Registration Dossier

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Please be aware that this old REACH registration data factsheet is no longer maintained; it remains frozen as of 19th May 2023.

The new ECHA CHEM database has been released by ECHA, and it now contains all REACH registration data. There are more details on the transition of ECHA's published data to ECHA CHEM here.

Diss Factsheets

Administrative data

Description of key information

In the key Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test with trimethoxy(methyl)silane, conducted according to OECD Test Guideline 422 and in compliance with GLP, the NOAEL for systemic effects was concluded to be 50 mg/kg bw/day based on organ weight and/or histomorphological changes in males (liver, thymus, thyroid, duodenum, jejunum, and red blood cell) and females (liver, thyroid, duodenum, jejunum, and adrenal gland) at dose levels at or above 250 mg/kg bw/day. In addition, a marked increase in prothrombin time was observed for males at 250 and 1000 mg/kg bw/day whereas females were unaffected, and exposure was associated with increased blood platelet concentration for males and females at 1000 mg/kg bw/day (Dow Corning Corporation, 2005).

In the key 90-day inhalation repeated dose toxicity study, conducted according to OECD Test Guideline 413 and in compliance with GLP, the NOAEL for systemic effects for trimethoxy(methyl)silane vapor administered six hours per day, five days per week via whole-body inhalation exposure to male and female Sprague-Dawley rats, was 100 ppm (equivalent to 0.56 mg/L) based on the increased incidence of grossly observed urinary bladder calculi along with the kidney dilation at the 400 ppm exposure level (Dow Corning Corporation, 2008).

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records
Reference
Endpoint:
short-term repeated dose toxicity: oral
Type of information:
experimental study
Adequacy of study:
key study
Study period:
19.11.2003 to 19.05.2005
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)
Qualifier:
according to guideline
Guideline:
other: USEPA OPPTS 870.3650
GLP compliance:
yes
Limit test:
no
Species:
rat
Strain:
other: Crl:CD(SD)
Sex:
male/female
Details on test animals or test system and environmental conditions:
TEST ANIMALS
- Source: No data
- Age at study initiation: Nine weeks
- Weight at study initiation: Males: 294.2-351.5; Females: 200.2-260.2 g
- Fasting period before study: None
- Housing: individually housed in suspended wire-mesh cages (pregnant rats in shoebox cages)
- Diet (e.g. ad libitum): Ad libitum (except during FOB)
- Water (e.g. ad libitum): Ad libitum (except during FOB)
- Acclimation period: Six days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20.2-22.5
- Humidity (%): 36.0-62.0
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 09.02.2004 To: 19.04.2005
Route of administration:
oral: gavage
Vehicle:
corn oil
Details on oral exposure:
PREPARATION OF DOSING SOLUTIONS: Conducted over nitrogen atmopshere. Test substance was placed into a volumetric flask and corn oil added to achieve the desired volume. The weight of the test substance added to the flask was used to calculate nominal dose solution concentrations. Dosing solutions were prepared at least once every two weeks consistent with the previously determined 15-day stability. The concentration, homogeneity and stability of the test substance in vehicle for at least 15 days.

VEHICLE
- Justification for use and choice of vehicle (if other than water): No data
- Concentration in vehicle: Various
- Amount of vehicle (if gavage): Up to 3 ml/kg
- Lot/batch no. (if required): 122K0131
- Purity: Considered 100%
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.
Duration of treatment / exposure:
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, seven days/week
Dose / conc.:
0 mg/kg bw/day (actual dose received)
Remarks:
Corn oil
Dose / conc.:
50 mg/kg bw/day (actual dose received)
Dose / conc.:
250 mg/kg bw/day (actual dose received)
Dose / conc.:
1 000 mg/kg bw/day (actual dose received)
No. of animals per sex per dose:
10
Control animals:
yes, concurrent vehicle
Details on study design:
- Dose selection rationale: Based on a range-finding study
- Rationale for animal assignment (if not random): Weight stratified randomisation process
- Rationale for selecting satellite groups: According to OECD TG 422
- Post-exposure recovery period in satellite groups: None
Observations and examinations performed and frequency:
Mortality/Morbidity: Animals were observed at least twice daily in their cages for moribundity and mortality throughout the in-life phase of the study.

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.

FOOD EFFICIENCY:
- Body weight gain in kg/food consumption in kg per unit time X 100 calculated as time-weighted averages from the consumption and body weight gain data: No

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: On day of scheduled termination.
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: Yes
- How many animals: Males and toxicity phase females
- Parameters checked in table 1 were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: On day of scheduled termination
- Animals fasted: Yes
- How many animals: Males and toxicity phase females
- Parameters checked in table 1 were examined.

