3-trimethoxysilylpropane-1-thiol

Toxicity to reproduction

Administrative data

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

16 Dec 2020 (experiment start) - final report date when available

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2021

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

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

Version / remarks:

2016

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: EPA OPPTS 870.3650, Combined Repeated Dose Toxicity Study with the Reproduction/Developmental Toxicity Screening Test

Version / remarks:

2000

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

3-trimethoxysilylpropane-1-thiol

EC Number:

224-588-5

EC Name:

3-trimethoxysilylpropane-1-thiol

Cas Number:

4420-74-0

Molecular formula:

C6H16O3SSi

IUPAC Name:

3-trimethoxysilylpropane-1-thiol

Test material form:

liquid

Test animals

Species:

rat

Strain:

Wistar

Details on species / strain selection:

The Wistar Han rat was chosen as the animal model for this study as it is an accepted rodent species for toxicity testing by regulatory agencies. Charles River Den Bosch has general and reproduction/developmental historical data in this species from the same strain and source. This animal model has been proven to be susceptible to the effects of reproductive toxicants.

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Deutschland, Sulzfeld, Germany
- Age at study initiation: 10-11 weeks (males) ; 13-14 weeks (females); (F1) x wks
- Weight at study initiation: (F1) Males: x-x g; Females: x-x g
- Fasting period before study: not specified
- Housing: polycarbonate cages (Makrolon, MIV/MIII type, height 18 cm). The cages contained appropriate bedding (Lignocel S 8-15, JRS - J.Rettenmaier & Söhne GmbH + CO. KG, Rosenberg, Germany). Animals were separated during designated procedures/activities. Main males and females were cohabitated on a 1:1 basis during the mating phase.
Diet (e.g. ad libitum): Pelleted rodent diet (SM R/M-Z from SSNIFF® Spezialdiäten GmbH, Soest, Germany), ad libitum (no access to food during motor activity measurements for a max. of 2 hours)
- Water (e.g. ad libitum): Municipal tap water via water bottles, ad libitum (no access during motor activity measurments for a max. of 2 hours)
- Acclimation period: 6 days prior to start of the pretest period (females) or 7 days before the commencement of dosing (males).
ENVIRONMENTAL CONDITIONS
- Temperature (°C): 18 to 24°C
- Humidity (%): 40 to 70%
- Air changes (per hr): Ten or greater air changes per hour with 100% fresh air (no air recirculation)
- Photoperiod (hrs dark / hrs light): 12 hour light/12 hour dark

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on exposure:

PREPARATION OF DOSING SOLUTIONS:
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 and dosed within 6 hours after adding the vehicle to the test item. Test item dosing formulations were kept at room temperature until dosing. If practically possible, the dosing formulations and vehicle were continuously stirred until and during dosing. Adjustment was made for specific gravity of the vehicle and test item. No correction was made for the purity/composition of the test item.


VEHICLE
- Justification for use and choice of vehicle (if other than water): Trial preparations were performed to select the suitable vehicle and to establish a suitable formulation procedure. These trials were not performed as part of this study and these preparations were not used for dosing.
- Concentration in vehicle: 0, 20, 60, 120 mg/mL
- Amount of vehicle (if gavage): 5 mL/kg bw
- Purity: not specified

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: maximum of 14 days
- Proof of pregnancy: vaginal plug / sperm in vaginal smear referred to as day 0 post-coitum
- After successful mating each pregnant female was caged (how): individually, in Makrolon plastic cages (MIII type, height 18 cm).
- Any other deviations from standard protocol: no

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Duplicate sets of samples (approximately 500 mg) for each sampling time point were sent to the analytical laboratory. Concentration results were considered acceptable if mean sample concentration results were within or equal to ± 10% for solutions of target concentration. Homogeneity results were considered acceptable if the coefficient of variation (CV) of concentrations was <= 10%.

