Dodecamethylpentasiloxane

Endpoint summary

Key value for chemical safety assessment

Effects on fertility

Description of key information

There are no reproductive dose toxicity data on dodecamethylpentasiloxane (CAS 141-63-9), so good quality data for the related substance, decamethyltetrasiloxane (141-62-8), have been used to assess the reproductive toxicity of dodecamethylpentasiloxane.
In the key combined repeated dose toxicity study with the reproduction / developmental toxicity screening test with decamethyltetrasiloxane (L4) conducted according to a protocol comparable to OECD Test Guideline 422 and in compliance with GLP (Dow Corning Corporation, 2007b) the NOAEC for general and reproductive toxicity was at least 400 ppm (the only concentration tested) according to the study report. However, it should be noted that three female rats in the 400 ppm group with evidence of copulation failed to deliver a litter. One of these three females showed signs of parturition (blood discharge) on gestation day 25, but no pups were found. However, seven implant sites were present. The remaining females produced litters that were similar to the controls.

The key combined repeated dose toxicity study with the reproduction / developmental toxicity screening test with the structural analogue, decamethyltetrasiloxane (141-62-8), is currenly used as interim approach to allow the conduct of risk characterisation. In order to investigate the reproduction toxicity of the registered substance, dodecamethylpentasiloxane (CAS 141-63-9) further, there is a test proposal for an extended one-generation reproductive toxicity study with the registered substance.

Link to relevant study records

Reference

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

27.10.2006 to 21.12.2007

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

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

Deviations:

yes

Remarks:

Only one concentration tested.

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Inc.
- Age at study initiation: 9 wks
- Weight at study initiation: (P) Males: 300.7-350 g; Females: 195.5-240 g
- Fasting period before study: No
- Housing: Individually housed in suspended wire-mesh cages. Except during mating, gestation and lactation periods. Mating: home cage of the male; Gestation: shoebox cages; Lactation: dams housed with litters.
- Diet (e.g. ad libitum): Ad libitum (except during inhalation exposure, FOB and motor activity assessments).
- Water (e.g. ad libitum): Ad libitum (except during inhalation exposure, FOB and motor activity assessments).
- Acclimation period: Five days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20.95-21.71
- Humidity (%): 31-69
- Air changes (per hr): 12.1
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 27.10.2006 To: 21.12.2007

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

clean air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 1000 litre stainless steel and glass, TSE-system style, whole-body inhalation exposure chambers.
- Method of holding animals in test chamber: In cages
- Source and rate of air: Nash Air Compressor (rate not specified).
- Method of conditioning air: Series of filters to remove contaminants.
- Temperature, humidity, pressure in air chamber: Temp: 19-25oC (no other information, but it was stated that conditions were maintained according to the protocol), humidity was 30-70%.
- Air change rate: 12-15 air changes per hour
- Treatment of exhaust air: No data

TEST ATMOSPHERE
- Brief description of analytical method used: Gas chromatography using a flame ionization detector
- Samples taken from breathing zone: yes

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: Continuous until evidence of copulation observed.
- Proof of pregnancy: vaginal plug or sperm in vaginal smear referred to as day 0 of pregnancy.
- After successful mating each pregnant female was caged (how): Shoebox cages.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Gas chromatography using a flame ionization detector (mean measured chamber concentration was 388+30.9 ppm).

Duration of treatment / exposure:

Males: 29 days
Toxicity group females: 28 days
Reproductive group females: 15 days prior to mating, through the mating period and up to day 19 of gestation.

Frequency of treatment:

Daily (seven days per week)

Dose / conc.:

5.1 mg/L air

Remarks:

equivalent to 400 ppm target concentration

No. of animals per sex per dose:

Ten

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Based on previously conducted study.

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed at least twice daily in their cages for mortality, morbidity and moribundity throughout the in-life phase of the study. General clinical observations were made at least once per day, beginning on the first day of treatment (except on days of detailed examinations). Clinical observations were also performed on all animals on the day of, but prior to, scheduled necropsy.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: All animals, once before the first exposure and weekly thereafter. 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 behaviour.

BODY WEIGHT: Yes
- Time schedule for examinations: Individual body weights were determined beginning with randomisation into test groups, on the first day of exposure, at least weekly thereafter, and the day of necropsy. During gestation, the females were weighed (at a minimum) on gestation days 0, 7, 14 and 20 within 24 hours after parturition, and day 4 postpartum.

