Tetradecamethylhexasiloxane

Endpoint summary

Description of key information

There are no repeated dose toxicity data on tetradecamethylhexasiloxane (L6), so good quality data for the related substances, dodecamethylpentasiloxane (L5, 161-53-9) and decamethyltetrasiloxane (L4, 141-62-8), have been used to assess the repeated dose toxicity of tetradecamethylhexasiloxane.

In the key 28-day repeated dose oral toxicity study, conducted according to OECD Test Guideline 407 and in compliance with GLP (Dow Corning Corporation, 2010), no biologically significant, treatment-related effects were reported in rats given dodecamethylpentasiloxane (L5) by oral gavage at 25, 250 or 1000 mg/kg bw/day. A NOAEL for systemic toxicity of ≥1000 mg/kg bw/day was concluded.

 

Following a compliance check draft decision (CCH-D-2114546156-49-01/D) for dodecamethylpentasiloxane (L5), dated 15th March 2021, the registrants intend to perform a 90-day repeated dose toxicity study with dodecamethylpentasiloxane (L5) via the oral route after receipt of the final decision from ECHA. As an interim approach, the subchronic toxicity endpoint for tetradecamethylhexasiloxane (L6) is fulfilled by use of read-across of an existing 90-day inhalation study with the analogue substance, decamethyltetrasiloxane (L4; CAS 141-62-8). However, this read-across will be replaced by the 90-day repeated dose toxicity study with dodecamethylpentasiloxane (L5) via the oral route when the study is available.

In a 90-day repeated dose inhalation toxicity study, conducted according to OECD Test Guideline 413 and in compliance with GLP (Dow Corning Corporation, 2010) inhalation of decamethyltetrasiloxane (L4) at concentrations of 70 and 400 ppm were well-tolerated and the concluded NOAEL for systemic toxicity in male and female rats was at least 400 ppm (equivalent to 5083 mg/m³).

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:

22 April 2009 to 23 September 2010

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

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method B.7 (Repeated Dose (28 Days) Toxicity (Oral))

Qualifier:

according to guideline

Guideline:

other: Japanese Guideline for Screening Toxicity Testing of Chemicals: Testing Methods for New Substances, enacted July 13, 1974, amended December 5, 1986

GLP compliance:

yes

Limit test:

no

Species:

rat

Strain:

other: Hsd:Sprague Dawley

Sex:

male/female

Details on test animals or test system and environmental conditions:

TEST ANIMALS
- Source: Harlan Laboratories, B.V.
- Age at study initiation: ~8 weeks
- Weight at study initiation: 236 to 272 g (males), 183 to 220 g (females)
- Fasting period before study: no data available
- Housing: groups of 5 in Makrolon type-4 cages
- Diet (e.g. ad libitum): ad libitum
- Water (e.g. ad libitum): ad libitum
- Acclimation period: 7 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 3
- Humidity (%): 30 to 70
- Air changes (per hr): 10 to 15
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: From: 22 April 2009 To: 27 May 2009 (satellite A) or 10 June 2009 (satellite B)

Route of administration:

oral: gavage

Vehicle:

corn oil

Remarks:

dried and deacidified

Details on oral exposure:

PREPARATION OF DOSING SOLUTIONS: The formulations were prepared weekly. L5 was weighed into a glass beaker on a tared Mettler balance. Thereafter the remaining vehicle was added. The mixtures were stirred and stored at room temperature. Homogeneity of the test substance in the vehicle was maintained during the daily administration period using a magnetic stirrer.

VEHICLE
- Justification for use and choice of vehicle (if other than water): no data available
- Concentration in vehicle: 0, 5, 50, 200 mg/ml
- Amount of vehicle (if gavage): 5 ml/kg bw
- Lot/batch no. (if required): no data available
- Purity: no data available

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

After the experimental start, samples of the vehicle and three samples (top, middle and bottom) of about 2 g of each concentration were taken prior to dosing for analysis of homogeneity, concentration and stability. About 2 g of each concentration was also taken for analysis during week 3 after commencement of dosing. A GC method was used for analysis. Accurate use of dodecamethylpentasiloxane (L5) and the corn oil vehicle were indicated and the application formulations were found to be homogeneously prepared. Formulations were stable.

