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Toxicological information

Repeated dose toxicity: inhalation

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Administrative data

Endpoint:
sub-chronic toxicity: inhalation
Type of information:
experimental study
Adequacy of study:
key study
Study period:
01.06.2009 to 17.09.2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2010
Report Date:
2010

Materials and methods

Test guideline
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)
GLP compliance:
yes
Limit test:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent

Test animals

Species:
rat
Strain:
Sprague-Dawley
Sex:
male/female
Details on test animals and environmental conditions:
TEST ANIMALS
- Source: Charles River Laboratories, Inc.
- Age at study initiation: 9 weeks minimum
- Weight at study initiation: Males: 233.4-271.4 g; Females: 183.6-217.7 g.
- Fasting period before study: No
- Housing: Individually housed in suspended wire-mesh cages.
- Diet (e.g. ad libitum): Ad libitum (except during exposure, FOB or motor activity assessments.
- Water (e.g. ad libitum): Ad libitum (except during exposure, FOB or motor activity assessments.
- Acclimation period: Five days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 20.5-23.2
- Humidity (%): 41-62
- Air changes (per hr): At least 10
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 17.06.2009 To: 30.03.2010

Administration / exposure

Route of administration:
inhalation: vapour
Type of inhalation exposure:
whole body
Vehicle:
clean air
Details on inhalation exposure:
GENERATION OF TEST ATMOSPHERE / CHAMBER DESCRIPTION
- Exposure apparatus: Exposures were conducted in 1000 litre stainless steel and glass TSE-system style inhalation chambers. The animal cage position assignment within each chamber was rotated daily. Generation of test substance vapour was performed using heated stainless steel J-tubes containing a column of stainless steel beads. The test substance was metered from reservoirs into J0tubes using a Fluid Metering Incorporation pump and Harvard model syringe pumps. Compressed air flowed through the J-tube directed to the inlet port at the top of the exposure chamber. Just prior to entering the exposure chamber, the carrier/vapour mixture was combined with chamber supply (dilution) air where is was diluted to the target chamber concentration as it entered the exposure chamber.
- Method of conditioning air: Conditioned building air passed through HEPA and activated charcoal filters before delivery to the chamber. Moisture was added as necessary to maintain relative humidity within the required range.
- Temperature, humidity, pressure in air chamber: 22 ±3oC, 50 ±20% (no information on pressure)
- Air change rate: 12-15 air changes of chamber volume per hour
- Treatment of exhaust air: No data

TEST ATMOSPHERE
- Brief description of analytical method used: Gas chromatography
- Samples taken from breathing zone: yes
Analytical verification of doses or concentrations:
yes
Details on analytical verification of doses or concentrations:
Homogeneity of the vapour concentration within the exposure chamber was evaluated prior to experimental start. A minimum of five locations were evaluated and compared to a reference location. Homogeneity of the vapour concentration was considered acceptable if all locations were within 10% of the reference location. Chamber atmosphere was analysed using a gas chromatography equipped with a flame ionisation detector to determine the actual chamber concentration of the test substance.
Duration of treatment / exposure:
90 days
Frequency of treatment:
Daily (seven days/week)
Doses / concentrationsopen allclose all
Dose / conc.:
70 ppm
Remarks:
target
Dose / conc.:
400 ppm
Remarks:
target
No. of animals per sex per dose:
Ten
Control animals:
yes, concurrent vehicle
Details on study design:
- Dose selection rationale: Exposure concentrations were selected based on the 28-day whole-body vapour inhalation study.
- Rationale for selecting satellite groups: To investigate the reversibility of any observed effects.
- Post-exposure recovery period in satellite groups: Control and 400 ppm groups.

Examinations

Observations and examinations performed and frequency:
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 exposure. Findings were noted for individual animals.

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: All animals reveived a detailed physical examination once before the first exposure and weekly thereafter. The observations were made outside the home cage in a standard arena.

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 the day of euthanasia.

FOOD CONSUMPTION:
- Individual food consumption was recorded at least weekly.

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
- Time schedule for examinations: Before initiation of exposure and near the end of exposure period. No examination at the end of the recovery period as no effects were found at the end of the treatment period.
- Dose groups that were examined: Control and treated groups (except recovery groups).

HAEMATOLOGY: Yes
- Time schedule for collection of blood: Prior to scheduled sacrifice.
- Anaesthetic used for blood collection: Yes (isoflurane)
- Animals fasted: Yes
- How many animals: All animals
- Parameters checked in table 1 were examined.

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: Prior to scheduled sacrifice.
- Animals fasted: Yes
- How many animals: All animals
- Parameters checked in table 1 were examined.

