1,1,1,3,3,3-hexamethyldisilazane

Endpoint summary

Description of key information

In an acute oral toxicity study with 1,1,1,3,3,3-hexamethyldisilazane (CAS 999-97-3, EC 213-668-5), conducted according to a protocol comparable to the now-deleted OECD Test Guideline 401 but without information on GLP compliance, the LD50 was concluded to be 1.1 ml/kg bw/day (equivalent to 847 mg/kg bw based on a density of 0.77 g/cm³) (Bayer, 1988).

In an acute inhalation toxicity study conducted according to OECD Test Guideline 403 and in compliance with GLP, the LC50 value for 1,1,1,3,3,3-hexamethyldisilazane in the Sprague-Dawley rat was determined to be 1516 ppm (equivalent to 10000 mg/m³) (Dow Corning Corporation, 2007).

In an acute dermal toxicity study conducted according to a protocol similar to OECD Test Guideline 402, but without information on GLP compliance, the LD50 for 1,1,1,3,3,3-hexamethyldisilazane was concluded to be 544 mg/kg bw in females and 585 mg/kg bw in males (based on a density of 0.77 g/cm³) (Bushy Run Research Centre, 1981).

Key value for chemical safety assessment

Acute toxicity: via oral route

Link to relevant study records

Reference

Endpoint:

acute toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

03.06.80 to 05.08.80

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Remarks:

The study was conducted according to a test protocol that is comparable to the appropriate OECD test guideline. It was not compliant with GLP.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 401 (Acute Oral Toxicity)

Version / remarks:

Study was conducted prior to the adoption of OECD test guidelines and GLP

GLP compliance:

no

Remarks:

Pre-GLP

Test type:

standard acute method

Limit test:

no

Species:

rat

Strain:

Wistar

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: No data
- Age at study initiation: No data
- Weight at study initiation: No data
- Fasting period before study: Yes, but period not given.
- Housing: Groups of 5 in Makrolon Type II cages
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: No data


ENVIRONMENTAL CONDITIONS
- Temperature (°C):22 ±2
- Humidity (%): 60 ±5
- Air changes (per hr): about 10
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: 03.06.80 To: 05.08.80

Route of administration:

oral: gavage

Vehicle:

unchanged (no vehicle)

Details on oral exposure:

MAXIMUM DOSE VOLUME APPLIED: 1.5 ml/kg bw

Doses:

0.1, 1.0, 1.2, 1.4 and 1.5 ml/kg bw

No. of animals per sex per dose:

Five

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: Daily observations and weighing once per week.
- Necropsy of survivors performed: yes
- Other examinations performed: Not clear

Statistics:

The acute oral LD50 was determined by probit-regression analysis.

Key result

Sex:

male/female

Dose descriptor:

LD50

Effect level:

1.1 mL/kg bw

95% CL:

>= 1 - <= 1.2

Remarks on result:

other: equivalent to 847 mg/kg bw based on a density of 0.77 g/cm³

Mortality:

See Table 1.

Clinical signs:

other: At doses of 1.0 ml/kg bw and above paralysis of hind limbs, sedation, anaesthesia and poor general condition were observed.

Gross pathology:

Redness of the stomach mucosal membrane among animals that died during the study and those sacrificed at the end of the observation period.

Other findings:

None reported

Table 1 Summary of mortality

Dose (ml/kg bw)	Dead/dosed	Days to death	Mortality (%)
Males
0.1	0/5	-	0
1.0	2/5	3	40
1.2	1/5	2	20
1.4	5/5	4	100
1.5	5/5	2	100
Females
0.1	0/5	-	0
1.0	2/5	3	40
1.2	4/5	4	80
1.4	4/5	7	80
1.5	5/5	2	100

 

Interpretation of results:

Category 4 based on GHS criteria

Conclusions:

In an acute oral toxicity study with 1,1,1,3,3,3-hexamethyldisilazane (CAS 999-97-3), conducted according to a protocol comparable to the now-deleted OECD Test Guideline 401 but without information on GLP compliance, the LD50 was concluded to be 1.1 ml/kg bw/day (equivalent to 847 mg/kg bw based on a density of 0.77 g/cm³).

