Dicyclopentyldimethoxysilane

Endpoint summary

Description of key information

In the key sub-acute oral toxicity study in rats with dicyclopentyl(dimethoxy)silane (CAS 126990-35-0) conducted according to OECD Test Guideline 407 and in compliance with GLP, the NOAEL was at least 1000 mg/kg bw/day, the highest dose tested (Huntingdon Life Sciences Ltd, 1995a).

There are no sub-chronic toxicity data for the registered substance, but data is available for the silanol hydrolysis product, dicyclopentylsilanediol. In this key oral gavage toxicity study in rats conducted according to a protocol equivalent to OECD Test Guideline 408 and in compliance with GLP, the NOAEL for dicyclopentylsilanediol was 200 mg/kg bw/day for females and 1000 mg/kg bw/day for males. A molecular weight correction is used to establish the corresponding dose of parent dicyclopentyl(dimethoxy)silane that would provide 200 mg/kg bw/day of dicyclopentylsilanediol.

The overall NOAEL of 200 mg/kg bw/day as silanol is equivalent to a dose of approximately 230 mg/kg bw/day as parent dicyclopentyl(dimethoxy)silane (Mitsubishi Chemical Safety Institute, 2000).

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

sub-chronic toxicity: oral

Type of information:

experimental study

Adequacy of study:

key study

Study period:

not reported

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Remarks:

Reviewer's note: this study is a part of safety evaluation project of the existing chemical substance by the Japanese authority and it is stated clearly in secondary summaries that this study was conducted in compliance with GLP. However, some pages, which may contain the confirmation of GLP compliance, are missing from the published study report.

Reason / purpose for cross-reference:

reference to same study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 408 (Repeated Dose 90-Day Oral Toxicity Study in Rodents)

Version / remarks:

OECD 408 compliance is not stated in the report but the report states each examinations/observations are performed in accordance with GLP and OECD guidelines.

Deviations:

yes

Remarks:

There is no description about functional observations. Preservation in the fixation medium of skin was not performed.

Principles of method if other than guideline:

not applicable

GLP compliance:

yes

Remarks:

Certificate is not included in the study report.

Species:

rat

Strain:

Crj: CD(SD)

Sex:

male/female

Details on test animals or test system and environmental conditions:

Condition of animal room though quarantine/acclimatization
Temperature: 22±2°C (allowable range: 19~25°C)
Relative humidity: 55±15 % (allowable range: 35~75%)
Ventilation: 12 times/hour supplied with all fresh air
Lighting hour: 12 hour/day (07:00~19:00)

Equipments of animal husbandry
4 or 5 animals (both sex)/cage before the allocation to test groups and 2 animals (both sex)/cage after the allocation to test groups in polycarbonate cages (265W x 426D x 200H mm, Tokiwa Kagaku Kikai Co., Ltd.) lined with sterilized floorcloth for experimental animal (BETA CHIP, Charles River Laboratories Japan Inc.) setting on steel racks (Tokiwa Kagaku Kikai Co., Ltd.). The locations of cages were exchanged weekly.

Food container and Water supply instrument
Sterilized stainless steel pellet-food containers (Tokiwa Kagaku Kikai Co., Ltd.) and sterilized polycarbonate water supply system (700 ml, Tokiwa Kagaku Kikai Co., Ltd.) were used.
They were exchanged weekly.
Pellet food for experimental animals (MF, Oriental Yeast Co., Ltd.) and tap water filtered through 5 μm filter and ultraviolet radiation were used.
Animals were allowed to free access to food and water. They were exchanged weekly.

The concentrations of pesticide residue in the food and floorcloth were conformed to the standard indicated by the study laboratory.
Water examination in accordance with Water Supply Act was performed and it was confirmed that analysed value were conformed to the standard.

Route of administration:

oral: gavage

Vehicle:

other: 0.1% Tween 80 added 0.5% CMC-Na solution

Details on oral exposure:

Using syringe with feeding tube.

Analytical verification of doses or concentrations:

yes

Details on analytical verification of doses or concentrations:

Homogeneity of the test substance in test solution and stability of test solutions in 8 days under refrigerated storage were examined before administration. And test solution of all the lots for each dose level was examined and the concentration was within +/- 10% of nominal concentration.

However, corresponding documentation is not included in the report.

