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Acute Toxicity: inhalation

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acute toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
30.08.2006 to 17.07.2007
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: The study was conducted according to an appropriate OECD test guideline, and in compliance with GLP.

Data source

Reference Type:
study report
Report Date:

Materials and methods

Test guideline
according to
OECD Guideline 403 (Acute Inhalation Toxicity)
Exposure period of six hours.
GLP compliance:
Test type:
standard acute method
Limit test:

Test material

Details on test material:
- Name of test material (as cited in study report): Hexamethyldisilazane
- Substance type: Silazane
- Physical state: Colourless liquid
- Analytical purity: 99.317 ± 0.1062%
- Impurities (identity and concentrations): No data
- Purity test date: No data
- Lot/batch No.: 0002364948
- Expiration date of the lot/batch: 02.07.2008
- Stability under test conditions: Stable
- Storage condition of test material: Room temperature under nitrogen

Test animals

Details on test animals and environmental conditions:
- 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

- 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

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
other: unchanged (no vehicle)
Details on inhalation exposure:
- 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

- 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:
Chamber atmosphere was analysed using a Varian 3400 gas chromatograph equipped with a flame ionization detector.
Duration of exposure:
6 h
Target: 900, 1200 and 3450; Nominal: 913, 1242, and 3755 ppm; Measured: 885, 1167 and 3400 ppm
No. of animals per sex per dose:
Control animals:
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
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.

Results and discussion

Effect levels
Dose descriptor:
Effect level:
1 516 ppm
Exp. duration:
6 h
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:
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 and soiling (around eyes or urogenital area).  The majority of the animals had returned to normal by day 3 or 4, however, one female was observed with decreased/absent activity and eye/urogenital soiling until day 5 before recovering. Clinical observations noted for all of the 1242 ppm group animals were similar to those noted for the 913 ppm group, with the additional observations of lethargy and labored respiration, which were not observed in the lower dose group. In the  animals which were found dead, many if not all of these observations persisted until death. In the animals which recovered and went on to the scheduled terminal sacrifice, these observations typically persisted until days 3 or 4, returning to normal by day 5. 
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

Any other information on results incl. tables

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


Applicant's summary and conclusion

Interpretation of results:
Migrated information Criteria used for interpretation of results: EU
Based on the results of an acute inhalation study (reliability score 1) in which OECD 403 was followed with the exception that a six, instead of four, hour exposure period was used, the LC50 value for hexamethyldisilazane in the Sprague-Dawley rat was determined to be 1516 ppm (10 mg/L).
Executive summary:

Based on the results of an acute inhalation study (reliability score 1) in which OECD 403 was followed with the exception that a six, instead of four, hour exposure period was used, Sprague-Dawley rats (5/sex/concentration) were exposed, whole body, to a vapour of hexamethyldisilazane (7 days/week). They were then observed for mortality and death for 14 days, after which time they were humanely killed and a gross necropsy was conducted. Body weights were also measured on Day 1 of exposure and then on Days 8 and 15. Animals that died spontaneously were also examined macroscopically. Initially, a limit test was conducted at a nominal concentration of 3755 ppm (measured 3400 ppm). Since this concentration killed all of the animals a further two concentrations of 1242 ppm and 913 ppm were tested. In the 1242 ppm group 50% of the animals died prior to the scheduled terminal sacrifice. No animals died in the 913 ppm group. The LC50 was subsequently calculated to be 1516 ppm. Body weight gains for the 913 ppm group averaged approximately 12%, while those of the surviving animals in 1242 ppm group averaged approximately -1% over the observation period. Clinical observations consisted of inactivity, lethargy, shallow and laboured breathing, lacrimation, cold to touch and soiling (urogenital and eyes), which stopped by Day 5 for surviving animals. Necropsy findings were 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.