2,4,6,8-tetramethylcyclotetrasiloxane

Developmental toxicity / teratogenicity

Administrative data

Endpoint:

developmental toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2011

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2012

Report date:

2012

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: OECD 422 (Combined Repeated Dose Toxicity Study with Reproduction/Developmental Toxicity Screening in the Rat)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Limit test:

no

Test material

Test material information

Constituent 1

Reference substance name:

2,4,6,8-tetramethylcyclotetrasiloxane

EC Number:

219-137-4

EC Name:

2,4,6,8-tetramethylcyclotetrasiloxane

Cas Number:

2370-88-9

Molecular formula:

C4H16O4Si4

IUPAC Name:

2,4,6,8-tetramethyl-1,3,5,7,2,4,6,8-tetroxatetrasilocane

Test animals

Species:

rat

Strain:

other: RccHan:WIST(SPF)

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan Laboratories, B.V., Netherlands
- Age at study initiation: 11 weeks
- Weight at study initiation: Males: 266-347g; Females: 181-225g
- Fasting period before study: No
- Housing: Individually in Makrolon type-3 cages
- Diet: Pelleted standard Kliba Nafag 3433 rodent maintenance diet (Provimi Kliba SA, Switzerland), ad libitum
- Water: Community tap-water ad libitum
- Acclimation period: 7 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 19-25
- Humidity (%): 30-70
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: To: 06 January to 01 March 2011

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: stainless steel sealed chamber
- Method of holding animals in test chamber: stainless steel wire cage units
- Source and rate of air: 40L/min
- System of generating particulates/aerosols: test material in glass flask, air pumped through flask at 40L/min
- Temperature, humidity, pressure in air chamber: 22.0 to 22.3 degrees C, 37.4 to 52.4%
- Air change rate: 10-15 per hour

TEST ATMOSPHERE
- Brief description of analytical method used: weighing test item reservoir before and after each exposure (nominal). On-line GC (analytical)
- Samples taken from breathing zone: yes

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Daily weighing of the test item reservoir before and after each exposure (nominal) and on-line GC (analytical)

Details on mating procedure:

- M/F ratio per cage: 1:1
- Length of cohabitation: up to 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: yes, female housed with male until evidence of mating was observed
- After successful mating each pregnant female was caged: in home cage

Duration of treatment / exposure:

6 hours

Frequency of treatment:

daily

Duration of test:

Males - at least 28 days
Females - up to approximately 7 weeks

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

0 ppm (nominal)

Doses / concentrations 2

Dose / conc.:

100 ppm (nominal)

Doses / concentrations 3

Dose / conc.:

1 000 ppm (nominal)

Doses / concentrations 4

Dose / conc.:

3 000 ppm (nominal)

Doses / concentrations 5

Dose / conc.:

2 000 ppm (nominal)

No. of animals per sex per dose:

10

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: based on 14-Days Dose Range-Finding Inhalation Toxicity Study in the Han Wistar Rat

High dose of 3000 ppm reduced to 2000 ppm from day 12 due to early deaths of 3 females and 1 male at the higher dose.

Examinations

Maternal examinations:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: twice daily

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: weekly then days 6, 6, 13 and 20 of gestation

BODY WEIGHT: Yes
- Time schedule for examinations: Females twice weekly during pre-pairing and pairing periods and on days 0, 7, 14 and 20 post-coitum and days 0, 1 and 4 post-partum

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

WATER CONSUMPTION: No

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on day 5 post-partum

Ovaries and uterine content:

The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: No
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes

The uteri of non-pregnant females were placed in a solution of ammonium sulfide to visualize possible hemorrhagic areas of implantation sites (Salewski. 1964)

Fetal examinations:

All pups were examined macroscopically for any structural change. Specimens of abnormal tissue were fixed in neutral phosphate buffered 4%
formaldehyde solution.

