Triethoxy(methyl)silane

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

OECD 422, oral, rat:

NOAEL reproduction: 750 mg/kg bw/day (highest dose tested)

Link to relevant study records

Reference

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

3 Oct 2011 - 28 Mar 2012

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Reason / purpose for cross-reference:

reference to same study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

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

Deviations:

yes

Remarks:

Dams with offspring and pups were terminated on Day 5 post-partum. Litter weights, anogenital distance and nipple retention were not measured. Thyroid hormones of pups were not assessed.

Qualifier:

according to guideline

Guideline:

other: Circular on Test Methods of New Chemical Substances (Japan)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Specific details on test material used for the study:

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: In the refrigerator
- Solubility and stability under test conditions: confirmed by IR at the end of the administration period
- Stability of the test substance in the solvent/vehicle: The test substance is stable for 8 days in the refrigerator and 24 hours at room temperature.

Species:

rat

Strain:

other: Crl:CD (SD)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories Japan, Inc., Atsugi, Japan
- Females nulliparous and non-pregnant: yes
- Age at study initiation: 10 weeks
- Weight at study initiation: 371 - 432 g (males), 223 - 274 g (females)
- Housing: individual animal in cage in steel cages before mating. During mating, one female and one male were in the same metal cage. From Day 17 in gestation period to Day 4 in the lactation period, one dam and its pups were in the plastic cage with white wood chip as bedding.
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): tap water ad libitum
- Acclimation period: 2 weeks

DETAILS OF FOOD AND WATER QUALITY:
- Diet: NMF food (Oriental Yeast Co., Ltd., Itabashi-ku, Japan) was provided ad libitum during the acclimation period and throughout the study. Food was removed the afternoon/evening prior to necropsy.
- Water: Quality of tap water was analysed quarterly.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 - 24
- Humidity (%): 40 - 56
- Air changes (per hr): 10 - 15
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 24 Oct To: 19 Dec 2011

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Each dosing formulation was prepared every 8 days. Stability of formulation was determined and stable for 8 days in the refrigerator and 24 hours at room temperature. Dosing solutions were prepared by adding the appropriate amount of the test article to a tared container and adding the appropriate amount of corn oil to yield the desired dose level. Dosing solutions were administered by oral gavage with a flexible stomach tube. The test article was administered at a dose volume of 5 mL/kg bw and was calculated from the most recent body weight. Until administration, stock solution was stored in a dark bottle and in a refrigerator (4 - 8°C).

VEHICLE
- Justification for use and choice of vehicle (if other than water): According to the preliminary test by using GC and IR due to the physical and chemical properties of the test substance, the test substance was stable in the corn oil.
- Concentration in vehicle: 6, 30 and 150 mg/mL
- Amount of vehicle (if gavage): 5 mL/kg b.w.

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: Study Day 15 up to Day 28
- Proof of pregnancy: Females rats were evaluated daily for evidence of copulation, by confirming the presence of either vaginal plug or sperm in vaginal smear referred to as Day 0 of pregnancy.
- After successful mating each pregnant female was caged (how): Day 0 of gestation was defined as the day where copulation was observed, at which time the female was individually caged.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analyses of the dosing formulations were conducted using GC to confirm the concentrations in all dose groups before and at the end of the administration period. The results of dose concentration analyses were determined to be 97.7 - 107.7%. These results were within the acceptable limits (100.0 ± 10.0% of nominal values).

Homogeneity of formulations was not determined.

Duration of treatment / exposure:

Males:
14 days before mating
14 days during mating
14 days after mating

Females:
14 days before mating
27 - 37 days during mating, gestation and lactation period

Males and females for recovery group:
42 days administration and 14 days post-exposure observation period

Frequency of treatment:

once daily, 7 days/week

Dose / conc.:

30 mg/kg bw/day (nominal)

Dose / conc.:

150 mg/kg bw/day (nominal)

Dose / conc.:

750 mg/kg bw/day (nominal)

No. of animals per sex per dose:

Male treatment group:
7 (control and 750 mg/kg bw/day)
12 (30 and 150 mg/kg bw/day)

Male recovery group:
5 (control and 750 mg/kg bw/day)

Female
12 (treatment group)
10 (recovery group)