Duration of treatment / exposure:

90 days

Frequency of treatment:

Once a day in the morning

Remarks:

Doses / Concentrations:
40, 200 and 1000 mg/kg bw/day (m/f)
Basis:
actual ingested

No. of animals per sex per dose:

10 male and 10 female in each dose group

Control animals:

yes, concurrent no treatment

Details on study design:

- Dose selection rationale: Highest dose was set at 1000 mg/kg as instructed in OECD guideline .

A 4-week recovery period was included for groups of 10 males and 10 females for the control and 1000 mg/kg bw/day dose level.

Positive control:

No

Observations and examinations performed and frequency:

The following items were examined. Here, the first day of dosing is indicated as day 1, and days 1 to 7 are indicated as 1 week. And the duration after day 91 was set as the recovery period.

1. Clinical observations
Observations were done twice a day (before and after dosing) during the dosing period, and once a day in the morning during the rest of the period.

2. Body weight
Body weights of all animals were weighed weekly using an electronic balance (EB-5000: Shimadzu Corporation). Also, it was weighed at the day of necropsy and the previous day.

3. Food intake
All individual food with tare was weighed using an electronic balance (EB-5000: Shimadzu Corporation) weekly and mean daily food intake per one animal was calculated.

4. Haematology
At the time of scheduled necropsy on days 91 and 119, all animals were fasted for more than 20 hours from the evening of the previous day, and anesthetized by intraperitoneal injection of thiopental sodium (Labonal®, Mitsubishi Tanabe Pharma Corporation). Blood was withdrawn from the inferior vena cava and the parameters indicated below were analyzed. For the analysis of parameters (9) and (10) indicated below, 3.2 w/v% sodium tri-citrate solution was used as anticoagulant, and plasma obtained by centrifugation was used for the analysis. For the analysis of other parameters, blood treated with EDTA-2K as anticoagulant was used.

Parameter Method
(1) Erythrocyte count(RBC): Sheath flow DC impedance detective method
(2) Haemoglobin concentration(Hb): SLS-haemoglobin method
(3) Haematocrit(Ht): Erythrocyte pulse wave height detection method
(4) Mean corpuscular volume (MCV): Calculated from (1) and (3)
(5) Mean corpuscular hemoglobin (MCV): Calculated from (1) and (2)
(6) Mean corpuscular hemoglobin concentration (MCHC): Calculated from (2) and (3)
(7) Reticulocyte count: Flow cytometry using argon laser
(8) Platelet count: Sheath flow DC impedance detective method
(9) Prothrombin time (PT): Quick one-stage method
(10) Activated partial thromboplastin time (APTT): Activated cephaloplastin method
(11) Leukocyte counts(WBC): RF/DC impedance detective method
(12) Differential white blood cell count: Measured Wright stained sample

Instruments used for measurement
(1)-(3),(8), (11): :NE-4500, Sysmex Corporation
(7): :R-2000, Sysmex Corporation
(9), (10): :KC 10A, Amelung
(12): MICROX HEG-50,Omron

5. Blood biochemistry
A part of blood sample obtained at scheduled necropsy was left at room temperature for more than 30 minutes, centrifuged and the following parameters were determined using the serum obtained. The serum remained after determination was kept in a freezer.

Parameter Method
(1) ASAT (GOT): UV-rate method (improved JSCC method)
(2) ALAT (GPT) : UV-rate method (improved JSCC method)
(3) gammma GT: gamma-glutamil-p- nitroanilido stroma method (improved JSCC method)
(4) ALP: p-nitrophenylphophate stroma method (improved JSCC method)
(5) Total bilirubin: Enzyme method (BOD method)
(6) Urea nitrogen: Enzyme-UVmethod (Urease-LEDH method)
(7) Creatinine: Jaffé method
(8) Glucose: Enzyme-UV method (GlcK-G6PDH method)
(9) Total cholesterol: Enzyme method (CES-CO-POD method)
(10) Triglyceride: Enzyme method (LPL-GK-G3PO-POD method)
(11) Total protein: Biuret method
(12) Albumin: BCG method
(13) A/G ratio: Calculated from (11) and (12)
(14) Calcium: OCPC method
(15) Inorganic phosphate: Enzyme method (PNP-XOD-POD method)
(16) Sodium (Na): Ion selective electrode method
(17) Potassium (K): Ion selective electrode method
(18) Chloride (Cl): Ion selective electrode method
Instrument used for measurement: HITACHI 736-10 type, Hitachi Ltd.

