Hazardous substance assessment – Cristobalite

Identification

Chemical name:

Cristobalite

CAS #:

14464-46-1

Chemical composition:

SiO ₂

Synonyms :

• Silica, crystalline – cristobalite
• Calcined diatomaceous earth
• Metacristobalite
• Calcined diatomite

UN #:

No chemical-specific UN # available

Pictogram(s):

Figure 1 – Text description

The symbol within the pictogram is a black silhouette of a person's head and chest with a white star shape spreading out from the center of the chest. This symbol indicates that hazardous products with this pictogram can cause certain health effects for example:

• carcinogenicity
• specific target organ effects following single or repeated exposure
• reproductive toxicity

WHMIS classification

Health hazards:

• Carcinogenicity – Category 1A
• Specific Target Organ Toxicity – Repeated Exposure – Category 1

Physical hazards:

Cristobalite does not meet the criteria for classification.

Health hazards

Acute Toxicity (Oral):

No data available

No data are available to determine whether cristobalite meets the classification criteria for a category of Acute Toxicity (Oral).

Acute Toxicity (Dermal):

No data available

No data are available to determine whether cristobalite meets the classification criteria for a category of Acute Toxicity (Dermal).

Acute Toxicity (Inhalation – Gases):

Not applicable

Cristobalite is not a gas. The classification criteria for Acute Toxicity (Inhalation – Gases) do not apply to this substance.

Acute Toxicity (Inhalation – Vapours):

No data available

No data are available to determine whether cristobalite meets the classification criteria for a category of Acute Toxicity (Inhalation – Vapours).

Acute Toxicity (Inhalation – Dusts and Mists):

No data available

No data are available to determine whether cristobalite meets the classification criteria for a category of Acute Toxicity (Inhalation – Dusts and Mists).

Skin Corrosion / Irritation:

No data available

No data are available to determine whether cristobalite meets the classification criteria for a category or subcategory of Skin Corrosion / Irritation.

Serious Eye Damage / Eye Irritation:

No data available

No data are available to determine whether cristobalite meets the classification criteria for a category or subcategory of Serious Eye Damage / Eye Irritation.

Respiratory Sensitization:

No data available

No data are available to determine whether cristobalite meets the classification criteria for a category or subcategory of Respiratory Sensitization.

Skin Sensitization:

No data available

No data are available to determine whether cristobalite meets the classification criteria for a category or subcategory of Skin Sensitization.

Germ Cell Mutagenicity:

Does not meet criteria

A category-based assessment cited several in vitro and in vivo studies for crystalline silica, with positive and negative genotoxicity and mutagenicity results^{Reference 1}. The positive genotoxicity results were ascribed to a secondary effect of oxidative damage, with no direct genotoxic effect expected.

Classification in a category or subcategory of this hazard class is based on an intrinsic ability to induce mutations in germ cells. As the positive effects noted above were secondary in nature, cristobalite does not meet the classification criteria of a category or subcategory of this hazard class.

Carcinogenicity:

Category 1A

Quartz silica, another polymorph of crystalline silica with similar properties, has been classified by the International Agency for Research on Cancer as a Group 1 carcinogen, namely that it is carcinogenic to humans ^{Reference 2}, and by the American Conference of Governmental Industrial Hygienists as A2, a suspected human carcinogen ^{Reference 3}. Respirable crystalline silica, primarily quartz dusts occurring in industrial and occupational settings, is known to be a human carcinogen according to the National Toxicology Program ^{Reference 4}.

Data collected from a multi-cancer occupational exposure case-referent study indicated that silica exposure increases the risk of lung cancer in humans ^{Reference 5}. Lung cancer rates in silicotics, as in workers affected with silicosis, who had no exposure to other known occupational carcinogens were 1.5 times higher than those of a referent group of coal miners with coal-worker’s pneumoconiosis and 2.4 times higher than those of a referent group of non-silicotic metal miners. Age- and smoking-adjusted lung cancer rates in silicotics were 3.9 times higher compared to a group of metal miners ^{Reference 6}. Lung cancer rates are higher in workers confirmed to have silicosis than in similarly exposed workers who do not have silicosis. Cancer risk is often more significant in workers exposed to crystalline silica over a 20-year period or to higher cumulative exposure levels ^{Reference 7}.