FOOD CONSUMPTION: Individual animal food consumption was recorded at least weekly on an individual animal basis for the periods listed: Male rats: two week pre-mating period only (feeder weights were taken on days 1, 8 and 15). Female rats: toxicity group on day 1 of exposure to necropsy (feeder weights were taken on day 1, 8, 15, 22 and the day prior to necropsy. Reproductive female rats: two week pre-mating period, gestation and postpartum (feeder weights were taken on days 1, 8, 15 and on gestation days 0, 7, 14, 20 and on day 0 and 4 postpartum).

WATER CONSUMPTION: No

OTHER: The duration of gestation was calculated from Day 0 gestation for each female. From Day 20 after evidence of mating, pregnant animals were checked at least three times daily for evidence of parturition.

Functional Observational Battery (FOB) performed on all adult males and all toxicity group females prior to the start of exposure and during the fourth week of exposure (prior to daily exposures).

Clinical pathology assessments on all adult male and toxicity group females - See section 7.5.2.

Oestrous cyclicity (parental animals):

No evidence that estrous cyclicity was investigated.

Sperm parameters (parental animals):

Parameters examined in male parental generations: testis weight and epididymis weight. Male reproductive organs were also examined in the histopathology examinations.

Litter observations:

STANDARDISATION OF LITTERS:
- Performed on day 4 postpartum: no

PARAMETERS EXAMINED
The following parameters were examined in F1 pups: each litter was examined as soon as possible after delivery to determine the number and sex of the pups, the number of live pups, number of pups dead, runts. Live pups were counted, sexed and the sex ratio calculated. Litter weights were taken within 24 hours of parturition and on day 4 post-partum.

GROSS EXAMINATION OF DEAD PUPS: yes, for external abnormalities. Possible cause of death was not determined for pups born or found dead.

Postmortem examinations (parental animals):

SACRIFICE
- Male animals: All surviving animals after 29 days exposure.
- Maternal animals: Day 4 postpartum.

GROSS NECROPSY
- Gross necropsy consisted of external and internal examinations including the cervical, thoracic, and abdominal viscera. For pregnant females, the number of corpora lutea and the number of implantation sites were recorded. For the three females with positive evidence of mating that failed to deliver a litter, the uterus was stained to enable counting of possible reabsorbed implant sites.

HISTOPATHOLOGY / ORGAN WEIGHTS: At necropsy, the following organs from males and toxicity group females were weighed: adrenal glands, brain, heart, lungs, kidneys, liver, spleen and thymus. Testes, epididymides, seminal vesicles and prostate weights were recorded for all male adult animals. Ovaries with oviducts and uterine weights were recorded for toxicity group females. Selected organs and tissues were examined histopathologically in the toxicity group males and females, not reproductive group females (see Section 7.5.2).

Postmortem examinations (offspring):

SACRIFICE: Day 4 post-partum.

GROSS NECROPSY: Dead and sacrificed pups examined for external gross abnormalities only.

HISTOPATHOLOGY / ORGAN WEIGHTS: Not conducted.

Statistics:

All data analyses was conducted using SAS version 9.1.3. Statistically significant probabilities were reported for p-values of <0.05, <0.02 and <0.01.

Reproductive indices:

Gestation length, mean number of implantation sites, mean number of corpora lutea, mean mating and fertility indices. Mean litter size, mean live litter size, mean litter weight, mean ratio live births/litter size.

Offspring viability indices:

Survival to postpartum day 4.

Clinical signs:

no effects observed

Description (incidence and severity):

No significant treatment-related clinical signs of toxicity were observed.

Mortality:

no mortality observed

Description (incidence):

No deaths occured during the study.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

Significant increases in body weight gains were noted in the 400 ppm parental females during the third week of gestation, which were not considered to be treatment-related. There were no statistically significant differences in food consumption in females. The food consumption for treated males was significantly decreased during weeks 1 and 2 and for total food consumption. However, food consumption for weeks 1 and 2 was within the normal range of the laboratory's historical controls. The difference was not considered to be related to treatment.

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not examined

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

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Description (incidence and severity):

There were no treatment-related alterations in haematology.

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

There were no treatment-related alterations in serum chemistry.

Urinalysis findings:

not examined

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

There appeared to be no functional or neurological effects of the test substance on the rats.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

One possible exposure-related finding was increased minimal alveolar histiocytosis in males in the 400 ppm exposure group. This is a common non-specific finding in inhalation studies; however, the minimal severity and fact that only one sex was affected made the significance of the finding uncertain. There were no other exposure-related in other tissues.