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

847 mg/kg bw

Acute toxicity: via inhalation route

Link to relevant study records

Reference

Endpoint:

acute toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

30.08.2006 to 17.07.2007

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 403 (Acute Inhalation Toxicity)

Deviations:

yes

Remarks:

Exposure period of six hours.

GLP compliance:

yes

Test type:

other: Similar to OECD 403

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Portage
- Age at study initiation: ≥10 weeks
- Weight at study initiation: Males: ≥223 g. Males: ≥347 g
- Fasting period before study: No
- Housing: Individually in suspended wire-mesh cages.
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: Six/seven days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 21-22
- Humidity (%): 32-64
- Air changes (per hr): 12.1 to 17.1
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: 05.10.2006 To: 03.01.2007

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Test substance vapour was generated using a heated stainless steel J-tube containing a column of stainless steel beads into which test substance was metered.
- Exposure chamber volume: 450 litre
- Method of holding animals in test chamber: None
- Source and rate of air: Building aor was passed through a Nash Air Compressor
- Method of conditioning air: Compressed air was passed through a series of filters to remove contaminants.
- Treatment of exhaust air: No data
- Temperature, humidity, pressure in air chamber: No data


TEST ATMOSPHERE
- Brief description of analytical method used: Chamber atmosphere was analysed using a Varian 3400 gas chromatograph equipped with a flame ionization detector.
- Samples taken from breathing zone: No data

Analytical verification of test atmosphere concentrations:

yes

Remarks:

Chamber atmosphere was analysed using a Varian 3400 gas chromatograph equipped with a flame ionization detector.

Duration of exposure:

6 h

Concentrations:

Target: 900, 1200 and 3450 (5.9, 7.8 and 22.6 mg/L); Nominal: 913, 1242, and 3755 ppm; Measured: 885, 1167 and 3400 ppm

No. of animals per sex per dose:

Five

Control animals:

no

Details on study design:

- Duration of observation period following administration: 14 days (animals killed on Day 15)
- Frequency of observations and weighing: Daily observations. Body weight measured on days 1 (first day of exposure), 8 and 15
- Necropsy of survivors performed: yes
- Other examinations performed: None

Statistics:

The mean lethal nominal chamber concentration (LC50), 95% confidence interval and approximate slope of the dose response curve were calculated using a SAS/STAT Spearman-Karber analysis. Means and standard deviations were determined for other data as appropriate.

Key result

Sex:

male/female

Dose descriptor:

LC50

Effect level:

1 516 ppm

Exp. duration:

6 h

Remarks on result:

other: equivalent to 10000 mg/m3

Mortality:

All animals on the 3755 ppm group died during the latter part of the six-hour exposure. In the 1242 ppm group 50% of the animals died prior to the scheduled terminal sacrifice. No animals died in the 913 ppm group.

Clinical signs:

other: There were no signs of toxicity before death in the animals of the highest dose group. In the lowest dose group clinical observations were: inactivity, lacrimation, eye lids partially closed, cold to the touch, muscles soft/limp, respiration slow/noisy an

Body weight:

Body weight gains for 913 ppm group averaged approximately 12%, while those for the  surviving animals in the 1242 ppm group averaged approxiately -1% over the 15 day observation period.

Gross pathology:

In the 3755 ppm group, five animals (three females and two males) presented with liver congestion, one of which also presented with spleen congestion, and two animals (males) presented with intestine (jejunum) congestion.  This represents a non-specific finding that indicates some increased circulation to the organ.  The remaining three animals showed no visible lesions.  All of the animals in this group died during the exposure.  In the 913 ppm group, one male animal presented with kidney foci depressed (minimal) and the remaining animals showed no visible lesions.  The minimal focal depressions in the kidneys of the one male represent a common spontaneous finding with no toxicological significance.  All of the animals in this group were necropsied at the scheduled terminal sacrifice on day 15.  In the 1242 ppm group, three animals (one male and two females), found dead on days 4 or 5, presented with decreased stomach ingesta, two of which (females) also presented with liver discoloration (pale).  The decreased stomach ingesta indicates that the animals were too sick to eat.  Pale livers can be caused by lipidosis or from autolysis; since these animals were found dead, it is assumed the latter. The two other animals which were found dead (on day 2) and the remaining animals which were necropsied at the scheduled terminal sacrifice showed no visible lesions.  