Several studies in rats have shown increases in lung tumours after chronic inhalation exposure to quartz silica at concentrations ranging from 1 to 50 milligrams per cubic metre (mg/m³) (1, 6 and 30 mg/m ³ of DQ-12 quartz silica; 12 and 50 mg/m ³ of Min-U-Sil 5 quartz silica) and over exposure durations ranging from 29 days to 2 years ^{Reference 7}.

The available data for crystalline silica, including those for quartz silica, a polymorph with similar properties, in a respirable form meet the classification criteria for Carcinogenicity – Category 1A [HPR 8.6.1].

Reproductive Toxicity:

No data available

No data are available to determine whether cristobalite meets the classification criteria for a category or subcategory of Reproductive Toxicity.

Specific Target Organ Toxicity – Single Exposure:

No data available

No data are available to determine whether cristobalite meets the classification criteria for a category of Specific Target Organ Toxicity – Single Exposure.

Specific Target Organ Toxicity – Repeated Exposure:

Category 1

Oral Route of Exposure: No data available

Dermal Route of Exposure: No data available

Inhalation Route of Exposure: Male Fischer‑344 rats (n=45) were exposed for 40 to 48 hours over an 8-day period to an aerosol containing 100% respirable particles of cristobalite at exposure concentrations of 0.058 to 0.073 milligrams per litre (mg/L). At each observation timepoint, 3 rats were sacrificed for histopathological exam and 3 for lavage and tissue studies. The timepoints for sacrifice were 0, 5, 12, 60 and 120 days after completion of aerosol exposure. All exposed animals exhibited inflammatory responses, with a statistically significant increase in multinucleated macrophages at 12 days post-exposure. By 120 days after exposure, many granulomas were observed mainly containing large macrophages and fibroblasts and there was extensive focal deposition of connective tissue in the lung ^{Reference 8}. The concentrations tested caused specific target organ toxicity and meet the guidance value for Category 1 of this hazard class, adjusted for the shorter exposure duration.

Exposure of rats to respirable cristobalite at a concentration of 0.0275 mg/L for 5 hours per day for 8 days led to a rapid influx of neutrophils and macrophages into alveolar and tissue compartments of the lung, followed by a more gradual accumulation of T lymphocytes and formation of multiple nodular inflammatory lesions. This inflammatory response persisted throughout 52 weeks after the end of the exposure ^{Reference 9}. Similar results were obtained in a second study by the same research group at a cristobalite concentration of 0.058 mg/L^{Reference 10}. The concentrations tested caused specific target organ toxicity and meet the guidance value for Category 1 of this hazard class, adjusted for the shorter exposure duration.

Groups of 24 CD rats were exposed 6 hours per day for 3 days to a concentration of 10 or 100 mg/m³ of cristobalite aerosol. The mass median aerodynamic diameter of the cristobalite particles tested was 3.4 to 3.6 μm, indicating the test material to be respirable. Cristobalite exposure at both of the concentrations tested produced pulmonary inflammatory responses characterized by neutrophil recruitment and consistently elevated biomarkers of cytotoxicity in bronchoalveolar lavage fluids compared to those of a sham control group. These inflammatory responses were persistent at observations made up to 90 days after exposure ^{Reference 11}. The concentrations tested caused specific target organ toxicity and meet the guidance value for Category 1 of this hazard class, adjusted for the shorter exposure duration.

The available animal data for cristobalite in a respirable form meet the classification criteria for Specific Target Organ Toxicity - Repeated Exposure - Category 1 based on lung effects [HPR 8.9.1].

Aspiration Hazard:

No data available

This substance is not a liquid hydrocarbon and no human data were identified as to its aspiration toxicity.