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: prior to the start of dosing and during the  last week of dosing. 
- Dose groups that were examined: adult males and  all toxicity group females
- Battery of functions tested: Unusual body movements, abnormal behaviour and/or posture, and resistence to removal, palperal closure, lacrimation, pupil size, pupil reactivity, salivation, muscle tone, extensor thrust response, reactivity to handling, level of ambulatory activity including rearing, responsiveness to sharp noise, touch, tail pinch, gait evaluation and quantity of urine and fecal pellets voided, behavior, skin or hair coat, respiration, muscle movements, eyes, urine or feces, soiling, general abnormalities and posture, rectal temperature, hindlimb/forelimb grip strength and landing foot splay. Motor activity assessment involved obtaining baseline motor activity data prior to the first dose administration to assist in evaluating potential treatment-related effects by allowing each rat to act as its own control.
Sacrifice and pathology:
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.  Complete necropsies were performed on the males and the toxicity group females and selected organs were weighed (adrenals, brain, heart, kidneys, liver, lungs, spleen, thymus, uterus, ovaries, testes, prostate, seminal vesicles, and epididymides). Microscopic examination was performed on protocol-specified tissues from all animals in the control and high dose group males and toxicity group females. Microscopic examination of the liver, thyroid, jejunum and duodenum was extended to males and toxicity group females in the 50 and 250 mg/kg dose groups. In addition, the adrenal gland from these middle dose groups was evaluated for the toxicity group females.
Statistics:
All data analyses were carried out using SAS version 8.2. Statistically significant probabilities were reported for /-values of <0.05, <0.02 and <0.01.

Body weight, body weight changes, organ weight, organ to body weight ratios, food consumption, hematology data, clinical chemistry and prothrombin times were analyzed using a one-way Analysis of Variance (ANOVA) if the data satisfied the requirements of normality of the residuals and homogeneity of variance as determined using the Shapiro-Wilk test for normality and Levene’s test for homogeneity of variance. If the data did not satisfy the parametric requirements, a Kruskal-Wallis test was used. If the ANOVA or Kruskal-Wallis test was significant, pair-wise comparisons of the dosed groups to control were made using the Dunnett’s Test or a Wilcoxon test, respectively.

The red blood morphology findings in the hematology data that were reported by severity grade; polychromasia, anisocytes, poikilocytosis, and ananthocytes were analyzed using a Cochran-Armitage trend test to indicate an increasing incidence trend regardless of grade with Fisher’s Exact tests used to indicate increased incidence (non-grade specific) over the control. To determine shifts in severity, analysis using the Kruskal-Wallis test was performed on the graded data only if there was at least once incidence of severity grade seen in the controls group. If the overall Kruskall-Wallis test was significant, pair wise comparisons of the graded animals between the control and treated groups was done using the Kruskal-Wallis.

Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
Clinical signs included transient inactivity or salivation following dosing.
Mortality:
mortality observed, treatment-related
Description (incidence):
There were two unscheduled deaths (one female each at 0 and 50 mg/kg  bw/day); both were related to dosing errors.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
Statistically significant decreases in body weight gain were noted for 1000 mg/kg bw/day group males. 
Food consumption and compound intake (if feeding study):
effects observed, treatment-related
Description (incidence and severity):
Statistically significant decreases in food consumption were noted for 1000 mg/kg bw/day group males. 
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
effects observed, treatment-related
Description (incidence and severity):
A marked increase in prothrombin time was observed for males at 250 and 1000 mg/kg bw/day whereas females were unaffected. Exposure was also associated with increased blood platelet concentration for males and females, and increased red blood cell concentration in males at 1000 mg/kg bw/day.
Clinical biochemistry findings:
no effects observed
Urinalysis findings:
not examined
Behaviour (functional findings):
no effects observed
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
Increased liver weight was observed for male and female animals at 250 and 1000 mg/kg bw/day.
Gross pathological findings:
no effects observed
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Exposure to MTMS was associated with histomorphological changes in males (liver, thymus, thyroid, duodenum, jejunum) and females (liver, thyroid, duodenum, jejunum, and adrenal gland) at dose levels at or above 250 mg/kg bw/day. 
Histopathological findings: neoplastic:
not examined
Key result
Dose descriptor:
NOAEL
Effect level:
50 mg/kg bw/day (nominal)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
histopathology: non-neoplastic
organ weights and organ / body weight ratios
Key result
Critical effects observed:
yes
Lowest effective dose / conc.:
250 mg/kg bw/day (actual dose received)
System:
other: hepatobiliary; gastrointestinal; endocrine; immune system
Organ:
adrenal glands
duodenum
jejunum
liver
thymus
thyroid gland
Treatment related:
yes
Dose response relationship:
yes
Relevant for humans:
not specified

Toxic Response/Effects by Dose Level:

50 mg/kg bw/day Methyltrimethoxysilane:
Males: None
Females:  None

250 mg/kg bw/day Methyltrimethoxysilane:
Males: 
Increased liver weight (absolute(relative): 19%* (25%*)
Thyroid gland follicular cell hyperplasia/hypertrophy: (incidence 6*/10)
Decreased thymus weight (absolute(relative): 28%*(24%*)
Increased prothrombin time: 2-fold*

Females:
Increased liver weight (absolute(relative): 37%* (41%*)
Centrilobular hepatocellular hypertrophy (incidence 5*/10)
Periportal vacuolation (incidence 10*/10)
Thyroid gland follicular cell hyperplasia/hypertrophy:
(incidence 10*/10)

1000 mg/kg bw/day Methyltrimethoxysilane:
Males:  
Increased liver weight (absolute(relative): 33%* (47%*) 
Diffuse hepatocellular hypertrophy (incidence 10*/10)
Thyroid gland follicular cell hyperplasia/hypertrophy: (incidence 10*/10)
Mucosal lipidosis: duodenum  (incidence 4*/10)
Mucosal lipidosis: jejunum (incidence 7*/10)
Decreased thymus weight (absolute(relative): 35%*(29%*)
Ancanthocytosis (incidence 5*/10)
Increased red blood cell concentration: 16%*
Increased prothrombin time: 2-fold*
Increased serum alanine aminotransferase (48%*)
Increased blood platelet concentration: 16*

