Hexamethyldisiloxane

Endpoint summary

Description of key information

In a 28-day repeated oral gavage study (Shin-Etsu Chemical Co, 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 for HMDS was 160 mg/kg bw/day based on reduced food consumption, reduced body weight gain, increase organ weights (liver, spleen and brain), changes to white cell count and corpuscular parameters in male rats that received 640 mg/kg bw/day.  

In a 2-generation reproductive toxicity whole body inhalation study in SD rats, the evaluation of endpoints relevant to the assessment of repeat dose toxicity resulted in the observation of brown pigment in the periportal areas of the liver in the F1 generation. These hepatic findings were considered to be human relevant and adverse, therefore the repeat dose NOAEC was 400 ppm (2657 mg/m³). 

In a two-year combined chronic toxicity and oncogenicity whole body vapour inhalation study in Fischer 344 rats, conducted to GLP (Research and Consulting Company Ltd, 2005), the target organs of hexamethyldisiloxane were kidney, nasal cavity and testes. Effects in the kidneys were considered species-specific (alpha-2 u-globulin mediated mechanism). Effects in the nasal cavity were were consistent with exposure to a mild irritant but also commonly seen in ageing rats and therefore considered to be non-specific and non-adverse. Effects on the testes (Leydig cell tumours) were increased following exposure to all concentrations, but they are considered to be a spontaneous finding as they are common to Fischer 344 rats and were also observed in control animals. Therefore the NOAEC for systemic effects relevant to humans is ≥5000 ppm (33200 mg/m³).

The key dermal study is a 28-day repeated dose dermal toxicity study in rats (Dow Corning Corporation, 1993), conducted using a protocol similar to OECD 410, and to GLP, the NOAEL was considered to be 1000 mg/kg bw/day.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

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

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes

Limit test:

no

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

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)

Dose / conc.:

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

Dose / conc.:

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

Dose / conc.:

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

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

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.

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.

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.

Critical effects observed:

not specified

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.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

160 mg/kg bw/day

Study duration:

subacute

Species:

rat

System:

cardiovascular

Organ:

blood

Repeated dose toxicity: inhalation - systemic effects

Link to relevant study records

Reference

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.

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes (incl. QA statement)

Limit test:

no

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

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

Dose / conc.:

100 ppm (nominal)

Dose / conc.:

400 ppm (nominal)

Dose / conc.:

1 600 ppm (nominal)

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

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.

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.

Key result

Dose descriptor:

NOAEC

Effect level:

400 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Hepatic effects

Critical effects observed:

not specified

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.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEC

2 657 mg/m³

Study duration:

subchronic

Species:

rat

System:

gastrointestinal tract

Organ:

liver

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

Endpoint:

chronic toxicity: inhalation

Remarks:

combined repeated dose and carcinogenicity

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

20.08.1997 to 30.08.2005

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 453 (Combined Chronic Toxicity / Carcinogenicity Studies)

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Fischer 344

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Laboratories, Raleigh, N. Carolina, USA
- Age at study initiation: Approximately 6 weeks
- Weight at study initiation: Males: 84.9 to 129.2 g: Females: 73.4 to 114.8 g.
- Fasting period before study: None
- Housing: Groups of five of the same sex in Makrolon type IV cages (except during exposure)
- Diet (e.g. ad libitum): Ad libitum (except during exposure)
- Water (e.g. ad libitum): Ad libitum (except during exposure)
- Acclimation period: ten days


ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22± 3
- Humidity (%): 40-70
- Air changes (per hr): 10-15
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: 01.09.1997 To: 14.09.1999

Route of administration:

inhalation: vapour

Type of inhalation exposure:

whole body

Vehicle:

other: unchanged (no vehicle)

Remarks on MMAD:

MMAD / GSD: N/A

Details on inhalation exposure:

GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Housed in groups of two of the same sex in stainless steel wire cages in sealed chambers used for group isolation.
- Method of holding animals in test chamber: cage
- Source and rate of air: No data
- Method of conditioning air: No data
- Temperature, humidity, pressure in air chamber: 22± 3oC, 40-60%, negative pressure of approximately 2-3 mm
- 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: No data

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

The concentration in each chamber of the dose groups was determined daily at least six times during the exposure period, starting 20 - 30 minutes after the beginning of generation and continued until pump off (at about 5.5 hours). Analytical concentrations were determined by gas chromatography analysis.

Duration of treatment / exposure:

12 or 24 months

Frequency of treatment:

6 hours/day, 5 days/week

Remarks:

Doses / Concentrations:
0.68-0.75, 2.64-2.89, 10.0-11.4 and 32.5-34.8 mg/l
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
97.1-107.1, 391.1-428.1, 1509.4-1720.8 and 4894.6-5241.0 ppm
Basis:
nominal conc.