Duration of treatment / exposure:

28 days

Frequency of treatment:

daily

Dose / conc.:

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

Dose / conc.:

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

Dose / conc.:

1 000 mg/kg bw/day (actual dose received)

No. of animals per sex per dose:

5 (with an additional 5 animals/sex given 0 or 1000 mg/kg bw for recovery phase - satellite B)

Control animals:

yes, concurrent vehicle

Details on study design:

- Dose selection rationale: results of range-finding study
- Rationale for selecting satellite groups: to assess recovery
- Post-exposure recovery period in satellite groups: 14 days

Positive control:

No positive control group

Observations and examinations performed and frequency:

CAGE SIDE OBSERVATIONS: Yes
- Time schedule: mortality/viability: twice daily; general clinical observations: before commencement of administration, twice daily on days 1 to 3, once daily on days 4 to 28 (treatment period), once daily on days 1 to 14 (recovery period)

DETAILED CLINICAL OBSERVATIONS: Yes
- Time schedule: The animals were observed in their home cages, outside their home cages in a standard arena and in the hand. The observations were performed once before commencement of administration and once weekly (weeks 1 to 3) thereafter

BODY WEIGHT: Yes
- Time schedule for examinations: weekly (during acclimation, treatment and recovery periods, and before necropsy)

FOOD CONSUMPTION: Yes
- Recorded once during the acclimatisation period and weekly thereafter.
- Food consumption for each animal determined and mean daily diet consumption calculated as g food/kg body weight/day: Yes
- Compound intake calculated as time-weighted averages from the consumption and body weight gain data: No

FOOD EFFICIENCY: No

WATER CONSUMPTION: No

OPHTHALMOSCOPIC EXAMINATION: No

HAEMATOLOGY: Yes
- Time schedule for collection of blood: after 4 weeks and at the end of the recovery period
- Anaesthetic used for blood collection: Yes (light isoflurane)
- Animals fasted: Yes (18 h)
- How many animals: all animals
- Parameters checked in table 1 were examined

CLINICAL CHEMISTRY: Yes
- Time schedule for collection of blood: after 4 weeks and at the end of the recovery period
- Animals fasted: Yes (18 h)
- How many animals: all animals
- Parameters checked in table 1 were examined

URINALYSIS: Yes
- Time schedule for collection of urine: after 4 weeks and at the end of the recovery period
- Metabolism cages used for collection of urine: Yes
- Animals fasted: Yes (18 h)
- Parameters checked in table 1 were examined

NEUROBEHAVIOURAL EXAMINATION: Yes
- Time schedule for examinations: during week 4, relevant parameters from a modified Irwin screen test were evaluated in all animals
- Dose groups that were examined: all groups
- Battery of functions tested: sensory activity / motor activity / grip strength / other: behaviour

OTHER: vaginal smear for oestrus
- Taken on day 22 of treatment

Sacrifice and pathology:

Sacrifice was after 28 days for the treatment only group and after 6 weeks for the recovery group.
GROSS PATHOLOGY: Yes (see table 2)
HISTOPATHOLOGY: Yes (for a comprehensive range of tissues in high-dose and control groups, and for livers only in other dose groups) (see table 2)

Other examinations:

No data available

Statistics:

The following statistical methods were used to analyse the results from investigations of body weight, grip strength, locomotor activity, clinical laboratory data, organ weights and ratios, and macroscopic findings:
1) The Dunnett-test based on a pooled variance estimate was applied if the variables could be assumed to follow a normal distribution for the comparison of the treated groups and the control groups for each sex.
2) The Steel-test (many-one rank test) was applied instead of the Dunnett-test when the data could not be assumed to follow a normal distribution.
3) Fisher's exact-test.

Clinical signs:

no effects observed

Description (incidence and severity):

No treatment-related signs of toxicity (hair loss noted around the eyes of two females at 25 mg/kg bw/day and periocular scabbing noted in control and treated animals).

