Cancer mortality in chrysotile miners and millers, Russian Federation: main results (Asbest Chrysotile Cohort-Study)

BACKGROUND

We investigated mortality in workers of the world's largest chrysotile mine and enrichment factories located in the town of Asbest, Russian Federation.

METHODS

This historical cohort study included all workers employed for at least 1 year between 1975 and 2010 and follow-up until the end of 2015. Cumulative exposure to dust was estimated based on workers' complete occupational history linked to dust measurements systematically collected from the 1950s. Exposure to chrysotile fibers was estimated using dust-to-fiber conversion factors. Relative risks (RRs) and 95% confidence intervals (CIs) were estimated as mortality rate ratios in Poisson regression models.

RESULTS

A total of 30 445 (32% women) workers accumulated 721 312 person-years at risk and 11 110 (36%) died. Of the workers, 54% had more than 30 years since their first exposure. We found an exposure-response between cumulative dust and lung cancer mortality in men. No clear association with dust exposure but a modest increase in the highest category of fiber exposure was seen for lung cancer in women. Mesothelioma mortality was increased (RR = 7.64, 95% CI = 1.18 to 49.5, to at least 80 fibers per cm3 years and RR = 4.56, 95% CI = 0.94 to 22.1, to at least 150 mg/m3 years [dust]), based on 13 deaths. For colorectal and stomach cancer, there were inconsistent associations. No associations were seen for laryngeal or ovarian cancer.

CONCLUSION

In this large-scale epidemiological study in the world's largest active asbestos mine, we confirmed an increased risk of mesothelioma with high fiber exposure and an increasing mortality for lung cancer in men with increasing dust exposure. Less clear-cut increased lung cancer mortality was seen in the women. Continued mortality follow-up is warranted.

Occupational cohort study of current and former workers exposed to chrysotile in mine and processing facilities in Asbest, the Russian Federation: Cohort profile of the Asbest Chrysotile Cohort study

A historical cohort study in workers occupationally exposed to chrysotile was set up in the town of Asbest, the Russian Federation, to study their cause-specific mortality, with a focus on cancer. Chrysotile has different chemical and physical properties compared with other asbestos fibres; therefore it is important to conduct studies specifically of chrysotile and in different geographical regions to improve the knowledge about its carcinogenicity. Setting was the town of Asbest, Sverdlovsk oblast, the Russian Federation. Participants were all current and former employees with at least one year of employment between 1/1/1975 and 31/12/2010 in the mine, enrichment factories, auto-transport and external rail transportation departments, the central laboratory, and the explosives unit of the company. Of the 35,837 cohort members, 12,729 (35.5%) had died (2,373 of them of cancer, including 10 of mesothelioma), 18,799 (52.5%) were known to be alive at the end of the observation period (2015), and 4,309 (12.0%) were censored before the end of 2015. Mean follow-up duration was 21.7 years in men and 25.9 years in women. The mean age at death was 59.4 years in men and 66.5 years in women. This is the largest occupational cohort of chrysotile workers to date, and the only one with a large proportion of exposed female workers.