Octamethyltrisiloxane

Toxicity to reproduction

Administrative data

Endpoint:

screening for reproductive / developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

27.10.2006 and 11.04.2008

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Cross-reference

Cross-reference 1

Reason / purpose for cross-reference:

reference to same study

Cross-reference 2

Reason / purpose for cross-reference:

reference to other study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2008

Report date:

2008

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

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

Test guideline 2

Qualifier:

according to guideline

Guideline:

other: US EPA Health Effects Test Guidelines OPPTS 870.3650 Combined repeated dose toxicity study with reproduction/developmental toxicity screening test

GLP compliance:

yes

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

Octamethyltrisiloxane

EC Number:

203-497-4

EC Name:

Octamethyltrisiloxane

Cas Number:

107-51-7

Molecular formula:

C8H24O2Si3

IUPAC Name:

2,2,4,4,6,6-hexamethyl-3,5-dioxa-2,4,6-trisilaheptane

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: at least 9 weeks
- Weight at study initiation: males: 270.1-346.6 g; females: 195.9-242.5 g
- Fasting period before study: no
- Housing: individually in suspended wire-mesh cages, except during mating, gestation and lactation
- Diet (e.g. ad libitum): ad libitum (except during inhalation exposure)
- Water (e.g. ad libitum): ad libitum (except during inhalation exposure)
- Acclimation period: five days prior to randomisation, 3 days acclimation to exposure caging and chambers (for 2.5 to 3.5 h (day1) or 5.5 to 6.5 h (days 2 and 3))

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19.81-23.24
- Humidity (%): 28-64
- Air changes (per hr): 10-20
- Photoperiod (hrs dark / hrs light): 12:12

IN-LIFE DATES: From: 21 November 2006 To: 17 December 2007

Administration / exposure

Route of administration:

inhalation: vapour

Type of inhalation exposure (if applicable):

whole body

Vehicle:

clean air

Details on exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Exposures were conducted in 1000-litre stainless steel and glass, TSE-system style, whole-body inhalation exposure chambers.
- Method of holding animals in test chamber: Animals were individually positioned within stainless steel exposure caging specifically designed for use in the TSE-system chambers (three levels of 24 compartments).
- Source and rate of air: dilution air stream building conditioned air; carrier air stream- compressed air filtered through a series of particulated filters prior to use in vapour generation
- Method of conditioning air: Activated carbon and HEPA filters for dilution air stream and particulate filters (Matheson Model 460/461; Balston Models 100-18-DX and 100-18-BX) for carrier air stream.
- System of generating particulates/aerosols: heated stainless steel J-tubes where mixed with a constant stream of filtered compressed air for vaporization. J-tubes heated to 60-110°C.
- Temperature, humidity, pressure in air chamber: Continuously monitored and recorded once every 30 minutes. Temperature: 22± 2 °C; Humidity: 36-39 %.
- Air flow rate: approximately 200 LPM
- Air change rate: 10-15 chamber air changes per hour
- Method of particle size determination: no data
- Treatment of exhaust air: No data

TEST ATMOSPHERE
- Brief description of analytical method used: See below.
- Samples taken from breathing zone: yes


TEST ATMOSPHERE
- Brief description of analytical method used:
- Samples taken from breathing zone: yes

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: Continuous until evidence of mating (maximum of 14 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
- After successful mating each pregnant female was caged (how): Home cage

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Chamber concentrations of test substance were evaluated a minimum of once per hour for each chamber throughout the daily exposure intervals, using gas chromatography:
Instrument: Varian model 3800 Gas Chromatograph.
Column: J&W Scientific DB-1, 30m x 0.53mm with 1.5um film thickness.
Carrier Gas: Helium, constant flow of 31.0 ml/min.
Sampling System: Electronically actuated VICI 12-port stream selector and VICI single injection valve with a 250 ul stainless steel sample loop.
Oven Ramp: Initial 125 °C for 1.0 min, ramp to 150 oC at 50 °C/min. hold for 1.0 min, total run time 2.5 min.
Detection: Flame ionization detector (FID), 300 °C isothermal.
Sampling Valve: Temperature 50 °C isothermal.

