Registration Dossier

No reproductive toxicity studies are available for dichlorosilane, therefore good quality data for the condensed hydrolysis product, synthetic amorphous silica (SAS) have been read-across.

In a 2-generation reproductive toxicity study (Wolterbeek et al. 2015) conducted according to OECD TG416 and GLP, Wistar rats were administered SAS (described as NM-200 synthetic amorphous silica) (in highly deionised water containing 10% fetal bovine serum) at doses of 100, 300 and 1000 mg/kg bw/day by oral gavage. The dosing schedule and investigations were conducted according to the OECD TG. There were no adverse findings in parental animals or offspring in any generation. Therefore, the NOAEL for general toxicity and reproductive toxicity was ≥1000 mg/kg bw/day.

Reference

Endpoint:: two-generation reproductive toxicity
Type of information:: experimental study
Adequacy of study:: key study
Study period:: No data
Reliability:: 2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:: guideline study
Qualifier:: according to guideline
Guideline:: OECD Guideline 416 (Two-Generation Reproduction Toxicity Study)
GLP compliance:: yes
Limit test:: no
Species:: rat
Strain:: Wistar
Sex:: male/female
Details on test animals or test system and environmental conditions:: TEST ANIMALS
- Source: Charles River Deutschland (Sulzfeld, Germany)
- Age at study initiation: (P) no data (4-5 weeks at purchase); (F1): 22 days
- Weight at study initiation: No data
- Fasting period before study: Not relevant
- Housing: Macrolon cages with a bedding of wood shavings and strips of paper as environmental enrichment. During mating a single female and male were housed together. Once mated the females were housed individually, and later they were housed individually with their litters.
- Diet : Ad libitum
- Water: Ad libitum
- Acclimation period: No data

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 2°C
- Humidity (%): 45-65%
- Air changes (per hr): approximately 10 changes per hour
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: No data
Route of administration:: oral: gavage
Vehicle:: other: highly deionised water containing 10% fetal bovine serum
Details on exposure:: PREPARATION OF DOSING SOLUTIONS: Once per week throughout the study, seven bottles per dosing group were prepared, each containing the relevant amount of test substance. On each day, the required amount of vehicle was added to achieve concentrations of 0, 10, 30 and 100 mg/ml test substance and stirred for at least 60 minutes.
Details on mating procedure:: - M/F ratio per cage: 1:1
- Length of cohabitation: Up to 2 weeks
- Proof of pregnancy: Sperm in vaginal smear referred to as day 0 of pregnancy
- After successful mating each pregnant female was caged (how): Individually (no further details)
Analytical verification of doses or concentrations:: yes
Details on analytical verification of doses or concentrations:: At various weeks during the study, samples were taken from each of the dosing formulations for analytical investigation of hydrodynamic diameters of the silica particles.
Details on study schedule:: - F1 parental animals not mated until at least 10 weeks after selected from the F1 litters.
- Selection of parents from F1 generation when pups were 22 days of age.
- Age at mating of the mated animals in the study: at least 10 weeks
Dose / conc.:: 100 mg/kg bw/day (actual dose received)
Dose / conc.:: 300 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:: 28 (F0), 4 (F1, F2)
Control animals:: yes, concurrent vehicle
Details on study design:: - Dose selection rationale: Random
Positive control:: None
Parental animals: Observations and examinations:: CAGE SIDE OBSERVATIONS: Yes, throughout the study, all animals were checked daily for clinical signs and abnormal behaviour.

DETAILED CLINICAL OBSERVATIONS: No data
- Limited information on this.

BODY WEIGHT: Yes
- Time schedule for examinations: The body weight of all males and females was recorded weekly during premating, and for males, weekly thereafter. Mated females were weighed on gestation days 0, 4, 7, 10, 14, 17 and 21 and during lactation on post-natal days 1, 4, 7, 10, 14, 17 and 21. Animals were also weighed on their scheduled necropsy day.

FOOD CONSUMPTION: During the premating period, food consumption was measured weekly for each cage. Individual food consumption of all mated females were recorded from gestation days 0-4, 4-7, 7-10, 10-14, 14-17 and 17-21 and for all females with live pups on post-partum days 1-4, 4-7, 7-10, 10-14, 14-17 and 17-21.

WATER CONSUMPTION: No
Oestrous cyclicity (parental animals):: Three weeks prior to the end of the premating period of the F0 and F1 generation, vaginal smears were made from each female to evaluate the estrous cycle length and normality.
Sperm parameters (parental animals):: Parameters examined in F0 and F1 male parental generations: testes weight, epididymis weight, caudal epididymal sperm count, sperm motility and testicular sperm count
Litter observations:: STANDARDISATION OF LITTERS
- Performed on day 4 postpartum: yes
- Maximum of 8 pups/litter (4/sex/litter as nearly as possible); excess pups were killed and discarded.

PARAMETERS EXAMINED
The following parameters were examined in F1 / F2 offspring: number and sex of pups, stillbirths, live births, postnatal mortality, presence of gross anomalies, weight gain, physical or behavioural abnormalities

GROSS EXAMINATION OF DEAD PUPS: a necropsy was performed on stillborn pups and pups that died during lactation.
Postmortem examinations (parental animals):: SACRIFICE
It is not clear from the publication when scheduled sacrifices occurred. The study is stated to be according to OECD TG 416, so timings are assumed to follow this guideline, i.e. F0 and F1 males dosed until they are no longer needed for assessment of reproductive effects and females are sacrificed after weaning of their litter.

