Asbestos is a general term for a group of naturally occurring, fibrous silicate minerals. Chrysotile, found in bundles of fibres that can exceed 10 cm in length, is the most abundant form and the only serpentine variety. The five amphibole varieties include amosite, crocidolite, actinolite, tremolite and anthophyllite. Asbestos has been useful for many commercial applications because of its heat resistance, tensile strength, insulating and friction characteristics, as well as its ability to be woven.
Asbestos can be released into the environment by natural and human activity sources. Asbestos fibers vary in length, diameter, and chemical composition, which affects their ability to enter and deposit in the lungs. This influences the body's ability to clear the substance. Thin fibers (≥8 μm long with a diameter ≤1.5 μm) have the greatest potential for entry into the lungs and carcinogenic potency.
Asbestos has been classified by IARC as Group 1, carcinogenic to humans, with well established links to pleural and peritoneal mesotheliomas and to lung cancer. A recent IARC review of Class 1 carcinogens reaffirmed this classification, also finding "sufficient evidence in humans" for ovarian cancer, and "limited evidence in humans" for colorectal, pharynx, and stomach cancers. There is a strong synergistic effect for lung cancer with smoking. Increases in laryngeal and some other cancers are also reported, although the strength of association varies. A U.S. Institute of Medicine panel concluded that there is sufficient evidence for larynx cancer and suggestive evidence for pharynx, stomach, and colorectal cancer.
Asbestosis, a serious disease characterized by scar tissue in the lungs and in the pleural membrane, is caused by exposure to high concentrations of asbestos. Symptoms include difficulty breathing, coughing, and in severe cases, heart enlargement, disability and death.
Prohibition on spraying of all forms of asbestos and on use of crocidolite and crocidolite-containing products
Ban on the use of all forms of asbestos
Chrysotile has always been the most important asbestos fibre used commercially. Amosite, crocidolite and actinolite were used in commercial products, while tremolite and anthophyllite were typically encountered as contaminants.
Asbestos was used primarily for roofing, thermal and electrical insulation, cement pipe and sheets, flooring, gaskets, friction materials, coatings, plastics, textiles, paper, and other products.
Use of asbestos peaked in the late 1960s and early 1970s, when there were more than 3,000 industrial applications or asbestos-containing products. When asbestos use hit its peak in 1973, US consumption totaled 801,000 tonnes (t) and the major markets in the US included asbestos-cement pipes (192,000 t); flooring (176,000 t); roofing (72,000 t); friction products, such as automobile brakes and clutches (64,000 t); and packing and gaskets (24,000 t).
Asbestos consumption in 2007 in the US totaled 1,730 tonnes and included roofing products (709 t); coatings and compounds, likely in roofing (606 t); and sundry other unknown or unspecified uses (415 t).
Canadian Production and Trade
Prior to the closure of two Canadian asbestos mines in 2011, Canada was a major producer and exporter of asbestos. Approximately 410,000 tonnes of asbestos was produced in Canada between 2008 and 2010, accounting for roughly 6% of total global production in the same period. Canada also imports some manufactured goods including friction materials, tubes and pipes, corrugated sheets and panels, paper, millboard, clothing, and other chrysotile based materials.
Production and Trade
2006 Canadian Production
Export: Mainly to India, Indonesia
135,459 t of 'asbestos'
Import: Mainly from China
22 t of 'asbestos'
Import: Mainly from the US
57 t of 'articles of asbestos-cement, cellulose fibre-cement or the like'
t = tonne
Inhalation is the most important route of occupational exposure. However, current asbestos related disease is associated with exposures that occurred 10 to 40 years ago due to the latency period between exposure and disease onset. Exposure sources at that time were associated with the use of asbestos in manufactured products and buildings, as well as in mining and milling of asbestos. Exposure sources today tend to be from contact with older asbestos-containing products and can be thought of as a secondary exposure from contact with those older materials.
CAREX Canada estimates that approximately 152,000 Canadians are exposed to asbestos in the workplace. The largest industrial groups exposed are specialty trade contractors, followed by building construction, automotive repair, and ship building respectively. By occupation, the largest exposed groups are carpenters and cabinetmakers, followed by construction trade helpers and labourers. Exposure in construction workers may be difficult to monitor due to the wide variety of worksites and the transient nature of employment for many workers. Despite this, the INSPQ in Quebec recently released a report on exposures to asbestos in the construction industry.
Other significant occupational groups that may be exposed to asbestos are electricians, plumbers, plaster and drywall installers, and auto mechanics.
In the environment, inhalation of asbestos contaminated air is the primary route of exposure. People may be exposed to higher-than-average levels of asbestos in air if they use asbestos-containing products, or live or work in buildings with deteriorating asbestos insulation or that have undergone poorly performed asbestos removal. Family members of asbestos workers may also be exposed through contaminated work clothing. CAREX Canada estimates that asbestos levels in indoor and outdoor air may be sources of elevated cancer risk (very low data quality).
Vermiculite insulation produced from the 1920s through the 1990s and used for home insulation may contain amphibole asbestos and could be an exposure hazard if it is disturbed. Vermiculite products marketed for garden use may also contain asbestos. An EPA study in the Seattle area in 2000 found 5 of 16 purchased products were contaminated with asbestos.
Although contaminated air is the most important route of exposure in the general population, ingestion of asbestos via drinking water may also be a source in areas where asbestos occurs (either naturally or from human activities). There is a great deal of debate on the carcinogenic role (if any) of exposure to asbestos via the drinking water. In general, consistent evidence does not exist to support this hypothesis. Currently, we estimate that exposure via drinking water or food and beverage is negligible.
Asbestos is geologically related to talc, and talc from some deposits can be contaminated with asbestos, especially anthophyllite and tremolite. Talc is a common ingredient in cosmetics, but the type currently used for this purpose in the US does not contain any detectable asbestos.
For more information, see CAREX Canada’s environmental exposure estimates for asbestos. Searches of environmental and consumer product databases yielded the following results on current potential for exposure to asbestos in Canada:
NPRI and US Household Products Database
Search term: 'asbestos (friable form)'
Released into Environment
Mining, waste services, refineries, and power generation (54 facilities)
Sent to off-site recycling
US Household Products 2013
Roofing sealant cements
t = tonne
Our team has performed a detailed scan of exposure control resources and assembled a compilation of key publications and resources. These are organized by type of exposure (environmental or occupational) and by specificity (general or carcinogen-specific). Please visit our Exposures Reduction Resources page to view.
We also recommend exploring the Prevention Policies Directory, a freely-accessible online tool offering information on policies related to cancer and chronic disease prevention. Providing summaries of the policies and direct access to the policy documents, the Directory allows users to search by carcinogen, risk factor, jurisdiction, geographical location, and document type. To learn more about policies specific to asbestos on the Directory, click here. For questions about this resource, please contact Michelle Halligan, from the prevention team at the Canadian Partnership Against Cancer.