Duration of treatment / exposure:

Six hours/day

Frequency of treatment:

Daily. Treatment of males and females began two weeks prior to initiating mating and continued through the mating period. Males were treated for 29 days and euthanised the day after the last treatment. Toxicity phase females were treated for 28 days then euthanised. Reproductive phase females were treated up to and including Day 19 of gestation. Dams were not exposed during the lactation period.

Details on study schedule:

Not applicable (screening test)

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

836 ppm (nominal)

Doses / concentrations 2

Dose / conc.:

1 651 ppm (nominal)

Doses / concentrations 3

Dose / conc.:

3 135 ppm (nominal)

Doses / concentrations 4

Dose / conc.:

806 ppm (analytical)

Doses / concentrations 5

Dose / conc.:

1 623 ppm (analytical)

Doses / concentrations 6

Dose / conc.:

3 146 ppm (analytical)

No. of animals per sex per dose:

10 per phase

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Based on previous (unspecified) studies.

Positive control:

Not applicable.

Examinations

Parental animals: Observations and examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: All animals were observed at least twice daily in their cages for mortality, morbidity and moribundity. General clinical observations were made at least once per day, beginning on the first day of treatment.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Once before the first exposure and weekly thereafter. The observations were made outside the home cage in a standard arena at approximately the same time each day. Examinations included, but were not limited to, changes in skin, fur, eyes, mucous membranes, occurrence of secretions and excretions, and autonomic activity. Changes in gait, posture and response to handling as well as the presence of clonic or tonic movement, stereotypies, difficult or prolonged parturition or bizarre behaviour were recorded.

BODY WEIGHT: Yes
- Time schedule for examinations: Individual body weights were determined beginning with randomisation into test groups, on the first day of exposure, at least weekly thereafter, and on the day of necropsy. During gestation, the females were weighed (at a minimum) on gestation Days 0, 7, 14 and 20, within 24 hours after parturition, and Day 4 postpartum.

FOOD CONSUMPTION: yes
- Individual animal food consumption was recorded at least weekly calculated as grams/animal/day.
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No data

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

Oestrous cyclicity (parental animals):

Not applicable (screening test)

Sperm parameters (parental animals):

Parameters examined in P male parental generations: testes weight, and epididymis weight.

Litter observations:

STANDARDISATION OF LITTERS
- Performed on day 4 postpartum: no

PARAMETERS EXAMINED
The following parameters were examined in F1 offspring: immediately after birth the number and sex of pups, the number of live pups, number of dead pups, runts and presence of any gross abnormalities were noted. Live pups were counted, sexed and the sex ratio calculated. Litter weights were taken within 24 hours of parturition and on postpartum day 4.

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

Postmortem examinations (parental animals):

SACRIFICE
- Male animals: All surviving animals on Day 30.
- Maternal animals: Post-partum day 4.

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

HISTOPATHOLOGY / ORGAN WEIGHTS
The tissues indicated in Table 2 (Section 7.5.2) were prepared for microscopic examination and weighed, respectively.

Postmortem examinations (offspring):

SACRIFICE
- Day 4 post-partum.

GROSS NECROPSY
- Gross necropsy consisted of external examinations.

HISTOPATHOLOGY / ORGAN WEIGHTS: not conducted.

Statistics:

ANOVA, Kruskal-Wallis test, Dunnett's test, Wilcoxon test. All data analysis was conducted using SAS version 9.1.3. Statistically significant probabilities were reported for p-values of <0.05, <0.02 and <0.01.

Reproductive indices:

Mating and fertility indices. Plus calculated reproductive parameters were mean gestation length, mean litter size, mean number of implantation sites, mean number of corpora lutea, mean mating and fertility indices.

