Do patterns of past asbestos use and production reflect current geographic variations of cancer risk?: mesothelioma in Ontario and British Columbia, Canada

Our plain-English summary of Do patterns of past asbestos use and production reflect current geographic variations of cancer risk?: mesothelioma in Ontario and British Columbia, Canada, by C.E. Slavik, P.A. Demers, L. Tamburic, et al (Cancer Causes & Control, 2023).

The study

• Authors: C.E. Slavik, P.A. Demers, L. Tamburic, H. Warden, C. McLeod
• Journal: Cancer Causes & Control
• Published: 2023;34(4):349-360
• Cited by: 1 article, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Purpose: Canada was a major global asbestos producer and consumer. Geographic patterns of Canadian asbestos use and mesothelioma, a highly fatal cancer linked to asbestos exposure, have not been previously reported. This study summarized key trends in mesothelioma incidence by geography and time in two Canadian provinces, Ontario and British Columbia (BC), and explored how past workforce characteristics and geographic trends in asbestos production and use may shape variations in regional rates of mesothelioma.

Methods: We report trends in mesothelioma incidence (1993-2016) for Ontario and British Columbia using population-based incidence data that were age-standardized to the 2011 Canadian population. Historical records of asbestos production and use were analyzed to geo-locate industrial point sources of asbestos in Ontario and BC. The prevalence of occupations in regions with the highest and lowest rates of mesothelioma in Ontario and BC were calculated using labor force statistics from the 1981 Canadian Census.

Results: Regional mesothelioma rates varied in both provinces over time; more census divisions in both Ontario and BC registered mesothelioma rates in the highest quintile of incidences during the period 2009 to 2016 than in any prior period examined. Certain occupations such as construction trades workers were more likely to be overrepresented in regions with high mesothelioma rates.

Conclusion: This work explored how studying asbestos exposure and mesothelioma incidence at small-scale geographies could direct cancer surveillance and research to more targeted areas. Findings indicated that regional variations in mesothelioma could signal important differences in past occupational and potentially environmental exposures.

© 2023. Crown.