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: dose levels were based on the results of a range-finding study, in which animals were orally exposed to 250, 500 and 1000 mg/kg bw/day for 14 days. No death occurred in all groups and effects on general clinical signs and body weight were not observed. Males exposed to 1000 mg/kg bw/day showed slightly decreased food consumption at the beginning of the study, decreased red blood cell count, haemoglobin and haematocrit, increased platelet and total protein, increased liver and thyroid weight and decreased testis weight. Males exposed to 500 mg/kg bw/day showed increased total protein and liver weight. Male 250 mg/kg bw/day group showed increased liver weight. Females exposed to 1000 mg/kg bw/day group showed decreased food consumption during the administration period, increased total protein, increased liver, thyroid and ovary weight. Therefore, 30, 150 and 750 mg/kg bw/day were selected as the dose levels for the main study.
- Post-exposure recovery period in satellite groups: 14 days

Positive control:

Not performed

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: three times a day

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Males in the treatment and recovery group and females in the recovery group were obsereved once prior to exposure, once a week during the administration period and recovery period.
Females in the treatment group were observed once prior to the exposure, once a week during mating period, on gestation Days (GD) 1, 7, 14, and 20, and on Day 4 post-partum.

BODY WEIGHT: Yes
- Time schedule for examinations: Males in the treatment and recovery groups and females in the recover y group were weighed on Day 1, 8, 15, 22, 29, 36 and 42 during administration period, on Day 1, 8 and 14 during recovery period, and before termination.
Parental females were weighed on Day 1, 8 and 15 during administration period (non-pregnant animals on Day 22), on GD 0, 7, 14 and 20, on Day 0 and 4 post-partum, and before termination.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No

Oestrous cyclicity (parental animals):

Performed dduring the pre-mating period

Sperm parameters (parental animals):

Parameters examined in P male parental generations:
testis weight and epididymis weight

Litter observations:

STANDARDISATION OF LITTERS
- Performed on Day 4 postpartum: no

PARAMETERS EXAMINED
The following parameters were examined in F1 offspring:
number and sex of pups, stillbirths, live births, presence of gross anomalies, postnatal mortality, weight gain

GROSS EXAMINATION OF DEAD PUPS:
no

Postmortem examinations (parental animals):

SACRIFICE
- Male animals: All surviving animals at the end of the administration or at the end of the observational period
- Maternal animals: All surviving animals were euthanised by isoflurane on post-partum Day 4.

GROSS NECROPSY
- Gross necropsy consisted of external and internal examinations including the cervical, thoracic, and abdominal viscera.

HISTOPATHOLOGY / ORGAN WEIGHTS
Tissues and organ taken for histopathological examination:
Adrenal, bone, bone marrow, femoral, cerebellum (pons), cerebrum, epididymis, eye, heart, duodenum, jejunum, ileum (Peyer's patch), cecum, colon, rectum, kidney, mesenteric and submandibular lymph nodes, liver, parathyroid, pancreas, pituitary, salivary gland submandibular, sciatic nerve, spleen, stomach, skeletal muscle, femoral, seminal vesicle (coagulating gland), spinal cord, thoracic, testis, thymus, trachea, thyroid, urinary bladder, ovary, uterus, vagina

The following organs were weighed:
Brain, pituitary, thyroids, thymus, heart, liver, spleen, kidneys, adrenals, ovaries, uterus, seminal vesicles, prostate, testis, epididymis,

Statistics:

Bartlett test, Dunnett's test, Steel test, F test, Student's t test, Aspin-Welch's t test, Fischer's test

Reproductive indices:

Copulation index, fertility index, gestation index, implantation index, and delivery index

Offspring viability indices:

Live birth index, viability index on postnatal Day 4, sex ration of total number of pups at birth, sex ration of live pups on Day 4

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

One male in the 750 mg/kg bw/day group died on Day 12 of administration. Before death, the male showed reddish urine and smudge of lower abdomen on Day 10, decreased spontaneous movement on Day 11, and prone/lateral position and pale skin on day 12. Reddish urine was also observed in one animal in the 750 mg/kg bw/day group on Week 1, 2 and 3.
One female in the 150 mg/kg bw/day treatment group died on Day 1 of the lactation period. However, there was no abnormal general condition reported.

Dermal irritation (if dermal study):

not examined

Mortality:

mortality observed, non-treatment-related

Description (incidence):

One male in the 750 mg/kg bw/day treatment group died on Day 12 of administration.
One female in the 150 mg/kg bw/day treatment group died on Day 1 post-partum.
All animals in the recovery groups survived the duration of the study.