Remarks:

Doses / Concentrations:
0.7, 2.7, 10.6 and 33.2 mg/l
Basis:
other: target conc.

Remarks:

Doses / Concentrations:
100, 400, 1600, and 5000 ppm
Basis:
other: target conc.

No. of animals per sex per dose:

Subgroup A.  20 rats/sex/group
Subgroup B. 20 rats/sex/group
Subgroup C. 65 rats/sex/group
Additionally, 10 males and 10 females were used for disease surveillance.

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale: Based on a 13-week whole body inhalation study in Fischer-344 rats. The choice of the highest concentration was based upon safety considerations and was set at half the Lower Explosive Limit for HMDS.
- Rationale for animal assignment (if not random): random, stratified by body weight
- Rationale for selecting satellite groups: None given
- Post-exposure recovery period in satellite groups: 12 months in subgroup B, none in subgroups A and B

Positive control:

None

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Daily


DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: Twice per week. Observations included but were not limited to changes in behavior, somatomotor activity, body position, respiration, alteration of skin (including skin lesions and hair loss), nose and eye. Additionally, palpation for early detection of non-visible masses was performed on a weekly basis from 6 months after start of exposure until termination. Special attention was given to mass development for each visible and palpable mass. The time of onset, location, size, appearance and progression of mass were recorded.

BODY WEIGHT: Yes
- Time schedule for examinations: Day 1 and 7 of acclimatisation, immediately before the first treatment, once weekly for the first 14 weeks, then every two weeks.

FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes (g/animal/day recorded).

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

OPHTHALMOSCOPIC EXAMINATION: Yes
- Timescale and animals examined: During the acclimitisation period animals were conducted on 20 animals/group/sex from subgroup C. Towards the end of the first year and towards study termination examinations were performed on 20 surviving animals/group/sex from subgroup C (some 400ppm females not examined).

HAEMATOLOGY: Yes
- Time schedule for collection of blood: after 3, 6 and 12 months of exposure in subgroup C.
- Anaesthetic used for blood collection: Yes (ether)
- Animals fasted: Yes, for 17 hours before sampling.
- How many animals: 20
- Parameters checked in No.1 were examined.


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: after 3, 6 and 12 months of exposure in subgroup C.
- Animals fasted: Yes, for 17 hours before sampling.
- How many animals: 20
- Parameters checked in table No.1 were examined.


URINALYSIS: Yes
- Time schedule for collection of urine: after 3, 6 and 12 months of exposure in subgroup C.
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes, urine collected during pre-blood sampling fasting period.
- Parameters checked in table No.1 were examined.


NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

GROSS PATHOLOGY: Yes (see table 2)
HISTOPATHOLOGY: Yes (see table 2)

Other examinations:

None reported

Statistics:

Analysis was two-tailed for significance levels of 5% and 1%. Analysis of body weight, food consumption, as well as organ weights and clinical pathology (not differential white cell counts) were analysed by a one way analysis of variance followed by comparison of the control group to each treated group by Dunnett's test. The Steel-test was applied instead of the Dunnett's test for the other parameters in the clinical laboratory investigations. Histopathology data were analysed independently using SAS/BASE and SAS/STAT software.

Clinical signs:

no effects observed

Mortality:

no mortality observed

Body weight and weight changes:

no effects observed

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:

effects observed, treatment-related

Haematological findings:

no effects observed

Clinical biochemistry findings:

no effects observed

Urinalysis findings:

no effects observed

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:

effects observed, treatment-related

Details on results:

CLINICAL SIGNS AND MORTALITY: There were no treatment-related clinical signs. There were no treatment-related deaths observed during the study. During the first year, 12 animals out of 1050 (two at 100 ppm, three at each 400 and 1600 ppm and four at 5000 ppm) died. Although, there were no deaths in the control group and the number of deaths was marginally higher in the higher exposure group, the distribution was considered to be incidental. Of the 12 animals that died prematurely during the first year 1 animal was from subgroup A, 2 animals were from subgroup B and 9 animals were from subgroup C. During the second year, the mortality rate was similar in control and treated animals and there were no differences between subgroup B and subgroup C animals.