Females (Toxicity Phase):
Increased liver weight (absolute(relative)): 197%* (200%*)
Centrilobular hepatocellular hypertrophy (incidence 10*/10)
Periportal vacuolation (incidence 8*/10)
Thyroid gland follicular cell hyperplasia/hypertrophy:(incidence 10*/10)
Adrenal gland hyperplasia/hypertrophy (incidence 10*/10)
Adrenal gland apoptosis (incidence 9*/10)
Adrenal gland lymphocytic infiltration: zona reticularis:(incidence 5*/10)
Mucosal lipidosis: duodenum  (incidence 5*/10)
Mucosal lipidosis: jejunum (incidence 5*/10)

Ancanthocytosis (incidence 4*/10)

Increased blood platelet concentration: 21%*

Where "*" denotes statistically different from control (p<0.05)

Conclusions:
In the key Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test with trimethoxy(methyl)silane, conducted according to OECD Test Guideline 422 and in compliance with GLP, the NOAEL for systemic effects was concluded to be 50 mg/kg bw/day based on organ weight and/or histomorphological changes in males (liver, thymus, thyroid, duodenum, jejunum, and red blood cell) and females (liver, thyroid, duodenum, jejunum, and adrenal gland) at dose levels at or above 250 mg/kg bw/day. In addition, a marked increase in prothrombin time was observed for males at 250 and 1000 mg/kg bw/day whereas females were unaffected, and exposure was associated with increased blood platelet concentration for males and females at 1000 mg/kg bw/day.
Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEL
50 mg/kg bw/day
Study duration:
subacute
Species:
rat
System:
other: hepatobiliary; gastrointestinal; endocrine; immune system
Organ:
adrenal glands
duodenum
jejunum
liver
thymus

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records
Reference
Endpoint:
sub-chronic toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2007
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)
GLP compliance:
yes
Limit test:
no
Species:
rat
Strain:
other: Crl: CD® (SD) IGS BR VAF/Plus®
Sex:
male/female
Details on test animals or test system and environmental conditions:
Seventy-eight female and seventy-eight male rats were obtained from Charles River Laboratories, Kingston, NY. Animals were 10 weeks old at experimental start.
Animal Receipt and Quarantine/Acclimation: Upon receipt, animal resource personnel inspected each animal. Animals judged to be in good health and suitable as test animals were quarantined/acclimated for a minimum of five days. The attending veterinarian examined all animals before release from quarantine/acclimation and documented the general state of animal health.
Animal Housing: Animals were individually housed in suspended wire-mesh cages during the course of the study. The cages were elevated above Bed-O’Cobs bedding and subjected to routine cleaning consistent with good housekeeping practices. Prior to exposure, animals were acclimated according to the following schedule:
Three days prior to exposure: Animals were placed in the exposure caging for 2.8 – 3.0 hours.
Two days prior to exposure: Animals were placed in the exposure caging for 6.0 hours.
One day prior to exposure: Animals were placed in the exposure caging for 6.0 – 6.1 hours in the inhalation chambers.
Following each exposure, the test article treated animals were housed in a separate animal room from the control animals.

Environmental Enrichment: Animals were given Gnaw PucksTM and Cozee PadsTM in their home cages for environmental enrichment.

Environmental Conditions: Animals were housed in environmentally controlled animal rooms. With the exception of the deviations noted in Table 13 environmental conditions were within 18 – 26°C for temperature, 30 – 70% relative humidity, and 10 – 15 air changes per hour. Lighting was controlled to provide a 12-hour fluorescent-light/dark cycle. Temperature and humidity were recorded approximately every fifteen minutes using a HOBO® data logger (Onset Computer, Bourne, MA; software: BoxCar® Pro 4.3.1.1.). In addition, twice a day on weekdays and once a day during weekends and holidays these values were manually recorded.

Basal Diet: Certified Rodent Diet #5002, PMI Nutritional International Inc., St. Louis, MO, was offered ad libitum except while animals were in the inhalation exposure cages and during the fasting period prior to terminal sacrifice. Manufacturer’s periodic analyses of the certified feed for the presence of heavy metals and pesticides was reviewed by the study director to ensure that none are present in concentrations that would be expected to affect the outcome of the study.

Drinking Water: Municipal water, further purified by reverse osmosis (RO) was available ad libitum except while animals were in the inhalation exposure cages. Water collected from the RO system was monitored on a semi-annual basis to determine compliance with the EPA drinking water standards. The most recent analysis was reviewed by the study director to ensure that there were no contaminants known to be present in water, at levels expected to interfere with the integrity of the study.
Route of administration:
inhalation
Type of inhalation exposure:
whole body
Vehicle:
other: unchanged (no vehicle)
Details on inhalation exposure:
Vapour Generation: Generation of test article vapor was performed using heated stainless steel J-tubes containing stainless steel beads. Test article was metered from reservoirs into J-tubes using either a Fluid Metering Incorporated (FMI®) pump or a Harvard model syringe pump equipped with Hamilton brand glass syringes. Compressed air flowed through the J-tube at a predetermined controlled rate. The carrier/vapour mixture passed from the J-tube directed to the inlet port at the top of the exposure chamber. Just prior to entering the exposure chamber, the carrier/vapour mixture was combined with chamber supply (dilution) air where it was diluted to the target chamber concentration as it entered the exposure chamber.

