1,1,1,3,5,5,5-heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Effect on fertility: via oral route

Endpoint conclusion:

no study available

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Effects on developmental toxicity

Description of key information

In the prenatal developmental toxicity study, conducted according to OECD TG 414 and in compliance with GLP, the concluded NOAEL for maternal toxicity and developmental toxicity is greater than 1000 mg/kg bw/day. There were no adverse effects observed (Charles River, 2019).

Link to relevant study records

Reference

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

23 Oct 2018 to 28 Jan 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:

2018

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.3700 (Prenatal Developmental Toxicity Study)

Version / remarks:

1998

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Specific details on test material used for the study:

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: at room temperature
- Stability under test conditions: stable
- Solubility and stability of the test substance in the solvent/vehicle: soluble in dried and deacidified corn oil
- Reactivity of the test substance with the solvent/vehicle of the cell culture medium: n/a

TREATMENT OF TEST MATERIAL PRIOR TO TESTING
- Treatment of test material prior to testing: Test item dosing formulations (w/w) were homogenized to visually acceptable levels at appropriate concentrations to meet dose level requirements. The dosing formulations were prepared daily as a solution and dosed within 6 hours after adding the vehicle to the test item.
- Preliminary purification step (if any): n/a
- Final dilution of a dissolved solid, stock liquid or gel: n/a
- Final preparation of a solid: n/a

Species:

rat

Strain:

Wistar

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories Deutschland, Sulzfeld, Germany
- Age at study initiation: 10-14 weeks old
- Weight at study initiation: 187 and 282 g
- Fasting period before study: no
- Housing: housed individually in Macrolon plastic cages
- Diet (e.g. ad libitum): Pelleted rodent diet ad libitum
- Water (e.g. ad libitum): Municipal tap water ad libitum
- Acclimation period: at least 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20 to 21°C
- Humidity (%): 48 to 59%
- Air changes (per hr): Ten or greater air changes per hour
- Photoperiod (hrs dark / hrs light): 12 hour light/12 hour dark cycle

Route of administration:

oral: gavage

Vehicle:

corn oil

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Analyses were performed using a validated analytical procedure. Dumplicate sets of samples were analysed for homogeneity and concentration. During the course of this study at one occasion during the treatment phase, stability of the prepared formulation was determined at 6 hours at room temperature under normal laboratory light conditions.

Details on mating procedure:

- Impregnation procedure: purchased timed pregnant

Duration of treatment / exposure:

from day 6 to day 20 post-coitum

Frequency of treatment:

daily

Duration of test:

until day 20 post-coitum

Dose / conc.:

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

Remarks:

control group

Dose / conc.:

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

Remarks:

low dose group

Dose / conc.:

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

Remarks:

middle dose group

Dose / conc.:

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

Remarks:

high dose group

No. of animals per sex per dose:

22 females per group

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: The dose levels were selected based on the results of a 14-day dose range finding study with oral exposure of 1,1,1,3,5,5,5-heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane in rats (Test Facility Study no. 20140140) in which dose levels of 20, 100 and 750 mg/kg bw/day were tested. No toxicity was observed at any dose level during this dose range finder.
- Rationale for animal assignment (if not random): random

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily
- Cage side observations checked included: general health/mortality and moribundity

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: once daily, beginning on Day 2 post-coitum and lasting up to the day prior to necropsy

BODY WEIGHT: Yes
- Time schedule for examinations: Animals were weighed individually on Days 2, 6, 9, 12, 15, 18 and 21 post-coitum.

FOOD CONSUMPTION: Yes
- Time schedule for examinations: Food consumption was quantitatively measured over Days 2-6, 6-9, 9-12, 12-15, 15-18 and 18-21 post-coitum.

WATER CONSUMPTION: Yes
- Time schedule for examinations: Water consumption was monitored on regular basis throughout the study by visual inspection of the water bottles/containers.