Duration of treatment / exposure:

At least 29 days. Main females were treated for 51-65 days; 14 days prior to mating and at least 13 days after delivery, up to and including the day before scheduled necropsy. Main females which failed to deliver were treated for 41-52 days. Recovery females were treated during the same period as Main females, until at least the day before the first scheduled necropsy of Main females. Main males and Recovery males were treated for 29 days, including a minimum of 14 days prior to mating and during the mating period for Main males. For both Main and Recovery males, treatment ended one day before scheduled necropsy of Main males.

Frequency of treatment:

Daily, 7 days a week

Details on study schedule:

N/A screening study

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 mg/kg bw/day (nominal)

Remarks:

Group 1 = Control group

Doses / concentrations 2

Dose / conc.:

100 mg/kg bw/day (nominal)

Remarks:

Group 2

Doses / concentrations 3

Dose / conc.:

300 mg/kg bw/day (nominal)

Remarks:

Group 3

Doses / concentrations 4

Dose / conc.:

600 mg/kg bw/day (nominal)

Remarks:

Group 4

No. of animals per sex per dose:

10 animals/sex/group in the main groups and 5/animals/sex/group in the recovery groups

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 Finder (DRF) with oral administration of 3-(trimethoxysilyl)propane-1-thiol (CAS 4420-74-0) in rats (Test Facility Reference No. 20244995), and a prematurely terminated OECD 422 study (Test Facility Study No. 20244996) in rats, and in an attempt to produce graded responses to the test item. See mode details under details of results.
- Rationale for animal assignment (if not random): random
- Fasting period before blood sampling for clinical biochemistry: yes
- Rationale for selecting satellite groups: not specified

Positive control:

No

Examinations

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule:
Animals were observed for general health/mortality and moribundity twice daily, in the morning and at the end of the working day. Animals were not removed from the cage during observation, unless necessary for identification or confirmation of possible findings.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule:
Once daily, beginning during the first administration of the test item and lasting throughout the dosing and recovery periods up to the day prior to necropsy.

Clinical observations included changes in gait, spontaneous activity, response to handling as well as the presence of clonic or tonic movements, stereotypes, difficult or prolonged parturition or bizarre behaviour, lethargy, recumbent position, convulsions, tremors, apnoea, asphyxia, vocalisation, diarrhoea, changes in the skin and fur, eyes and mucous membranes (salivation, discharge), piloerection and pupil size.

BODY WEIGHT: Yes
- Time schedule for examinations:
Animals were weighed individually on the first day of treatment (prior to dosing), and weekly thereafter. Mated main females were weighed on days 0, 4, 7, 11, 14, 17, and 20 post-coitum and during lactation on PND 1, 4, 7, and 13. A terminal weight was recorded on the day of scheduled necropsy

FOOD CONSUMPTION AND COMPOUND INTAKE : Yes
- Time schedule: Food consumption was quantitatively measured weekly, except for Main males and Main females which were housed together for mating and for Main females without evidence of mating. Food consumption of mated Main females was measured on days 0, 4, 7, 11, 14, 17, and 20 post-coitum and during lactation on PND 1, 4, 7, and 13

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

WATER CONSUMPTION AND COMPOUND INTAKE: Yes
- Time schedule: Water consumption was monitored on regular basis throughout the study by visual inspection of the water bottles. No quantitative investigation was introduced as no effect was suspected.

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: At the end of the treatment period or end of the recovery period on the day of scheduled necropsy
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: Yes
- How many animals: All animals
- Parameters checked in Table 1 below were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: At the end of the treatment period or end of the recovery period on the day of scheduled necropsy
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: Yes
- How many animals: All animals
- Parameters checked in Table 1 below were examined.

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations:
Functional tests performed after dosing, after completion of clinical observations. During week 4 of treatment for 5 selected main males and all recovery males, and during last week of lactation for 5 selected main females and all recovery females. As potential treatment-related findings were noted in locomotor activity in recovery females at the end of the treatment period, locomotor activity measurements were also conducted for all Recovery females at the end of the recovery period
- Battery of functions tested: hearing ability, pupillary reflex, static righting reflex, fore- and hind-limb grip strength, locomotor activity (total movements and ambulations).

