Reaction mass of disodium hexatitanium tridecaoxide and disodium trititanium heptaoxide

Genetic toxicity: in vivo

Administrative data

Endpoint:

in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Justification for type of information:

Sodium titanates are effectively the sodium salts of the unstable titanic acid (titanium hydroxide). Titanium hydroxide is hard to isolate without rapid hydrolysis to titanium dioxide and sodium chloride. It is therefore proposed to base environmental and health assessment on these two hydrolysis products. There has been extensive research on similar substances in the ‘titanate’ grouping and these all exhibit similar behaviour in that under acid biological conditions (eg if ingested) or if dispersed in water, there is dissociation of the ions and subsequent hydrolysis / oxidation. Read-across justification for the use of TiO2 data is available in section 13.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

2015

Report date:

2015

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

Version / remarks:

Mammalian Erythrocyte Micronucleus Test (1997).

Principles of method if other than guideline:

Six pigment-grade (pg) or ultrafi ne (uf)/nanoscale (anatase and/or rutile) titanium dioxide (TiO 2 ) particulates were evaluated for in vivo genotoxicity (OECD 474 Guidelines) in male and female rats by two different laboratories. All test materials were robustly characterized. The BET surface areas of the pg and uf samples ranged from 7 to 17 m 2 /g and 50 to 82 m 2 /g respectively. The materials were assessed for induction of micronuclei and toxicity in bone marrow by analyzing peripheral blood reticulocytes (RETs) byfl ow cytometry. Single oral gavage doses of 500, 1000 or 2000 mg/kg body weight (bw) of each material were implemented with concurrent negative (water) and positive controls (cyclophosphamide).

GLP compliance:

yes

Type of assay:

mammalian erythrocyte micronucleus test

Test material

Test material information

Constituent 1

Reference substance name:

Titanium dioxide

EC Number:

236-675-5

EC Name:

Titanium dioxide

Cas Number:

51745-87-0

Molecular formula:

O2Ti

IUPAC Name:

Titanium dioxide

Test material form:

solid: particulate/powder

Specific details on test material used for the study:

3 pigment-grade, and 3 ultrafi ne titanium dioxide (TiO 2 ) forms were used in this study. The series of samples analyzed spanned the range from test particles containing both anatase and rutile crystallites to both ultrafi ne and pigmentary materials composed of primarily rutile or anatase crystallites.

Test animals

Species:

rat

Strain:

other: Crl:CD(SD) rats and Wistar Crl:WI (Han) rats

Sex:

male/female

Details on test animals or test system and environmental conditions:

Crl:CD(SD) rats were obtained from Charles River Breeding Laboratories, Raleigh, North Carolina, USA. Wistar Crl:WI (Han) rats were obtained from Charles River, Sulzfeld, Germany. Animals were housed and maintained in facilities accredited by the Association for Assessment and Accreditation of Laboratory Animal Care (AAALAC) International in accordance with the principles described in the Guide to Care and Use of Laboratory Animals . Tap water and pelleted chow (Certifi ed diet from PMI ® Nutrition International, LLC, Harlan or Purina) or Atromin 1324 were available ad libitum throughout the study.

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

The test materials, vehicle, and the positive control were administered as single doses by oral gavage, based on the potential and relevant route for human exposure to TiO 2 in food or dietary supplements. This exposure strategy was considered suitable and most appropriate for the purpose of these studies, mimicking the likely human exposure route for any food or dietary supplement application incorporating TiO2 particles. Sterile water was used as the vehicle in all cases

Details on exposure:

Based on range-fi nding results, doses of 500, 1000, and 2000 mg/kg body weight (bw) of each test material were selected for the micronucleus tests. Concurrent control groups were administered sterile water, as the vehicle (negative) control, or 10 mg/kg bw of cyclophosphamide (positive control).

Duration of treatment / exposure:

On the day of dosing, all study animals were between 7 and 8 weeks of age, with body weights within ± 20% of the mean. Five animals per sex per dose group (seven in the highest dose group) were dosed by oral gavage (dose volume 10 mL/kg bw) as follows: 1) vehicle control (0 mg/kg bw); 2) low dose (500 mg/kg bw); 3) intermediate dose (1000 mg/kg bw); 4) high dose (2000 mg/kg bw); and 5) positive (cyclophosphamide) control (10 mg/kg bw).

Frequency of treatment:

Single dose

Post exposure period:

Approximately 48 and 72 h after exposure, blood samples were collected and 20,000 RETs per animal were analyzed.

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 mg/kg bw (total dose)

Doses / concentrations 2

Dose / conc.:

500 mg/kg bw (total dose)

Doses / concentrations 3

Dose / conc.:

1 000 mg/kg bw (total dose)

Doses / concentrations 4

Dose / conc.:

2 000 mg/kg bw (total dose)

No. of animals per sex per dose:

Five animals per sex per dose group (seven in the highest dose group)

Control animals:

yes, concurrent vehicle

Positive control(s):

positive controls (cyclophosphamide)

Examinations

Tissues and cell types examined:

The materials were assessed for induction of micronuclei and toxicity in bone marrow by analyzing peripheral blood reticulocytes (RETs) by flow cytometry.

Evaluation criteria:

The objective of these six studies was to evaluate the potential of the test materials, namely 3 pigment-grade, and 3 ultrafi ne titanium dioxide (TiO2 ) forms, to induce micronuclei in rat bone marrow by analyzing micronucleated reticulocytes (MN-RETs) in rat peripheral blood cells. An increase in the frequency of MN-RETs relative to negative controls would indicate that a test material induces chromosomal and/or cell spindle damage in erythroblasts. Possible toxic effects (inhibition of erythropoiesis) may be indicated by a signifi cant decrease in the frequency of reticulocytes (RETs) among the total erythrocytes [RETs plus normochromatic erythrocytes (NCEs)].

Statistics:

A test was considered valid if the range of MN-RET values in the vehicle control animals were within reasonable limits of the laboratory historical control range, and if the positive control induced a signifi cant increase in the frequency of MN-RETs as compared to the vehicle control group, judged by biological and/or statistical signifi cance (p 0.05).

Results and discussion

Test results

Key result

Sex:

male/female

Genotoxicity:

negative

Toxicity:

no effects

Vehicle controls validity:

valid

Negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

Titanium was present in blood and liver of untreated (control) rats. Tissue concentrations of rats treated with 500, 1000, or 2000 mg TiO2 /kg/bw did not show a dose-dependent increase in titanium content. Single oral intubation resulted in no discernible dose-dependent increases of TiO2 in the blood and liver of treated rats relative to control rats.

Applicant's summary and conclusion

Conclusions:

Under the conditions of these six studies, uf-1, uf-2, uf-3, pg-1, pg-2, and pg-3 titanium dioxide did not induce biologically relevant increases in micronucleated RETs in rat peripheral blood. Accordingly, all of the test materials were concluded to be essentially negative in the in vivo Mammalian Erythrocyte Micronucleus Test specifi c to oral administration, noting that the result can at least in part be attributed to the lack of achieving exposure of the test substance to the bone marrow even at the OECD 474 limit dose of 2000 mg/kg bw, when dosed by oral administration. With the exception of demonstrated target cell exposure, all other criteria for valid studies were met.