Other effects:

not examined

Reproductive function: oestrous cycle:

not examined

Reproductive function: sperm measures:

no effects observed

Description (incidence and severity):

There was no effect on testes or epididymides weights. No other parameters were examined.

Reproductive performance:

effects observed, treatment-related

Description (incidence and severity):

Three female rats in the 400 ppm group with evidence of copulation failed to deliver a litter. One of these three females showed signs of parturition (blood discharge) on gestation day 25, but no pups were found. However, seven implant sites were present. The remaining females produced litters that were similar to the controls.
There were no treatment-related effects apparent for any of the reproductive endpoints. There were no changes observed in the litter size, male-to-female ratio, pup body weights or the pup survival.

Key result

Dose descriptor:

NOAEC

Effect level:

>= 400 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

reproductive performance

other: No significant treatment-related effects on males or toxicity phase females.

Critical effects observed:

no

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

no effects observed

Sexual maturation:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Histopathological findings:

not examined

There were no adverse effects for the pups up to postpartum day 4.

Dose descriptor:

NOAEC

Generation:

F1

Effect level:

>= 400 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No adverse effects on pups.

Critical effects observed:

no

Reproductive effects observed:

no

Conclusions:

In a combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test conducted using a protocol comparable to OECD 422 and to GLP (reliability score 1) the NOAEC for general and reproductive toxicity was at least 400 ppm (the only concentration tested) according to the study report. However, it should be noted that three female rats in the 400 ppm group with evidence of copulation failed to deliver a litter. One of these three females showed signs of parturition (blood discharge) on gestation day 25, but no pups were found. However, seven implant sites were present. The remaining females produced litters that were similar to the controls.

Effect on fertility: via oral route

Endpoint conclusion:

no study available

Effect on fertility: via inhalation route

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

5 083 mg/m³

Study duration:

subacute

Species:

rat

Effect on fertility: via dermal route

Endpoint conclusion:

no study available

Additional information

There are no reproductive dose toxicity data on dodecamethylpentasiloxane (CAS 141-63-9), so good quality data for the related substance, decamethyltetrasiloxane (141-62-8), have been used to assess the reproductive toxicity of dodecamethylpentasiloxane.

In the key combined repeated dose toxicity study with the reproduction / developmental toxicity screening test with decamethyltetrasiloxane (L4) conducted according to a protocol comparable to OECD Test Guideline 422 and in compliance with GLP (Dow Corning Corporation, 2007b) the NOAEC for general and reproductive toxicity was at least 400 ppm (the only concentration tested) according to the study report. No deaths occured during the study. No significant treatment-related clinical signs of toxicity were observed. Significant increases in body weight gains were noted in the 400 ppm parental females during the third week of gestation, which were not considered to be treatment-related. There were no statistically significant differences in food consumption in females. The food consumption for treated males was significantly decreased during weeks 1 and 2 and for total food consumption. However, food consumption for weeks 1 and 2 was within the normal range of the laboratory's historical controls. The difference was not considered to be related to treatment. There were no treatment-related alterations in haematology and serum chemistry. There appeared to be no functional or neurological effects of the test substance on the rats.There were no differences in absolute organ weights. The spleen to body weight ratio was slightly lower for toxicity group females, but not males, exposed to 400 ppm test substance. There was no histopathological correlate, nor any effect of exposure in other lymphoid tissues. This was considered to be random variation and not of toxicological significance. There were no gross lesions attributed to the test substance. One possible exposure-related finding was increased minimal alveolar histiocytosis in males in the 400 ppm exposure group. This is a common non-specific finding in inhalation studies; however, the minimal severity and fact that only one sex was affected made the significance of the finding uncertain. There were no other exposure-related in other tissues. Three female rats in the 400 ppm group with evidence of copulation failed to deliver a litter. One of these three females showed signs of parturition (blood discharge) on gestation day 25, but no pups were found. However, seven implant sites were present. The remaining females produced litters that were similar to the controls. There were no treatment-related effects apparent for any of the reproductive endpoints. There were no changes observed in the litter size, male-to-female ratio, pup body weights or the pup survival. There was no effect on testes or epididymides weights.