IMMUNOLOGY: No

Oestrous cyclicity (parental animals):

Estrous cycles were evaluated by examining the vaginal cytology of samples obtained by vaginal lavage.
Daily vaginal lavage was performed for all females (Main and Recovery) during 14 days prior to treatment (pretest period) and the first 14 days of treatment. For Main females, daily vaginal lavage was continued during mating until evidence of copulation was observed. On the day of necropsy, a vaginal lavage was also taken from Main females to determine the stage of estrous

Sperm parameters (parental animals):

Parameters examined in male parental generations: testes and epdidymis weight.
For the testes of all selected Main males of Groups 1 and 4, and all Main males that failed to sire, a detailed qualitative examination was made, taking into account the tubular stages of the spermatogenic cycle.

Litter observations:

STANDARDISATION OF LITTERS
- Performed on day 4 postpartum: yes
- If yes, maximum of 8 pups/litter (4/sex/litter as nearly as possible); excess pups were euthanised by decapitation. Blood samples were collected from two of the surplus pups (if possible, from one male and one female pup) and samples were pooled to one sample per litter. Selective elimination of pups, e.g. based upon body weight or AGD, was not done. All remaining pups were euthanized on PND 14-16.

PARAMETERS EXAMINED
The following parameters were examined in F1] offspring:
Number and sex of pups, stillbirths, live births, postnatal mortality, presence of gross anomalies, weight gain, physical or behavioural abnormalities, anogenital distance (AGD), presence of nipples/areolae in male pups, T4 levels. Particular attention should be paid to the external reproductive genitals which should be examined for signs of altered development.

GROSS EXAMINATION OF DEAD PUPS:
[yes, for external and internal abnormalities; presence of milk in stomach; and if possible defects or cause of death evaluated]

ASSESSMENT OF DEVELOPMENTAL NEUROTOXICITY: No

ASSESSMENT OF DEVELOPMENTAL IMMUNOTOXICITY: No

Postmortem examinations (parental animals):

SACRIFICE
- Male animals: All surviving animals [Following completion of the mating period for Main males which sired or failed to sire; after the recovery period of at least 14 days for Recovery males]
- Female animals: All surviving animals [At PND 14-16 for Main females which delivered; Post-coitum Days 25-26 for Main feamles with evidence of mating which failed to deliver; After the recovery period of at least 14 days for Recovery females]

GROSS NECROPSY / HISTOPATHOLOGY / ORGAN WEIGHTS: Yes
Gross necropsy consisted of external and internal examinations, including examination of the cranial, thoracic and abdominal cavities and their contents, as well as reproductive organs.

A number of organs from all selected main animals and all recovery animales (see Table 2 below) as well as from males that failed to sire and females that failed to deliver (see Table 3 below) were prepared for microscopic examination and weighed.

All tissues indicated in these tables were examined by board-certified toxicological pathologist with training and experience in laboratory animal pathology. For the testes of all selected Main males of Groups 1 and 4, and all Main males that failed to sire, a detailed qualitative examination was made, taking into account the tubular stages of the spermatogenic cycle.

Postmortem examinations (offspring):

SACRIFICE
- Pups younger than 7 days were euthanized by decapitation.
- All remaining pups (PND 14-16), except for the two pups per litter selected for blood collection were euthanized by an intraperitoneal injection of sodium pentobarbital.
- The pups selected for blood collection on PND 14-16 were anesthetized using isoflurane followed by exsanguination.

GROSS NECROPSY / HISTOPATHOLOGY
Sex was determined both externally and internally. Descriptions of all external abnormalities were recorded. Particular attention was paid to the external reproductive genitals to examine signs of altered development.
In addition, blood was collected from two pups per litter, and the thyroid from two pups per litter (if possible one male and one female pup) was preserved in 10% buffered formalin. The pups selected for blood sampling were the same pups as selected for thyroid preservation.

