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Repeated dose toxicity: inhalation

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short-term repeated dose toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
February to March 2014
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Study conducted to a design based on an appropriate guideline but with fewer animals and fewer parameters evaluated, and in compliance with GLP.

Data source

Reference Type:
study report
Report date:

Materials and methods

Test guideline
equivalent or similar to guideline
OECD Guideline 412 (Subacute Inhalation Toxicity: 28-Day Study)
: Six animals per sex per group, only two test substance exposure levels tested, clinical pathology parameters not investigated and only respiratory tract tissues and gross lesions examined microscopically.
Principles of method if other than guideline:
Establish potential effect on respiratory tract and compare with hydrogen chloride.
GLP compliance:
yes (incl. QA statement)
Limit test:

Test material

Constituent 1
Chemical structure
Reference substance name:
EC Number:
EC Name:
Cas Number:
Molecular formula:
Constituent 2
Reference substance name:
Hydrogen chloride
EC Number:
EC Name:
Hydrogen chloride
Cas Number:
Molecular formula:
ClH or HCl
Hydrogen chloride
Test material form:
other: vapour

Test animals

other: Crl:CD(SD)
Details on test animals or test system and environmental conditions:
- Source: Charles River (US)
- Age at study initiation: approximately 8 weeks
- Weight at study initiation: 266 to 329g males, 182 to 220g females
- Fasting period before study: no
- Housing: individually in wire mesh cages
- Diet (ad libitum): PMI Nutrition International, LLC Certified Rodent LabDiet® 5002
- Water (ad libitum): Reverse osmosis-treated tap water
- Acclimation period: 21 days

- Temperature (°C): 21.0 to 22.1
- Humidity (%): 32.5 to 43.8
- Air changes (per hr): 10
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 25 February 2014 To: 21 March 2014

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
Remarks on MMAD:
MMAD / GSD: not applicable.
Details on inhalation exposure:
- Exposure apparatus: 205-L polycarbonate whole-body inhalation exposure chambers, with polyvinyl chloride (PVC) dispersion and exhaust tubes and ethylene propylene diene monomer (EPDM) seals
- Method of holding animals in test chamber: plastic nose-only exposure restraint tubes
- Source of air: facility breathing quality, in-house compressed air source
- Method of conditioning air: HEPA- and charcoal-filtered, temperature- and humidity-controlled source
- System of generating DCDMS vapour: the vapour generators consisted of a sealable 4-neck reaction flask (1000 mL) maintained at room temperature. DCDMS from the original container was transferred to a smaller secondary vial that was placed into the flask after the lid was removed from the vial. Using a Coilhose Pneumatics regulator and a digital mass flowmeter, nitrogen was metered to 1 port of the reaction flask to act as a carrier gas for the test substance vapour. A second port was used as an outlet for delivery of DCDMS vapour to a tee fitting where dilution nitrogen was added. Dilution nitrogen flow was controlled using a Coilhose Pneumatics regulator and a digital mass flowmeter. Test substance vapour was directed to the exposure chamber inlet where it mixed with humidified dilution supply air.
- System of generating HCl vapour: A generation bag was prepared by diluting 1400 mL of neat HCl gas in 22 L of nitrogen or by diluting 350 mL of neat HCl in 5.5 L of nitrogen. The generation bag was placed in a 130-L stainless steel and glass whole body chamber. Compressed air was added to create a positive pressure within the generation chamber and to force the HCl gas mixture from the generation bag through 40 inches of ⅛-inch Teflon line to the exposure chamber. Compressed air delivery to the generation chamber was controlled using a Coilhose Pneumatics regulator equipped with a needle valve. The test atmosphere from the generation bag was metered to the exposure chamber using a Gilmont rotameter-type flowmeter. Dilution nitrogen was added prior to the chamber inlet using a Coilhose Pneumatics regulator with metering using a Top-Trak digital mass flow meter. The nitrogen and HCl gas mixture was mixed with chamber supply air at the chamber inlet.
- Temperature, humidity, pressure in air chamber:
- Air flow rate: 72L/minute
- Air change rate: approximately 21 per hour
- Treatment of exhaust air: facility exhaust system, which consisted of charcoal- and HEPA-filtration