6. Urinalysis
Using fresh urine collected from 10 males at day 87 and 10 females at day 88 of each group, the following parameters were examined.
In the results, changes attributable to dosing of test substance were not observed. Therefore, other parameter and the urinalysis of recovery period were not examined.

Parameter Method
(1) pH: Test paper method (Multisticks, Bayer Sankyo Co.)
(2) Protein: Test paper method (Multisticks, Bayer Sankyo Co.)
(3) Glucose: Test paper method (Multisticks, Bayer Sankyo Co.)
(4) Ketone body: Test paper method (Multisticks, Bayer Sankyo Co.)
(5) Bilirubin: Test paper method (Multisticks, Bayer Sankyo Co.)
(6) Occult blood: Test paper method (Multisticks, Bayer Sankyo Co.)
(7) Urobilinogen: Test paper method (Multisticks, Bayer Sankyo Co.)
Instrument: Clinitech 100, Bayer Sankyo Co.

7. Ophthalmologic examination
Anterior eye, optic media and fundus oculi were investigated using slit lamp (SL-14, Kowa Co.) and fundus camera (GENESIS K9L29, Kowa Co.) for all male at the day before dosing and all female at two days before dosing during quarantine period, and for male at day 88 and female at day 89 of control group and all 1000 mg/kg group during dosing period.
The investigation of optic media and fundus oculi was conducted after ocular instillation of mydriatic (Mydrin-P,Santen Pharmaceutical Co., Ltd.).
In the results, changes attributable to dosing of test substance were not observed. Therefore, the investigation in all male and female of 40 and 200mg/kg group during dosing period and recovery period were not conducted.

Sacrifice and pathology:

(1) Organ weights
Organs indicated below from all animals were weighed using an electronic balance (AEG-120: Shimadzu Corporation). In addition, relative organ weights (ratio to body weight) were calculated based on the body weights at necropsy. Weight of pituitary and thyroid were weighed after formalin fixation.

Brain, heart, liver, kidneys, adrenals, thymus, spleen, testes, epididymis, ovaries, uterus, pituitary, thyroid, lung.

(2) Macroscopic pathology
All animals were euthanized by exsanguination after cutting the abdominal aorta, and necropsied.

(3) Histopathology
The following organs, tissues were collected from all animals, fixed and preserved in 10 vol% neutral phosphate-buffered formalin. However, eye balls and harderian gland were fixed in Davidson’s fluid, and testes and epididymis were fixes in Bouin's fluid.

Brain, spinal cord (cervical cord, center part of thoracic spinal cord, lumbar cord), pituitary, thyroid and parathyroid(both), thymus, trachea and lungs, heart, main artery, glandula salivaria (both), liver, spleen, kidney (both),adrenal (both), pancreas, testes (both), epididymis (both), ventral prostate, seminalvesicle, ovary (both),uterus, vagina, skin, gullet, stomach, duodenum, jejunum, ileum, cecum, colon, rectum, bladder, submandibular lymph node, mesenteric lymph node, mammary gland. tailor muscle and sciatic nerve (one side), sternum and bone marrow, eye ball and harderian gland (both), femur (including joint) and sciatic nerve (one side), exorbital lacrimal gland (both), macroscopic lesions.

Haematoxyline and eosin stained sample were prepared routinely on all of the above organs/tissues from the control and all male and female animals of 1000 mg/kg group, lung, liver and kidney from all male and female animals of 40 and 200 mg/kg group, and abnormal sites of all animals including control are examined under microscope.

As a result, further investigation to lung, kidney and pituitary was performed.

Other examinations:

None

Statistics:

The metrical data was analyzed by multiple comparison method for the statistical significance. Namely, the homogeneity of variance was examined by Bartlett test, then, one way analyses of variance were conducted where the variances were shown to be homogenous, or Kruskal-Wallis tests were conducted where the variances were shown to be unequal. Analysis for significant differences by Dunnett’s test or by Dunnett multiple comparison was conducted where significant difference was observed.

The enumeration data was analyzed by Chi-square verification of a x b. Differences between the control group and the dose groups were analyzed by Chi-square verification of Armitage where the significant difference was shown.

The parameters indicated below were statistically analyzed. The results of clinical observations, ophthalmologic examination and the histopathological examination were not analyzed statistically.

Multiple comparisons: body weight, food intake, haematology data, blood biochemistry data, organ weights.

