Titanium carbide

Carcinogenicity

Administrative data

Endpoint:

carcinogenicity: inhalation

Type of information:

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

Adequacy of study:

weight of evidence

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:

reference to same study

Data source

Reference

Reference Type:

publication

Title:

Pulmonary Responses of Rats Exposed to Titanium Dioxide (TiO2) by Inhalation for Two Years.

Author:

Lee, K.P.; et al.

Year:

1985

Bibliographic source:

Toxicol Appl Pharmacol 79:179-192

Materials and methods

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Rats were exposed to TiO2 by inhalation exposure to concentrations of 0, 10, 50, and 250 mg/m³ for 6 h/day, 5 days/week for 2 years.

GLP compliance:

no

Test material

Reference

Name:

Unnamed

Type:

Constituent

Test material form:

not specified

Details on test material:

- Name of test material (as cited in study report): Titanium dioxide
- Substance type: inorganic
- Physical state: solid
- Analytical purity: not reported

Test animals

Species:

rat

Strain:

Crj: CD(SD)

Sex:

male/female

Details on test animals and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Wilmington, Mass.)
- Age at study initiation: no data
- Weight at study initiation: no data
- Housing: no data
- Diet: ad libitum, Purina Rodent Chow
- Water: ad libitum
- Acclimation period: no data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23 +/- 2
- Humidity (%): 50 +/- 10
- Photoperiod: 12 hours dark/light cycle
No further details are given.

Administration / exposure

Route of administration:

inhalation: dust

Type of inhalation exposure (if applicable):

whole body

Vehicle:

air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Plexiglas sample-feed tube attached to perpendicularly to the vertical axis of the elutriator.
- Method of holding animals in test chamber: tube
- Source and rate of air: no data
- Method of conditioning air: Elutriator
- System of generating particulates/aerosols: Atmospheres of TiO2 were generated by metering the dust into an apparatus containing a vertical elutriator (an inverted Plexiglas U-shaped tube) connected in series to a settling chamber. An Accu-Rate, variable-speed screw-feeder was used to meter TiO2 into a plexiglas sample-feed tube attached perpendiculary to the vertical axis of the elutriator. Dust was dispersed by an air-jet directed along the sample feed tube axis and passing into the elutriator. Initial settling of the heavier, nonrespirable dust fractions took place in the elutriator; the lighter fraction passed into the final settling chamber (a 50 l battery jar) from which the respirable fraction was diverted into the exposure chamber.
- Temperature, humidity, pressure in air chamber: no data
- Air flow rate: no data
- Air change rate: no data
- Method of particle size determination: no data
- Treatment of exhaust air: no data

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Chamber concentrations were determined gravimetrically.

Duration of treatment / exposure:

24 month

Frequency of treatment:

6 hours/day, 5 days/week

Post exposure period:

none

Doses / concentrations

Doses / concentrations 1

Remarks:

Doses / Concentrations:
0 mg/m³
Basis:
nominal conc.

Doses / concentrations 2

Remarks:

Doses / Concentrations:
10 mg/m³
Basis:
nominal conc.

Doses / concentrations 3

Remarks:

Doses / Concentrations:
50 mg/m³
Basis:
nominal conc.

No. of animals per sex per dose:

A total of 400 male and female rats was divided into four groups of 100 males and 100 females each.

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: results from previous inhalation studies
- Rationale for animal assignment (if not random): no data
- Rationale for selecting satellite groups: no data
- Post-exposure recovery period in satellite groups: no data
- Section schedule rationale (if not random): no data

Positive control:

no data

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: no data

DETAILED CLINICAL OBSERVATIONS: Yes

BODY WEIGHT: Yes
- Time schedule for examinations: no data

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No data

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: No

HAEMATOLOGY: No

CLINICAL CHEMISTRY: No

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Five males and five females from each group were killed at 3 and 6 month of exposure, and subsequently, 10 males and 10 females were killed after one year of exposure. At the end of the 2 year exposure all rats were killed. All rats were subsjected to gross and microscopic evaluation.

HISTOPATHOLOGY: Lung tissue was fixed with Bouin`s solution by intratracheal instillation under low pressure for light microscopy. The trachea, thyroid, adrenal glands, testes, and kidneys were fixed in Bouin`s solution. All other tissues were fixed in 10% formalin solution. Paraffin sections were stained by hematoxylin and eosin, modified trichrome, silver impregnation, and periodic acid-Schiff (PAS) methods. For TEM the excised lung samples were fixed in 3 % glutaraldehyde for approx. 1 h. Then they were rinsed in Millonig`s phosphate buffer, postfixed for 2 h at 4°C in 1 % osmium tetraoxide, dehydrated in alcohol, and embedded in Epon. 1 µm sections were stained with toluidine blue and used to locate areas for EM. For SEM lung samples were fixed overnight in 3 % glutaraldehydem rinsed in Millonig`s phosphate buffer and then postfixed in 1 % osmic acid for 2 h. The tissue samples were mounted on aluminium stubs, placed on a rotary device in a vacuum evaporator, and coated evenly with approx. 200 Â of gold-palladium.

