Triethoxy(2,4,4-trimethylpentyl)silane

Endpoint summary

Description of key information

In the 90-day oral repeated dose toxicity study, conducted according to OECD Test Guideline 408 and in compliance with GLP, a systemic NOAEL of 150 mg/kg bw/day was concluded based on no treatment-related effects in any of the test animals (BSL Bioservice, 2015).

There are no repeated dose inhalation toxicity data on triethoxy(2,4,4-trimethylpentyl)silane, so good quality data for the structural analogue trimethoxy(2,4,4-trimethylpentyl)silane (CAS 34396-03-7), have been used to assess the repeated dose inhalation toxicity of triethoxy(2,4,4-trimethylpentyl)silane.

In the 28-day inhalation repeated dose toxicity study with triethoxy(2,4,4-trimethylpentyl)silane, conducted according to OECD Test Guideline 412 and in compliance with GLP, the NOAEL for systemic toxicity was concluded to be at least 3 mg/l (nominal) based no adverse systemic effects (Hoechst Pharma Forschung Toxikologie und Pathologie, 1986b).

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River, 97633 Sulzfeld, Germany
- Age at study initiation: males: 7-8 weeks old, females: 7-8 weeks old.
- Weight at study initiation: males: 151.1 – 184.6 g; females: 122.0 – 148.1 g
- Fasting period before study: not indicated
- Housing: Animals of the same sex were housed in groups of up to five in type IV polysulphone cages on Altromin saw fibre bedding (lot no. 02102140605)
- Diet (e.g. ad libitum): Free access to Altromin 1324 maintenance diet for rats and mice (lot no. 1526)
- Water (e.g. ad libitum): Free access to tap water, sulphur acidified to a pH of approximately 2.8 (drinking water, municipal residue control, microbiological controls at regular intervals)
- Acclimation period: minimum 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 3°C
- Humidity (%): 55 ± 10%
- Air changes (per hr): 10 x / hour
- Photoperiod (hrs dark / hrs light): Artificial light, sequence being 12 hours light, 12 hours dark

Route of administration:

oral: gavage

Vehicle:

corn oil

Details on oral exposure:

The test item formulation or vehicle was administered at a single dose to the animals by oral gavage. The application volume for all groups was 5 mL/kg body weight.

For each animal the individual dosing volume was calculated on the basis of the body weight most recently measured.

The doses were selected in consultation with the sponsor.

Analytical verification of doses or concentrations:

no

Details on analytical verification of doses or concentrations:

Stability of the dosing formulations was tested once at the beginning of the treatment period. In the first week of treatment, at the beginning of the second month of treatment and at the end of the treatment period, samples for the testing of homogeneity were taken from the top, middle and bottom of the freshly prepared high and low-dose formulations and stored between -15 and -35 °C.

Duration of treatment / exposure:

90 days

Frequency of treatment:

Daily, 7 days per week

Dose / conc.:

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

Dose / conc.:

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

Dose / conc.:

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

No. of animals per sex per dose:

10/sex/dose

Details on study design:

The highest dose level was chosen with the aim of inducing toxic effects, but no death or severe suffering. Thereafter, a descending sequence of dose levels was selected with a view to demonstrate any dosage related response and NOAEL.
The animals in the control group were handled in an identical manner to the test group subjects and received corn oil using the same volume as used for the high dose group.

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: once before the first administration and at least once a week thereafter

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Minimum once a day, twice daily all animals were observed for morbidity and mortality except on weekends and public holidays when observations were made once daily.

BODY WEIGHT: Yes
- Time schedule for examinations: The body weight was recorded once before the assignment to the experimental groups, on the first day of administration and weekly during the treatment and recovery period.

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study):
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No, food consumption was measured weekly during the treatment and recovery period.

- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: Ophthalmological examination, using an ophthalmoscope was made at the first administration and in the last week of the treatment period.
- Dose groups that were examined: All animals, as well as at the end of the recovery period in the recovery animals.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: At the end of the treatment and recovery period, prior to or as part of the sacrifice of the animals.
- Anaesthetic used for blood collection: No data
- Animals fasted: Yes
- Parameters checked: haematocrit, haemoglobin content, red blood cell count, mean corpuscular volume, mean corpuscular haemoglobin, mean corpuscular concentration, reticulocytes, platelet count, white blood cells, neutrophils, lymphocytes, monocytes, eosinophils, basophils, large unstained cells, coagulation parameters (prothrombin time, activated partial thromboplastin time)

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: at the end of the treatment and recovery period prior to or as part of the sacrifice of the animals
- Animals fasted: No data
- Parameters checked: alanine aminotransferase, aspartate-aminotransferase, alkaline phosphatase, creatinine, total protein, albumin, urea, total bilirubin, total bile acids, total cholesterol, glucose, potassium, sodium

URINALYSIS: Yes
- Time schedule for collection of urine: prior to or as part of the sacrifice of the animals
- Metabolism cages used for collection of urine: No data
- Animals fasted: No data
- Parameters checked: specific gravity, nitrite, pH, protein, glucose, ketone bodies, urobilinogen, bilirubin, blood, leukocytes.

FUNCTIONAL OBSERVATIONS: Yes
- Time schedule for examinations: Once before the first exposure and once in the last week of the recovery period.
- Dose groups that were examined: All animals
- Battery of functions tested: other: sleep, moving around cage, piloerection, vocalisation, grooming, grip strength, visual palcing, positional passivity, equilibrium reflex, startle response, sterotypical behaviour, unusual behaviour, seizures, twitches, tremors, gait etc.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes.

-Organs weighed at necropsy: liver, kidneys, adrenals, testes, epididymides, prostate, seminal vesicles, coagulating glands, ovaries, uterus with cervix, thymus, thyroid/parathyroid glands, spleen, brain, pituitary gland, heart. The wet weight of the organs of all sacrificed animals was taken from sacrificed animals as soon as possible. Paired organs were weighed together.

-Preserved and examined tissues: brain, spinal cord, eye, liver, kidneys, adrenal glands, stomach, heart, ovaries, uterus with cervix, vagina, testes, apididymides, prostrate and seminal vescles with coagulating glands as a whole. Small and large intestines, thymus, thyroid glands, spleen, lung and trachea, mammary glands, skin, urinary bladder, lymphnodes, perpheral nerve with skeletal muscle, sternum with bone marrow, pituitary gland, oesophagus

HISTOPATHOLOGY: Yes

Clinical signs:

no effects observed

Description (incidence and severity):

No test item related clinical findings were observed in this study. The clinical findings were either rare incidental findings or were observed in similar frequency also in control animals. The effects are not considered to be adverse.

