Titanium carbide

Repeated dose toxicity: oral

Administrative data

Endpoint:

chronic toxicity: oral

Type of information:

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

Adequacy of study:

key study

Study period:

no data

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Meets generally accepted scientific standards, well documented and acceptable for assessment.

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1979

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

A bioassay of titanium dioxide for possible carcinogenicity was conducted by administering the test chemical in feed to Fischer 344 rats and B6C3F1 mice.

GLP compliance:

no

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Titanium dioxide

EC Number:

236-675-5

EC Name:

Titanium dioxide

Cas Number:

13463-67-7

IUPAC Name:

dioxotitanium

Test material form:

solid: particulate/powder

Remarks:

migrated information: powder

Details on test material:

- Name of test material (as cited in study report): Titanium dioxide
- Substance type: inorganic
- Physical state: solid; white pigment possessing great covering or opacifying power
- Analytical purity: > 98 %
- Impurities (identity and concentrations): Lot No. 402110C46 also contained 0.15% aluminum by atomic absorption. Other impurities in the 0.1-1.0% range (identified by spark source mass spectrometry) were niobium and chlorine (Lot Nos. 402129A29 and 402129B20), phosphorus (all three lots), silicon (Lot Nos. 402110C46 and 402129B20), calcium (Lot No. 402110C46), and potassium (Lot No. 402129B20).
- Lot/batch No.: Lot Nos. 402110C46, 402129A29, 402129B20; Three lots of titanium dioxide anatase, designated Unitane® 0-220, were obtained from American Cyanamid Company, Wayne, New Jersey.
- Other: Moisture content < 0.4 %

Test animals

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
On arrival at the laboratory, the rats were quarantined for 30 days and the mice for 15 days, determined to be free from observable disease or parasites, and assigned to the dosed or control groups based on initial individual body weight, so that the of mean animal body weights per group were approximately equal.
- Source: Frederick Cancer Research Center, Maryland
- Age at study initiation: 64 days
- Weight at study initiation: not reported
- Fasting period before study: not reported
- Housing: in polycarbonate cages covered with stainless steel cage lids and non-woven fiber filter bonnets. Initially 5 rats were housed per cage; at week 48 the males were divided into groups of 2 or 3 per cage.
- Diet: ad libitum
- Water: ad libitum

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24
- Humidity (%): 45-55
- Air changes (per hr): 12
- Photoperiod: 12 hours dark/light cycle

Administration / exposure

Route of administration:

oral: feed

Vehicle:

corn oil

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:

DIET PREPARATION
- Rate of preparation of diet (frequency): Diets were prepared once per week and stored at room temperature until used.
- Mixing appropriate amounts with (Type of food): TiO2 was incorporated into the basal diet of Wayne® Lab Blox animal meal (Allied Mills, Inc., Chicago, 111.) by thorough mixing in a Patterson-Kelly twin-shell blender equipped with an intensifier bar.
- Storage temperature of food: RT

VEHICLE: corn oil
- Justification for use and choice of vehicle (if other than water): not reported
- Concentration in vehicle: Corn oil (Duke's, C. F. Sauer Co., Richmond, Va.) was added to the dosed diets and to the diets for the matched controls to give a final concentration of 2%.
- Amount of vehicle (if gavage):
- Lot/batch no. (if required): no data
- Purity: no data

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

As a quality control measure, selected samples from freshly prepared mixtures were stored at 4°C and aliquots from these samples, containing approximately 50 micrograms of titanium dioxide were later analyzed for titanium dioxide by the method described by the Association of Official Analytical Chemists (1975). At each dietary concentration, the mean value obtained by the analytical method was within 4% of the theoretical value, although the coefficient of variation was nearly 30%. This variation appears to be due to the difficulty in obtaining a homogeneous mix of a fine powder in feed.