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

no effects observed

Ophthalmological findings:

not examined

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

1) At the end of administration period
Males in the 750 mg/kg bw/day treatment group showed increased platelet numbers and fibrinogen value and prolonged prothrombin time and activated partial thromboplastin time (APTT). The mode of action is not clear but this can be caused by the test substance.
Females in the 750 mg/kg bw/day treatment group showed prolonged APTT, decreased relative and a bsolute neutrophil counts, and increased relative lymphocyte and eosinophil counts. The forementioned changes were considered as incidental due to the slight changes.
Females in the 750 mg/kg bw/day recovery group showed prolonged PT and APTT and increased MCV. Although the relative neutrophil counts were decreased, the absolute counts were not changed. This change was considered to be incidental.
No changes were found in the 30 and 150 mg/kg bw/day treatment group in comparison with the control group.

2) At the end of the recovery period
Males in the 750 mg/kg bw/day recovery group showed increased platelet. No changes were observed in females after recovery period in comparison with the control group.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

1) At the end of the administration period
Males in the 750 mg/kg bw/day treatment group showed increased γ-GTP, decreased total bilirubin, decreased potassium, increased calcium, increased total protein, and decreased A/G ratio. Decreased AST was not considered as toxicological effect. Total bilirubin was also decreased in male 150 mg/kg bw/day treatment group.
Females in the 750 mg/kg bw/day treatment group showed increased γ-GTP, decreased total bilirubin, increased BUN and decreased A/G ratio.
Females in the 750 mg/kg bw/day recovery group showed increased γ-GTP, increased total protein, and decreased A/G ratio. Decreased AST was not considered as toxicological effect.
No significant changes in clinical biochemistry parameters were observed in the 30 and 150 mg/kg bw/day treatment group compared to the control group.

2) At the end of the recovery period
Males in the 750 mg/kg bw/day recovery group showed decreased total bilirubin. Slight increased albumin was considered as the physiological variation because this change was not observed at the end of the administration period.
Females in the 750 mg/kg bw/day recovery group didn’t show the any differences as compared with the control group.

Urinalysis findings:

effects observed, non-treatment-related

Description (incidence and severity):

1) At the end of administration period
Yellow urine was observed in 5 males and 3 females in the 750 mg/kg bw/day tratment group.
Increased urine volume and decreased osmotic pressure were observed in male in the 150 mg/kg bw/day treatment group. These changes regarding urine volume and osmotic pressure were not dose-depending.

2) At the end of the recovery period
Potassium value was increased in males in the 750 mg/kg treatment group. This change was regarded to be incidental because it was only a slight change and no abnormality was found at the end of the administration.

Behaviour (functional findings):

effects observed, non-treatment-related

Description (incidence and severity):

1) During administration
Hearing was decreased in 30 mg/kg bw/day treatment group on Week 6 of administration. However, this change was not dose-depending. Since the dead male animal in the 750 mg/kg bw/day treatment group was not able to walk on Day 11 of administration, detailed clinical signs were not tested.
Females in the 750 mg/kg bw/day recovery group showed also decreased hearing in Week 1 of administration. This was regarded to be incidental because no changes were found afterward in this group and in females of the treatment group at the same time.

2) During recovery period
The increased hearing in females in the 750 mg/kg bw/day recovery group in Week 1 of recovery period was also regarded to be incidental because no change was observed at other time point and general condition was not abnormal.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Exposure of the test material to male and female rats resulted in effects being observed in the following organs: kidney, urinary bladder, liver, and thyroid. In the kidney, there were minimal tubular regeneration (4/6 males in the 750 mg/kg bw/day treatment group), eosinophilic body found in tubular cell (minimal 3/6, mild 1/6 males in the 750 mg/kg bw/day treatment group) and minimal transitional hyperplasia/hypertrophy observed (1/6 males in the 750 mg/kg bw/day treatment group). In the urinary bladder, there was transitional hyperplasia/hypertrophy seen (minimal 2/6 and moderate 1/6 males in the 750 mg/kg bw/day treatment group, minimal 3/12 females in the 750 mg/kg bw/day treatment group). The observed transitional hyperplasia/hypertrophy in male rats in the 30 mg/kg bw/day treatment group was concluded to be not treatment-related effects but instead caused by incidental inflammation of the urinary bladder. In the liver, there was centrilobular hepatocytic hypertrophy observed (minimal 3/6 males in the 750 mg/kg bw/day treatment group, minimal 9/11 and mild 2/12 females in the 750 mg/kg bw/day treatment group, minimal 4/9 females in the 150 mg/kg bw/day treatment group, and minimal 4/6 and mild 1/6 females in the 750 mg/kg bw/day recovery group). In the thyroids, there was hypertrophy in follicular cell (minimal 2/12 males in the 150 mg/kg bw/day treatment group, mild 6/6 males in the 750 mg/kg bw/day treatment group, minimal 10/12 and mild 1/12 females in the 750 mg/kg bw/day treatment group, and minimal 1/5 and mild 4/5 females in the 750 mg/kg bw/day recovery group). The effect observed in the liver is concluded to be associated with induction of drug metabolising enzyme. It is well known that a substance which induces drug metabolising enzyme also promotes metabolism of thyroid hormone and causes hypertrophy of follicular cell through the hypothalamus-hypophysis system as a secondary effect. Effects observed in the transitional epithelium of the kidneys were also noted in the urinary bladder. The mode of action causing this effect was not clear according to this test result. However, the effects on the transitional epithelium in the kidneys and urinary bladder were reversed by the end of the recovery period; these effects were therefore concluded to be reversible.