Inhalation Chambers: Exposures were conducted in 2000-liter stainless steel and glass Rochester-style inhalation chambers and stainless steel exposure caging (four layers of 20 animal compartments). The animal cage position assignment within each chamber was rotated daily. Chamber temperature, relative humidity, and airflow were monitored and recorded during the acclimation period similar to that anticipated for the exposure periods. Vapor generation systems were not in operation during acclimation. The chambers were targeted for 12 – 15 chamber volume air changes per hour and environmental conditions of 20 ± 3°C and 50 ± 20%RH. Chamber airflow, temperature and relative humidity were monitored continuously and values recorded approximately once every 30 minutes during exposures. Chamber oxygen content was monitored, and manually recorded, once during the first day of exposure to ensure that under applied experimental conditions the oxygen content was above the minimum 19% acceptable limit.
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Test Atmosphere Monitoring: The test atmosphere from each chamber was sampled by an automated sampling system. The system was designed such that test atmosphere was continuously pulled from the chamber and delivered to the analyzer through individual chamber sample lines and a stream selector valve. The sample lines were continuously purged with fresh chamber atmosphere during the entire exposure period.
Chamber atmosphere was analyzed using a gas chromatograph equipped with a flame ionization detector (GC/FID) to determine the actual chamber concentration of test article. In addition, given the potential hydrolysis of methyltrimethoxysilane in humid air, the methyl alcohol concentration within each chamber was also determined. The concentration of test article in the chamber atmosphere during the exposure period was evaluated a minimum of once every 60 minutes. Methyl alcohol (a known hydrolysis product of methyltrimethoxysilane) concentrations were measured from each exposure chamber a minimum of seven times during each day’s exposure period. A continuously purged sample line was used to transfer chamber atmosphere to the GC/FID for analysis.
The GC/FID methods were established prior to the experimental start date. Standard curves relating test article vapor concentration and methanol concentration to GC/FID response were established before the first exposure and then again as necessary. Preparation of calibration curves involved bag standards at five different levels that bracketed the expected range of test article or methyl alcohol chamber concentrations. The peak area attributed to the test article or methyl alcohol was plotted against the nominal bag standard concentration. Linear regression analysis of these data was performed to define the parameters of the calibration curve. Acceptance criteria for the GC/FID calibration curve included linear regression correlation coefficient of > 0.98 and < 10% difference between the prepared bag standard concentration and the calculated bag standard concentration derived from the linear regression equation of the calibration curve.
Each calibration curve was verified prior to the exposure period by analysis of a bag standard. The bag standard actual concentration derived from the calibration curve needed to be within 10% of the bag standard nominal concentration for the calibration curve to be considered acceptable for use.
The mean daily actual measured methyltrimethoxysilane vapor concentration was compared with the daily-calculated nominal concentration as a quality control mechanism to evaluate exposure system performance. A difference of ≤15% was considered acceptable for the 25 ppm targeted exposure level, and ≤10% at all other target levels.
Homogeneity of test atmosphere within each chamber was evaluated once prior to initiation of animal exposures. Acceptance criteria required the mean values for each chamber zone not exceed 10% difference from the reference zone (approximate sampling location used during animal exposures).
The stability of methyltrimethoxysilane vapor in a gas bag and sample line loss was evaluated using prepared bag standards. Stability was considered acceptable over the time the measured concentration did not exceed 10% difference from the original concentration measured immediately following preparation.
Exposure chambers were leak tested prior to the first exposure to ensure proper operation. Acceptance criteria required that the mean chamber airflow measured at the inlet not be more than 10% different from the airflow measured on the exhaust side.
Duration of treatment / exposure:
Exposure levels and treatment regimen: Test article was administered by whole-body vapour inhalation. Animals were positioned in the chambers and the exposure period was defined as a 6-hr/day exposure at the target concentration. Animals were removed from the chambers after a second T99 had expired. The T99 period was considered as the time required for the chamber to reach 99% of the target concentration or clearance of 99% of the achieved concentration following generation of test article. Based on chamber flow rate and size, the T99 period was calculated to be 23 minutes for all chambers. For practical purposes, the T99 2 minutes was used for this study.
The target exposure levels were: 0, 25, 100, 400 and 1600 ppm trimethoxy(methyl)silane in air. These exposure levels were determined based on results from a previously conducted 14-day range finding study (Dow Corning Corporation, 2007). Exposures were conducted at approximately the same time each day, five days per week over the course of thirteen weeks.
Frequency of treatment:
6 hours/day, 5 days/week at target concentrations
Dose / conc.:
0 mg/L air (analytical)
Remarks:
Control group
Dose / conc.:
0.14 mg/L air (analytical)
Remarks:
equivalent to 25 ppm
Dose / conc.:
0.56 mg/L air (analytical)
Remarks:
equivalent to 100 ppm
Dose / conc.:
2.2 mg/L air (analytical)
Remarks:
equivalent to 400 ppm
Dose / conc.:
8.9 mg/L air (analytical)
Remarks:
equivalent to 1600 ppm
No. of animals per sex per dose:
10/sex/dose level plus and additional 10/sex/control and high dose groups for a 28-day recovery period
Control animals:
yes, concurrent vehicle
Details on study design:
This study was conducted following the general principals of the OECD Guidelines for Testing Chemicals, “Subchronic Inhalation Toxicity 90-Day Study”, No. 413, adopted May 12, 1981. The study was conducted to evaluate the toxic effects of, and subsequent recovery from, whole-body vapor inhalation exposure of methyltrimethoxysilane. Five (5) groups of 10 male and 10 female Sprague-Dawley rats were exposed to target methyltrimethoxysilane exposure concentrations of 0 (control), 25, 100, 400 and 1600 ppm, 5 days per week for thirteen weeks. Additional satellite groups of 10 males and 10 females were included in the 0 and 1600 ppm target groups for evaluation of a 28-day post exposure recovery period. Exposures terminated on study 90 with non-recovery animals euthanized on study day 91. Recovery group animals remained for 28-days post exposure and were euthanized on study day 119.
Observations and examinations performed and frequency:
Mortality/Morbidity/Moribundity: All animals were observed in their cages for mortality, morbidity, and moribundity at least twice daily on weekdays, and once daily during weekends and holidays.
Clinical Observations: General clinical observations were made at least once a day, beginning on the first day of exposure, at approximately the same time each day. The health condition of the animals was recorded. Clinical observations included, but were not limited to, changes in the skin, fur, eyes, and mucous membranes, respiratory system, circulatory system, autonomic and central nervous systems, motor activity, and behavior patterns. General clinical observations were performed on all animals on the day of, and prior to, their scheduled necropsy.