Mortality:

no mortality observed

Description (incidence):

No mortality occurred in the control or any of the dose groups during the treatment period of this study.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

The body weight development of all groups was within the expected range of variation with no test item related effects. In accordance to the body weight development no effects on food consumption were recorded.

Food consumption and compound intake (if feeding study):

no effects observed

Food efficiency:

not specified

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

not specified

Ophthalmological findings:

no effects observed

Haematological findings:

no effects observed

Description (incidence and severity):

No influence of triethoxy(2,4,4-trimethylpentyl)silane on any of the analysed parameters of hematology and blood coagulation independent of the gender of the animals was observed at the end of the treatment and after the recovery period.

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

All clinical biochemistry parameters analyzed at the end of the treatment and recovery phase did not indicate toxicologically relevant findings which are related to the test item.

Urinalysis findings:

no effects observed

Description (incidence and severity):

Abnormalities observed in urinalysis were incidental findings and are not assumed to be toxicologically relevant. Therefore the test item is assumed to show no effects on parameters of urinalysis.

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

No relevant effects were observed in any of the parameters of the functional observation battery with no biologically relevant differences in body temperature between the groups.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

Changes in organ weights were either related to female cycle, rare single cases or within normal range of variation with no toxicological relevance.

Gross pathological findings:

no effects observed

Description (incidence and severity):

The recorded pathological changes were either isolated findings, were observed in control animals or were related to female cycle and are therefore considered to be normal background alterations.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

Histopathologically adaptive and therefore non-adverse urothelial hyperplasia with minor degree was found in the urinary bladder of males and females receiving 50 mg/kg/day and 150 mg/kg/day.

Histopathological findings: neoplastic:

no effects observed

Key result

Dose descriptor:

NOAEL

Effect level:

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

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No adverse systemic effects were observed in any of the test animals at doses of 15, 50 and 150 mg/kg bw/day.

Critical effects observed:

no

Formulation analytics revealed that all samples were stable; the nominal concentrations were confirmed for all dose groups and that all samples were homogenous.

Conclusions:

In the 90-day oral repeated dose toxicity study, conducted according to OECD Test Guideline 408 and in compliance with GLP, a systemic NOAEL of 150 mg/kg bw/day was concluded based on no treatment-related effects in any of the test animals.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

150 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)

Principles of method if other than guideline:

Recovery period: 15 d

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Strain: Hoe: WISKf (SPF71)
- Source: Hoechst AG, Pharma-Forschung-Toxikologie; breeding under SPF conditions
- Age at study initiation: 5-6 weeks
- Weight at study initiation: Males: 137-150 g. Females: 137-146 g
- Fasting period before study: No
- Housing: : 5 per Makrolon cage
- Diet (e.g. ad libitum): Ad libitum except during exposure
- Water (e.g. ad libitum): Ad libitum except during exposure
- Acclimation period: No data


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22± 2
- Humidity (%): 50± 20
- Air changes (per hr): 10
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

nose only

Vehicle:

other: Air

Mass median aerodynamic diameter (MMAD):

< 6 µm

Remarks on MMAD:

MMAD / GSD: Particle size (mean): 99.98% of the particle in 0.3 mg/l group, 99.98% of the particle in 1.5 mg/l group and 99.87% of the particle in 3.0 mg/l group are below 6 µm.

Details on inhalation exposure:

Duration of exposure: 6h/d, 5d/w
Exposure: Animals were exposed to the test atmosphere in nose-only inhalation units
Exposure apparatus: The inhalation chamber used in the study were stainless steel/glass cylindrical columns. Each column had a volume of 80 L and consisted of a top assembly with the inlet of the test atmosphere, one rodent tube section and the bottom, the base assembly with the exhaust port.
Method of holding animals in test chamber: Nose only; cylindrical tubes.
Method of conditioning air: Compressed air (4 bar), oil separation filter/absolute filter; to achieve requested air humidity moistened air was feeded directly in the chamber
System of generating particulates/aerosols: The inhalation equipment was designed to expose the animals to a continuous supply of fresh test atmosphere. The test atmosphere was generated by passing test material to special nozzels. The operating pressure was 4 bar.
Temperature, humidity: 20.0 - 23.5°C, 31.5-60.6%
Contineous measurement of CO-, CO2- and O2-concentration during exposure in exposure chamber; CO: 0 ppm; CO2: 3800 - 7900 ppm; O2: 19.8 - 20.6 Vol %
Air flow rate: Air inlet 800 L/h; 1100 L/h exhausted
Method of particle size determination: The particle size distribution was measured using an APS 33 Aerodynamik Particle Sizer from TSI Inc., St Paul.
The aerodynamic diameter range measured with this analyzer covered 0.486 to > 15.4 micrometer.
Measurements were performed daily 30 minutes, 2 and 4 hours respectively after starting the exposure.
After the end of the exposure period, the arithmetic means together with the standard deviations based
on the 3 points in time were calculated using a statistics program.
The statistics program was used further to calculate an overall arithmetic mean for each dose group
based on the arithmetic means for each single day of exposure.
Brief description of analytical method used:
Gravimetric verification of concentrations
Gravimentric measurements were performed using a membrane filter, pore size 0.65 micrometer,
50 mm diameter (sartorius Membranfilter GmbH, Göttingen). The air flow rate was 3 l/min, which
is equivalent to an intake velocity of 1.25 m/sec.
Gravimetric measurements were performed daily in the exposure chambers 30 minutes, 2 and 4 hours respectively after starting the exposure.
Chemical verification of concentrations
Within 60 minutes 31 liter aerosol from the exposure chambers was pumped through 3 gas-washing bottles filled with acetone (PESTANAL, RIEDEL DE HAEN) connected in series and standing in a cool trap. Thereof aliquotes were taken and analysed using a gas chromatograph.
The concentration of isooctyltrimethoxysilane in the exposure chambers was calculated based on the results of the GC and
considering the aerosol- and acetone volumina.
Sampling was performed on day 1, 8, 15, 22 and 27 of the treatment.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Gravimetric verification of concentrations
Gravimentric measurements were performed using a membrane filter, pore size 0.65 micrometer,
50 mm diameter (sartorius Membranfilter GmbH, Göttingen). The air flow rate was 3 l/min, which
is equivalent to an intake velocity of 1.25 m/sec.
Gravimetric measurements were performed daily in the exposure chambers 30 minutes, 2 and 4 hours respectively after starting the exposure.

