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

Toxicity to reproduction

Administrative data

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

04.09.2007-14.11.2008

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

The study was conducted according to the appropriate OECD test guideline, and in compliance with GLP.

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2008

Report date:

2008

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 422 (Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test)

Deviations:

no

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

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

EC Number:

213-668-5

EC Name:

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

Cas Number:

999-97-3

Molecular formula:

C6H19NSi2

IUPAC Name:

bis(trimethylsilyl)amine

Test material form:

liquid

Details on test material:

- Name of test material (as cited in study report): Hexamethyldisilazane
- Physical state: Colourless liquid
- Stability under test conditions: Stable
- Storage condition of test material: Room temperature under nitrogen

Test animals

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories Inc, Portage, MI
- Age at study initiation: Minimum of nine weeks
- Weight at study initiation: Males: 291.8 to 354.8 g; Females: 200.5 to 254.9 g
- Fasting period before study: No
- Housing: Individually in suspended wire-mesh cages elevated over bedding except during mating when animals were cohoused in the home cage of the male.
- Diet (e.g. ad libitum): Ad libitum, except during exposure period
- Water (e.g. ad libitum): Ad libitum, except during exposure period
- Acclimation period: Seven days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19.04-22.86
- Humidity (%): 33-66
- Air changes (per hr): 11.8-14.3
- Photoperiod (hrs dark / hrs light):


IN-LIFE DATES: From: 27.09.2007 To: 05.03.2008

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: 2000 litre stainless steel and glass Rochester-style inhalation chambers.
- Method of holding animals in test chamber: four levels of 20 individual animal compartments. The animal cage position assignment within each chanber was rotated daily.
- Source and rate of air: Building air (rate: no data)
- Method of conditioning air: Air from a Nash Air Compressor was passed through a series of filters to remove contaminants. This conditioned air was then passed through HEPA and activated charcoal filters before delivery to the chmabers.
- Temperature, humidity, pressure in air chamber: 22 ±3oC, 50 ±20% humidity, no data on pressure
- Air flow rate: No data
- Air change rate: 10-15 chamber volume air changes per hour
- Treatment of exhaust air: No data


TEST ATMOSPHERE
- Brief description of analytical method used: Automated sampling system designed so that test atmosphere continuously pulled from the chamber and delivered to analyser. Analysis was done using a gas chromatograph equipped with a flame ionisation detector to determine the actual chamber concentrations of test substance.
- Samples taken from breathing zone: No data

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: up to seven days
- Proof of pregnancy: vaginal plug or sperm in vaginal smear referred to as day 0 of pregnancy
- Further matings after two unsuccessful attempts: No data
- After successful mating each pregnant female was caged (how): Individually. Pregnant females were moved into shoebox cages.
- Any other deviations from standard protocol: None evident

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Automated sampling system designed so that test atmosphere continuously pulled from the chamber and delivered to analyser. Analysis was done using a gas chromatograph equipped with a flame ionisation detector to determine the actual chamber concentrations of test substance.

Duration of treatment / exposure:

Exposure period: Males (14 days premating and mating up to 28 days): Females (premating 14 days, mating, gestation, and postpartum days 1-3 up to 42 days
Premating exposure period (males): 14 days
Premating exposure period (females): 14 days
Duration of test: Males 28 days; Females up to 42 days

Frequency of treatment:

6 hours/day, 7 days/week

Details on study schedule:

Screening study only, so F1 matings were not conducted.

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 ppm (nominal)

Remarks:

Group 1 - Control Group

Doses / concentrations 2

Dose / conc.:

25 ppm (nominal)

Remarks:

Group 2 (0.16 mg/L)

Doses / concentrations 3

Dose / conc.:

100 ppm (nominal)

Remarks:

Group 3 (0.66 mg/L)

Doses / concentrations 4

Dose / conc.:

400 ppm (nominal)

Remarks:

Group 4 (2.66 mg/L)

No. of animals per sex per dose:

10 males and 20 females (including 10 for toxicity group)

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale:Based on previous study.
- Rationale for animal assignment (if not random): Random

Positive control:

None

Examinations

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily for mortality, and daily for clinical signs of toxicity (including abnormalities in nesting)

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Once before the first exposure and then weekly.