Other findings:

None reported

Table 1 Mortality results and time to death.

Sex	Exposure concentration (ppm)	Number of deaths	Time to death
Male	3755	5/5	During exposure period
	1242	3/5	Two on Day 2 and one on Day 5
	913	0/5	No deaths
Female	3755	5/5	During exposure period
	1242	2/5	One on each of Days 4 and 5
	913	0/5	No deaths

                        

Interpretation of results:

Category 4 based on GHS criteria

Remarks:

Criteria used for interpretation of results: EU

Conclusions:

In an acute inhalation toxicity study (reliability score 1) conducted according to OECD Test Guideline 403 and in compliance with GLP, the LC50 value for 1,1,1,3,3,3-hexamethyldisilazane in the Sprague-Dawley rat was determined to be 1516 ppm (equivalent to 10000 mg/m³).

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LC50

Value:

10 000 mg/m³ air

Acute toxicity: via dermal route

Link to relevant study records

Reference

Endpoint:

acute toxicity: dermal

Type of information:

experimental study

Adequacy of study:

key study

Study period:

No data

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study with acceptable restrictions

Remarks:

The study was conducted according to a test protocol that is comparable to the appropriate OECD test guideline. It was not compliant with GLP.

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 402 (Acute Dermal Toxicity)

GLP compliance:

no

Test type:

standard acute method

Limit test:

no

Species:

rabbit

Strain:

New Zealand White

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: No data
- Age at study initiation: No data
- Weight at study initiation: 2-3 Kg
- Fasting period before study: No data
- Housing:No data
- Diet (e.g. ad libitum): No data
- Water (e.g. ad libitum): No data
- Acclimation period: No data


ENVIRONMENTAL CONDITIONS
- Temperature (°C): No data
- Humidity (%): No data
- Air changes (per hr): No data
- Photoperiod (hrs dark / hrs light): No data


IN-LIFE DATES: No data

Type of coverage:

occlusive

Vehicle:

unchanged (no vehicle)

Details on dermal exposure:

TEST SITE
- Area of exposure: No data
- % coverage: No data
- Type of wrap if used: Impervious sheet


REMOVAL OF TEST SUBSTANCE
- Washing (if done): Yes
- Time after start of exposure: 24 hours


TEST MATERIAL
- Amount(s) applied (volume or weight with unit): Males: 1.0, 0.71 and 0.5 ml/kg bw; females: 16.0, 4.0, 1.0, 0.5 and 0.25 ml/kg bw
- Concentration (if solution): Undiluted
- Constant volume or concentration used: yes

Duration of exposure:

24 hours

Doses:

1.0, 0.71, and 0.50 mL/kg bw (770, 550, and 385 mg/kg bw based on a density of 0.77 g/cm3) in males and 16.0, 4.0, 1.0, 0.5, and 0.25 mL/kg bw (12,320, 3080, 770, 385, 193 mg/kg bw based on a density of 0.77 g/cm3) in females

No. of animals per sex per dose:

Four (except 16 and 4 ml/kg bw levels used two females each)

Control animals:

not required

Details on study design:

- Duration of observation period following administration: 14 days
- Frequency of observations and weighing: Observations were made daily. Weights were measured before dosing and on Days 7 and 14.
- Necropsy of survivors performed: yes

Statistics:

LD50s were calculated using the 'moving average method'.

Key result

Sex:

male

Dose descriptor:

LD50

Effect level:

585 mg/kg bw

Based on:

test mat.

Key result

Sex:

female

Dose descriptor:

LD50

Effect level:

544 mg/kg bw

Based on:

test mat.

Mortality:

Males: 4/4, 1/4 and 0/4 at 1.0, 0.71 and 0.5 ml/kg bw, respectively.
Females: 2/2, 2/2, 4/4, 0/4 and 0/4 at 16.0, 4.0, 1.0, 0.5 and 0.25 ml/kg bw, respectively.

