Introduction Mining involves many exposures associated with increased respiratory disease risk, including crystalline silica, diesel engine exhaust, arsenic, nickel, and other metal compounds.

Objectives To investigate the risk of non-malignant respiratory disease (NMRD) in a cohort of Ontario mixed-ore miners.

Methods The Ontario Mining Master File (MMF) contains 90,000 work histories collected during mandatory annual medical exams from 1928 to 1988. Record linkages with provincial hospital and outpatient databases (1999–2017) were performed to ascertain respiratory disease incidence. Incidence rates were compared to provincial rates using standardized incidence ratios (SIR). Internal comparisons were made using Poisson regression to estimate age and birth year-adjusted incidence rate ratios (RRs) and 95% confidence intervals (CIs) for NMRDs. Stratified analyses were conducted for types of mining and ore mined.

Results The linked cohort of 30,413 males displayed significantly increased risks for COPD (SIR=2.65, CI=2.58–2.71), pulmonary fibrosis (SIR=2.02, CI=1.85–2.20), and silicosis (SIR=15.72, CI=14.55–20.65). Excesses of silicosis were observed for underground miners (SIR=17.41, CI=14.55–20.65), surface miners (SIR=19.58, CI=15.20–24.82) and mixed-ore miners (SIR=25.52, CI=20.98–30.76). Surface miners had an increased risk of silicosis compared to never surface miners. This risk increased with increasing duration of employment with the highest employment duration (≥10 years) yielding an RR of 3.49 (CI 1.69–7.21).

Conclusion Results are consistent with previous findings of an excess risk of respiratory disease (NMRD) among Ontario mine workers. This study provides increased understanding of these risks in relation to occupational factors and highlights a potentially overlooked increased risk of silicosis among surface mine workers in Ontario that bears further scrutiny. These results are supported by the unexpectedly high respirable crystalline silica exposures measured in Ontario mines surface operations as part of the related Ontario Mines Exposure Database (OMED). Together with the MMF the OMED exposure data provides future opportunities to test new hypotheses, including the impact of combined exposures among miners.