Trichloro(ethyl)silane

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Study period:

2005

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: 1a The study was conducted according to an appropriate OECD test guideline, and in compliance with GLP, using a closely related test substance.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2005

Report date:

2005

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: USEPA OPPTS 870.3650

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Trimethoxy(methyl)silane

EC Number:

214-685-0

EC Name:

Trimethoxy(methyl)silane

Cas Number:

1185-55-3

IUPAC Name:

trimethoxy(methyl)silane

Details on test material:

The test article, methyltrimethoxysilane, was received from Gelest Inc, Morrisville, Pennsylvania, for Silicones Environmental, Health and Safety Council of North America, as follows:
Methyltrimethoxysilane
Lot No. 9H-7709
CAS No. 1185-55-3
Clear liquid

Characterization analyses were performed by Dow Corning Corporation Health and Environmental Sciences Laboratory. The purity of the test article was 96.74%. The test article was stored in sealed containers (FF) at room temperature and was considered stable under these conditions. A reserve sample of the test article was retained.

The test article, methyltrimethoxysilane (Lot No. 9H-7709) was characterized according to current EPA Good Laboratory Practice Standards. The characterization included physical description, GC-FID for area % purity, and GC-MS for identification of the major component in the test article.

The physical description of the test article was observed to be a clear liquid. The GC-FID analyses of methyltrimethoxysilane afforded a mean area % purity of 96.74 +/- 0.001. The GC-MS data verified the major component in the test article to be methyltrimethoxysilane and the minor components to be methanol, Dimethoxydimethylsilane and dimethoxymethyldisiloxane. Also, the mass spectrum of each component in the test article was consistent with that of reference mass spectra found in library searches.

Test animals

Species:

rat

Strain:

other: Crl:CD®(SD)IGS BR VAF/Plus®

Details on test animals or test system and environmental conditions:

ANIMAL RECEIPT AND ACCLIMATION
Ninety female and forty five male Crl:CD®(SD)IGS BR VAF/Plus® rats were received from Charles River Laboratories, Portage, MI. The animals were 9 weeks old. Upon receipt, each animal was inspected by animal resource personnel and animals judged to be in good health and suitable as test animals were quarantined for six days. During the quarantine period animal resource personnel observed each animal at least once daily. The attending veterinarian examined all animals before release from quarantine and documented the general state of animal health.

ANIMAL HOUSING
Animals were individually housed in suspended wire-mesh cages elevated over Bed-O’Cobs Alf-a’ bedding, during quarantine and throughout the course of the study, with the following exceptions. During cohabitation, reproductive group females were paired 1 to 1 with a male from the same treatment group in suspended wire-mesh cages elevated over Bed-O’Cobs Alf-a’ bedding. The animals were paired in the home cage of the male. On day 0 of gestation, reproductive group females were moved into shoebox cages containing Bed-O’ Cobs Combination bedding and remained there throughout the remainder of the study. The results of the manufacturer’s periodic analysis of the Bed-O’ Cobs Combination bedding were reviewed to ensure that there were no contaminants present at levels that would be expected to affect the outcome of the study. The cages, bedding/fecal pans were routinely cleaned, consistent with good husbandry practices.

DIET, DRINKING WATER AND MAINTENANCE
PMIcertified Rodent Diet #5002, manufactured by PMI Nutritional International, St. Louis, MO, was offered ad libitum except during functional observational battery assessment period. Males and toxicity group females were fasted prior to necropsy by removing food on the evening of the day before necropsy. The results of the manufacturer’s periodic analyses of the certified feed were reviewed to ensure that heavy metals and pesticides were not present in concentrations that would be expected to affect the outcome of the study.

Municipal water, further purified by reverse osmosis was available ad libitum except during performance of functional observational battery testing. The drinking water was monitored on at least a semi-annual basis to determine compliance with the U.S.E.P.A. drinking water standards. The most recent analysis was reviewed and there were no contaminants in the water known to be present at levels expected to interfere with the integrity of the study.

ENVIRONMENTAL CONDITIONS
Animals were housed in an environmentally controlled animal room (12-hour fluorescent light/dark cycle, 68.3-72.5 °F (20.2 - 22.5°C), 36.0-62.0% relative humidity, 10-15 air changes per hour) throughout the in-life phase of the study. Temperature and humidity were continuously monitored. The most recent air change verification was reviewed by the study director.