Histopathological findings: neoplastic:

no effects observed

Reproductive function: oestrous cycle:

no effects observed

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

no effects observed

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS)
There were no statistically significant differences between controls and treatment groups in the mean body weights on any of the test groups.
There were no differences in the average daily food consumption between controls and the males groups for any of the measured time periods. In the reproductive group females, at 30 and 750 mg/kg bw/day showed a significant increase (p< 0.05 and p<0.01, respectively) in food consumption compared to control at day 2 during the lactation period. But this change was not regarded as treatment related due to the lack of dose response.

REPRODUCTIVE FUNCTION: SPERM MEASURES (PARENTAL ANIMALS)
There was no statistically significant difference across treatment groups for sperm measures.

REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS)
There was no statistically significant difference across treatment groups for estrous cycle, mean days until copulation for males and females, copulation index, insemination index, fertility index, delivery index, gestation length in days, number of corpora lutea, number of implantation sites, implantation index, live birth index, and viability index on postnatal day 4.

ORGAN WEIGHTS (PARENTAL ANIMALS)
No remarkable changes were found in organ weights of reproductive organs in all treatment groups compared to the control group.

GROSS PATHOLOGY (PARENTAL ANIMALS)
No remarkable changes were found in reproductive organs in all treatment groups compared to the control group.

Dose descriptor:

NOAEL

Effect level:

750 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no reproductive toxicity observed

Critical effects observed:

not specified

Clinical signs:

no effects observed

Dermal irritation (if dermal study):

not examined

Mortality / viability:

no mortality observed

Description (incidence and severity):

There were no statistically significant differences between controls and treatment groups in live birth index, viability index on postnatal Day 4, sex ratio of delivered pups and liveborns, and sex ratio of live pups on Day 4.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

No significant difference was found in any treated groups from control group.

Food consumption and compound intake (if feeding study):

not examined

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Sexual maturation:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Description (incidence and severity):

There were no abnormal findings in male and female pups.
Although one pup had a vestigial tail in 30 mg/kg bw/day, this was considered as effect not associated with the test item.

Histopathological findings:

not examined

Behaviour (functional findings):

not examined

Developmental immunotoxicity:

not examined

VIABILITY (OFFSPRING)
There were no statistically significant differences between controls and treatment groups in live birth index, viability index on postnatal Day 4, sex ratio of delivered pups and liveborns, and sex ratio of live pups on Day 4.

BODY WEIGHT (OFFSPRING)
No significant difference was found in any treated groups from control group.

GROSS PATHOLOGICAL FINDINGS
There were no abnormal findings in male and female pups. Although one pup had a vestigial tail in 30 mg/kg bw/day, this was considered as effect not associated with the test item.

Key result

Dose descriptor:

NOAEL

Generation:

F1

Effect level:

750 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no reproductive toxicity observed

Critical effects observed:

no

Reproductive effects observed:

no

Table 2. Summary of mean reproductive parameters for reproductive group female rats