Chemical verification of concentrations
Within 60 minutes 31 liter aerosol from the exposure chambers was pumped through 3 gas-washing bottles filled with acetone (PESTANAL, RIEDEL DE HAEN) connected in series and standing in a cool trap. Thereof aliquotes were taken and analysed using a gas chromatograph.
The concentration of isooctyltrimethoxysilane in the exposure chambers was calculated based on the results of the GC and
considering the aerosol- and acetone volumina.
Sampling was performed on day 1, 8, 15, 22 and 27 of the treatment.

Duration of treatment / exposure:

28 days + 14 days recovery

Frequency of treatment:

Five days per week; six hours per day

Dose / conc.:

0.32 mg/L air (analytical)

Remarks:

0.3 mg/L air nominal conc.

Dose / conc.:

1.54 mg/L air (analytical)

Remarks:

1.5 mg/L air nominal conc.

Dose / conc.:

2.89 mg/L air (analytical)

Remarks:

3.0 mg/L nominal conc.

No. of animals per sex per dose:

Ten

Control animals:

other: Air

Details on study design:

- Dose selection rationale: No data
- Rationale for animal assignment (if not random): Random
- Rationale for selecting satellite groups: Five animals of each sex and group were used to assess recovery from treatment-related effects
- Post-exposure recovery period in satellite groups: 15 days

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes


DETAILED CLINICAL OBSERVATIONS: Mortality, behavior and general state of health (before and after exposure and during exposure; one time per day during weekend); Neurological disorders, opacity of eyes, damage of oral mucosa, disorder of tooth growth (weekly)


BODY WEIGHT: Yes
- Time schedule for examinations: Before exposure began and then twice per week.


FOOD CONSUMPTION: Yes
- Food consumption for each animal determined: Twice per week.


WATER CONSUMPTION: Yes
- Time schedule for examinations: Once per week.


OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: Weekly
- Dose groups that were examined: all dose groups and control

HAEMATOLOGY: Yes
- Time schedule for collection of blood: One day after the last exposure five animals of each sex, then 15 days after last exposure the remaining five animals of each sex.
- Anaesthetic used for blood collection: No
- Animals fasted: No data
- Parameters checked in table 1 were examined.


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of serum: One day after the last exposure five animals of each sex, then 15 days after last exposure the remaining five animals of each sex (Nembutal narcosis).
- Parameter checked in table 1 were examined.


URINALYSIS: Yes
- Time schedule for collection of urine: At the end of the exposure period
- Parameters checked in table 1 were examined.


NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations (neurological disorders): Once per week.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table 2)
HISTOPATHOLOGY: Yes (see table 2)

Other examinations:

None

Statistics:

The following parameters have been checked inter-collective concerning statistical significance (p = 0.05) in accordance with internal SOP: body weight, body weight gain; haematology (excluding differential blood count, heinz bodies, reticulocytes); clinical chemistry (excluding bilirubin direct, methemoglobin, g-glutamyltranspeptitase); serum electrophoresis, relative organ weights, pH-value urine.

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Following exposure each animal of the high dose group had a staggering gait, which was resolved by the next day. In the mid dose group, animals that showed a lack of coordination following exposure were recovered within two hours after exposure. The low dose and control group animals did not have any clinical signs.

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

no effects observed

Description (incidence and severity):

On days 1 and 3 males of the high and mid dose group had a slightly increased body weight in comparison to the air control animals. Females of the high dose group had a slightly reduced body weight on day 14 and days 21-31.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

Males from high and mid dose groups on days 3-29 and females on days 3-31 had slight reductions in feed intake.

Food efficiency:

not examined

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

effects observed, treatment-related

Description (incidence and severity):

In high dose males there was an increased water consumption on day 7 until the recovery period. Females of this group had elevated water consumption on days 7-29. In the mid dose group males, water consumption was increased from day 14 until recovery, and in females of this group from day 14-29.

Ophthalmological findings:

no effects observed

Description (incidence and severity):

No effects on the eyes.

Haematological findings:

no effects observed

Description (incidence and severity):

Statistically significant effects one day after the end of exposure were as follows: increased albumin in mid dose females, increased alpha globulin in high dose males, decreased alpha globulin in mid and high dose females, increased albumin to globulin ratio in mid dose females. Statistically significant effects 15 days after the end of exposure were as follows: increased albumin in low dose males and high dose males and females, decreased beta globulin in low and high dose males, decreased g1 globulin in low dose male and females and high dose females, and increased albumin to globulin ratio in low and high dose males. However, all values were in the normal range and were not considered to be toxicologically relevant.

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

Statistically significant effects one day after the end of exposure were as follows: increased albumin in mid dose females, increased alpha globulin in high dose males, decreased alpha globulin in mid and high dose females, increased albumin to globulin ratio in mid dose females. Statistically significant effects 15 days after the end of exposure were as follows: increased albumin in low dose males and high dose males and females, decreased beta globulin in low and high dose males, decreased g1 globulin in low dose male and females and high dose females, and increased albumin to globulin ratio in low and high dose males. However, all values were in the normal range and were not considered to be toxicologically relevant.

Urinalysis findings:

no effects observed

Description (incidence and severity):

No treatment-related effects.

Behaviour (functional findings):

not examined

Description (incidence and severity):

Not examined but there were no neurological disorders observed in the clinical observations.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

There were statistically significant increases in lung weight in mid dose males one day after exposure, and lung weight in high dose females 15 days after exposure. However, all values were within the normal range, and there were no corresponding histopathological findings.

Gross pathological findings:

no effects observed

Description (incidence and severity):

There were no treatment-related macroscopic changes identified.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

There were no findings in the control, low and mid dose groups. In the high dose group three males and one female had signs of minimal irritation in the alveoli (isolated and small clusters of foam cells). There were no other treatment-related effects.

Histopathological findings: neoplastic:

not examined

Key result

Dose descriptor:

NOAEC

Effect level:

>= 3 mg/L air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Only minor and reversible effects have been observed at 3 mg/l.