- Brief description of DCDMS analytical method used: Gas chromatograph with flame ionisation detector (GC-FID)
- DCDMS Samples taken from breathing zone: yes
- Brief description of HCl analytical method used: Gas chromatograph with halogen-specific detector (GC-XSD)
- DCDMS Samples taken from breathing zone: yes
Analytical verification of doses or concentrations:
Details on analytical verification of doses or concentrations:
Analyzed concentrations were determined at specified intervals using the following chromatographic methods. For DCDMS generation/exposure systems, pre-dilution samples were collected from the test substance vapour delivery line to the exposure chamber prior to the chamber inlet (where the vapour was diluted with humidified supply air). Analyzed concentrations of DCDMS vapour in nitrogen were determined at approximately 30-minute intervals by a gas chromatograph with flame ionization detector (GC-FID#2). The DCDMS vapour concentrations prior to dilution with supply air were targeted at 100 ppm and 500 ppm for Chambers 3 and 4, respectively. These target vapour concentrations in nitrogen were determined based on a 20x dilution factor with supply air to obtain the desired chamber exposure concentration (5 and 25 ppm, respectively). Chamber samples from within the DCDMS exposure chambers and the control chamber were collected from the approximate animal breathing zone of each chamber and analyzed using an additional gas chromatograph with flame ionization detector (GC-FID#1). For the 2 DCDMS chambers, samples were collected at approximately hourly intervals. The DCDMS vapour concentrations within these exposure chambers (following dilution with humidified air) represented the residual parent compound (portion remaining that had not undergone hydrolysis). For the filtered air control chamber, samples were collected one time during each exposure using a Tedlar gas bag and appropriate sample pump.

For the HCl gas and high concentration DCDMS chambers samples for determination of total chlorine content were collected from the approximate animal-breathing zone within the exposure chambers and were analyzed using a gas chromatograph with halogen specific detector (GC#1-XSD). Samples were analyzed approximately hourly for the HCl chamber and once daily for the high concentration DCDMS chamber.
Duration of treatment / exposure:
6 hours and 13 minutes
Frequency of treatment:
5/days/week for 4 weeks
Doses / concentrationsopen allclose all
Doses / Concentrations:
dichloro(dimethyl)silane 5.3 and 25 ppm
nominal conc.
Doses / Concentrations:
dichloro(dimethyl)silane 0.83 and 2.6 ppm
analytical conc.
Doses / Concentrations:
hydrogen chloride 50 ppm
nominal conc.
Doses / Concentrations:
hydrogen chloride 49 ppm
analytical conc.
No. of animals per sex per dose:
Control animals:
yes, concurrent vehicle
Details on study design:
- Dose selection rationale: in a previous 90-day inhalation study, administration of 50 ppm hydrogen chloride resulted in an increased incidence of generally minimal effects in the nasal cavity, thus the same concentration was selected to produce similar effects. As dichloro(dimethyl)silane liberates 2 molar equivalents of HCl upon hydrolysis, 25 ppm dichloro(dimethyl)silane was selected as an equivalent concentration. The lower dichloro(dimethyl)silane concentration was selected to be equivalent to the reported HCl NOAEC.
Positive control:
Hydrogen chloride


Observations and examinations performed and frequency:
- Time schedule: during exposure and approximately 1 hour after exposure

- Time schedule: twice pre-study, weekly during study period and on day of scheduled necropsy

- Time schedule for examinations: daily during first week, twice during second week, then weekly

- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
- Time schedule: weekly



Sacrifice and pathology:
GROSS PATHOLOGY: Yes (see table)
ORGAN WEIGHTS: Yes (see table)
HISTOPATHOLOGY: Yes (see table)
All statistical tests were performed using WTDMS™ unless otherwise noted. Analyses were conducted using two-tailed tests (except as noted otherwise) for minimum significance levels of 1% and 5%, comparing each test substance-treated group to the control group by sex.

Body weight, body weight change, food consumption, and organ weight data were subjected to a parametric one way ANOVA (Snedecor and Cochran, 1980) to determine intergroup differences. If the ANOVA revealed statistically significant (p<0.05) intergroup variance, Dunnett's test (Dunnett, 1964) was used to compare the test substance treated groups to the control group. The positive control data were evaluated using the 2-sample t-test (Sokal and Rohlf, 1981) and compared to the vehicle control group.