Parameters Measured
Individual Body Weights: Individual body weights were recorded for randomization, weekly throughout the duration of the study, then again prior to sacrifice on the day of scheduled termination.
Individual Food Consumption: Feeder weights were recorded weekly throughout the duration of the study.
Ophthalmic Examinations: Examinations were performed on all animals prior to group assignment. Animals with findings noted during this initial examination were not used on study. Additional examinations were conducted during the final week of exposure prior to 90-day terminal sacrifice, and during the final week of the 28-day post exposure recovery period. An indirect ophthalmoscope (following dilation using mydriatic eye drops) was used for all examinations.
Sacrifice and pathology:
Clinical Pathology: Food was removed from all animals on the evening prior to scheduled termination. Clinical pathology assessments were made on all surviving animals from which adequate samples were collected.
Blood samples were collected for hematological and clinical chemistry evaluations from all animals on the day of scheduled euthanasia as a terminal procedure. While under Isoflurane® anesthesia, a syringe and needle were used to collect blood samples from the abdominal vena cava and distributed to three sample collection tubes containing either sodium citrate, EDTA, or no anticoagulant.

Hematology: Blood samples for the following hematology tests were collected into test tubes containing EDTA. Hematology samples were analyzed within 24 hours of collection. Analysis was performed using the Cell-Dyn 3700TM (Abbott Diagnostics, Dallas, TX).
Erythrocyte count Hemoglobin
Erythrocyte Indices (MCV, MCH, MCHC) Hematocrit
Leukocyte counts (total and differential) Platelet count
Blood samples for coagulation assessment (prothrombin time) were placed into test tubes containing sodium citrate, centrifuged within two hours of collection and the plasma separated for testing. Samples were maintained at room temperature (18-24 oC) or refrigerated (2-8 oC) prior to analysis. Analysis was conducted within 24 hours of collection. Analysis was preformed using the ACL 100TM (Beckman Coulter, Fullerton, CA).

The following serum chemistries were determined:
Alanine aminotransferase Glucose
Albumin Phosphorus
Alkaline phosphate Potassium
Aspartate aminotransferase Sodium
Calcium Total bilirubin
Cholesterol Total protein
Chloride Urea nitrogen
Creatinine
Blood samples were placed into test tubes without anticoagulant, allowed to clot and centrifuged within two hours of collection and the serum separated for testing. For bilirubin and total protein analysis, the serum samples were frozen at  -20C, until analysis. Samples were analyzed using the Cobas Integra 400 plusTM (Roche Diagnostics, Indianapolis, IN).

Gross Pathology: All animals were subjected to a full gross necropsy which included examination of the external body surface, all orifices, as well as the cranial, thoracic and abdominal cavities including contents.