In plain English

This study mapped mesothelioma (all sites) in Ontario and British Columbia, Canada. The authors compared age-standardized incidence rates for males and females combined across census divisions in three periods between 1993 and 2016. They also mapped historical sites of asbestos production and use, and compared 1981 census occupation data between census divisions with the highest and lowest rates. More census divisions in both provinces were in the highest rate group in 2009 to 2016 than in earlier periods. Lambton, Ontario, and Kootenay Boundary, British Columbia, had the highest rates in their provinces; Kootenay Boundary reached 6.3 per 100,000 in 2009 to 2016. Chemical, petroleum, plastics and rubber facilities clustered around Sarnia in Lambton. In 1981, high-rate divisions had larger shares of construction workers in both provinces (Ontario 7.4% versus 5.3%; British Columbia 10.6% versus 8.8%). Processing workers, however, were more common in low-rate British Columbia divisions. The authors concluded that regional variations could signal differences in past occupational and potentially environmental exposures. They noted that their list of asbestos sites was surely an underestimate.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Geographic (map-based) descriptive study. It compared regional mesothelioma incidence rates with the locations of historical asbestos-producing and asbestos-using industries and with 1981 census occupation data. It was part of a larger study of mesothelioma incidence and prognosis in the two provinces.
• Who was studied: Populations of census divisions in Ontario and British Columbia, Canada. Rates covered mesothelioma (all sites), males and females combined, age-standardized to the 2011 Canadian population, in three 8-year periods from 1993 to 2016. Annual crude rates by sex for Ontario, British Columbia and Quebec (1992 to 2018) were also compared. Case counts were not given.
• Exposure: No fiber types were specified. Exposure was represented by mapped locations of historical asbestos mines, four Johns Manville processing plants (late 1960s), and facilities reporting asbestos use, storage or disposal between 1992 and 2006. Shipyards and boat facilities were also mapped. In addition, the study used the share of the 1981 workforce in each occupation group.
• Main results:
  • In both provinces, more census divisions had rates in the highest quintile in 2009 to 2016 than in any earlier period examined.
  • Ontario, 1993 to 2000: only two census divisions were in the highest quintile, Lambton (4.7 per 100,000) and Stormont, Dundas and Glengarry (2.4 per 100,000).
  • Ontario, 2001 to 2008: 10 census divisions were in the highest quintile, with Lambton highest at 7.1 per 100,000.
  • Ontario, 2009 to 2016: 12 census divisions were in the highest quintile, and Lambton remained highest at 4.4 per 100,000.
  • In Renfrew, Ontario, the rate went from 0.2 per 100,000 (1993 to 2000) to 1.5 per 100,000 (2009 to 2016). This was the largest percentage change in Ontario, an increase of more than 500%.
  • British Columbia, 2009 to 2016: 9 census divisions were in the highest quintile, with Kootenay Boundary again highest at 6.3 per 100,000.
  • In Okanagan-Similkameen, British Columbia, the rate went from 1.4 per 100,000 (1993 to 2000) to 4.1 per 100,000 (2009 to 2016), an increase of about 200%.
  • Around Sarnia, in Lambton (Ontario's highest-rate census division), the asbestos-related facilities mapped included a cluster in the chemical, petroleum, plastics and rubber manufacturing industries.
  • Ontario, 1981 workforce: clerical occupations made up 22.6% of the workforce in the lowest-rate census divisions versus 15.4% in the highest-rate divisions (p less than 0.001).
  • Ontario, 1981 workforce: the highest-rate census divisions had higher shares in material processing (6.4% vs 2.8%), farming (5.0% vs 2.4%) and construction (7.4% vs 5.3%) than the lowest-rate divisions.
  • British Columbia, 1981 workforce: processing occupations made up 9.1% of the workforce in the lowest-rate census divisions versus 5.5% in the highest-rate divisions (p less than 0.001). This is the reverse of the Ontario pattern.
  • British Columbia, 1981 workforce: the highest-rate census divisions had higher shares in farming (3.6% vs 1.6%), construction (10.6% vs 8.8%) and mining (1.1% vs 0.8%) than the lowest-rate divisions (p less than 0.001).
  • Across provinces, rates appeared highest in Quebec, then British Columbia, then Ontario. Rates among females in Ontario have recently surpassed those among females in British Columbia.
  • Among males, rate differences were statistically significant between Ontario and British Columbia and between Ontario and Quebec, but not between British Columbia and Quebec (p = 0.424).
  • As printed (data not shown), mined volumes were approximately 400 tonnes in Ontario (ending 1977), 2500 tonnes in British Columbia (ending 1992) and 37,300 tonnes in Quebec (ending 2010).
• The authors' conclusion: The authors concluded that regional variations in mesothelioma could be a sign of important differences in past occupational and potentially environmental exposures.
• Limitations the authors state:
  • The list of locations where asbestos was used or produced is surely an underestimate, because many data sources were created after peak use.
  • Because numbers were small, regional rates combined both sexes, although males make up significantly more cases.
  • The study did not quantify actual asbestos exposures among farming occupations.
  • The study did not examine environmental or neighbourhood exposures, which the authors expect to become increasingly important.
  • Quebec incidence rates were not available after 2010, so the three provinces could not be compared over the last decade.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Mesothelioma.

Medical terms in this study, explained in our Lexicon: Mesothelioma, Asbestos Exposure, Environmental Exposure.

Related studies

• Identification of occupational cancer risks in British Columbia, Canada: a population-based case-control study of 1,155 cases of colon cancer — R. Fang, N. Le, et al. (2011)
• Surveillance of mesothelioma and workers' compensation in British Columbia, Canada — T.L. Kirkham, M.W. Koehoorn, et al. (2011)
• Cohort mortality study of pulp and paper mill workers in British Columbia, Canada — P.R. Band, N.D. Le, et al. (1997)
• Identification of occupational cancer risk in British Columbia: a population-based case-control study of 2,998 lung cancers by histopathological subtype — A.C. MacArthur, N.D. Le, et al. (2009)
• An approach to estimating the environmental burden of cancer from known and probable carcinogens: application to Ontario, Canada — S.L. Greco, E. MacIntyre, et al. (2020)
• Malignant mesothelioma in British Columbia in 1982 — A. Churg (1985)

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