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EC number: 231-130-8 | CAS number: 7440-21-3
- Life Cycle description
- Uses advised against
- Endpoint summary
- Appearance / physical state / colour
- Melting point / freezing point
- Boiling point
- Density
- Particle size distribution (Granulometry)
- Vapour pressure
- Partition coefficient
- Water solubility
- Solubility in organic solvents / fat solubility
- Surface tension
- Flash point
- Auto flammability
- Flammability
- Explosiveness
- Oxidising properties
- Oxidation reduction potential
- Stability in organic solvents and identity of relevant degradation products
- Storage stability and reactivity towards container material
- Stability: thermal, sunlight, metals
- pH
- Dissociation constant
- Viscosity
- Additional physico-chemical information
- Additional physico-chemical properties of nanomaterials
- Nanomaterial agglomeration / aggregation
- Nanomaterial crystalline phase
- Nanomaterial crystallite and grain size
- Nanomaterial aspect ratio / shape
- Nanomaterial specific surface area
- Nanomaterial Zeta potential
- Nanomaterial surface chemistry
- Nanomaterial dustiness
- Nanomaterial porosity
- Nanomaterial pour density
- Nanomaterial photocatalytic activity
- Nanomaterial radical formation potential
- Nanomaterial catalytic activity
- Endpoint summary
- Stability
- Biodegradation
- Bioaccumulation
- Transport and distribution
- Environmental data
- Additional information on environmental fate and behaviour
- Ecotoxicological Summary
- Aquatic toxicity
- Endpoint summary
- Short-term toxicity to fish
- Long-term toxicity to fish
- Short-term toxicity to aquatic invertebrates
- Long-term toxicity to aquatic invertebrates
- Toxicity to aquatic algae and cyanobacteria
- Toxicity to aquatic plants other than algae
- Toxicity to microorganisms
- Endocrine disrupter testing in aquatic vertebrates – in vivo
- Toxicity to other aquatic organisms
- Sediment toxicity
- Terrestrial toxicity
- Biological effects monitoring
- Biotransformation and kinetics
- Additional ecotoxological information
- Toxicological Summary
- Toxicokinetics, metabolism and distribution
- Acute Toxicity
- Irritation / corrosion
- Sensitisation
- Repeated dose toxicity
- Genetic toxicity
- Carcinogenicity
- Toxicity to reproduction
- Specific investigations
- Exposure related observations in humans
- Toxic effects on livestock and pets
- Additional toxicological data
Carcinogenicity
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
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.
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.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.
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