BODY WEIGHT AND WEIGHT GAIN:  In males, the difference in mean body weight noted between the exposed animals and the respective controls were considered to be unrelated to the test article treatment. In  groups 4 (1600 ppm) and 5 (5000 ppm) females, the mean body weight were significantly reduced from the respective control values on 27 occasions for subgroup A (12 months of exposure) and 29 occasions for subgroup C (two years exposure). However, the differences were marginal (-2 to -8% from control) and there was up to -4% difference in body weight from control before the start of exposures at week 1. In addition, there was no exposure-response relationship in body weight between the groups and there was no confirmation of a similar response in the subgroup B (12 months exposure and 12 months recovery).  This finding is probably related with a slight reduction in food consumption noted in these animals which was considered to be test article related. 

FOOD CONSUMPTION: Slight reduction in food consumption noted in females of two highest concentration groups, which was considered to be test article related. No such effect observed at lower concentrations.

OPHTHALMOSCOPIC EXAMINATION: After one year and towards the end of the two year exposure, all examined animals (100%) showed corneal opacity.   

HAEMATOLOGY: The changes noted in the hematological parameters between 400 and 5000 ppm consisted of occasional slightly reduced hemoglobin concentration, hematocrit and mean cell hemoglobin concentration and increased mean cell volume.  These findings were not toxicologically significant.

CLINICAL CHEMISTRY: The increase in urea and creatinine and imbalances of electrolytes in the urine may be related to the morphological tubular changes noted in the kidneys. Other findings in the clinical biochemistry included an increase in lipids and proteins and changes in enzyme activities suggest metabolic adaptive changes, primarily related to the liver. These findings were not toxicologically significant.

URINALYSIS: No treatment-related findings.

ORGAN WEIGHTS: The increased relative testes weights in group 5 (5000 ppm) subgroup A males and of the absolute and relative testes weights in subgroup C males of the mid-high (1600 ppm) and high exposure levels (5000 ppm) were considered to be test article-related. These findings also correlated with the results of the histopathological examination. In males from subgroup A, an increase in absolute and relative liver weight at 5000 ppm and the relative liver weight at 1600 ppm were noted. However, there were no correlated findings in the histopathological examination. Therefore, the increase liver weight in males but not in females after the one year of exposure could be the consequence of a transient metabolic adaptation without any toxicological relevance. This finding was not detected in subgroup C animals of both sexes. Statistically significant increase in relative kidney weight was observed in males of high exposure group (5000 ppm) after one year of exposure (subgroup A). In other subgroups (B and C) the increase in kidney weights was not consistent between the different exposure levels. 

GROSS PATHOLOGY:  In subgroup A (one year of exposure), an enlarged liver was noted in group 5 (5000 ppm).  In subgroup C (two years exposure), nodules in the kidneys were present in 3 males from group 4 (1600 ppm) and 7 males from group 5 (5000 ppm).  In group C, the incidence of enlarged testes was higher in all treated male groups than in the control group. The observation in groups 4 and 5 correlated with recorded increase in testicular weight for these groups and the results of the histopathological examination.

HISTOPATHOLOGY: NON-NEOPLASTIC: At interim sacrifice after one year exposure as well as at terminal sacrifice after two years, a variety of non-neoplastic and neoplastic findings were noted in this study which were considered to be incidental findings commonly observed in rats of this age and strain and which did not distinguish exposed animals from controls. There were no microscopic findings associated with the noted increase in liver weight.  The increase in kidney weight correlated with an increase in the incidence/severity of chronic nephropathy only in the 24 month treatment group males and females. Calcified cylinders in the papillary tubules were noted in 19 male animals each of group 4 and 5 following one year of exposure. The incidence of this finding was noted in 24 males of group 3, 63 males in group 4 and all 65 males of group 5 following two year sacrifice. The severity of this alteration was dose-dependent. Tubular granular casts and tubular hyaline casts were noted in male animals of all groups, including controls. The incidence of these casts was statistically significantly increased in males of high exposure group. Cortical mineralization was noted in the male and female animals in groups 3, 4 and 5. The incidence of transitional cell hyperplasia of the renal papilla was statistically increased in males of groups 4 and 5 in subgroup C.  

Animals sacrificed after one year of exposure (subgroup A): Kidneys:  Increased incidence of calcified cylinders in the tubules of the papilla in males at 1600 and 5000 ppm; increased incidence of tubular hyaline casts in males of group 5(5000 ppm) and females of group 4 (1600 ppm). Testes:  Multifocal Leydig cell hyperplasia present in all males. An increased severity of Leydig cell hyperplasia was noted in all groups exposed to HMDS. Nasal Cavity:  Increased incidence of eosinophilic inclusions in the male olfactory and respiratory epithelium. Animals sacrificed one year of exposure and one year of recovery (subgroup B): Kidneys: Increased incidence of calcified cylinders in the tubules of the papilla in males of groups 3, 4 and 5; increased incidence of transitional cell hyperplasia in males of groups 4 and 5; increased incidence of tubular hyaline casts in males of group 5. Nasal cavity: Increased incidence of eosinophilic inclusions in olfactory/respiratory epithelium in males of groups 4 and 5 and in females of groups 2 to 5. Sternum: Increased incidence of enchondral hyperostosis in males of group 5 whereas the incidence decreased in females of groups 2 to 5.         

