Zirconium dichloride oxide

Genetic toxicity: in vivo

Administrative data

Endpoint:

in vivo mammalian somatic cell study: cytogenicity / bone marrow chromosome aberration

Type of information:

experimental study

Adequacy of study:

disregarded due to major methodological deficiencies

Study period:

no data

Reliability:

3 (not reliable)

Rationale for reliability incl. deficiencies:

significant methodological deficiencies

Remarks:

Bone marrow was only collected once at 24 hours rather than at 12-18 hours and 24 h thereafter, colchicine was given 2 hours before sampling rather than 3-5 hours before sampling; a positive control was not used; results were not presented per animal and no listing of the different types of structural chromosome aberrations was presented. Oral administration was unspecified.

Data source

Reference

Reference Type:

publication

Title:

Unnamed

Year:

1990

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 475 (Mammalian Bone Marrow Chromosome Aberration Test)

Deviations:

yes

Remarks:

See rationale for reliability scoring.

GLP compliance:

not specified

Type of assay:

chromosome aberration assay

Test material

Test material information

Constituent 1

Reference substance name:

Zirconium dichloride oxide

EC Number:

231-717-9

EC Name:

Zirconium dichloride oxide

Cas Number:

7699-43-6

Molecular formula:

Cl2OZr

IUPAC Name:

Dichloro(oxo)zirconium

Test material form:

solid: crystalline

Details on test material:

- Name of test material (as cited in study report): zirconium oxychloride
- Physical state: crystals

Test animals

Species:

mouse

Strain:

Swiss

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Age at study initiation: 8-9 weeks of age
- Weight at study initiation: 28-30 g
- Diet (e.g. ad libitum): ad libitum Gold Mohur mice feed; manufactured by Lipton India Limited
- Water (e.g. ad libitum): ad libitum
- Houding: Temperature controlled chambers

Administration / exposure

Route of administration:

oral: unspecified

Vehicle:

- Vehicle(s)/solvent(s) used: distilled water

Details on exposure:

no data

Duration of treatment / exposure:

single oral administration

Frequency of treatment:

single dose

Post exposure period:

not applicable

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

225 other: mg/kg actual ingested - males

Doses / concentrations 2

Dose / conc.:

750 other: mg/kg actual ingested - males

Doses / concentrations 3

Dose / conc.:

2 250 other: mg/kg actual ingested - males

Doses / concentrations 4

Dose / conc.:

220 other: mg/kg actual ingested - females

Doses / concentrations 5

Dose / conc.:

734 other: mg/kg actual ingested - females

Doses / concentrations 6

Dose / conc.:

2 200 other: mg/kg actual ingested - females

No. of animals per sex per dose:

5

Control animals:

yes, concurrent vehicle

Positive control(s):

no data

Examinations

Tissues and cell types examined:

Bone marrow was flushed out and prepared for analysis of chromosomal aberration.

Details of tissue and slide preparation:

CRITERIA FOR DOSE SELECTION: Doses were calculated as fractions of the LD50 dose determined for the test substance.

TREATMENT AND SAMPLING TIMES (in addition to information in specific fields): A single oral administration of the test substance and animals were sacrificed 24 hours after adminstration.

DETAILS OF SLIDE PREPARATION: 2 h before sacrifice, all mice were intraperitoneally injected with colchicine, 4 mg/kg. Bone marrow was flushed out and prepared for analysis of chromosomal aberrations, following the usual hypotonic acetic acid-ethanol fixation and Giemsa staining schedule. Slides were coded and scored blind for total chromosomal abnormalities.

Evaluation criteria:

50 well-scattered metaphase plates per animal and a total of 250 metaphase plates per sex per treatment group were observed for chromosomal aberrations. 5000 cells per sex per treatment were scored to estimate divisional frequency.

