Silica, crystalline
Silica, crystalline, primarily exists as quartz and is a common component in various natural and industrial materials, such as sand, glass, and ceramics. It is classified as a human carcinogen, particularly linked to an increased risk of lung cancer due to inhalation of respirable crystalline silica dust in occupational settings. Notably, exposure to crystalline forms like quartz and cristobalite is specifically associated with respiratory diseases, including silicosis, which is a lung condition resulting from prolonged exposure to silica dust. Workers in industries such as mining, ceramics, and construction are particularly vulnerable to these health risks. Although crystalline silica is prevalent in many everyday materials, safety regulations have been established to mitigate exposure in workplaces. The understanding of silica's health impacts has evolved over decades, with increasing awareness leading to its regulation under occupational health standards. Given its widespread presence, awareness of silica-related risks is crucial for protecting worker health and safety.
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Silica, crystalline
RoC status: Reasonably anticipated human carcinogen since 1991; known human carcinogen since 2000
Also known as: Quartz, cristobalite, tridymite, sand, crystalline silicon dioxide
Related cancers:Lung cancer is related to exposure to respirable quartz and cristobalite but not to amorphous silica.
Definition: Respirable crystalline silica, primarily quartz dusts occurring in industrial and occupational settings, is known to be a human carcinogen, based on studies in humans indicating a causal relationship between exposure to respirable crystalline silica and increased lung cancer rates in workers. Respirable crystalline silica was first listed in the Sixth Report on Carcinogens (RoC), published in 1991 by the National Toxicology Program of the U.S. Department of Health and Human Services, as “reasonably anticipated to be a human carcinogen” based on evidence of carcinogenicity in experimental animals; however, the listing was revised to “known to be a human carcinogen” in the Ninth Report on Carcinogens in 2000.
Exposure route:Inhalation
Where found: Silica sand has been used in the manufacture of glass and ceramics and in foundry castings and has been used as an abrasive in sandpaper and grinding and polishing agents. It is also found in sandblasting materials, in oil and natural gas recovery, in quarries, in water filtration for sewage treatment plants, and in the production of silicon. Cristobalite is a major component of refractory silica bricks. Extremely fine grades of silica sand known as flours may be used in toothpaste, scouring powders, metal polishes, paints, rubber, paper, plastics, wood fillers, cements, road-surfacing materials, and foundry applications. Crystalline silica is also found in tobacco products.
At risk: Quarry and granite workers as well as workers involved in the ceramic, pottery, refractory brick, and diatomaceous earth industries are most at risk.
Etiology and symptoms of associated cancers: Marked and persistent inflammation, specifically inflammatory cell-derived oxidants, may provide a mechanism by which respirable crystalline silica exposure can result in lung cancer.
History: Crystalline silica is composed of silicon and oxygen. The mineral is ubiquitous in both nature and people’s daily lives. Scientists have known for decades that prolonged excessive exposure to crystalline silica dust in mining environments can cause silicosis, a lung disease. During the 1980s, studies were conducted that suggested that crystalline silica also was a carcinogen. As a result of these findings, crystalline silica has been regulated under the Occupational Safety and Health Administration’s Hazard Communication Standard (HCS).
Bibliography
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Natl. Inst. for Occupational Safety and Health. "Silica." CDC.gov. Centers for Disease Control and Prevention, 17 July 2013. Web. 8 Jan. 2015.
Natl. Toxicology Program, US Dept. of Health and Human Services. "Silica, Crystalline (Respirable Size)."13th Report on Carcinogens (2014).Natl. Toxicology Program, 2 Oct. 2014. Web. 8 Jan. 2015.
Occupational Safety and Health Admin., US Dept. of Labor. "OSHA Fact Sheet: Crystalline Silica Exposure Health Hazard Information." OSHA.gov. OSHA, 2002. Web. 8 Jan. 2015.
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