Trimethoxysilane

Endpoint summary

Description of key information

The key study (BRRC, 1995) for repeated dose toxicity via the inhalation route was similar to OECD Test Guideline 413 and in compliance with GLP, except that very low concentrations were used. There were no local nor systemic adverse effects up to the highest dose tested (0.5 ppm).

In other similarly reliable studies the NOAECs were 0.5 and 0.2 ppm, with effects observed at 5 and 1 ppm, respectively. However, in those studies that tested above 0.5 ppm, it does appear that most of the effects are a consequence of the severe local effects on the respiratory tract and that no distinct systemic effects were observed.

There are no reliable data available that investigate the potential for trimethoxysilane to cause systemic toxicity following repeated dermal or oral exposure. Further testing for these endpoints is not relevant for the current Annex requirements. Furthermore, reliable measured data are available for the ultimate hydrolysis product, silicic acid, which indicate no hazard for systemic toxicity.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

19.08.1993 to 06.01.1995

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)

Deviations:

yes

Remarks:

Low exposure concentrations and exposure 5 days/week

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan Sprague Dawley Inc
- Age at study initiation: approximately 47 days
- Weight at study initiation: Males: 197.2-240.1 g; Females: 129.7-186.1 g
- Fasting period before study: No data
- Housing: Individually in stainless steel, wire mesh cages.
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: two weeks


ENVIRONMENTAL CONDITIONS
- Temperature (°F): 66-77
- Humidity (%): 40-70
- Air changes (per hr): No data
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: 20.09.1993 To: 23.12.1993

Route of administration:

inhalation

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
The inhalation chambers, constructed from stainless steel with glass windows for animal observation, were rectangular (213 x 98 x 207 cm) in shape. The volume of each chamber was approximately 4320 litres.
- Method of holding animals in test chamber: No data
- Source and rate of air: No data
- Method of conditioning air: No data
- Temperature, humidity, pressure in air chamber: Mean temperature of approximately 23oC, humidity of approximately 45. No data on pressure.
- Air flow rate: 1000 l/min
- Air change rate: 13-14 air changes/hour
- Treatment of exhaust air: No data


TEST ATMOSPHERE
- Brief description of analytical method used: Sampling done with impingers and a double beam spectrophotometer.
- Samples taken from breathing zone: yes, the distribution of TMS vapour was measured at five positions for each individual chamber distribution test. Each chamber was tested once prior to the initiation of the study. The distribution tests simulated actual animal exposures including the use of similar animal cages, cage carriers with collection trays and airflow rates. No animals were present in the exposure chambers.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentration of TMS vapour in the exposure chamber atmosphere was monitored throughout the 66 days of exposure by sampling with impingers. The impingers contained a solution of acidic ammonium molybdate and sodium bisulfite. TMS reacted with the molybdate and formed a blue coloured product. The absorbance of the solution was measured at 620 nm with a double-beam spectrophotometer.

Duration of treatment / exposure:

90 days

Frequency of treatment:

6 hr/day, 5 day/wk

Remarks:

Doses / Concentrations:
0.02, 0.1, and 0.5 ppm
Basis:

No. of animals per sex per dose:

10 with an additional 5 rats/sex in the control and high exposure groups

Control animals:

other: yes, filtered air only

Details on study design:

- Dose selection rationale: Based on dose range-finding study
- Rationale for animal assignment (if not random): Random
- Rationale for selecting satellite groups: To investigate the reversibility of any effects
- Post-exposure recovery period in satellite groups: Five animals/sex in the control and 0.5 ppm groups were maintained for a 4-week recovery period. 

Positive control:

None

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- All animals were individually observed for signs of toxic effects except during the exposures. During the exposures, observations were recorded on a group basis. Preceding and following each exposure, observations were recorded for animals exhibiting overt signs. At the time of body weight measurement and just prior to sacrifice, detailed observations were performed on all animals. On non exposure days, the animals were observed once per day for overt clinical signs and twice per day for mortality.


DETAILED CLINICAL OBSERVATIONS: No data


BODY WEIGHT: Yes
- Time schedule for examinations: On the morning prior to initiation of the first exposure, weekly throughout the study, and immediately preceding sacrifice.


FOOD CONSUMPTION: Yes, measured weekly during the study and recovery period.


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: Yes, measured weekly during the study and recovery period.


OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: Prior to the first exposure, during week 14 of the study, and after the four week recovery period.
- Dose groups that were examined: All


HAEMATOLOGY: Yes
- Time schedule for collection of blood: Weeks 6 and 14
- Anaesthetic used for blood collection: Yes, methoxyflurane
- Animals fasted: No
- How many animals: 10/group/sex
- Parameters checked in table No.1 were examined.


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: Weeks 6 and 14
- Anaesthetic used for blood collection: Yes, methoxyflurane
- Animals fasted: No
- How many animals: 10/group/sex
- Parameters checked in table No.1 were examined


URINALYSIS: Yes
- Time schedule for collection of urine: Following the fourth exposure week, during week 13, and during week 18 (control and high concentrations)
- Metabolism cages used for collection of urine: Yes
- Animals fasted: No
- Parameters checked in table No.1 were examined.


NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

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

Statistics:

The data for quantitative, continuous variables were intercompared for the three exposure groups and the control group by use of Levene's test for equality of variances, analysis of variance (ANOVA), and t-tests. Nonparametric data were statistically evaluated using the Kruskal-Wallis test followed by the Mann-Whitney U-test. Incidence data were compared using Fisher's Exact test. For all statistical tests the probability value of <0.05 (two-tailed) was used as the critical level of significance.

Clinical signs:

no effects observed

Description (incidence and severity):

The exposure regimen produced no mortality or exposure-related clinical signs. There were some signs due to procedural trauma, in all groups including the controls.

Mortality:

no mortality observed

Description (incidence):

The exposure regimen produced no mortality or exposure-related clinical signs. There were some signs due to procedural trauma, in all groups including the controls.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

No exposure-related effects.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

No exposure-related effects.

Food efficiency:

not examined

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

no effects observed

Description (incidence and severity):

No exposure-related effects. There were sporadic significant increases in water consumption observed in all exposure groups, but there was no trend and they were therefore not considered an adverse effect of treatment.

Ophthalmological findings:

no effects observed

Description (incidence and severity):

No exposure-related effects. There were signs of trauma caused by the bleeding procedure. There were also sporadic occurrences of conjunctivitis in all groups including the controls. The authors suggested that such occurrences in animals exposed to TMS could have been a sign of mild irritation, but there was no concentration response trend.

Haematological findings:

no effects observed

Description (incidence and severity):

No exposure-related effects. In females at week 6 there was a significant increase in hemoglobin (intermediate and high) and hematocrit (all exposure groups) observed. There were no significant differences at week 14. Due to the lack of a concentration-related response the described differences were not believed to be exposure-related.

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

No exposure-related effects. Total and direct bilirubin values were significantly decreased in low and high group males, and low and intermediate group females at week 6. Calcium was significantly lower in intermediate group females at week 6. At week 14, potassium was significantly lower in low group males. No significant clinical chemistry findings were noted at week 14. Due to the lack of a concentration-related response the described differences were not believed to be exposure-related.

Urinalysis findings:

no effects observed

Description (incidence and severity):

No exposure-related effects. Significant decreases in urine creatinine were observed in males (low group) at weeks 5 and 13, and week 18 (high group). Males had significant decreases in alpha-2u-globulin (low group) and urine total protein (all groups) at week 13. Females from the low and high group had increased urine total protein at week 13. Males had decreased alpha-2u-globulin at week 18. Low group males had increased urine total volume at week 13. Due to the lack of a concentration-related response the described differences were not believed to be exposure-related.

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

No exposure-related effects. In males, absolute thyroid gland weight was significantly increased at week 14 (low and intermediate groups). No other differences in absolute or relative organ weights were observed in males from any exposure group during the exposure or recovery phases of the study. In females, absolute ovary weight, ovary and spleen weights as a percent of final body weight were significantly lower, and brain weight was significantly higher at week 18 (high group), However, these are not believed to be exposure related since the effects were observed at the end of the recovery period only.

Gross pathological findings:

no effects observed

Description (incidence and severity):

No exposure-related findings.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

No exposure-related findings. Microscopic diagnosis in males sacrificed at week 14 revealed significant increases in sinus erythrocytosis ( intermediate group), and hemorrhage of the thymic region (intermediate group). However, these findings are not believed to be exposure related. No significant differences in microscopic diagnoses were observed in females sacrificed at weeks 14 and 18.

