Chloro(methyl)silane

Endpoint summary

Additional information

There are no in vivo data on the toxicokinetics of chloro(methyl)silane. The following summary has therefore been prepared based on the physicochemical properties of the substance itself and its hydrolysis products. Chloro(methyl)silane is a moisture-sensitive, volatile liquid that hydrolyses rapidly in contact with water (half-life <1 minute at pH 7), generating HCl and methylsilanol. Human exposure can occur via the inhalation or dermal routes. Relevant inhalation exposure would be to the hydrolysis products (hydrolysis would occur rapidly when inhaled, even if a mixture of parent and hydrolysis products were present in air). The substance would also hydrolyse rapidly in contact with moist skin. The resulting HCl hydrolysis product would be severely irritating or corrosive.

Absorption

Oral: Significant oral exposure is not expected for this corrosive substance.

Dermal: The molecular weights of the parent and hydrolysis product, methylsilanol, are favourable for dermal absorption. However, the high water solubility (1.05E+04 mg/l) and predicted log K_ow(0.05) of the hydrolysis product suggest that it is too hydrophilic to cross the lipid rich stratum corneum. Therefore dermal uptake is likely to be low. A well conducted guideline study conducted to OECD 428 and GLP (reliability score 1) is available for 14 -C trimethylsilanol (for which an OECD 422 oral study is read across to chloro(methyl)silane). In that study, the total percentage of the dose of 14C-trimethylsilanol absorbed was estimated to be <0.08% of the applied dose. Almost all (99.9%) of the recovered 14C-TMS volatilised from the skin surface and was captured in the charcoal baskets placed above the exposure sites. The majority of the absorbed dose penetrated through the skin to the receptor fluid. Therefore once hydrolysis has occurred, absorption of trimethylsilanol is poor. Since the other hydrolysis product, HCl is corrosive to the skin, damage to the skin might increase penetration. There are no reliable studies to check for signs of dermal toxicity, and skin irritation/corrosion studies did not report any signs of systemic toxicity.

Inhalation: The high water solubility of methylsilanol might lead to some of this hydrolysis product being retained in the mucous of the lungs. As with dermal exposure, damage to membranes caused by the corrosive nature of the HCl hydrolysis product might enhance the uptake. There are no inhalation studies on chloro(methyl)silane to check for signs of absorption.

Distribution

All absorbed material is likely to be in the form of the hydrolysis products, methylsilanol and hydrogen chloride. Methylsilanol is a small molecule, and is likely to be widely distributed, but its hydrophilic nature will limit its diffusion across membranes (including the blood-brain and blood-testes barriers) and its accumulation in fatty tissues. Hydrogen and chloride ions will enter the body’s natural homeostatic processes.

Metabolism

Chloro(methyl)silane is rapidly hydrolysed to methylsilanol and hydrogen chloride in the presence of moisture. Most if not all of this will have occurred before absorption into the body. There is no data regarding the metabolism of methylsilanol. Genetic toxicity tests in vitro showed no observable differences in effects with and without metabolic activation.

Excretion

The low molecular weight and high water solubility of methylsilanol suggest that it is likely to be rapidly eliminated via the kidneys in urine. There is therefore no evidence to suggest that this substance will accumulate in the body.