Statistics:

The results obtained for total chromosomal abnormalities were statistically analysed for dose response following trend test according to Margolin et al., 1986. The level of significance was established at p

Results and discussion

Test results

Sex:

male/female

Genotoxicity:

positive

Toxicity:

yes

Vehicle controls validity:

valid

Negative controls validity:

not applicable

Positive controls validity:

not specified

Additional information on results:

Observations made 24 h after the administration of zirconium oxychloride in concentrations of 2250 and 750 mg/kg body weight in males and 2200 and 734 mg/kg body weight in females increased the divisional frequency in comparison to control. However, mitotic divisional frequency was not enhanced appreciably by the lowest dose used (225 mg/kg for males and 220 mg/kg for females).
Control: 2.74% mitotic cells in males and 2.90% in females
Low dose: 3.10% mitotic cells in males and 3.96% in females
Mid dose: 5.50% mitotic cells in males and 5.60% in females
High dose: 4.90% mitotic cells in males and 5.80% in females

Animals exposed to the test substance reported significant enhancement of the frequency of aberrant metaphases as compared with the control. The percentages of total abnormalities were increased considerably in both sexes with all concentrations used. The degree of increase was directly proportional to the concentration and was significant between the control and the next dose used and also between the consecutive doses.
In general, the abnormalities were relatively higher in the female mice than in the male ones, but the difference was not statistically significant. Induced abnormalities included both chromosomal aberrations and spindle disturbances. The former were mainly chromatid and chromosome breaks with a few cases of centric fusion. The action of zirconium appears to be on different phases of the cell cycle.
Total aberrant metaphases (mean):
control: 5.6% in males and 5.2% in females
Low dose: 10.8% in males and females
Mid dose: 18.0% in males and 19.0% in females
High dose: 22.5% in males and 24.8% in females

Applicant's summary and conclusion

Conclusions:

Under the test conditions the frequencies of aberrations were directly proportionate to the concentration used. Female mice were found to be more susceptible than male mice, though not to a significantly higher level. The results of this study should be treated with great care for the following reasons:
1) Only total chromosomal abnormalities are presented, which include structural chromosome aberrations and spindle disturbances, the latter being
polyploidy. Polyploidy is a disturbance in mitotic processes and cell cycle progression. An increase in polypoloidy may indicate that a chemical has the potential to induce numerical aberrations. However, polyploidy is not related to clastogenicity, and should therefore be included separately from the structural chromosome aberrations. As this study does not distinguish between the two, a conclusion on clastogenicity cannot be drawn.
2) An aqueous solution of zirconium oxychloride is given to the mice. It is known from water solubility/hydrolysis experiments that the substance in water will cause a drop in pH by the release of H+ ions. Apart from the fact that the mice have probably been dosed corrosive solutions, there is some evidence that H+ ions can cause chromosomal damage (refer to IARC monograph 54-8 (1992; p. 203) on hydrochloric acid). It can thus not be ruled out that the observed effects in the bone marrow have been caused by the low pH after dissolving the test substance in water.
3) No data was presented on whether the substance can actually reach the bone marrow and whether this test is thus biologically relevant. Some evidence exists that zirconium oxychloride is poorly absorbed by mice after oral administration of an aqueous solution of 1500 mg/kg (Delongeas et al., 1983, J. Pharmacol. 14(4) 437-447). It reaches the blood and after 6 h a maximal blood concentration of 2.9 mg Zr/L (i.e. about 10 mg zirconium oxychloride per liter) was reached. In a similar but more extensive study in rats given aqueous solutions of 3000 mg zirconium oxychloride/kg, the maximal blood concentration was reached after 6 hours being about 0.3 mg Zr/L (i.e. about 1 mg zirconium oxychloride per liter). Using metabolic cages it was shown that within 24 hours 90-98% of the given dose was excreted via feces and minimal amounts via urine. This shows that the substance is hardly absorbed as it is excreted via feces.
In the same study of Delongeas et al. (1983), tissue distribution reveals that the small absorbed fraction is distributed and fixed in the ovaries, liver and lung, and to a lesser degree in bone and CNS. All together this raises the question whether the substance in the current study has reached the bone marrow to a sufficient extent in order to induce effects.