Mortality:

no mortality observed

Description (incidence):

All animals survived to scheduled necropsy.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

No treatment-related effects (mean body weight was not affected by the end of treatment, but was significantly elevated in treated males and females on day 8 of the recovery period).

Food consumption and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

no adverse effects.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

not examined

Haematological findings:

no effects observed

Description (incidence and severity):

A number of statistically significant differences to the control parameters were noted in rats treated with 1000 mg/kg bw/day. However, these differences were either gender-specific, due to slightly high control values, or were not supported by concomitant changes in related parameters, and considered to be unrelated to the treatment.

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

The few differences noted in the clinical biochemistry parameters were considered to be unrelated to the treatment.

Urinalysis findings:

no effects observed

Description (incidence and severity):

After the end of the treatment period, the urinalysis parameters of the males and females were unaffected at all dose levels and no late effects were evident after the end of the recovery period.

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

There were no treatment-related findings in the FOB. Minor transient differences in the mean locomotor activity in males at 1000 mg/kg bw/day were considered to be unrelated to the test substance. In males treated with 1000 mg/kg bw/day, the mean locomotor activity during 0-10 minutes was significantly increased when compared with the control males. Females were unaffected at this dose.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

With the exception of the changes in the mean absolute and relative liver weights, none of the differences in organ weights or ratios were accompanied by microscopical changes and were therefore considered to be unrelated to treatment. The increased mean absolute and relative liver weights were considered to be related to metabolic adaptation, and were reflected in microscopic findings. These findings were not evident after the recovery period. Elevated liver weights, particularly in combination with hepatocellular hypertrophy, was considered reversible and considered to be an adaptive finding without adverse toxicological relevance.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

No gross findings, considered to be exposure-related, were noted in this study.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Although the presence of higher mean levels of α-2u-globulin of the punctate staining pattern in the kidneys of male rats at 250 or 1000 mg/kg bw/day were considered to be possible treatment-related effects, the lack of a dose-response relationship or any morphological changes in the kidneys was considered to indicate that these changes were of no toxicological relevance. The toxicologically irrelevant elevation of α-2u-globulin protein in the kidneys of male rats is a well-known species- and gender-specific phenomenon and, in the absence of any correlating morphological changes, was not considered to be adverse. Hepatocellular hypertrophy was also evident in 1000 mg/kg bw/day animals. The hepatocellular hypertrophy, noted after the treatment period, is considered to be an adaptive process due to enzyme induction rather than a toxic effect, and was reversible after the end of the recovery period. Perilobular fatty change (at 0, 25, 250 and 1000 mg/kg bw/day with dose dependent occurrence and severity) noted after the end of the treatment period reverted to control levels after recovery, was not considered adverse.

Histopathological findings: neoplastic:

not examined

Other effects:

no effects observed

Description (incidence and severity):

The sampling and evaluation of the stage of estrus on day 22 of treatment did not indicate any abnormal distributions of diestrus, metestrus, proestrus or estrus.

Key result

Dose descriptor:

NOAEL

Effect level:

>= 1 000 mg/kg bw/day (actual dose received)

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: no toxicologically-relevant treatment-related effects at any dose

Critical effects observed:

no

Conclusions:

In a GLP 28-day study performed according to OECD Test Guideline 407, no biologically significant, treatment-related effects were reported in rats given dodecamethylpentasiloxane (L5) by oral gavage at 25, 250 or 1000 mg/kg bw/day. An NOAEL of >=1000 mg/kg bw/day was derived.

Executive summary:

In a GLP study performed according to OECD Test Guideline 407, groups of five male and five female rats (with additional satellite groups of five males and five females given the top and the control dose) were treated with dodecamethylpentasiloxane (L5) via the oval (gavage) route for 28 days. Doses of 25, 250 or 1000 mg/kg bw/day were administered, with a concurrent control group treated with the vehicle alone (corn oil) at 5 ml/kg bw.