Other examinations:

no data

Statistics:

no specified

Results and discussion

Results of examinations

Clinical signs:

effects observed, treatment-related

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

effects observed, treatment-related

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 specified

Haematological findings:

not specified

Clinical biochemistry findings:

not specified

Urinalysis findings:

not specified

Behaviour (functional findings):

not specified

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

effects observed, treatment-related

Details on results:

There were no abnormal clinical signs, body weight changes, or excess mortality in any exposed group when compared to control groups.

CLINICAL SIGNS AND MORTALITY : In the lungs of rats exposed to 10 mg/m³ white foci (< 1mm) were scattered sparsely throughout the pleural surface while a more dense accumulation of white foci was seen in the periphery of the lobes. At 50 mg/m³ these foci increased in number and size (< 2 mm). At 250 mg/m³ the lungs were voluminous and showed a white "paint brushed" appearance, contained rough pleural surfaces, and failed to collapse.

- significant increae of rhinitis, tracheitis, and pneumonia in all exposed rats. The severity of the lesions was dose-dependent.

BODY WEIGHT AND WEIGHT GAIN (See Table 1): Mean body weights of all TiO2-exposed groups were generally lower that those of the controls. Although there was no dose-related trend for these body weigh effects, the mean weights for male and female rats exposed to 250 mg/m^3 was consistently lower than those for rats exposed to 10 or 50 mg/m^3. The differences in the mean body weight gain among all treatment groups parallelled the mean body weight effects.

ORGAN WEIGHTS: The lung weights at 10 mg/m³ were comparable to those of the control group, but at 50 mg/m³, an increase in lung weights was statistically significant. The lung weights at 250 mg/m³ were more than twice the weight of control lungs. The tracheobronchial lymph nodes were markedly enlarged in a dose-related fashion and showed a white "chalky mass" appearance.

GROSS PATHOLOGY: During the gross pathological examinations, TiO2 deposits were observed on skin and the mucosa of the nasal cavity, trachea, bronchus and gastrointestinal tract of rats exposed to this compound. The pleural surfaces of the lungs contained scattered white foci which were present in greater numbers and larger sizes in rats exposed to the higher TiO2 concentrations. Subpleural cholesterol granulomas appeared on the lungs of rats in the 50 and 250 mg/m^3 treatment groups as slightly elevated gray nodules. The lungs of rats in the 250 mg/m^3 treatment groups were white in appearance, voluminous, of rubbery consistency and failed to collapse upon opening the chest cavity at necropsy.
The tracheabronchial lymph nodes were markedly swollen and appeared as chalky masses in all exposure groups. Most of these gross observations were apparent at six months with the severity and frequency of occurrence increasing over time.

HISTOPATHOLOGY: NON-NEOPLASTIC (see table 2): All TiO2 exposed groups showed slight increases in the incidences of pneumonia, tracheitis, and rhinitis with squamous metaplasia of the anterior nasal cavity.
The lung reaction was characterised by dust-laden macrophage (dust cell) infiltration in the alveolar ducts and adjoining alveoli with hyperplasia of Type II pneumocytes. Rats at 50 and 250 mg/m³ exposure revealed a dose-dependent dust cell accumulation, a foamy macrophage response, type II pneumocyte hyperplasia, alveolar proteinosis, alveolar bronchiolarisation, cholesterol granulomas, focal pleurisy, and dust deposition in the tracheobronchial lymph nodes. Minute collagenised fibrosis occurred in the in the alveolar walls enclosing large dust cell aggregates. The pulmonary lesions with massive dust accumulation appeared to be the result of an overwhelmed lung clearance mechanism at 250 mg/m³ TiO2 exposure.

HISTOPATHOLOGY: NEOPLASTIC: Bronchioloalveolar adenomas and cystic keratinising squamous cell carcinoma occurred at 250 mg/m³ TiO2 exposure (the tumours produced were ultimately characterised as primarily benign pulmonary keratin cysts (Warheit and Frame,2006)), while no compound-related lung tumours were found in rats exposed either to 10 or 50 mg/m³.

Relevance of carcinogenic effects / potential:

According to the results of this study TiO2 is not considered to be a rodent carcinogen below particle overload conditions.

Effect levels

1

Dose descriptor:

NOAEC

Effect level:

50 mg/m³ air (nominal)

Based on:

test mat.

Sex:

male/female

Remarks on result:

other: Effect type: carcinogenicity (migrated information)

2

Dose descriptor:

NOAEC

Effect level:

10 mg/m³ air (nominal)

Based on:

test mat.

Sex:

male/female

Remarks on result:

other:

Remarks:

Effect type: other: non-neoplastic changes (migrated information)

Any other information on results incl. tables

Table1: Lung and final body weights of rats exposed to TiO₂at 0, 10, 50, or 250 mg/m³.