The key combined repeated dose toxicity study with the reproduction / developmental toxicity screening test with the structural analogue, decamethyltetrasiloxane (141-62-8), is currenly used as interim approach to allow the conduct of risk characterisation. In order to investigate the reproduction toxicity of the registered substance, dodecamethylpentasiloxane (CAS 141-63-9) further, there is a test proposal for an extended one-generation reproductive toxicity study with the registered substance.

Effects on developmental toxicity

Description of key information

There are no developmental toxicity data on dodecamethylpentasiloxane (L5). Good quality data for the related substance, decamethyltetrasiloxane (L4; CAS 141-62-8), have been used for developmental toxicity in first species (rats) of dodecamethylpentasiloxane (L5).

In order to further investigate the developmental toxicity potential of the registered substance there is a test proposal with the registered substance, dodecamethylpentasiloxane (L5; CAS 141-63-9) to conduct a prenatal developmental toxicity study in second species (rabbits), according to OECD Test Guideline 414 and in compliance with GLP.

 

In the key prenatal developmental toxicity study for decamethyltetrasiloxane (L4) in rats, conducted according to OECD Test Guideline 414 and in compliance with GLP, the NOAEL for maternal and developmental toxicity was concluded to be equal to or greater than 1000 mg/kg bw/day (the highest dose tested) based on no treatment-related adverse effects observed (Covance Laboratories Limited, 2020). Liver weights were slightly increased at all dose levels of 100 mg/kg/day, or above. The increase in liver weights may indicate a non-adverse, adaptive response to general toxic insult, and may be the major factor contributing to the elevated thyroid stimulating hormone (TSH) levels. Consequently, the levels of thyroxine (T4) or triiodothyronine (T3) were reduced, as would be expected in a normal physiologically functioning system. Furthermore, the higher incidence of follicular cell hypertrophy was considered secondary to the increase in TSH, although no increase in hypertrophy was evident at 100 mg/kg bw/day.

Link to relevant study records

Reference

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

20 November 2019 to 13 March 2020

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:

Adopted 25 June 2018

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 870.3700 (Prenatal Developmental Toxicity Study)

Version / remarks:

August 1998

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: Japanese Ministry of Agriculture, Forestry and Fisheries, Test Data for Registration of Agricultural Chemicals, 12 Nohsan No. 8147, Agricultural Production Bureau

Version / remarks:

November 24, 2000

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Remarks:

Crl:CD(SD)

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River (UK) Ltd.
- Age at study initiation: 68 to 81 days old
- Weight at study initiation: 203 to 300 g
- Fasting period before study: not specified
- Housing: During acclimatisation the animals were housed in groups of four; during mating the animals were housed in groups of two (one (stock) male and one female); during gestation the pregnant females were housed individually.
- Diet (e.g. ad libitum): SDS VRF1 Certified pelleted diet, ad libitum
- Water (e.g. ad libitum): Potable water from the public supply, ad libitum
- Acclimation period: 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20-24°C
- Humidity (%): 40-70%
- Air changes (per hr): Not specified. Filtered fresh air which was passed to atmosphere and not recirculated.
- Photoperiod (hrs dark / hrs light): 12 hours light: 12 hours dark

Route of administration:

oral: gavage

Vehicle:

corn oil

Remarks:

dried and de-acidified

Details on exposure:

PREPARATION OF DOSING SOLUTIONS: Formulation were prepared in a glove box under nitrogen. An appropriate volume of vehicle was dispensed into
containers prior to starting test formulations. Then a series of formulations at the required concentrations were prepared by adding an appropriate volume of test item to an appropriate volume of dried and de-acidified corn oil. The dose formulations were prepared weekly.

VEHICLE
- Justification for use and choice of vehicle (if other than water): Based on the test item characteristics and in consultation with the study Sponsor.
- Concentration in vehicle: 0, 29.5, 88.5, 295 mg/mL
- Amount of vehicle (if gavage): 4 mL/kg bw

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Before commencement of treatment, the suitability of the proposed mixing procedures was determined and specimen formulations were analysed to assess the stability and homogeneity of the test item in the liquid matrix.
Samples of each formulation prepared for administration on the first and last preparations of treatment were analysed for achieved concentration of the test item.