BODY WEIGHT: Yes
- Time schedule for examinations: First day of dosing, and at least weekly thereafter, and on day of sacrifice.

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

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: No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: On the day of scheduled sacrifice as a terminal procedure.
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: Yes, overnight
- How many animals: All males and toxicity phase females. Details reported in Section 7.5.3

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: On the day of scheduled sacrifice as a terminal procedure.
- Animals fasted: Yes, overnight
- How many animals: All males and toxicity phase females. Details reported in Section 7.5.3

URINALYSIS: No

NEUROBEHAVIOURAL EXAMINATION: Yes, details reported in Section 7.5.3

Oestrous cyclicity (parental animals):

Not examined

Sperm parameters (parental animals):

Testes were weighed and examined microscopically.

Litter observations:

STANDARDISATION OF LITTERS
- Performed on day 4 postpartum: No, all animals were killed in Day 4 post-partum for exminations.


PARAMETERS EXAMINED
The following parameters were examined in F1 offspring: mating, pregnancy, duration of gestation, mean litter size, mean live litter size, mean litter weight, mean ratio of live births/litter size, and sex ratio.  The number of corpora lutea and the number of uterine implantation sites were determined for all females.


GROSS EXAMINATION OF DEAD PUPS: yes, for external and internal abnormalities; possible cause of death was not determined for pups born or found dead.

Postmortem examinations (parental animals):

SACRIFICE
- Male animals: All surviving animals after 29 days treatment.
- Maternal animals: All surviving animals on day 4 post-partum

GROSS NECROPSY
- Gross necropsy consisted of external and internal examinations including the cervical, thoracic, and abdominal viscera.

HISTOPATHOLOGY / ORGAN WEIGHTS: See Section 7.5.3

Postmortem examinations (offspring):

SACRIFICE
- All offspring on day 4 post-partum
- These animals were subjected to gross necropsy examinations.

HISTOPATHOLOGY / ORGAN WEIGTHS: Not conducted

Statistics:

All data analysis was carried out using SAS version  8.2 or 9.1.3. Descriptive toxicology endpoints:  Parametric data was tested using Analysis of Variance (ANOVA) followed by Dunnett's Test (if significant); nonparametric data was tested by Kruskal-Wallis Test followed by Wilcoxon.  Repeated measures ANOVA was applied to data sets of multiple measurements  across time.  Histomorphology:  Cochran-Armitage Trend test for severity with Fisher's Exact Test for  pairwise comparisons.  Kruskal-Wallis was used to test for shifts in  grade with the Wilcoxon test used to test pairwise comparisons.   Functional observational battery:  ANCOVA (baseline as covariate), repeated measures ANOVA, Mixed modeling, and Jonckeere-Terpstra test (categorical endpoints).

Reproductive indices:

Mating and fertilty indices

Offspring viability indices:

None

Results and discussion

Results: P0 (first parental generation)

General toxicity (P0)

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Clinical signs attributed to test article included uncoordinated gait (not beyond day 10 or 11) and decreased activity noted immediately after exposure in both sexes from the highest dose group. These clinical signs persisted for some time following the exposure period with animals returning to normal prior to the next day's exposure.

Dermal irritation (if dermal study):

not examined

Mortality:

no mortality observed

Description (incidence):

There were no deaths.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

There was a statistically significant decrease in absolute body weights for females (-15%) with a corresponding decrease in total weight gain compared to controls for both sexes (62 and 25% for females and males, respectively) in the highest dose group. Absolute body weights for the mid dose group females were identified as statistically decreased (-7%) from controls, however, total and percent weight gain were not different.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

Total food consumption was statistically decreased for the highest dose group males and females.