Duration of treatment / exposure:

103 weeks

Frequency of treatment:

7 days/week

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0 ppm
Basis:
nominal in diet

Doses / concentrations 2

Remarks:

Doses / Concentrations:
25000 ppm
Basis:
nominal in diet

Doses / concentrations 3

Remarks:

Doses / Concentrations:
50000 ppm
Basis:
nominal in diet

No. of animals per sex per dose:

50 males and 50 females per dose

Control animals:

yes, plain diet

Details on study design:

- Dose selection rationale: Subchronic feeding studies were conducted to estimate the maximum tolerated doses of titanium dioxide, on the basis of which two
concentrations were selected for administration in the chronic studies. On the basis of results from a 14-day (repeated dose) oral range-finding study, doses of 6,250, 12,500, 25,000, 50,000, or 100,000 ppm were administered in the diet in the Subchronic studies. Ten males and 10 females of each species were administered the test chemical at each dose, and 10 males and 10 females received basal diets. Dosed animals received the' test compound for 13 consecutive weeks. There were no deaths, and dosed animals had mean body weight gains that were comparable to those of the controls. No gross or microscopic pathology was found that could be related to the administration of the test chemical. On the basis of these results, the high dose in the chronic studies was set at 50,000 ppm, the maximum amount allowed for use in chronic bioassays in the Carcinogenesis Testing Program, and the low dose was set at 25,000 ppm.

Positive control:

no

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed twice daily for signs of toxicity. Clinical signs and the presence of palpable masses were recorded every week.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: weekly

BODY WEIGHT: Yes
- Time schedule for examinations: every 2 weeks for the first 12 weeks and every month thereafter.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption was recorded every 2 weeks for the first 12 weeks and every month thereafter.

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 AND COMPOUND INTAKE (if drinking water study): No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: No

CLINICAL CHEMISTRY: Yes / No / No data
- Time schedule for collection of blood:
- Animals fasted: Yes / No / No data
- How many animals:
- Parameters checked in table [No.?] were examined.

URINALYSIS: Yes / No / No data
- Time schedule for collection of urine:
- Metabolism cages used for collection of urine: Yes / No / No data
- Animals fasted: Yes / No / No data
- Parameters checked in table [No.?] were examined.

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

The pathologic evaluation consisted of gross and microscopic examination of major tissues, major organs, and all gross lesions from killed animals and from animals found dead. The tissues were preserved in 10% buffered formalin, embedded in paraffin, sectioned, and stained with hematoxylin and eosin. The following tissues were examined microscopically: brain (frontal cortex and basal ganglia, parietal cortex and thalamus, and cerebellum and pons), pituitary, spinal cord (if neurologic signs were present), eyes (if grossly abnormal), esophagus, trachea, salivary glands, mandibular lymph node, thyroid, parathyroid, heart, thymus, lungs and mainstem bronchi, liver, gallbladder (mice), pancreas, spleen, kidney, adrenal, stomach, small intestine, colon, urinary bladder, prostate or uterus, testes or ovaries, sternebrae, femur, or vertebrae including marrow, mammary gland, tissue masses, and any gross lesion.

Other examinations:

not reported

Statistics:

Statistical analyses for a possible dose-related effect on survival used the method of Cox (1972) for testing two groups for equality and Tarone's (1975)
extensions of Cox's methods for testing for a dose-related trend. One-tailed P values have been reported for all tests except the departure from linearity test, which is only reported when its two-tailed P value is less than 0.05.
To determine whether animals receiving the test chemical developed a significantly higher proportion of tumors than did the control
animals the one-tailed Fisher exact test (Cox, 1970) was used to compare the tumor incidence of a control group with that of a group of dosed animals at each
dose level. When results for a number of dosed groups (k) are compared simultaneously with those for a control group, a correction to ensure an overall significance level of 0.05 may be made. The Bonferroni inequality (Miller, 1966) requires that the P value for any comparison be less than or equal to 0.05/k. In
cases where this correction was used, it is discussed in the narrative section. It is not, however, presented in the tables, where the Fisher exact P values are shown.
The Cochran-Armitage test for linear trend in proportions, with continuity correction (Armitage, 1971), was also used when appropriate.

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

Water consumption and compound intake (if drinking water study):

not specified

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

not specified

Gross pathological findings:

no effects observed

Histopathological findings: non-neoplastic:

no effects observed

Histopathological findings: neoplastic:

no effects observed

Details on results:

CLINICAL SIGNS
The clinical signs observed in the dosed groups were generally comparable to those of the control group and included alopecia, sores, and lacrimating, protruding, and/or pale eyes. From weeks 88 through 104, hunched appearance and thinness were noted more frequently in the dosed males and females than in
their respective controls. Urine stains were noted on the dosed rats of each sex. Animals in all of the dosed groups had white feces.