Histopathological findings: neoplastic:

not examined

Other effects:

not specified

Key result

Dose descriptor:

NOEC

Effect level:

>= 0.51 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No adverse effects observed

Remarks on result:

not determinable due to absence of adverse toxic effects

Critical effects observed:

no

Conclusions:

In a good quality 90-day inhalation study (reliability score 2) conducted in a study comparable to OECD Test Guideline 413 and in compliance with GLP, the NOAEC for trimethoxysilane was greater than 0.51 ppm (the highest dose tested) in rats exposed six hours/day, five days/week, followed by a four-week recovery period.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

19.08.1993 to 06.01.1995

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)

Deviations:

yes

Remarks:

Low exposure concentrations and exposure 5 days/week

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan Sprague Dawley Inc
- Age at study initiation: approximately 47 days
- Weight at study initiation: Males: 197.2-240.1 g; Females: 129.7-186.1 g
- Fasting period before study: No data
- Housing: Individually in stainless steel, wire mesh cages.
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: two weeks


ENVIRONMENTAL CONDITIONS
- Temperature (°F): 66-77
- Humidity (%): 40-70
- Air changes (per hr): No data
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: 20.09.1993 To: 23.12.1993

Route of administration:

inhalation

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
The inhalation chambers, constructed from stainless steel with glass windows for animal observation, were rectangular (213 x 98 x 207 cm) in shape. The volume of each chamber was approximately 4320 litres.
- Method of holding animals in test chamber: No data
- Source and rate of air: No data
- Method of conditioning air: No data
- Temperature, humidity, pressure in air chamber: Mean temperature of approximately 23oC, humidity of approximately 45. No data on pressure.
- Air flow rate: 1000 l/min
- Air change rate: 13-14 air changes/hour
- Treatment of exhaust air: No data


TEST ATMOSPHERE
- Brief description of analytical method used: Sampling done with impingers and a double beam spectrophotometer.
- Samples taken from breathing zone: yes, the distribution of TMS vapour was measured at five positions for each individual chamber distribution test. Each chamber was tested once prior to the initiation of the study. The distribution tests simulated actual animal exposures including the use of similar animal cages, cage carriers with collection trays and airflow rates. No animals were present in the exposure chambers.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentration of TMS vapour in the exposure chamber atmosphere was monitored throughout the 66 days of exposure by sampling with impingers. The impingers contained a solution of acidic ammonium molybdate and sodium bisulfite. TMS reacted with the molybdate and formed a blue coloured product. The absorbance of the solution was measured at 620 nm with a double-beam spectrophotometer.

Duration of treatment / exposure:

90 days

Frequency of treatment:

6 hr/day, 5 day/wk

Remarks:

Doses / Concentrations:
0.02, 0.1, and 0.5 ppm
Basis:

No. of animals per sex per dose:

10 with an additional 5 rats/sex in the control and high exposure groups

Control animals:

other: yes, filtered air only

Details on study design:

- Dose selection rationale: Based on dose range-finding study
- Rationale for animal assignment (if not random): Random
- Rationale for selecting satellite groups: To investigate the reversibility of any effects
- Post-exposure recovery period in satellite groups: Five animals/sex in the control and 0.5 ppm groups were maintained for a 4-week recovery period. 

Positive control:

None

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- All animals were individually observed for signs of toxic effects except during the exposures. During the exposures, observations were recorded on a group basis. Preceding and following each exposure, observations were recorded for animals exhibiting overt signs. At the time of body weight measurement and just prior to sacrifice, detailed observations were performed on all animals. On non exposure days, the animals were observed once per day for overt clinical signs and twice per day for mortality.


DETAILED CLINICAL OBSERVATIONS: No data


BODY WEIGHT: Yes
- Time schedule for examinations: On the morning prior to initiation of the first exposure, weekly throughout the study, and immediately preceding sacrifice.


FOOD CONSUMPTION: Yes, measured weekly during the study and recovery period.


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: Yes, measured weekly during the study and recovery period.


OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: Prior to the first exposure, during week 14 of the study, and after the four week recovery period.
- Dose groups that were examined: All


HAEMATOLOGY: Yes
- Time schedule for collection of blood: Weeks 6 and 14
- Anaesthetic used for blood collection: Yes, methoxyflurane
- Animals fasted: No
- How many animals: 10/group/sex
- Parameters checked in table No.1 were examined.