Animals sacrificed after two years of exposure (subgroup C): Kidneys: Calcified cylinders in males of groups 3 (400 ppm), 4 (1600 ppm) and 5 (5000 ppm); transitional cell hyperplasia observed in males of groups 4 and 5; increased incidence of tubular pigment deposits in males of groups 4 and 5 whereas the incidence decreased in females of group 2 (100 ppm) and 5 (5000 ppm). Lungs: Increased incidence of alveolar histiocytosis in females of groups 4 and 5; increased focal alveolitis in males and females of group 5; increased foreign body granuloma in males of group 5. Nasal Cavity: Increased incidence and severity of eosinophilic inclusions in the olfactory/respiratory epithelium in males of groups 4 and 5. Sternum/Femur: Increased incidence and severity of enchondral hyperostosis in the male sternum of group 5 whereas the incidence decreased in both sexes and femur of females in groups 2 to 5 and in the femur of males in groups 2 to 4. Bone marrow: Increased incidence of atrophy in females of group 5.

HISTOPATHOLOGY: NEOPLASTIC: In the testes, there was statistically significantly increased incidence of Leydig cell tumors at all exposure levels when compared to controls after one year of exposure (subgroup A). The majority of animals in subgroups B (one year of exposure and one year of recovery) and C (two years of exposure) developed Leydig cell tumors regardless of exposure. From the neoplastic findings diagnosed in this study, the occurrence of renal tubular adenomas and carcinomas in males of groups 4 and 5 after two years of exposure are not excluded as possibly related to the exposure to the test article, since these findings did not occur in control group 1(0 ppm), groups 2 (100 ppm) and 3 (400 ppm).

Dose descriptor:

NOAEC

Remarks:

rat

Effect level:

>= 5 000 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: Based there being no toxicologically relevant effects relevant to humans.

Critical effects observed:

not specified

Vapor inhalation exposure of Fischer 344 rats to HMDS for up to two years produced calcified cylinders in tubules of the

kidney papilla in the male rats. However, these effects in the kidneys, do not adversely affect the survival of the

animals, and may be considered as a starting change of renal toxicity. The occurrence of renal tubular adenomas and

carcinomas in some males may be related to test article exposure. A follow-up study showed that an alpha 2

u-globulin mediated mechanism was responsible for the observed nephropathy and kidney neoplasia in the male rats.

The inconsistency with the increase or decrease hyperostosis between sexes and between different bones (sternum and

femur), as well as the lack of dose-response in females, suggests there is little toxicological significance to these

findings. The increased incidence of eosinophillic inclusions in the olfactory epithelium may be related to

nasal irritation caused by mildly irritant chemicals and are also commonly seen in ageing rats. Test article-related

increase of the testicular weight was correlated with the macroscopic finding of increased incidence of enlarged

testes in all treated groups. Increased severity in Leydig cell hyperplasia and increased incidence in Leydig cell

tumors were observed at all exposure levels after one year. Leydig cell tumors occur spontaneously and are very common

in Fischer 344 rats. In fact, following the 2 year sacrifice, almost all males, both control and treated, showed this finding. The one-year data indicate that HMDS exposure accelerated progression of this common tumor. No microscopic findings were considered to be related to HMDS exposures.

Conclusions:

In a two-year combined chronic toxicity and oncogenicity whole body vapor inhalation study in Fischer 344 rats, conducted to GLP (reliability score 1), the target organs of hexamethyldisiloxane were kidney, nasal cavity and testes. Effects in the kidneys were considered species specific (alpha-2
u-globulin mediated mechanism). Effects in the nasal cavity were consistent with exposure to a mild irritant but also commonly seen in ageing rats and therefore considered to be non-specific, non-adverse and of low toxicological importance. Effects on the testes (Leydig cell tumours) were increased following exposure to all concentrations, but they are considered to be a spontaneous finding as they are common to Fischer 344 rats and were also observed in control animals. It was thought that HMDS might accelerate progression to this common tumour. NOAEC was not reported by the authors of the study. However, it is the opinion of the EPSR author that the NOAEC for systemic effects relevant to humans is greater than or equal to 5000 ppm (33200 mg/m3).