Critical effects observed:

no

Conclusions:

In the 28-day inhalation repeated dose toxicity study with triethoxy(2,4,4-trimethylpentyl)silane, conducted according to OECD Test Guideline 412 and in compliance with GLP, the NOAEL for systemic toxicity was concluded to be at least 3 mg/l (nominal) based no adverse systemic effects.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

3 000 mg/m³

Study duration:

subacute

Species:

rat

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)

Principles of method if other than guideline:

Recovery period: 15 d

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Strain: Hoe: WISKf (SPF71)
- Source: Hoechst AG, Pharma-Forschung-Toxikologie; breeding under SPF conditions
- Age at study initiation: 5-6 weeks
- Weight at study initiation: Males: 137-150 g. Females: 137-146 g
- Fasting period before study: No
- Housing: : 5 per Makrolon cage
- Diet (e.g. ad libitum): Ad libitum except during exposure
- Water (e.g. ad libitum): Ad libitum except during exposure
- Acclimation period: No data


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22± 2
- Humidity (%): 50± 20
- Air changes (per hr): 10
- Photoperiod (hrs dark / hrs light): 12/12

Route of administration:

inhalation: aerosol

Type of inhalation exposure:

nose only

Vehicle:

other: Air

Mass median aerodynamic diameter (MMAD):

< 6 µm

Remarks on MMAD:

MMAD / GSD: Particle size (mean): 99.98% of the particle in 0.3 mg/l group, 99.98% of the particle in 1.5 mg/l group and 99.87% of the particle in 3.0 mg/l group are below 6 µm.

Details on inhalation exposure:

Duration of exposure: 6h/d, 5d/w
Exposure: Animals were exposed to the test atmosphere in nose-only inhalation units
Exposure apparatus: The inhalation chamber used in the study were stainless steel/glass cylindrical columns. Each column had a volume of 80 L and consisted of a top assembly with the inlet of the test atmosphere, one rodent tube section and the bottom, the base assembly with the exhaust port.
Method of holding animals in test chamber: Nose only; cylindrical tubes.
Method of conditioning air: Compressed air (4 bar), oil separation filter/absolute filter; to achieve requested air humidity moistened air was feeded directly in the chamber
System of generating particulates/aerosols: The inhalation equipment was designed to expose the animals to a continuous supply of fresh test atmosphere. The test atmosphere was generated by passing test material to special nozzels. The operating pressure was 4 bar.
Temperature, humidity: 20.0 - 23.5°C, 31.5-60.6%
Contineous measurement of CO-, CO2- and O2-concentration during exposure in exposure chamber; CO: 0 ppm; CO2: 3800 - 7900 ppm; O2: 19.8 - 20.6 Vol %
Air flow rate: Air inlet 800 L/h; 1100 L/h exhausted
Method of particle size determination: The particle size distribution was measured using an APS 33 Aerodynamik Particle Sizer from TSI Inc., St Paul.
The aerodynamic diameter range measured with this analyzer covered 0.486 to > 15.4 micrometer.
Measurements were performed daily 30 minutes, 2 and 4 hours respectively after starting the exposure.
After the end of the exposure period, the arithmetic means together with the standard deviations based
on the 3 points in time were calculated using a statistics program.
The statistics program was used further to calculate an overall arithmetic mean for each dose group
based on the arithmetic means for each single day of exposure.
Brief description of analytical method used:
Gravimetric verification of concentrations
Gravimentric measurements were performed using a membrane filter, pore size 0.65 micrometer,
50 mm diameter (sartorius Membranfilter GmbH, Göttingen). The air flow rate was 3 l/min, which
is equivalent to an intake velocity of 1.25 m/sec.
Gravimetric measurements were performed daily in the exposure chambers 30 minutes, 2 and 4 hours respectively after starting the exposure.
Chemical verification of concentrations
Within 60 minutes 31 liter aerosol from the exposure chambers was pumped through 3 gas-washing bottles filled with acetone (PESTANAL, RIEDEL DE HAEN) connected in series and standing in a cool trap. Thereof aliquotes were taken and analysed using a gas chromatograph.
The concentration of isooctyltrimethoxysilane in the exposure chambers was calculated based on the results of the GC and
considering the aerosol- and acetone volumina.
Sampling was performed on day 1, 8, 15, 22 and 27 of the treatment.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Gravimetric verification of concentrations
Gravimentric measurements were performed using a membrane filter, pore size 0.65 micrometer,
50 mm diameter (sartorius Membranfilter GmbH, Göttingen). The air flow rate was 3 l/min, which
is equivalent to an intake velocity of 1.25 m/sec.
Gravimetric measurements were performed daily in the exposure chambers 30 minutes, 2 and 4 hours respectively after starting the exposure.

Chemical verification of concentrations
Within 60 minutes 31 liter aerosol from the exposure chambers was pumped through 3 gas-washing bottles filled with acetone (PESTANAL, RIEDEL DE HAEN) connected in series and standing in a cool trap. Thereof aliquotes were taken and analysed using a gas chromatograph.
The concentration of isooctyltrimethoxysilane in the exposure chambers was calculated based on the results of the GC and
considering the aerosol- and acetone volumina.
Sampling was performed on day 1, 8, 15, 22 and 27 of the treatment.

Duration of treatment / exposure:

28 days + 14 days recovery

Frequency of treatment:

Five days per week; six hours per day

Dose / conc.:

0.32 mg/L air (analytical)

Remarks:

0.3 mg/L air nominal conc.

Dose / conc.:

1.54 mg/L air (analytical)

Remarks:

1.5 mg/L air nominal conc.

Dose / conc.:

2.89 mg/L air (analytical)

Remarks:

3.0 mg/L nominal conc.

No. of animals per sex per dose:

Ten

Control animals:

other: Air

Details on study design:

- Dose selection rationale: No data
- Rationale for animal assignment (if not random): Random
- Rationale for selecting satellite groups: Five animals of each sex and group were used to assess recovery from treatment-related effects
- Post-exposure recovery period in satellite groups: 15 days

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes


DETAILED CLINICAL OBSERVATIONS: Mortality, behavior and general state of health (before and after exposure and during exposure; one time per day during weekend); Neurological disorders, opacity of eyes, damage of oral mucosa, disorder of tooth growth (weekly)


BODY WEIGHT: Yes
- Time schedule for examinations: Before exposure began and then twice per week.


FOOD CONSUMPTION: Yes
- Food consumption for each animal determined: Twice per week.


WATER CONSUMPTION: Yes
- Time schedule for examinations: Once per week.


OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: Weekly
- Dose groups that were examined: all dose groups and control

HAEMATOLOGY: Yes
- Time schedule for collection of blood: One day after the last exposure five animals of each sex, then 15 days after last exposure the remaining five animals of each sex.
- Anaesthetic used for blood collection: No
- Animals fasted: No data
- Parameters checked in table 1 were examined.


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of serum: One day after the last exposure five animals of each sex, then 15 days after last exposure the remaining five animals of each sex (Nembutal narcosis).
- Parameter checked in table 1 were examined.


URINALYSIS: Yes
- Time schedule for collection of urine: At the end of the exposure period
- Parameters checked in table 1 were examined.


NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations (neurological disorders): Once per week.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table 2)
HISTOPATHOLOGY: Yes (see table 2)

Other examinations:

None

Statistics:

The following parameters have been checked inter-collective concerning statistical significance (p = 0.05) in accordance with internal SOP: body weight, body weight gain; haematology (excluding differential blood count, heinz bodies, reticulocytes); clinical chemistry (excluding bilirubin direct, methemoglobin, g-glutamyltranspeptitase); serum electrophoresis, relative organ weights, pH-value urine.

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Following exposure each animal of the high dose group had a staggering gait, which was resolved by the next day. In the mid dose group, animals that showed a lack of coordination following exposure were recovered within two hours after exposure. The low dose and control group animals did not have any clinical signs.

Mortality:

mortality observed, treatment-related

Body weight and weight changes:

no effects observed

Description (incidence and severity):

On days 1 and 3 males of the high and mid dose group had a slightly increased body weight in comparison to the air control animals. Females of the high dose group had a slightly reduced body weight on day 14 and days 21-31.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

Males from high and mid dose groups on days 3-29 and females on days 3-31 had slight reductions in feed intake.

Food efficiency:

not examined

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

effects observed, treatment-related

Description (incidence and severity):

In high dose males there was an increased water consumption on day 7 until the recovery period. Females of this group had elevated water consumption on days 7-29. In the mid dose group males, water consumption was increased from day 14 until recovery, and in females of this group from day 14-29.

Ophthalmological findings:

no effects observed

Description (incidence and severity):

No effects on the eyes.

Haematological findings:

no effects observed

Description (incidence and severity):

Statistically significant effects one day after the end of exposure were as follows: increased albumin in mid dose females, increased alpha globulin in high dose males, decreased alpha globulin in mid and high dose females, increased albumin to globulin ratio in mid dose females. Statistically significant effects 15 days after the end of exposure were as follows: increased albumin in low dose males and high dose males and females, decreased beta globulin in low and high dose males, decreased g1 globulin in low dose male and females and high dose females, and increased albumin to globulin ratio in low and high dose males. However, all values were in the normal range and were not considered to be toxicologically relevant.

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

Statistically significant effects one day after the end of exposure were as follows: increased albumin in mid dose females, increased alpha globulin in high dose males, decreased alpha globulin in mid and high dose females, increased albumin to globulin ratio in mid dose females. Statistically significant effects 15 days after the end of exposure were as follows: increased albumin in low dose males and high dose males and females, decreased beta globulin in low and high dose males, decreased g1 globulin in low dose male and females and high dose females, and increased albumin to globulin ratio in low and high dose males. However, all values were in the normal range and were not considered to be toxicologically relevant.

Urinalysis findings:

no effects observed

Description (incidence and severity):

No treatment-related effects.

Behaviour (functional findings):

not examined

Description (incidence and severity):

Not examined but there were no neurological disorders observed in the clinical observations.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

There were statistically significant increases in lung weight in mid dose males one day after exposure, and lung weight in high dose females 15 days after exposure. However, all values were within the normal range, and there were no corresponding histopathological findings.

Gross pathological findings:

no effects observed

Description (incidence and severity):

There were no treatment-related macroscopic changes identified.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

There were no findings in the control, low and mid dose groups. In the high dose group three males and one female had signs of minimal irritation in the alveoli (isolated and small clusters of foam cells). There were no other treatment-related effects.

Histopathological findings: neoplastic:

not examined

Key result

Dose descriptor:

NOAEC

Effect level:

>= 3 mg/L air (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Only minor and reversible effects have been observed at 3 mg/l.

Critical effects observed:

no

Conclusions:

In the 28-day inhalation repeated dose toxicity study with triethoxy(2,4,4-trimethylpentyl)silane, conducted according to OECD Test Guideline 412 and in compliance with GLP, the NOAEL for systemic toxicity was concluded to be at least 3 mg/l (nominal) based no adverse systemic effects.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

3 000 mg/m³

Study duration:

subacute

Species:

rat

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

In the 90-day oral repeated dose toxicity study, conducted according to OECD Test Guideline 408 and in compliance with GLP, four groups of 10 male and 10 female rats were dosed via gavage with 0, 15, 50 and 150 mg/kg bw/day for 90 consecutive days. The highest dose level was chosen with the aim of inducing toxic effects, but no death or severe suffering. Thereafter, a descending sequence of dose levels was selected with a view to demonstrate any dosage related response and NOAEL. Animals of an additional control group were handled identically as the dose groups but received corn oil, the vehicle used in the study. To detect possible delayed occurrence or persistence of, or recovery from toxic effect additional 5 mate and 5 female Wistar rats were treated in the high dose and control group (recovery groups), respectively, Those animals were observed for a period of 28 days following the last administration of the test item. During the period of administration, all animals were observed precisely each day for signs of toxicity. All animals were sacrificed and observed macroscopically. Body weight and food consumption were measured weekly/. At the conclusion of the treatment period, all animals were sacrificed and subjected to necropsy. The wet weight of a subset of tissues was taken and a set of organs/tissues was preserved. A full histopathological evaluation of the tissues was performed on high dose and control animals. These examinations were extended to animals of all other dose groups for treatment-related changes that were observed in the high dose group. Only organs and tissues of the other dose groups showing changes in the high dose group were examined (i.e. urinary bladder). These examinations were also extended to animals subjected to necropsy at the end of the recovery period. Any gross lesion macroscopically identified was examined microscopically in all animals.

No test item related clinical findings were observed in the study. The clinical findings were either rare incidental findings or were observed in similar frequency also in control animals. The effects are not considered to be adverse. No mortality occurred in the control or any of the dose groups during the treatment period of the study. The body weight development of all groups was within the expected range of variation with no test item related effects. In accordance to the body weight development no effects on food consumption were recorded. No influence of triethoxy(2,4,4-trimethylpentyl)silane on any of the analysed parameters of haematology and blood coagulation independent of the gender of the animals was observed at the end of the treatment and after the recovery period. All clinical biochemistry parameters analysed at the end of the treatment and recovery phase did not indicate toxicologically relevant findings which are related to the test item. Abnormalities observed in urinalysis were incidental findings and are not assumed to be toxicologically relevant. Therefore, the test item is concluded to show no effects on parameters of urinalysis. No relevant effects were observed in any of the parameters of the functional observation battery with no biologically relevant differences in body temperature between the groups. Changes in organ weights were either related to female cycle, rare single cases or within normal range of variation with no toxicological relevance. The recorded pathological changes were either isolated findings, were observed in control animals or were related to female cycle and are therefore considered to be normal background alterations. Histopathologically adaptive and therefore non-adverse urothelial hyperplasia with minor degree was found in the urinary bladder of males and females receiving 50 mg/kg/day and 150 mg/kg/day.