Histomorphology: Eyes were preserved in Davidson’s solution until processing with the testes and epididymides preserved in Bouin’s solution for 24 – 36 hours then transferred into 70% ethanol until processing. All other tissues were placed in 10% Neutral Buffered Formalin for preservation. Tissue processing included routine procedures including embedding in paraffin, sectioning and staining with hematoxylin and eosin for evaluation.
Histomorphological examination was conducted on all tissues collected from both the recovery and non-recovery animals in groups 1 and 5. Following initial review, additional selected tissues including urinary bladder, kidney, liver, lung and prostate were evaluated for groups 2, 3, and 4.
Other examinations:
The following organs were weighted: adrenals, kidneys, liver, lung, testes, ovaries, brain, epididymides, seminal vesicles and prostate.
Statistics:
Daily mean inhalation exposure concentrations and environmental conditions, along with standard deviations, were calculated using Microsoft Office Excel. Mean and standard deviation were calculated for body weights, changes in body weights, food consumption, organ weights, hematology and clinical chemistry values, using ProvantisTM, version 6.5. Environmental conditions of animal rooms were monitored and recorded using a HOBO® data logger (Onset Computer, Bourne, MA; software: BoxCar® Pro 4.3.1.1.)
All data analysis was carried out using SAS version 9.1.3. Statistically significant probabilities were reported for p-values of < 0.05, <0.02, and < 0.01.
Data from the recovery groups was analyzed separately from the 90 day groups. Body weight, changes in body weight, food consumption data, organ weight, organ to body weight ratios, hematology data, clinical chemistry and prothrombin times were analyzed using a one-way Analysis of Variance (ANOVA) if the data satisfied the requirements of normality of the residuals and homogeneity of variance as determined using the Shapiro-Wilk test for normality and Levene’s test for homogeneity of variance. If the data did not satisfy the parametric requirements, a Kruskal-Wallis test was used. If the ANOVA or Kruskal-Wallis test was significant, pair-wise comparisons of the exposed groups to control were made using the Dunnett’s Test or a Wilcoxon test, respectively.
For variables with multiple measurements across time (body weight and food consumption), a repeated measurements ANOVA was performed to determine if there was a time by exposure group interaction.
Clinical signs:
effects observed, treatment-related
Description (incidence and severity):
There were no test article-related changes in clinical pathology or serum chemistry. Test article-related clinical signs for the group 5 male included decreased activity, soiling around muzzle, abdomen and urogenital regions with gross pathological findings including dilation of kidneys and urinary bladder with calculus in bladder. Test article-related clinical signs reported for all surviving animals were limited to groups 4 and 5 and primarily included soiling of the urogenital and abdominal regions of both sexes.
Mortality:
mortality observed, treatment-related
Description (incidence):
Two animals were found dead (one group 4 male on study day 25; one group 5 male on study day 72) and one animal (control group male on study day 65) was sacrificed moribund prior to terminal sacrifice.
Body weight and weight changes:
effects observed, treatment-related
Description (incidence and severity):
Mean body weights trended lower than controls over the exposure period for group 5 males (~6%) and groups 4 and 5 females (~5%). Statistically significant decreases were noted during week one for group 3 and week two for group 5 only. A statistically significant decrease in mean body weight was measured in the group 5 recovery group females beginning exposure week four. This difference persisted through the completion of exposures and into week one of the post exposure recovery period. Although not statistically significant, body weights remained decreased from controls for males (~4%) and females (~6%) during the recovery period.
Food consumption and compound intake (if feeding study):
no effects observed
Description (incidence and severity):
here were no differences in food consumption for either sex, in any of the 90-day exposure groups. Weekly comparison of recovery group food consumption yielded statistical differences during weeks 6, 7, 8 and 10 for group 5 males and weeks 4 and 5 for group 5 females. Food consumption was similar to controls for both sexes in group 5 during each week of the 28-day post exposure period.
Food efficiency:
not examined
Ophthalmological findings:
no effects observed
Description (incidence and severity):
There were no test article-related ophthalmic finding at the end of the 90-day exposure period.
Haematological findings:
no effects observed
Description (incidence and severity):
There were no test article-related changes in clinical pathology.
Clinical biochemistry findings:
no effects observed
Description (incidence and severity):
There were no test article-related changes in serum chemistry.
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Immunological findings:
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Description (incidence and severity):
In females, absolute adrenal gland weights were statistically increased in group 4 (18%) and group 5 (25%). Relative to body weight, female adrenal glands were statistically increased (27%) for group 5. There was no histological correlate and the finding was not present in males or in recovery group females. In males, group 4 kidney weight was increased, but a comparable effect was not seen in group 5.
Also in males, the weights of testes and epididymides were statistically decreased in recovery group rats exposed to 1600 ppm. This finding correlated histologically with two recovery group males showing marked testicular seminiferous tubule degeneration and corresponding epididymal oligospermia (one unilateral, one bilateral). In regular study (90-day) rats, seminiferous tubule degeneration was observed only in one control and one low-exposure (25 ppm) rats. These findings were considered common spontaneous findings in young Sprague-Dawley rats and not test article-related.
Gross pathological findings:
effects observed, treatment-related
Description (incidence and severity):
Test article-related gross necropsy findings were primarily limited to the group 4 and 5 animals and included moderate dilation of the kidney, decreased soft testes, and calculi in the urinary bladder.
Neuropathological findings:
not examined
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Description (incidence and severity):
Histomorphologic changes included minimal to moderate urinary bladder hyperplasia and inflammation in all group 5 males and 9/10 females. Kidney changes were characterized by hyperplasia of the pelvic epithelium and/or granulomatous inflammation. The one group 5 male animal found dead on study day 72, demonstrated an apparent urinary obstruction possibly leading to acute uremia, with calcification of the aorta and pulmonary hemorrhagic edema as secondary effects. Additional changes included prostatic inflammation in moderate or severe degrees in two 1600 ppm exposure group 5 rats.
Following the 28-day recovery period, calculi were observed in the group 5 males only. Minimal to moderate hyperplasia of urinary bladder epithelium persisted in most rats, and exposure-related urinary bladder calculi were observed in several. Chronic or granulomatous inflammation in the renal pelvis was observed in several female rats. In male rats, there was no histomorphological evidence of a residual effect on the kidneys after the recovery period. In females, the incidence of pelvic epithelial hyperplasia and inflammation was modestly increased over controls. There were no indications of a residual effect on the prostate gland following the recovery period. No animals had more than mild inflammation of the prostate gland, and the incidence of inflammation was higher in control animals.
Histopathological findings: neoplastic:
no effects observed
Details on results:
Average measured methyltrimethoxysilane exposure concentrations included below the limit of quantitation (BLQ), 25 +/- 0.8, 99 +/- 3.2, 398 +/- 12.8, and 1612 +/- 35.6 ppm for groups 1 through 5, respectively. Calculated nominal concentrations included 23 +/- 0.4, 94 +/- 1.6, 383 +/- 10.4, and 1570 +/- 48.9 ppm for groups 2 through 5, respectively. Mean measured methyl alcohol concentrations were below the limit of calibration (8.7 ppm) for for all exposure groups except group 5 which was 19 +/- 3.7 ppm.
Key result
Dose descriptor:
NOAEC
Effect level:
0.56 mg/L air (analytical)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
body weight and weight gain
clinical signs
gross pathology
histopathology: non-neoplastic
mortality
organ weights and organ / body weight ratios
Dose descriptor:
LOAEL
Effect level:
2.2 mg/L air (analytical)
Based on:
test mat.
Sex:
male/female
Basis for effect level:
histopathology: non-neoplastic
Key result
Critical effects observed:
yes
Lowest effective dose / conc.:
2.2 mg/L air (analytical)
System:
urinary
Organ:
bladder
kidney
Treatment related:
yes
Dose response relationship:
yes
Relevant for humans:
not specified

