Silicon

Endpoint summary

Description of key information

Animal data on acute toxicity of synthetic amorphous silica which can be used for read-across do not show acute oral, inhalation or dermal toxicity.

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

LD50

Value:

5 000 mg/kg bw

Quality of whole database:

Robust study available, read-across justified.

Acute toxicity: via inhalation route

Endpoint conclusion

Endpoint conclusion:

no study available

Acute toxicity: via dermal route

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Additional information

Acute toxicity studies have not been performed with silicon. Repeated dose inhalation tests with silicon (14- and 90 -day studies in rats) did not show any signs of acute effects.

Data are available on the acute toxicity of synthetic amorphous silica. The surface of silicon is composed of a thin oxidized silicon layer resembling the surface of amorphous silicon dioxide. Both silicon and amorphous silica release silicon from particles. Based on the comparative in vitro data on the dissolution kinetics of silicon and synthetic amorphous silica in different artificial biological fluids, it can be presumed that the bioavailabity of silicon from silicon particles is similar or slightly lower than that for synthetic amorphous silica. Therefore, the assessment of acute toxicity may lean on data from amorphous silica. A detailed description of the justifications for read-across is available in Section 13 of the Iuclid dossier.

According to available data, the acute oral toxicity of synthetic amorphous silica is very low: no signs of toxicity were observed at doses of up to 5,000 mg SiO₂/kg bw. LD₅₀values for the various types of synthetic amorphous silica studied were quite similar. Amorphous silica is not toxic via the dermal route.

Based on the facts that

1) the solubility of silicon in biological fluids is similar or lower than the solubility of amorphous silica, and

2) the systemic toxicity of the silicon ion is low (as shown by the low acute oral toxicity),

3) no systemic effects were observed after repeated exposure to silicon

it can be surmised that no acute inhalation toxicity of silicon is expected, either.

Conclusion: Silicon is not acutely toxic via oral, inhalation or dermal routes. No classification is suggested.

Justification for selection of acute toxicity – oral endpoint
Read-across to guideline study performed with synthetic amorphous silica. No acute effects observed, LD50 > 5000 mg/kg.

Justification for selection of acute toxicity – dermal endpoint
Read-across to studies performed with synthetic amorphous silica. No acute effects observed, LD50 > 5000 mg/kg.

Justification for classification or non-classification

Read-across to synthetic amorphous silica. All LD₅₀ are above classification cut-off limits.