tert-butylchlorodimethylsilane

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:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Remarks:

The restrictions were the number of cells evaluated to determine mitotic index deviated from guideline, and reporting wes less detailed than the current guideline stipulatess.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1982

Report date:

1982

Materials and methods

Test guideline

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 475 (Mammalian Bone Marrow Chromosome Aberration Test)

Deviations:

yes

Remarks:

Number of cells evaluated, detail of reporting

Principles of method if other than guideline:

Rodent Bone Marrow Cytogenetic Assay as recommended by the Ad Hoc Committee on Chromosome Methodologies in Mutagen Testing (Toxicology & Applied Pharm 22: 269-275, 1972) with modifications per the EPA Gene-Tox Program Cytogenetics Committee (12/3 to 12/5, 1980, Washington, D.C.).

Studies were conducted in accordance with the recommendations of an ad hoc committee on chromosome methodologies in mutagen testing (EMS/IMR,  1972).

GLP compliance:

yes

Remarks:

with no documenting of raw data from range finding, or quarantine or pre-trial healt of animals

Type of assay:

chromosome aberration assay

Test material

Test material information

Constituent 1

Reference substance name:

Chlorotrimethylsilane

EC Number:

200-900-5

EC Name:

Chlorotrimethylsilane

Cas Number:

75-77-4

Molecular formula:

C3H9ClSi

IUPAC Name:

chloro(trimethyl)silane

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male

Details on test animals or test system and environmental conditions:

Weight at study initiation: 250-320 g for range finding; approximately 280 g for cytogenetics study
TEST ANIMALS
- Source: Gofmor Farms Westboro MA USA (range finding); Charles River Laboratories, Wilmingtom MA USA
- Age at study initiation: no information
- Weight at study initiation: 250-320 g for range finding; approximately 280 g for cytogenetics study
- Assigned to test groups randomly: [no/yes, under following basis: ]
- Fasting period before study: no information
- Housing: 6-7 per cage
- Diet (e.g. ad libitum): no information
- Water (e.g. ad libitum): no information
- Acclimation period: no information

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20
- Humidity (%): 50
- Air changes (per hr): no information
- Photoperiod (hrs dark / hrs light): no information

IN-LIFE DATES (from beginning of cytogenetic study): From: 1981-06-02 To: 1981-09-28

Administration / exposure

Route of administration:

intraperitoneal

Vehicle:

Vehicle = Negative control: Paraffin oil;
The negative control, paraffin oil, was used in each assay, as recommended by sponsor

Duration of treatment / exposure:

6, 24 or 48 hours

Frequency of treatment:

One i.p. injection/rat

Post exposure period:

6, 24 or 48 hours

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

10 mg/kg bw/day (nominal)

Doses / concentrations 2

Dose / conc.:

19 mg/kg bw/day (nominal)

Doses / concentrations 3

Dose / conc.:

37 mg/kg bw/day (nominal)

Doses / concentrations 4

Dose / conc.:

74 mg/kg bw/day (nominal)

No. of animals per sex per dose:

First range-finding: 2 animals/dose group;  
Second range-finding: 10 animals/dose group; 
Cytogenetic studies: 6 animals/dose group/time point to achieve the minimum number of 5 animals per dose for analysis

Control animals:

yes, concurrent vehicle

Positive control(s):

Cyclophosphamide (22 mg/kg)

Examinations

Tissues and cell types examined:

Suitable cell spreads were those with both properly condensed and well-spread chromosomes. A minimum of 100 metaphase cells was evaluated per animal.

Details of tissue and slide preparation:

Rats were sacrificed at the scheduled times and bone marrow was aspirated from the femur.  
Approximately four slides were prepared from each animal.  
Slides were fixed, stained and permanently mounted.  
Suitable cells were photographed using a 100X objective.  
Suitable spreads consisted of those which had both properly condensed and well-spread chromosomes.
In  general,  a minimum of 100 metaphase cells was analyzed per animal, and 5 animals were analyzed for each dose.  
The choice of animals to be used for analysis was based on the quality of the slides.

