Dichloro(methyl)(vinyl)silane

Endpoint summary

Description of key information

There are no repeated dose toxicity data on dichloro(methyl)(vinyl)silane or its hydrolysis product, methyl(vinyl)silanediol, so good quality data for the related substance trimethoxyvinylsilane have been used to assess the general systemic toxicity of dichloro(methyl)(vinyl)silane.
In an oral OECD 422 study ( Hashima Labs, no date) in rats, trimethoxyvinylsilane was administered by gavage at doses up to 1000 mg/kg bw/day, for approximately 28 days. The LOAEL was 62.5 mg/kg bw/day (based on decreased relative thymus weight in females and histopathological changes in the urinary bladder of males) and the NOAEL was < 62.5 mg/kg bw/day for both sexes.
In a 14-week whole-body inhalation study (BRRC, 1990) in which rats were exposed to trimethoxy(vinyl)silane at concentrations up to 400 ppm, a concentration of 100 ppm was a LOAEC (effects included decreased urine osmolality and sodium, potassium and chloride concentrations in males and slight decrease in body weight and body weight gain in females), and 10 ppm (58 mg/m3) was a NOAEC.

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Dose descriptor:

LOAEL

62.5 mg/kg bw/day

Study duration:

subacute

Species:

rat

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Dose descriptor:

NOAEC

58 mg/m³

Study duration:

subchronic

Species:

rat

Additional information

There are no repeated dose toxicity data on dichloro(methyl)(vinyl)silane or its hydrolysis product, methyl(vinyl)silanediol, so good quality data for the related substance trimethoxyvinylsilane have been used to assess the general systemic toxicity of dichloro(methyl)(vinyl)silane. Local effects from the other hydrolysis product, hydrogen chloride (HCl) are not addressed by these data.

Dichloro(methyl)(vinyl)silane hydrolyses rapidly in contact with water (half-life <1 minute at pH 7), generating HCl and methyl(vinyl)silanediol. Trimethoxy(vinyl)silane (CAS 2768 -02 -7) hydrolyses more slowly at pH 7 (half-life <2.4 hours at 50°C and pH7)

, but under acidic conditions such as in the stomach following ingestion, much more rapid hydrolysis can be expected based on experience with other methoxysilanes. The relevant hydrolysis products are methanol and vinylsilanetriol. The silanol hydrolysis products for the registered substance and the surrogate substance are therefore similar in chemical structure, the only difference being the replacement of -CH₃ with an extra Si-OH group. Both have high water solubility and very low log K_ow (log K_ow -0.05 and -2.0, respectively). Acute oral toxicity data for other related silanols [e.g. dimethylsilanediol and methylsilanetriol (as the potassium salt)] indicate there are no significant toxicological differences between silanediol and silanetriol analogues. Data obtained via the oral route for trimethoxyvinylsilane are therefore considered appropriate for read-across to dichloro(methyl)(vinyl)silane.

 

For the inhalation route, the hydrolysis rate of trimethoxyvinylsilane in the respiratory tract and lungs is unknown, but is likely to be slower than that of dichloro(methyl)(vinyl)silane. For dichloro(methyl)(vinyl)silane, the species absorbed following inhalation exposure are mainly hydrolysis products, whereas for trimethoxyvinylsilane, absorption of the parent substance may be more significant. Trimethoxyvinylsilane has a higher log K_ow value (1.08) therefore the proportion of inhaled material which is systemically absorbed is likely to be greater than for dichloro(methyl)(vinyl)silane. Nevertheless, in the absence of other data, the inhalatory NOAEL for trimethoxy(vinyl)silane is considered to represent a reasonable worst-case for read-across to dichloro(methyl)vinylsilane.

It is of note that the oral NOAEL in rats for methanol is greater (500 mg/kg bw/day) than the dose that is expected to be generated from hydrolysis of trimethoxy(vinyl)silane in the stomach. Therefore the effects of trimethoxy(vinyl)silane following a dose of 62.5 mg/kg bw/day are not thought to be attributable to methanol. Similarly, following inhalation of methanol the NOAEC is an order of magnitide greater than the NOAEC for trimethoxy(vinyl)silane, and it therefore unlikely that systemic effects observed following inhalation of trimethoxy(vinyl)silane are due to methanol.

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Repeated dose toxicity: via oral route - systemic effects (target organ) urogenital: urinary bladder

Justification for classification or non-classification

Based on the observed effects on the urinary bladder of males at all dose levels, it is appropriate to classify trimethoxyvinylsilane as STOT RE 2 (bladder) following oral exposure, according to the criteria of Regulation 1272/2008. However, at the dose levels tested, corrosive effects of trichloro(vinyl)silane would outweigh any potential systemic effects. It is therefore not considered appropriate to classify trichloro(vinyl)silane for repeated dose toxicity.