GROSS NECROPSY
- Gross necropsy consisted of external and internal examinations

HISTOPATHOLOGY / ORGAN WEIGHTS
The adrenals, brain, epididymides, kidneys, liver, ovaries, pituitary gland, prostate, seminal vesicles with coagulating glands, spleen, testes, thyroid, uterus with cervix (after counting of implantation sites), vagina and all gross lesions were weighed (except vagina) and preserved for microscopic examination for the control and the highest dose groups and on macroscopic abnormalities of all groups. Also, reproductive organs of F0 and F1 males who failed to sire, and of the non-mated/non-pregnant females from the low and mid dose groups were examined microscopically.
Postmortem examinations (offspring):: SACRIFICE
- The F1 offspring not selected as parental animals and all F2 offspring were sacrificed at 21 days of age.
- Of the remaining F1 pups, one male and one female from each litter were selected for a thorough necropsy, and the brain, spleen and thymus were weighed. Sexual maturation was studied by scoring the day of vaginal opening in females and testes descent and preputial separation in males from post-natal days 31, 21 and 39, respectively.

HISTOPATHOLOGY / ORGAN WEIGHTS
As for parental animals.
Statistics:: For some offspring viability data, sexual maturation, some sperm parameters and organ weights: Anova followed by Dunnett's multiple comparison test.
For some offspring data: Fisher's exact test.
For precoital time, gestation time and post-implantation loss per animal: Kruskal-Wallis + Mann-Whitney U test.
For some offspring data: Kruskal-Wallis followed by Dunnett's multiple comparison.
For some sperm parameters: Kruskal-Wallis non-parametric analysis of variance followed by Mann-Whitney U test.
Reproductive indices:: Mating, fertility, fecundity, gestation
Offspring viability indices:: Live birth, viability (day 4), viability (day 21)
Clinical signs:: no effects observed
Body weight and weight changes:: no effects observed
Food consumption and compound intake (if feeding study):: no effects observed
Organ weight findings including organ / body weight ratios:: no effects observed
Histopathological findings: non-neoplastic:: no effects observed
Other effects:: not examined
Reproductive function: oestrous cycle:: no effects observed
Reproductive function: sperm measures:: no effects observed
Reproductive performance:: no effects observed
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 adverse effects were observed in parental animals.
Critical effects observed:: no
Clinical signs:: no effects observed
Mortality / viability:: no mortality observed
Body weight and weight changes:: no effects observed
Sexual maturation:: no effects observed
Organ weight findings including organ / body weight ratios:: no effects observed
Gross pathological findings:: no effects observed
Histopathological findings:: no effects observed
Dose descriptor:: NOAEL
Generation:: F1
Effect level:: >= 1 000 mg/kg bw/day (actual dose received)
Based on:: test mat.
Sex:: male/female
Basis for effect level:: other: No adverse effects were observed in any of the F1 offspring.
Critical effects observed:: no
Dose descriptor:: NOAEL
Generation:: F2
Effect level:: >= 1 000 mg/kg bw/day (actual dose received)
Based on:: test mat.
Sex:: male/female
Basis for effect level:: other: No adverse effects were observed in any of the F2 offspring.
Critical effects observed:: no
Reproductive effects observed:: no
Conclusions:: Based on a two-generation reproductive toxicity study in Wistar rats conducted in accordance with OECD TG 416 and to GLP the NOAEL for reproductive toxicity of synthetic amorphous silica was ≥1000 mg/kg bw/day as no adverse effects on reproductive parameters were observed up to the highest dose tested. The NOAEL for general systemic toxicity was also ≥1000 mg/kg bw/day as there were no signs of adverse effects in any of the parental animals in any generation up to the highest dose tested.

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 000 mg/kg bw/day

Study duration:

subchronic

Species:

rat

Quality of whole database:

The key study was conducted according to OECD TG 416 and to GLP, without any significant deviations, and is therefore a suitable key study.

Endpoint conclusion:

no study available

Endpoint conclusion:

no study available

There are no adequate reproductive toxicity data on dichlorosilane so good quality data for the hydrolysis products polysilicic acid (equivalent to synthetic amorphous silica) have been used to assess the potential for adverse effects on fertility following exposure to dichlorosilane.

Overview

It is considered not to be ethical to perform reproductive toxicity testing with dichlorosilane by any route of exposure due to its known corrosive properties, which dominate the toxicity profile of this substance. Following repeated oral dosing, the corrosive nature of the product could affect the lining of the stomach, giving rise to hyperplasia and a subsequent reduced food intake. This would confound the interpretation of any systemically driven effects. A guideline-compliant repeated-dose inhalation study should elicit systemic toxicity at the highest test concentration. Since the local corrosive effects of dichlorosilane would be significant, a valid inhalation study according to the relevant guidelines is technically not feasible to do. It is also unlikely that any systemic effects would be seen at dose levels made sufficiently low (< 10 ppm) to prevent the known corrosive effects and/or distress in the test species. This has been confirmed in a 28-day inhalation study with another chlorosilane, dichloro(dimethyl)silane (WIL, 2014) in which there were no effects of treatment on clinical signs, body weight or food consumption that would indicate a systemic effect. Furthermore, the histopathology in the study indicated that the effects in the upper respiratory tract were similar to HCl. It is therefore concluded that HCl will dominate the inhalation toxicity profile of dichlorosilane.

With regard to the dermal and inhalation routes, due to the known corrosive effects of dichlorosilane, appropriate H-phrases and P-statements are included in the labelling, meaning that repeated skin and inhalation exposure is not expected. Any accidental skin contact or inhalation exposure could cause severe local effects but would be unlikely to cause any systemic effects.

ORAL ROUTE

SYSTEMIC EFFECTS

There are no adequate reproductive toxicity data on dichlorosilane so good quality data for synthetic amorphous silica (CAS 112926-00-8) have been used to assess the reproductive toxicity of dichlorosilane.