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

33 200 mg/m³

Study duration:

chronic

Species:

rat

Repeated dose toxicity: dermal - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: dermal

Type of information:

experimental study

Adequacy of study:

key study

Study period:

08.11.1991 to 12.12.1991

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 410 (Repeated Dose Dermal Toxicity: 21/28-Day Study)

Deviations:

yes

Remarks:

No urinalysis

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Portage, MI
- Age at study initiation: Approximately 8 weeks
- Weight at study initiation: Males: 229-262 g; Females: 206-241 g
- Fasting period before study: No
- Housing: Individually in standard stainless steel wire cages
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: Seven days


ENVIRONMENTAL CONDITIONS
- Temperature (°F): 68-73
- Humidity (%): 30-70
- Air changes (per hr): No data
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: 13.11.1991 To: 12.12.1991

Type of coverage:

occlusive

Vehicle:

unchanged (no vehicle)

Details on exposure:

TEST SITE
- Area of exposure: Dorsal
- % coverage: 10 %
- Type of wrap if used: Plastic wrap and cloth bandage
- Time intervals for shavings or clipplings: as needed


REMOVAL OF TEST SUBSTANCE
- Washing (if done): yes, with a wet gauze
- Time after start of exposure: Six hours


TEST MATERIAL
- Amount(s) applied (volume or weight with unit):
- Concentration (if solution):
- Constant volume or concentration used: yes/no
- For solids, paste formed: yes/no

USE OF RESTRAINERS FOR PREVENTING INGESTION: no, not required with wrap used.

Analytical verification of doses or concentrations:

no

Duration of treatment / exposure:

28 Days

Frequency of treatment:

6 hours per day, 5 days per week for a period of 28 days

Dose / conc.:

100 mg/kg bw/day

Dose / conc.:

500 mg/kg bw/day

Dose / conc.:

1 000 mg/kg bw/day

No. of animals per sex per dose:

Ten

Control animals:

other: yes, wrapped without test substance

Details on study design:

- Dose selection rationale: No data
- Rationale for animal assignment (if not random): Random
- Rationale for selecting satellite groups: No satellite groups
- Post-exposure recovery period in satellite groups: No post-exposure period

Positive control:

None

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily on weekdays for general appearance, behavioral abnormalities, signs of toxicity and mortality.

DETAILED CLINICAL OBSERVATIONS: No


DERMAL IRRITATION: Yes


BODY WEIGHT: Yes
- Time schedule for examinations: On the initial day of the study, weekly during the study period and just prior to necropsy.


FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No data. Food consumption was measured weekly throughout the study period.


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


OPHTHALMOSCOPIC EXAMINATION: No


HAEMATOLOGY: Yes
- Time schedule for collection of blood: At study termination
- Anaesthetic used for blood collection: Yes (ketamine HCl)
- Animals fasted: Yes, for 16 hours
- How many animals: All
- Parameters checked in table No.1 were examined.


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: At termination of the study
- Animals fasted: Yes, for 16 hours
- How many animals: All
- Parameters checked in table No.1 were examined.


URINALYSIS: No


NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

See Table 2. Organs examined at necropsy (macroscopic and microscopic):  At the end of dosing a complete necropsy was performed on all animals. The liver, kidneys, adrenals brain, spleen, ovaries and testes were examined and weighed. A complete set of organs/tissues were collected and retained in 10% buffered formalin. All tissues from the control and high dose groups were processed and examined microscopically. 

Other examinations:

None reported.

Statistics:

Statistical Methods:  Data was evaluated by two-sided Welch Trend Test.  All follow-up tests were one-sided and in the same direction as the overall trend.  P<0.05 was used as a critical level of significance.

Clinical signs:

no effects observed

Dermal irritation:

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:

no effects observed

Clinical biochemistry findings:

no effects observed

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:

no effects observed

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY: No deaths, overt signs of toxicity or changes in any of the control or treated animals. 

BODY WEIGHT AND WEIGHT GAIN: A slight but statistically significant decrease in body weight gains was observed in the high dose males during the last week of the study.

FOOD CONSUMPTION: A slight but statistically significant decrease in food consumption was observed in the high dose males during the last week of the study.

HAEMATOLOGY: No adverse changes occurred.

CLINICAL CHEMISTRY: No adverse changes occurred.

ORGAN WEIGHTS: A statistically significant decrease in liver and kidney weights were noted in the high dose males when expressed as organ to brain weight ratio.

GROSS PATHOLOGY: No adverse findings.

HISTOPATHOLOGY: Histopathology of organs and tissues for control and high dose group animals revealed no effects attributable to test material treatment. 