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day # day 21 post-coitum
- Organs examined: At necropsy the following examinations were perfomed: the number of corpora lutea; the weight of the uterus; number of implantation sites; number and distribution of live and dead fetuses; number and distribution of embryo-fetal deaths; the sex of each fetus based on anogenital distance. Uterus and thyroid gland were weighed. The thyroid gland was collected from all animals and preserved in 10% neutral buffered formalin. Thyroid glands of all animals were embedded in paraffin, sectioned, mounted on glass slides, and stained with hematoxylin and eosin and examined during histopathology.

OTHER:
THYROID HORMONE
- Time schedule for examinations: Blood of F0-animals was collected on the day of scheduled necropsy. Animals were not fasted overnight. Anesthetic was not used. The samples were examined for triiodothyronine (T3), thyroxine (T4) and thyroid-stimulating hormone (TSH) levels.

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:

All statistical tests were conducted at the 5% significance level. All pairwise comparisons were conducted using two sided tests and were reported at the 1% or 5% levels.
Numerical data collected on scheduled occasions for the listed variables were analyzed as indicated according to sex and occasion. Descriptive statistics number, mean and standard deviation (or %CV or SE when deemed appropriate) were reported whenever possible. Inferential statistics were performed according to the matrix below when possible, but excluded semi-quantitative data, and any group with less than 3 observations.
The following pairwise comparisons were made:
Group 2 vs. Group 1
Group 3 vs. Group 1
Group 4 vs. Group 1

Clinical signs:

no effects observed

Description (incidence and severity):

No treatment related clinical signs were noted.

Dermal irritation (if dermal study):

not examined

Mortality:

no mortality observed

Description (incidence):

No mortality occurred during the study period.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

Mean body weights, body weight gain and weight gain corrected for gravid uterus of treated animals were considered to be unaffected by treatment up to 1000 mg/kg bw/day.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

Food consumption before or after correction for body weight was similar to the control level over the study period.

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:

no effects observed

Description (incidence and severity):

Organ weights and organ weight-to-body weight ratio of treated animals were considered to be similar to those of control animals.

Gross pathological findings:

no effects observed

Description (incidence and severity):

Macroscopic observations at necropsy did not reveal any alterations that were considered to have arisen as a result of treatment.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

Follicular cell hypertrophy was present in the thyroid gland at increased incidence in females treated at 300 and 1000 mg/kg bw/day at minimal degree.
Based on the low severity, which was within background severity for this finding, and the lack of macroscopic findings or organ weight changes in the thyroid gland this was considered non-adverse.

Histopathological findings: neoplastic:

not examined

Other effects:

no effects observed

Description (incidence and severity):

Slightly increased serum levels of thyroid stimulating hormone (TSH) were noted at 1000 mg/kg bw/day (1.6x of controls), however without reaching statistical significance. This slight increase was mainly caused by Animal No. 80, for which a TSH serum level of 3.390 uLU/mL (7.4x of the mean control level) was measured. After exclusion of this individual animal, the mean TSH level at 1000 mg/kg bw/day was comparable to that of the controls and remained within the available historical control data . This slight difference in TSH was therefore considered not to be test-item related.
Serum levels of total T3 and T4 were considered to be unaffected by treatment up to 1000 mg/kg bw/day

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

Details on maternal toxic effects:

The numbers of pregnant females, corpora lutea and implantation sites, and pre-implantation loss in the control and test groups were similar and within the range of normal biological variation.

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

Abnormalities:

no effects observed

Fetal body weight changes:

no effects observed

Description (incidence and severity):

There were no toxicologically relevant effects on fetal body weights (both sexes) noted after treatment up to 1000 mg/kg bw/day.

Changes in sex ratio:

no effects observed

Description (incidence and severity):

The male:female ratio was unaffected by treatment up to 1000 mg/kg bw/day.

Changes in litter size and weights:

no effects observed

Description (incidence and severity):

There were no treatment-related effects on litter size of any group.

External malformations:

no effects observed

Description (incidence and severity):

No treatment related external malformations and variations were seen in any group.
For one fetus at 1000 mg/kg bw/day, a domed head was observed, which was caused by internal hydrocephaly as was confirmed at soft-tissue cephalic examination. Due to the single occurrence at 1000 mg/kg bw/day and as internal hydrocephaly (without domed head) was also observed at soft-tissue cephalic examination in control fetus, this malformation was considered to be of spontaneous origin.