Clinical signs:

other: See Table 1

Gross pathology:

See Table 1

Other findings:

See table 1

Table 1 Summary of mortality, clinical and necropsy findings.

Group (ml/kg bw)	Number of deaths/total exposed	Time to death (d)	Clinical observations	Necropsy findings
Males
0.5	0/4	-	Sluggishness on Days 1 and 2 (2/4), skin erythema, edema, necrosis on Day 1 and desquamation by Day 14.	Trachea red (1/4), liver with tan foci (coccodiae; 1/4)
0.71	1/4	3	Prostration in one animal, skin erythema and necrosis, and scabs by Day 14.	Nothing remarkable
1.0	4/4	1, 1, 2, 3	Prostration in two animals, skin erythema, edema and necrosis	Lung & liver dark (1/4), trachea red (2/4), bladder distended filled with red/yellow liquid (1/4)
Females
0.25	0/4	-	Capillary injection, erythema, necrosis, spots of ecchymosis on Day 1, desquamation, scabs at 14 days.	Lungs mottled dark red (2/4) and trachea slight redness along mucous lining (1/4)
0.5	0/4	-	Sluggishness on Day 1, skin erythma, edema and necrosis on Day 1 with desquamation and scabs by Day 14.	Lungs and trachea dark red (1/4)
1.0	4/4	1, 1, 1, 3	Lethargy, slow and shallow breathing (1 hour), skin erythema and necrosis	Lungs mottled dark red (2/4) and trachea dark red (1/4)
4.0	2/2	1, 1	Signs of discomfort, lethargy slow and shallow breathing (30 mins), skin erythema and necrosis	Lungs with dark red patches
16.0	2/2	0, 0 (within 2 hours)	Signs of discomfort, skin erythema and necrosis	Nothing remarkable

Interpretation of results:

Category 3 based on GHS criteria

Remarks:

Criteria used for interpretation of results: EU

Conclusions:

In an acute dermal toxicity study conducted according to a protocol that was comparable to OECD Test Guideline 402, but without information on GLP compliance, the LD50s for 1,1,1,3,3,3-hexamethyldisilazane (CAS 999-97-3) was concluded to be 544 mg/kg bw in females and 585 mg/kg bw in males (based on density of 0.77 g/cm3).

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

LD50

Value:

544 mg/kg bw

Additional information

In the key acute oral toxicity study conducted according to a protocol similar to the now deleted OECD Test Guideline 401 and without information on GLP compliance (Bayer, 1988), Wistar rats (5/sex/dose) were exposed by oral gavage to 1,1,1,3,3,3-hexamethyldisilazane at doses of 0.1, 1.0, 1.2, 1.4 and 1.5 ml/kg bw. The animals were then observed for 14 days for signs of toxicity. Animals were weighed before dosing and on day 7 and 14 of the observation period. At doses of 1.0 ml/kg bw and above paralysis of hind limbs, sedation, anaesthesia, poor general condition and reduced body weight were observed. Necropsy revealed redness of the stomach mucosal membrane among animals that died during the study and those that were sacrificed at the end of the observation period. No deaths or signs of toxicity were observed at the lowest dose. There were 4/10, 5/10 (1 female and 4 males), 9/10 and 10/10 deaths at 1.0, 1.2, 1.4 and 1.5 ml/kg bw. The LD₅₀ was calculated to be 1.1 ml/kg bw/day.

In the supporting acute oral toxicity study conducted according to a protocol similar to the now deleted OECD Test Guideline 401 and without information on GLP compliance, 1,1,1,3,3,3-hexamethyldisilazane was administered by oral gavage to BR Long-Evans derived rats (5/sex/dose) at doses of 0.05, 0.1, 0.25, 0.50, 0.90, 0.95, 1.00, 2.50 ml/kg bw. The animals were then observed for 14 days. There were no deaths up to a dose of 0.9 ml/kg bw. Mortalities for 0.95, 1 and 2.5 ml/kg were 7/10, 6/10 and 10/10, respectively. All animals died within one day of dosing.