Toxic Response/Effects by Dose Level:
25 ppm (ca. 0.14 mg/L):
No findings attributed to test article 

100 ppm (ca. 0.56 mg/L):
No findings attributed to test article 

400 ppm (ca. 2.2 mg/L): 
Clinical signs:
- Increased incidence of abdominal and urogenital soiling
Gross pathology:
- Calculi in the urinary bladder (2 males)
Histomorphologic changes: 
- Urinary bladder epithelial hyperplasia in males and females 
Organ weights: 
Female adrenal weight increase (absolute):  18%* 

1600  ppm (ca. 8.9 mg/L):
Clinical signs:
- Increased incidence of abdominal and urogenital soiling
Gross pathology:
- Calculi in urinary bladder of 4 males and 1 female, persisting through  28-day recovery
- Kidney dilation 

Organ weights:
Female adrenal weight increase (absolute/relative):  
Absolute:  25%*         Relative:  27%*

Female kidney weight increase (relative):
Relative:  12%* 

Absolute adrenal weights were significantly increased compared to  controls for group 4 (18%) and 5 (25%) females.  Adrenal and kidney to  

body weight ratios were also significantly increased compared to controls  for group 5 (27% and 12%, respectively) females.

Histomorphologic changes:
- Kidney:  hyperplasia of the pelvic epithelium and granulomatous  inflammation for males
- Urinary bladder:  epithelial hyperplasia in males and females
- Prostate:  slight increase in severity of inflammation 
* Statistically significant finding

"        Body weight:  absolute and percent gain was within normal limits for  all test groups
"        Food/water consumption:  within normal limits for all test groups
"        Description, severity, time of onset and duration of clinical signs:   The increased incidence of abdominal and urogenital soiling at the 400  

and 1600 ppm exposure levels was observed beginning on exposure day 11 and persisting on and off throughout the completion entire 90-day  

exposure duration..
"        Ophthalmologic findings incidence and severity:  No test article  attributed findings
"        Hematological findings incidence and severity:  No test article  attributed findings
"        Clinical biochemistry findings incidence and severity:  No test article  attributed findings
"        Mortality and time to death:  One (1) 400 ppm group 4 male on study day  25, One (1) 1600 ppm group 5 male on study day 72.
"        Gross pathology incidence and severity:  increased incidence of urinary  bladder calculi and dilation of the kidneys as described above.
"        Organ weight changes:  Kidney and adrenal glands related to treatment  as specified above.
"        Histopathology incidence and severity:  Urinary bladder epithelial  hyperplasia in both sexes at 400 and 1600 ppm and hyperplasia of the  

pelvic epithelium along with granulomatous inflammation for 1600 ppm male  kidneys.  Prostatic inflammation seen in all groups with a slight  

increase in severity at the 1600 ppm level.

Conclusions:
In the 90-day inhalation repeated dose toxicity study, conducted according to OECD Test Guideline 413 and in compliance with GLP, the NOAEL for systemic effects for trimethoxy(methyl)silane vapor administered six hours per day, five days per week via whole-body inhalation exposure to male and female Sprague-Dawley rats, was 100 ppm (equivalent to 0.56 mg/L) based on the increased incidence of grossly observed urinary bladder calculi along with the kidney dilation at the 400 ppm exposure level.
Endpoint conclusion
Endpoint conclusion:
adverse effect observed
Dose descriptor:
NOAEC
560 mg/m³
Study duration:
subchronic
Species:
rat
System:
urinary
Organ:
bladder
kidney

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion
Endpoint conclusion:
no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion
Endpoint conclusion:
no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