Details on mating procedure:

- Impregnation procedure: cohoused
- M/F ratio per cage: 1:1 ratio
- Length of cohabitation: not specified
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy: Ejected copulation plugs in cage tray and vaginal smears were checked for the presence of sperm

Duration of treatment / exposure:

During gestation days 6 to 19

Frequency of treatment:

daily

Duration of test:

20 days

Dose / conc.:

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

Remarks:

Control group

Dose / conc.:

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

Remarks:

Low dose (LD)

Dose / conc.:

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

Remarks:

Middle dose (MD)

Dose / conc.:

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

Remarks:

High dose (HD)

No. of animals per sex per dose:

20 females per group

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: The doses used in this study (0, 100, 300 and 1000 mg/kg bw/day) were selected in conjunction with the Sponsor based on the findings of a preliminary embryo-foetal study (Covance Study Number: FD94JJ; Covance CRS Limited, 2020). In that study, doses of 500, 750 or 1000 mg/kg bw/day were generally well tolerated in life with no adverse effects on general condition, body weight gain or food intake. No changes were seen in tissues during macroscopic examination, however liver weights were increased at all dose levels. On Day 20 of gestation, mean number of implantations, resorptions and the number of live young was considered to be unaffected by treatment.
- Rationale for animal assignment (if not random): random

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 and cage-trays were inspected daily for evidence of animal ill-health among the occupant(s). Signs associated with dosing were recorded daily at pre-dose administration, 1 to 2 hours after dosing and as late as possible on the working day after dosing.
- Cage side observations checked included: general health and signs associated with dosing

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: 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, 6-20 after mating.

FOOD CONSUMPTION: Yes
- Time schedule: The weight of food supplied to each adult, that remaining and an estimate of any spilled was recorded for the periods Days 0-2, 3-5, 6-7, 8-10, 11-13, 14-16 and 17-19 after mating inclusive.

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day # 20
- Organs examined: At necropsy thyroid with parathyroids, liver, kidneys and any macroscopic abnormalities were collected; thyroid with parathyroids, liver, kidneys (weighed together) and gravid Uterus (with cervix) were weighed at necropsy; thyroid with parathyroids were examined at histology and pathology (light microscopy).

OTHER: Thyroid hormone analysis
- Time schedule: Blood samples were collected at scheduled termination.
- Parameters analysed: Triiodothyronine (T3) Thyroxine (T4) Thyroid stimulating hormone (TSH)
- Fasting before collection of blood samples: No overnight deprivation of food.
- Anaesthetic used: Isoflurane

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
- Other: foetuses (live or dead): 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: Yes: [half per litter]
- Other: anogenital distance

Statistics:

Data relating to food consumption were analysed on a cage basis. For all other adult parameters, the analyses were carried out using the individual animal as the basic experimental unit. For litter/foetal findings the litter was taken as the treated unit and the basis for statistical analysis and biological significance was assessed with relevance to the severity of the anomaly and the incidence of the finding within the background control population.
The following sequence of statistical tests was used for body weight, gravid uterus weight, food consumption, implantations, litter size, sex ratio - percentage male, post implantation survival index, ano-genital distance and organ weight data:
A parametric analysis was performed if Bartlett's test for variance homogeneity was not significant at the 1% level. 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.
A non-parametric analysis was performed if Bartlett's test was still significant at the 1% level. The H1 approximate test, the non-parametric equivalent of the F1 test, 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, Steel's test was performed instead.
For organ weight data, analysis of covariance was performed using terminal body weight, unless non-parametric methods were applied. The treatment comparisons were made on adjusted group means. Similarly, for the litter average anogenital distance, analysis of covariance was performed using the average pup body weight/foetal weight for each litter.
Significant differences between the groups compared were expressed at the 5% (p<0.05) or 1% (p<0.01) level.

Historical control data:

See attached files.

Clinical signs:

no effects observed

Description (incidence and severity):

There were no clinical signs considered related to treatment and no signs seen in association with dosing with decamethyltetrasiloxane at dose levels up to 1000 mg/kg bw/day.

Mortality:

no mortality observed

Description (incidence):

No mortality was observed for any test group.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

There was no adverse effect of treatment on body weight gain during gestation at 100, 300 or 1000 mg/kg bw/day.
Mean body weight and overall body weight gain of treated females was slightly higher than the control females, although statistical significance was only attained for gains. When overall body weight gain was adjusted for the contribution of the gravid uterus, differences from the control group no longer attained statistical significance. In the absence of any consistent dose-response, these differences in body weight gains were considered to be incidental and unrelated to treatment.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

There was no effect of treatment with decamethyltetrasiloxane on food intake at 100, 300 or 1000 mg/kg bw/day.

