Mesothelioma is an aggressive and highly fatal cancer that occurs in the lining of the lungs or abdomen and is primarily caused by exposure to asbestos. Approximately 80-85% of mesothelioma cases are attributable to occupational asbestos exposure [5-7]. It is estimated that annually in Ontario 140 mesotheliomas are a result of occupational exposure to asbestos and approximately 55,000 workers are still exposed to asbestos [Figure 1] [4-5]. Mesothelioma has very poor survival; In Ontario, median survival between 1993 and 2017 was 8.6 months, with 38% survival at one year and only 4.7% at five years [5].

Figure 1. Number of mesothelioma cases in Ontario, 1992-2017 [5]

Asbestosis is a serious disease characterized by lung tissue scarring caused by inhaling asbestos fibres. Symptoms include difficulty breathing, coughing, and in severe cases heart enlargement, disability, and death [3].

Asbestos is one of the most important causes of lung cancer after cigarette smoking. There is evidence that asbestos exposure and cigarette smoking have a positive synergistic interaction, with both additive and multiplicative effects on lung cancer risk [8]. In Ontario, occupational exposure to asbestos causes 630 lung cancers annually[4].

The ODSS was used to detect risks of disease across hundreds of industry and occupation groups. Worker groups with higher risks of asbestos-related disease are highlighted here. The following results show the % increase in risk among groups of workers by industry or occupation compared to all other workers followed in the ODSS.

Asbestos mining

Asbestos mining was a small industry in Northeastern Ontario that predominantly operated from 1950-1978 [9-10]. Only a small group of these miners were captured in the ODSS. However, this small group demonstrated a dramatically higher risk of mesothelioma compared to other workers. This is expected as these workers had very high levels of exposure to asbestos. Lung cancer risk was also 393% higher for asbestos miners compared to other workers in ODSS.

Building maintenance and repair

Ongoing exposure to asbestos can occur among workers during the removal of asbestos-containing products, maintenance, renovation, or demolition of older buildings. Asbestos was used in many different construction materials including insulation, drywall, flooring, and cement. Insulators have a particularly high risk due to the prevalence and high levels of asbestos in insulation materials installed prior to 1990 [11]. Any workers working close to or with asbestos-containing materials are at risk of inhaling asbestos fibres.

In the ODSS, workers employed in construction trades occupations had the greatest risk of both mesothelioma and asbestosis compared to other workers. Insulating workers, pipefitters and plumbers, electricians and carpenters were among the occupations with highest incidence rates, but many more were at increased risk [12].

Education services

Substantial amounts of asbestos were used in schools and university buildings to protect them from fires. Upon further analysis, the elevated risks in the education sector was largely associated with occupations involved in the maintenance of school buildings as opposed to teaching activities. Approximately 25% of mesothelioma and asbestosis cases were among school cleaning and janitorial staff, and approximately 40% of the cases were among construction and maintenance workers. Approximately 20% of the mesothelioma cases were observed among teaching and related staff.

Excess risks of asbestos-related disease among teaching staff may be due to exposure in schools, but some of those in teaching also had previous compensation claims indicating previous employment in other industries, such as manufacturing. However, the ODSS does not have complete work histories for all workers. A large US study saw similar increased risks among teaching occupations and suggested a previous history of employment in other occupations with probable asbestos exposure, environmental, residential, or spousal exposure may have contributed to their risk of mesothelioma [13].

Metal-related work

Increased risks of mesothelioma and asbestosis were observed for workers in metal-related manufacturing in the ODSS.

Working with metal products can involve extreme heat in many processes such as forming, shaping, and welding. Asbestos was a common insulating material used in machinery, equipment, and protective clothing for hot metalworking processes. Gloves, jackets, masks, and aprons contained asbestos as it was able to effectively protect workers from the extreme heat. Some metal products would also be finished with an asbestos-containing coating for durability and fire-proofing. Increased risks of mesothelioma and asbestosis have been reported in previous studies in metal-related industries and occupations, attributing this risk to asbestos in the work environment [14-16].

