
- Battery of functions tested:
* Sensory activity: observations in home cage (body position, tremors, twitches, convulsions, bizarre/stereotypic behavior), removal from home cage (ease of removal, vocalization), observations in arena (rearing, ataxic, hypotonic and impaired gait, overall gait incapacity, bizarre/stereotypic behavior, palpebral closure, tremors, twitches, convulsions, piloerection, respiratory rate/pattern, locomotor activity level, arousal, grooming, defecation, urination, olfactory response), handling observations (lacrimation, pupil size, salivation, urinary staining, diarrhea, body and abdominal tones, extensor thrust, corneal reflex, pinna reflex, toe and tail pinch, visual placing), on surface (auricular startle, air righting reflex), on top of box (positional passivity)
* Grip strength: forelimb, hindlimb, hindlimb splay
* Motor activity: activity counts recorded by microcomputer in 6 successive 10-minute sessions
* Other: body temperature
Sacrifice and pathology:
GROSS PATHOLOGY: Yes (external examination, including identification of all clinically recorded lesions, and detailed internal examination)
ORGAN WEIGHTS: Yes (adrenals, brain, heart, kidneys, liver, lungs, ovaries or testes, pituitary, prostate, spleen, thymus, thyroid, uterus)
HISTOPATHOLOGY: Yes (following standard list of tissues + abnormalities): adrenal, aorta, bone marrow, sternum, brain, bronchus, nasal cavity, cecum, colon, duodenum, epididymis, esophagus, eye, heart, ileum, jejunum, kidney, larynx, liver, lung, mandibular lymph node, mesenteric lymph node, mammary gland (M&F), skeletal muscle , optic nerve, sciatic nerve, pancreas, parathyroid, pharynx, pituitary gland, prostate, salivary gland, seminal vesicle, skin, cervical spinal cord, spleen, stomach, testis, thymus, thyroid, tongue, trachea, urinary bladder, bronchial lymph node, mediastinal lymph node, pancreatic lymph node, ovary, uterus.
Other examinations:
Not applicable
Statistics:
- Group mean values (with standard deviations) analyzed for homogeneity of variance using Bartlett's test
- Homogeneous data analyzed using Analysis of Variance and differences from controls assessed using Dunnett's 't' test
- Heterogeneous data analyzed using Kruskal-Wallis test and differences from controls assessed using Dunn's test
- Frequency data, gross pathology and histopathology findings analyzed using Fisher's exact probability test
Clinical signs:
no effects observed
Description (incidence and severity):
No relevant (treatment-related) effects were observed.
Mortality:
no mortality observed
Description (incidence):
No relevant (treatment-related) effects were observed.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
- No relevant changes in females
- Statistically significantly lower mean body weight gains in high-dose males when compared to controls in weeks 2 and 8
- Overall body weight gain of high-dose males marginally inferior to that of controls, although not statistically significant
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
- No relevant changes in females
- Food consumption of high-dose males marginally lower than that of controls although without statistical significance
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
no effects observed
Description (incidence and severity):
No relevant (treatment-related) effects were observed.
Haematological findings:
effects observed, treatment-related
Description (incidence and severity):
- No relevant changes in red blood cell count, hemoglobin, hematocrit, erythrocyte indices, platelet count, mean platelet volume, total or differential white blood cell counts except neutrophil counts, prothrombin time, blood cell morphology
- Statistically significantly elevated segmented neutrophil counts (when expressed as percentages of white blood cells) in low-dose and mid-dose females and high-dose males and females at weeks 6 and/or 13 compared to controls
- When expressed in absolute terms, segmented neutrophil counts in low-dose females and mid-dose and high-dose males and females elevated at weeks 6 and 13 compared to controls
Clinical biochemistry findings:
no effects observed
Description (incidence and severity):
No relevant (treatment-related) effects were observed.
Urinalysis findings:
no effects observed
Description (incidence and severity):
No relevant (treatment-related) effects were observed.
Behaviour (functional findings):
no effects observed
Description (incidence and severity):
No relevant (treatment-related) effects were observed.
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
- No relevant changes in adrenals, brain, heart, kidneys, liver, ovaries or testes, pituitary, prostate, spleen (females), thymus, thyroid or uterus weights
- Statistically significant higher lung (absolute and relative) weights in mid-dose and high-dose groups compared to controls
- Change in lung weight seen in all treated groups, although not always statistically significant
- Statistically significantly higher spleen (relative) weights and higher spleen (absolute) weights in high-dose males compared to controls
Gross pathological findings:
effects observed, treatment-related
Description (incidence and severity):
- No relevant findings at external examination, including identification of all clinically recorded lesions, and at detailed internal examination, except for lungs and lymph nodes
- Lungs: discoloration or pale areas (30 rats each in mid-dose and high-dose groups), pale foci (4 rats in low-dose group), uncollapsed parenchyma (2 rats in mid-dose group and 30 in high-dose group)
- Lymph nodes: enlargement and/or pale discoloration of the bronchial lymph nodes (28 rats in low-dose group, 30 each in mid-dose and high-dose groups), mediastinal lymph nodes (1 rat in control group, 12 in low-dose group, 18 in mid-dose group and 20 in high-dose group), pancreatic lymph nodes (3 rats in control group, 1 each in mid-dose and high-dose groups)
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
- No relevant findings in adrenals, aorta, bone marrow, sternum, brain, cecum, colon, duodenum, epididymis, esophagus, eye, heart, ileum, jejunum, kidney, mesenteric lymph node, mammary gland, skeletal muscle , optic nerve, sciatic nerve, pancreas, parathyroid, pharynx, pituitary gland, prostate, salivary gland, seminal vesicle, skin, cervical spinal cord, stomach, testis, thymus, thyroid, tongue, urinary bladder, ovary, uterus
- Pigment accumulation and/or alveolar epithelial/lymphoid hyperplasia in the lungs (in low-dose, mid-dose and high-dose groups)
- Lymphoid hyperplasia of the bronchial or mediastinal (in low-dose, mid-dose and high-dose groups) and pancreatic (in mid-dose group) lymph nodes
- Metaplasia and/or pigment accumulation in larynx (in low-dose, mid-dose and high-dose groups)
- Pigment accumulation in bronchial or mediastinal lymph nodes, nasal cavity and bronchi (in low-dose, mid-dose and high-dose groups), in trachea and pancreatic lymph nodes (in mid-dose and high-dose groups), and in liver, mandibular lymph nodes and spleen (high-dose group only)
Histopathological findings: neoplastic:
no effects observed
Dose descriptor:
NOEC
Effect level:
0.507 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
male/female
Basis for effect level:
clinical signs
mortality
ophthalmological examination
clinical biochemistry
urinalysis
behaviour (functional findings)
Dose descriptor:
NOEC
Effect level:
0.507 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
female
Basis for effect level:
body weight and weight gain
food consumption and compound intake
Dose descriptor:
NOEC
Effect level:
0.051 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
male
Basis for effect level:
body weight and weight gain
food consumption and compound intake
Dose descriptor:
NOEC
Effect level:
0.005 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
male
Basis for effect level:
haematology
Dose descriptor:
LOAEC
Effect level:
0.005 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
female
Basis for effect level:
haematology
Dose descriptor:
NOAEC
Effect level:
0.005 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
male/female
Basis for effect level:
organ weights and organ / body weight ratios
Dose descriptor:
LOAEC
Effect level:
0.005 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
male/female
Basis for effect level:
gross pathology
histopathology: non-neoplastic
Dose descriptor:
LOAEC
Effect level:
0.051 mg/L air (analytical)
Based on:
test mat.
Remarks:
Gravimetric concentration
Sex:
male/female
Basis for effect level:
histopathology: non-neoplastic
Critical effects observed:
not specified

