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Description of key information

Key value for chemical safety assessment

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Introduction

There are no in vivo data on the toxicokinetics of trimethoxysilane. The following summary has therefore been prepared based on validated predictions of the physicochemical properties of the substance itself and its hydrolysis products. Trimethoxysilane is a volatile liquid which hydrolyses rapidly in contact with water. Exposure may occur via the inhalation or dermal routes. Relevant inhalation exposure is likely to be a mixture of parent and hydrolysis products. The substance would also hydrolyse rapidly in contact with moist skin. The toxicokinetic behaviour of methanol has been extensively reported in the literature and is not discussed further in this summary.

Absorption

Oral

Significant oral exposure is not expected for this corrosive substance.

Dermal

The low molecular weights of the parent and hydrolysis products favour dermal absorption. However, the water solubility and partition coefficient of silanetriol suggest that it might be too hydrophilic to cross the lipid rich stratum corneum. Therefore dermal uptake is likely to be low. The water solubility and partition coefficient of the parent substance suggest that dermal absorption is possible. Acute dermal toxicity studies using trimethoxysilane show signs of systemic toxicity (including effects on the lungs and liver), and therefore also indicate the occurrence of dermal absorption. Since this substance is corrosive to the skin, damage to the skin might increase penetration. However, dermal penetration will be limited by rapid evaporation from the skin.

Inhalation

Trimethoxysilane will rapidly hydrolyse in the lungs. The hydrophilic hydrolysis product, silanetriol, is likely to be retained in the mucous of the lungs, and inhibited from penetrating the lung epithelium. Any remaining parent substance is more likely to be absorbed passively across the respiratory tract epithelium. Damage caused due to the corrosive nature of trimethoxysilane could lead to increased absorption following inhalation.

Distribution

Absorbed trimethoxysilane will completely hydrolyse in the blood. Since the hydrolysis product is a small molecule, it 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.

Metabolism

Absorbed trimethoxysilane is expected to completely hydrolyse to methanol and silanetriol in the blood. There are no further data that can be used to characterise the metabolic profile of this substance. Genetic toxicity tests in vitro showed no observable differences in effects with and without metabolic activation.

Excretion

The high water solubility and low log Kow indicate that the substance is likely to be rapidly eliminated via the kidneys into the urine. There is therefore no evidence to suggest that this substance will accumulate in the body.