3-(trimethoxysilyl)propyl isocyanate

Endpoint summary

Description of key information

There are no repeated dose toxicity data for the registered substance, 3-(trimethoxysilyl)propyl isocyanate, therefore data for the immediate disintegration/hydrolysis product have been used.

The key repeated dose toxicity study is a 90-day oral (gavage) study with the immediate disintegration/hydrolysis product, 3-(trimethoxysilyl)propylamine, conducted in male and female rats, according to OECD Test Guideline 408 and in compliance with GLP. The study concluded a LOAEL of <100 mg/kg bw/day. This LOAEL related to local effects. The NOAEL for systemic effects was concluded to be 100 mg/kg bw/day, based on changes in oestrous cyclicity. These effects may be related to low and/or reduced body weight resulting from and therefore secondary to local effects. This will be clarified in the EOGRT test on the immediate disintegration/hydrolysis product, 3-(trimethoxysilyl)propylamine.

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

Study period:

4th December 2017 to 1st March 2019

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)

Version / remarks:

19998

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Species:

rat

Strain:

Wistar

Remarks:

(Han)

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Deutschland, Sulzfeld, Germany.
- Females (if applicable) nulliparous and non-pregnant: yes
- Age at study initiation: 6 weeks
- Weight at study initiation: 120 to 184 g.
- Fasting period before study: no
- Housing: polycarbonate cages (Makrolon type IV, height 18 cm) with appropriate bedding (Lignocel S 8-15, JRS), up to 5 animals of same sex and dose per cage.
- Diet: ad libitum
- Water: ad libitum
- Acclimation period: 7 days

DETAILS OF FOOD AND WATER QUALITY:
Food was Pelleted rodent diet (SM R/M-Z) from SSNIFF® Spezialdiäten GmbH, Soest, Germany. Water was municipal tap water and water analyses was performed periodically.

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22-23°C
- Humidity (%): 37-59%
- Air changes (per hr): Ten or more
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 14 Feb 2018 To: 16 May 2018

Route of administration:

oral: gavage

Vehicle:

corn oil

Remarks:

Dehydrated and deacidified, specific gravity 0.92

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS:

The dosing formulations were prepared daily as a solution and dosed within 1 hour after adding vehicle to the test item. As aspiration is a known hazard with the oral dosing of this type of test item (aminosilane), the feeding tube was thoroughly cleaned before administering the test item to the animals and the total volume was dispensed before the feeding tube was withdrawn. The first day of dosing was designated as Day 1.
The dosing formulations were stirred continuously during dose administration.

VEHICLE
- Justification for use and choice of vehicle (if other than water): none given in study report
- Concentration in vehicle: 20, 60 and 200 mg/mL for 100, 300 and 1000 mg/kg bw/day
Adjustment was made for specific gravity of the vehicle (0.92) and test item (1.0140). No correction was made for the purity/composition of the test item.
- Amount of vehicle (if gavage): Dosing volume: 5 ml/kg

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Doses were collected for concentration (all groups) and Homogeneity (low and high dose groups) in Week 1, Week 2 and Week 13.
Concentration Analysis
Duplicate sets of samples (approximately 500 mg) for each sampling time point were sent to the analytical laboratory. In Week 2, additional duplicate top, middle, and bottom samples of Group 2, using pre-weighed test item, were measured. Concentration results were considered acceptable if mean sample concentration results were within or equal to ± 10% for solutions of target concentration.
Homogeneity Analysis
Duplicate sets of samples (approximately 500 mg) for each sampling time point were sent to the analytical laboratory. In Week 2, additional duplicate top, middle, and bottom samples of Group 2, using pre-weighed test item, were measured. Homogeneity results were considered acceptable if the coefficient of variation (CV) of concentrations was ±10%.
Stability Analysis
Stability analyses performed previously in conjunction with the method development and validation study (Test Facility Study No. 20136855) demonstrated that the test item is stable in the vehicle when prepared and stored under the same conditions at concentrations bracketing those used in the present study. Stability data have been retained in the study records for Test Facility Study No. 20136855.

