Silane

Endpoint summary

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

There are no in vitro or in vivo data on the toxicokinetics of silane (CAS 7803-62-5; EC No. 232-263-4). The following summary has therefore been prepared based on validated predictions of the physicochemical properties of the substance. For the purposes of this summary only qualitative statements or predictions will be made.

Silane (SiH₄) is an inorganic gas at standard temperature and pressure. It ignites spontaneously in air. Pure silane does not react with pure water, but in the presence of trace alkali, hydrolysis to silica (SiO₂.nH₂O) and hydrogen is rapid and complete. The relevant route of exposure to humans is inhalation of the gas.

Absorption

Oral

Significant oral exposure is not expected for this pyrophoric substance. Should it occur then gastrointestinal absorption of insoluble silica gel will be minimal (Carlisle, 1986).

Dermal

Significant dermal exposure is not expected for this pyrophoric substance. Should it occur then the parent substance is expected to react with moisture on the skin producing insoluble silicon dioxide which would not be absorbed.

Inhalation

Silane has a low molecular weight and reasonable water solubility and is therefore expected to penetrate the lower respiratory tract. The acute inhalation data available for silane indicate that it (or hydrolysis products) was absorbed as there were adverse effects on the kidneys in an acute study (Takebayashi, 1993).

Distribution

Since silica is insoluble, it would probably precipitate in the blood following hydrolysis of silane. Pathological examinations in one of the acute inhalation studies (Tabebayashi, 1993) revealed signs of silica precipitate reaching the kidneys, spleen, bone marrow and thymus (macrophage activity).

Metabolism

Pure silane does not react with pure water, but in the presence of trace alkali, hydrolysis to silica (SiO₂.nH₂O) and hydrogen is rapid and complete. Since the pH of the lung epithelium is neutral, hydrolysis would not be expected. In support of this is the finding that there were no silicosis-type effects in the lungs of animals used in the repeated dose toxicity study; however, the study might not have been of sufficient duration (four weeks) to show such effects. Blood has a pH of 7.35–7.45, so hydrolysis is possible once silane has been absorbed into the bloodstream.

Excretion

Some inhaled gas is likely to be exhaled before absorption can occur. Some hydrogen following hydrolysis, might also be excreted via exhaled air. Silica is excreted via the kidneys in urine.