Chi-square test verification: Urinalysis, histopathology

Clinical signs:

effects observed, treatment-related

Description (incidence and severity):

Transient ataxia of gait and salivation in male and female of 200 and 1000 mg/kg group and a decrease in locomotor activity in male and female of 1000 mg/kg group were observed. The frequency of observations of transient ataxia at 200 and 1000 mg/kg/day decreased as the administration period went by.

Mortality:

mortality observed, treatment-related

Description (incidence):

Transient ataxia of gait and salivation in male and female of 200 and 1000 mg/kg group and a decrease in locomotor activity in male and female of 1000 mg/kg group were observed. The frequency of observations of transient ataxia at 200 and 1000 mg/kg/day decreased as the administration period went by.

Body weight and weight changes:

effects observed, treatment-related

Description (incidence and severity):

Decrease in weight in female of 1000 mg/kg at days 78, 85 and 90 was observed.

Food consumption and compound intake (if feeding study):

effects observed, treatment-related

Description (incidence and severity):

There were no changes considered to be attributable to dosing of test substance.

Food efficiency:

not specified

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

not specified

Ophthalmological findings:

effects observed, treatment-related

Description (incidence and severity):

There were no changes considered to be attributable to dosing of test substance.

Haematological findings:

effects observed, treatment-related

Description (incidence and severity):

There were no changes considered to be attributable to dosing of test substance.

Clinical biochemistry findings:

effects observed, treatment-related

Description (incidence and severity):

Increase in total cholesterol in female of 200 and 1000 mg/kg group, decrease in triglyceride in male of 1000 mg/kg group, in A/G ratio in male of 1000 mg/kg group were observed. Not seen in the investigation at the end of recovery period.

Urinalysis findings:

effects observed, treatment-related

Description (incidence and severity):

There were no changes considered to be attributable to dosing of test substance.

Behaviour (functional findings):

not examined

Organ weight findings including organ / body weight ratios:

effects observed, treatment-related

Description (incidence and severity):

Increase in absolute and relative liver weight in females of 1000 mg/kg group, increase in relative liver weight in males of 200 and 1000 mg/kg group, relative kidney weight and relative epididymis weight in males of 1000 mg/kg group were observed at the end of dosing period. In the investigation at the end of recovery period. Among these changes, only increase in relative liver weight in females of 1000 mg/kg group was observed, but it was reduced compared to the value at the end of dosing period. Further to this, increase in relative kidney weight was observed at the end of recovery period.

Gross pathological findings:

effects observed, treatment-related

Description (incidence and severity):

Enlarged liver in 9 males of 1000 mg/kg group, dark colored liver in 1 male of 1000mg/kg were observed at the end of dosing period. These changes were not seen in the investigation at the end of recovery period.

Histopathological findings: non-neoplastic:

effects observed, treatment-related

Description (incidence and severity):

Centrilobular hypertrophy of hepatocytes in 2 females of 200 mg/kg group, 8 male and all female of 1000 mg/kg group, diffuse hypertrophy of follicular epithelial cells of thyroid in 3 males and 7 females of 1000 mg/kg group, mild hyaline droplet inproximal tubular epithelial cell of kidney in 5 males of control group, 7 males of 40 mg/kg group, 6 males of 200 mg/kg group and 3 males of 1000 mg/kg group, moderate in 1 male of control group, 0 male of 40 mg/kg group, 0 male of 200 mg/kg group and 6 males of 1000 mg/kg group were observed at the end of dosing period. Among them, diffuse hypertrophy of follicular epithelial cells of thyroid in 1 male of 1000 mg/kg group and expression of hyaline droplet in proximal tubular epithelial cell of kidney in 7 male of control group and 4 male of 1000mg/kg group were observed at the end of recovery period.
However, centrilobular hypertrophy of hepatocytes is considered an adaptive response, hypertrophy of follicular epithelial cells of thyroid was caused by hypertrophy of hepatocytes and hyaline droplet is known as specific symptom to male rat. Therefore these are not considered as adverse effects.

Histopathological findings: neoplastic:

not specified

Dose descriptor:

NOAEL

Effect level:

200 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

female

Basis for effect level:

other: Non-reversible increased relative kidney and liver weight at 1000 mg/kg/day. No associated histopathological changes.

Dose descriptor:

NOAEL

Effect level:

1 000 mg/kg bw/day (nominal)

Based on:

test mat.

Sex:

male

Basis for effect level:

other: Highest dose level tested.