Offspring viability indices:

mean live litter size, mean litter weight, mean ratio live births/litter size

Results and discussion

Results: P0 (first parental generation)

General toxicity (P0)

Clinical signs:

no effects observed

Body weight and weight changes:

no effects observed

Food consumption and compound intake (if feeding study):

no effects observed

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Other effects:

not examined

Reproductive function / performance (P0)

Reproductive function: oestrous cycle:

not examined

Reproductive function: sperm measures:

no effects observed

Reproductive performance:

no effects observed

Details on results (P0)

CLINICAL SIGNS AND MORTALITY (PARENTAL ANIMALS):
See Section 7.5.2. Repeated dose toxicity: inhalation

BODY WEIGHT AND FOOD CONSUMPTION (PARENTAL ANIMALS):
See Section 7.5.2. Repeated dose toxicity: inhalation

TEST SUBSTANCE INTAKE (PARENTAL ANIMALS):
See Section 7.5.2. Repeated dose toxicity: inhalation

REPRODUCTIVE FUNCTION: ESTROUS CYCLE (PARENTAL ANIMALS):
Not evaluated

REPRODUCTIVE FUNCTION: SPERM MEASURES (PARENTAL ANIMALS)
Testes weight, absolute (g): 3.624 (0.180), 3.464 (0.231), 3.426 (0.230), 3.483 (0.301)
Testes weight, relative to body weight: 0.00882 (0.00060), 0.00856 (0.00063), 0.00865 (0.00131), 0.00864 (0.00116)
Seminal vesicle weight, absolute (g): 1.828 (0.190), 1.665 (0.185), 1.531 (0.285), 1.638 (0.204)
Seminal vesicle weight, relative to body weight: 0.00444 (0.00043), 0.00411 (0.00045), 0.00388 (0.00086), 0.00405 (0.00060)
Epididymides weight, absolute (g): 1.302 (0.109), 1.223 (0.121), 1.236 (0.085), 1.182 (0.104)
Epididymides weight, relative to body weight: 0.00317 (0.00028), 0.00302 (0.00030), 0.00311 (0.00042), 0.00293 (0.00036)
Prostate weight, absolute (g): 0.886 (0.133), 0.789 (0.116), 0.944 (0.379), 0.847 (0.174)
Prostate weight, relative to body weight: 0.00216 (0.00035), 0.00195 (0.00028), 0.00233 (0.00074), 0.00209 (0.00042)

REPRODUCTIVE PERFORMANCE (PARENTAL ANIMALS)
Number of females allowed to deliver: 10/10, 8/10, 10/10, 10/10
Number of gravid females: 10, 8, 10, 10
Days gestation: 22 (1), 22 (0), 22 (0), 22 (0)
Total pups: 16 (2), 15 (1), 16 (2), 15 (2)
On female in the 800 ppm group failed to mate during the mating period. A second 800 ppm group female had no evidence of copulation; however, when euthanised had 15 pups in utero. The eight remaining females produced litters that were similar in all respects to control litters.

ORGAN WEIGHTS (PARENTAL ANIMALS)
See Section 7.5.2. Repeated dose toxicity: inhalation
See REPRODUCTIVE FUNCTION: SPERM MEASURES (PARENTAL ANIMALS) above

GROSS PATHOLOGY (PARENTAL ANIMALS):
See Section 7.5.2 Repeated dose toxicity: inhalation

HISTOPATHOLOGY (PARENTAL ANIMALS):
See Section 7.5.2 Repeated dose toxicity: inhalation
KEY EFFECT: hepatic brown pigment accumulation, was observed only in males at 1600 and 3200 ppm. The pigment accumulation was accompanied by bile duct proliferation and chronic inflammation.

In the kidney of the male rats there was protein droplet nephropathy. In the minimal degree, there were occasional renal proximal tubule cells that contained protein droplets which were angular in shape. At 800 ppm, this was the only indication of an effect. At higher concentrations these cystalline droplet shapes were more common, and the portion of the cortex with visible droplet accumulation increased, along with individual cell necrosis and tubular basophilia. At 3200 ppm, moderate to marked nephropathy was observed in some animals, which included the above changes, as well as granular casts, which are accumulations of necrotic cell debris, at the cortical-medullary border. Although not definitive, the sex selectivity and histomorphological features are consistent with alpha-2-U-globulin nephropathy.