Skeletal malformations:

no effects observed

Description (incidence and severity):

There were no treatment-related skeletal malformations observed following treatment up to 1000 mg/kg bw/day.
An increased incidence of skeletal variations was noted after treatment at 300 and 1000 mg/kg bw/day and included caudal shift of the pelvic girdle (incidences were 7.0x and 6.1x of control at 300 and 1000 mg/kg bw/day, respectively) and the presence of a 14th full rib (1.8x and 1.4x of control, respectively). As the incidences observed at these dose levels were near or above the maximum historical control value, a test item-related effect could not be excluded. However, as both variations also occur regularly in control animals, the increased incidences were considered to be non-adverse.

Visceral malformations:

no effects observed

Description (incidence and severity):

There were no treatment-related effects on visceral morphology following treatment up to 1000 mg/kg bw/day.
Besides the two fetuses (one control and one at 1000 mg/kg bw/day) with internal hydrocephaly, no other visceral malformations were observed. Visceral variations that were observed (small supernumerary liver lobes and convoluted ureter), occurred incidentally in the control and low dose groups only and were considered to be unrelated to treatment.

Other effects:

no effects observed

Description (incidence and severity):

There were no toxicologically relevant effects on fetal anogenital distance before and after correction for body weight up to 1000 mg/kg bw/day

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

Abnormalities:

no effects observed

Developmental effects observed:

no

Table 1: Summary of Microscopic Findings in females – Terminal Euthanasia

Dose level (mg/kg bw/day):	0	50	300	1000
THYROID GLANDS^a	22	22	22	22
Follicular cell hypertrophy
Minimal	1	2	7	13

^a = Number of tissues examined from each group

Conclusions:

In the prenatal developmental toxicity study, conducted according to OECD TG 414 and in compliance with GLP, the concluded NOAEL for maternal toxicity and developmental toxicity is greater than 1000 mg/kg bw/day. There were no adverse effects observed.

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

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

In the prenatal developmental toxicity study, conducted according to OECD TG 414 and in compliance with GLP, time-mated female Wistar Han rats were treated with 1,1,1,3,5,5,5-heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane from day 6 to 20 post-coitum, inclusive, by daily oral gavage at dose levels of 50, 300 and 1000 mg/kg bw/day. The rats of the control group received the vehicle, dehydrated and deacidified corn oil, alone (Charles River, 2019).

Test formulations preparedwere considered homogeneous at the concentrations tested and analysis of the accuracy revealed acceptable levels. Test formulations preparedwere consideredstable for at least 6 hours at room temperature under normal laboratory light conditions.

No mortality occurred during the study period and no test item-related changes were noted in clinical appearance, body weight, food consumption, thyroid hormones, macroscopic examination and organ weights in maternal animals.

Follicular cell hypertrophy of the thyroid gland was recorded at increased incidence at 300 and 1000 mg/kg bw/day for maternal rats. As the low severity observed was within the background severity for this finding, and based on the lack of macroscopic findings or organ weight changes in the thyroid gland, this was considered to be non-adverse. 

Developmental results

No test item-related changes were noted in litter size, post-implantation loss, sex ratio, fetal body weights, ano-genital distance, external and visceral malformations and developmental variations. 

An increased incidence of skeletal variations was noted after treatment at 300 and 1000 mg/kg bw/day in fetuses and included caudal shift of the pelvic girdle (incidences were 7.0x and 6.1x of control at 300 and 1000 mg/kg bw/day, respectively) and the presence of a 14th full rib (1.8x and 1.4x of control, respectively). As the incidences observed at these dose levels were near or above the maximum historical control value, a test item-related effect could not be excluded. However, as both variations also occur regularly in control animals, the increased incidences were considered to be non-adverse.

Based on the finding of this study, the concluded NOAEL for maternal and developmental toxicity was greater than 1000 mg/kg bw/day.

Justification for classification or non-classification

Based on the available data, 1,1,1,3,5,5,5-heptamethyl-3-[(trimethylsilyl)oxy]trisiloxane is not classified for effects on reproduction or development according to Regulation (EC) No 1272/2008.