Results and discussion

Results of examinations

Clinical signs:
no effects observed
no mortality observed
Body weight and weight changes:
no effects observed
Food consumption and compound intake (if feeding study):
no effects observed
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
not examined
Haematological findings:
not examined
Clinical biochemistry findings:
not examined
Urinalysis findings:
not examined
Behaviour (functional findings):
not examined
Organ weight findings including organ / body weight ratios:
effects observed, treatment-related
Gross pathological findings:
no effects observed
Histopathological findings: non-neoplastic:
effects observed, treatment-related
Histopathological findings: neoplastic:
no effects observed
Details on results:
Higher mean adrenal gland weights were noted in the 25 ppm dichloro(dimethyl)silane group males and females, lower mean thymus weights were noted in the 25 ppm DCDMS group females, and lower mean spleen weights were noted in the 5 and 25 ppm dichloro(dimethyl)silane and 50 ppm HCl group females.

Histopathologic changes were observed within nasal cavity levels I through III in the dichloro(dimethyl)silane and HCl-exposed males and females.

Histologic changes in the dichloro(dimethyl)silane and HCl-exposed animals were mainly confined to the anterior nasal cavity and included squamous epithelial hyperplasia, hyperkeratosis, interstitial edema, mucous cell hyperplasia, degeneration of the respiratory epithelium, and subacute inflammation. The most prominent changes were observed in nasal cavity level I, the nasal vestibule, in which squamous epithelial hyperplasia and hyperkeratosis were observed in both test substance-exposed groups and the 50 ppm HCl gas-exposed group, and interstitial edema was observed in the 25 ppm dichloro(dimethyl)silane-exposed group males and females (as well as a single 50 ppm HCl-exposed female). Squamous epithelial hyperplasia was also observed in nasal level II. Changes in nasal levels II and III generally were observed at a higher incidence and severity in the HCl-exposed animals when compared with the dichloro(dimethyl)silane-exposed animals, and included mucous cell hyperplasia and degeneration of respiratory epithelium. The respiratory epithelial degeneration was mainly observed in the 50 ppm HCl group animals (aside from a single 25 ppm dichloro(dimethyl)silane group male). Subacute inflammation was also observed in nasal levels II and III. It was observed at a similar incidence and severity in the 25 ppm DCDMS group males when compared with the 50 ppm HCl group males. However, it was observed in the majority of 50 ppm HCl group females but not in any 25 ppm DCDMS females.

Only interstitial edema in nasal level I and subacute inflammation in males, primarily in nasal level III, had higher incidences in the 25 ppm dichloro(dimethyl)silane group compared to the 50 ppm HCl group. The remaining nasal cavity findings were either predominantly observed in the 50 ppm HCl group (degeneration of the respiratory epithelium and subacute inflammation in females), were observed at a slightly higher incidence in the 50 ppm HCl group (squamous epithelial hyperplasia and mucous cell hyperplasia), or were observed at a similar incidence in both groups (hyperkeratosis).

Overall, the histopathology observations in the nasal cavity did not suggest greater irritant effects for the 25 ppm dichloro(dimethyl)silane group compared with the 50 ppm HCl group.

Mild acute inflammation was observed in the larynx of a single 25 ppm DCDMS exposed male and a single 50 ppm HCl-exposed male

Effect levels

Dose descriptor:
Basis for effect level:
other: local irritant effects noted in the nasal cavity at both 5 and 25 ppm (26 or 132 mg/m3) DCDMS. Similar findings recorded for 50 ppm HCl, which were generally comparable in incidence and severity to 25 ppm DCDMS.
Remarks on result:
not determinable
no NOAEC identified

Target system / organ toxicity

Critical effects observed:

Applicant's summary and conclusion

Inhalation administration of dichloro(dimethyl)silane at targeted concentrations of 5 or 25 ppm, or hydrogen chloride at 50 ppm, to rats for 5 days per week for 4 weeks, resulted in subacute inflammation, hyperplasia and/or hyperkeratosis of the squamous epithelium and mucous cell hyperplasia of the respiratory epithelium in the anterior nasal cavity. Exposure to 25 ppm dichloro(dimethyl)silane or 50 ppm hydrogen chloride was also associated with interstitial edema and respiratory epithelial degeneration within the anterior nasal cavity and acute inflammation in the larynx. Generally the incidence and severity of effects were similar in the 25 ppm dichloro(dimethyl)silane and 50 ppm hydrogen chloride groups. Overall, the histopathology observations in the nasal cavity did not suggest a greater irritant effect for the 25 ppm dichloro(dimethyl)silane group compared with the 50 ppm HCl group.