OCRC Report: Ontario Uranium Miners Cohort Study

Navaranjan G, Berriault C, Do M, et al. Toronto, Canada, February 2015. Report prepared for the Canadian Nuclear Safety Commission.

Purpose: This study is an updated analysis of mortality and cancer incidence for a cohort of Ontario uranium miners exposed to radon decay products (RDP). The cohort had been created previously using the Ontario Mining Master File (1954-1986) and data from the National Dose Registry (1954-2004). For this update the mortality follow-up of the cohort between 1954 and 2007 was expanded by linking to records in the Canadian Mortality Database, adding 21 years of additional follow-up. Similarly cancer incidence from 1969 and 2005 was ascertained by linking to the Canadian Cancer Database at Statistics Canada. Annual exposure to radon, in working level months (WLMs), was available for each cohort member.

Results: Compared to Canadian males, increased numbers of deaths for lung cancer , silicosis, and accidents, poisoning, or violence were observed. Lung cancer incidence among male miners was also increased relative to the Canadian population. Results suggest a strong dose-response relationship between exposure to radon decay products and lung cancer mortality and lung cancer incidence. There was about a two-fold increase in the risk of lung cancer mortality and lung cancer incidence.

Conclusions: The large cohort and national linkage allowed for the sample size to address several gaps in the literature including risks of cancer incidence, associations with specific histological groups and regional analyses of miners. However, limitations of the present study include lack of data on potential confounders and co-exposures of RDP including: smoking status, and silica, arsenic, and diesel exhaust concentrations. Finally, the low doses experienced by these Ontario miners, particularly after better ventilation was introduced in 1970, may be similar to the level of exposures experienced by present-day uranium miners. Thus, an analysis of Ontario miners may provide valuable information to aid in the evaluation of current radiation protection practices.