Critical effects observed:

not specified

Conclusions:

In a 90-day repeated dose toxicity study with dicyclopentylsilanediol, conducted according to a protocol equivalent to OECD Test Guideline 408 and in compliance with GLP (certificate not included), the No Observed Effect Level (NOEL) was reported to be 40 mg/kg w/day based on clinical signs (transient ataxia, decreased locomotor activity), changes in clinical chemistry, organ weights and histopathological findings. Examination of the data indicates that for the purposes of hazard assessment the No Observed Adverse Effect Level (NOAEL) for females was 200 mg/kg bw/day based on increased kidney weight at 1000 mg/kg bw/day which was not completely reversed at the end of a 14-day recovery period. There were no associated histopathological changes in the kidneys in females. The NOAEL for males was 1000 mg/kg bw/day.

Executive summary:

The following evaluation of the pathological findings was prepared by the REACH data submitter:

Blood chemistry:
High and medium dose females showed increased Total Cholesterol and no signicant changes  of Triglyceride at the end of exposure period. Total Cholesterol increase showed a strong tendency for reversibilty. At the end of recovery period no significant differences were found when compared with control group animals.

Male animals showed no significant changes of Total Cholesterol at the end of exposure and recovery period. High dose males showed a decrease of triglyceride of low statistical signifcance at the end of the exposure period which showed tendency for reversibilty at the end of the recovery period. The value was still below the control group but not statistically significant.

Total organ weight
No statistical signifcant changes of organ weight were found in male animals at any dose level.

High dose females showed a statistically significant increase of liver weight at the end of exposure period. There was no significant difference of high dose female liver weight at the end of recovery period when compared with the control group.

Relative organ weight
Relative liver weight was statistically significantly increased in male medium and high dose groups. Relative kidney weight was increased only in the male high dose group. Both effects were reversible in males as there were no significant differences compared to control group animals at the end of the recovery period.

High dose female animals showed statistically signicant increase of liver weight at the end of exposure and recovery period. But there is a clear tendency for reversibility shown by the decrease of liver weight at the end of recovery when compared with the liver weight at the end of exposure.

Relative kidney weight showed an increase of low statistical significance at the of recovery period but not at the end of exposure period.

Histopathological findings
Centrilobular hepatocyte hypertrophy (slight (5 animals) and moderate (3 animals)), and hyaline droplets in proximal tubules (slight (3 animals ) and moderate (6 animals)), were found in high dose males. Also high dose females showed centroilobular hepatocyte hypertrophy (slight (5 animals ) and moderate (5 animals)) degree. No significant kidney changes were found in female animals.

At the end of the recovery period no statistically significant differences were found between the high dose and control group.  


Summary and determination of NOAEL
At the end of the exposure period there were dose-dependent test item-related effects on kidney and liver, reflected especially by an increase of absolute and particularly relative organ weight. These weight changes were associated only in females with changes of total cholesterol in high and medium dose group, and in high dose males with a decrease of triclyceride. Significant histopathological changes of liver were only found in high dose male and female animals and significant histopathological kidney changes were only found in high dose animals.  

All effects observed in the study showed strong tendency for reversibility as they were not found at the end of recovery period. Only high dose female animals showed at the end of the recovery period still a significant increase of relative liver and kidney weight. No increase of absolute and relative liver and kidney weight  was found in medium dose females at the end of exposure period.

Based on the increase of relative kidney and liver weight  (which were not associated with significant histopathological changes) in high dose females at the end of recovery period  the NOAEL is 200 mg/kg bw in female animals. The NOAEL for male animals is 1000 mg/kg bw.  

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

230 mg/kg bw/day

Study duration:

subchronic

Species:

rat

System:

urinary

Organ:

kidney

Additional information

Three 28-day oral gavage studies and two oral shorter studies (10 and 7 days) are available for dicyclopentyl(dimethoxy)silane (CAS 126990-35-0), all with a reliability score of 1, and all reporting a NOAEL of at least 1000 mg/kg bw/day. The key study was selected as it was the most recent study with the most comprehensive investigations. For the inhalation route there was one 4-day vapour inhalation study in which there were no systemic effects, but the findings might indicate that the test substance has potential to cause local irritation of the respiratory tract. No 90-day studies are available for the registered substance, but a 90-day oral gavage study is available for the silanol hydrolysis product, dicyclopentylsilanediol.