Over the course of the study, a range of parameters were investigated (mortality, clinical signs of toxicity, food consumption, body weight, behaviour). During week 4, a functional observation battery was carried out and grip strength and locomotor activity tests were performed. Necropsy was performed immediately after treatment at 28 days, or after a recovery period of 14 days (satellite groups), and macro- and microscopic analyses were performed. Blood and urine were taken for analysis immediately after treatment and after the recovery period.

Under the conditions of this study, no biologically-significant, treatment-related effects were observed at any dose.

An NOAEL of >=1000 mg/kg bw/day was derived.

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: 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:

01.06.2009 to 17.09.2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)

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 Laboratories
- 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 (%): 30-70
- 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

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 J0 tubes 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 chamber air changes 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. Exposure concentration was evaluated at least once every 60 min.

Duration of treatment / exposure:

90 days

Frequency of treatment:

Daily (seven days/week)

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. The high exposure level of 400 ppm is the highest vapour concentration that could be reproducibly generated without the formation of aerosol and the exposure level of 70 ppm was chosen to be in the range of values based on GHS guidance, 0.2-1 mg/L (1 mg/L = 79 ppm for L4), for Category 2 classification.
- Rationale for selecting satellite groups: To investigate the reversibility of any observed effects after 28 day recovery period.
- Post-exposure recovery period in satellite groups: Control and 400 ppm groups.

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 received 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
- 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 group).
- 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, Functional Observational Battery (FOB) data and motor activity, mean haematology and clinical chemistry values, urinalysis values and histopathology data were evaluated. Data analysis was carried out in the Provantis v8.2 system for body weight ratios, food consumption, hematology, clinical chemistry and prothrombin times. These data were analysed using ANOVA. If data did not satisfy the requirements of normality of the residuals (Wilks-Shapiro) and homogeneity of variance (Bartlett's) a log of rank transformation was performed. If the ANOVA was significant (p<0.05), pair-wise comparisons of the exposed groups to control were made using Dunnett's test. Clinical signs data were analysed using Mixed Modelling repeated measures. FOB data were analysed using a combination of ANCOVA with baseline evaluations used as the covariate and repeated measures ANOVA. Categorical FOB data were analysed using the Joncheere-Terpsta test. Clinical pathology data were analysed with Provantis v8.2 and SAS v9.1.3. Statistically significant probabilities were reported for p values of <0.05 and <0.01.

Clinical signs:

no effects observed

Description (incidence and severity):

There were no statistically significant clinical observations noted between control and treated groups.

Mortality:

no mortality observed

Description (incidence):

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. These animals also had a few specific individual findings and both had lymphosarcoma. There were no other deaths.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

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 and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

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.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

no effects observed

Description (incidence and severity):

No adverse effects

Haematological findings:

no effects observed

Description (incidence and severity):

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.

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

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.

Urinalysis findings:

no effects observed

Description (incidence and severity):

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.

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.

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

There were no statistically significant or biologically relevant findings.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

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 pathological findings:

no effects observed

Description (incidence and severity):

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.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

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. 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.

Histopathological findings: neoplastic:

not examined

Key result

Dose descriptor:

NOAEC

Effect level:

>= 400 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No adverse treatment-related effects.

Critical effects observed:

no

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.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

5 083 mg/m³

Study duration:

subchronic

Species:

rat

Repeated dose toxicity: inhalation - local effects

Link to relevant study records

Reference

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

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 413 (Subchronic Inhalation Toxicity: 90-Day Study)

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 Laboratories
- 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 (%): 30-70
- 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

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 J0 tubes 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 chamber air changes 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. Exposure concentration was evaluated at least once every 60 min.

Duration of treatment / exposure:

90 days

Frequency of treatment:

Daily (seven days/week)

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. The high exposure level of 400 ppm is the highest vapour concentration that could be reproducibly generated without the formation of aerosol and the exposure level of 70 ppm was chosen to be in the range of values based on GHS guidance, 0.2-1 mg/L (1 mg/L = 79 ppm for L4), for Category 2 classification.
- Rationale for selecting satellite groups: To investigate the reversibility of any observed effects after 28 day recovery period.
- Post-exposure recovery period in satellite groups: Control and 400 ppm groups.

