Registration Dossier

Toxicological information

Carcinogenicity

Currently viewing:

Administrative data

Description of key information

Silicon has not been tested in chronic studies. One critical study is the two year rat and mouse feeding study with micronized silica gel (Syloid) by Takizawa et al. (1988). No increased incidence of cancer was observed in this study. Epidemiological studies from silicon/ferrosilicon industry have not raised any concern on lung carcinogenicity.

Key value for chemical safety assessment

Carcinogenicity: via oral route

Endpoint conclusion
Endpoint conclusion:
no adverse effect observed

Additional information

Silicon has not been tested in chronic studies. Human epidemiological data from ferrosilicon/silicon manufacturing do not show increased incidence of cancer attributed to silicon exposure. Because of insensitivity of epidemiological studies, this data cannot, however, be used as any definitive proof of non-carcinogenicity of silicon.

Some data is available on the carcinogenicity of synthetic amorphous silica. A critical study is the two-year rat and mouse feeding study with micronized silica gel (Syloid) by Takizawa et al. (1988). No increased incidence of cancer was observed in this study. Although the group sizes were small causing uncertainty in the interpretation, it suggests non-carcinogenicity of amorphous silica via the oral route. This conclusion is supported by negative in vitro and in vivo mutagenicity data (see Chapter 'Mutagenicity'). Considering the carcinogenicity of silicon, these studies are relevant in the assessment since 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. Silicon has been shown to be released in the form of monosilicic acid, which represents the bioavailable form of silicon and is the form in which silicon has been found in blood, regardless of the source. The comparative in vitro data on the dissolution kinetics of silicon and amorphous silica (silica fume and synthetic amorphous silica) in different artificial biological fluids show that the dissolution of silicon from silicon particles in vitro is similar or slightly lower than from amorphous silica particles (pyrogenic silica or silica fume) and it is justified to use read-across from amorphous silicon dioxide to silicon. A detailed description of the justifications for read-across is available in Section 13 of the Iuclid dossier.

Crystalline silicon dioxide is an inhalation carcinogen, but its carcinogenicity is related to its specific crystalline structure formed by Si and oxygen and its biopersistence, not to silicon ion. The surface of silicon is composed of a thin layer of amorphous silica. Therefore, the data on inhalation carcinogenicity of amorphous silica is considered relevant for the assessment of silicon. Available (limited) data on amorphous silicon dioxide does not raise concern on inhalation carcinogenicity of amorphous silicon dioxide. IARC evaluated the carcinogenicity of Crystalline and amorphous silica in 1997. According to IARC (1997) crystalline silica inhaled in the form of quartz or cristobalite from occupational sources is carcinogenic to humans (Group 1) whereas amorphous silica is not classifiable as to its carcinogenicity to humans (Group 3).

Metallurgical silicon contains small amounts of impurities, the main metallic impurities present at levels >0.1% w/w in bulk material being iron (<3%) and aluminium and calcium (<1.5%). Iron is an essential element and not carcinogenic. The same applies to calcium. Also aluminium is not carcinogenic (IPCS 1997) and aluminium salts are widely used antacidal medicines. 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 (Aerosil Ox50, see Chapter 'Toxicokinetics').

Conclusion: Based on available data, silicon is not likely to be carcinogen. No further testing is suggested.


Justification for selection of carcinogenicity via oral route endpoint:
Read-across to amorphous silicon dioxide.

Justification for classification or non-classification

Although there is no specific data on the carcinogenicity of silicon, the weight of evidence supports the non-carcinogenicity of elemental silicon. An oral carcinogenicity study with amorphous silica showed negative results. Epidemiological data do not raise concerns on lung carcinogenicity of silicon. Crystalline silicon dioxide is an inhalation carcinogen, but its carcinogenicity is related to its specific crystalline structure formed by Si and oxygen and its biopersistence, not to silicon ion. The surface of silicon is composed of a thin layer of amorphous silica. Therefore, the data on inhalation carcinogenicity of amorphous silica is considered relevant for the assessment of silicon. Available (limited) data on amorphous silicon dioxide does not raise concern on inhalation carcinogenicity of amorphous silicon dioxide

Metallurgical silicon contain small amounts of impurities, the main metallic impurities present at levels >0.1% w/w in bulk material being iron (<3%) and aluminium and calcium (<1.5%). These are not carcinogenic, either.