The LD₅₀ was calculated to be 1.0 ml/kg bw. Clinical signs at doses of  0.05, 0.1 and 0.25 ml/kg bw included decreased activity and ataxia.  At 0.5 and 0.9 ml/kg, clinical signs included decreased activity or sedate, ataxia or incoordination, urinary incontinence and decreased respiration. In addition, animals dosed at 0.9 ml/kg also exhibited exophthalmia, and extremities bright red in colour. Clinical signs at dose levels of 0.95 ml/kg  and higher were similar to those observed at lower dose levels, and may also have included one or more of the following: pilo-erection, lacrimation, cold to touch and salivation (FDRL, 1977).

The key study for acute oral toxicity was one of two reliability score 2 studies. The most recent was selected as the key study; however, these studies gave very similar results. Many reliability score 4 studies are also available to support the LD₅₀ from the key study.

In the key acute inhalation toxicity study (Dow Corning Corporation, 2007), conducted according to OECD Test Guideline 403 and in compliance with GLP, male and female Sprague-Dawley rats were exposed to 1,1,1,3,3,3-hexamethyldisilazane at nominal concentrations of 913, 1242, and 3755 ppm via whole-body inhalation for six hours. Following exposure, the animals were observed daily for clinical signs of toxicity. Weights were measured before dosing and on Days 8 and 15. The animals were examined macroscopically during necropsy. All animals in the 3755 ppm group died during the latter part of the 6-hour exposure. In the 1242 ppm group, 50% of the animals died prior to the scheduled terminal sacrifice. No animals died in the 913 ppm group. Clinical observations consisted of inactivity, lethargy, shallow and laboured breathing, lacrimation, cold to touch and soiling (urogenital and eyes). Necropsy findings consisted of liver, spleen and intestine congestion in the 3755 ppm group, one instance of focal depressions in the kidney in the 913 ppm group and decreased stomach ingesta and liver discolouration in the 1242 ppm group. These findings were judged to be non-specific, spontaneous or autolytic changes with no toxicological significance. The LC₅₀was concluded to be 1516 ppm (equivalent to 10000 mg/m³).

Other supporting studies for the inhalation route were available. The most reliable study, which had a reliability score 1, was selected as the key study.

In the key acute dermal toxicity study (Bushy Run Research Center, 1981), conducted according to a protocol similar to OECD Test Guideline 402, but without information on GLP compliance, male and female New Zealand white rabbits were subject to an occlusive 24-hour dermal application of undiluted 1,1,1,3,3,3-hexamethyldisilazane at doses of 1.0, 0.71, and 0.50 ml/kg bw (770, 550, and 385 mg/kg bw based on density of 0.77 g/cm³)

and 16.0, 4.0, 1.0, 0.5, and 0.25 ml/kg bw (12 320, 3080, 770, 385, 193 mg/kg bw based on a density of 0.77 g/cm³ ), respectively. Following exposure the animals were observed daily for clinical signs of toxicity. Weights were measured before dosing and on Days 7 and 14. The animals were observed macroscopically during necropsy. At doses of 1.0 ml/kg bw all animals died, and one male died at 0.71 ml/kg bw. There were no other deaths. All groups showed signs of severe skin irritation. The observed clinical signs included sluggishness, prostration, lethargy, slow and shallow breathing, discomfort and skin corrosion. The LD50 was concluded to be 544 mg/kg bw in females and 585 mg/kg bw in males (based on a density of 0.77 g/cm³).

The key study was the only one reliable study for the dermal route; however, supporting reliability 4 studies gave similar results.

Justification for classification or non-classification

Based on the available data, 1,1,1,3,3,3-hexamethyldisilazane (CAS 999-97-3, EC 213-668-5) requires classification as acute oral toxicity Cat. 4 (oral) 'H302: Harmful if swallowed', acute dermal toxicity Cat. 3 'H311: Toxic in contact with skin' and acute toxic (vapour) toxicity Cat. 4 'H332: Harmful if inhaled' according to Regulation (EC) 1272/2008.