Biohazardous Infectious Materials:

Not applicable

Cristobalite is not a microorganism, protein or nucleic acid.

Physical hazards

Explosives:

Not evaluated
Explosives are excluded from the HPAand its regulations. Explosives are regulated under the Explosives Act. For more information, visit Natural Resources Canada.

Flammable Gases:

Not applicable

Cristobalite is not a gas. The classification criteria for Flammable Gases do not apply to this substance.

(Flammable) Aerosols:

Not evaluated

Classification of a hazardous product in the Flammable Aerosols or Aerosols hazard class is product dependent.

Oxidizing Gases:

Not applicable

Cristobalite is not a gas. The classification criteria for Oxidizing Gases do not apply to this substance.

Gases Under Pressure:

Not applicable

Cristobalite is not a gas. The classification criteria for Gases Under Pressure do not apply to this substance.

Flammable Liquids:

Not applicable

Cristobalite is not a liquid. The classification criteria for Flammable Liquids do not apply to this substance.

Flammable Solids:

Does not meet criteria

Cristobalite is not combustible^{Reference 12}.

The available data do not meet the classification criteria for a category of Flammable Solids.

Self-reactive Substances and Mixtures:

Does not meet criteria

Cristobalite is not combustible^{Reference 12}.

The available data do not meet the classification criteria for a category of Self-reactive Substances and Mixtures.

Pyrophoric Liquids:

Not applicable

Cristobalite is not a liquid. The classification criteria for Pyrophoric Liquids do not apply to this substance.

Pyrophoric Solids:

Does not meet criteria

Cristobalite is not combustibleReference 12.

The available data do not meet the classification criteria for a category of Pyrophoric Solids.

Self-heating Substances and Mixtures:

Does not meet criteria

Cristobalite is not combustibleReference 12.

The available data do not meet the classification criteria for a category of Self-heating Substances and Mixtures.

Substances and Mixtures Which, in Contact with Water, Emit Flammable Gases:

Excluded from classification

Cristobalite is soluble in water to some extent^{Reference 7} and forms a stable mixture and is, therefore, excluded from classification [HPR 7.12.1(1)(c)].

Oxidizing Liquids:

Not applicable

Cristobalite is not a liquid. The classification criteria for Oxidizing Liquids do not apply to this substance.

Oxidizing Solids:

No data available

No data are available to determine whether cristobalite meets the classification criteria for a category of Oxidizing Solids.

Organic Peroxides:

Not applicable

Cristobalite is not an organic peroxide. The classification criteria for Organic Peroxides do not apply to this substance.

Corrosive to Metals:

No data available

No data are available to determine whether cristobalite meets the classification criteria for a category of Corrosive to Metals.

Combustible Dusts:

Does not meet criteria

Cristobalite is not combustible^{Reference 12}.

The available data do not meet the classification criteria for a category of Combustible Dusts.

Simple Asphyxiants:

Not applicable

Cristobalite is not a gas. The classification criteria for Simple Asphyxiants do not apply to this substance.

Pyrophoric Gases:

Not applicable

Cristobalite is not a gas. The classification criteria for Pyrophoric Gases do not apply to this substance.

Chemicals Under Pressure:

Not evaluated

Classification of a hazardous product in the Chemicals Under Pressure hazard class is product dependent.

Regulatory and other information

Regulatory information:

Hazardous substance assessments are prepared by Health Canada as educational and information resources. Under the HPA, suppliers of hazardous products must, upon the sale or importation of a hazardous product, provide a safety data sheet and label that meet the requirements set out in the HPR.

Other information:

The information and classifications contained in these hazardous substance assessments are based on publicly available sources, such as peer-reviewed literature or reports by international bodies. New information, including proprietary information, could have an impact on the classification of substances or hazardous products containing them. It is the responsibility of the supplier to ensure the accuracy, sufficiency and reliability of their hazardous product classifications.

Last updated:

2024

Prepared by:

Workplace Hazardous Materials Bureau, Health Canada

References