Statistics:

See repeated dose toxicity endpoint 7.8.1.089

Reproductive indices:

Reproductive-type parameters evaluated were evidence of mating, pregnancy and duration of gestation, lenght and regularity of the estrous cycle, and number of uterine implantation sites.

Offspring viability indices:

Pups were examined daily for survival, external abnormalities and clinical signs. Number and sex of the pups, the number of pups alive per litter, number of pups dead were noted. All pups were counted, weighed, sexed and the sex ratio calculated.

Results and discussion

Results: P0 (first parental generation)

General toxicity (P0)

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Abnormal gait, belly sliding behaviour and back scratching were noted in all males and females at 600 mg/kg bw/day. Lethargy in males and females was noted at 600 mg/kg bw/day.
Uncoordinated movements as well as yellow staining/discoloration of the genital region in females only were observed at 600 mg/kg bw/day.
These effects were considered adverse clinical signs.
Hunched posture, salivation and incidental findings including alopecia, piloerection and scabs were also observed but were not considered not to be toxicologically relevant.

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:

effects observed, treatment-related

Description (incidence and severity):

Body weights and body weight gain was considered to be affected by treatment with the test item in males and main females at 600 mg/kg bw/day.

In males at 600 mg/kg bw/day, mean body weight and mean body weight gain were decreased throughout the treatment period (not always reaching statistical significance), followed by only slight recovery during the 14 days treatment-free Recovery Period. Mean body weights were 5% and 4% lower compared to the concurrent control group at the end of the treatment period and end of the recovery period, respectively.
In females at 600 mg/kg bw/day, mean body weight gain was decreased between post-coitum Days 7-20 (not always reaching statistical significance), followed by values that were similar to the concurrent control group during the lactation period. At the end of the periods of gestation and lactation, mean body weight were 6% lower compared to the concurrent control group. In non-pregnant recovery females, body weight was considered to be unaffected by treatment with the test item up to 600 mg/kg bw/day.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Food consumption before or after correction for body weight was considered affected by treatment with the test item in males and main females at 600 mg/kg bw/day.

In males at 600 mg/kg bw/day, a trend towards lower mean absolute and relative food consumption was observed (-19 and -17% of control, respectively; not statistically significant) over Days 1-8 of the premating period which recovered to levels similar to the concurrent control thereafter.
In main females at 600 mg/kg bw/day, mean absolute and relative food consumption were decreased from post-coitum Days 14-17 up to and including Lactation Days 7-13.

During the last interval of the lactation period, mean absolute and relative food consumption were 24 and 21% lower compared to the concurrent control, respectively (not always reaching statistical significance).

Food efficiency:

not examined

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

not specified

Ophthalmological findings:

not examined

Haematological findings:

effects observed, non-treatment-related

Description (incidence and severity):

Hematology findings in males comprised of higher white blood cell and neutrophil concentrations (at 600 mg/kg bw/day), and monocyte concentrations (starting at 300 mg/kg bw/day), in Main females of higher reticulocyte concentration and red blood cell distribution width gated (starting at 300 mg/kg bw/day), and lower neutrophil and monocyte concentrations (at 600 mg/kg bw/day), and in Recovery females of higher red blood cell concentration, and lower mean corpuscular volume and mean corpuscular hemoglobin (at 600 mg/kg bw/day). Except for monocyte concentration in males and red blood cell concentration in recovery females, partial recovery was seen for all other differences at the end of the recovery period.
These findings were considered non adverse since these changes were not associated with any adverse pathological alterations.