Tissue/Lesion

Incidence of microscopic findings

(/No. of animals examined)

 

 

 

 

 

 

 

 

Males - 0 mg/L

Females - 0 mg/L

Males - 0.005 mg/L

Females - 0.005 mg/L

Males - 0.0505 mg/L

Females - 0.0505 mg/L

Males - 0.5075 mg/L

Females - 0.5075 mg/L

Bronchi

pigment accumulation

0/15

0/15

1/15

0/15

5/15*

4/15*

15/15*

15/15*

Nasal cavity:

 

 

 

 

 

 

 

 

- Goblet cell hypertrophy and/or hyperplasia

0/15

0/15

0/15

1/15

0/15

0/15

1/15

2/15

- Pigment accumulation

0/15

0/15

12/15*

3/15

15/15*

11/15*

15/15*

15/15*

Larynx:

 

 

 

 

 

 

 

 

- Metaplasia

0/15

0/15

3/15

3/15

9/15*

6/15*

13/15*

9/15*

- Pigment accumulation

0/15

0/15

6/15*

0/15

9/15*

7/15*

12/15*

9/15*

Liver

pigment accumulation

0/15

0/15

0/9

0/1

0/7

0/5

6/15*

5/15*

Lungs:

 

 

 

 

 

 

 

 

- Pigment accumulation

0/15

0/15

15/15*

15/15*

15/15*

15/15*

15/15*

15/15*

- Alveolar epithelial hyperplasia (with severity)