Duration of treatment / exposure:

90 days (minimum)

Frequency of treatment:

Once daily, seven days a week.

Dose / conc.:

0 mg/kg bw/day (nominal)

Remarks:

Vehicle

Dose / conc.:

100 mg/kg bw/day (nominal)

Remarks:

Low dose

Dose / conc.:

300 mg/kg bw/day (nominal)

Remarks:

Mid dose

Dose / conc.:

1 000 mg/kg bw/day (nominal)

Remarks:

High dose

No. of animals per sex per dose:

10 animals per sex per group in each main group, with an additional 5 animals per sex in recovery groups (vehicle and 1000 mg/kg bw groups).

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: limit dose
- Rationale for animal assignment (if not random): Random
- Rationale for selecting satellite groups: none given in study report
- Post-exposure recovery period in satellite groups: two weeks
- Section schedule rationale (if not random): Random

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Daily

BODY WEIGHT: Yes
- Time schedule for examinations: weekly

FOOD CONSUMPTION
- Food consumption was quantitatively measured weekly starting on Day 1 and continuing weekly throughout the Dosing and Recovery Periods.

WATER CONSUMPTION
- Water consumption was monitored on regular basis throughout the study by visual inspection of the water bottles

OPHTHALMOSCOPIC EXAMINATION: Yes
- Time schedule for examinations: during pre-treatment in all animals and at end of dosing period in vehicle and high dose animals.
- Dose groups that were examined: The eyes were examined using an ophthalmoscope after application of a mydriatic agent (Tropicol 5 mg/mL solution, THEA Pharma, Wetteren, Belgium) during pre-treatment in all Main Study and Recovery animals, and at the end of the Dosing Period in Week 13 in all Group 1 (vehicle) and 4 (high dose) Main study and Recovery animals.

HAEMATOLOGY: Yes
- Time schedule for collection of blood: end of treatment (all animals) end of recovery (vehicle and high dose animals only)
- Anaesthetic used for blood collection: yes - isoflurane
- Animals fasted: Yes
- How many animals: 10 per group (end of treatment); 5 per group (end of recovery)
- Parameters checked in Table 1 were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: end of treatment (all animals) end of recovery (vehicle and high dose animals only)
- Animals fasted: Yes / No / Not specified
- How many animals: 10 per group (end of treatment); 5 per group (end of recovery)
- Parameters checked in Table 2 were examined.

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: once, during week 12-13
- Dose groups that were examined: all groups, 5 animals per sex per group
- Battery of functions tested: hearing ability / pupillary reflex / static righting reflex / fore- and hind-limb grip strength / locomotor activity

IMMUNOLOGY: No

OTHER: Oestrous cycle determination: Daily vaginal lavage was performed for all females from Week 11 (Day 71) up to and including Week 13 (Day 91).
Oestrous cycles were evaluated by examining the vaginal cytology of samples obtained by vaginal lavage.

Sacrifice and pathology:

GROSS PATHOLOGY: Yes

HISTOPATHOLOGY: Yes (see Table 3)

Statistics:

All statistical tests were conducted at the 5% significance level. All pairwise comparisons were conducted using two sided tests and were reported at the 1% and 5% levels.
Numerical data collected on scheduled occasions for the listed variables were analysed as indicated according to sex and occasion. Descriptive statistics number, mean and standard deviation (or %CV or SE when deemed appropriate) were reported whenever possible. Inferential statistics were performed according to the matrix below when possible, but excluded semi-quantitative data, and any group with less than 2 observations.
The following pairwise comparisons were made:
Group 2 (low dose) vs. Group 1 (vehicle)
Group 3 (mid dose) vs. Group 1 (vehicle)
Group 4 (high dose) vs. Group 1 (vehicle)
Parametric
Datasets with at least 3 groups (the designated control group and 2 other groups) were compared using Dunnett-test (many-to-one-t-test).
Non-Parametric
Datasets with at least 3 groups was compared using a Steel-test (many-to-one rank test).
The motor activity data set was compared using an overall Kruskal-Wallis.
Incidence
An overall Fisher’s exact test was used to compare all groups at the 5% significance level. The above pairwise comparisons were conducted using Fisher’s exact test whenever the overall test is significant.