Dose descriptor:

NOAEL

Remarks:

relevant to human

Effect level:

>= 1 000 mg/kg bw/day

Sex:

male/female

Basis for effect level:

other: No adverse effects relevant to humans.

Dose descriptor:

NOAEL

Remarks:

rats

Effect level:

>= 1 000 mg/kg bw/day

Sex:

male/female

Basis for effect level:

other: No adverse effects.

Critical effects observed:

not specified

Conclusions:

In a 28-day repeated dose dermal toxicity study in rats, conducted using a protocol similar to OECD 410, and to GLP, the NOEL for hexamethyldisiloxane was considered to be 500 mg/kg/day, based on reduced kidney and liver weights in males. There were no such effects in females. Overall, the NOAEL was considered to be ≥1000 mg/kg bw/day for human relevant effects. The effects on kidney and liver weights were not accompanied by histopathological findings and were not observed in females, therefore are not considered adverse.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 000 mg/kg bw/day

Study duration:

subacute

Species:

rat

Repeated dose toxicity: dermal - local effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: dermal

Type of information:

experimental study

Adequacy of study:

key study

Study period:

08.11.1991 to 12.12.1991

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Reason / purpose for cross-reference:

reference to other study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 410 (Repeated Dose Dermal Toxicity: 21/28-Day Study)

Deviations:

yes

Remarks:

No urinalysis

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

Sprague-Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Charles River Breeding Laboratories, Portage, MI
- Age at study initiation: Approximately 8 weeks
- Weight at study initiation: Males: 229-262 g; Females: 206-241 g
- Fasting period before study: No
- Housing: Individually in standard stainless steel wire cages
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: Seven days


ENVIRONMENTAL CONDITIONS
- Temperature (°F): 68-73
- Humidity (%): 30-70
- Air changes (per hr): No data
- Photoperiod (hrs dark / hrs light): 12/12


IN-LIFE DATES: From: 13.11.1991 To: 12.12.1991

Type of coverage:

occlusive

Vehicle:

unchanged (no vehicle)

Details on exposure:

TEST SITE
- Area of exposure: Dorsal
- % coverage: 10 %
- Type of wrap if used: Plastic wrap and cloth bandage
- Time intervals for shavings or clipplings: as needed


REMOVAL OF TEST SUBSTANCE
- Washing (if done): yes, with a wet gauze
- Time after start of exposure: Six hours


TEST MATERIAL
- Amount(s) applied (volume or weight with unit):
- Concentration (if solution):
- Constant volume or concentration used: yes/no
- For solids, paste formed: yes/no

USE OF RESTRAINERS FOR PREVENTING INGESTION: no, not required with wrap used.

Analytical verification of doses or concentrations:

no

Duration of treatment / exposure:

28 Days

Frequency of treatment:

6 hours per day, 5 days per week for a period of 28 days

Dose / conc.:

100 mg/kg bw/day

Dose / conc.:

500 mg/kg bw/day

Dose / conc.:

1 000 mg/kg bw/day

No. of animals per sex per dose:

Ten

Control animals:

other: yes, wrapped without test substance

Details on study design:

- Dose selection rationale: No data
- Rationale for animal assignment (if not random): Random
- Rationale for selecting satellite groups: No satellite groups
- Post-exposure recovery period in satellite groups: No post-exposure period

Positive control:

None

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: Twice daily on weekdays for general appearance, behavioral abnormalities, signs of toxicity and mortality.

DETAILED CLINICAL OBSERVATIONS: No


DERMAL IRRITATION: Yes


BODY WEIGHT: Yes
- Time schedule for examinations: On the initial day of the study, weekly during the study period and just prior to necropsy.


FOOD CONSUMPTION:
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: No data. Food consumption was measured weekly throughout the study period.


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


OPHTHALMOSCOPIC EXAMINATION: No


HAEMATOLOGY: Yes
- Time schedule for collection of blood: At study termination
- Anaesthetic used for blood collection: Yes (ketamine HCl)
- Animals fasted: Yes, for 16 hours
- How many animals: All
- Parameters checked in table No.1 were examined.


CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: At termination of the study
- Animals fasted: Yes, for 16 hours
- How many animals: All
- Parameters checked in table No.1 were examined.


URINALYSIS: No


NEUROBEHAVIOURAL EXAMINATION: No

Sacrifice and pathology:

See Table 2. Organs examined at necropsy (macroscopic and microscopic):  At the end of dosing a complete necropsy was performed on all animals. The liver, kidneys, adrenals brain, spleen, ovaries and testes were examined and weighed. A complete set of organs/tissues were collected and retained in 10% buffered formalin. All tissues from the control and high dose groups were processed and examined microscopically. 

