Trichlorosilane

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

Study period:

1982-04-21 to 1982-05-14

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

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 474 (Mammalian Erythrocyte Micronucleus Test)

Deviations:

yes

Remarks:

only 1000 cells scored (compared to 2000 in the guideline).

Principles of method if other than guideline:

Micronucleus test in vivo: Matter and Schmid, 1971, Mut. Res. 12: 417-425.

GLP compliance:

yes

Type of assay:

micronucleus assay

Test material

Test material information

Constituent 1

Reference substance name:

Trimethoxysilane

EC Number:

219-637-2

EC Name:

Trimethoxysilane

Cas Number:

2487-90-3

Molecular formula:

C3H10O3Si

IUPAC Name:

Trimethoxysilane

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

female

Details on test animals or test system and environmental conditions:

TEST ANIMALS

- Source: Spartan Research Laboratories, Inc. Harlet, MI

- Weight at study initiation: 100 to 175 grams

- Housing: Animals housed individually

- Diet: PURINA Rodent Laboratory Chow, ad libitum

- Water: ad libitum

Administration / exposure

Route of administration:

inhalation

Vehicle:

- Vehicle(s)/solvent(s) used: air

- Concentration of test material in vehicle: 100 ppm

Details on exposure:

TYPE OF INHALATION EXPOSURE: nose only

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION

- Exposure apparatus: specially constructed glass chamber

- System of generating particulates/aerosols: vapours were generated by bubbling clean, dry air through the liquid test material

Duration of treatment / exposure:

4 hour(s)

Frequency of treatment:

Single 4 hour exposure

Post exposure period:

30 hours

Doses / concentrations

Dose / conc.:

100 ppm (nominal)

No. of animals per sex per dose:

5 animals per dose level

Control animals:

yes, concurrent no treatment

Positive control(s):

triethylenemelamine

- Route of administration: split-dose intraperitoneal injection (0 and 24 hours)

- Doses / concentrations: 0.5 mg/kg/dose

Examinations

Tissues and cell types examined:

Animals were exposed to the test article by acute inhalation. They were sacrificed, the bone marrow is extracted and smear preparations made and stained. Polychromatic erythrocytes are scored for micronuclei under the microscope. Both positive and negative (solvent) controls are used in each experiment.

Details of tissue and slide preparation:

At sacrifice the adhering soft tissue and epiphyses of both tibiae were removed. The marrow was aspirated from the bone and transferred to centrifuge tubes containing 5 ml fetal calf serum (one tube for each animal). Following centrifugation to pellet the tissue, the supernatant was drawn off and portions of the pellet was spread on slides and air-dried. The slides were then stained in May-Gruenwald Solution and Giemsa. A thousand polychromatic erythrocytes (PCEs) per animal were scored. The frequency of micronucleated was expressed as percent micronucleated cells based on the total PCEs present in the scored optic field.

Evaluation criteria:

In the normal animal, the normocytes/PCE's is approximately 2. If an agent inhibits the proliferation of erythroblasts the proportion of PCE's is generally reduced. If the agent promotes chromosome breakage or acts as a spindle poison, generally the proportion of red normocytes increases.

Statistics:

Mean normocyte and polychromatic erythrocytes calculated as well as ratio of normocytes to PCE's. Student T-test was used to confirm no difference between the PCE MN count for study groups A(treated) and D(control).

Results and discussion

Test results

Key result

Sex:

female

Genotoxicity:

negative

Toxicity:

yes

Vehicle controls validity:

valid

Negative controls validity:

valid

Positive controls validity:

valid

Additional information on results:

RESULTS OF RANGE-FINDING STUDY

- Dose range: 100 ppm

- Clinical signs of toxicity in test animals: To ensure that the Micronucleus Assay was performed on animals exposed to a lethal concentration of the test material (Group A), a second group of animals (Group B) was simultaneously exposed to the chemical via inhalation as a positive control for lethality. The data demonstrates that both groups (A&B) was exposed to a lethal concentration of the test material. All five animals in Group B experienced weight loss and died within the 14 day observation period. At autopsy all five animals showed extensive lung damage with haemorrhage and atelectasis. Animals exposed via inhalation to the test material all showed slight to moderate evidence of lung damage in the form of petechial haemorrhage and focal atelectasis. Some evidence of kidney congestion was noted in several animals. No abnormal pathology was evident in either the positive control (C) or negative control (D) groups.

- Evidence of cytotoxicity in tissue analysed: The ratio of normocytes to PCE's obtained with both the test material treatment (Group A = 10.64) and the negative control (Group D = 10.28) closely approximate the normal expected ratio and were fairly consistent. The mean normocyte count from the positive control group was elevated (Group C = 19.4) indicating that the animals responded to a known clastogen (chromosome breaking agent). This same trend verified by the increase in percentage of micronucleated PCEs in the positive control group.

- Harvest times: Group A (Treatment group): 30 hours after exposure. Group C (Positive Control): 30 hours. Group D (Negative Control): 30 hours.

- High dose: 100 ppm

RESULTS OF DEFINITIVE STUDY

- Induction of micronuclei (for Micronucleus assay): Within normal range for all groups

- Ratio of PCE/NCE (for Micronucleus assay): Within normal range for all groups

- Statistical evaluation: Comparison of the study groups by Student T-test using a SAS computer program confirms there is no difference between the mean PCE micronucleus count for study groups A and D (test article and negative control) (<.0001) while the positive control is definitely positive (p>0.5) compared to the former groups.

Any other information on results incl. tables

The following table indicates that the animals responded to the positivecontrol substance. Both normocytes/PCE **

ratio and % of micronucleated PCEs weresignificantly increased in the positive control group when compared to test material-treated group.

Table 3 : Mean Results of in vivo micronucleus test with mouse bone marrow

		Test Group (A)	Positive Control (C)	Negative Control (D)
Number of cells evaluated		1000	1000	1000
Sampling time (h)		30h	30h	30h
Number of erythrocytes	Normocytes / Field	10.64	19.4	10.28
	PCE / Field	4.36	4.56	4.36
	Micronuclei / 1000 PCE	6.8	39.2	5.6
Ratio of erythro­cytes	Normochromatic / polychromatic	2.52	4.38	2.39
	% Micronucleated PCE	0.68	3.92	0.56

 

Applicant's summary and conclusion

Conclusions:

Trimethoxysilane (CAS 2487-90-3) has been tested in a reliable in vivo mammalian micronucleus assay, conducted according to a protocol similar to OECD Test Guideline 474 and in compliance with GLP. Trimethoxysilane did not induce chromosome breakage or act as a spindle poison in the rodent micronucleus assay even when animals were exposed to lethal concentrations. There is no evidence from this study that mortality involves genotoxicity. In conclusion, trimethoxysilane is concluded to be non-mutagenic in Sprague-Dawley rats.