The systemic NOAEL was concluded to be 150 mg/kg bw/day based on no treatment-related effects in any of the test animals up to the highest dose tested (150 mg/kg bw/day) (BSL Bioservice, 2015).

The key subchronic study is supported by two reliable sub-acute dose toxicity studies with triethoxy(2,4,4-trimethylpentyl)silane.

In the first 28-day oral (gavage) repeated dose toxicity study (Chemicals Evaluation and Research Institute, 2001a), conducted according to OECD Test Guideline 407 and in compliance with GLP, 6 male and 6 female rats were given triethoxy(2,4,4-trimethylpentyl)silane in olive oil for 28 days at doses of 8, 40, 200 and 1000 mg/kg bw/day. Additional animals were included to the control and high dose group and were subject to recovery evaluation for 14 days following the last treatment.

During the dosing period, salivation was observed in treated and vehicle-treated groups. At 1000 mg/kg bw/day reduced spontaneous locomotion, lacrimation, reddish tears and moist hair on the lower abdomen with staining were observed in male and female animals. Reduced body weight without full recovery was noted for male and female rats at 1000 mg/kg bw/day. Reduced food intake was noted for male and female rats at 1000 mg/kg bw/day. During recovery period no difference from controls was noted in males, but females had reduced food intake on day 8. Prolonged activated partial thromboplastin time was noted at for male and female rats 1000 mg/kg bw/day, which was considered to be secondary to liver effects. In addition, reduced monocyte proportion in differential white blood count was noted for male rats at 1000 mg/kg bw/day, which was within historical range. These effects were fully reversible following the 14-day recovery period. Reduced sodium was seen in male rats at all dose levels. Increased total cholesterol was reported for male rats at 200 and male and female rats at 1000 mg/kg bw/day. In addition at 1000 mg/kg bw/day increased gamma-GTP and reduced total protein were noted for male rats, while increased GPT, reduced blood glucose, creatine and chlorine in were noted for female rats. Many of the biochemistry observations for the 1000 mg/kg bw/day groups (males and females) remained until the end of the recovery period. Several of these findings were suggested to be secondary to effects on the liver. During urinalysis, turbid urine with granular decayed cell debris was noted for males and females at 200 and 1000 mg/kg bw/day. Increased urinary volume was also noted for males at 1000 mg/kg bw/day. During organ weight analysis, reduced absolute adrenal gland weight was noted for males at 8 mg/kg bw/day, reduced absolute brain and spleen weight was noted for males at 1000 mg/kg bw/day and increased relative liver weight was noted for males at ≥200 mg/kg bw/day. Increased relative liver weight was also seen for females at 1000 mg/kg bw/day. Increased relative kidney weight was noted for males and females at 1000 mg/kg bw/day. At the end of the recovery period increased relative kidney weight was still seen in males and increased relative brain weight in females. During gross pathology, enlarged liver was noted for both sexes at 1000 mg/kg bw/day. In addition there was as sporadic reporting of skin scab formation females at 8 and 1000 mg/kg bw/day, blackish region of mucosa of the glandular stomach in males at 40, 200, 1000 mg/kg bw/day and vehicle control females and tubercles of the spleen in males at 40 mg/kg bw/day. With the exception of liver enlargement, the other macroscopic changes were noted in 1 out of 6 rats of each group that was affected.

At the end of the recovery period changes to the glandular stomach were observed in vehicle control males and females at 1000 mg/kg bw/day - different groups from those affected during treatment, reduced testis and epididymis were noted in males at 1000 mg/kg bw/day. In each case 1 out of 6 rats of each group was affected. At histopathology, diffuse hyperplasia of the transitional epithelium of the bladder was seen in 1 out of 6 males and in 1 out of 6 females at 200 mg/kg bw/day and in 5 out of 6 males and 6 out of 6 females at 1000 mg/kg bw/day. No effects were reported at 40 mg/kg bw/day. Centrilobular hypertrophy of hepatocytes was seen in 2 out of 6 males and 5 out of 6 females at 1000 mg/kg bw/day and no effects reported at 200 mg/kg bw/day. After the recovery period bladder effects remained in 4 out of 6 males and 6 out of 6 females at 1000 mg/kg bw/day, although the severity was reduced in many cases.

The systemic NOAEL was concluded to be 40 mg/kg bw/day, based on urological and liver effects, partially reversible, at 200 and 1000 mg/kg bw/day.  

In the second 28-day oral (gavage) repeated dose toxicity study (BSL Bioservice, 2001d), conducted according to OECD Test Guideline 407 and in compliance with GLP, 5 male and 5 female Wistar rats per group were given triethoxy(2,4,4-trimethylpentyl)silane in carboxymethyl cellulose at doses of 150, 500 and 1000 mg/kg bw/day for 28 days. Throughout the study period, all rats survived the treatment period without showing relevant clinical-toxic effects. No significant differences in weight gain between the test- and control- groups could be detected in male and female animals at the 95% confidence level. The mean weight gain in all groups was not as high as expected according to the standard growth curve for this strain especially in the male animals. The authors thought that the diminished weight gain in all animals might be due to the daily treatment. A slightly lower weight gain was observed in the female high dose group and all male dose groups compared to the controls, without reaching statistical significance. One female in the high dose group showed a marked reduction in weight gain. This finding was due to an abscess that was found during the necropsy. With the exception of the female animal with the abscess, all animals showed normal food intake and no significant reduction in food consumption was found at the 95% confidence level. There were no treatment-related effects on haematology, clinical chemistry and urinalysis parameters. The mean relative and absolute liver weight in female high dose animals, the relative liver weight in female medium dose animals and the relative liver weight in male high dose animals was slightly higher than the corresponding controls (differences were statistically significant, p<0.05).  The mean absolute spleen weights of the male medium dose animals were slightly lower than the corresponding control group, just reaching statistical significance (p<0.05). No abnormal findings in any animals were observed during gross pathology. There were treatment and dose-related changes in the keratinised gastric mucosa in male rats, the change being present in all dose groups (male high, medium and low, and female high, medium and low dose groups 5/5, 4/5, 2/5 and 1/5, 3/5, 1/5, respectively). In female rats the changes were detected at a lesser frequency and only at 'minimal' severity. The associated changes were acanthosis and hyperkeratosis. The axillary tissue in the high dose female with an abscess was determined to be a foreign body granuloma. The systemic NOAEL was concluded to be 150 mg/kg bw/day.