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Slight to (incidentally) moderate rales were noted for males and females treated at 100 mg/kg/day and higher, with a dose-related increase in incidence (i.e. few animals affected on some occasions at the low dose level to most or all animals affected on many occasions at the high dose level).
In addition, hunched posture, laboured or deep respiration, gasping, squeaking, piloerection, diarrhoea and/or ptosis were noted on a few occasions in individual males and females at 1000 mg/kg/day.
In females at 1000 mg/kg/day, these signs were no longer present after cessation of treatment, whereas laboured respiration, rales, piloerection and ptosis were still observed in males on some occasions during the recovery period.
Salivation seen after dosing among males and females treated at 100 mg/kg/day and higher was not considered toxicologically relevant, taking into account the nature and minor severity of the effect and its time of occurrence (i.e. after dosing). This sign was considered to be a physiological response related to taste of the test item rather than a sign of systemic toxicity.

Mortality:

mortality observed, treatment-related

Description (incidence):

Six premature deaths from the 1000 mg/kg/day dose group between Days 62 and 87. One male was found dead (Animal No. 45) and one male (Animal No. 42) and four females (Animal Nos. 92, 96, 98, and 100) were euthanized in extremis. All animals had respiratory clinical observations prior to death (rales, gasping, abdomen distended with gas, and/or deep/laboured breathing). Other clinical signs noted prior to death included hunched posture, piloerection, diarrhoea, abdomen filled with gas and/or lean appearance. Except for animal No. 92, a severe body weight loss up to 22% was observed in all found dead or euthanized animals. All but one (Animal No. 92, euthanized in extremis) had distention of the gastrointestinal tract with gas at necropsy. Due to the suspicion of gavage-related reflux, the caudal nasal cavities and nasopharynx were evaluated in these animals, in addition to the protocol tissue list.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Body weights and body weight gain were decreased with statistical significance for males at 1000 mg/kg/day from Weeks 5 and 7 onwards, respectively, and this persisted until the end of the 2-week recovery period (body weight gain was 0.84x of controls at the end of treatment and 0.83x at the end of recovery).

Ophthalmological findings:

no effects observed

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

At the end of treatment, increased neutrophil count (1.73x and 2.50x for males and females, respectively) and/or monocyte count (males, 2.00x of controls) were noted at 1000 mg/kg/day.
At the end of the 2-week recovery period, neutrophil count was still increased in both sexes, but without reaching statistical significance.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

At the end of treatment, alanine aminotransferase (ALAT) and aspartate aminotransferase activity (ASAT) were slightly increased in males at 1000 mg/kg/day (2.02x and 1.36x of controls, respectively).
In addition, decreased total protein (0.96x and 0.92x in males and females, respectively) and albumin levels (0.92x in females), and increased bile acids (1.66x in females) were noted. Sodium and chloride concentrations were increased in all treated male groups, however lacking a dose relationship (1.06x, 1.06x and 1.04x for sodium and 1.07x, 1.05x and 1.03x for chloride at dose levels of 100, 300 and 1000 mg/kg/day, respectively). In females, this was only noted for sodium (1.01x for all dose levels).
At the end of the 2-week recovery period, all above mentioned parameters were similar between animals treated at 1000 mg/kg/day and controls.
It should be noted that high alanine aminotransferase and aspartate aminotransferase activity were noted for two individual females at 1000 mg/kg/day (Animal Nos. 94 and 95).
Any other statistically significant changes in clinical biochemistry parameters were considered to be unrelated to treatment as these occurred in the absence of a dose-related trend.

