Silicon

Endpoint summary

Additional information

There is no information on the mutagenicity of silicon. In vivo and in vitro studies on the mutagenicity of amorphous silicas have not shown relevant positive responses. In one micronucleus induction study in vitro, the positive response has most probably resulted from the reported high concomitant cytotoxicity. The contradictory results from in vitro Comet assays of silicas require more positive backing from results obtained from other methods. The high sensitivity of the assay makes its reproducibility vulnerable to test conditions. Thus, based on the weight-of-evidence, amorphous silica is non-genotoxic. The surface of the silicon is composed of a thin oxidized silicon layer resembling the surface of amorphous silicon dioxide and both silicon and amorphous silica release silicon from particles. According to the comparative in vitro data on the dissolution kinetics of silicon and synthetic amorphous silica in different artificial biological fluids dissolution of silicon ion from silicon particles in vitro is similar or slightly lower than from amorphous silica particles (pyrogenic silica or silica fume). Thus, read-across between silicon and amorphous silicon doxide is justified and there is no reason to assume that silicon would differ from amorphous silicon dioxide in terms of its mutagenicity.

A detailed description of the justifications for read-across is available in Section 13 of the Iuclid dossier.

The main elemental impurities of silicon, which bulk concentration exceeds the classification cut-off limit of 0.1% and which are dissolved in measurable amounts in artificial biological fluids include iron, aluminium and calcium. None of these exerts mutagenic properties. In addition, the dissolution of these elements from silicon matrix is very restricted because of the protective silicon oxide layer and did not differ significantly from the release of these elements from pyrogenic amorphous silica in vitro (see Chapter 'Toxicokinetics').

Short description of key information:
No studies available on silicon. Read-across to synthetic amorphous silica has been done. Both in vitro and in vivo studies with synthetic amorphous silica suggest non-mutagenicity of silicon.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Silicon has not been tested for mutagenicity. Valid in vivo and in vitro studies on the mutagenicity of amorphous silicas have not shown relevant positive responses.

The surface of silicon is composed of a thin oxidized silicon layer resembling the surface of amorphous silicon dioxide and both silicon and amorphous silica release silicon from particles. According to the comparative in vitro data on the dissolution kinetics of silicon and synthetic amorphous silica in different artificial biological fluids dissolution of silicon ion from silicon particles in vitro is similar or slightly lower than from amorphous silica particles (pyrogenic silica). Thus, there is no reason to believe that silicon would differ from amorphous silicon dioxide in terms of its mutagenicity.

The main elemental impurities of silicon do not have mutagenic properties.

Conclusions: Silicon is not mutagenic. No classification or further testing is suggested.