Our goal is to estimate Canadians’ potential exposures to known and suspected carcinogens in the workplace. Estimates of the numbers of workers exposed to specific carcinogens have been calculated by industry, occupation, province and sex. Where data are available, levels of exposure expected in Canadian workplaces have also been estimated.
These estimates are important for developing prevention strategies for cancer and other occupationally-related diseases, for targeting high-risk groups, for determining the occupational burden of cancer in Canada, and for creating new epidemiologic studies that are able to increase our ability to recognize and prevent occupational cancers.
Our estimates are produced following a general approach to ensure transparency, scientific rigor, ease of interpretation, and comparability between substances. The approach is flexible, and may be adjusted for substances with unique data sources or particular challenges with respect to uncertainty. For instance, we used a modified approach to assess occupational exposure to antineoplastics and solar ultraviolet radiation.
CAREX Canada is committed to providing estimates that are as accurate as possible. A challenge that we face is a general lack of current occupational exposure data. This may affect both our prevalence estimates and levels of exposure estimates, especially when the use of a substance has changed substantially since the 1990s. We welcome comments and additional data sources from researchers and other stakeholders in occupational health.
Exposure prevalence estimates approach
To generate the exposure prevalence estimates, we combined information gathered in a scientific literature review, data included in the Canadian Workplace Exposure Database (CWED), information from previous CAREX projects in Europe, Canadian-specific information on exposure from government and other sources, and CAREX occupational hygienists’ expert assessment. The main goal of the information collection was to gather current information on Canadian uses of a substance, potential industries and occupations where exposure may occur, and exposure circumstances. Where exposure data is available in the CWED, we identified industries and occupations where exposure has been measured. This allowed us to confirm exposed jobs and industries flagged during our literature review, and to flag new industries that we had not originally considered.
Level of exposure estimates approach
For substances with sufficient Canadian exposure measurement data in the CWED, we generated estimates of the level of exposure. Exposure concentration thresholds relevant to workplace exposure limits and cancer health outcomes were selected for each of these substances. Based on the number of measurements available in the CWED and their concentrations, exposure may be categorized into three categories: low, moderate or high. Details of the categorization criteria are available for each substance with exposure level estimates, such as wood dust and benzene.
Canadian Workplace Exposures Database
The Canadian Workplace Exposure Database (CWED) is a national exposure database that has been created as an important part of CAREX Canada. The CWED contains measurement data on exposure to known, probable and possible carcinogens in Canada from a variety of sources.
Data from the CWED is useful for both cancer prevention and research. To learn more about the Canadian Workplace Exposure Database, please see our brochure [PDF]. Some examples of how the CWED can be used are shown below.
Changes in Benzene Exposure Levels Over Time
Workplace exposure data from BC and Ontario show that exposure to benzene declined over the 1980s. This could be due to the reduction of allowable benzene in gasoline in the late 1980s in Canada. The CWED could help show the impact of regulatory change on workers’ exposure to carcinogens.
Industry-specific Differences in Exposure to Benzene
This chart shows the mean benzene concentrations in the workplaces most frequently sampled for benzene in Ontario between 1981 and 1996. The CWED helps to identify at-risk groups of workers to target educational, regulatory, or other prevention efforts. Industries with higher exposure are not necessarily the most frequently sampled. CWED can also be used to identify industries where further data need to be collected.
External Sources of Benzene Exposure Data
Workers in gasoline stations are at risk of exposure to benzene, but in BC and Ontario, very few samples have been taken. In these cases, external data (from other agencies, countries, or published literature) can be used in the CWED to estimate exposure.