Trichloro(methyl)silane

Toxicity to reproduction

Administrative data

Endpoint:

one-generation reproductive toxicity

Remarks:

based on generations indicated in Effect levels (migrated information)

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: Guideline study

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:

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

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

Test animals

Species:

rat

Strain:

other: Crl:CD®(SD)IGS BR VAF/Plus®

Sex:

male/female

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 oF, 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.

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).

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 oC
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 oC for 3 min to 210 oC at 17 oC/min
Detector: Flame Ionization Detector (FID)
Detector Temp: 300 oC

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 95-07%, 95-97% and 99-100% of the target concentration, respectively.

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:

daily

Details on study schedule:

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. A functional observational battery (FOB) evaluation for signs of neurobehavioral effects was performed on all adult males
and all toxicity group females prior to the start of dosing and during the last week of dosing. Body weights and food consumption were recorded
weekly. From all males and all toxicity group females, blood samples were obtained on the day of scheduled necropsy for hematology and
clinical chemistry parameters evaluations. Animals were subjected to a complete gross necropsy. Many tissues and organs were collected for
histological examination and were weighed.

Doses / concentrations

Remarks:

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

No. of animals per sex per dose:

10/sex/dose level

Control animals:

yes, concurrent vehicle

Examinations

Parental animals: Observations and 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. In addition, detailed clinical observations (functional observational battery [FOB] conducted out of the home cage) and locomotor activity were evaluated for all adult male and toxicity phase females once prior to the start of test article administration (baseline evaluations) and again during the last week of the test article administration. Blood samples were collected from males and toxicity group females on the day of scheduled termination for analysis of hematology and serum chemistry parameters.

Litter observations:

All reproductive phase females were allowed to deliver and rear their offspring to lactation day 4; surviving dams and pups were euthanized and examined on lactation day 4.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. Individual gestation length was calculated using the date delivery started. Abnormal behavior of the offspring was recorded. The dam and litter remained together until PND 4.

Mean measured parameters were calculated for:
Days of gestation
Undetermined sex
Male pups/litter
Female pups/litter
Males/Females per litter
Total pups/litter
Viable (live) pups/litter
Viable/Total pups per litter

Initial litter weight at parturition (g)
Initial average pup weight at parturition (g)
Final litter weight at PND 4 (g)
Final average pup weight at PND 4 (g)

Total number of implants
Corpora counts

Postmortem examinations (parental animals):

Clinical pathology assessments (hematology and serum chemistry) and macroscopic and microscopic examinations (including organ weights) were also performed on the appropriate groups of adult males and toxicity phase females. 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.

Postmortem examinations (offspring):

Intact offspring dying from PND 0 to 4 were necropsied. Cannibalized pups were discarded without necropsy. Tissues were preserved in 10% neutral-buffered formalin for possible future histopathologic examination only as deemed necessary by gross findings. The carcass of each pup was then discarded.

Statistics:

Reproductive parameters with the exception of litter size were analyzed using an ANCOVA (Analysis of Covariance) with liter size as the covariate. Litter size was analyzed using an ANOVA.

Reproductive indices:

Male (Female) Mating Index (%)
Male Fertility Index (%)
Male Copulation Index (%)
Female Fertility Index (%)
Female Conception Index (%)

Offspring viability 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: P0 (first parental generation)

General toxicity (P0)

Clinical signs:

effects observed, treatment-related

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Reproductive function / performance (P0)

Reproductive performance:

no effects observed

Details on results (P0)

"Mortality and day of death:         None.
"Number pregnant per dose level:  10
"Number aborting:  0 "Number of resorptions, early/late if available:  None detected.
"Number of implantations: Group Mean (standard deviation):  Control:  15 (2.2);    50 mg/kg: 16 (2.0);    250 mg/kg: 16 (1.4);  1000 mg/kg: 16 (1.9) 
"Number of corpora lutea: Group Mean (standard deviation): Control: 19(4.7); 50 mg/kg: 19(3.1); 250 mg/kg:18(2.0); 1000 mg/kg:  17(3.9)
"Duration of Pregnancy:  Group Mean (standard deviation):        Control: 21  (0.5); 50 mg/kg: 21(0.5); 250 mg/kg: 22(0.5);   1000 mg/kg: 22(0.5)
"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.
"Description, severity, time of onset and duration of clinical signs:  Thirty percent of the animals in the 50 m/kg/day dose group and 100 % of the animals in the 250 and 1000 mg/kg/day dose groups exhibited a transient period of salivation and/or  abnormal inactivity at least once over the course of treatment  immediately after dosing.
"Gross pathology incidence and severity:  Gross pathology of the  reproductive/developmental group animals was not an endpoint for this study.
"Organ weight changes, particularly effects on total uterine weight:   Organ weight was not assessed in the reproductive/developmental group animals.
"Histopathology incidence and severity:  Histopathology was not assessed in the reproductive/developmental group animals. No treatment-related effects were observed in any of the reproductive parameters evaluated. All females bred successfully and delivered live litters. 

There were no treatment-related effects apparent for any of the reproductive endpoints. All females bred successfully and delivered live litters. Litter sizes were comparable for all groups. Differences in group mean values for the treated groups relative to the control group were small and none were found to be statistically significant.

Effect levels (P0)

Dose descriptor:

NOAEL

Effect level:

>= 1 000 mg/kg bw/day

Results: F1 generation

General toxicity (F1)

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

no effects observed

Gross pathological findings:

no effects observed

Details on results (F1)

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 (F1)

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

>= 1 000 mg/kg bw/day

Overall reproductive toxicity

Reproductive effects observed:

not specified

Any other information on results incl. tables

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

NOAEL (NOEL) (maternal toxicity): 1000 mg/kg/day
NOAEL (NOEL) (reproductive toxicity): 1000 mg/kg/day
LOAEL (LOEL):        N/A

Applicant's summary and conclusion

Conclusions:

No data on the reproductive toxicity of trichloro(methyl)silane are available, therefore data on methyltrimethoxysilane have been read-across. The basis for this read-across is that trichloro(methyl)silane and methyltrimethoxysilane are both rapidly hydrolysed to methylsilanetriol. Exposure to methyltrimethoxysilane was not associated with reproductive toxicity. The findings support a NOAEL of at least 1000 mg/kg bw/day. However, since trichloro(methyl)silane is corrosive, additional local effects can be expected for this substance.