Urinalysis findings:

not examined

Behaviour (functional findings):

no effects observed

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Test item-related lower liver weights were noted in females at the end of the treatment period in the 1000 mg/kg/day group as shown in Table 4.

Gross pathological findings:

no effects observed

Neuropathological findings:

no effects observed

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Test item-related microscopic findings after treatment were noted in the larynx, nasal cavity, nasopharynx, stomach, large intestine, mesenteric lymph node of males and females and Harderian gland in males and are summarized in Table 5 to Table 12.

Histopathological findings: neoplastic:

no effects observed

Other effects:

effects observed, treatment-related

Description (incidence and severity):

An increased incidence in irregular oestrous cycle was noted in a few females at 1000 mg/kg/day and an acyclic oestrous cycle was noted in one female each at 300 and 1000 mg/kg/day. These changes are considered to be adverse although they may be secondary to reduced body weights secondary to local effects.

Details on results:

Microscopic effects in larynx and caudal nasal cavity that were observed at all dose levels are consistent with gavage related reflux. Changes were noted during microscopic examination of the large intestines and stomach, and in mesenteric lymph node and harderian glands. Microscopic changes were noted in the stomach from 300 mg/kg bw/day and in the cecum at 1000 mg/kg bw/day.
Following the 2-week treatment free period there was partial recovery of the clinical signs and microscopic findings in the larynx, stomach, and large intestines; no recovery of the mesenteric lymph node; and full recovery of the Harderian gland.
The adverse histologic changes in the upper airways noted starting at 100 mg/kg/day were considered by the study author to be strongly suggestive of a pathogenesis that is related to a combination of the irritant nature of the test item, the administration procedure, and the test species. While this may be important for dose selection for future rat studies, this may not necessarily be relevant to other species.
Based on these results, the no-observed-adverse-effect level (NOAEL) is considered to be100 mg/kg/day.

Dose descriptor:

NOAEL

Effect level:

100 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Changes in oestrous cyclicity observed at 1000 and 3000 mg/kg bw/day.

Dose descriptor:

LOAEL

Remarks:

Local effects

Effect level:

>= 0 - < 100 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

histopathology: non-neoplastic

Critical effects observed:

no

Table 4 Mean Percent Liver Differences from respective Control Groups

	Females
	Main Study			Recovery
Dose level (mg/kg/day)	100	300	1000	1000
BODY WEIGHT	-1	0	-3	0
LIVER
Absolute	1	-2	-14^**	-4
Relative to body weight	2	-2	-12^**	-4

*: P<0.05, **: P<0.01

Table 5 Summary Test Item-Related Microscopic Findings in the Larynx, Nasopharynx and Nasal Cavity – Scheduled Euthanasia Animals (Day 91-92)

	Males				Females
Dose level mg/kg bw/day	0	100	3000	1000	0	100	300	1000
Larynx^a	10	10	10	8	10	10	10	8
Erosion/ulceration	0	0	5	4	0	1	0	0
Minimal	-	-	4	1	-	1	-	-
Slight	-	-	1	3	-	-	-	-
Metaplasia squamous	0	0	1	8	0	0	1	8
Minimal	-	-	1	2	-	-	-	2
Slight	-	-	-	2	-	-	1	3
Moderate	-	-	-	4	-	-	-	3
Inflammation acute	0	0	3	1	0	1	0	0
Minimal	-	-	2	1	-	1	-	-
Slight	-	-	1	-	-	-	-	-
Inflammation, chronic	0	0	0	4	0	0	0	3
Minimal	-	-	-	2	-	-	-	-
Slight	-	-	-	2	-	-	-	3
Hyperplasia, epithelial	0	0	4	1	0	0	0	2
Minimal	-	-	3	-	-	-	-	-
Slight	-	-	1	1	-	-	-	2
Pharynx, nasal^ab	0	3	3	0	0	6	3	0
Squamous metaplasia	-	0	0	-	-	0	1	-
Minimal		-	-			-	1
Exudate	-	1	1	-	-	2	1	-
Minimal		-	-			1	1
Slight		1	1			1	-
Erosion/ulceration	-	0	2	-	-	1	0	-
Slight		-	1			1	-
Moderate		-	1			-	-
Nasal Cavity^ab	0	3	3	0	0	6	3	0
Turbinate fusion	-	2	2	-	-	6	2	-
Minimal		-	-			-	2
Slight		1	1			5	-
Moderate		1	1			1	-
Exudate	-	1	2	-	-	2	2	-
Minimal		-	-			1	-
Slight		1	2			1	2
Erosion/ulceration	-	0	2	-	-	3	1
Minimal		-	-			1	-
Slight		-	2			2	1