Dichlorosilane, like all inorganic chlorosilanes, is a severely corrosive substance that is decomposed by water, producing silicic acid and HCl. The reaction is highly exothermic (Merck, 2013). Hydrolysis half-life is approximately 5 seconds at 25°C and pH 4, 7 and 9. The initial products of hydrolysis are hydrogen chloride and silanediol. The silanediol is expected to react rapidly to produce hydrogen and monosilicic acid. Hydrogen would be released to the atmosphere immediately.

Monosilicic acid condenses to insoluble polysilicic acid [equivalent to synthetic amorphous silica (SAS)] at concentrations higher than 100 -150 mg/l ‘SiO₂equivalent’ in water (Holleman-Wiberg, 2001). At very high concentration, polysilicic acid can condense to silicon dioxide (SiO₂). The hydrolysis products of hydrochloric acid and (poly)silicic acid are significant for the chemical safety assessment (CSR).

Monosilicic acid and polysilicic acid are naturally occurring substances which are ubiquitous in the environment. Soluble monosilicic acid is the major bioavailable form of silicon and plays an important role in the biogeochemical cycle of silicon (ECETOC, 2006). Typical background concentrations of monosilicic acid in the environment are up to 75 mg/l ‘SiO₂equivalent’ in river water and up to 14 mg/l ‘SiO₂equivalent’ in seawater (Iler, 1979).

The literature gives various values for the solubility of silicic acid, determined indirectly as ‘SiO₂equivalent’ because the soluble species cannot be directly measured:

The solubility of monosilicic acid according to Alexander et al. (1954) at 25 °C:

150 mg/l ‘SiO₂equivalent’ at pH 2.0 and pH 3.0
130 mg/l ‘SiO₂equivalent’ at pH 4.2
110 mg/l ‘SiO₂equivalent’ at pH 5.7
100 mg/l ‘SiO₂equivalent’ at pH 7.7
490 mg/l ‘SiO₂equivalent’ at pH 10.3
1120 mg/l ‘SiO₂equivalent’ at pH 10.6

The solubility of monosilicic acid according to Goto and Okura (1953) at 25 °C:

120 mg/l ‘SiO₂equivalent’ at pH 2.0
150 mg/l ‘SiO₂equivalent’ at pH 7.0

The solubility of monosilicic acid according to Elmer and Nordberg (1958) at neutral pH:

170 mg/l ‘SiO₂equivalent’ at 35 °C
270 mg/l ‘SiO₂equivalent’ at 65 °C
465 mg/l ‘SiO₂equivalent’ at 95 °C

With the described properties of dichlorosilane in mind it is not possible to conduct reproductive toxicity studies in experimental animals due to the corrosive nature of this substance. Nor can the hydrolysis product, monosilicic acid, be tested as it is not possible to isolate this substance. However, from physicochemical properties, it is known that following ingestion of dichlorosilane, the conditions in the stomach are such that following an initial rapid hydrolysis to soluble monosilicic acid, this monomer will start to condense to form insoluble polysilicic acid (equivalent to SAS). This condensation will start to occur once the concentration of monosilicic acid reaches approximately 150 mg/l in the gastric juices.

Monosilicic acid (soluble silica) undergoes condensation reactions in solution at about 100 -150 mg/l ‘SiO₂ equivalent’. The solubility of monosilicic acid in water is 150 mg/l ‘SiO₂equivalent'.

Following dosing by oral gavage, partitioning will occur between the dose vehicle and the aqueous environment in the stomach.

Mass dosed (in mg/day) = Body weight (in kg) x dose level (in mg/kg bw/day)

Dose concentration (in mg/l) = mass dosed (in mg/day)÷volume (in l)

So, the dose level (mg/kg bw/day) required to reach the dose concentration of 150 mg/l 'SiO₂ equivalent', the estimated (conservative) maximum concentration of silicic acid that can occur in the stomach before condensation to insoluble polysilicic acid (equivalent to SAS) begins is calculated as follows:

Body weight of rat = 0.3kg

Dose level = X

Estimated aqueous volume = 0.0015 l

Dose concentration = 150 mg/l

150 mg/l = 0.3 kg x dose level (mg/kg bw/day)÷0.0015l

Dose level = 0.75 mg/kg bw/day 'SiO₂equivalent'

Therefore, based on a condensation limit of 150 mg/l, the maximum dose level that could be used in practice to ensure exposure mainly to monosilicic acid in the stomach of experimental animals is approximately 0.75 mg/kg bw/day or less of 'SiO₂ equivalent'.

A correction for molecular weight gives a maximum dose level for dichlorosilane:

Mr [dichlorosilane] = 101.01 g/mol

Mr [silicon dioxide] = 60.08 g/mol

Dose level [dichlorosilane] = [Dose level [silicon dioxide] x Mr [dichlorosilane]]

Mr [silicon dioxide]

= (0.75 mg/kg bw/day) x (101.01 g/mol)

(60.08 g/mol)

= 1.26 mg/kg bw/day

Therefore, based on a condensation limit of 150 mg/l the maximum dose level of dichlorosilane that can be dosed to ensure exposure mainly to monosilicic acid is approximately 1.26 mg/kg bw/day.

For comparison purposes, using the above calculation, the following shows the dose concentrations for the dose levels typically used in experimental animal studies (100, 300 and 1000 mg/kg bw/day).

Body weight = 0.3 kg

Total amount dosed = 30 mg

Estimated aqueous volume = 1.5 ml

Dose concentration = 20,000 mg/l

Body weight = 0.3 kg

Total amount dosed = 90 mg

Estimated aqueous volume = 1.5 ml

Dose concentration = 60,000 mg/l

Body weight = 0.3 kg

Total amount dosed = 300 mg

Estimated aqueous volume = 1.5 ml

Dose concentration = 200,000 mg/l

Therefore, dosing at these levels clearly gives a dose concentration in the stomach that far exceeds the dose at which condensation to polysilicic acid (equivalent to SAS) starts to occur. Consequently, the majority of the dose in the stomach will be present as insoluble polysilicic acid (equivalent to SAS). In all cases only approximately 150 mg/l will be present as soluble monosilicic acid.