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 received 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
- 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 group).
- 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, Functional Observational Battery (FOB) data and motor activity, mean haematology and clinical chemistry values, urinalysis values and histopathology data were evaluated. Data analysis was carried out in the Provantis v8.2 system for body weight ratios, food consumption, hematology, clinical chemistry and prothrombin times. These data were analysed using ANOVA. If data did not satisfy the requirements of normality of the residuals (Wilks-Shapiro) and homogeneity of variance (Bartlett's) a log of rank transformation was performed. If the ANOVA was significant (p<0.05), pair-wise comparisons of the exposed groups to control were made using Dunnett's test. Clinical signs data were analysed using Mixed Modelling repeated measures. FOB data were analysed using a combination of ANCOVA with baseline evaluations used as the covariate and repeated measures ANOVA. Categorical FOB data were analysed using the Joncheere-Terpsta test. Clinical pathology data were analysed with Provantis v8.2 and SAS v9.1.3. Statistically significant probabilities were reported for p values of <0.05 and <0.01.

Clinical signs:

no effects observed

Description (incidence and severity):

There were no statistically significant clinical observations noted between control and treated groups.

Mortality:

no mortality observed

Description (incidence):

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. These animals also had a few specific individual findings and both had lymphosarcoma. There were no other deaths.

Body weight and weight changes:

no effects observed

Description (incidence and severity):

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 and compound intake (if feeding study):

no effects observed

Description (incidence and severity):

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.

Food efficiency:

not examined

Water consumption and compound intake (if drinking water study):

not examined

Ophthalmological findings:

no effects observed

Description (incidence and severity):

No adverse effects

Haematological findings:

no effects observed

Description (incidence and severity):

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.

Clinical biochemistry findings:

no effects observed

Description (incidence and severity):

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.

Urinalysis findings:

no effects observed

Description (incidence and severity):

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.

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.

Behaviour (functional findings):

no effects observed

Description (incidence and severity):

There were no statistically significant or biologically relevant findings.

Immunological findings:

not examined

Organ weight findings including organ / body weight ratios:

no effects observed

Description (incidence and severity):

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 pathological findings:

no effects observed

Description (incidence and severity):

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.

Neuropathological findings:

not examined

Histopathological findings: non-neoplastic:

no effects observed

Description (incidence and severity):

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. 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.

Histopathological findings: neoplastic:

not examined

Key result

Dose descriptor:

NOAEC

Effect level:

>= 400 ppm

Based on:

test mat.

Sex:

male/female

Basis for effect level:

other: No adverse treatment-related effects.

Critical effects observed:

no

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.

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

5 083 mg/m³

Study duration:

subacute

Species:

rat

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

No data are available for the registration substance, tetradecamethylhexasiloxane (L6), so reliable data for the related substances, dodecamethylpentasiloxane (L5, 141-63-9) and decamethyltetrasiloxane (L4, 141-62-8) have been used to assess the repeated dose toxicity of tetradecamethylhexasiloxane.

Following a compliance check draft decision (CCH-D-2114546156-49-01/D) for dodecamethylpentasiloxane (L5), dated 15th March 2021, the registrants intend to perform a 90-day repeated dose toxicity study with dodecamethylpentasiloxane (L5) via the oral route after receipt of the final decision from ECHA. As an interim approach, the subchronic toxicity endpoint for tetradecamethylhexasiloxane (L6) is fulfilled by use of read-across of an existing 90-day inhalation study with the analogue substance, decamethyltetrasiloxane (L4; CAS 141-62-8). However, this read-across will be replaced by the 90-day repeated dose toxicity study with dodecamethylpentasiloxane (L5) via the oral route when the study is available.

In the key repeated dose oral toxicity study, conducted according to OECD Test Guideline 407 and in compliance with GLP (Dow Corning Corporation, 2010), groups of five male and five female rats (with additional satellite groups of five males and five females given the top and the control dose) were treated with the registered substance, dodecamethylpentasiloxane (L5) (CAS 141-63-9) via the oval (gavage) route for 28 days. Doses of 25, 250 or 1000 mg/kg bw/day were administered, with a concurrent control group treated with the vehicle alone (corn oil) at 5 ml/kg bw.