		Control (0 mg/kg bw/day)	30 mg/ kg bw/day	150 mg/ kg bw/day	750 mg/ kg bw/day
Corpora lutea counts	mean	16.6	16.8	16.2	16.8
	S.D.	1.8	2.0	2.4	2.7
	N	12	12	10	12
Total implants	mean	15.3	15.6	15.2	14.9
	S.D.	1.9	1.4	1.8	2.2
	N	12	12	10	12
Days gestation	mean	22.5	22.0	22.3	22.0
	S.D	0.5	0.3	0.5	0.3
	N	12	12	10	12
Total live pups day 0	mean	13.4	14.3	14.4	13.3
	S.D.	1.7	1.8	1.7	2.4
	N	12	12	10	12
Male pups	mean	6.8	7.0	7.2	6.6
	S.D.	2.4	1.5	2.1	2.2
	N	12	12	10	12
Female pups	mean	6.6	7.3	7.2	6.7
	S.D	2.1	1.9	2.1	2.8
	N	12	12	10	12
Delivered males/Delivered pups (%)	mean	0.50	0.49	0.51	0.51
	S.D	0.16	0.10	0.13	0.16
	N	12	12	10	12
Day 4 viable pups	mean	13.2	14.1	14.4	13.2
	S.D	1.7	1.6	1.7	2.4
	N	12	12	9 a)	12
Viable/total liveborns (%)	mean	98.2	99.1	99.3	99.4
	S.D.	3.3	3.2	2.2	1.9
	N	12	12	10	12
Initial Male Average Pup Weight (g) [Live Pups only]	mean	6.7	6.6	6.7	6.7
	S.D.	0.3	0.4	0.5	0.6
	N	12	12	10	12
Initial Female Average Pup Weight (g) [Live Pups only]	mean	6.3	6.2	6.3	6.4
	S.D.	0.6	0.4	0.4	0.5
	N	12	12	10	12
Final Average Male Pup (g)	mean	10.3	10.2	10.0	10.2
	S.D.	0.9	0.9	0.9	1.5
	N	12	12	9 a)	12
Final Average Female Pup (g)	mean	9.6	9.8	9.4	10.0
	S.D.	1.1	0.7	0.9	1.5
	N	12	12	9 a)	12

 

a)     One dam died on lactation Day 1

Conclusions:

Based on the results of this study, the NOAEL for reproductive toxicity was set at 750 mg/kg bw/day, the highest dose tested. No adverse effects on development of offspring were observed up to and including 750 mg/kg bw/day.

Effect on fertility: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

750 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

The study was carried out in accordance with an appropriate OECD test guideline and in compliance with GLP and is therefore considered to be reliability 1.

Effect on fertility: via inhalation route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

Studies were chosen as key when the available study was of relevance and sufficient quality for classification, labelling and risk assessment.

 

A key OECD 422 combined repeated dose/reproductive and developmental screening study is available by the oral route for triethoxy(methyl)silane. 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. Therefore, exposure to triethoxy(methyl)silane was not associated with reproductive toxicity and a NOAEL of 750 mg/kg bw/day was identified (METI, 2012).

 

Effects on developmental toxicity

Description of key information

OECD 414, oral, rat:

NOAEL developmental and maternal: 1000 mg/kg bw/day

OECD 422, oral, rat:

NOAEL developmental: 750 mg/kg bw/day (highest dose tested)

Link to relevant study records

Reference

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

August 2019 through November 2019

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 414 (Prenatal Developmental Toxicity Study)

Version / remarks:

25 June 2018

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Department of Health of the Government of the United Kingdom

Limit test:

no

Species:

rat

Strain:

other: Crl:CD(SD)

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River (UK) Ltd.
- Age at study initiation: 70 to 79 days old
- Weight at study initiation: 231 to 294 g
- Fasting period before study:
- Housing: Housed up to 4 animals per cage during acclimazation; housed one stock male and one female during mating; individually housed during gestation. Cages comprised of a polycarbonate body with a stainless steel mesh lid. Solid (polycarbonate) bottom cages were used during the acclimatization and gestation periods.
- Diet: SDS VRF1 Certified pelleted diet (manufactured in Witham, Essex, England), available ad libitum
- Water: Water from the public, available ad libitum
- Acclimation period: Six days before commencement of pairing

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24
- Humidity (%): 40-70
- Air changes (per hr): at least 15 air changes/hour
- Photoperiod (hrs dark / hrs light): 12 hours light : 12 hours dark

Route of administration:

oral: gavage

Vehicle:

other: Dried and de-acidified corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: The required amount of test item was added to the required volume of vehicle. The formulation was stirred using a magnetic stirrer under a fume hood until uniformly mixed and then transferred to final containers, via syringe, while magnetically stirring. A series of formulations at the required concentrations were prepared by dilution of individual weighing of the test item in ascending order of concentration.