In the key Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test, conducted according to OECD Test Guideline 422 and in compliance with GLP (Dow Corning Corporation, 2005), trimethoxy(methyl)silane was administered by oral gavage to 10 male and 10 female rats per group at dose levels of 0, 50, 250 and 1000 mg/kg bw/day for at least 28 days. Clinical signs included transient inactivity or salivation following dosing. The dose levels were based on the results of a dose range-finding study (Dow Corning Corporation, 2004). There were two unscheduled deaths (one female each at 0 and 50 mg/kg bw/day); both were related to dosing errors. Statistically significant decreases in body weight gain and food consumption were noted for 1000 mg/kg bw/day group males. A marked increase in prothrombin time was observed for males at 250 and 1000 mg/kg bw/day whereas females were unaffected. Exposure was also associated with increased blood platelet concentration for males and females, and increased red blood cell concentration in males at 1000 mg/kg bw/day. Increased liver weight was observed for male and female animals at 250 and 1000 mg/kg bw/day. Histomorphological changes were observed in males in liver, thymus, thyroid, duodenum, jejunum and females in liver, thyroid, duodenum, jejunum, and adrenal gland at dose levels at or above 250 mg/kg bw/day. Based on the findings of this study, the NOAEL for systemic effects was concluded to be 50 mg/kg bw/day.

In the key 90-day inhalation repeated dose toxicity study, conducted according to OECD Test Guideline 413 and in compliance with GLP (Dow Corning Corporation, 2008), trimethoxy(methyl)silane vapor concentrations of 0, 0.14, 0.56, 2.2 and 8.9 mg/L (0, 25, 100, 400, 1600 ppm) were administered for six hours per day, five days per week via whole-body inhalation exposure to male and female Sprague-Dawley rats for 90 days, followed by a 28-day recovery period for control and high dose animals. The concentration levels were based on the results of a dose range-finding study (Dow Corning Corporation, 2007).

Test material-related clinical signs included decreased activity, soiling around muzzle, abdomen and urogenital regions with gross pathological findings including dilation of kidneys and urinary bladder with calculus in bladder. Test material-related clinical signs included soiling of the urogenital and abdominal regions of both sexes.

Mean body weights trended lower than controls over the exposure period for test animals. This difference persisted through the completion of exposures and into week one of the post exposure recovery period. There were no differences in food consumption for either sex, in any of the 90-day exposure groups.

Test material-related gross necropsy included moderate dilation of the kidney, decreased soft testes, and calculi in the urinary bladder. Histomorphologic changes included minimal to moderate urinary bladder hyperplasia and inflammation. Kidney changes were characterized by hyperplasia of the pelvic epithelium and/or granulomatous inflammation. One male animal found dead on study day 72, demonstrated an apparent urinary obstruction possibly leading to acute uraemia, with calcification of the aorta and pulmonary haemorrhagic edema as secondary effects. Additional changes included prostatic inflammation in moderate or severe degrees in two 1600 ppm exposure group rats.

Minimal to moderate hyperplasia of urinary bladder epithelium persisted in most rats, and exposure-related urinary bladder calculi were observed in several. Chronic or granulomatous inflammation in the renal pelvis was observed in several female rats. In male rats, there was no histomorphological evidence of a residual effect on the kidneys after the recovery period. In females, the incidence of pelvic epithelial hyperplasia and inflammation was modestly increased over controls. There were no indications of a residual effect on the prostate gland following the recovery period. No animals had more than mild inflammation of the prostate gland, and the incidence of inflammation was higher in control animals.

In females, absolute adrenal gland weights were statistically increased but without histological correlate and the finding was not present in males or in recovery group females. In males, increases in kidney weight were observed.

Also in males, the weights of testes and epididymides were statistically decreased in recovery group rats exposed to 1600 ppm. This finding correlated histologically with two recovery group males showing marked testicular seminiferous tubule degeneration and corresponding epididymal oligospermia (one unilateral, one bilateral). In regular study (90-day) rats, seminiferous tubule degeneration was observed only in one control and one low-exposure (25 ppm) rats. These findings were considered to be common spontaneous findings in young Sprague-Dawley rats and not test material-related. There were no test material-related changes in clinical pathology or serum chemistry.

Based on these findings, the NOAEL for systemic effects for trimethoxy(methyl)silane vapor administered six hours per day, five days per week via whole-body inhalation exposure to male and female Sprague-Dawley rats, was 100 ppm (equivalent to 0.56 mg/L).

The Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test with the structural analogue triethoxy(methyl)silane, conducted according to OECD Test Guideline 422 and in compliance with GLP (Bozo Research Center, 2012), has been included to the dossier to support the read-across approach used for developmental toxicity in first species.

Exposure to triethoxy(methyl)silane at doses of 0, 30, 150 and 750 mg/kg bw/day demonstrated histomorphological changes such as transitional epithelial cell hyperplasia in the kidney and urinary bladder of male rats and transitional epithelial cell hyperplasia in the urinary bladder in female rats observed in the 750 mg/kg bw dose group. In the 150 mg/kg bw/day dose group, hypertrophy of follicular cell in the thyroid of male rats and centrilobular hepatocyte hypertrophy in female rats were considered as an adaptive response caused by induction of drug metabolising enzymes. The NOAEL for systemic toxicity was determined to be 150 mg/kg bw/day based on transitional epithelial cell hyperplasia in the kidney and urinary bladder of male rats and transitional epithelial cell hyperplasia in the urinary bladder in female rats observed in the 750 mg/kg bw dose group.

 

Justification for classification or non-classification

Based on the available data, trimethoxy(methyl)silane does not require classification for target organ toxicity following repeated exposure according to Regulation (EC) No. 1272/2008.