Hexamethyldisiloxane

Repeated dose toxicity: oral

Administrative data

Endpoint:

short-term repeated dose toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

14-02-1994 to 17-08-1994

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1994

Report date:

1994

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 407 (Repeated Dose 28-Day Oral Toxicity Study in Rodents)

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:

trimethyl[(trimethylsilyl)oxy]silane

Test material form:

other: solution

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 Japan, Inc.
- Age at study initiation: Five weeks old
- Weight at study initiation: Males: 126.9-144.8 g; Females: 110-127.5 g.
- Fasting period before study:
- Housing: Individually in hanging stainless steel cage with wire mesh floor
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: No data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 23 ± 2
- Humidity (%): 55 ± 10
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 29-03-1994 To: 10-05-1994

Administration / exposure

Route of administration:

oral: gavage

Vehicle:

olive oil

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS: The test substance was weighed accuratly and dissolved in olive oil. The formulation was diluted with olive oil to make the three lower conccentrations. These formulations were prepared once per week for dosing.

Analytical verification of doses or concentrations:

not specified

Duration of treatment / exposure:

28 days (plus 14 day post-exposure observation period for the control, 160 and 640 mg/kg bw/day groups)

Frequency of treatment:

once daily (7 days per week)

Doses / concentrations

Doses / concentrations 1

Dose / conc.:

8 mg/kg bw/day (actual dose received)

Doses / concentrations 2

Dose / conc.:

40 mg/kg bw/day (actual dose received)

Doses / concentrations 3

Dose / conc.:

160 mg/kg bw/day (actual dose received)

Doses / concentrations 4

Dose / conc.:

640 mg/kg bw/day (actual dose received)

No. of animals per sex per dose:

Six

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: Based on a preliminary 14 day oral gavage study
- Post-exposure recovery period in satellite groups: 14 days to investigate reversibility of effects

Examinations

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: At least once per day

DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: Yes
- Time schedule for examinations: Two days before commencement of dosing, the first day of dosing (day 1) and then on days 3, 5, 8, 10, 12, 15, 17, 19, 22, 24, 26 and 28. Then on recovery days 1, 3, 5, 8, 10, 12 and 14.

FOOD CONSUMPTION:
- once before dosing then twice per week.

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 AND COMPOUND INTAKE (if drinking water study): No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: At the end of the dosing period and 14-day observation period
- Anaesthetic used for blood collection: Yes (ether)
- Animals fasted: Yes, overnight for 16-20 hours
- How many animals: All animals
- Parameters checked in table [No.1] were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: At the end of the dosing period and 14-day observation period
- Animals fasted: Yes, overnight for 16-20 hours
- How many animals: All animals
- Parameters checked in table [No.1] were examined.

URINALYSIS: Yes
- Time schedule for collection of urine: At the end of the dosing period and 14-day observation period during the 16 hour fasting period
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes
- Parameters checked in table [No.1] were examined.

NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see Table 2)
HISTOPATHOLOGY: Yes, details are given in Table 2. For the recovery group liver and kidneys of males in the 640 mg/kg bw/day group were examined.

Statistics:

All data regarding body weight, food consumption, haematology, clinical chemistry, urine volume and organ weights were analysed using Bartlett's test for homogeneity of variance at a significance level of 5%. The data of homogenous variance were analysed for significant difference by one way analysis of variance. Then if there were a significant difference in it by the analysis, it was analysed for significant difference in comparison with that of the control group by Dunnett's test in case of equal number of data, otherwise, i.e. in case of unequal number, by Scheffe's test. The data of not homogenous variance was analysed by Kruskal-wallis's test. Then if there were a significant difference in it by the test, it was analysed for difference in comparison with the control group by nonparametric Dunnet's test in case of equal number of data, otherwise, i.e. in case of unequal number, by nonparametric Scheffe's test.

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:

effects observed, treatment-related

Clinical biochemistry findings:

effects observed, treatment-related

Urinalysis findings:

effects observed, treatment-related

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Gross pathological findings:

effects observed, treatment-related

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY: No mortality and no test substance-related clinical signs in any dose group

BODY WEIGHT AND WEIGHT GAIN: Body weight gain was suppressed from day 19 to 28 in males of the 640 mg/kg bw/day group.