Non-metal manufacturing

Increased risk of mesothelioma and asbestosis was also observed in the ODSS among workers in non-metal manufacturing. Those working in non-metallic mineral manufacturing industries are at particularly high risk as this group includes those that create asbestos-containing products. Asbestos-insulated heating equipment was used in various non-metal manufacturing industries as it aids in processing or shaping different materials. Chemical manufacturing industries also used similar heating equipment to produce chemical reactions. Asbestos-coated workbenches and protective clothing were also used as it is resistant to chemicals and does not dissolve in water nor evaporate [17].

Asbestos was also used as a filler in plastic products which would make the final products resistant to moisture, heat, acid, and electricity and was commonly incorporated into tools and cookware products. Exposure may also have occurred through asbestos contaminated talc which is used in the production of many products including ceramics, plastics, and paper materials [18].

Motor vehicle manufacturing and repair

Asbestos-containing materials have historically been widely used in brake pads and other friction products used in motor vehicles, such as clutch pads. Although the manufacturing and use of asbestos-containing parts in the auto industry ceased in Canada in the 1980s, replacement parts would continue to be imported until the 2018 federal ban on the sale and use of asbestos products [19]. Older vehicles on the road still have asbestos-containing parts and occupational exposures during vehicle handling and repairing processes may continue to affect workers. In the ODSS, motor vehicle mechanics and repairers had a 33% increased risk of mesothelioma compared to all other workers.

Regulations under environmental protection and management statute govern asbestos management and disposal in Ontario. These regulations provide requirements for how asbestos waste is managed once it leaves the workplace, regarding transportation, storage, disposal, labelling of containers, protective clothing and equipment for workers, and permitting and reporting requirements [20]. Environmental regulations focused on the transportation and disposal of asbestos containing materials define asbestos waste as “solid or liquid waste that contains asbestos in more than a trivial amount”. Under Occupational Health & Safety regulations, materials containing a minimum of 0.5% asbestos are considered to be asbestos-containing [20]. It is required that asbestos waste only be transported by a driver trained in asbestos waste management. There is also legislation that provides training and education for specific workers, such as those employed in the construction sector in Ontario [20].

Assessment of asbestos risk varies by jurisdiction in Canada. In Ontario, risk categories are defined by Type 1 (low risk), Type 2 (moderate risk), and Type 3 (high risk). There are a number of operations that fall under each type and details can be found in the Asbestos Management in Canada: Assessing the Need for a National Standard report [20].

The technical guideline for asbestos exposure management programs by the Government of Canada also provides a detailed description of risk levels and control measures [21]. There are federal and provincial regulations that outline approaches to control asbestos exposure based on the level of risk for workers which include [22-25]:

• • Engineering controls (i.e. using a vacuum with a high efficiency particulate air (HEPA) filter)
  • Administrative controls (i.e. providing change rooms and laundering services at the worksite)
  • Training staff
  • Exposure monitoring
  • Wearing personal protective equipment

There is also the Ontario Asbestos Workers Registry which tracks exposure to asbestos-containing materials so that asbestos-exposed workers can be identified and advised to receive a medical examination after 2000 hours of exposure (equivalent to one full year’s employment) [26].

Recently, the Lung Cancer Screening Pilot for People at High Risk was introduced in Ontario to be able to diagnose high-risk individuals with lung cancer early on, when treatment is more effective. Eligibility is currently based on age and smoking status, but occupational exposures, such as asbestos, is being discussed and may be considered in the future [27].

Canadians who are diagnosed with asbestos-related diseases (i.e. mesothelioma or asbestosis) that were exposed to asbestos in the workplace may be eligible for the workers’ compensation through the Workplace Safety and Insurance Board (WSIB) [28-29].

The 2018 ban on asbestos was a positive step to reduce the burden of asbestos-related disease but exposure to asbestos in existing buildings and previously manufactured products remain an important concern for some workers. Asbestos-related disease will continue to be diagnosed today as a result of past exposure due to the long period between exposure to asbestos and disease onset. Continued awareness and monitoring of asbestos exposure and asbestos-related disease will continue to be important for decades to come to keep workers safe.

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