Over the course of the study, a range of parameters were investigated (mortality, clinical signs of toxicity, food consumption, body weight, behaviour). During week 4, a functional observation battery was carried out and grip strength and locomotor activity tests were performed. Necropsy was performed immediately after treatment at 28 days, or after a recovery period of 14 days (satellite groups), and macro- and microscopic analyses were performed. Blood and urine were taken for analysis immediately after treatment and after the recovery period.

Under the conditions of this study, no biologically-significant, treatment-related effects were observed at any dose lever for any of the examined parameters. Therefore, the NOAEL for systemic toxicity was concluded to be at least 1000 mg/kg bw/day, the highest dose tested.

In a 90-day repeated dose inhalation toxicity study, conducted according to OECD Test Guideline 413 and in compliance with GLP (Dow Corning Corporation, 2010b) inhalation of decamethyltetrasiloxane at concentrations of 70 and 400 ppm were well-tolerated. The high exposure level of 400 ppm is the highest vapour concentration that could be reproducibly generated without the formation of aerosol. 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 (equivalent to 5083 mg/m³).

In the supporting repeated dose inhalation study conducted according to OECD Test Guideline 422 and in compliance with to GLP (Dow Corning Corporation, 2007), whole body exposure of rats to decamethyltetrasiloxane (L4) for 28 days did not result in any adverse effects attributable to treatment. Therefore the NOAEC for systemic toxicity of the adult rats was considered to be at least 400 ppm (the highest concentration tested), which is equivalent to 5083 mg/m³.

Read-across justification

To reduce animal testing REACH recommends to make use of a read-across approach where appropriate based on the high accordance in properties relevant for the specific endpoint. In the case of repeated dose toxicity and reproductive toxicity relevant properties are structural similarity as well as physical-chemical and basic toxicological parameters in the same range. In the following paragraphs the read-across approach for L6 is evaluated point by point. Further information can be found in the supporting report (PFA, 2013u) attached in Section 13 of the IUCLID 6 dossier.  

Read-across hypothesis

The hypothesis is that the target (registered) source substance and the (read-across) substances have similar toxicological properties because they are fully methyl-substituted linear siloxanes with similar physicochemical properties and are structurally similar with similar hydrolysis rates. Hydrolysis rates have been compared based on predicted values, as measured hydrolysis half-lives are available only for L3, and these are consistent with the predicted values.

Summary of key physicochemical and repeated dose toxicity data for linear siloxanes

Substance	L4	L5	L6
Chemical name	Decamethyl tetrasiloxane	Dodecamethyl pentasiloxane	Tetradecamethylhexasiloxane
CAS number	141-62-8	141-63-9	107-52-8
Molecular weight	310.69	384.85	459
Water solubility (mg/l)	6.7E-03 at 23°C	7.0E-05 at 23°C	2.3E-06 at 20°C
Log Kow	8.21 (measured) at 25.1°C	9.41 (measured) at 25°C	>9.41 (read across from L5) at 20°C
Vapour pressure	73 Pa at 25°C	7.8 Pa at 25°C	0.27 Pa at 20°C
Ultimate hydrolysis products	Dimethylsilanediol and trimethylsilanol	Dimethylsilanediol and trimethylsilanol	Dimethylsilanediol and trimethylsilanol
Hydrolysis half-life (pH 7, 20-25°C, predicted)	630 hours	2000 hours	6300 hours
Hydrolysis half-life (pH 7, 37.5°C)	270 hours	490 hours	1600 hours
Hydrolysis half-life (pH 2, 37.5°C)	19 seconds	60 seconds	108 seconds
Sub-acute oral toxicity NOAEL (mg/kg bw/day	25 mg/kg bw/day (Dow Corning Corporation, 2010c)	≥1000 (Dow Corning Corporation, 2010a)	-
Sub-chronic inhalation toxicity NOAEC (mg/l)	5.1 (Dow Corning Corporation, 2010b)	-	-

(a) Structural similarity

L6, L5 and L4 are closely related substances, consisting of chains of six, five and four silicon atoms joined by five, four and three oxygen atoms, i.e. they have five, four or three Si-O groups and a terminal silicon, substituted with fourteen, twelve and ten methyl groups respectively.