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

The vehicle and test article formulations were administered orally by gavage, via a 3-4 inch, 15-18 gauge, animal feeding needle and syringe once daily. Volume administrations did not exceed 3 mL/kg of body weight except for a few instances. The volume administered was based upon the most recent body weight.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentration of methyltrimethoxysilane (MTMS) in corn oil dosing solutions was determined prior to the beginning of the definitive study.

Preparation of Solvent Standards: Stock solvent standards of MTMS in toluene were prepared under a nitrogen atmosphere by weighing an amount of MTMS and mixing with a known volume of toluene. Aliquots of the stock solution were then further diluted with toluene to cover the standard range from approximately 100 µg MTMS/ml toluene to approximately 1000 µg/ml. New solvent standards were prepared with each dosing solution analysis. An aliquot of each solvent standard was placed in an autosampler vial and analyzed.

Preparation of Dosing Solutions for Analysis of Concentration Verification: Aliquots of dosing formulations were volumetrically measured into volumetric flasks, diluted to volume with toluene and mixed well. Aliquots of the diluted dosing solutions were placed in autosampler vials and were analyzed with the solvent standards for determination of the concentration of MTMS.

Gas Chromatography Analysis: A set of solvent standards comprising of at least five concentrations was used to establish a calibration curve. Trendlines and their mathematical equations were generated by linear regression analysis of the peak areas resulting from the analysis of the solvent standards using Microsoft Excel 2000 (Version 9.0). The dosing solution verifications were performed by comparing the target concentration of the dose solutions to the mean observed test substance concentration found by refitting the peak areas resulting from the dosing solution dilution samples to the standard curve. The limit of quantitation was set at the level of the lowest standard analyzed and was equal to 5 mg MTMS/ml dosing solution. The conditions used were as follows:
Injection: 1 µl, split 50:1
Injector Temp: 160 °C
Carrier Gas: Helium
Column Flow: 1.3 ml/min
Hydrogen Flow: 30 ml/min
Air Flow: 400 ml/min
Combined Flow: 25 ml/min (constant column + make-up flow)
Column: HP-5MS, 30 m x 0.25 mm, 0.25 µm film thickness
Oven Temp: 70 °C for 3 min to 210 °C at 17 °C/min
Detector: Flame Ionization Detector (FID)
Detector Temp: 300 °C

Homogeneity and Stability: Homogeneity and stability of MTMS in corn oil dosing solutions was performed as part of the pilot study with MTMS. The dosing solutions were found to be homogeneous and stable up to 15 days if aliquoted into separate vials for daily usage.

Concentration Verification: Verification of each dosing concentration was conducted following each new preparation. New dosing solutions were prepared at least every 15 days in order to stay within the stability timeframe established in the pilot study.

Results: Dose solution analysis for concentration determined that each batch of 50, 250 and 1000 mg/kg/day dose solution was within 95-97%, 95-97% and 99-100% of the target concentration, respectively.

Details on mating procedure:

A 1:1 mating ratio was used. After dosing on study day 14, the animals were paired by placing the lowest numbered ear tag reproductive group female within each group in the home cage of the male with the lowest numbered ear tag from the same group (one exception was that reproductive group female D1185 was paired with male D1224). Female animals were housed continuously with the same male until evidence of copulation was obtained. Females were evaluated daily for evidence of copulation, as indicated by either a vaginal copulatory plug or sperm in the vaginal smear. Day 0 of gestation was defined as the day evidence of copulation was obtained, at which time the female was returned to her home cage (shoebox cage).

Duration of treatment / exposure:

Test substance was administered once daily by oral gavage, seven days per week at approximately the same time each day. Dose levels of methyltrimethoxysilane (MTMS) were 0 (control), 50, 250 and 1000 mg MTMS/kg/day. MTMS, dissolved in corn oil, was administered by oral gavage once each day for up to 51 consecutive days. Females in each dose level were divided into a toxicity (10 animals/group) and a reproductive group (10 animals/group). A single group of males (10 animals/group) were used for both the toxicity and reproductive phases of the study. Toxicity group females and males were treated for 28 and 29 days, respectively. Reproductive group females were treated for 14 days prior to the mating period, during the mating period, and then up to and including post partum day 3, for a total of up to 51 days.