Clinical biochemistry findings:

effects observed, non-treatment-related

Description (incidence and severity):

Clinical biochemistry findings in males comprised of higher alanine aminotransferase and aspartate aminotransferase activity (starting at 300 mg/kg bw/day), and bile acid and urea concentration (at 600 mg/kg bw/day), and in Main females of higher alanine aminotransferase activity and albumin concentration, and lower inorganic phosphate concentration (all at 600 mg/kg bw/day), and in recovery females of higher bile acid concentration and lower total protein concentration, albumin concentration and calcium concentration (all at 600 mg/kg bw/day). Except for bile acid concentration (males), total protein concentration, albumin concentration and calcium concentration (females), (partial) recovery was noted for all other changes at the end of the recovery period. These findings were considered non adverse since these changes were not associated with any adverse pathological alterations.

Urinalysis findings:

not examined

Behaviour (functional findings):

effects observed, non-treatment-related

Description (incidence and severity):

In main females, mean total movements and ambulations were increased (1.34x and 1.29x of control, respectively) at 600 mg/kg bw/day.
In recovery females, mean total movements was decreased (0.88x of control mean) at 600 mg/kg bw/day at the end of the treatment period and recovered to control levels at the end of the recovery period. Mean ambulations were considered not affected by treatment with the test item at 600 mg/kg bw/day at the end of the treatment and recovery period.
Motor activity was considered not to be affected by treatment with the test item in males up to 600 mg/kg bw/day. All groups showed a similar motor activity habituation profile with in general a decreasing trend in activity over the duration of the test period. Hearing ability, pupillary reflex, static righting reflex and grip strength were normal in all examined animals up to 600 mg/kg bw/day.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Treatment-related bladder findings were observed in both sexes at 300 and 600 mg/kg bw/day but, with the exception of one female at 600 mg/kg bw/day, are considered non-adverse by the Registrant. In addition, non-adverse mesenteric lymph node findings were seen in males at these two doses.

Minimal to slight urothelial hyperplasia/hypertrophy was noted in the urinary bladder of males and females treated at 300 and 600 mg/kg bw/day. This finding showed no recovery after the treatment free recovery period. In a single female at 600 mg/kg bw/day, effects of a degenerative nature also were seen and included ulcer of the urothelium, haemorrhage, oedema and subepithelial fibrosis. However, based on a review of all available rat data across a wide range of silicon-based compounds including multiple trimethoxysilanes, the silicon industry considers diffuse urothelial hyperplasia in the bladder without atypia to be an adaptive (non-adverse) response to physical or chemical irritation. Thus, except for the single female with degenerative bladder histopathology at 600 mg/kg bw/day, the bladder urothelial hyperplasia seen at 300 and 600 mg/kg bw/day for 3-(trimethoxysilyl)propane-1-thiol is assessed as non-adverse by the Registrants.

In the mesenteric lymph nodes of males at 300 and 600 mg/kg bw/day, sinus histiocytosis observed was without any degenerative finding and there was partial/ongoing recovery after the treatment-free recovery period. Therefore, this finding was considered non adverse.

Histopathological findings: neoplastic:

no effects observed

Other effects:

no effects observed

Description (incidence and severity):

No treatment-related toxicologically significant changes were noted in T4 thyroid hormone levels.

Reproductive function / performance (P0)

Reproductive function: oestrous cycle:

no effects observed

Description (incidence and severity):

Length and regularity of the estrous cycle were considered not to have been affected by treatment with the test item up to 600 mg/kg bw/day. All females had regular cycles of 4 to 5 days, except for Recovery Female No. 96 (600 mg/kg bw/day) which had an irregular cycle during the Treatment Period that was characterized by an extended di estrous period. Given the incidental nature, this finding was considered not related to treatment with the test item.

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

no effects observed

Description (incidence and severity):

Mating index was not affected by treatment with the test item up to 600 mg/kg bw/day. All Main females showed evidence of mating, which resulted in a mating index of 100% for all groups.
Precoital time was not affected by treatment with the test item up to 600 mg/kg bw/day. All paired females showed evidence of mating within 5 days, except for Female Nos. 53, 57 (control) and 70 (100 mg/kg bw/day) for which mating took 14, 13 and 14 days, respectively.