In the key 28-day oral gavage study conducted according to OECD Test Guideline 407 and in compliance with GLP (Huntingdon Life Sciences Ltd., 1995a), the NOAEL for dicyclopentyl(dimethoxy)silane was at least 1000 mg/kg bw/day in rats, as no treatment-related toxic effects relevant to humans were observed at any dose tested.

A treatment-related effect was observed in the liver of high dose female rats. Minimal centrilobular hepatocyte hypertrophy was observed for three rats with associated macroscopic liver enlargement for two rats and increased group mean liver weight. Possible associated biochemical changes (higher cholesterol and triglycerides, lower glucose, alanine aminotransferase levels and aspartate aminotransferase) were recorded. This liver finding was not present at the end of the two-week recovery period and was considered (by the study authors) to be adaptive in nature and not a toxic effect. Therefore this effect has been excluded from considerations for the NOAEL.

The finding of a minimal degree of eosinophilic inclusions in cortical tubules was observed in the kidneys of male rats of the high dose group. This is characteristic of light hydrocarbon nephropathy syndrome, and whilst treatment-related, is not relevant to humans. Therefore this effect is excluded from considerations for the NOAEL.

Lower than control lymphocyte were recorded for the high dose rats and females of the mid dose group, at the end of the treatment period. There were no associated pathological changes, the effect was not observed at the end of the recovery period and the animals were in good general health. Therefore this effect is excluded from considerations for the NOAEL.

In a 90-day oral gavage study with the silanol hydrolysis product, dicyclopentylsilanediol (CAS 211495-85-1), the NOAEL was concluded to be 200 mg/kg bw/day in rats (Mitsubishi Chemical Safety Institute, 2000). Treatment-related adaptive effects on the liver, similar to those seen with the parent substance in the 28-day study were observed and associated biochemical changes were also seen. During the dosing period, transient ataxia and salivation in males and females of the 200 and 1000 mg/kg groups, and a decrease in locomotor activity in males and females of the 1000 mg/kg group were observed. The frequency of observations of ataxia decreased throughout the dosing period.

High and medium dose females showed increased total cholesterol and no significant changes of triglyceride at the end of exposure period. Total cholesterol increase showed a strong tendency for reversibility. At the end of recovery period no significant differences were found when compared with control group animals.

Male animals showed no significant changes to total cholesterol at the end of exposure and recovery period. High dose males showed a decrease of triglyceride of low statistical significance at the end of the exposure period which showed tendency for reversibility at the end of the recovery period. The value was still below the control group but not statistically significant. No statistically significant changes to absolute organ weights were found in male animals at any dose level. Relative liver weight was statistically significantly increased in males in the medium and high dose groups. Relative kidney weight was increased only in the male high dose group. Both effects were reversible in males as there were no significant differences compared to control group animals at the end of the recovery period.

High dose females showed a statistically significant increase of absolute and relative liver weight at the end of exposure period. There was no significant difference of high dose female liver weight at the end of recovery period when compared with the control group. But there is a clear tendency for reversibility shown by the decrease of liver weight at the end of recovery when compared with the liver weight at the end of exposure. Relative kidney weight showed an increase of low statistical significance at the end of recovery period but not at the end of exposure period.

Centrilobular hepatocyte hypertrophy (slight (5 animals) and moderate (3 animals)), and hyaline droplets in proximal tubules (slight (3 animals) and moderate (6 animals)), were found in high dose males. Also high dose females showed centrilobular hepatocyte hypertrophy (slight (5 animals) and moderate (5 animals)) degree. Hyaline droplet formation is relevant only for male rats and is therefore not considered as adverse for hazard assessment purposes. No significant kidney histopathological changes were found in female animals. At the end of the recovery period no statistically significant differences were found between the high dose and control group.

At the end of the exposure period there were dose-dependent test substance-related effects on kidney and liver, reflected especially by an increase of absolute, and particularly relative, organ weight. These weight changes were associated only in females with changes of total cholesterol in high and medium dose group, and in high dose males with a decrease of triclyceride. Significant histopathological changes of liver were only found in high dose male and female animals and significant histopathological kidney changes were only found in high dose animals.  All effects observed in the study showed strong tendency for reversibility as they were not found at the end of recovery period. Only high dose female animals had a significant increase of relative liver and kidney weight at the end of the recovery period. No increase of absolute and relative liver and kidney weight was found in medium dose females at the end of exposure period.

