Silica (Crystalline) Profile
FIBERS AND DUSTS – KNOWN CARCINOGEN (IARC 1)
CAS No. 14464-46-1 (Cristabolite)
Silica (Crystalline) Profile
- One of the most common minerals on earth and a basic component of soil, sand, and rocks
- Associated cancer: Lung cancer
- Most important route of exposure: Inhalation
- Uses: Foundry castings, cement, abrasives and sandblasting materials, hydraulic fracturing, ceramics and pottery, metal production, and water filtration at treatment plants
- Occupational exposures: Approx. 380,000 Canadians are exposed to silica at work, primarily in the construction sector
- Fast fact: Exposure concerns arise when products containing silica are disturbed by grinding, cutting, drilling or chipping, creating respirable particulate.
Silica is one of the most common minerals on earth and is a basic component of soil, sand, and rocks including granite and quartzite. Silica exists in both crystalline and amorphous (non-crystalline) forms. Conversion from amorphous to crystalline form can occur at high heat. Quartz is the most common form of crystalline silica and the most commonly used industrially. Cristobalite also has important industrial uses. Tridymite is found in rocks and is not an important industrial product. There are numerous other synonyms and product names for silica; see the International Agency for Research on Cancer (IARC) for more information.
Crystalline silica is used extensively in many industrial applications because of its unique physical and chemical properties. Health concerns arise when products containing silica are disturbed by grinding, cutting, drilling, or chipping, which creates respirable dust.
IARC’s 1997 classification of crystalline silica as Group 1, a known human carcinogen, is specifically for quartz and cristobalite silica inhaled from occupational sources. The 2012 IARC review of Class 1 carcinogens reaffirmed this classification. Epidemiological studies show a relationship between occupational exposure to crystalline silica and increased risk of lung cancer, with the strongest link in quarry and granite workers and workers involved in ceramic, pottery, refractory brick, and diatomaceous earth industries. Increased risk was not evident with exposure to amorphous silica.
Silicosis, a non-reversible fibrotic lung disease, is caused by inhaling crystalline silica particles. Silicosis is typically categorized as chronic (> 10 years exposure), accelerated (high concentrations over 5-10 years), or acute (short term exposure at high concentrations). Besides silicosis and lung cancer, occupational silica exposure has also been linked to pulmonary tuberculosis, chronic obstructive pulmonary disease, and rheumatoid arthritis.[7,8]
Regulations and Guidelines
|Canadian Jurisdictions||OEL1 (mg/m3)|
|Canada Labour Code||0.025 [r]|
|AB||0.025 [r, cristobalite, quartz]|
|BC, MB, NL, NS, PE||0.025 [r]|
|NB||0.05 [r, cristobalite]
|ON||0.05 [r, cristobalite]
0.1 [r, quartz, tripoli]
2 [r, silica fume]
|NT, NU, SK||0.05 [r, cristobalite, quartz]
0.1 [r, tripoli]
|QC||0.05 [r, cristobalite, tridymite]
0.1 [r, quartz, tripoli]
|YT2||300 particles/mL [quartz, tripoli]
150 particles/mL [cristobalite, tridymite]
|Other Jurisdiction||OEL (mg/m3)|
|ACGIH 2018 TLV||0.025 [r]|
1: OEL for both quartz and cristobalite, unless otherwise specified.
2: Exposure limit determined with a konimeter, an instrument that measures dust in mines.
mg/m3 = milligrams per cubic meter
r = respirable fraction
tm = total mass
ACGIH = American Conference of Governmental Industrial Hygienists
TLV = threshold limit value
Canadian Environmental Guidelines
|Health Canada||DSL – high priority substances with greatest
potential for exposure (quartz cristobalite)
|Challenge to Industry||Batch 12B (Health) for quartz and cristobalite||2006|
|Ontario Ambient Air Quality Criteria||24 hour: 5 µg/m3 [respirable (<10µg diameter)
cristabolite, quartz, or tridymite]
DSL = domestic substances list
Applications for silica differ depending on the particle size, which is divided into three general size categories: lump silica, 0.3 – 15 cm; sand, 75 μm – 3 mm; and flour, < 75 μm.
Lump silica is used as flux for smelting operations, in silicon and ferrosilicon alloys, and for silica brick. This size fraction is not of concern for health effects as it is too large to inhale.
Sand, the most common size fraction of natural crystalline silica, has many applications. For example, it may be used in foundry castings, Portland cement, abrasives and sandblasting materials, and hydraulic fracturing.[3,32] It may also be used as a raw material for producing silicon and ferrosilicon metals, or as a filter for large volumes of water, i.e. in municipal water and sewage treatment plants.[3,32] When sand has more than 98% silica and low iron content it can be used for glass and ceramic production.
Flours are formed by grinding quartz, quartzite, sand, and sandstone. Flours are very fine grades of crystalline silica and are used in the ceramic and pottery industry, in manufacturing chrysotile cement, as a filler in rubber and paints, and as an abrasive in soaps and cleaners.
Canadian Production and Trade
Quebec, Ontario, and Alberta are the primary silica producers in Canada, followed by Saskatchewan, BC, and Nova Scotia. There are silica deposits in all Canadian provinces, however not all are in commercial operation.
Canadian production of silica fulfills most of its domestic requirements, however high quality sands for glass and foundry applications are imported from the US.
Production and Trade
TOTAL: 1,690,000 t
|Export||396,263 t of ‘silica sands and quartz sands’||2015|
|Import||9,176,168 t of ‘silica sands and quartz sands’||2015|
t = tonne
Environmental Exposures Overview
The general population can be exposed to crystalline silica through industrial and non-industrial sources, although levels of exposure are expected to be very low and therefore not a risk for cancer. Non-industrial sources include desert dust and sandstorms in hilly areas, and farming, construction, and demolition activities. Non-occupational inhalation of quartz may also occur when using certain commercial products, such as cleansers, cosmetics, art clays, pet litter, talcum powder, paint, and mortar. Industrial sources include factories involved in quartz crushing, agate grinding, ceramics, slate pencil, mining and milling of sand stones, silica flour milling, and granite. People living in the vicinity of factories such as these may be exposed to silica.
Occupational Exposures Overview
Inhalation is the most important route of occupational exposure to silica.
CAREX Canada estimates that approximately 380,000 Canadians are exposed to silica in their workplace. The largest industrial group exposed is construction. In terms of occupation, the largest occupational groups exposed to silica were construction trades labourers, heavy equipment operators, and plasterers and drywallers.
Exposure to crystalline silica, especially quartz, may also occur in a number of other industries and occupations due to its wide and variable use. Workers can be exposed in industries such as mining, agriculture, and various manufacturing industries.[1,3,4] Job tasks that are typically associated with exposure to silica include grinding, sandblasting, crushing, chipping, mixing, and plowing.
For more information, see the occupational exposure estimate for silica.
- Maciejewska A. “Occupational Exposure Assessment for Crystalline Silica Dust: Approach in Poland and Worldwide.” Int J Occup Med Environ Health 2008;21(1)1-23.
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