Chlorodimethylsilane

Endpoint summary

Additional information

Introduction

There are no in vivo data available on the toxicokinetics of chlorodimethylsilane, so the following summary has therefore been prepared based on validated predictions of the physicochemical properties of the substance itself and its hydrolysis products. Chlorodimethylsilane is a moisture-sensitive, volatile liquid. Rapid hydrolysis occurs, producing dimethylsilanol and hydrogen chloride (HCl). Exposure may 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. Therefore only toxicokinetics of the hydrolysis product dimethylsilanol are discussed further. 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 weight of dimethylsilanol favours absorption across the skin. The water solubility (6170 mg/l) and predicted log K_ow (0.6) also suggest that it will be absorbed across the skin. The partition coefficient isn’t quite optimal (1-4 is optimal) for dermal absorption, but together with the optimal water solubility, there is a strong case for moderate dermal absorption. Since the other hydrolysis product, HCl, is corrosive to the skin, damage to the skin might increase penetration. There are no dermal studies or skin irritation studies to consult for evidence of systemic availability. However, there is an in vitro percutaneous absorption study on trimethylsilanol (an analogue of the hydrolysis product, dimethylsilanol), which demonstrated that the majority of trimethylsilanol (approximately 99%) is volatilsed from the surface of human skin within 24 hours. Therefore it is anticipated that the majority of dimethylsilanol will also volatilised off the skin before absorption can occur.

Inhalation

The partition coefficient for dimethylsilanol (log Kow of 0.6) indicates that it is likely to be absorbed directly across the respiratory tract epithelium by passive diffusion. As with dermal exposure, damage to membranes caused by the corrosive nature of the HCl hydrolysis product might enhance the uptake. Acute inhalation studies showed local signs but no definite systemic effects.

Distribution

Dimethylsilanol molecules are small, and are likely to be widely distributed. The partition coefficient of 0.6 suggests that this hydrolysis product is likely to distribute into cells and the intracellular concentration may be slightly higher than extracellular concentration particularly in fatty tissues.

Metabolism

Chlorodimethylsilane is rapidly hydrolysed to dimethylsilanol and hydrogen chloride in the presence of moisture with a half-life of <1 minute. There are no data regarding the further metabolism of dimethylsilanol. Genetic toxicity tests with chlorodimethylsilane in vitro showed no observable differences in effects with and without metabolic activation.

Excretion

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