^a = Number of tissues examined from each group.

^b = Tissues examined only from a select number of test item-treated animals per group.

Table 6 Test Item-Related Microscopic Findings in the Larynx – Recovery Euthanasia Animals (Day 105)

	Males				Females
Dose level (mg/kg/day)	0	100	300	1000	0	100	300	1000
Larynx^a	10			5	10			3
Metaplasia squamous	0			4	0			1
Minimal	-			1	-			1
Slight	-			3	-			-
Inflammation, chronic	0			2	0			0
Minimal	-			2	-			-

^a = Number of tissues examined from each group.

Table 7 Test Item-Related Microscopic Findings in the Stomach – Scheduled Euthanasia Animals (Day 91-92)

	Males				Females
Dose level (mg/kg/day)	0	100	300	1000	0	100	300	1000
Stomach^a	10	10	10	8	10	10	10	8
Erosion/ulceration	0	0	0	3	0	0	1	0
Minimal	-	-	-	3	-	-	1	-
Basophilia, mucosa	0	0	0	5	0	0	0	4
Minimal	-	-	-	2	-	-	-	2
Slight	-	-	-	3	-	-	-	2
Infiltrate, inflammatory cell	3	0	0	6	0	0	1	2
Minimal	3	-	-	2	-	-	-	-
Slight	-	-	-	4	-	-	1	2
Hemorrhage	1	0	0	4	0	0	0	1
Minimal	1	-	-	3	-	-	-	1
Slight	-	-	-	1	-	-	-	-

^a = Number of tissues examined from each group.

Table 8 Test Item-Related Microscopic Findings in the Stomach – Recovery Euthanasia Animals (Day 105)

	Males				Females
Dose level (mg/kg/day)	0	100	300	1000	0	100	300	1000
Stomach^a	5	-	-	5	5	-	-	3
Basophilia, mucosa	0			0	0			1
Minimal	-			-	-			1
Infiltrate, inflammatory cell	0			1	1			0
Minimal	-			-	1			-
Slight	-			1	-			-

^a = Number of tissues examined from each group.

Table 9 Test Item-Related Microscopic Findings in Large Intestine and Mesenteric Lymph Node – Scheduled Euthanasia Animals (Day 91-92)

	Males				Females
Dose level (mg/kg/day)	0	100	300	1000	0	100	300	1000
Cecum^a	10	10	10	8	10	10	10	8
Basophilia, mucosal	0	10	10	8	0	7	7	8
Minimal	-	4	-	1	-	6	5	-
Slight	-	6	8	4	-	1	2	3
Moderate	-	-	2	3	-	-	-	5
Single cell necrosis, mucosa	0	0	0	8	0	0	0	6
Minimal	-	-	-	1	-	-	-	5
Slight	-	-	-	-	-	-	-	1
Colon^a	10	10	10	8	10	10	10	8
Basophilia, mucosal	0	0	0	0	0	0	0	1
Slight	-	-	-	-	-	-	-	1
Rectum^a	10	10	9	8	10	10	10	8
Basophilia, mucosal	0	0	2	6	0	0	1	8
Minimal	-	-	2	3	-	-	1	7
Slight	-	-	-	3	-	-	-	1
Mesenteric lymph node^a	10	10	10	8	10	10	10	8
Macrophage aggregate, increased	1	1	3	6	0	1	3	5
Minimal	1	1	3	2	-	1	3	4
Slight	-	-	-	4	-	-	-	-
Moderate	-	-	-	-	-	-	-	1