OTHER FINDINGS (PARENTAL ANIMALS):
None

Effect levels (P0)

Dose descriptor:

NOAEC

Effect level:

>= 3 146 ppm

Based on:

test mat.

Sex:

female

Basis for effect level:

other: No adverse effects on any of the reproductive parameters evaluated.

Target system / organ toxicity (P0)

Critical effects observed:

no

Results: F1 generation

General toxicity (F1)

Clinical signs:

no effects observed

Mortality / viability:

no mortality observed

Body weight and weight changes:

no effects observed

Sexual maturation:

not examined

Organ weight findings including organ / body weight ratios:

not examined

Gross pathological findings:

no effects observed

Histopathological findings:

not examined

Details on results (F1)

(Mean (and standard deviation) for control, low-, mid- and high-exposure groups, respectively)

VIABILITY (OFFSPRING):
Day 4 viable pups: 15 (2), 15 (1), 15 (2), 14 (2)
Viable/Total: 0.98 (0.04), 0.99 (0.02), 0.94 (0.07), 0.98 (0.04)

CLINICAL SIGNS (OFFSPRING):
No adverse effects (except - see gross pathology)

BODY WEIGHT (OFFSPRING):
Initial litter weight (g): 95.4 (14.6), 98.0 (11.8), 99.7 (15.8), 98.3 (8.5)
Initial average pup weight (g): 6.2 (0.5), 6.4 (0.6), 6.4 (0.5), 6.8 (0.4)
Final litter weight (g): 153.1 (19.7), 159.2 (17.7), 154.3 (22.3), 153.9 (11.1)
Final average pup weight (g): 10.1 (0.9), 10.6 (1.1), 10.5 (1.0), 10.9 (0.9)

SEXUAL MATURATION (OFFSPRING):
Not evaluated

ORGAN WEIGHTS (OFFSPRING):
Not evaluated

GROSS PATHOLOGY (OFFSPRING)
In the low-exposure group, one male pup was born without a tail, penile and anal opening.

HISTOPATHOLOGY (OFFSPRING):
Not evaluated

OTHER FINDINGS (OFFSPRING):
None reported

One male pup was born without a tail, penile and anal opening. There were no changes observed in the litter size, male-to-female ratio, pup body weights or the pup survival. Differences in group mean values for the treated groups relative to the control group were small and none were found to be statistically significant.

Effect levels (F1)

Dose descriptor:

NOAEC

Generation:

F1

Effect level:

>= 3 146 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no statistically significant treatment-related adverse effects seen at any tested concentration

Target system / organ toxicity (F1)

Critical effects observed:

no

Overall reproductive toxicity

Reproductive effects observed:

no

Any other information on results incl. tables

No statistically significant differences in any of the reproductive parameters measured in any treatment groups.

Tables 24 - Summary of mean reproductive parameter for reproductive group female rats

Tables 25 - Summary of reproductive performance for reproductive group female rats

Applicant's summary and conclusion

Conclusions:

In an inhalation Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test conducted to OECD 422 and to GLP (reliability score 1) the NOAEC for the reproductive toxicity of octamethyltrisiloxane was at least 3146 ppm as no adverse effects were observed on reproductive parameters in rats. The NOAEC for general toxicity was <806 ppm based on protein droplet nephropathy and hepatic brown pigment accumulation.

Executive summary:

In a Combined Repeated Dose Toxicity Study with the Reproduction / Developmental Toxicity Screening Test (OECD Guideline 422), performed to GLP, the potential inhalation toxicity of octamethyltrisiloxane was evaluated in Sprague-Dawley rats. Animals were exposed to target concentrations of 0, 800, 1600 or 3200 ppm for 6 hours/day for 29 days in the toxicity test and up to 42 days in the reproductive/developmental screening test.

No treatment-related effects were observed in any of the reproductive parameters evaluated. Differences in mean values for the treated groups relative to the control group were small and none were found to be statistically significant.

The NOAEC for the reproductive toxicity of octamethyltrisiloxane was 3146 ppm on the basis of this screening test.