0/15

0/15

1/15(+)

0/15

11/15* (+ to ++)

5/15* (+ to ++)

14/15* (+ to +++)

15/15* (+ to ++)

- Lymphoid hyperplasia

0/15

0/15

0/15

0/15

0/15

1/15

12/15*

7/15*

Mandibular lymph nodes:

pigment accumulation

0/15

0/15

0/3

0/5

0/5

0/3

6/15*

6/15*

Spleen:

pigment accumulation

0/15

0/15

0/1

0/0

0/0

0/0

6/15*

3/15

Trachea:

pigment accumulation

0/15

0/15

0/15

0/15

1/15

1/15

14/15*

14/15*

Bronchial lymph nodes:

 

 

 

 

 

 

 

 

- Pigment accumulation

0/15

0/15

13/13*

14/15*

15/15*

15/15*

15/15*

15/15*

- Lymphoid hyperplasia

0/15

0/15

11/13*

13/15*

15/15*

15/15*

15/15*

15/15*

Mediastinal lymph nodes:

 

 

 

 

 

 

 

 

- Pigment accumulation

0/0

0/1

2/2

10/10

8/10

9/9

9/9

9/10

- Lymphoid hyperplasia

0/0

0/1

2/2

10/10

9/10

9/9

9/9

9/10

Pancreatic lymph nodes:

 

 

 

 

 

 

 

 

- Pigment accumulation

-

0/2

-

0/0

-

1/1

-

1/1

- Lymphoid hyperplasia

-

0/2

-

0/0

-

1/1

-

0/1

* p < 0.05

+: slight

++: mild

+++: moderate

Conclusions:
An overall NOEC was not established in the study report based on changes in hematology (females only), macroscopic observations at necropsy and histopathology at the lowest concentration tested, i.e. 0.005 mg/L. However, considering that lymphoid hyperplasia in the bronchial lymph nodes may not represent a specific toxic effect, but rather a non-specific adaptive response to the overloading of pulmonary alveolar macrophages by inorganic poorly soluble particles, and considering that alveolar epithelial hyperplasia in the lungs represents a more sensitive indication of adverse effects in the rat following inhalatory exposure to very high particulate concentrations, the LOAEC can be set at 0.0505 mg/l (50.5 mg/m3) based on the incidence and severity of alveolar epithelial hyperplasia in the lungs.
Executive summary:

In an OECD TG 413 compliant study, the potential general toxicity of Cerium Oxide was tested following repeated nose-only inhalation of a dry powder aerosol of cerium dioxide (mass median aerodynamic diameter = 1.8-2.2 µm, geometric standard deviation = 1.8-1.9) to 7-week old Sprague-Dawley rats (15/ sex) for 6 hours a day, 5 days a week, for 13 weeks, at the gravimetric concentrations of 0 (air), 0.005, 0.0505 or 0.5075 mg/L (0, 5, 50.5 or 507.5 mg/m3, respectively). Observations and measurements included mortality, clinical signs, body weight, food consumption, Functional Observational Battery, motor activity, hematology, clinical biochemistry, urinalysis, ophthalmological examination, gross pathological examination, organ weights and histopathological examination of selected tissues.

 

No treatment-related deaths or clinical signs occurred during the study. There were no effects on ophthalmology, clinical chemistry, urinalysis at any dose level. No behavioural changes following either acute or subchronic exposure and no significant differences in motor activity were observed in treated groups in the Functional Observational Battery assessment.

 

Treatment-related changes included changes in hematology, lung and spleen weights, macroscopic observations at necropsy and histopathology of the respiratory tract and lymphoreticular system.

 

Statistically significant increases in absolute and differential segmented neutrophil counts were observed at weeks 6 and 13 in females at 0.005 mg/L and above and in males at 0.0505 mg/L and above. Statistically significant increases in the absolute and relative weight of the lungs were noted for both males and females exposed to 0.0505 mg/L and above. Male rats exposed to 0.5075 mg/L also had a statistically significantly increase in the relative spleen weight. At necropsy, discoloration or pale areas and uncollapsed parenchyma in the lungs were observed in males and females at 0.0505 mg/L and above, and pale foci in females at 0.005 mg/L. Enlargement or pale discoloration of the bronchial, mediastinal and pancreatic lymph nodes were also observed in all treated groups.

 

Microscopically, pigmented material accumulation in the lungs, bronchial, mandibular and mediastinal or pancreatic lymph nodes, trachea, bronchi, larynx, nasal cavity, liver and spleen, as well as alveolar epithelial hyperplasia in the lungs, metaplasia in larynx, and lymphoid hyperplasia in lymph nodes and lungs, correlating with the presence of pigment in these tissues, were seen in all treated groups with a clear dose-response relationship.