Overall, it can be concluded that gavaging dichlorosilane at doses unlikely to cause local corrosive effects and at doses that give mainly soluble monosilicic acid (2 mg/kg bw/day or less) would be unethical based on animal usage. However, because the vast majority of a gavaged dose will rapidly condense to insoluble polysilicic acid it is appropriate to use toxicology data on SAS to address the potential for oral reproductive toxicity of dichlorosilane.

The key study for reproductive toxicity is a 2-generation reproductive toxicity study (Wolterbeek et al. 2015) conducted according to OECD test guideline 416 and in compliance with GLP. Wistar rats were administered SAS (described as NM-200 synthetic amorphous silica) (in highly deionised water containing 10% fetal bovine serum) at doses of 100, 300 and 1000 mg/kg bw/day by oral gavage. There were no adverse findings in parental animals or offspring in any generation. Therefore, the NOAEL for general toxicity and reproductive toxicity was ≥1000 mg/kg bw/day in this study.

Limited data are available regarding the reproductive toxicity in animals following oral, dermal or inhalation exposure to hydrogen chloride. However, protons and chloride ions exist as normal constituents of body fluid in animals, hence low concentrations of hydrogen chloride appear not to cause adverse effects in animals. Therefore the hydrolysis product of dichlorosilane, HCl, would not be expected to cause reproductive toxicity in experimental animals or humans following initial exposure to dichlorosilane.

References

Alexander G.B., Heston W.M. and Iler R.K. (1954) J. Phys. Chem., 58, 453.

Cotton F.A. and Wilkinson G. (1999) Advanced Inorganic Chemistry, 6^thEdition, p271

ECETOC (2006) Synthetic Amorphous Silica (CAS No. 7631-86-9), JACC REPORT No. 51

Elmer and Nordberg (1958) J. Am.Chem. Soc., 41, 517

Goto K. and Okura T. (1953) Kagaku, 23, 426.

Holleman-Wiberg, (2001) Inorganic Chemistry, Academic Press, p. 865

Iler, Ralph K. (1979) The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties and Biochemistry of Silica, Wiley, p. 13.

Jones, R. G., Wataru, A., and Chojnowski, J. (2000) Silicon-Containing Polymers: The Science and Technology of Their Synthesis, Kluwer Academic Press pp168-169

Merck Index (2013) Monograph Number. 8639 (15th Ed)

No developmental toxicity studies are available for dichlorosilane, therefore good quality data for the condensed hydrolysis product, synthetic amorphous silica (SAS) have been read-across. In a prenatal developmental study (Hofmann et al., 2015) conducted according to OECD TG 414 and to GLP, pregnant Wistar rats were administered SAS (described as NM-200 synthetic amorphous silica) (in highly deionised water containing 10% fetal bovine serum) at doses of 100, 300 and 1000 mg/kg bw/day by oral gavage on gestation days 6-19. The dosing schedule and investigations were conducted according to the OECD TG. There were no adverse, treatment-related findings in parental animals or offspring. There were several incidental fetal malformations and variations, which all occurred at a rate no larger than that of the control/historical controls, without statistical significance and without a dose-response relationship. Therefore, the NOAEL for general toxicity and developmental (including teratogenicity) toxicity was ≥1000 mg/kg bw/day.

Reference

Endpoint:: developmental toxicity
Type of information:: experimental study
Adequacy of study:: key study
Study period:: No data
Reliability:: 1 (reliable without restriction)
Rationale for reliability incl. deficiencies:: guideline study
Qualifier:: according to guideline
Guideline:: OECD Guideline 414 (Prenatal Developmental Toxicity Study)
Qualifier:: according to guideline
Guideline:: EPA OPPTS 870.3700 (Prenatal Developmental Toxicity Study)
GLP compliance:: yes
Limit test:: no
Species:: rat
Strain:: Wistar
Details on test animals or test system and environmental conditions:: TEST ANIMALS
- Source: Charles River Laboratories, Germany GmbH
- Age at study initiation: 12-15 weeks
- Weight at study initiation: 195.3- 271g
- Fasting period before study: Not relevant
- Housing: Individually in Macrolon type III cages, with a bedding of dust-free wood shavings and wooden gnawing blocks as environmental enrichment.
- Diet (e.g. ad libitum): Ad libitum
- Water (e.g. ad libitum): Ad libitum
- Acclimation period: 5 days

ENVIRONMENTAL CONDITIONS
- Temperature (°C): 22 ± 2°C
- Humidity (%): 30-70%
- Air changes (per hr): approximately 15 changes per hour
- Photoperiod (hrs dark / hrs light): 12/12

IN-LIFE DATES: No data
Route of administration:: oral: gavage
Vehicle:: other: highly deionised water containing 10% fetal bovine serum
Details on exposure:: PREPARATION OF DOSING SOLUTIONS: Dosing formulations of synthetic amorphous silica were pre-pared with highly deionized water containing 10% fetal bovine serum in order to avoid agglomeration.
Analytical verification of doses or concentrations:: yes
Details on analytical verification of doses or concentrations:: The formulations were analysed by scanning electron microscopy after shock freezing and in situ analytical ultracentrifugation.
Details on mating procedure:: - Impregnation procedure: cohoused
- If cohoused:
- M/F ratio per cage: 1-2 untreated females with 1 untreated male
- Length of cohabitation: Not stated but mating occurred between 15:30 and 7.30 on the day after cohousing started.
- Verification of same strain and source of both sexes: yes
- Proof of pregnancy: sperm in vaginal smear referred to as day 0 of pregnancy
Duration of treatment / exposure:: Gestation day 6-19
Frequency of treatment:: One dose per day
Duration of test:: Approximately 21 days
Dose / conc.:: 100 mg/kg bw/day
Dose / conc.:: 300 mg/kg bw/day
Dose / conc.:: 1 000 mg/kg bw/day
No. of animals per sex per dose:: 25 females per dose
Control animals:: yes, concurrent vehicle
Details on study design:: - Dose selection rationale: Highest dose was chosen as the limit dose according to the test guideline.
Maternal examinations:: CAGE SIDE OBSERVATIONS: Yes
- Time schedule: described as 'regular'