The study authors reported the No Observed Effect Level of the substance to be 40 mg/kg bw/day based on the transient clinical effects at this dose level. The author of this review considers that the No Observed Adverse Effect Level (NOAEL) for dicyclopentylsilanediol relevant for hazard assessment and risk characterisation is 200 mg/kg bw/day for females based on non-reversible increased relative kidney weight at 1000 mg/kg bw/day. The NOAEL for males was 1000 mg/kg bw/day.

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 dicyclopentyl(dimethoxy)silane is evaluated point by point

Read-across hypothesis

The toxicity of dicyclopentyl(dimethoxy)silane and dicyclopentylsilanediol after oral application is similar. Dicyclopentyl(dimethoxy)silane hydrolyses very rapidly in the stomach to dicyclopentylsilanediol and methanol.

Analogue approach justification

(a) Structural similarity

Both the registration and read-across substances are structurally similar, containing two cyclopentyl sidechains bound to silica and, following rapid hydrolysis in the gut, two silanol (-SiOH) groups. They form part of a small analogue group which also includes the direct pre-cursor of dicyclopentylsilanediol, dicyclopentyl(dimethoxy)silane.

(b) Similar physicochemical characteristics

The key physicochemical parameters are summarised below.

CAS Number	126990-35-0	017865-32-6	211495-85-1
Chemical Name	Dicyclopentyl (dimethoxy)silane	Cyclohexyl dimethoxymethylsilane	Dicyclopentylsilanediol
Si hydrolysis product	Dicyclopentylsilanediol	Cyclohexylmethylsilanediol	N/A
Molecular weight	228.41	188.34	200.36
log Kow (parent)	5 - 5.5	4.3	3.1
log Kow (silanol hydrolysis product)	3.1	1.9	N/A
Water sol (parent)	5.32 mg/l	151 mg/l	2.55E+03 mg/l
Water sol (silanol hydrolysis product))	2.55E+03 mg/l	3.24E+04 mg/l	N/A
Vapour pressure (parent)	4 Pa	63 Pa	2.9E-4
Hydrolysis t1/2 at pH 7 and 25°C	19 hours	19 hours (read-across)	N//A

 

The registered substance, dicyclopentyl(dimethoxy)silane, hydrolyses in contact with water, generating dicyclopentylsilanediol and methanol. At pH 7 and 25°C the rate of hydrolysis is moderate, with a half-life of 19 hours. However at acidic pH the reaction is rapid. The half-life at pH 4 and 25°C was determined to be 0.17 hours and would be considerably shorter at lower pH and higher temperature in the stomach following oral dosing. Compared to the typical gastric emptying half-life for liquids in the order of 11 - 30 minutes (RIVM, http://www.rivm.nl/interspeciesinfo/intra/human/stomach/db_human_stomach.jsp), several to many hydrolysis half-lives would therefore have occurred and absorption in the intestine would almost exclusively relate to hydrolysis products.

 (c) Similar toxicokinetics

Given the low vapour pressure of dicyclopentyl(dimethoxy)silane, significant inhalation exposure is not expected and any repeated dose testing with the parent substance would therefore be performed by the oral route. In view of the rapid hydrolysis following oral dosing, it is therefore appropriate to read-across the available data for the silanol hydrolysis product to address the potential for systemic organ toxicity. In the event of any exposure to humans by the inhalation route, the higher log K_ow value for the parent (5.5 compared to 3.1 for dicyclopentylsilanediol), means that uptake across the respiratory tract is more favourable for the hydrolysis product (EU Risk Assessment Technical Guidance Document, Part 1, 2003). Furthermore, any systemically absorbed parent material will continue to hydrolyse in vivo. The saturated vapour concentration of dicyclopentyl(dimethoxy)silane in air is approximately 370 mg/m³, based on a vapour pressure of 4 Pa, thus the maximum theoretically achievable daily dose for a standard 6-hour inhalation study exposure period is approximately 110 mg/kg bw/day (rat default respiratory volume 0.29 m³/kg bw for a 6-hour period, REACH Technical Guidance Chapter R.8). Since the oral study included doses up to 1000 mg/kg bw/day (1140 mg/kg bw/day as parent), the dose levels tested by the oral route therefore exceed the maximum dose that could be achieved by the inhalation route and can be considered as a worst-case with respect to systemic toxicity. There was no evidence of systemic effects in a limited 4-day inhalation study (DCC, 1993).