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: Weeks 6 and 14
- Anaesthetic used for blood collection: Yes, methoxyflurane
- Animals fasted: No
- How many animals: 10/group/sex
- Parameters checked in table No.1 were examined


URINALYSIS: Yes
- Time schedule for collection of urine: Following the fourth exposure week, during week 13, and during week 18 (control and high concentrations)
- Metabolism cages used for collection of urine: Yes
- Animals fasted: No
- Parameters checked in table No.1 were examined.


NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

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

Statistics:

The data for quantitative, continuous variables were intercompared for the three exposure groups and the control group by use of Levene's test for equality of variances, analysis of variance (ANOVA), and t-tests. Nonparametric data were statistically evaluated using the Kruskal-Wallis test followed by the Mann-Whitney U-test. Incidence data were compared using Fisher's Exact test. For all statistical tests the probability value of <0.05 (two-tailed) was used as the critical level of significance.

Clinical signs:

no effects observed

Description (incidence and severity):

The exposure regimen produced no mortality or exposure-related clinical signs. There were some signs due to procedural trauma, in all groups including the controls.

Mortality:

no mortality observed

Description (incidence):

The exposure regimen produced no mortality or exposure-related clinical signs. There were some signs due to procedural trauma, in all groups including the controls.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

No exposure-related effects.

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

No exposure-related effects.

Food efficiency:

not examined

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

no effects observed

Description (incidence and severity):

No exposure-related effects. There were sporadic significant increases in water consumption observed in all exposure groups, but there was no trend and they were therefore not considered an adverse effect of treatment.

Ophthalmological findings:

no effects observed

Description (incidence and severity):

No exposure-related effects. There were signs of trauma caused by the bleeding procedure. There were also sporadic occurrences of conjunctivitis in all groups including the controls. The authors suggested that such occurrences in animals exposed to TMS could have been a sign of mild irritation, but there was no concentration response trend.

Haematological findings:

no effects observed

Description (incidence and severity):

No exposure-related effects. In females at week 6 there was a significant increase in hemoglobin (intermediate and high) and hematocrit (all exposure groups) observed. There were no significant differences at week 14. Due to the lack of a concentration-related response the described differences were not believed to be exposure-related.

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

No exposure-related effects. Total and direct bilirubin values were significantly decreased in low and high group males, and low and intermediate group females at week 6. Calcium was significantly lower in intermediate group females at week 6. At week 14, potassium was significantly lower in low group males. No significant clinical chemistry findings were noted at week 14. Due to the lack of a concentration-related response the described differences were not believed to be exposure-related.

Urinalysis findings:

no effects observed

Description (incidence and severity):

No exposure-related effects. Significant decreases in urine creatinine were observed in males (low group) at weeks 5 and 13, and week 18 (high group). Males had significant decreases in alpha-2u-globulin (low group) and urine total protein (all groups) at week 13. Females from the low and high group had increased urine total protein at week 13. Males had decreased alpha-2u-globulin at week 18. Low group males had increased urine total volume at week 13. Due to the lack of a concentration-related response the described differences were not believed to be exposure-related.

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

No exposure-related effects. In males, absolute thyroid gland weight was significantly increased at week 14 (low and intermediate groups). No other differences in absolute or relative organ weights were observed in males from any exposure group during the exposure or recovery phases of the study. In females, absolute ovary weight, ovary and spleen weights as a percent of final body weight were significantly lower, and brain weight was significantly higher at week 18 (high group), However, these are not believed to be exposure related since the effects were observed at the end of the recovery period only.

Gross pathological findings:

no effects observed

Description (incidence and severity):

No exposure-related findings.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

No exposure-related findings. Microscopic diagnosis in males sacrificed at week 14 revealed significant increases in sinus erythrocytosis ( intermediate group), and hemorrhage of the thymic region (intermediate group). However, these findings are not believed to be exposure related. No significant differences in microscopic diagnoses were observed in females sacrificed at weeks 14 and 18.

Histopathological findings: neoplastic:

not examined

Other effects:

not specified

Key result

Dose descriptor:

NOEC

Effect level:

>= 0.51 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No adverse effects observed

Remarks on result:

not determinable due to absence of adverse toxic effects

Critical effects observed:

no

Conclusions:

In a good quality 90-day inhalation study (reliability score 2) conducted in a study comparable to OECD Test Guideline 413 and in compliance with GLP, the NOAEC for trimethoxysilane was greater than 0.51 ppm (the highest dose tested) in rats exposed six hours/day, five days/week, followed by a four-week recovery period.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

2.5 mg/m³

Study duration:

subchronic

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

Three reliability score 2 studies were available for the inhalation route, one of 90-day duration and the others of 28-days and 9-days. The most recent of these was the 90-day study and this was selected as the key study.