DETAILED CLINICAL OBSERVATIONS: No data

BODY WEIGHT: Yes
- Time schedule for examinations: described as 'regular'

FOOD CONSUMPTION AND COMPOUND INTAKE (if feeding study): Yes (described as 'regular')

WATER CONSUMPTION: No

POST-MORTEM EXAMINATIONS: Yes
- Sacrifice on gestation day 20
- Organs examined: uterus and ovaries
Ovaries and uterine content:: The ovaries and uterine content was examined after termination: Yes
Examinations included:
- Gravid uterus weight: Yes
- Number of corpora lutea: Yes
- Number of implantations: Yes
- Number of early resorptions: Yes
- Number of late resorptions: Yes
Fetal examinations:: - External examinations: Yes: all per litter
- Soft tissue examinations: Yes: half per litter
- Skeletal examinations: Yes: half per litter
- Head examinations: Yes, but no data on number examined
Statistics:: The data for food consumption, maternal, litter weight and body weight change, carcass and gravid uterus weight, number of corpora lutea and implantations, number of resorptions, number of live fetuses, percent pre- and post- implantation loss, percent live fetuses per litter, number of pups per litter, post- implantation loss, and mean placental weights were analysed by the two-sided Dunnett’s test for the hypothesis of equal means. The female mortality, number of pregnant females, and number of litters with fetal findings, were analysed by pairwise comparison of each dose group with the control group using the one-sided Fisher’s exact test for the hypothesis of equal proportions. Proportions of fetuses per litter with findings were analyzed by pairwise comparison of each dose group with the control group by a one-sided Wilcoxon test for the hypothesis of equal medians.
Details on maternal toxic effects:: Maternal toxic effects:no effects

Details on maternal toxic effects:
Results are summarised in Tables 1 and 2. There was no treatment-related mortality or clinical signs of toxicity, and there was no effect on body weight gain or food consumption. Gravid uterine weights were not influenced by treatment with SAS. No treatment-related macroscopic findings were observed at necropsy. The conception rate, mean number of corpora lutea, implantation sites, and post-implantation loss were comparable in all groups. The only minor difference to control values was pre-implantation loss (slightly higher in the groups treated with SAS); however, a compound-related effect can be excluded as treatment started after implantation.
: Key result
Dose descriptor:: NOAEL
Effect level:: >= 1 000 mg/kg bw/day (actual dose received)
Based on:: test mat.
Basis for effect level:: other: maternal toxicity
Abnormalities:: no effects observed
Details on embryotoxic / teratogenic effects:: Embryotoxic / teratogenic effects:no effects

Details on embryotoxic / teratogenic effects:
Results are summarised in Table 1. No dead fetuses were noted. The sex distribution of the fetuses was comparable in all groups. Mean fetal weights did not show any biologically relevant differences between the test substance-treated groups and the control. External malformations were recorded for one fetus each in the low- and high- dose group. Both fetuses concerned had multiple malformations. Mandibular micrognathia mirrored the severely malformed skull bones found during skeletal examination in one fetus; these findings were considered related to each other. The cleft palate observed in the other fetus is present in the historical control data at a comparable incidence. Both findings were considered to be spontaneous in nature and without a relation to dosing. The total incidence of external malformations in treated animals did not differ significantly from that of the control group. One soft tissue malformation (i.e. supernumerary liver lobes unilateral) was observed in the control group. Skeletal malformations were noted in single fetuses at 0, 100, and 1000 mg/kgbw/day. Each of them affected individual fetuses and neither statistically significant differences between the test groups nor a dose–response relationship was observed. The overall incidences of skeletal malformations were comparable to those found in the historical control data.

Three soft tissue variations, i.e. short innominate, enlarged atrial chamber of the heart and uni- or bilateral dilation of renal pelvis, were detected. These findings observed in 1–5 fetuses of 1–4 litters at 0, 100, 300 and 1000 mg/kgbw/day showed no dose–response relationship. The observable differences between the groups reflect the usual fluctuation for this parameter and were clearly within the range of the historical control data. For all groups, skeletal variations of different bone structures were observed, with or without effects on corresponding cartilage. The observed skeletal variations were related to several parts of fetal skeletons and appeared without a relation to dosing. The overall incidences of skeletal variations were comparable to the historical control data. The incidence of the variations observed showed no dosing-related statistical significance and were within historical control ranges. Therefore these observations are not considered toxicologically relevant.
: 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: There were no adverse effects on developmental parameters.
Abnormalities:: no effects observed
Developmental effects observed:: no
Conclusions:: Based on a prenatal developmental toxicity study in Wistar rats conducted in accordance with OECD TG 414 and to GLP the NOAEL for developmental toxicity was ≥1000 mg/kg bw/day as no adverse effects on developmental parameters were observed up to the highest dose tested. The NOAEL for general systemic toxicity was also ≥1000 mg/kg bw/day as there were no signs of adverse effects in any of the maternal animals up to the highest dose tested.

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEL

1 000 mg/kg bw/day

Study duration:

subacute

Species:

rat

Quality of whole database:

The key study was conducted according to OECD TG 414 and to GLP, without any significant deviations, and is therefore a suitable key study.