Exposure concentration	Final body weights		Lung weight		Lung/body weight ratio
	Male	Female	Male	Female	Male	Female
0 mg/m³ (Control)	780.0	557.1	3.25	2.35	0.44 (0.17)^a	0.43 (0.08)
10 mg/m³	778.0	597.6	3.56	2.76	0.46 (0.18)	0.47 (0.01)
50 mg/m³	769.3	566.9	4.47*	3.10*	0.59 (0.09)*	0.74 (0.18)*
250 mg/m³	743.3	508.6	7.84*	7.21*	1.07 (0.16)*	1.46 (0.39)*

^aStandard deviation

*Significantly different (p < 0.05) from control group by Dunnett`s test.

Table2: Incidence of main nonneoplastic lesions in the nasal cavity and trachea

	Control		10 mg/m³		50 mg/m³		250 mg/m³
	I (♂)	II (♀)	III (♂)	IV (♀)	V (♂)	VI (♀)	VII (♂)	VIII (♀)
Nasal cavity	(79)	(76)	(71)	(74)	(73)	(74)	(76)	(73)
Rhinitis, anterior	25	18	57	36	48	34	70	63
Rhinitis, posterior	13	3	13	10	3	1	14	18
Sq. metaplasia, anterior	8	7	26	14	20	21	44	40
Sq. metaplasia, posterior	-	1	-	-	-	1	1	2
Trachea	(79)	(77)	(68)	(74)	(74)	(69)	(77)	(65)
Tracheitis	2	1	52	34	53	37	61	28

( ) the number of rats examined is in parentheses

Table3: Incidence of main nonneoplastic lesions in the nasal cavity and trachea

	Control		10 mg/m³		50 mg/m³		250 mg/m³
	I (♂)	II (♀)	III (♂)	IV (♀)	V (♂)	VI (♀)	VII (♂)	VIII (♀)
Lung	(79)	(77)	(71)	(75)	(75)	(74)	(77)	(74)
Aggregates, foamy alveolar macrophage	14	8	19	15	53	70	76	74
Alveolar cell hyperplasia, TiO2deposition	-	--	67	72	75	74	77	74
Alveolar proteinosis	-	-	-	-	38	45	75	71
Bronchiolarization, alveoli	1	1	-	3	24	57	63	73
Broncho/bronchiolar pneumonia	1	1	7	11	8	10	7	5
Cholesterol granuloma	7	2	9	6	56	53	75	71
Collagenized fibrosis	11	3	7	4	49	41	76	73
Pleurisy	4	2	7	7	28	26	55	66
Anaplastic carcinoma, large cell	-	-	1	-	-	-	-	-
Bronchioalveolar adenoma	2	-	1	-	1	-	12	13
Squamous cell carcinoma	-	-	-	1	-	-	1	13

( ) In parentheses is the number of rats examined

Applicant's summary and conclusion

Conclusions:

A NOEC of Titanium dioxide of 50 mg/m³ for carcinogenicity, and a NOEC of 10 mg/m³ for non-neoplastic changes was established.

Executive summary:

In a combined repeated dose and carcinogenicity study Titanium dioxide was administered to 400 male and female Crj: CD(SD) rats by inhalation at nominal concentrations of 0, 10, 50, and 250 mg/m³ 6 hours a day, 5 days a week for 24 month. 

There were no abnormal clinical signs, body weight changes, or excess mortality in any exposed group. Exposed groups showed slight increases in the incidence of pneumonia, tracheitis, and rhinitis with squamous metaplasia in the anterior nasal cavity. The lung reaction was characterized by dust-laden macrophage (dust cell) infiltration in the alveolar ducts and adjoining alveoli with hyperplasia of type II pneumocytes. Exposure to 50 and 250 mg/m³ resulted in dose dependent dust cell accumulation, a foamy macrophage response, type II pneumocyte hyperplasia, alveolar proteinosis, alveolar brochiolarization, cholesterol granulomas, focal pleurisy, and dust deposition in the tracheobronchial lymph nodes. The pulmonary lesions with massive dust accumulation appeared to be the result of an overwhelmed lung clearance mechanism at 250 mg/m³ exposure., Bronchioloalveolar adenomas and cystic keratinizing squamous cell carcinomas occurred at 250 mg/m³ exposure.

Based on the findings at the low dose (alveolar cell hyperplasia, broncho/bronchiolar pneumonia) the concentration of 10 mg/m³ is considered as NOEC for non-neoplastic changes in this study.
Bronchioloalveolar adenomas and cystic keratinizing squamous cell carcinoma occurred at 250 mg/m³ TiO2 exposure (the tumours produced were ultimately characterized as primarily benign pulmonary keratin cysts (Warheit and Frame,2006)), while no compound-related lung tumors were found in rats exposed either to 10 or 50 mg/m³. Thus, the concentration of 50 mg/m³ represents the NOEC for carcinogenicity in rats.