Frequency of treatment:

7 days/week

Duration of test:

Males and toxicity group females were sacrificed after they had been treated for 28 days. Reproductive group females and pups were sacrificed
on day 4 postpartum.

Doses / concentrations

Remarks:

Doses / Concentrations:
0, 50, 250, and 1000 mg/kg/day
Basis:

No. of animals per sex per dose:

10/sex/dose level

Control animals:

yes, concurrent vehicle

Details on study design:

Reproductive and Developmental Parameters: Evidence of mating and the duration of gestation was calculated for each female. Beginning on gestation day 20, pregnant animals were checked at least three times daily for evidence of parturition. Dams and pups were euthanized on postnatal day 4 and examined for external gross lesions.

Examinations

Maternal examinations:

Mortality/Morbidity: Animals were observed at least twice daily in their cages for moribundity and mortality throughout the in-life phase of the study.
Clinical observations:
Daily Observations: General clinical examinations were made at lease once a day and were conducted immediately after dosing. The examinations included, but were not limited to, changes in the skin, fur, eyes, mucous membranes, respiratory, circulatory, autonomic and central nervous system functions, motor activity and behavior patterns. Findings were recorded for individual animals. General clinical examinations were not performed on days when detailed physical examinations were performed.
Detailed Physical Examinations: All animals received a detailed physical examination once before the first dose administration (to allow for within-subject comparisons), and weekly thereafter. Examinations were made outside the home cage in a standard arena at approximately the same time each day. Observations were detailed and carefully recorded. Examinations included, but were not limited to, changes in skin, fur eyes, mucous membranes, occurrence of secretions and excretions, and autonomic activity. Changes in gait, posture and response to handling as well as the presence of clonic or tonic movement, stereotypies, difficult or prolonged parturition or bizarre behavior were recorded. The presence or absence of findings was recorded for individual animals.

Body weights and food consumption were recorded weekly. Additional body weights for reproductive group females were obtained on gestational day 0, 7, 14, and 20, and within 24 hours of parturition, and on postnatal day 4. Individual food consumption was determined for each group following group specific schedules.

Ovaries and uterine content:

For females that delivered or had macroscopic evidence of implantation, the numbers of former implantation sites and corpora lutea were recorded. Recognizable fetuses for the females euthanized in extremis were examined externally and preserved in 10% neutral-buffered formalin. For females that failed to deliver, a pregnancy status was determined. Uteri with no macroscopic evidence of implantation were opened and subsequently placed in a 10% ammonium sulfide solution for detection of early implantation loss.

Fetal examinations:

Each litter was examined following delivery to determine the number and sex of the pups, stillbirths, live births, runts, sex ratio, and the presence of any gross abnormalities. Litter weights were taken within 24 hours of parturition and on day 4 postpartum.

Statistics:

Reproductive parameters with the exception of litter size were analyzed using an ANCOVA (Analysis of Covariance) with litter size as the covariate. Litter size was analyzed using an ANOVA.
Statistically significant probabilities are reported at either the p<0.05 or p<0.01 levels.

Indices:

On the day parturition was initiated (PND 0), the pups were sexed and examined for gross malformations, and the numbers of still born and live pups were recorded.

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Details on maternal toxic effects:
"Body weight: No statistically significant differences in treatment group maternal body weight relative to control group animals.
"Food/water consumption: No statistically significant differences in treatment group maternal food consumption relative to control group animals.

Effect levels (maternal animals)

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day

Basis for effect level:

other: maternal toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
No gross abnormalities were found for any of the pups, with the exception of a single runt in the 50 mg/kg/day group.

Effect levels (fetuses)

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day

Basis for effect level:

other: teratogenicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

Result: Maternal toxicity was not apparent at any dose level.  NOAEL = 1000  mg/kg/day.  Developmental toxicity was not apparent at any dose level.   

NOAEL = 1000 mg/kg/day.

Grossly visible abnormalities, external, soft tissue and skeletal abnormalities:  None.

Litter sizes were comparable for all groups.  No gross abnormalities were  found for any of the pups, with the exception of a single runt in the 50  

mg/kg bw/day group.

Applicant's summary and conclusion

Conclusions:

Exposure to methyltrimethoxysilane was not associated with developmental toxicity. The findings support a NOAEL of 1000 mg/kg/day.