URINALYSIS: Yes
- Time schedule for collection of urine: 12-24 hours prior to necropsy.
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes / No / No data
- Parameters checked in table 1 were examined.

NEUROBEHAVIOURAL EXAMINATION: Yes, FOB and motor activity evaluations were performed.
- Time schedule for examinations: Prior to exposure and during the last week of exposure.
- Dose groups that were examined: Control and treated animals (except recovery gorup).
- Battery of functions tested: cage-side obs, hand-held obs, open field obs, categorical obs, measurements/counts, motor activity.
Sacrifice and pathology:
GROSS PATHOLOGY: Yes (see table 2). All animals were subjected to a complete gross necropsy which included examination of the external surface and all orifices of the body, the cranial, thoracic and abdominal cavities and their contents.
HISTOPATHOLOGY: Yes (see table 2). Selected tissues and organs required for histopathological examination from all animals were taken and preserved. Selected organs were also weighed. Histopathology was not performed on the recovery groups as no effects were observed at the end of the treatment period.
Statistics:
Mean body weight values and body weight changes, mean food consumption values, mean organ weight and organ weight to body weight ratios, FOB and motor activity, mean haematology and clinical chemistry values, urinalysis values and histopathology data were evaluated.

Results and discussion

Results of examinations

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):
no effects observed
Food efficiency:
not examined
Water consumption and compound intake (if drinking water study):
not examined
Ophthalmological findings:
no effects observed
Haematological findings:
no effects observed
Clinical biochemistry findings:
no effects observed
Urinalysis findings:
no effects observed
Behaviour (functional findings):
no effects observed
Organ weight findings including organ / body weight ratios:
no effects observed
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: Two animals in the control group were subjected to unscheduled necropsies on Days 72 and 77. These animals had similar gross findings including enlarged spleen and liver, small thymus and exorbital lacrimal glands. There were no other deaths. There were no statistically significant clinical observations noted between control and treated groups.

BODY WEIGHT AND WEIGHT GAIN: There were no statistically significant differences between controls and treatment groups in the mean body weights on any of the three groups: males and females in the main groups and the recovery groups. There were no statistically significant differences between controls and the treatment groups in mean body weight gains for any interval for males and females in the main groups. There was a statistically significant increase (57%) and decrease (34%) in body weight gain compared to control values for the recovery group males during week 2 and 4 of study, respectively. Weight gain for the recovery group females was statistically increased, from controls on week 6, 10 and 17, respectively.

FOOD CONSUMPTION: There were no statistically significant differences between controls and treatment groups in weekly mean food consumption for males in the main groups. There was a statistically significant difference in weekly mean food consumption during the first week of study for the recovery group male group. The only statistically significant results in the main group females was a difference in weekly mean food consumption for the 70 ppm main group females during the fourth week of the study. There were no statistically significant difference between control and treated groups for the recovery group females.

OPHTHALMOSCOPIC EXAMINATION: No adverse effects.

CLINICAL CHEMISTRY: Male rats in the main study Group 2 had statistically significant differences (p<0.05) noted for alanine aminotransferase and total bilirubin in Group 3. These were an increase of 22.5% for alanine aminotransferase and a decrease of 16.6% for total bilirubin as compared to the concurrent control group. There was a statistically significant decrease (p<0.05) in recovery Group 3 for albumin. This was a decrease of 5.7% compared to concurrent control. Although there were statistical differences the mean values, as well as individual values, were within the historical range for these parameters.

Statistically significant decreases were noted for female rats in the main study Groups 2 and 3 for aspartate aminotransferase and total bilirubin (p<0.05). These were decreases of 30% and 28.9% for aspartate aminotransferase and 15.7% and 14.4% for total bilirubin as compared to the concurrent control groups. There was a statistically significant decrease (p<0.05) in the recovery group 3 for creatinine, which was a decrease of 12.5% from concurrent controls. Although these were statistically different, the mean values were within the historical range for these parameters. There were individual values below the historical range for alanine aminotransferase in Groups 2 and 3, but individual values for total bilirubin and creatinine were within the historical range.

The statistically significant findings observed in males and females may be treatment-related; however, were not considered toxicologically significant since the values were within the historical control ranges and there were no histomorphological correlates. There were no other significant differences noted in the other clinical chemistry parameters across either sex.

HAEMATOLOGY: There were no statistically significant differences in the main study for male rats. However, there were statistically significant decreases (p<0.05) in recovery Group 3 for red blood cells and monocytes. This was a decrease of 3.3% for red blood cells and 25.4% and 29.5%, respectively, for the monocytes (percent and absolute). The mean values for these parameters, as well as individual values, were within the historical range.