In the key 90-day inhalation study (BRRC, 1995) conducted according to a protocol comparable to OECD Test Guideline 413 and in compliance with GLP, Sprague-Dawley rats (10 with an additional 5 rats/sex in the control and high exposure groups) were exposed to trimethoxysilane vapour for 90 days over a 13-week period for 6 hours/day, 5 days/week, followed by a 4-week recovery period. Mean exposure concentrations of 0.02, 0.099 and 0.51 ppm were achieved. This exposure regimen did not produce any exposure-related effects upon clinical signs, body weight and body weight gains, food and water consumption, ophthalmic evaluations, haematology, clinical chemistry, serum protein fractions, urine chemistry, urinalysis, absolute and relative organ and tissue weights, or gross and microscopic evaluations of organs and tissues. Therefore, the NOEC was determined to be at least 0.51 ppm under the conditions of this study.

The supporting studies were in agreement with the key study and are summarised below.

In a IUCLID summary of a four week inhalation study (reliability score 2) that was conducted to OECD Test Guideline 412 (except that exposure was 5 days/week, 7h/day), Sprague-Dawley rats were exposed to a vapour of trimethoxysilane at concentrations of 0, 0.5, 5 and 10 ppm for 28 days (Dow Corning Corporation, 1980). At the end of exposure or during the course of the study, a complete necropsy was performed on all animals. The liver, kidneys adrenal glands, brain, gonads, pituitary, spleen, lungs and thyroid were examined and weighed and preserved for a microscopic examination. All of the high exposure rats, and 4/10 rats in the 5.0 ppm exposure group died or were sacrificed during the course of the study. Prior to death, these animals exhibited general weakness, a reduction in food consumption and body weight, lung congestion, nasal discharge and associated perinasal staining. None of the low exposure animals or the air controls revealed similar findings. Blood biochemical and urinary parameters were normal in the 5.0 and 0.5 ppm exposure groups. The high mortality rate in the 10.0 ppm exposure group precluded a complete analyses. Gross pathological examination of the high and intermediate exposure groups revealed areas of focal reddening and atelestasis in the lungs as well as a failure of the lungs to collapse upon being removed from the thoracic cavity. The lung weight of intermediate and high exposure males was increased with respect to the controls but a similar result was not obtained for the females. Histopathological evaluation of high and low exposure groups and the air controls demonstrated a 100% incidence of bronchitis, bronchiolitis and associated upper respiratory tract involvement in the high exposure group and no effect in the control and low exposure groups. It was concluded that the NOAEL for trimethoxysilane was 0.5 ppm in rats.

In a letter from Union Carbide to the USEPA submitted under TSCA, a nine day inhalation study (reliability score 2) was summarised (Union Carbide, 1991). The study was broadly comparable to OECD Test Guideline 412, but there was no information on its GLP status. Fischer 344 rats were exposed to trimethoxysilane vapour at concentrations of 0.2, 0.9 and 4.9 ppm for six hours/day, for five days, followed by a two day rest period, followed by a further four days exposure. Animals were observed for clinical signs, their body weights measured, and haematology examination conducted after the final exposure. A macroscopic examination was conducted and organ weights recorded. Microscopic examinations of various organs and tissues were conducted (no further details). In the 4.9 ppm group 14/15 and 12/15 males and females died (days 8 -12), respectively. In the low dose group only minimal respiratory tract effects were observed. In the mid dose group there was weight loss, increase lung weight, moderate respiratory tract injury and lymphoid tissue depletion in the lymph nodes. In the high dose group there was severe irritancy in the respiratory tract, weight loss, decreased organ weights (notably spleen), increased erythrocyte count, haemoglobin concentration and haematocrit, lymphocytopenia, lymphoid tissue depletion (spleen, lymph nodes and thymus), and severe respiratory tract injury. The NOAEL was concluded to be 0.2 ppm.

Justification for classification or non-classification

Since the effects observed in the available inhalation studies were a result of the local corrosive effects of trimethoxysilane (covered by the STOT SE classification), a classification for Specific Target Organ Toxicity following repeated exposure is not required under Regulation (EC) No. 1272/2008