The purpose of this project was to examine cancer and chronic respiratory disease risk among workers with contemporary asbestos exposure using the Ontario Asbestos Workers Register (AWR). This project also assessed the utility of the AWR data for occupational disease surveillance in Ontario.
Asbestos is classified as a known human carcinogen by the International Agency for Research on Cancer (IARC), and exposure can lead to lung cancer, mesothelioma, asbestosis and other respiratory diseases. Research on asbestos and occupational health has historically focused on miners and manufacturing workers, but contemporary exposure to asbestos occurs among workers involved in removal and remediation of asbestos-containing materials (ACM) or maintenance and renovation of ACM containing structures.
The Ontario Asbestos Workers Register (AWR) was developed in 1986 to monitor exposure to asbestos-containing materials (ACM) so that asbestos-exposed workers could be identified and information on potential health impacts could be provided to both the worker and their primary health care provider. Employers of asbestos-exposed workers in Ontario are required to register them with the AWR, and thus the AWR provides valuable information on asbestos-exposed workers outside of mining and manufacturing.
A retrospective cohort of workers with occupational exposure to asbestos in Ontario was created from the AWR records. The cohort was followed for disease diagnoses using a number of administrative health databases that provided information on health outcomes, including: the Ontario Health Insurance Plan’s Registered Persons Database, the Ontario Health Insurance Plan (OHIP) claims database, the Discharge Abstract Database, the National Ambulatory Care Reporting System, and the Ontario Cancer Registry. Health risks for these workers were assessed by comparing the risk of disease among asbestos workers to the general Ontario population, and to other asbestos workers with lower levels of exposure. Risk was compared among asbestos workers according to reported working hours in Type II and Type III activities, and duration of employment. Risks were also evaluated among males and females separately and according to industry sector of work.
The cohort developed from the AWR contained information on 26,302 workers successfully linked to the health databases, including 25,479 men and 823 women. The major industries represented were construction (61%), manufacturing (18%), educational services (8%), utilities (4%), and administrative support, waste management and remediation services (2%).
For both men and women, the relative risk of mesothelioma, pulmonary fibrosis, and chronic obstructive pulmonary disease (COPD) was much higher among asbestos-exposed workers than the general population. Relative risk of asbestosis was also much higher among asbestos-exposed men than the general population, but there were too few cases among women to report. The relative risk of lung cancer was only slightly elevated in men, though more substantially elevated in women.
Total asbestos exposure measured in hours of reported Type II and III activities was strongly associated with all the diseases described above. The top third of people, who averaged 1,000 hours of exposure, had a 210% higher risk of mesothelioma, 30% higher risk of lung cancer, 230% higher risk of asbestosis, 86% higher risk of pulmonary fibrosis and 34% higher risk of COPD than the lowest third (who averaged only 8 reported hours). When disease risk was examined by industry, workers in the construction industry had a 230% higher risk of mesothelioma, 76% higher risk of lung cancer, and 52% higher risk of COPD.
Asbestos exposure during the period of operation of the AWR were generally much lower that levels during earlier decades. Despite this, the AWR successfully identified a high-risk population for asbestos-related cancer and non-malignant respiratory disease.
While this study demonstrates that the AWR can be used to generate results useful for surveillance and prevention efforts, it was created to benefit the registered workers through improving early detection and secondary prevention. When a registered worker reaches 2000 hours, equivalent to one year of full-time work, their results were to be reviewed by the Ministry’s Provincial Physician and the worker notified. Although the health effects observed in this study may be due exposures not captured by the AWR, the threshold of 2000 hours should be re-examined.
Despite the federal ban on asbestos in Canada (2018), jobs dealing with historical ACM will remain a concern with the need to maintain and remediate existing asbestos in buildings. Future analyses of the AWR with longer follow-up may be able to explore the risk of disease associated with more recent asbestos exposure.
This study was funded by a grant from the Ontario Ministry of Labour, Training and Skills Development’s Research Opportunities Program.