Endpoint conclusion:

no study available

Endpoint conclusion:

no study available

There are no adequate developmental toxicity data on dichlorosilane so good quality data for the hydrolysis products polysilicic acid (equivalent to synthetic amorphous silica) have been used to assess the potential for adverse effects on development following exposure to dichlorosilane.

Overview

It is considered not to be ethical to perform developmental toxicity testing with dichlorosilane by any route of exposure due to its known corrosive properties, which will dominate the toxicity profile of this substance. Following repeated oral dosing, the corrosive nature of the product could affect the lining of the stomach, giving rise to hyperplasia and a subsequent reduced food intake. This would confound the interpretation of any systemically driven effects. A guideline-compliant repeated-dose inhalation study should elicit systemic toxicity at the highest test concentration. Since the local corrosive effects of dichlorosilane would be significant a valid inhalation study according to the relevant guidelines is technically not feasible to do. It is also unlikely that any systemic effects would be seen at dose levels made sufficiently low (< 10 ppm) to prevent the known corrosive effects and/or distress in the test species. This has been confirmed in a 28-day inhalation study with another chlorosilane, dichloro(dimethyl)silane (WIL, 2014) in which there were no effects of treatment on clinical signs, body weight or food consumption that would indicate a systemic effect. Furthermore, the histopathology in the study indicated that the effects in the upper respiratory tract were similar to HCl. It is therefore concluded that HCl will dominate the inhalation toxicity profile of dichlorosilane.

With regard to the dermal and inhalation routes, due to the known corrosive effects of dichlorosilane, appropriate H-phrases and P-statements are included in the labelling, meaning that repeated skin and inhalation exposure is not expected. Any accidental skin contact or inhalation exposure could cause severe local effects but would be unlikely to cause any systemic effects.

ORAL ROUTE

SYSTEMIC EFFECTS

There are no adequate developmental toxicity data on dichlorosilane so good quality data for synthetic amorphous silica (CAS 112926-00-8) have been used to assess the developmental toxicity of dichlorosilane. Local effects from the hydrolysis product, hydrogen chloride (HCl) are not addressed by these data.

Dichlorosilane, like all inorganic chlorosilanes, is a severely corrosive substance that is decomposed by water, producing silicic acid and HCl. The reaction is highly exothermic (Merck, 2013). The initial products of hydrolysis are hydrogen chloride and silanediol.

The silanediol is expected to react rapidly to produce hydrogen and monosilicic acid. Hydrogen would be released to the atmosphere immediately.

Monosilicic acid condenses to insoluble polysilicic acid [equivalent to synthetic amorphous silica (SAS)] at concentrations higher than 100-150 mg/l ‘SiO₂equivalent’ in water (Holleman-Wiberg, 2001). At very high concentration, polysilicic acid can condense to silicon dioxide (SiO₂). The hydrolysis products of hydrochloric acid and (poly)silicic acid are significant for the chemical safety assessment (CSR).

Monosilicic acid and polysilicic acid are naturally occurring substances which are ubiquitous in the environment. Soluble monosilicic acid is the major bioavailable form of silicon and plays an important role in the biogeochemical cycle of silicon (ECETOC, 2006). Typical background concentrations of monosilicic acid in the environment are up to 75 mg/l ‘SiO₂equivalent’ in river water and up to 14 mg/l ‘SiO₂equivalent’ in seawater (Iler, 1979).

The literature gives various values for the solubility of silicic acid, determined indirectly as ‘SiO₂equivalent’ because the soluble species cannot be directly measured:

The solubility of monosilicic acid according to Alexander et al. (1954) at 25 °C:

150 mg/l ‘SiO₂equivalent’ at pH 2.0 and pH 3.0
130 mg/l ‘SiO₂equivalent’ at pH 4.2
110 mg/l ‘SiO₂equivalent’ at pH 5.7
100 mg/l ‘SiO₂equivalent’ at pH 7.7
490 mg/l ‘SiO₂equivalent’ at pH 10.3
1120 mg/l ‘SiO₂equivalent’ at pH 10.6

The solubility of monosilicic acid according to Goto and Okura (1953) at 25 °C:

120 mg/l ‘SiO₂equivalent’ at pH 2.0
150 mg/l ‘SiO₂equivalent’ at pH 7.0

The solubility of monosilicic acid according to Elmer and Nordberg (1958) at neutral pH:

170 mg/l ‘SiO₂equivalent’ at 35 °C
270 mg/l ‘SiO₂equivalent’ at 65 °C
465 mg/l ‘SiO₂equivalent’ at 95 °C

With the described properties of dichlorosilane in mind it is not possible to conduct developmental toxicity studies in experimental animals due to the corrosive nature of this substance. Nor can the hydrolysis product, monosilicic acid, be tested as it is not possible to isolate this substance. However, we know from physicochemical properties that following ingestion of dichlorosilane, the conditions in the stomach are such that following an initial rapid hydrolysis to soluble monosilicic acid, this monomer will start to condense to form insoluble polysilicic acid (equivalent to SAS). This condensation will start to occur once the concentration of monosilicic acid reaches approximately 150 mg/l in the gastric juices.

Monosilicic acid (soluble silica) undergoes condensation reactions in solution at about 100-150 mg/l ‘SiO₂ equivalent’. The solubility of monosilicic acid in water is 150 mg/l ‘SiO₂equivalent'.

Following dosing by oral gavage, partitioning will occur between the dose vehicle and the aqueous environment in the stomach.