 

Based on the findings at 0.005 mg/L, no NOEC was established in this study. The concentration of 0.005 mg/L (5 mg/m3) was a LOAEC in the study, based on the increased incidence of lymphoid hyperplasia in the bronchial lymph nodes of rats of both genders.

 

However, considering that lymphoid hyperplasia in the bronchial lymph nodes may not represent a specific toxic effect, but rather a non-specific adaptive response to the overloading of pulmonary alveolar macrophages by inorganic poorly soluble particles, and considering that alveolar epithelial hyperplasia in the lungs represents a more sensitive indication of adverse effects in the rat following inhalatory exposure to very high particulate concentrations, the concentration of 0.0505 mg/l (50.5 mg/m3) can be considered as a LOAEC based on the incidence and severity of alveolar epithelial hyperplasia in the lungs.

 

Based on the classification criteria of Annex VI Directive 67/548/EEC or UN/EU GHS and considering the interspecies differences between rats and non-rodent mammals regarding location of the inhaled particles during chronic exposure, no significant effect of relevance to human health were observed in this study. No systemic toxic effects specific to cerium dioxide as such were observed. The observed effects were rather consistent with a species-specific phenomenon of "lung overload" inflammatory response in the rat following inhalation of poorly soluble particles of low toxicity and resulting "portal-of- entry" effects, with a limited relevance to the human occupational situation given the levels of exposure. Therefore no classification is warranted for this endpoint.

 

This study is classified as acceptable. It satisfies the OECD 413 guideline requirements on subchronic inhalation toxicity.

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion
Endpoint conclusion:
no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

All the data below relate to the micrometric (bulk) cerium dioxide.

 

Animal data:

The general toxicity of cerium dioxide was tested in rats using both oral (OCDE 422) and inhalation (OCDE 413) routes, in a subacute and subchronic toxicity study, respectively.

 

Following daily oral administration for ~37 days (males) to 40-45 days (females), no toxicologically meaningful sign of toxicity was observed up to the highest dose of 1000 mg/kg. The NOAEL was therefore set at the limit dose for repeat-dose toxicity, 1000 mg/kg bw/day.

 

Following nose-only inhalation for 90 days (6 hours/day, 5 days/week) at 0, 5, 50.5 or 505.7 mg/m3, significant changes in segmented neutrophil counts, lung and spleen weights, lung and lymph node gross appearance at necropsy and lung, respiratory tract and lymphoreticular system histopathology, were noted in groups exposed to cerium dioxide. No NOAEC was determined in the study report based on effects at the low concentration. This study identified a LOAEC of 5 mg/m3 in rats, based on the increased incidence of lymphoid hyperplasia in the bronchial lymph nodes of male and female rats. However, considering that lymphoid hyperplasia in the bronchial lymph nodes may not represent a specific toxic effect, but rather a non-specific adaptive response to the overloading of the pulmonary alveolar macrophages by inorganic poorly soluble particles in rats (Ref. Cohen MD et al. External Peer Review Meeting on the Toxicological Review for Cerium Oxide and Cerium Compounds. 2008), and considering that alveolar epithelial hyperplasia in the lungs represents a more sensitive indication of adverse effects, the concentration of 0.0505 mg/L (50.5 mg/m3) can be regarded as a LOAEC in rats based on the incidence and severity of alveolar epithelial hyperplasia in the lungs following exposure for 13 weeks.

 

In the case of an inorganic particulate material such as cerium dioxide, a distinction has to be made between chemical-specific and inert particle-induced toxicity. Lung overload-related inflammatory response is commonly observed in rats following inhalation exposure to poorly soluble particles. The concept of overload applies specifically to poorly soluble particles with low cytotoxicity. The hallmark of particle overload is impaired alveolar clearance which, in rats exposed to poorly soluble particles, is associated with altered macrophage function, pulmonary inflammation, centri-acinar interstitial and alveolar accumulation of particles, and inflammation-induced epithelial cell proliferation (Ref. ILSI Risk Science Institute. The relevance of the rat lung response to particle overload for human risk assessment: A workshop consensus report. Inhalation Toxicology, 12:1-17, 2000). In terms of risk assessment, lung overload conditions are not relevant to human health because of interspecies differences. The distribution of the retained particles within the lung compartments is different between species. It has been shown that during chronic inhalation exposure, particles are retained to a greater degree in interstitial locations in lungs of non-human primates and dogs than in lungs of rats, and that the interspecies differences in particle location might contribute to corresponding differences in tissue response (Ref. Snipes MB. Current information on lung overload in non-rodent mammals: contrast with rats. Inhalation Toxicology, 8(suppl):91-109, 1996). These differences combined with the fact that human macrophages have five times the volume of rat macrophages are considered to account for the tendency of rats to respond to poorly soluble particles with more chronic inflammation and epithelial responses compared to humans (Ref. Oberdörster G. Toxicokinetics and effects of fibrous and non- fibrous particles. Inhalation Toxicology, 14:29-56, 2002).