^a = Number of tissues examined from each group.

Table 10 Test Item-Related Microscopic Findings in Large Intestine and Mesenteric Lymph Node – Scheduled Euthanasia Animals (Day 105)

	Males				Females
Dose level (mg/kg/day)	0	100	300	1000	0	100	300	1000
Cecum^a	5	-	-	5	5	-	-	3
Infiltration, inflammatory cell	0			0	0			2
Minimal	-			-	-			-
Slight	-			-	-			2
Colon^a	5	-	-	5	5	-	-	3
Basophilia, mucosal	0			3	0			1
Slight	-			3	-			1
Mesenteric lymph node^a	5	-	-	5	5	-	-	3
Macrophage aggregate, increased	4			5	1			2
Minimal	4			3	1			1
Slight	-			2	-			1

^a = Number of tissues examined from each group.

Table 11 Test Item-Related Microscopic Findings in the Harderian gland – Scheduled Euthanasia Animals (Day 91-92)

	Males				Females
Dose level (mg/kg/day)	0	100	300	1000	0	100	300	1000
Harderian gland^a	10	10	10	8	10	10	10	8
Atrophy	1	2	0	4	0	1	0	1
Minimal	1	2	-	2	-	-	-	-
Slight	-	-	-	2	-	1	-	1

^a = Number of tissues examined from each group.

 

Table 12 Summary Test Item-Related Microscopic Findings in the Harderian gland– Scheduled Euthanasia Animals (Day 105)

	Males				Females
Dose level (mg/kg/day)	0	100	300	1000	0	100	300	1000
Harderian gland^a	5	-	-	5	5	-	-	3
Atrophy	1			1	0			0
Minimal	1			1	-			-

^a = Number of tissues examined from each group.

Refer to the attached files for summary, individual and histopathology result tables.

Conclusions:

3-(Trimethoxysilyl)propylamine has been administered to rats once daily by oral gavage for 90 days, in a study conducted according to OECD TG 408 and in compliance with GLP (Charles River Laboratories, 2018). In this study the high dose of 1000 mg/kg/day was not well tolerated with unscheduled deaths in males and females at 1000 mg/kg bw/day and adverse clinical signs of respiratory distress with correlating microscopic findings affecting the larynx (starting at 300 mg/kg bw/day), nasal cavities and/or nasopharynx (starting at 100 mg/kg bw/day). Adverse microscopic findings were also noted in the stomach (starting at 300 mg/kg bw/day), and cecum (at 1000 mg/kg bw/day).
The clinical/microscopic signs of respiratory distress (due to reflux) and effects in the stomach (and cecum) were considered to be adverse but secondary to the local site-of-contact effects of the test item, rather than a systemic effect of the test item. Therefore, these findings are not considered in the derivation of the NOAEL. Based on these effects, the LOAEL for local effects is considered to be <100 mg/kg bw/day.
An increased incidence in irregular oestrous cycle was noted in a few females at 1000 mg/kg bw/day and an acyclic oestrous cycle was noted in one female each at 300 and 1000 mg/kg bw/day. These changes could have occurred due to the low and/or reduced body weight of those individual females at the end of the treatment period and are considered to be adverse.
Based on the adverse increased incidence in irregular oestrous cycle and/or acyclic oestrous cycles from 300 mg/kg bw/day onwards, the no-observed-adverse-effect level (NOAEL) was 100 mg/kg bw/day.
The conclusion that the oestrus cyclicity observations are adverse is conservative, however, the effects may be related to low and/or reduced body weight resulting from and therefore secondary to local effects. This will be clarified in the EOGRT test.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

100 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

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

There are no repeated dose toxicity data for the registered substance, 3-(trimethoxysilyl)propyl isocyanate, therefore data on the immediate disintegration/hydrolysis product, 3-(trimethoxysilylpropylamine (CAS 13822-56-5) have been used to address the repeated dose toxicity endpoint.