Details on results (P0)

During the prematurely terminated OECD 422 study (dose levels: 0, 100, 300 and 1000 mg/kg bw/day), 1/15 males and 1/15 females at 1000 mg/kg bw/day were found dead on treatment Day 6 and all remaining males and females at 1000 mg/kg bw/day were euthanized in extremis due to the severe toxicity observed within one week of dosing. Most animals at 1000 mg/kg bw/day had lost more than 10% (10-19%) of their body weight within 5 days of treatment and/or showed one or a combination of the following clinical symptoms: hunched posture, flat posture, uncoordinated movements, decreased locomotor activity, tremor, lethargy, slow breathing and red discoloration of the urine. Macroscopic examination indicated that the stomach was severely affected at 1000 mg/kg bw/day as it was thickened, had an irregular surface and contained multiple foci.
Salivation, scabs and wounds were noted at 100 and 300 mg/kg bw/day. Body weight (gain) and food consumption was similar to control at 100 and 300 mg/kg bw/day. Macroscopic examination revealed no abnormalities at 300 mg/kg bw/day.

Based on the above described results of the 14-Day DRF with oral gavage administration of 3 (trimethoxysilyl)propane-1-thiol in rats (Test Facility Study No. 20244995) and prematurely terminated OECD 422 study (Test Facility Study No. 20244996), a dose level of 600 mg/kg bw/day was considered to be well tolerated. Therefore, this dose level was selected as the highest dose level for the current OECD 422 study (Test Facility Study No. 20281767). A mid- and low-dose level of 300 and 100 mg/kg bw/day were chosen in order to provide information on possible dose-response relationships.

Effect levels (P0)

1

Key result

Dose descriptor:

NOAEL

Remarks:

reproductive

Effect level:

>= 600 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Based on the absence of reproductive effects

2

Dose descriptor:

NOAEL

Remarks:

systemic

Effect level:

300 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical signs

body weight and weight gain

food consumption and compound intake

histopathology: non-neoplastic

Remarks on result:

other: See other information on results

Target system / organ toxicity (P0)

Critical effects observed:

yes

Lowest effective dose / conc.:

600 mg/kg bw/day (nominal)

System:

urinary

Organ:

bladder

Treatment related:

yes

Results: F1 generation

General toxicity (F1)

Clinical signs:

effects observed, non-treatment-related

Description (incidence and severity):

Less milk, pale appearance and/or cold to touch was recorded in one or two litters at 600 mg/kg bw/day on PND 1, 2, 3 and/or 4. These clinical signs were considered not to be toxicologically relevant as these were only evident for a short duration (i.e. 1 or 2 days) and in a subset of pups from one or two litters at 600 mg/kg bw/day.
The nature and incidence of other clinical signs remained within the range considered normal for pups of this age and were therefore considered not to be related to treatment with the test item.

Dermal irritation (if dermal study):

not examined

Mortality / viability:

mortality observed, non-treatment-related

Description (incidence and severity):

The live birth indices were 100, 97, 98, 97% for the control, 100, 300 and 600 mg/kg bw/day groups, respectively.
Three pups (Litter No. 67) at 100 mg/kg bw/day, two pups (Litter No. 80) at 300 mg/kg bw/day, and three pups (Litter No. 95) at 600 mg/kg bw/day were found dead at the first litter check. At necropsy, no milk in the stomach was noted for all these dead pups, except for one dead pup from Litter No. 67 which was already partially cannibalized.
No toxicological relevance was attributed to these dead pups since the mortality incidence did not show a dose-related trend and remained within the range considered normal for pups of this age.