 (d) Similar acute toxicity

Acute oral toxicity studies are available for both dicyclopentyl(dimethoxy)silane (Section 5.2.1) and the dicyclopentylsilanediol (Mitsubishi Chemical Safety Institute, study owned by Japanese authority, http://dra4.nihs.go.jp/mhlw_data/jsp/ResultPageENG.jsp?condition_item=%95%A8%8E%BF%96%BC%8F%CC&condition_keyword=Dicyclopentylsilanediol&condition_type=*), in which the LD₅₀(rat) was >2000 mg/kg bw. No clinical signs or evidence of organ toxicity were observed with the registered substance in the key study (Safepharm Laboratories Ltd, 1995a), although reversible clinical signs were seen in some animals in one of the supporting studies (Huntingdon Research Centre, 1995a). For dicylopentylsilanediol one female of the 2000 mg/kg group died. Clinical signs observed were as follows: ataxic gait, decrease in locomotor activity, abnormal gait, crouching, a prone, lateral or supine position, hypothermia, and bradypnea. No changes attributable to the administration of dicyclopentylsilanediol were observed in the body weight or necropsy findings. The observed clinical signs for the hydrolysis product are indicative of a narcotic effect which was not observed at the maximum dose level of 2000 mg/kg bw with the parent material in all available acute studies, therefore read-across of the repeated-dose study could be considered a worst case.

 (e) Similar repeated dose toxicity

Like the acute toxicity endpoints, in a number of existing 28-day repeated dose studies with both dicyclopentyl(dimethoxy)silane and cyclohexyl(dimethoxy)methylsilane, a similar pattern of mild and often non-adverse effects was seen when compared with the findings in the 90-day study for dicyclopentylsilanediol.

Dicyclopentyl(dimethoxy)silane was tested in a four week oral toxicity in the rat with a two week recovery period (Huntingdon Life Sciences Ltd, 1995). Dose levels were 0, 15, 150 and 1000 mg/kg bw/day. The high dose group showed increased triglyceride and cholesterol. High and medium dose groups showed liver weight increases and the high dose group also had hypertrophy of hepatocytes. Kidneys in the high dose group showed eosinoophilic inclusions in the cortical tubes. All changes were considered to be reversible. The NOEL was 15 mg/kg bw/day and the NOAEL was 1000 mg/kg bw/day.

Additional 28-day studies are available for both cyclohexyl(dimethoxy)methylsilane and dicyclopentyl(dimethoxy)silane, showed NOAEL ≥1000 mg/kg bw/day. In these studies some adaptive liver changes of reversible character are also described.

The liver and kidney effects observed in sub-acute studies with the parent materials are similar to each other and to those seen in the sub-chronic study with dicyclopentylsilanediol, described above.

No adverse effects on the reproductive organs examined in these studies were reported in any case.

Column 2 of REACH Annex XI states that the sub-chronic toxicity study does not need to be conducted if "a substance undergoes immediate disintegration and there are sufficient data on the cleavage products (both for systemic effects and effects at the site of uptake) ".

Methanol has been extensively studied in rodents and primates by both oral and inhalation routes and an existing EU IOEL value of 260 mg/m³(8-hour time weighted average) has been established (Directive 2006/15/EC).

The reported NOAEL methanol for rats (90-day, oral) is 500 mg/kg bw/day (OECD SIAR, 2004, citing US EPA IRIS database) and does not contribute to the effects seen in 28 day oral studies with dicyclopentyl(dimethoxy)silane. Effects seen in the 90-day study with the silanol hydrolysis product, dicyclopentylsilanediol, are comparable to those seen in the 28-day studies with parent material and at the NOAEL of 200 mg/kg bw/day no effects from exposure to methanol would be expected in rats.

It is therefore reasonable to include a molecular weight correction to establish the relevant dose level of parent dicyclopentyl(dimethoxy)silane that would provide 200 mg/kg bw/day of dicyclopentylsilanediol. The NOAEL for dicyclopentyl(dimethoxy)silane is therefore approximately 230 mg/kg bw/day. However, no further molecular weight correction is introduced for read-across to cyclohexyl(dimethoxy)methylsilane.

Conclusion

The close correspondence of existing toxicological study results, as well as physicochemical properties means that the read-across is justified. Available results for other key endpoints such as ecotoxicity, biodegradation and bioaccumulation (see IUCLID Section 13) strengthen this justification.

Justification for classification or non-classification

Based on the available data, dicyclopentyl(dimethoxy)silane is not classified for specific target organ toxicity following repeated exposures according to Regulation (EC) No 1272/2008.