Hexamethyldisiloxane

Repeated dose toxicity: inhalation

Administrative data

Endpoint:

sub-chronic toxicity: inhalation

Type of information:

experimental study

Adequacy of study:

key study

Study period:

09.12.2003 to 20.06.2006

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

The general toxicity endpoints examined in the study were considered sufficient to define a general toxicity NOAEC.

Data source

Reference

Reference 1

Reference Type:

study report

Title:

Unnamed

Year:

2006

Report date:

2006

Reference 2

Reference Type:

other: Study report amendment

Title:

Unnamed

Year:

2008

Report date:

2008

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 416 (Two-Generation Reproduction Toxicity Study)

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Hexamethyldisiloxane

EC Number:

203-492-7

EC Name:

Hexamethyldisiloxane

Cas Number:

107-46-0

Molecular formula:

C6H18OSi2

IUPAC Name:

trimethyl[(trimethylsilyl)oxy]silane

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.
- Age at study initiation: 7 weeks
- Weight at study initiation: Males (P): 243 - 313 g; Females: 141 - 196 g; Males (F1): 381 - 603 g; Females: 223 - 362 g
- Fasting period before study: None
- Housing: Individually in stainless steel wire-mesh cages, mating in home cage of male, following mating females were removed to plastic maternity cages until lactation day 21, then transferred back to wie-mesh cages.
- Diet (e.g. ad libitum): Ad libitum (except during exposure)
- Water (e.g. ad libitum): Ad libitum (except during exposure)
- Acclimation period: 21 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ±3
- Humidity (%): 50± 20
- Air changes (per hr): Minimum 10
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 03.12.2003 To: 12.12.2005

Administration / exposure

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: 2.0 m3 stainless steel and glass whole body inhalation chambers
- Method of holding animals in test chamber: None
- Source and rate of air: No data
- Method of conditioning air: No data
- Temperature, humidity, pressure in air chamber: 19-27oC, 34-66%, slight negative pressure, respectively
- Air flow rate: No data
- Air change rate: 12-15 changes/hour
- Treatment of exhaust air: No data


TEST ATMOSPHERE
- Brief description of analytical method used: Gas chromatography
- Samples taken from breathing zone: yes, samples were taken from the approximate middle of each chamber

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Gas chromatography

Duration of treatment / exposure:

At least 70 days prior to mating, throughout mating, gestation through gestation day 20. After parturition, exposure of the F0 and F1 females was re-initiated on lactation day 5 and continued through the day prior to euthanasia . Premating exposure period (males): 70 days.
Premating exposure period (females): 70 days. Duration of test: appproximately 18 months.

Frequency of treatment:

6 hours/day, 7 days/week

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

100 ppm (nominal)

Doses / concentrations 2

Dose / conc.:

400 ppm (nominal)

Doses / concentrations 3

Dose / conc.:

1 600 ppm (nominal)

Doses / concentrations 4

Dose / conc.:

5 000 ppm (nominal)

No. of animals per sex per dose:

30

Control animals:

yes

Details on study design:

- Dose selection rationale: based on the results of a previous study (no details given)
- Rationale for animal assignment (if not random): random

Positive control:

None

Examinations

Observations and examinations performed and frequency:

Parental animals: Observations and examinations
CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed twice daily for appearance, behavior moribundity and mortality.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Weekly

BODY WEIGHT AND FOOD CONSUMPTION: Yes
- Time schedule for examinations: Weekly body weights and food consumption were recorded on gestation days (GD) 0, 4, 7, 11, 14 and 20 and on Postnatal days (PND) 1, 4, 7, 14 and 21 for females in the F0 and F1 generations.

WATER CONSUMPTION: No

Sacrifice and pathology:

SACRIFICE
- Male animals: All surviving animals as soon as possible after the last litters in each generation were produced.
- Maternal animals: All surviving animals after the last litter of each generation was weaned.

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

HISTOPATHOLOGY / ORGAN WEIGHTS

Organs examined at necropsy (macroscopic and microscopic): Complete detailed necropsy was conducted. Organ weights: Adrenal glands, brain, epididymis (total and cauda), kidneys, liver, lungs, ovaries, pituitary gland, prostate gland, seminal vesicles with coagulating glands and accessory fluids, spleen, testes, thyroid gland, uterus with oviducts and cervix Histopathologic evaluation: Adrenal glands, brain, cervix, coagulated glands, epididymis (right), kidneys, liver, lungs, ovaries, oviducts, pituitary gland, prostate gland, seminal vesicles, testes, thyroid gland, uterus, vagina, vas deferens, all gross (internal) lesions.
Postmortem examinations (Offspring)
Nonselected F1 pups were necropsied on PND 21 or 28, and nonselected F2 pups were necropsied on PND 21. Selected organs were weighed from F1 and F2 pups (one/sex/litter) that were necropsied on PND 21. Selected F2 rats not allocated for neuropathology and brain dimension measurements were necropsied following completion of reflex ontogeny evaluations (PND 61) or at study termination (PND 72). Each surviving F1 parental animal received a complete detailed gross necropsy following the completion of weaning of the F2 pups; selected organs were weighed.