Viability indices were 100, 99, 100 and 97% for the control, 100, 300 and 600 mg/kg bw/day groups, respectively.
One pup (Litter No. 72) at 100 mg/kg bw/day and three pups (one in Litter No. 91 and two in Litter No. 95) at 600 mg/kg bw/day were missing on PND 2 or 3. These missing pups were most likely cannibalized.
Previous to death, the pup from Litter No. 72 displayed lethargy and less milk in the stomach at first litter check. The pup from Litter No. 91 presented with less milk in its stomach at PND 1, and both pups from Litter No. 95 were pale at PND 1 and/or 2 of which one contained less milk in its stomach on PND 2.
No toxicological relevance was attributed to these missing pups and clinical signs since the mortality incidence did not show a dose-related trend and remained within the range considered normal for pups of this age.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Body weights of pups were affected by treatment with the test item at 600 mg/kg bw/day, but were considered by the Registrants to be secondary to maternal systemic toxicity.

Mean pup body weights were decreased at 600 mg/kg bw/day in both sexes throughout the lactation period (not statistically significant on PND 1). At PND 13, mean pup body weights were 24, 22 and 23% lower than control in males, females or combined sexes, respectively.

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

Anogenital distance (AGD):

no effects observed

Description (incidence and severity):

Anogenital distance (absolute and normalized for body weight) in male and female pups was considered not to be affected by treatment with the test item up to 600 mg/kg bw/day. All values remained within the normal range of biological variation.

Nipple retention in male pups:

no effects observed

Description (incidence and severity):

Treatment with the test item up to 600 mg/kg bw/day had no effect on areola/nipple retention. For none of the examined male pups nipples were observed at PND 13.

Organ weight findings including organ / body weight ratios:

no effects observed

Gross pathological findings:

effects observed, non-treatment-related

Description (incidence and severity):

No macroscopic findings were noted among pups that were considered to be related to treatment with the test item up to 600 mg/kg bw/day.
The nature and incidence of macroscopic findings remained within the range considered normal for pups of this age, and were therefore considered not to be related to treatment with the test item.

Histopathological findings:

not examined

Other effects:

no effects observed

Description (incidence and severity):

Serum T4 levels in male and female PND 14-16 pups were considered not to be affected by treatment with the test item up to 600 mg/kg bw/day.

Developmental neurotoxicity (F1)

Behaviour (functional findings):

not examined

Developmental immunotoxicity (F1)

Developmental immunotoxicity:

not examined

Effect levels (F1)

Key result

Dose descriptor:

NOAEL

Remarks:

systemic

Generation:

F1

Effect level:

>= 600 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Lower pup body weight throughout the lactation period secondary to maternal systemic toxicity at 600 mg/kg bw/day.

Target system / organ toxicity (F1)

Key result

Critical effects observed:

no

Overall reproductive toxicity

Key result

Reproductive effects observed:

no

Any other information on results incl. tables

As discussed under the histopathology results, the silicon industry considers diffuse urothelial hyperplasia in the bladder without atypia to be an adaptive (non-adverse) response to physical or chemical irritation based on a review of all available rat data across a wide range of silicon-based compounds including multiple triethoxysilanes. Thus, with the exception of the single female with bladder urothelial hyperplasia combined with degenerative bladder histopathology at 600 mg/kg bw/day, the Registrants consider the male and female bladder urothelial hyperplasia at 300 and 600 mg/kg bw/day to be non-adverse.

Applicant's summary and conclusion

Conclusions:

In a combined repeated dose oral toxicity study with the reproduction / developmental toxicity screening test, with the registered substance 3-(trimethoxysilyl)propane-1-thiol and conducted according to OECD Test Guideline 422 and in compliance with GLP, the NOAEL for reproductive effects was concluded to be equal to or higher than 600 mg/kg bw/day based on no adverse effects on reproduction parameters. The NOAEL for parental systemic effects was concluded to be 300 mg/kg bw/day based on based on adverse clinical signs, decreased body weight, body weight gain, and/or food consumption in both sexes at 600 mg/kg bw/day. A single female at 600 mg/kg bw/day also had bladder urothelial hyperplasia combined with degenerative bladder histopathology.