Food efficiency:

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 treated females on Day 20 was marginally higher than control, and consistent with small differences in litter size rather than any treatment-related effect.
The group mean weight of the liver adjusted by terminal body weights was higher in treated females, when compared with the controls (between 114 – 123%). The group mean values for kidney weights or thyroid and parathyroid weights were similar to Control.

Gross pathological findings:

no effects observed

Description (incidence and severity):

The macroscopic examination performed on Day 20 after mating revealed no test item-related findings.
The incidence and distribution of all findings were considered to be unrelated to treatment.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Changes related to treatment with decamethyltetrasiloxane given by oral gavage were seen in the thyroid glands. An increase in the incidence of diffuse follicular cell hypertrophy, when compared to controls, was seen in females given 300 or 1000 mg/kg bw/day.

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 slightly higher concentrations in all treated groups, although there was no dose-response.
There was a slight decrease in the mean serum thyroxine (T4) and triiodothyronine (T3) concentration in all treated groups, although there was no dose-response.

Details on results:

Increased liver weights were anticipated, based on the findings of a 28-day study (ECHA), and were evident in this study. The increase in liver weights seen in all treated females may indicate a non-adverse, adaptive response to general toxic insult, and may be the major factor contributing to the elevated thyroid stimulating hormone (TSH) levels. Consequently, the levels of thyroxine (T4) or triiodothyronine (T3) were reduced, as would be expected in a normal physiologically functioning system. Furthermore, the higher incidence of follicular cell hypertrophy was considered secondary to the increase in TSH, although no increase in hypertrophy was evident at 100 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:

effects observed, non-treatment-related

Description (incidence and severity):

All animals were found to be pregnant at macroscopic examination, with the exception of animal No. 38 receiving 100 mg/kg bw/day, therefore, reproductive assessment is based on 20, 19, 20 and 20 litters from the control, 100, 300 and 1000 mg/kg bw/day groups, respectively.

Details on maternal toxic effects:

There was no effect of maternal treatment on embryo-foetal survival, as assessed by the number of resorptions or incidence of post-implantation losses, or subsequent live litter size at 100, 300 or 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.

Basis for effect level:

other: No adverse effects were observed.

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

Description (incidence and severity):

Litter and foetal weights were unaffected by maternal treatment with decamethyltetrasiloxane at 100, 300 and 1000 mg/kg bw/day.

Changes in postnatal survival:

not examined

External malformations:

effects observed, non-treatment-related

Description (incidence and severity):

At 1000 mg/kg bw/day there was a slight increase in incidence of variation in contralateral lens shape and oval lenses. All incidences are within historical control data range. Incomplete lens shape variation is a transient stage in foetal development, indicative of foetal immaturity and considered not to be adverse.

Skeletal malformations:

effects observed, non-treatment-related

Description (incidence and severity):

The incidence of major abnormalities showed no relationship to maternal treatment. Across the treated groups and compared to concurrent control, there was an increase in foetal and litter incidences of delayed ossification affecting the cranial centres, hyoid, 1st to 4th sternebrae, thoracic and sacral/caudal vertebrae and pelvic bones. All incidences are within historical control data range. Incomplete ossification is a transient stage in foetal development, indicative of foetal immaturity and considered not to be adverse.

Visceral malformations:

no effects observed

Other effects:

no effects observed

Description (incidence and severity):

Anogenital distances were unaffected by treatment with decamethyltetrasiloxane at 100, 300 and 1000 mg/kg bw/day.

Details on embryotoxic / teratogenic effects:

There was no effect of maternal treatment on embryo-foetal survival and subsequent live litter size at 100, 300 or 1000 mg/kg bw/day. Sex ratio was similar to the control group in all treated groups indicating no selective effect of sex on embryo-foetal survival.
There were no major abnormalities that were considered treatment-related at foetal examination. Minor abnormalities included an increase in incidence of delayed ossification across all treated groups and lens shape variation at 1000 mg/kg bw/day. These abnormalities are considered transient stages in foetal development, indicative of foetal immaturity and considered not to be adverse.

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 developmental effects were observed.

Abnormalities:

no effects observed

Developmental effects observed:

no

The mean analysed concentrations of decamethyltetrasiloxane were within 5% of the nominal values, confirming the accuracy of formulation preparation.