Organs examined at necropsy (macroscopic and microscopic): Complete detailed necropsy was conducted. Organ weights: Adrenal glands, brain, epididymis (total and cauda), kidneys, liver, lungs, ovaries, pituitary gland, prostate gland, seminal vesicles with coagulating glands and accessory fluids, spleen, testes, thyroid gland, uterus with oviducts and cervix Histopathologic evaluation: Adrenal glands, brain, cervix, coagulated glands, epididymis (right), kidneys, liver, lungs, ovaries, oviducts, pituitary gland, prostate gland, seminal vesicles, testes, thyroid gland, uterus, vagina, vas deferens, all gross (internal) lesions.

Statistics:

Statistical methods: Parametric analysis was screened for homogeneity of variance using Levene's test and normality using Shapiro-Wilk's test. If the data was not homogenous and normal, then the data were analyzed using nonparametric statistics (Kruskal-Wallis ANOVA test followed by the Mann-Whitney U-test). Homogeneous data was analyzed by Chi-Square test with Yates correction factor, One-way ANOVA with Dunnett's test and Kolmogorov-Smirnov test (one-tailed test). FOB data and histopathological findings were compared to the control group using a two-tailed Fisher's Exact test. P< 0.05 or P < 0.01.

Results and discussion

Results of examinations

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

effects observed, treatment-related

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

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:

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS): No test article-related mortalities or clinical findings were observed in this study. One female in the F1 generation (highest dose group) died of dystocia (17 dead fetused in utero).

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS): Lower weekly body weight gains were noted for F0 males and females in the 1600 and 5000 ppm groups and F1 males in the 5000 ppm group. Mean body weights in the 1600 ppm group for both the F0 and F1 generations were generally similar to control group values, while those in the 5000 ppm group were reduced throughout the majority of both the F0 and F1 generations. Food consumption was lower for the 5000 ppm group males during the premating period (F0) and throughout the entire generation (F1). Food consumption for F1 females in the 5000 ppm group was reduced during the first week following weaning (week 17-18) only.

ORGAN WEIGHTS (PARENTAL ANIMALS): Test article-related higher kidney weights were noted for F0 and F1 males in the 1600 and 5000 ppm groups. Corresponding histopathological effects of HMDS in this study were similar to those previously reported in rats. Higher mean relative liver weights were noted for the F1 males in 1600 and 5000 ppm groups.

GROSS PATHOLOGY (PARENTAL ANIMALS): No adverse treatment-related findings.

HISTOPATHOLOGY (PARENTAL ANIMALS): Test article-related higher kidney weights were noted for F0 and F1 males in the 1600 and 5000 ppm groups. Corresponding histopathological effects of HMDS in this study were similar to those previously reported (Cassidy et al., 2001) in rats following long-term inhalation exposure at 593 and 5012 ppm. These findings included hyaline droplets (F0 and F1 males at 5000 ppm) and increased incidence and severity of basophilic tubules in the kidneys (F0 males, F1 males and F1 females at 5000 ppm). Male rat-specific hyaline droplet (consistent with alpha 2 urinary globulin) nephropathy was associated with the increase in basophilic tubules. Other test article related microscopic findings, including brown pigment in the periportal areas of the liver for F0 males in the 5000 ppm group and F1 males and females in the 1600 and 5000 ppm groups. This pigment was accompanied by infiltration of primarily mononuclear inflammatory cells and/or bile duct hyperplasia in the liver in the F0 and F1 5000 ppm groups, and corresponded to higher mean relative liver weights for the F1 males in the 1600 and 5000 ppm groups. Under polarised light some pigment accumulations show birefringence, but this finding was not consistent in size or between animals. In the 5000 ppm group F1 males and females, brown pigment was also noted in the medullary macrophages of the mesenteric lymph nodes and alveolar macrophage aggregates were noted for F0 and F1 males and females in the 5000 ppm group. Effects in the lungs were diagnosed as idiopathic rat respiratory syndrome, and were not therefore related to treatment.

Effect levels

Key result

Dose descriptor:

NOAEC

Effect level:

400 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Hepatic effects

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

In a two-generation reproductive toxicity study on HMDS, conducted to GLP (reliability score 2) the NOAEC for parental toxicity relevant to humans was 400 ppm based on microscopic liver findings in the F0 males of the 5000 ppm group and F1 males and females in the 5000 and 1600 ppm groups.