Objectives Summing the impact of occupational carcinogens is challenging, and previous studies have relied upon broad assumptions to calculate summary attributable fractions (AFs). As part of an effort to estimate the occupational cancer burden in Canada, we present an approach that uses detailed exposure assessment data and probabilities to calculate a combined AF for nine lung carcinogens.

Methods CAREX Canada estimates of exposure prevalence and level for five major lung carcinogens (silica, diesel, PAHs, nickel, and chromium) and prevalence alone for four exposure circumstances (welding, painting, iron and steel foundries, and rubber production) were merged to identify areas of overlap by detailed industry (328 groups) and occupation (520 groups). Exposure circumstances were removed from the assessments of relevant individual carcinogens to prevent double-counting. Exposure overlap was treated probabilistically, and where co-exposure occurred, the highest RR was assigned.

Results There were 3.8 million Canadians alive in 2011 who were ever exposed to at least one of the nine occupational lung carcinogens during our risk exposure period of 1961–2000. Of these, 87% had been exposed to one carcinogen, and 13% to two; exposure to more three or more carcinogens was relatively uncommon (<1%).

Individually, the highest lung cancer burdens are attributed to asbestos (1904 cancers), silica (573 cancers) and diesel (562 cancers). From the nine carcinogens combined, we estimate that each year 1510 new cases of lung cancer (AF = 6.4%) in Canada are attributable to occupational exposure.

Conclusions Our combined occupational lung cancer burden estimate is conservative, as we did not account for synergy between exposures, and did not include asbestos-related lung cancers, which were estimated using a different methodology. Much of this work was enabled by the detailed CAREX Canada exposure assessment, but we remain limited by the lack of detailed historical exposure assessment for asbestos.