Mass dosed (in mg/day) = Body weight (in kg) x dose level (in mg/kg bw/day)

Dose concentration (in mg/l) = mass dosed (in mg/day)÷volume (in l)

So, the dose level (mg/kg bw/day) required to reach the dose concentration of 150 mg/l 'SiO₂ equivalent', the estimated (conservative) maximum concentration of silicic acid that can occur in the stomach before condensation to insoluble polysilicic acid (equivalent to SAS) begins is calculated as follows:

Body weight of rat = 0.3kg

Dose level = X

Estimated aqueous volume = 0.0015 l

Dose concentration = 150 mg/l

150 mg/l = 0.3 kg x dose level (mg/kg bw/day)÷0.0015l

Dose level = 0.75 mg/kg bw/day 'SiO₂equivalent'

Therefore, based on a condensation limit of 150 mg/l, the maximum dose level that could be used in practice to ensure exposure mainly to monosilicic acid in the stomach of experimental animals is approximately 0.75 mg/kg bw/day or less of 'SiO₂ equivalent'.

A correction for molecular weight gives a maximum dose level for dichlorosilane:

Mr [dichlorosilane] = 101.01 g/mol

Mr [silicon dioxide] = 60.08 g/mol

Dose level [dichlorosilane] = [Dose level [silicon dioxide] x Mr [dichlorosilane]]

Mr [silicon dioxide]

= (0.75 mg/kg bw/day) x (101.01 g/mol)

(60.08 g/mol)

= 1.26 mg/kg bw/day

Therefore, based on a condensation limit of 150 mg/l the maximum dose level of dichlorosilane that can be dosed to ensure exposure mainly to monosilicic acid is approximately 2 mg/kg bw/day.

For comparison purposes, using the above calculation, the following shows the dose concentrations for the dose levels typically used in experimental animal studies (100, 300 and 1000 mg/kg bw/day).

Body weight = 0.3 kg

Total amount dosed = 30 mg

Estimated aqueous volume = 1.5 ml

Dose concentration = 20,000 mg/l

Body weight = 0.3 kg

Total amount dosed = 90 mg

Estimated aqueous volume = 1.5 ml

Dose concentration = 60,000 mg/l

Body weight = 0.3 kg

Total amount dosed = 300 mg

Estimated aqueous volume = 1.5 ml

Dose concentration = 200,000 mg/l

Therefore, dosing at these dose levels clearly gives a dose concentration in the stomach that far exceeds the dose at which condensation to polysilicic acid (equivalent to SAS) starts to occur. Consequently, the majority of the dose in the stomach will be present as insoluble polysilicic acid (equivalent to SAS). In all cases only approximately 150 mg/l will be present as soluble monosilicic acid.

Overall, it can be concluded that gavaging dichlorosilane at doses unlikely to cause local corrosive effects and at doses that give mainly soluble monosilicic acid (2 mg/kg bw/day or less) would be unethical based on animal usage. However, because the vast majority of a gavaged dose will rapidly condense to insoluble polysilicic acid it is appropriate to use toxicology data on SAS to address the potential for oral toxicity of dichlorosilane.

The key developmental study is a prenatal developmental study (Hofmann et al., 2015) conducted according to OECD test guideline 414 and in compliance with GLP. Pregnant Wistar rats were administered SAS (described as NM-200 synthetic amorphous silica) (in highly deionised water containing 10% fetal bovine serum) at doses of 100, 300 and 1000 mg/kg bw/day by oral gavage on gestation days 6-19. There were no adverse, treatment-related findings in parental animals or offspring. There were a number of incidental fetal malformations and variations, which all occurred at a rate no larger than that of the control/historical controls, without statistical significance and without a dose-response relationship. Therefore, the NOAEL for general toxicity and developmental (including teratogenicity) toxicity was ≥1000 mg/kg bw/day in this study.

Limited data are available regarding the developmental toxicity in animals following oral, dermal or inhalation exposure to hydrogen chloride. However, protons and chloride ions exist as normal constituents of body fluid in animals, hence low concentrations of hydrogen chloride appear not to cause adverse effects in animals. Therefore, the hydrolysis product of dichlorosilane, HCl, would not be expected to cause developmental toxicity in experimental animals or humans following initial exposure to dichlorosilane.

References

Alexander G.B., Heston W.M. and Iler R.K. (1954) J. Phys. Chem., 58, 453.

Cotton F.A. and Wilkinson G. (1999) Advanced Inorganic Chemistry, 6^thEdition, p271

ECETOC (2006) Synthetic Amorphous Silica (CAS No. 7631-86-9), JACC REPORT No. 51

Elmer and Nordberg (1958) J. Am.Chem. Soc., 41, 517

Goto K. and Okura T. (1953) Kagaku, 23, 426.

Holleman-Wiberg, (2001) Inorganic Chemistry, Academic Press, p. 865

Iler, Ralph K. (1979) The Chemistry of Silica: Solubility, Polymerization, Colloid and Surface Properties and Biochemistry of Silica, Wiley, p. 13.

Jones, R. G., Wataru, A., and Chojnowski, J. (2000) Silicon-Containing Polymers: The Science and Technology of Their Synthesis, Kluwer Academic Press pp168-169

Merck Index (2013) Monograph Number. 8639 (15th Ed)

Based on the available read-across data from the hydrolysis products amorphous polysilicic acid [synthetic amorphous silica – SAS], dichlorosilane does not require classification for toxicity to reproduction according to Regulation (EC) No. 1272/2008.