Statistics:

Means and standard deviations of various data were calculated.
The Dunnett-test (many to one t-test) based on a pooled variance estimate was applied if the variables would be assumed to follow a normal distribution for the comparison of the treated groups and the control groups for each sex.
The Steel-test (many-one rank test) was applied instead of the Dunnett-test when the data could not be assumed to follow a normal distribution.
Fisher's exact-test [see References (6)] was applied if the variables could be dichotomized without loss of information.

Indices:

Litter size
Live births
Still births
Sex ratio
Body weight

Historical control data:

Included

Results and discussion

Results: maternal animals

Maternal developmental toxicity

Details on maternal toxic effects:

Maternal toxic effects:yes

Details on maternal toxic effects:
Reduced body weight gain and reduced food consumption during pre-paring period. Adverse renal and urinary tract pathology. Also pathology changes in heart, liver, lung and adrenal gland all noted at 3000/2000 and 1000 ppm

Effect levels (maternal animals)

Key result

Dose descriptor:

NOAEC

Effect level:

3 000 ppm

Based on:

test mat.

Basis for effect level:

other: developmental toxicity

Remarks on result:

other: equivalent to 29510 mg/m3 based on MW of 240.5094 for 2,4,6,8-tetramethylcyclotetrasiloxane

Maternal abnormalities

Abnormalities:

no effects observed

Results (fetuses)

Details on embryotoxic / teratogenic effects:

Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
None

Effect levels (fetuses)

Key result

Dose descriptor:

NOAEC

Effect level:

>= 3 000 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No adverse effects observed.

Remarks on result:

other: equivalent to 29510 based on MW of 240.5094 for 2,4,6,8-tetramethylcyclotetrasiloxane

Fetal abnormalities

Abnormalities:

no effects observed

Overall developmental toxicity

Developmental effects observed:

no

Applicant's summary and conclusion

Conclusions:

No effects on development were observed up to the highest dose level and therefore the NOAEC for development was considered to be 3000/2000 ppm (equivalent to 29510/19674 mg/m3 based on MW of 240.5094 for 2,4,6,8-tetramethylcyclotetrasiloxane).

Executive summary:

In a well-conducted, GLP compliant, OECD 422 study (reliability 1) treatment with the test item at the dose level of 3000 ppm caused early death of three females. After reduction of the high-dose level to 2000 ppm, two further females were found dead. Uremia resulting from the impairment of the urinary tract was indicated as a cause of the early deaths. The early deaths of animals might be due to the initial higher exposure to the test item at the concentration of 3000 ppm. All remaining animals survived the scheduled study period.

Treatment with 2,4,6,8-tetramethylcyclotetrasiloxane caused a reduction of food consumption in males at all dose levels and in females at the dose level of 3000/2000 ppm. Body weight gains and body weights were reduced at the dose level of 3000/2000 ppm in both sexes. Effects on food consumption, body weight gain and body weights were considered not to be adverse.

At the dose level of 3000/2000 ppm, lower number of corpora lutea was noted. As a consequence, a lower implantation rate and a lower number of living pups at first litter check were noted. Although the differences to the control values were not statistically significant, they were below the range of the historical control values and were therefore considered to be related to the treatment with the test item. These effects occurred at the dose level at which severe maternal toxicity was noted early on in the study and therefore may be secondary to the maternal toxicity. Both possibilities: a reduction of corpora lutea as a specific effect of the test item or as an effect secondary to the maternal toxicity may be taken into consideration. In this view, the reduction of the number of corpora lutea and consequent reduction of number of pups may be an adverse effect. However, higher body weights and body weight gain of pups was noted at the high-dose level indicating that the development of pups was not affected by the treatment.

No effects on development were observed up to the highest dose level and therefore the NOAEL for development was considered to be 3000/2000 ppm (equivalent to 29510/19674 mg/m3 based on MW of 240.5094 for 2,4,6,8-tetramethylcyclotetrasiloxane).