MORTALITY
In the male rats, 36/50 (72%) of the high-dose group, 37/50 (74%) of the low-dose group and 31/50 (62%) of the matched controls were alive at week 104. In the females, 34/50 (68%) of the high-dose group, 36/50 (72%) of the low-dose group and 36/50 (72%) of the matched controls were alive at week 104. Sufficient numbers of rats of each sex were at risk for the development of late-appearing tumors.

BODY WEIGHT AND WEIGHT GAIN
Administration of Titanium dioxide had no effect on the mean body weights of either the male or the female rats.

HISTOPATHOLOGY: NEOPLASTIC (if applicable)
The tumor types have been encountered previously as a spontaneous lesion, and with only a few exceptions, occurred with no appreciable difference in frequency between control and dosed groups. In the male rats, pheochromocytomas of the adrenal medulla (matched control: 7/49 (14 %); low dose: 9/49 (18 %); high dose: 14/50 (28 %)) and fibromas of the subcutaneous tissue (matched control: 1/49 (2 %); low dose: 5/50 (10 %); high dose 5/50 (10 %) were observed with slightly greater frequency in dosed groups; the number of neoplasms was compatible with incidences of these tumours in historical-control rats of this age and strain. In the female rats, endometrial stromal polyps were observed more frequently in dosed groups (matched control: 6/50 (12 %); low dose: 15/50 (30 %); high dose 10/49 (20 %)) than in control groups, but the incidence of lesions is comparable with that in historical controls. The incidence of these tumours is not significant when compared with that in the control. Thus, these lesions are not considered to be related to administration of Titanium dioxide.

Effect levels

Dose descriptor:

NOEL

Effect level:

> 50 000 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: With the exception of white faeces, there was no other clinical sign that was judged to be related to titanium dioxide exposure.

Target system / organ toxicity

Critical effects observed:

not specified

Any other information on results incl. tables

In the female rats, C-cell adenomas or carcinomas of the thyroid occurred at incidences that were dose related (P = 0.013), but were

not high enough (P = 0.043 for direct comparison of the high-dose group with the control group) to meet the level of P = 0.025 required

by the Bonferroni criterion (controls 1/48, low- dose 0/47, high-dose 6/44). Thus, these tumors of the thyroid were not considered to be related to the administration of the test chemical.

Inflammatory, degenerative, and hyperplastic lesions that occurred were similar in number and kind to those naturally occurring lesions found in aged Fischer 344 rats. Based on the histopathologic examination, titanium dioxide was neither toxic nor carcinogenic to Fischer 344 rats under the conditions of this bioassay.

Applicant's summary and conclusion

Conclusions:

Based on the histopathological examination, TiO2 was neither toxic nor carcinogenic to F344 rats under the conditions of this bioassay.

Executive summary:

In a chronic toxicity study Titanium dioxide (> 98%) was administered to 50 F344 rats per sex and dose in the diet at dose levels of 0, 25000, and 50000 ppm for 103 weeks.

Administration of titanium dioxide had no appreciable effect on the mean body weights of rats of either sex. With the exception of white feces, there was no other clinical sign that was judged to be related to the administration of titanium dioxide. Survival of the rats at the end of the bioassay was not affected by the test chemical. Sufficient numbers of dosed and control rats of each sex were at risk for development of late-appearing tumors.

In the female rats, C-cell adenomas or carcinomas of the thyroid occurred at incidences that were dose related (P = 0.013), but were not high enough (P = 0.043 for direct comparison of the high-dose group with the control group) to meet the level of P = 0.025 required by the Bonferroni criterion (controls 1/48, low-dose 0/47, high-dose 6/44). Thus, these tumors of the thyroid were not considered to be related to the administration of the test chemical.

It is concluded that under the conditions of this bioassay, titanium dioxide was not carcinogenic by the oral route for Fischer 344 rats. A NOEL of 50000 ppm was established.

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