		NM-200 dose (mg/kg bw/day)
Parameter of reproductive performance	Generation	0	100	300	1000
Mating index (%)	F0	96	100	100	100
	F1	100	100	100	100
Fertility index (%)	F0	96	100	96	96
	F1	98	93	93	89
Fecundity index (%)	F0	100	100	96	96
	F1	89	93	93	89
Gestation index (%)	F0	100	96	100	100
	F1	100	100	96	96
Precoital time (days)	F0	2.7±0.21	2.8±0.25	2.3±0.19	2.5±0.21
	F1	2.8±0.27	2.5±0.2	2.4±0.2	2.4±0.26
Gestation time (days)	F0	21.7±0.09	21.6±0.11	21.6±0.1	21.6±0.1
	F1	21.3±0.09	21.2±0.08	21.4±0.12	21.3±0.09
Postimplantation loss per animal (%)	F0	8.6±2.66	10.5±3.72	9.5±2.54	10.1±2.52
	F1	8.9±1.48	13.6±3.68	17.6±5.47	14.8±4.91

		NM-200 dose (mg/kg bw/day)
	Generation	0	100	300	1000
Pups delivered (total)	F0	10.3±2.9	10.7±2.3	11.3± 2.0	11.0±1.5
	F1	11.5 ±1.6	10.7±2.8	10.4±2.8	11.0± 2.6
Live birth index (%)	F0	97.3±9.9	94.8± 19.1	96.5±12.7	98.7± 4.9
	F1	96.2±6.1	90.7± 17.3	94.2±12.7	93.5± 16.1
Pup mortality day 1 (%)	F0	2.7±9.9	5.2± 19.1	3.5±12.7	1.3± 4.9
	F1	3.8±6.1	9.3± 17.3	5.8 ±19.0	6.5± 16.1
Viability index day 4 (%)	F0	99.3±2.5	99.6± 2.0	98.9±4.2	98.8± 3.5
	F1	84.7±28.0	83.8± 34.6	95.3 ± 20.0	73.8±42.3
Viability index day 21 (%)	F0	100±0	100±0	100±0	100±0
	F1	100±0	99.5 ±2.6	98.6 ±6.8	100±0
Whole litter losses (litters lost/total number of litters)	F0	2/27	2/28	2/27	0/27
	F1	1/25	3/26	1/25	4/24
Sex ratio day 1 (% males)	F0	51.9±17.6	43.9± 12.2	50.8 ±15.6	51.1± 10.9
	F1	47.4± 16.2	52.6±21.4	45.3± 19.6	42.3± 15.4

Dose (mg/kg bw/d)		0 (vehicle control)	100	300	1000
Females mated	N	25	25	25	25
Pregnant	N	22	21	25	23
Conception rate	%	88	84	100	92
Aborted	N	0	0	0	0
Premature births	N	0	0	0	0
Dams with viable fetuses	N	22	21	25	23
Dams with total litter loss	N	0	0	0	0
Female mortality	N	0	0	0	0
Pregnant at terminal sacrifice	N	22	21	25	23
	%	88	84	100	92
Corpora lutea^D	mean ± SD	14.2 ± 2.4	13.9 ± 2.08	14.0 ± 1.99	14.7 ± 2.03
Implantation sites^D	mean ± SD	13.5 ± 2.56	12.5 ± 2.8	12.8 ± 1.62	13.4 ± 2.27
Pre-implantation loss (%)^D	mean ± SD	4.9 ± 7.31	9.4 ± 17.69	7.7 ± 11.81	8.4 ± 12.31
Post-implantation loss (%)^D	mean ± SD	8.3 ± 9.96	5.2 ± 5.22	9.9 ± 16.2	6.0 ± 3.56
Early resorptions (%)^D		7.6 ± 9.27	5.2 ± 5.22	9.9 ± 16.2	5.6 ± 3.75
Late resorptions (%)^D		0.7 ± 2.26	0	0	0.3 ± 1.49
Dead fetuses		0	0	0	0
Dams with viable fetuses	N	22	21	25	23
Live fetuses^D	mean ± SD	12.4 ± 2.59	11.8 ± 2.71	11.5 ± 2.47	12.7 ± 2.23
Live fetuses (% implantation)^D	mean ± SD	91.7 ± 9.96	94.8 ± 5.22	90.1 ± 16.2	94.0 ± 3.56
Males^D	mean ± SD	5.9 ± 1.7	5.5 ± 1.91	6.5 ± 1.85	5.7 ± 1.79
Males (%)^D	mean ± SD	43.7 ± 10.64	46.5 ± 18.79	50.9 ± 14.23	43.2 ± 13.09
Females^D	mean ± SD	6.5 ± 1.95	6.3 ± 2.76	5.0 ± 2.34	6.9 ± 2.21
Females (%)^D	mean ± SD	48.0 ± 11.17	48.3 ± 18.55	39.2 ± 15.98	50.9 ± 11.85
Sex ratio (% males)		47.4	46.8	56.3	45.4
Placental weights^D	mean ± SD	0.47 ± 0.040	0.47 ± 0.042	0.46 ± 0.038	0.47 ± 0.038
	N	22	21	25	23
Of male fetuses^D	mean ± SD	0.49 ± 0.038	0.48 ± 0.036	0.47 ± 0.043	0.48 ± 0.037
	N	22	21	25	23
Of female fetuses^D	mean ± SD	0.46 ± 0.042	0.46 ± 0.052	0.46 ± 0.044	0.46 ± 0.041
	N	22	20	25	23
Fetal weights^D	mean SD	3.4 ± 0.26	3.4 ± 0.15	3.4 ± 0.24	3.4 ± 0.14
	N	22	21	25	23
Males^D	mean SD	3.5 ± 0.27	3.4 ± 0.18	3.5 ± 0.24	3.5 ± 0.14
	N	22	21	25	23
Females^D	mean SD	3.3 ± 0.25	3.3 ± 0.17	3.4 ± 0.28	3.3 ± 0.15
	N	22	20	25	23

Dose (mg/kg bw/d)		0 (vehicle control)	100	300	1000
Litters evaluated	N	22	21	25	23
Fetuses evaluated	N	272	248	288	291

Total Malformations
Fetal incidence	N	3	1	0	1
	%	1.1	0.4	0.0	0.3
Litter incidence^F	N	2	1	0	1
	%	9.1	4.8	0.0	4.3
Affected fetuses per litter^W	mean% ± SD	1.3 ± 4.07	0.4 ± 1.98	0.0 ± 0.00	0.3 ± 1.60