 

In the case of the present 13-week inhalation rat study using cerium dioxide, initially no NOAEC was determined in the study report because of the occurrence of lymphoid hyperplasia in the bronchial lymph nodes at all test concentrations. The lymphoid hyperplasia likely reflects an inflammatory response due to the cerium dioxide particles delivered by dendritic cells from the tracheobronchial region to the bronchial lymph nodes. However from a chemical-specific toxicity standpoint, lymphoid hyperplasia is not known to be on the pathogenetic pathway for adverse effects resulting from continued inhalatory exposure to poorly soluble particles, or to represent an adverse effect in itself. Studies in rats exposed under overloading conditions have shown that enlarged lymph nodes can occur without functional impairment of the antibody-forming function of the lymphocytes (Ref. Bice DE et al. Effects of inhaled diesel exhaust on immune responses after lung immunization. Fundam Appl Toxicol, 5:1075-86, 1985). The negative results obtained with cerium dioxide in the Popliteal Lymph Node Assay conducted on Brown-Norway rats, a rat strain well known for its high sensitivity to immunotoxicants, on popliteal lymph node weights and tritiated thymidine incorporation, as well as on blood Ig E concentrations, further illustrate the absence of immunotoxicity of cerium dioxide. Clinically, a comprehensive review of human lung pathology indicates that bronchial lymph node hyperplasia is not regarded as a diagnostic marker of specific lung diseases (Ref. Travis WD et al. Non-neoplastic Disorders of the Lower Respiratory Tract. American Registry of Pathology & Armed Forces Institute of Pathology,Washington DC. pp. 277-281, 2002). Rather, lymph node hyperplasia appears to be a secondary response to other conditions. Therefore, lymph node hyperplasia should be considered as an adaptive response and alveolar epithelial hyperplasia in the lungs appears more clearly as an indication of adverse effects, and should therefore be considered for the NOAEC/LOAEC determination.

 

In conclusion, the oral toxicity of cerium dioxide has been shown to be extremely low based on the absence of adverse effects in rats up to the limit-dose level of 1000 mg/kg bw. Following inhalatory exposure, the observed toxic effects can be described as "portal-of-entry" effects. As an insoluble particle, the absorption of cerium dioxide or its translocation from the lung to blood circulation is expected to be minimal. The effects observed in rats in respiratory tract and lymphoreticular system appear to be due to the physical deposition of cerium dioxide particles in the lungs and the subsequent inflammatory reaction to the particles, and are not due to a chemical reaction of cerium dioxide with lung tissues. No systemic toxic effects specific to cerium dioxide as such were observed in the rat following 13-week inhalatory exposure.

 

Human data:

Some rare occurrences of cerium dioxide pneumoconiosis are described in the literature. However, these cases appear ancient (old procedures of industrial hygiene were in force), no information on  the level of exposure to cerium dioxide are provided, the patients often did not use their protection equipment, and the imputability to cerium dioxide is doubtful due to the simultaneous exposure of the patients to other chemical agents in an occupational background. In one case report (Nappée et al., 1972), the pneumoconiosis did not result in any impairment of the respiratory function, but rather appeared as a pulmonary overload of cerium oxide which is opaque to X-rays. In another clinical case (Le Magrex et al., 1979; Sinico et al., 1982), the clinical evolution was favourable following withdrawal of the patient from exposure to dusts and initiation of a corticotherapy, resulting in the regression of the X- ray lesions and the improvement of the patient's general condition.

 

Repeated dose toxicity: inhalation - systemic effects (target organ) respiratory: lung

Justification for classification or non-classification

Based on the classification criteria of Annex VI Directive 67/548/EEC or UN/EU GHS and considering the interspecies differences between rats and non-rodent mammals regarding location of the inhaled particles during chronic exposure, no significant effect of relevance to human health were observed in this study. No systemic toxic effects specific to cerium dioxide as such were observed. The observed effects were rather consistent with a species-specific phenomenon of "lung overload" inflammatory response in the rat following inhalation of poorly soluble particles of low toxicity and resulting "portal-of- entry" effects, with a limited relevance to the human occupational situation given the levels of exposure. Therefore no classification is warranted for this endpoint.