VEHICLE
- Preparation of vehicle: 50% silica, 25% aluminum oxide neutral and 25% aluminum oxide activated acidic (40g, 20g and 20g respectively per liter of oil) were mixed. The dry mixture was placed in a vented oven set to 250 ºC overnight or for at least eight hours. The oil and dry materials were mixed in a suitable container, using a stir bar on a magnetic stirring plate, for at least two hours under a nitrogen purge and then allowed to dry to room temperature. The oil and dry materials mix was allowed to settle for a minimum of 30 minutes. The oil was filtered with 0.22 µm cellulose acetate filter system with vacuum to remove the alumina and silica.
- Amount of vehicle (if gavage): 4 mL/kg body weight.

Analytical verification of doses or concentrations:

yes

Remarks:

The mean concentrations of formulation samples taken from the first and last preparation were within 3% of the nominal concentration, confirming the accuracy of formulation. The difference from mean remained within 3%, confirming precise analysis.

Details on analytical verification of doses or concentrations:

Before commencement of treatment, the suitability of the proposed mixing procedures was determined and specimen formulations at 1 and 250 mg/mL were analyzed to assess the stability and homogeneity of the test item in the liquid matrix. Stability was confirmed as one day at ambient temperature (15 to 25 ºC) and fifteen days at refrigerated temperature (2 to 8 ºC).

Samples of each of the first and last preparation formulations were analyzed for achieved concentration of the test item.

Details on mating procedure:

- Impregnation procedure: cohoused
- M/F ratio per cage: 1:1
- Verification of same strain and source of both sexes: yes; a colony of stud males was maintained specifically for the purpose of mating; these animals were not part of the study and were maintained as stock animals.
- Proof of pregnancy: evidence of vaginal plug and sperm in vaginal smear referred to as day 0 of pregnancy

Duration of treatment / exposure:

From Day 6 to Day 19 (inclusive) after mating

Frequency of treatment:

Daily

Dose / conc.:

100 mg/kg bw/day (actual dose received)

Dose / conc.:

300 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:

20 females per dose

Control animals:

yes, concurrent no treatment

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Animals were inspected visually at least twice daily for evidence of ill-health or reaction to treatment. Cages were inspected daily for evidence of animal ill-health amongst the occupant(s).

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Detailed observations were recorded daily during the treatment period at the following times in relation to dose administration: pre-dose observation; one to two hours after completion of dosing; as late as possible in the working day. A detailed physical examination was performed on each animal on Days 0, 5, 12, 18 and 20 after mating to monitor general health.

BODY WEIGHT: Yes
- Time schedule for examinations: The weight of each adult was recorded on Days 0, 3 and 6-20 after mating.

FOOD CONSUMPTION: Yes
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 20
- Organs examined: See Table 1

OTHER: A thyroid hormone analysis was performed on all animals, which occurred as scheduled termination. Animals were no fasted. Samples were analyzed for serum thyroxine (T4) and triiodothyronine (T3) levels, as well as thyroid-stimulating hormone (TSH).

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes

Fetal examinations:

- External examinations: Yes: all per litter
- Soft tissue examinations: Yes: half per litter
- Skeletal examinations: Yes: half per litter
- Head examinations: Yes: half per litter

Statistics:

The following sequence of statistical tests was used for body weight, gravid uterus weight, food consumption, corpora lutea, implantations, pre/post implantation loss, live young, sex ratio - percentage male, placental, litter and fetal weights and organ weight data:

A parametric analysis was performed if Bartlett's test for variance homogeneity was not significant at the 1% level. For pre-treatment data, analysis of variance was used to test for any group differences. Where this was significant (p<0.05) inter group comparisons using t-tests, with the error mean square from the one-way analysis of variance, were made. For all other analyses the F1 approximate test was applied. If the F1 approximate test for monotonicity of dose-response was not significant at the 1% level, Williams' test for a monotonic trend was applied. If the F1 approximate test was significant, suggesting that the dose response was not monotone, Dunnett's test was performed instead.

A non-parametric analysis was performed if Bartlett's test was still significant at the 1% level following both logarithmic and square-root transformations. Forpre-treatment data, Kruskal-Wallis’ test was used to test for any group differences. Where this was significant (p<0.05) inter group comparisons using Wilcoxon rank sum tests were made. For all other analyses the H1 approximate test, the non-parametric equivalent of the F1 test described above, was applied. If the H1 approximate test for monotonicity of dose-response was not significant at the 1% level, Shirley's test for a monotonic trend was applied. If the H1 approximate test was significant, suggesting that the dose-response was not monotone, Steel's test was performed instead.

For organ weight data, analysis of covariance was performed using terminal body weight as covariate, unless non-parametric methods were applied.