Table 1: Summary of findings in the thyroid gland for animals killed on Day 20 after mating

Group/sex	1F	2F	3F	4F
Dose (mg/kg bw/day)	0	100	300	1000
Hypertrophy, Follicular Cells
Minimal	2	3	8	13
Total	2	3	8	13
Number of tissues examined	20	20	19	20

See attachments for results tables.

Conclusions:

In a prenatal developmental toxicity study for decamethyltetrasiloxane in rats, conducted according to OECD Test Guideline 414 and in compliance with GLP, the NOAEL for maternal and developmental toxicity was concluded to be equal to or greater than 1000 mg/kg bw/day (the highest dose tested) based on no treatment-related adverse effects observed. Liver weights were slightly increased at all dose levels of 100 mg/kg/day, or above. The increase in liver weights may indicate a non-adverse, adaptive response to general toxic insult, and may be the major factor contributing to the elevated thyroid stimulating hormone (TSH) levels. Consequently, the levels of thyroxine (T4) or triiodothyronine (T3) were reduced, as would be expected in a normal physiologically functioning system. Furthermore, the higher incidence of follicular cell hypertrophy was considered secondary to the increase in TSH, although no increase in hypertrophy was evident at 100 mg/kg bw/day.

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

There are no developmental toxicity data on dodecamethylpentasiloxane (L5). Good quality data for the related substance, decamethyltetrasiloxane (L4; CAS 141-62-8), have been used for developmental toxicity in first species (rats) of dodecamethylpentasiloxane (L5). See attachment to Section 13 for justification of read-across.

In order to further investigate the developmental toxicity potential of the registered substance there is a test proposal with the registered substance, dodecamethylpentasiloxane (L5; CAS 141-63-9) to conduct a prenatal developmental toxicity study in second species (rabbits), according to OECD Test Guideline 414 and in compliance with GLP.

In the key prenatal developmental toxicity study, conducted according to OECD Test Guideline 414 and in compliance with GLP, decamethyltetrasiloxane (L4) in dried and de-acidified corn oil was administered orally by gavage to 20 pregnant female Sprague-Dawley rats per group at doses of 0, 100, 300 or 1000 mg/kg bw/day during gestation days (GDs) 6 to 19 (Covance Laboratories Limited, 2020).  A similarly constituted control group received the vehicle, dried and de-acidified corn oil at the same volume dose as treated groups over the same treatment period. The dose level selection was based on the findings of a preliminary prenatal developmental toxicity study (Covance CRS Limited, 2020) and in consultation with the study Sponsor. The highest dose in the main study was therefore selected with the aim to induce slight toxic effects but no severe suffering or death of the animals.

Clinical observations, body weight and food consumption were recorded for all the female rats throughout the study period. On GD 20, all females were sacrificed and subject to necropsy. Blood samples were taken for thyroid hormone analysis prior to terminal sacrifice. The kidneys, liver and thyroid gland were weighed, retained in fixative and thyroid with parathyroid tissues were processed and examined microscopically. The gravid uterine weight was recorded and then the uterine contents were examined with the numbers of corpora lutea, implantations, early and late resorptions and live and dead foetuses. Foetuses were weighed and sexed. Anogenital distance was measured for foetuses and all foetuses were examined macroscopically at necropsy. Foetuses were then placed in appropriate fixative and subsequently subjected to detailed internal visceral examination or skeletal examination.

The clinical condition, body weight/ body weight gain or food consumption of pregnant females receiving 100, 300 or 1000 mg/kg bw/day decamethyltetrasiloxane was unaffected by the treatment. Liver weights were slightly increased at all dose levels of 100 mg/kg bw/day, or above. There were no treatment-related abnormalities seen for adults at macroscopic examination on study day 20. Serum samples taken for thyroxine (T4), triiodothyronine (T3) and thyroid stimulating hormone (TSH) on day 20 of gestation revealed that the T4 and T3 concentrations were slightly lower and the TSH levels were higher, when compared with controls, in treated female groups. This was considered secondary to effects on the liver, but the extent of the differences and evidence of normally functioning thyroid feedback system do not indicate adversity. An increase in the incidence of diffuse follicular cell hypertrophy, when compared to controls, was seen in females given 300 or 1000 mg/kg bw/day.