The key repeated dose toxicity study was a 90-day oral (gavage) study in male and female rats with the immediate disintegration/hydrolysis product, 3-(trimethoxysilyl)propylamine, conducted according to OECD Test Guideline 408 and in compliance with GLP (Charles River Laboratories, 2018). In this study the high dose of 1000 mg/kg bw/day was not well tolerated with unscheduled deaths in males and females at 1000 mg/kg bw/day and adverse clinical signs of respiratory distress with correlating microscopic findings affecting the larynx (starting at 300 mg/kg bw/day), nasal cavities and/or nasopharynx (starting at 100 mg/kg bw/day). Adverse microscopic findings were also noted in the stomach (starting at 300 mg/kg bw/day), and cecum (at 1000 mg/kg bw/day).

The clinical/microscopic signs of respiratory distress (due to reflux) and effects in the stomach (and cecum) were considered to be adverse but secondary to the local site-of-contact effects of the test item, rather than a systemic effect of the test item.  Therefore, these findings are not considered in the derivation of the NOAEL. Based on these effects, the LOAEL for local effects is considered to be <100 mg/kg bw/day.

An increased incidence in irregular oestrous cycle was noted in a few females at 1000 mg/kg bw/day and an acyclic oestrous cycle was noted in one female each at 300 and 1000 mg/kg bw/day. These changes could have occurred due to the low and/or reduced body weight of those individual females at the end of the treatment period and are considered to be adverse.

Based on the adverse increased incidence in irregular oestrous cycle and/or acyclic oestrous cycles from 300 mg/kg bw/day onwards, the no-observed-adverse-effect level (NOAEL) was considered to be 100 mg/kg bw/day. 

The conclusion that the oestrus cyclicity observations are adverse is conservative, however, the effects may be related to low and/or reduced body weight resulting from and therefore secondary to local effects. This will be clarified in the EOGRT test proposed for the intermediate hydrolysis product, 3-(trimethoxysilyl)propylamine, (CAS 13822-56-5).

Justification for use of data for the hydrolysis product, 3-(trimethoxysilyl)propylamine, (CAS 13822-56-5)

The registered substance, 3-(trimethoxysilyl)propyl isocyanate (CAS 15396-00-6) is a trimethoxysilane with a propyl side-chain that has an isocyanate functional group at the opposite end from the trimethoxysilane group.

The isocyanate group in 3-(trimethoxysilyl)propyl isocyanate (CAS 15396-00-6) hydrolyses very rapidly under physiological conditions (half-life 1 minute at 37°C and pH 7), forming an amine. Therefore, the substance hydrolyses very rapidly to give the immediate hydrolysis product, 3-(trimethoxysilyl)propylamine (CAS 13822-56-5). 3-(Trimethoxysilyl)propylamine (CAS 13822-56-5) has been predicted to hydrolyse rapidly under conditions relevant for oral exposure. The estimated hydrolysis half-life at pH 2 (relevant for oral exposure) and 37.5°C is approximately 5 seconds. Therefore, the test organism is expected to be mainly exposed to the hydrolysis products, 3-aminopropylsilanetriol and methanol.

Justification for classification or non-classification

Based on the available data, 3-(trimethoxysilyl)propyl isocyanate does not require classification for repeat dose toxicity according to Regulation (EC) No 1272/2008.