Other examinations:

None reported.

Statistics:

Statistical Methods:  Data was evaluated by two-sided Welch Trend Test.  All follow-up tests were one-sided and in the same direction as the overall trend.  P<0.05 was used as a critical level of significance.

Clinical signs:

no effects observed

Dermal irritation:

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:

no effects observed

Clinical biochemistry findings:

no effects observed

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:

no effects observed

Histopathological findings: neoplastic:

not examined

Details on results:

CLINICAL SIGNS AND MORTALITY: No deaths, overt signs of toxicity or changes in any of the control or treated animals. 

BODY WEIGHT AND WEIGHT GAIN: A slight but statistically significant decrease in body weight gains was observed in the high dose males during the last week of the study.

FOOD CONSUMPTION: A slight but statistically significant decrease in food consumption was observed in the high dose males during the last week of the study.

HAEMATOLOGY: No adverse changes occurred.

CLINICAL CHEMISTRY: No adverse changes occurred.

ORGAN WEIGHTS: A statistically significant decrease in liver and kidney weights were noted in the high dose males when expressed as organ to brain weight ratio.

GROSS PATHOLOGY: No adverse findings.

HISTOPATHOLOGY: Histopathology of organs and tissues for control and high dose group animals revealed no effects attributable to test material treatment. 

Dose descriptor:

NOAEL

Remarks:

relevant to human

Effect level:

>= 1 000 mg/kg bw/day

Sex:

male/female

Basis for effect level:

other: No adverse effects relevant to humans.

Dose descriptor:

NOAEL

Remarks:

rats

Effect level:

>= 1 000 mg/kg bw/day

Sex:

male/female

Basis for effect level:

other: No adverse effects.

Critical effects observed:

not specified

Conclusions:

In a 28-day repeated dose dermal toxicity study in rats, conducted using a protocol similar to OECD 410, and to GLP, the NOEL for hexamethyldisiloxane was considered to be 500 mg/kg/day, based on reduced kidney and liver weights in males. There were no such effects in females. Overall, the NOAEL was considered to be ≥1000 mg/kg bw/day for human relevant effects. The effects on kidney and liver weights were not accompanied by histopathological findings and were not observed in females, therefore are not considered adverse.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 000

Study duration:

subacute

Species:

rat

Additional information

In the key repeated dose study for the oral route (Shin-Etsu Chemical Co, 1994) Sprague-Dawley rats (6 animals/sex/dose) were given HMDS (in olive oil) by oral gavage at a dose of 8, 40, 160 or 640 mg/kg bw/day, 7 days/week for 28 days. The control group received the vehicle only. The exposure period was followed by a 14 -day observation period for the control, 160 and 640 mg/kg bw/day groups. The animals were observed throughout for signs of toxicity, their body weights and food consumption were measured, and haematology, clinical chemistry, urinalysis, macroscopic and microscopic examinations were conducted. Body weight gain and food consumption were reduced from day 19 to 28 in males of the highest dose group. Also in males of the highest dose group, white blood cell count was increased and mean corpuscular volume and mean corpuscular haemoglobin were decreased 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 this same group of animals. 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. There were also effects in male rats that were related to alpha 2u-globulin nephropathy and can therefore be dismissed as species-specific and therefore not relevant to humans (Dow Corning Corporation, 2007). The NOAEL was 160 mg/kg bw/day.

For the oral route there is a supporting non-standard study (Dow Corning Corporation, 2007). This well conducted 28-day oral gavage study in rats, was conducted to investigate the alpha 2u-globulin mediated effects of HMDS. The study demonstrated that the characteristics of alpha 2u-globulin nephropathy increased with an increasing dose of HMDS. Therefore the mechanism leading to adverse kidney effects, including kidney tumour formation, in male rats following administration of HMDS is species-specific and not relevant to human hazard assessment.

In a 2-generation reproductive toxicity study (WIL Research Laboratories, 2006) Sprague-Dawley rats (30 animals/sex/dose) were exposed to HMDS at a concentration of 100, 400, 1600 or 5000 ppm, 6 hours/day, 7 days/week. Exposure started at least 70 days prior to mating, throughout mating, during gestation through to gestation day 20, therefore animals were exposed for at least 90 -days. The NOAEC for parental toxicity relevant to humans was 400 ppm (2657 mg/m³) based on microscopic liver findings (brown pigment in the periportal areas) in the F₀ males of the 5000 ppm group and F₁ males and females in the 5000 and 1600 ppm groups. Although this was a reproductive toxicity study, endpoints relevant to repeat dose toxicity were evaluated and among the many repeat dose inhalation studies for HMDS, the hepatic findings observed in this study were recorded at the lowest exposure concentration. Therefore this study was selected as the key study for repeat dose toxicity.