The increase in liver weights seen in all treated females may indicate a non-adverse, adaptive response to general toxic insult, and may be the major factor contributing to the elevated thyroid stimulating hormone (TSH) levels. Consequently, the levels of thyroxine (T4) or triiodothyronine (T3) were reduced, as would be expected in a normal physiologically functioning system. Furthermore, the higher incidence of follicular cell hypertrophy was considered secondary to the increase in TSH, although no increase in hypertrophy was evident at 100 mg/kg bw/day.

All animals were found to be pregnant at macroscopic examination, with exception of one animal treated with 100 mg/kg bw/day, with the mean number of corpora lutea, implantations, resorptions, the number of live young and sex ratio considered to be unaffected by treatment with decamethyltetrasiloxane.

Group mean litter and foetal weights were unaffected by treatment with decamethyltetrasiloxane. There were no major foetal abnormalities considered to be related to treatment. Minor abnormalities included an increase in incidence of delayed ossification across all treated groups and lens shape variation at 1000 mg/kg bw/day but all incidences were within the historical control data (HCD) range. These abnormalities are considered to be transient stages in foetal development, indicative of foetal immaturity and considered not to be adverse.

The NOAEL for maternal and developmental toxicity was concluded to be equal to or greater than 1000 mg/kg bw/day (the highest dose tested) based on no treatment-related adverse effects observed.

In the preliminary study for effects on embryo-foetal development, not conducted according to a guideline or in compliance with GLP, decamethyltetrasiloxane (L4) was administered orally (gavage) to female rats at doses of 0, 500, 750 or 1000 mg/kg bw/day in corn oil during gestation days 6 to 19 (Covance CRS Limited, 2020). Clinical observations, body weight and food consumption were recorded. Adult females were examined macroscopically at necropsy on Day 20 after mating and the gravid uterus weight was recorded. Liver and kidney weights were also recorded. All foetuses were examined macroscopically at necropsy. No unscheduled mortality, signs associated with dosing or clinical signs occurred during the study. The mean gravid uterine weight and body-weight gain (adjusted for gravid uterine weight), was slightly high at 1000 mg/kg bw/day group and associated with the slight increase in food intake at this dose level. Embryo-foetal survival was considered unaffected by the treatment. Liver weights were increased in all treated groups. There were no macroscopic findings considered to be related with treatment in adults or foetuses. Dose levels of 0, 100, 300 and 1000 mg/kg bw/day were selected for the main prenatal developmental toxicity study.

In a combined repeated dose toxicity study with the reproduction / developmental toxicity screening test with decamethyltetrasiloxane (L4) conducted according to a protocol comparable to OECD Test Guideline 422 and in compliance with GLP (Dow Corning Corporation, 2007) the NOAEC for general and developmental toxicity was at least 400 ppm (the only concentration tested) according to the study report. No deaths occurred during the study. No significant treatment-related clinical signs of toxicity were observed. Significant increases in body weight gains were noted in the 400 ppm parental females during the third week of gestation, which were not considered to be treatment-related. There were no statistically significant differences in food consumption in females. The food consumption for treated males was significantly decreased during weeks 1 and 2 and for total food consumption. However, food consumption for weeks 1 and 2 was within the normal range of the laboratory's historical controls. The difference was not considered to be related to treatment. There were no treatment-related alterations in haematology and serum chemistry. There appeared to be no functional or neurological effects of the test substance on the rats.There were no differences in absolute organ weights. The spleen to body weight ratio was slightly lower for toxicity group females, but not males, exposed to 400 ppm test substance. There was no histopathological correlate, nor any effect of exposure in other lymphoid tissues. This was considered to be random variation and not of toxicological significance. There were no gross lesions attributed to the test substance. One possible exposure-related finding was increased minimal alveolar histiocytosis in males in the 400 ppm exposure group. This is a common non-specific finding in inhalation studies; however, the minimal severity and fact that only one sex was affected made the significance of the finding uncertain. There were no other exposure-related in other tissues. Three female rats in the 400 ppm group with evidence of copulation failed to deliver a litter. One of these three females showed signs of parturition (blood discharge) on gestation day 25, but no pups were found. However, seven implant sites were present. The remaining females produced litters that were similar to the controls. There were no treatment-related effects apparent for any of the reproductive endpoints. There were no changes observed in the litter size, male-to-female ratio, pup body weights or the pup survival. There was no effect on testes or epididymides weights.

Justification for classification or non-classification

Dodecamethylpentasiloxane (L5) is not classified for reproductive or developmental toxicity according to Regulation (EC) No 1272/2008.