Registration Dossier

Administrative data

Description of key information

Bioelution data for TiC support read-across between TiO2 and TiC. Details are given in the attached read-across report. Titanium dioxide did not show adverse effects in a chronic oral repeated dose toxicity study in rats, with a NOAEL of 3,500mg/kg bw/day. Titanium dioxide is not absorbed to any relevant extent through human skin, thus no toxic effects can be expected via the dermal route of exposure. Titanium dioxide showed fibrogenic effects in a chronic inhalation repeated dose toxicity study in rats with a NOAEC of 10 mg/m³. This is considered a rodent specific overload effect with limited significance in human risk assessment.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records
Reference
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.
Reason / purpose:
reference to same study
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
Species:
rat
Strain:
Fischer 344
Sex:
male/female
Details on test animals 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
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
Remarks:
Doses / Concentrations:
0 ppm
Basis:
nominal in diet
Remarks:
Doses / Concentrations:
25000 ppm
Basis:
nominal in diet
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
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.
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.
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.
Critical effects observed:
not specified

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.

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.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEL
3 500 mg/kg bw/day
Study duration:
chronic
Species:
rat
Quality of whole database:
The key study is compliant and of good quality (Klimisch score II).

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records
Reference
Endpoint:
repeated dose toxicity: inhalation
Remarks:
combined repeated dose and carcinogenicity
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
Reason / purpose:
reference to same study
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
Limit test:
no
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.
Route of administration:
inhalation: dust
Type of inhalation exposure:
whole body
Vehicle:
air
Remarks on MMAD:
MMAD / GSD: 1.5 - 1.7 µm; 84 % < 13 µm MMD
Details on inhalation 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

TEST ATMOSPHERE
- Brief description of analytical method used: Chamber concentrations were maintained by controlling the dust-feed rate into the generation apparatus and by diluting the dust stream as it entered the chamber. Chamber concentrations were determined gravimetrically.
- Samples taken from breathing zone: 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
Remarks:
Doses / Concentrations:
0 mg/m³
Basis:
nominal conc.
Remarks:
Doses / Concentrations:
10 mg/m³
Basis:
nominal conc.
Remarks:
Doses / Concentrations:
50 mg/m³
Basis:
nominal conc.
Remarks:
Doses / Concentrations:
250 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
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
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.
Dose descriptor:
NOAEC
Remarks:
for carcinogenicity in rats
Effect level:
50 mg/m³ air (nominal)
Based on:
test mat.
Sex:
male/female
Dose descriptor:
NOAEC
Remarks:
non-neoplastic changes
Effect level:
10 mg/m³ air (nominal)
Based on:
test mat.
Sex:
male/female
Critical effects observed:
not specified

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

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 hyperülasia 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.

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed
Dose descriptor:
NOAEC
10 mg/m³
Study duration:
chronic
Species:
rat
Quality of whole database:
A chronic study elucidating the long term effects of Titanium dioxide to rats after oral application was chosen (key study).

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion
Endpoint conclusion:
no study available

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

Potential titanium ion release by different routes of human exposure can be compared for different titanium substances by using in vitro bioelution testing. Bioelution has been assessed for TiC in four artificial body fluids. These data support read-across between TiO2 and TiC. Details are given in the attached read across report. A bioassay of titanium dioxide for possible carcinogenicity was conducted by the National Cancer Institute (1979). Titanium dioxide was administered via feed to Fischer 344 rats and B6C3F1 mice. It was concluded that under the conditions of this assay the test substance was not carcinogenic by the oral route for Fisher 344 rats or B6C3F1 mice.

In a publication of Lee et al. (1985) cystic keratinizing squamous lesions were reported to be produced in rats after chronic exposures to high concentrations of pigment-grade TiO2 particles. Furthermore chronic inhalation exposure of rats to very high doses of particles can result in inflammation, fibrosis, and some lung tumors. Exposures to TiO2 resulted in impairment of alveolar macrophage clearance functions, sustained persistent pulmonary inflammation, and enhanced cell proliferative responses. The keratin cysts are a species specific lesion that is unique to the rat under conditions of particle overload.

A more comprehensive histopathological evaluation determined that the keratinizing lesions were not neoplastic (IARC Monograph 93).

Bermudez et al. (2002 and 2004) showed the species specific response to chronic exposure with TiO2. Rats, hamster, and mice were exposed to 0, 10, 50 and 250 mg/m³ TiO2 for 13 weeks. The lung burdens of the species were equivalent, but rats had more severe and persistent inflammatory response than mice and hamster. The major species specific reactions to TiO2 exposure were described to be a faster pulmonary clearance of dust in hamsters than in rats and mice, particle overload was observed in mice and rats, pulmonary cellular and tissue responses to particle overload were different in the species. Rats developed greater and sustained lung inflammatory response and a significantly more intensive epithelial and fibroproliferative response. These results were also shown by a companion study with ultra-fine titanium dioxide.

Warheit et al. (1997) showed that the lungs of particle-overloaded rats are characterized by impaired pulmonary clearance, sustained pulmonary inflammation, cellular hypertrophy, and hyperplasia. These effects are likely to result in the development of overload-related pulmonary tumors.

In summary, the results of the studies show that pulmonary tumors in TiO2-exposed rats are developed only after chronic, 2-year inhaled doses which produced massive particle overload in the lung (250 mg/m³) associated with marked, sustained inflammation. Despite particle overload and persistent pulmonary inflammation was observed after a two year exposure to 50 mg/m³ TiO2 no lung tumors were observed.

The tumorigenic response observed in the rat lung was shown to be species specific and restricted to doses in which there is an overload to the particle clearance mechanism. The species-specific response to particulate exposure is not relevant for extrapolating results to humans for purposes of determining human cancer risk.


Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:
A chronic study elucidating the long term effects of Titanium dioxide to mice and rats after oral application was chosen (key study).

Justification for classification or non-classification

The publication by the National Cancer Institute (1979) is considered as the key study for repeated dose toxicity via oral application and will be used for classification. Based on the lack of adverse effects, the no observed adverse effect level (NOAEL) via oral application for titanium dioxide was established to be 3500 mg/kg bw/day.

The classification criteria according to regulation (EC) 1272/2008 as specific target organ toxicant (STOT) repeated exposure, oral are not met since no reversible or irreversible adverse health effects were observed immediately or delayed after exposure and the no observed adverse effect level (NOAEL) via oral application is above the guidance value for a Category 2 classification (100 mg/kg bw/day). Therefore, no classification for specific target organ toxicant (STOT) repeated exposure via the oral route is required.

The species specific sensitivity of rats to the exposure with titanium dioxide and lung damage under conditions of particle overload was demonstrated.

In the rat particle overload finally results in fibroproliferative disease, septal fibrosis, hyperplasia and eventually lung tumours. However, similar pathological changes are not observed in other common laboratory rodents, non-human primates or in exposed humans. According to regulation (EC) 1272/2008, a classification for specific target organ toxicity repeated exposure shall be taken into account only when reliable evidence associating repeated exposure to the substance with a consistent and identifiable toxic effect demonstrates support for the classification. These adverse health effects include consistent and identifiable toxic effects in humans, or in experimental animals, toxicologically significant changes which have affected the function or morphology of a tissue/organ, or have produced serious changes to the biochemistry or haematology of the organism and these changes are relevant for human health.

No systemic toxicity was shown from the results of chronic inhalation exposure to high concentrations of pigment grade titanium dioxide. Particle overload was observed with the rat being the most sensitive species.