Indices:

Pre-implantation loss (%) = ((Number of copora lutea - Number of implantations)/Number of corpora lutea) X 100
Post-implantation loss (%) = ((Number of copora lutea - Number of implantations)/Number of implantations) X 100

Historical control data:

Historical Control data was included and used for the evaluation of both fetal and litter incidences.

Clinical signs:

no effects observed

Dermal irritation (if dermal study):

not examined

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

effects observed, non-treatment-related

Description (incidence and severity):

At 1000 mg/kg bw/day group mean food consumption was slightly lower, and attained statistical significance, during Days 6-18 of gestation when compared with the group mean food consumption of the control group.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

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):

The mean gravid uterine weight for females treated with triethoxy(methyl)silane was comparable to the mean gravid uterine weight from the control females, as was adjusted body weight gain.

The weight of the liver was higher in females treated with 1000 mg/kg bw/day when compared with the controls (136% of the controls, respectively) and slightly higher in females receiving 300 mg/kg bw/day (109% of the controls, respectively). The weight of the thyroids and parathyroids were higher in females receiving 1000 mg/kg bw/day triethoxy(methyl)silane (129% of the controls, respectively). The weight changes stated above all attained statistical significance.

Gross pathological findings:

no effects observed

Neuropathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

In the thyroids, minimal/slight follicular cell hypertrophy was seen in all treated groups, with a clear relationship to dose. The hypertrophy was considered to account for the statistically significant higher than control group mean bodyweight adjusted thyroid weights for females that received 1000 mg/kg bw/day. This effect is likely secondary to the increase in TSH, which is a compensatory feedback mechanism to increase thyroid hormone production by the thyroid gland and part of a homeostatic response by the hypothalamic-pituitary-thyroid axis.

Histopathological findings: neoplastic:

not examined

Other effects:

effects observed, treatment-related

Description (incidence and severity):

The analysis of serum TSH concentrations performed at scheduled termination on Day 20 of gestation revealed that the TSH level at 1000 mg/kg bw/day was found to be statistically significantly higher compared to the control group at the 0.1% (p < 0.001) level.

There was a decrease in T4 and T3 concentration in females receiving 1000 mg/kg bw/day triethoxy(methyl)silane, both were found to be statistically significantly lower compared to the control group at the 0.1% (p < 0.001) level.

It was concluded that there was an effect of triethoxy(methyl)silane on serum T3, T4 and TSH concentrations in pregnant rats at a dose level of 1000 mg/kg bw/day, administered via oral gavage. It is possible that the change in TSH and thyroid hormones were secondary to liver enzyme induction and enhanced metabolism and clearance of thyroid hormones, which is consistent with increased liver weights.

Number of abortions:

no effects observed

Pre- and post-implantation loss:

no effects observed

Total litter losses by resorption:

no effects observed

Early or late resorptions:

no effects observed

Dead fetuses:

no effects observed

Changes in pregnancy duration:

no effects observed

Changes in number of pregnant:

no effects observed

Other effects:

not examined

Key result

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Basis for effect level:

other: No adverse effects observed

Key result

Abnormalities:

no effects observed

Fetal body weight changes:

no effects observed

Reduction in number of live offspring:

no effects observed

Changes in sex ratio:

no effects observed

Changes in litter size and weights:

no effects observed

Changes in postnatal survival:

no effects observed

External malformations:

no effects observed

Skeletal malformations:

effects observed, non-treatment-related

Description (incidence and severity):

At 1000 mg/kg bw/day there was a slight increase in incidence of cranial interparietal fissure(s) compared to concurrent control and was outside historical control data range. In isolation and at such low incidence this was not considered adverse.

Visceral malformations:

effects observed, non-treatment-related

Description (incidence and severity):

At 1000 and 300 mg/kg bw/day there was a slight increase in the incidence of partially undescended thymus compared to concurrent control but was within historical control data range and therefore considered unrelated to treatment. This is a transient stage in fetal development and therefore not considered adverse.

Other effects:

not examined

Key result

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no adverse effects observed

Key result

Abnormalities:

no effects observed

Key result

Developmental effects observed:

no

Conclusions:

Based on the results of this study, no adverse effects on development of offspring were observed up to and including 1000 mg/kg bw/day, the highest dose tested.

Effect on developmental toxicity: via oral route

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 000 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

The study was carried out in accordance with an appropriate OECD test guideline and in compliance with GLP and is therefore considered to be reliability 1.

