Tetramethyl orthosilicate

Genetic toxicity: in vivo

Administrative data

Endpoint:

in vivo mammalian somatic cell study: cytogenicity / erythrocyte micronucleus

Remarks:

Type of genotoxicity: chromosome aberration

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1987-03-23 - 1987-08-04

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: The study was conducted according to an appropriate OECD test guideline, with acceptable restrictions. The restrictions were that the report lacked details and only 1000 PCEs were scored for micronuclei. The study was compliant with GLP.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1987

Report date:

1987

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 474 (Mammalian Erythrocyte Micronucleus Test)

GLP compliance:

yes

Type of assay:

micronucleus assay

Test material

Test material information

Constituent 1

Reference substance name:

Tetramethyl orthosilicate

EC Number:

211-656-4

EC Name:

Tetramethyl orthosilicate

Cas Number:

681-84-5

Molecular formula:

C4H12O4Si

IUPAC Name:

tetramethyl silicate

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: cannot be read in report
- Age at study initiation: not stated in report
- Weight at study initiation: animals were weighed, but weights are not recorded in the study report.
- Assigned to test groups randomly: yes
- Fasting period before study: none
- Housing: individually
- Diet (e.g. ad libitum): ad libitum except during exposure period
- Water (e.g. ad libitum): ad libitum except during exposure period
- Acclimation period: no information

ENVIRONMENTAL CONDITIONS
Procedures outlined in "Standard operating procedures for the Acute toxicology laboratory" were adhered to, but details are not given in the study report.

Administration / exposure

Route of administration:

inhalation: vapour

Vehicle:

- Vehicle(s)/solvent(s) used: air
- Justification for choice of solvent/vehicle: none given
- Concentration of test material in vehicle: 30 ppm

Details on exposure:

TYPE OF INHALATION EXPOSURE: whole body

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Air/vapour mixture passed directly into an inlet port at top of 450 litre stainless steel and glass exposure chamber.
- Method of holding animals in test chamber: animals loose in chamber, on two planes of 10 rats per plane.
- Source and rate of air: not stated in report
- Method of conditioning air:
- System of generating particulates/aerosols: J-shaped glass generating tube with glass beads by a low flow FMI laboratory pump.
- Temperature, humidity, pressure in air chamber: not stated in report
- Air flow rate:
- Air change rate:
- Method of particle size determination:
- Treatment of exhaust air:

TEST ATMOSPHERE
- Brief description of analytical method used:
- Samples taken from breathing zone: yes/no

Duration of treatment / exposure:

4 hours

Frequency of treatment:

once

Post exposure period:

24, 48 and 72 hours sacrifice times

Doses / concentrations

Remarks:

Doses / Concentrations:
30 ppm
Basis:
other: Acute vapour inhalation

No. of animals per sex per dose:

Five animals per sex per time period

Control animals:

yes

Positive control(s):

_ Positive control substance: cyclophosphamide
- Justification for choice of positive control(s): none stated, but standard positive control substance
- Route of administration: single ip injection
- Doses / concentrations: 25 mg/kg bw

Examinations

Tissues and cell types examined:

Femoral bone marrow

Details of tissue and slide preparation:

CRITERIA FOR DOSE SELECTION: limit dose

TREATMENT AND SAMPLING TIMES ( in addition to information in specific fields): 30 ppm - 24, 48 and 72 hours. Negative control 24 and 72 hours. Positive control 48 hours.

DETAILS OF SLIDE PREPARATION: Following centrifugation in 2ml foetal bovine serum, portions of the pellet were spread on slides, two slides per animal per sample time. Slides were air dried for an hour prior to fixing in methanol for five minutes then air dried. Slides were stained with a fluorescent stain, Acridine Orange, diluted with Sorensens phosphate buffer (pH 6.8) for four minutes. Slides were rinsed in three changes of Sorensens phosphate buffer for nine minutes. Coverslips were then sealed on the slides.

METHOD OF ANALYSIS: slides were coded and anlaysed in a blind study. 1000 PCE's were scored per animal and the frequency of micronuclei was determined as the number of polychromatic erythrocytes containing one or more micronuclear inclusion bodies per thousand PCE's.

Evaluation criteria:

None stated in report

Statistics:

Statistical analysis was performed using the Wilcoxon Rank-Sum test.

Results and discussion

Test results

Sex:

male/female

Genotoxicity:

negative

Toxicity:

not specified

Remarks:

the NCE/PCE ratio was variable due to difficulty in scoring NCEs.

Vehicle controls validity:

valid

Negative controls validity:

not valid

Positive controls validity:

valid

Additional information on results:

RESULTS OF RANGE-FINDING STUDY
- Dose range:
- Solubility:
- Clinical signs of toxicity in test animals:
- Evidence of cytotoxicity in tissue analyzed:
- Rationale for exposure:
- Harvest times:
- High dose with and without activation:
- Other:

RESULTS OF DEFINITIVE STUDY
- Types of structural aberrations for significant dose levels (for Cytogenetic or SCE assay):
- Induction of micronuclei (for Micronucleus assay):
- Ratio of PCE/NCE (for Micronucleus assay):
- Appropriateness of dose levels and route:
- Statistical evaluation:

Any other information on results incl. tables

Micronuclear response of male and female rate

Dose	Male/female	Sampling time (hours)	Mean number of PCE	Mean number of PCE with MN	Mean % of MN
Vehicle* control	Male	24	1004.20	2.60	0.26
Vehicle control*	Female	24	1027.20	3.80	0.38
30 ppm	Male	24	1008.00	1.80	0.18
30 ppm	Female	24	1009.20	1.60	0.16
Positive control	Male	48	1009.40	60.2	5.62**
Positive control	Female	48	1009.20	67.20	6.24**
30 ppm	Male	48	1010.80	1.40	0.14
30 ppm	Female	48	1006.40	1.20	0.12
Vehicle* control	Male	72	1003.40	1.60	0.16
Vehicle* control	Female	72	1005.40	1.20	0.12
30 ppm	Male	72	1004.60	2.20	0.22
30 ppm	Female	72	1009.60	1.40	0.14

*Vehicle control: sham exposed to air

** Statistically significant at the % confidence interval (p<0.05)

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): negative
Tetramethyl orthosilicate was tested in an in vivo rat micronucleus assay according to OECD 474, and in compliance with GLP. No evidence of a test substance mediated induction of micronuclei was observed following inhalation exposure to the maximum tolerated dose. It was noted that the NCE/PCE ratio was variable due to difficulty in scoring NCEs. It is concluded that the test substance is not genotoxic under the conditions of the test.