(b) Similar toxicokinetics

The read-across of data from decamethyltetrasiloxane and dodecamethylpentasiloxane to tetradecamethylhexasiloxane is justified by the similarities in structure and physicochemical properties of the two substances. They have extremely low water solubility (6.7E-03 mg/l at 23°C, L4; 7.0mg/l at 23°C, L5 and 2.3E-06 mg/l at 20°C, L6) and high octanol-water partition coefficients (log K_ow = 8.21 at 25.1°C, L4; , 9.41 at 25°C, L5; and >9.41 at 25°C, L6 (by read-across from L5)). These properties indicate that absorption of parent is likely to be low via oral and dermal routes of exposure. Once absorbed these substances are likely to distribute into tissues, particularly fatty tissues.

The substances belong to the structural class of siloxanes (alkyl, vinyl, aryl or hydrogen substituted) and the substances hydrolyse slowly at pH 7 (see Table 5.6.3) therefore hydrolysis is not of relevance in terms of toxicological studies by the inhalation route. For the oral route, the hydrolysis rate is predicted to be fast at pH 2 and 37.5°C with half-lives of 19 seconds (L4), 60 seconds (L5) and 108 seconds (L6), and the substances share common ultimate hydrolysis products, trimethylsilanol and dimethylsilanediol. However, in view of the high lipophilicity and poor water solubility of the parent substances it is likely that some unhydrolysed material is adsorbed onto food present in the stomach and thus the true rate of degradation in the stomach is difficult to predict.

(c) Acute toxicity

Toxicity studies indicate that neither L4 nor L5 is acutely toxic via the dermal route (see acute dermal toxicity section). Nor are they irritating in reliable studies (see irritation section).

(d) Repeated dose toxicity

Repeated sub-acute oral toxicity studies are available for decamethyltetrasiloxane and dodecamethylpentasiloxane, in which both substances led to adaptive changes in the liver (25, 250 and 1000 mg/kg bw/day for both substances), and decamethyltetrasiloxane caused accumulation of brown pigment in the bile ducts (250 and 1000 mg/kg bw/day), but other relevant findings were unremarkable and there were no apparent effects on the reproductive organs examined at necropsy. The observed effects with L5 were not considered to be adverse with respect to setting a NOAEL and deriving DNEL for human hazard assessment purposes, whereas for L4 accumulation of brown pigment was considered to be adverse. Further studies are underway to determine the nature of the pigment. A 90-day inhalation study is also available with L4 in which no adverse effects were observed at the highest achievable test concentration of 400 ppm. The study with L5 was selected as read-across for repeated dose toxicity by the oral route because L5 is closer in molecular weight to the registered substance than L4, and the accumulation of brown pigment observed with L4 was not seen in studies on L5. The trend in physicochemical properties from L4 to L6 support read-across from L5 rather than L4.

(e) Conclusion

Overall, these two substances have similar toxicological profiles. After considering all of the above factors it is deemed appropriate to read-across data from L5 to L6.

References

Dow Corning Corporation (2010b). A 90-day subchronic whole body inhalation toxicity study of decamethyltetrasiloxane (L4) with a 28-day recovery period in Sprague-Dawley rats. Testing laboratory: Health and Environmental Sciences, Dow Corning Corporation (no further details). Report no.: 2010-I0000-62271. Report date: 2010-09-17. Dow Corning Corporation (2010c). 28-Day oral (gavage) toxicity study in the Sprague-Dawley rat with decamethyltetrasiloxane (L4). Testing laboratory: Not given. Report no.: 2009-I0000-61677. Report date: 2010-08-03.

PFA, 2013u, Peter Fisk Associates, Analogue report - mammalian toxicity of linear and branched siloxanes, PFA.300.002.008

Justification for classification or non-classification

Tetradecamethylhexasiloxane (L6) is not classified for adverse effects following repeated dose exposures according to Regulation (EC) No 1272/2008.