In these two subacute (28-days repeated) oral toxicity studies different strains of rats and different vehicles for substance application were used. Based on these differences, the partially different behaviour of the substance in these two tests can be explained (strain specific effects, normal biological variation, different resorption due to different vehicles). Nevertheless, in general no severe systemic toxicological effects were observed in either test.

The changes in the liver seen in both tests can be described as an adaptative response to the substance because of metabolism of the parent substance and/or the hydrolysis products, especially ethanol. Irritation effects of the substance were observed on the keratinized gastric mucosa (BSL Bioservice, 2001d) and on the transitional epithelium of the bladder (Chemicals Evaluation and Research Institute, 2001a). There is an indication of reversibility of the effects.

Different NOAELs were defined in these two tests, which can be explained by the different dose levels selected for each. Effects in the 200 mg/kg bw/day dose group (Chemicals Evaluation and Research Institute, 2001a) were without morphological findings (relative liver weight) or were very slight to slight in few animals, only (hyperplasia of transitional epithelium of the bladder).

In a 14-day oral dose range finding study with triethoxy(2,4,4-trimethylpentyl)silane, the test substance was orally administered daily in graduated doses (500, 1000 and 2000 mg/kg bw/day in carboxymethylcellulose to 5ml/kg bw) to three groups of male and female rats (HSDBrl:WH Wistar) by gavage, using a stomach tube. All rats survived the test period, without showing any clinical signs, and were sacrificed on day 14. There were no relevant weight gain differences between the three groups, and all animals showed normal food intake. There were no treatment-related effects on haemotology and clinical chemistry values. Therefore the NOAEL was ≥ 2000 mg/kg bw/day (BSL Bioservice 2000b).

The available Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test with the structural analogue trimethoxy(2,4,4-trimethylpentyl)silane (CAS 34396-03-7) has been included to support the read-across approach used for the registered substance, triethoxy(2,4,4-trimethylpentyl)silane (CAS 35435-21-3).

In a Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test, conducted according to OECD Test Guideline 422 and in compliance with GLP, 50, 150 and 300 mg/kg bw/day of trimethoxy(2,4,4-trimethylpentyl)silane (CAS 34396-03-7) in corn oil were administered daily by oral gavage to male and female rats for 28 and 63 days, respectively. The female rats were treated during pre-mating period, mating period, throughout gestation and up until post-natal day 13. In order to allow a detection of possible delayed occurrence or persistence of or recovery from toxic effects, additional animals in recovery groups (12 males and 12 females) were observed for a period of 14 days following the last administration. Animals in the recovery groups were not mated and dosed for 28 days (males) or until the first scheduled kill of dams (females) (BSL BIOSERVICE, 2020).

During the period of administration, the animals were observed each day for signs of toxicity. At the conclusion of the test, all animals were sacrificed and observed macroscopically. Body weight and food consumption were measured weekly. Haematological and clinical biochemistry evaluations were performed on blood samples collected at terminal sacrifice from five randomly selected males and females from each group. Urinalysis was performed on samples collected at terminal sacrifice from five randomly selected males from each group. Functional observations, including sensory reactivity to different stimuli, grip strength, motor activity assessments and other behaviour observations were performed in the week before the treatment in all animals and in the last week of treatment in five randomly selected males and females of each group.

After 14 days of treatment of both male and female, animals were mated (1:1) for a maximum of 14 days. The subsequent morning onwards, the vaginal smears of females were checked to confirm the evidence of mating. After the confirmation of the mating, females were separated and housed individually. Females were allowed to give birth and each litter was examined as soon as possible after delivery of the dam to establish the number and sex of pups, stillbirths, live births, runts and the presence of gross abnormalities.  Live pups were counted, sexed and litters weighed within 24 hours of parturition, on day 4 and day 13 post-partum. The anogenital distance (AGD) of each pup was measured on PND 0. The number of nipples/areolae in male pups was counted on PND 12. Blood samples from the day 13 pups and the adult males were assessed for serum levels for thyroid hormones (T4). The males were sacrificed after completion of the mating period on treatment days 29 and 30 and the females, along with their pups, were sacrificed on post-natal day 13. Non-pregnant females were sacrificed on day 26. The number of implantation sites and corpora lutea was recorded for each parental female at necropsy. Pups sacrificed on post-natal day 4 or 13 and those found dead were carefully examined for gross external abnormalities. A full histopathological evaluation of preserved tissues designated for microscopic evaluation was performed on high dose and control animals, in non-pregnant female animals and male mating partners of the LD and MD animals. Due to pathological findings on the initially examined animals of the high dose group, the histopathological evaluation was extended to peripheral nerves left/right, spinal cord, nerve roots with ganglia L4, urinary bladder, kidney, intestine, mesenteric lymph nodes, thymus and liver were examined microscopically in all animals. Additionally, OilRed O staining was performed on ileum (animal no. 32), duodenum (animal no. 37), jejunum (animal no. 39) and mesenteric lymph node (animals no. 84 and 92). For the testes, a detailed qualitative examination was made, taking into account the tubular stages of the spermatogenic cycle. Thyroid/parathyroid glands from pups and adult animals were examined. All gross lesions macroscopically identified were examined microscopically in all animals.

No mortality occurred during the treatment period or recovery period of this study. No consistent clinical signs of toxicity were seen in this study. There were no ophthalmoscopic findings in this study. Trimethoxy(2,4,4-trimethylpentyl)silane had no effect on functional behavioural parameters evaluated at the end of the treatment and recovery period. The test item had no effect on body weight and food consumption in this study.  Oestrous cycle was not affected by treatment with the test item. In each group 10/10 animals were pregnant, pre-coital interval and duration of gestation showed no test item-related or statistically significant effect. Maternal behaviour was normal in all groups. There were no effects on total number of pups born, number of male pups, number of female pups, sex ratio, number of live pups, still birth, runts on PND 0 as well as number of live pups, number of male and female pups and sex ratio on PND 4 and PND 13 when compared with the controls. Litter weight was not notably different between dose groups and control group.