Food efficiency:

not specified

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

not specified

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

Decreased glucose along with increased cholesterol levels, were noted in the highest dose group females with cholesterol and sodium levels statistically increased in the highest dose group males.

Urinalysis findings:

not examined

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

There were no treatment-related effects on the neurobiological function as evaluated through FOB and motor activity evaluations.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Histopathological examination of tissues and organs for control and high exposure animals demonstrated an increased incidence of centrilobular hypertrophy in the liver of high dose group females. Evaluation of intermediate dose levels confirmed this finding was limited to high dose group females. There were no other test article-related histopathological findings.

Histopathological findings: neoplastic:

no effects observed

Other effects:

not specified

Reproductive function / performance (P0)

Reproductive function: oestrous cycle:

not examined

Reproductive function: sperm measures:

not examined

Reproductive performance:

no effects observed

Description (incidence and severity):

The fertility rate was high resulting in at least 9 litters per group. At all concentrations, there were no treatment-related effects on the mean duration of gestation, number of implantations and mean number of corpora lutea per dam.

Effect levels (P0)

1

Dose descriptor:

NOAEC

Remarks:

General Toxicity

Effect level:

100 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

clinical signs

body weight and weight gain

food consumption and compound intake

clinical biochemistry

organ weights and organ / body weight ratios

histopathology: non-neoplastic

2

Key result

Dose descriptor:

NOAEC

Remarks:

Reproductive toxicity

Effect level:

>= 400 ppm

Sex:

male/female

Remarks on result:

not determinable due to absence of adverse toxic effects

Results: F1 generation

General toxicity (F1)

Clinical signs:

no effects observed

Dermal irritation (if dermal study):

not examined

Mortality / viability:

no mortality observed

Description (incidence and severity):

A Group 2-female delivered a normal size litter which included one dead, edematous foetus. This was considered an isolated, spontaneous finding with no additional occurences observed within this or any other exposure group.

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

not specified

Food efficiency:

not specified

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

not specified

Ophthalmological findings:

not examined

Haematological findings:

not examined

Clinical biochemistry findings:

not examined

Urinalysis findings:

not examined

Sexual maturation:

not examined

Anogenital distance (AGD):

not examined

Nipple retention in male pups:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Histopathological findings:

not examined

Other effects:

not specified

Developmental neurotoxicity (F1)

Behaviour (functional findings):

not examined

Developmental immunotoxicity (F1)

Developmental immunotoxicity:

not examined

Effect levels (F1)

Key result

Dose descriptor:

NOAEC

Generation:

F1

Effect level:

>= 400 ppm (nominal)

Based on:

test mat.

Sex:

male/female

Remarks on result:

not determinable due to absence of adverse toxic effects

Target system / organ toxicity (F1)

Key result

Critical effects observed:

no

Overall reproductive toxicity

Key result

Reproductive effects observed:

no

Any other information on results incl. tables

Table 1 Summary of reproductive parameter findings*

Parameter	Control	25ppm	100ppm	400ppm
Length of gestation	21	22	22	22
Male pups	8	7	7	7
Female pups	7	8	9	8
Sex ratio	1.2	0.9	0.9	1.0
Total pups (mean)	15	15	15	15
Initial litter weight (g)	88.1	94.5	98.1	96.2
Initial average pup weight (g)	6.2	6.5	6.4	6.5
Implantation sites	16	16	16	15
Number of corpora lutea	17	17	17	16
Number pregnant	10	9	10	10

*There were no statistically significant differences found.

Applicant's summary and conclusion

Conclusions:

In a repeated dose inhalation toxicity with the reproduction/developmental toxicity screening test conducted according to OECD Test Guideline 422 and in compliance with GLP with the registered substance 1,1,1,3,3,3-hexamethyldisilazane (CAS 999-97-3, EC 213-668-5), there were no treatment related-effects observed in any of the reproductive parameters evaluated in males and females animals up to the highest concentration. Therefore the NOAEC for reproductive toxicity was considered to be equal to or greater than 400 ppm (2.66 mg/L) in rats.