Reaction mass of decamethyltetrasiloxane; dodecamethylpentasiloxane; hexamethyldisiloxane; octamethyltrisiloxane

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

09.12.2003 to 20.06.2006

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Cross-reference

Reason / purpose for cross-reference:

reference to same study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2006

Report date:

2006

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 416, January 22, 2001, and Revised Draft Guideline 426, October, 1999

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: EPA Test Guidelines 870.3800-Reproduction and Fertility Effects, August, 1998 and 870.6300, Developmental Neurotoxicity Study, August, 1998

GLP compliance:

yes

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:

Hexamethyldisiloxane

Test animals

Species:

rat

Strain:

Sprague-Dawley

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 wire-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 (if applicable):

whole body

Vehicle:

unchanged (no vehicle)

Details on 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: 19-27°C, 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

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: 21 days (or until evidence of mating)
- Proof of pregnancy: vaginal plug / sperm in vaginal smear referred to as day 0 of pregnancy
- Further matings after two unsuccessful attempts: no
- After successful mating each pregnant female was caged (how): in a plastic maternity cages

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 prior to mating
Premating exposure period (females): 70 days prior to mating

Frequency of treatment:

6 hours/day, 7 days/week

Duration of test:

approximately 18 months

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

100 ppm

Doses / concentrations 2

Dose / conc.:

400 ppm

Doses / concentrations 3

Dose / conc.:

1 600 ppm

Doses / concentrations 4

Dose / conc.:

5 000 ppm

No. of animals per sex per dose:

30

Control animals:

yes

Details on study design:

No further details.

Examinations

Maternal 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
- 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. 

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes, but this being a two-generation study, the pregnancies were not interrupted as would be done in a purely developmental study.
Examinations included:
- Gravid uterus weight: No
- Number of corpora lutea: No
- Number of implantations: No
- Number of early resorptions: No
- Number of late resorptions: No

Fetal examinations:

The treatment regimen for this study was previously described in section 7.8.1.  This study was also conducted to determine the potential of HMDS to cause functional and/or morphological changes to the nervous system of the developing rat (F2 generation) following the exposure of the F0 and F1 generations.  Developmental landmarks (balanopreputial separation and vaginal patency) were evaluated for the selected F1 and F2 rats.  10 F2 pups/sex/group were selected for neurobehavioral testing, neuropathology, brain weights and/or brain dimension measurements (PND 21 or 72).  Designated tissues from F2 pups selected for neuropathological evaluation or exhibiting developmental abnormalities suggestive of an exposure related effect, were examined microscopically.

Statistics:

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.

Indices:

Reproductive parameters (days between pairing and coitus, length of gestation, evidence of parturation difficulties, mating, fertility, copulation and conception indices, testicular and epididymal sperm counts, sperm production rate sperm motility and morphology, ovarian primordial follicle count), developmental landmarks (e.g., balanopreputial separation and vaginal patency). Mean litter size, postnatal survival (postnatal day 0 to 4), postnatal survival for other intervals up to day 21.

Historical control data:

No data

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:no effects

Effect levels (maternal animals)

1

Dose descriptor:

NOAEL

Effect level:

>= 5 000 ppm

Based on:

test mat.

Basis for effect level:

other: maternal toxicity

2

Dose descriptor:

NOAEC

Effect level:

1 600 ppm

Based on:

test mat.

Basis for effect level:

other: other:

3

Dose descriptor:

other: NOAEC

Effect level:

1 600 ppm

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
The attainment of landmarks of sexual development (balanopreputial separation and vaginal patency) were unaffected by HMDS exposure.  No test article related effects on anogenital distance were noted for F2 offspring.  Brain size and weight for F2 animals on PND 21 and 72 were unaffected by parental test article exposure; no macroscopic, histopathological or morphometric evidence of neuropathology was observed.  The only test article-related effect on attainment of developmental landmarks noted for F2 pups was a slight delay in attainment of the surface righting response for females in the 5000 ppm group.  Effects on developmental neurobehavioral endpoints consisted of increased motor activity for F2 females in the 5000 ppm group on PND 13 and 21. The higher total activity counts on PND 21 were the result of an attenuated habituation.  By PND 61, a normal pattern of habituation was observed for these females.  No effects on motor activity were observed for F2 males at any exposure level.  Decreases in the average and peak responses to the acoustic startle response stimulus (VAVE and VMAX, respectively) were observed on PND 20 for F2 males and females at 5000 ppm.  However, no effects on the time from latency to peak response to the acoustic startle response stimulus (TMAX) were observed.   Grossly visible abnormalities, external, soft tissue and skeletal abnormalities:  No treatment-related gross external malformations were reported.

Effect levels (fetuses)

Dose descriptor:

NOAEL

Effect level:

>= 5 000 ppm

Based on:

test mat.

Basis for effect level:

other: teratogenicity

Fetal abnormalities

Abnormalities:

not specified

Overall developmental toxicity

Developmental effects observed:

not specified

Any other information on results incl. tables

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. 

Applicant's summary and conclusion

Conclusions:

Based on the results of an inhalation two-generation reproductive toxicity study in rats conducted to OECD test 416 and GLP, the NOAEL for developmental neurobehavioral endpoints was considered to be 1600 ppm. This was based on a lack of habituation exhibited in the locomotor activity assessments and delayed attainment of the surface righting response in the 5000 ppm group F2 females, and decreases in average and peak acoustic startle response on PND 20 in the 5000 ppm group F2 males and females. The NOAEL for neuropathologic endpoints was considered to be 5000 ppm. In the F2 generation, offspring body weight gains were persistently decreased in the 5000 ppm group from PND 4-14, and this lead to decreased body weights at late as PND 49 in male offspring. The few "findings" at the 1600 ppm and lower exposure levels lacked consistency (along the time line), were if insufficient magnitude and insufficiently dose-responsive. In the F1 generation, effects on body weights were only observed in the 5000 ppm group. The NOAEC for developmental effects was therefore 1600 ppm.