| Agent Name |
Silica, crystalline |
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| CAS Number |
14808-60-7, 14464-46-1, 15468-32-3, 1317-95-9 |
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| Formula |
O2-Si |
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| Major Category |
Mineral Dusts |
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| Synonyms |
Cristobalite; Quartz; Tridymite; Tripoli; [NIOSH] |
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| Category |
Fibrogenic Dusts |
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| Description |
Colorless, odorless solid. [Note: A component of many mineral dusts.]; [NIOSH] |
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| Sources/Uses |
Quartz is present in most sedimentary and igneous rocks: granite has 25-40% quartz; shales have 22% quartz; sandstones have 67% quartz. Workers are exposed in hard-rock mining, foundries, ceramic manufacturing, and road construction. Cristobalite, mostly from calcined diatomaceous earth, is used to manufacture water glass, abrasives, ceramics and enamels. Cristobalite is also used to purify oils. [ACGIH] Crystalline silica not bound to other minerals is "free" silica. [Rom, p. 364] |
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| Comments |
Silica occurs in both crystalline and amorphous forms. Quartz is the most common crystalline form, and it causes most cases of silicosis. [Harber, p. 373] Silica exposure is associated with lung fibrosis (silicosis) and increased risk of lung cancer.[ACGIH] Classic silicosis is caused by low to moderate silica exposure for 20 years or more. Disabling complications include tuberculosis and progressive massive fibrosis. Diagnosis is made by 1.) history of sufficient exposure; 2.) x-ray findings of silicosis; and 3.) absence of miliary tuberculosis and fungal infections. Open lung biopsy is usually not necessary. [Rom, p. 371]"The possible association of silica and glomerulonephritis is suggested by animal studies, case-control studies, and multiple case reports."[LaDou, p. 371] |
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| Reference Link |
OSHA: Silica, Crystalline |
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| Exposure Assessment |
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| Skin Designation (ACGIH) |
No |
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| Bioaccumulates |
Yes |
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| TLV (ACGIH) |
0.02 mg/m3, respir. fraction(cristobalite, quartz, tripoli) |
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| PEL (OSHA) | 30 mg/m3/%SiO2+2, total dust, 10 mg/m3/%SiO2+2, respir. dust(quartz, tripoli), Value calculated from respir. dust formula for quartz(cristobalite, tridymite) |
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| IDLH (NIOSH) |
25 mg/m3(cristobalite, tridymite), 50 mg/m3(quartz, tripoli) |
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| Excerpts from Documentation for IDLHs |
Basis for revised IDLH: The available toxicological data contain no evidence that an acute exposure to a high concentration of crystalline silica would impede escape or cause any irreversible health effects within 30 minutes. However, the revised IDLHs for crystalline silica are 25 mg/m3 for Cristobalite and Tridymite and 50 mg/m3 for Quartz and Tripoli, based on being 500 times the 1989 OSHA PELs of 0.05 mg/m3 and 0.1 mg/m3, respectively (500 is an assigned protection factor for respirators and was used arbitrarily during the Standards Completion Program for deciding when the "most protective" respirators should be used for particulates). [Note: NIOSH recommends that the "most protective" respirators be worn for all varieties of crystalline silica at concentrations above 25 mg/m3.] |
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| Adverse Effects |
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| Fibrogenic |
Yes |
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| Chronic Bronchitis |
Yes |
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| Lung Cancer |
Yes |
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| Nephrotoxin |
Yes |
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| IARC Carcinogen |
Known Carcinogen |
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| Links to Other NLM Databases |
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| Health Studies |
Human Health Effects from Hazardous Substances Data Bank: CRYSTALLINE SILICA
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