FOOD CONSUMPTION: Food consumption was decreased from day 8 to 28 in males of the 640 mg/kg bw/day group. Food consumption was increased in this group during the recovery period.

HAEMATOLOGY: White blood cell count was increased and mean corpuscular volume and mean corpuscular haemoglobin were decreased in males of the 640 mg/kg bw/day group at the end of the exposure period. At the end of the recovery period white blood cell count and platelet count were increased, and haemoglobin concentration and haematocrit value were decreased in males of the 640 mg/kg bw/day group. Activated partial thromboplastin time was delayed in males of the 160 mg/kg bw/day group.

CLINICAL CHEMISTRY: Gamma-GTP, total cholesterol, total protein and calcium were increased, A/G ratio was decreased and GOT, GTP, cholinesterase and total bilirubin were decreased in males of the 640 mg/kg bw/day group at the end of the exposure period. At the end of the recovery period IP was increased in males of the 160 mg/kg bw/day and higher groups, and total cholesterol was increased in males of the 640 mg/kg bw/day group.

URINALYSIS: Turbid urine (3/6) and acidised urine in pH were observed in males of the 640 mg/kg bw/day, and turbid urine (1/6) was observed in a female of the vehicle control group at the end of the exposure period.

ORGAN WEIGHTS: At the end of the dosing period absolute and relative liver weights, relative spleen weight and relative brain weight were increased in males of the 640 mg/kg bw/day group. At the end of the recovery period absolute and relative spleen weights and relative liver weight were increased in males of the 640 mg/kg bw/day group.

GROSS PATHOLOGY: At the end of the dosing period the following were noted: dark brownish change (6/6) and enlargement (6/6) of the liver, enlargement (4/6) of the hepatic lymph node, apparent spotty pattern of surface (2/6) and pelvic dilatation (1/6) in the kidney were observed in males of the 640 mg/kg bw/day group. Apparent spotty pattern of surface was observed in the kidney of males (6/6) of the 160 mg/kg bw/day group. Blackish region of mucosa (1/6) in the glandular stomach and small (1/6) of the ovary were observed in a female of the 160 mg/kg bw/day. Pelvic dilatation (1/6) was observed in the kidney of the 40 mg/kg bw/day group. Enlargement (1/6) of the spleen and blackish region of mucosa (2/6) in the glandular stomach were observed in females of the 8 mg/kg bw/day group. At the end of the recovery period the following were noted: dark brownish change (5/6) in the liver, enlargement (4/6) of the hepatic lymph node and blackish spot (1/6) and blackish region (1/6) of mucosa in the glandular stomach were observed in males of the 640 mg/kg bw/day group. Whitish spot (1/6) in the heart and enlargement (1/6) of the testes in males of the 160 mg/kg bw/day group and blackish region (1/6) of mucosa in the glandular stomach in a male of the vehicle control group were observed. Small (1/6) of the kidney, blackish region (1/6) of mucosa in the glandular stomach and small (1/6) of the adrenal gland were observed in females of the 640 mg/kg bw/day group.

HISTOPATHOLOGY: Bile stasis, cell infiltration around bile stasis and swelling of hepatocytes in both sexes, bile duct proliferation, single cell necrosis and increase of mitoses of hepatocytes and deposition of brown pigment and increase of histiocytic cells in the hepatic lymph node in males of the 640 mg/kg bw/day group at the end of the dosing period were considered to be treatment-related. An increase in eosinophilic bodies in the kidney was considered to be treatment-related in males of the 40 mg/kg bw/day and above groups.

Effect levels

Key result

Dose descriptor:

NOAEL

Effect level:

160 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: Based on reduced food consumption, reduced body weight gain, reduced liver weight, changes to white cell count and corpuscular parameters.

Target system / organ toxicity

Critical effects observed:

not specified

Applicant's summary and conclusion

Conclusions:

In a 28-day repeated oral gavage study (Shin-Etsu, 1994) in rats that was conducted using a test protocol that is comparable to the appropriate OECD test guideline, and in compliance with GLP, the NOAEL was 160 mg/kg bw/day based on reduced food consumption, reduced body weight gain, increased liver weight, changes to white cell count and corpuscular parameters in male rats.