Statistics:

A comparison of the expected and observed distribution values was performed using the Chi2 test as a measure of "goodness of fit".  The  
Wilcoxon test was used as a non-parametric test to compare the  distribution of breaks per animal between the negative control animals  
and the highest test doses.

Results and discussion

Test results

Sex:

male

Genotoxicity:

negative

Toxicity:

yes

Remarks:

deaths occurred at doses of 45 mg/kg and above

Vehicle controls validity:

valid

Negative controls validity:

not applicable

Positive controls validity:

valid

Additional information on results:

Mortality indicated in range-finding studies  

Any other information on results incl. tables

The doses used in the cytogenetic study were based on the range-finding experiments.  In the first study, all animals dosed with 3672, 918, and 367 mg/kg and 1 of 2 animals dosed with either 93 or 37 mg/kg died within three days.  In the second study, 3 of 10 animals dosed with 90 mg/kg died and 2 of 10 animals dosed with 45 mg/kg died.  None of the other animals died.

For the cytogenetic experiments, four target doses were chosen: 74, 37, 19 and 10 mg/kg.  Since all the animals lived, the top three dosage groups were chosen for analysis.

There was no evidence that silane, chlorotrimethyl- induced chromosomal damage in rats following IP injection, including complex rearrangements. COntrol values were comparable to historical controls. A summary of the total number of cells analyzed for each dose at each time of sacrifice in provided in the table below:

Summary of Chromosome Aberration Data at three respective intervals

Test Chemical	Dose (mg/kg)	No. of cells	Gaps	Breaks	Other	% Abnormal Cells
Paraffin oil (1 ml): • at 6 hours • at 24 hours^* • at 48 hours	-- -- --	497 622 586	3 17 4	2 6 9	0 0 0	0.40 0.96 1.54
Silane, chlorotrimethyl-: • at 6 hours • at 24 hours • at 48 hours	19 37 74 19 37 74 19^* 37^* 74	542 548 521 398 549 548 501 410 523	5 2 5 3 7 6 16 3 11	2 1 9 1 3 4 6 8 12	0 0 0 0 0 0 0 0 0	0.37 1.28 1.73 0.25 0.55 0.73 1.20 1.95 2.29
Cyclophosphamide • at 24 hours	22	523	ND	>65	7 quads

^* Chromosomal preparations of bone marrow cells could be made only from four animals.

ND = not determined

Quad = quadriradial

No complex rearrangements such as quadriradials, triradials, or ring chromosomes were detected in animals injected with the test substance.

 

A comparison of the frequencies of breaks for doses of silane, chlorotrimethyl- with the negative control at the three time points shows no significant differences.  These frequencies are similar to those recorded for control animals in previous testing.  The frequency of breaks in previous negative control animals ranged from 0 to 2.6%, a range compatible with all the results obtained in this project.  The conclusion based on comparison to historical data is confirmed by a statistical analysis using the Wilcoxon test that demonstrated that there was no difference between the number of breaks per animal for the negative control groups and the test groups.  The use of the Chi² test as a measure of “goodness to fit” indicated that the distribution of breaks per animal closely followed the Poisson distribution.

The animals injected with cyclophosphamide (positive control) had both a large number of breaks and complex rearrangements.

Applicant's summary and conclusion

Conclusions:

Chloro(trimethyl)silane has been tested in a reliable assay according to a protocol that is similar to OECD Test Guideline 475 and in compliance with GLP. Appropriate concurrent negative and positive controls were included, and the expected responses were observed. The test substance, chloro(trimethyl)silane (CAS No. 75-77-4), did not cause an increase in the frequency of chromosomal breaks or aberrations in bone marrow cells of rats. Thus, there was no evidence in this study that it caused chromosomal damage.