Lower mean pup weight in the HD groups is assumed to be related to the slightly lower body weight observed in females of this group, compared to controls, during the lactation period. There were no test item-related effects on the number of corpora lutea or implantation sites, percent pre-implantation loss and post-implantation loss in any of the dose groups. There were no test item-related effects on the reproductive indices (copulation, fertility, viability and delivery indices) in the dose groups. The mortality of pups between PND 0 and PND 4 and between PND 4-13 was not considerably different between the dose groups and the control group. Very slight differences in anogenital distance in male (slightly shorter) and females (slightly longer) are not considered toxicologically relevant. No relevant test item effect was observed in nipple retention on PND 13. Serum T4 levels of males and of male and female PND 13 pups were not affected by treatment with trimethoxy(2,4,4-trimethylpentyl)silane. Few dead or missing pups were noted in dose groups and control group, independent of treatment. At the end of the treatment and recovery period there were no relevant alterations in haematological and clinical biochemistry parameters of parental animals in any of the dose groups. Trimethoxy(2,4,4-trimethylpentyl)silane had no effect on urinary parameters in this study. At the HD level, liver and kidney weights of male animals were increased moderately, when compared to controls. No relevant changes were observed in liver or kidney weight of females of this dose group. Changes in kidney and liver weight coincided with histopathological findings. Slightly higher adrenal gland weight in females of the HD group coincided with minimal to slight hypertrophy of the fasciculata cortical layer with cytoplasmic vacuolation and is assumed to be stress-related. At necropsy of the parental animals no test item-related, but only incidental macroscopic alterations were noted. Test-item exposure at 300 mg/kg bw/day, but not at 50 or 150 mg/kg bw/day, caused an adverse symmetric polyneuropathy in both sexes, but more pronounced in females. After the 14-day-recovery period, this lesion persisted. The most significant lesions were observed at the dorsal spinal nerve root L4. Given the lack of lesions within the ganglia, spinal cord, cranial nerves and brain, considering that demyelination was the most prominent histological feature, the lesion was diagnosed as a peripheral myelinopathy. The test item is considered to cause Wallerian-type demyelination (either by direct myelin damage, by interfering with myelin synthesis or by selective toxicity to Schwann cells) in peripheral nerves, followed by secondary axonal degeneration. No changes compatible with myofiber atrophy by denervation were observed in the studied muscles, therefore suggesting a most likely damage of the sensory tracts. In the urinary tract, the diffuse urothelial hyperplasia at ≥150 mg/kg bw/day was considered a dose-dependent adverse induced effect caused by the test-item, which did not show any significant improvement after the recovery period. Urothelial damage was most likely related to direct toxic damage to the renal urothelial cells or to induced changes in urine physical properties with subsequent urothelial hyperplastic reaction. The excessive presence of hyaline droplets in the renal cortex is also deemed to be item-related and might represent intratubular accumulation of protein, and based on the presence only in males most likely an increase in α2-microglobulin. Tubular basophilia is associated with renal tubular regeneration. The slight urothelial hyperplasia seen in one control male rat was a focal lesion, considered to be a background finding.

Presence of lipid accumulation in the intestine, Peyer’s patches, mesenteric lymph nodes, and thymus from high dose male rats suggests a test-item related impairment in the process of lipid transport through the lacteals (small intestine - Peyer’s patches - mesenteric lymph nodes). Very similar histopathological findings have been recorded in few previous studies in rats associated with interference in the intestinal lipid uptake, re-synthesis, or transport through the lacteals caused by treatments with puromycin, ethionine or a glucose inhibitor. The pathogenesis to explain the presence of lipid vacuoles in the thymic cortex is not clear, and its significance is uncertain. Under the conditions of this study and in the absence of associated tissue damage, lipid accumulation in high dose males was considered non-adverse, and deemed to be an adaptative change to alteration in lipid transport from the intestine to the lymphatic vessels. In the lungs from rats of the HD group, minor and scattered alveolar histiocytosis and perivascular/peribronchiolar granulocytic infiltrates were found that are commonly reported as a background finding in untreated control animals rats. In the present study, there was an increased incidence and severity of these changes in the treated group, especially in females, most likely associated with accidental deviation of the product from oral gavage and is not considered to be an adverse effect of trimethoxy(2,4,4-trimethylpentyl)silane (CAS 34396-03-7). The increase in frequency and severity of hepatic hypertrophy compared to normal range levels seeing control animals, observed at ≥ 50 mg/kg bw/day, is a relatively common finding following enzymatic induction by xenobiotic and is considered an adaptive response to chemical stress and was not considered to be an adverse effect of the test item. The induced hepatocellular hypertrophy in females at 300 mg/kg bw/day explains the increase in this organ weight. The lymphoid depletion in lymph nodes, thymic atrophy, and hypertrophy of the adrenal gland detected in treated animals at 150 and 300 mg/kg bw/day is considered a stress-related finding, which in turn might be indirectly linked to the test item. In females, the latter two findings were also observed both in control and treated females, which might be related to stress or to pregnancy. It is unclear whether there is an association between the test item and the thrombus and endarteritis found in the brachial plexus of rat No. 15 and No. 35. A traumatic origin of the vascular damaged cannot be ruled out. No test-item induced histological findings were observed in reproductive organs.

The systemic NOAEL was determined to be 50 mg/kg bw/day for male and female rats based on adverse polyneuropathy (at 300 mg/kg bw/day) and urinary damage (at >= 150 mg/kg bw/day) (BSL BIOSERVICE, 2020).

There are no repeated dose inhalation toxicity data on triethoxy(2,4,4-trimethylpentyl)silane, so good quality data for the structural analogue trimethoxy(2,4,4-trimethylpentyl)silane (CAS 34396-03-7), have been used to assess the repeated dose inhalation toxicity of triethoxy(2,4,4-trimethylpentyl)silane (see read-across justification attached to Section 13).

In the 28-day inhalation repeated dose toxicity study with trimethoxy(2,4,4-trimethylpentyl)silane, conducted according to OECD Test Guideline 412 and in compliance with GLP (Hoechst Pharma Forschung Toxikologie und Pathologie, 1986b), four groups of 10 males and 10 females rats were exposed to the aerosol of trimethoxy(2,4,4-trimethylpentyl)silane (CAS 34396-03-7) at concentrations of 0, 0.3, 1.5 and 3 mg/l for 28 days (6 hours/day, 5 days/week). After the exposure period five male and five female rats of each group were kept during a 14-day recovery period before necropsy. Only some clinical signs have been observed shortly after exposure in the high and mid dose group. There were no treatment related effects on haematology, clinical chemistry, urinalysis, organ weights and gross pathology. There were signs of minimal alveolar irritation (isolated and small clusters of foam cells) in several high dose animals. Overall, the systemic and local NOAEC was concluded to be 3 mg/l. Based on gravimetrical and chemical verification of the exposure concentrations it can be concluded that animals were exposed to a mixture of aerosol/vapour and therefore systemic availability of the substance is expected.

Justification for classification or non-classification

Based on the available data, triethoxy(2,4,4-trimethylpentyl)silane does not require classification for specific target organ toxicity following repeated exposure according to Regulation (EC) No. 1272/2008.