Females in Group 2 of the main study had statistically significant decreases (p<0.05) for haemoglobin and haematocrit (4.1% and 4.7%, respectively). The mean values, as well as individual values, for haemoglobin and haematocrit were within the historical range. There were no statistical differences noted in the female recovery groups.

The statistically significant findings observed in males and females may be treatment-related; however, were not considered toxicologically significant since the values were within historical control ranges and there were no histomorphological correlates. There were no other significant differences noted in the other haematology parameters across groups for either sex.

URINALYSIS: Urine from the male rats in the main Group 3 had a statistically significant decrease for volume (p<0.01) and statistically significant increases for specific gravity (p<0.01) and urobilinogen (p<0.05), but no differences noted in the recovery groups. In the categorical variables there was protein >=300 mg/dl noted in Groups 1, 2 and 3 of the main group (2, 4 and 6 animals, respectively) and in the recovery Groups 1 and 3 (4 and 5 animals), although not statistically significant. The decrease in urinary output and the increase of protein in the urine appear to be dose responsive. Since BUN and creatinine were similar to control values and there were no correlated histomorphological changes in the kidney, these findings may be considered treatment-related; however, not toxicologically significant.

Neoplasms were observed in two of the Group 1 control males and in one of the Group 3 males. The benign subcutaneous fibroma in the Group 3 male was considered an incidental finding unrelated to test substance administration.

Urine from the female rats in the main groups did not have statistically significant differences for the continuous variables, but a statistically significant difference (p<0.05) was noted in Group 3 of the recovery group for urobilinogen. In the categorical variables there was protein >=300 mg/dl noted one each in Groups 1 and 2 of the main group and one in recovery Group 3, although not statistically significant.

NEUROBEHAVIOUR: There were no statistically significant or biologically relevant findings.

ORGAN WEIGHTS: There were no statistically significant differences compared to controls noted for organ weights and organ weight to body weight ratios for males in the main groups and the recovery groups. There was a statistically significant differences noted for the liver weight to body weight ratio in females of 400 ppm main group compared to controls (7.9% increase). There was also a statistically significant increase in uterus weight, absolute and relative (67 and 60% increase, respectively) in females of the recovery group 400 ppm. These increases in organ weights may be treatment-related and were not considered adverse as there were no histopathological correlates.

GROSS PATHOLOGY: Only occasional findings were observed, which for the most part had no corresponding microscopic finding. Discolouration of the adrenal glands and white single discolouration of the pituitary gland were also noted; pituitary observations were limited to females from Groups 2 and 3. Most of the adrenal findings had no corresponding microscopic finding, although one Group 3 male with a small adrenal gland did have a minimal decrease of the cortex of the adrenal gland. With the exception of one of the pituitaries from the Group 2 female, wherein the corresponding microscopic finding was minimal focal hyperplasia, none of the pituitary gross observations had corresponding microscopic findings. Enlarged uterus in a Group 2 female was correlated microscopically with dilatation of the horns due to the estrus stage.

Occasional other gross observations were noted but were considered sporadic and not indicative of a treatment-related effect.

HISTOPATHOLOGY: No treatment-related findings were observed in evaluated tissues from Group 3 males and females at the terminal sacrifice, except for a statistically significant increased incidence of alveolar macrophages in the Group 3 females. Alveolar macrophages of minimal severity were observed in the lung of five of ten Group 3 females but not in control female lungs. This is a very common incidental finding; however. it was statistically significant and appears to be treatment-related in females, although not considered an adverse effect. Alveolar macrophages were observed in control and high dose males; however, not a statistically significant increase above control values.

Effect levels

Dose descriptor:
NOAEC
Effect level:
>= 400 ppm
Based on:
test mat.
Sex:
male/female
Basis for effect level:
other: No adverse treatment-related effects.

Target system / organ toxicity

Critical effects observed:
no

Applicant's summary and conclusion

Conclusions:
In a 90-day inhalation study conducted to OECD 413 and to GLP (reliability score 1) inhalation of decamethyltetrasiloxane at concentrations of 70 and 400 ppm were well tolerated. There were no clinical signs or treatment-related effects associated with exposure in the ophthalmologic endpoints, body weights, food consumption and rat neurobiological function. Certain changes in serum chemistry and haematology parameters, urinary volumes and organ weights (absolute and relative) may be treatment-related, but not toxicologically significant. The only treatment-related microscopic finding in Group 3 females was an increased incidence of alveolar macrophages, though not considered an adverse effect. Based on the results of this study the NOAEL for decamethyltetrasiloxane for systemic toxicity in male and female rats is at least 400 ppm.