Effect on developmental toxicity: via inhalation route

Endpoint conclusion:

no study available

Effect on developmental toxicity: via dermal route

Endpoint conclusion:

no study available

Additional information

An OECD 414 developmental toxicity study is available by the oral route for triethoxy(methyl)silane. Pregnant female Sprague-Dawley rats were treated with 100, 300 and 1000 mg/kg bw/day by oral gavage from gestation days 6 to 19. A control group received dried and de-acidified corn oil at the same volume dose as the treated groups. Animals were killed on gestation day 20 for reproductive assessment and fetal examination.

The clinical condition of females receiving 100, 300 or 1000 mg/kg bw/day triethoxy(methyl)silane was unaffected by treatment. The overall group mean body weight performance and overall gain (Day 6-20) of females treated with triethoxy(methyl)silane at 100, 300 or 1000 mg/kg bw/day was comparable to that of the control group. The mean gravid uterine weight for females treated with triethoxy(methyl)silane was comparable to the mean gravid uterine weight from the control females, as was adjusted body weight gain. The group mean food consumption of females treated with 100 or 300 mg/kg bw/day triethoxy(methyl)silane was generally similar to the controls during gestation Days 6-20. At 1000 mg/kg bw/day, mean food consumption was slightly and statistically significantly lower during Days 6-18 of gestation compared to the control group.
At macroscopic examination there were no adverse findings in the females related to treatment with triethoxy(methyl)silane. The weight of the liver was slightly higher in females receiving 300 mg/kg bw/day, and the weight of the liver and thyroids were higher in females receiving 1000 mg/kg bw/day triethoxy(methyl)silane, when compared with the control group, all attaining statistical significance. In the thyroids, minimal/slight follicular cell hypertrophy was seen in all treated groups, with a clear relationship to dose. The hypertrophy was considered to account for the statistically significant higher than control group mean bodyweight adjusted thyroid weights for females that received 1000 mg/kg bw/day. This effect is likely secondary to the increase in TSH, which is a compensatory feedback mechanism to increase thyroid hormone production by the thyroid gland and part of a homeostatic response by the hypothalamic-pituitary-thyroid axis.
At scheduled termination, serum samples taken for thyroxine (T4), triiodothyronine (T3) and thyroid stimulating hormone (TSH) revealed that the T4 and T3 concentrations were slightly lower and the TSH levels were higher, when compared with the controls in females receiving 1000 mg/kg bw/day. Statistical evaluation displayed significant difference between mean T3 and T4, and TSH concentration in samples from control females and females receiving 1000 mg/kg bw/day. It was concluded that there was an effect of triethoxy(methyl)silane on serum T3, T4 and TSH concentrations in pregnant rats at a dose level of 1000 mg/kg bw/day, administered via oral gavage. It is possible that the change in TSH and thyroid hormones were secondary to liver enzyme induction and enhanced metabolism and clearance of thyroid hormones, which is consistent with increased liver weights.
On Day 20 of gestation, all animals were found to be pregnant at macroscopic examination, with the mean number of corpora lutea, implantations, resorptions, the number of live young and sex ratio considered to be unaffected by treatment with triethoxy(methyl)silane. Group mean placental, litter and fetal weights were all considered to be unaffected by treatment with triethoxy(methyl)silane. There was no effect on the ano-genital distance of fetuses whose mother were treated with triethoxy(methyl)silane.
There were no major fetal abnormalities considered to be related to treatment. At 1000 mg/kg bw/day, there was a slight increase in the incidence of the minor finding cranial interparietal fissure(s) compared with concurrent control and outside the historical control data (HCD) range. In isolation and at such low incidence this was not considered adverse.
It was therefore concluded that the no observed adverse effect level (NOAEL) for maternal toxicity and embryo-fetal toxicity is 1000 mg/kg bw/day.

This result is supported by an OECD 422 combined repeated dose/reproductive and developmental screening study by the oral route for triethoxy(methyl)silane (METI 2012). There were no treatment-related effects apparent for any of the developmental endpoints and litter sizes were comparable for all groups. No gross abnormalities were found for any of the pups, with the exception of a single pup in the 30 mg/kg bw/day group which had a vestigial tail. Therefore, exposure to triethoxy (methyl) silane was not associated with developmental toxicity and a NOAEL of 750 mg/kg bw/day was identified.

Justification for classification or non-classification

The available data on reproduction and developmental toxicity do not meet the criteria for classification according to Regulation (EC) 1272/2008 and are therefore conclusive but not sufficient for classification of the registered substance.

No information is available on effects via lactation.