In a two-year combined chronic toxicity and oncogenicity whole body vapour inhalation study (Research and Consulting Company Ltd, 2005) Fischer 344 rats were exposed to HMDS 6 hours/day, 5 days/week at a target concentration of 700, 2700, 10600 or 33200 mg/m³. The animals were divided into three subgroups: Subgroup A  (20 rats/sex/group), exposed for 12 months with a treatment-free observation period of 12 months; Subgroup B (20 rats/sex/group), exposed for 12 months; Subgroup C (65 rats/sex/group), exposed for 24 months. The animals were examined in detail in accordance with OECD test guideline 453.

HMDS produced calcified cylinders in tubules of the kidney papilla in the male rats. However, these effects in the kidneys, do not adversely affect the survival of the animals, and may be considered as a starting change of renal toxicity. The occurrence of renal tubular adenomas and carcinomas in some males may be related to test substance exposure. A follow-up study showed that an alpha 2 u-globulin mediated mechanism was responsible for the observed nephropathy and kidney neoplasia in the male rats. The increased incidence of eosinophillic inclusions in the olfactory epithelium might be related to nasal irritation caused by mildly irritant chemicals and are also commonly seen in ageing rats, and was considered not to be adverse. Test article-related increase of the testicular weight was correlated with the macroscopic finding of increased incidence of enlarged testes in all treated groups. Increased severity in Leydig cell hyperplasia and increased incidence in Leydig cell tumors were observed at all exposure levels after one year. Leydig cell tumors occur spontaneously and are very common in Fischer 344 rats. In fact, following the 2 year sacrifice, almost all males, both control and treated, showed this finding. The one-year data indicate that HMDS exposure accelerated progression of this common tumor. No microscopic findings were considered to be related to HMDS exposures. Therefore the NOAEC for systemic effects relevant to humans is 33200 mg/m³. The additional inhalation studies show a similar spectrum of effects and therefore support the findings of this study.

In the key dermal repeated dose toxicity study (Dow Corning Corporation, 1993) Sprague-Dawley rats (10 animals/sex/dose) were exposed to undiluted HMDS under occlusive conditions at a dose of 0, 100, 500 or 1000 mg/kg bw/day, 6 hours/day, 5 days/week for 28 days. The animals were then observed and examined according to OECD test guideline 410, except that urinalysis was not included. Overall, the NOAEL is considered to be ≥1000 mg/kg bw/day. Although the observed body weight gain and food consumption differences from control were greater than 10%, the difference in absolute body weight between the control and 1000 mg/kg bw/d group was less than 10%. It is commonly accepted that findings are not considered adverse unless the difference from control group is greater than 10% (Andrew, 2005; LASA, 2009). There were also significantly lower liver and kidney weights when compared to brain weight. Evaluating changes in relative organ-to-brain weight is a standard approach for sex organs since maintaining the brain and the ability to reproduce are very vital functions for the rat. For deriving a systemic NOAEL, organ-to-body weight ratios, rather than organ-to-brain weight ratios are the most appropriated evaluations (Bailey et al., 2004). In this study, liver and kidney to body weight ratios were not significantly different from controls after exposure. Additionally, these changes in absolute liver and kidney weights were not associated with any histopathological effects. Consistent with ECETOC Technical Report No. 85, (Recognition of, and Differentiation between, Adverse and Non-adverse Effects in Toxicology Studies): “there may be effects in toxicity studies that do not represent any functional impairment in the test organism. Such effects are considered not to be adverse”, therefore based on the weight of evidence evaluation of the effects observed at 1000 mg/kg/day, these are not considered adverse and therefore, the NOAEL is 1000 mg/kg/day.

Andrew, D. (2005) PSD Guidance Document: Interpretation of Liver Enlargement in Regulatory Toxicity Studies; United Kingdom Health and Safety Executive Pesticide Publication.

Bailey, S.A., Zidell, R.H. and Perry, R.W. (2004). Relationships between Organ Weight and Body/Brain Weight in the Rat: What is the Best Analytical Endpoint? Toxicol Pathol 32: 448-466.

LASA (2009) Guidance on Dose Level Selection for Regulatory General Toxicity Studies for Pharmaceuticals.

Justification for classification or non-classification

There is no evidence to suggest that hexamethyldisiloxane (HMDS) should be classified for adverse effects following repeated exposure by any route according to Regulation (EC) No 1272/2008.