To investigate the chronic respiratory disease and cancer experience of an Ontario hard rock mining cohort in relation to occupational factors such as duration of employment in mining and the type of mining performed, with follow-up of 18 years for respiratory disease and 53 years for cancer incidence and mortality.
Mining is an important industry in Ontario, employing thousands of workers to extract ores from underground mines and quarries. Despite the economic benefits, there are adverse health consequences. In addition to the physical dangers posed by mining activities, miners are also exposed to a variety of known carcinogens including crystalline silica, diesel exhaust, radon decay products, arsenic, cadmium, nickel, and chromium. Many of these exposures can have both short and long-term adverse health effects contributing to the development of cancers and other chronic diseases.
The long-term health concerns of these miners were recognized in the early days of mining. These concerns provided the impetus for the development and maintenance of the Mining Master File (MMF). The MMF is a centralized database of information on 93,000 Ontario mining industry workers who were employed until the program was discontinued in 1988. The MMF data was collected during required annual medical examinations from 1928 to 1988 for underground miner certification by the province. This included mining employment histories spanning 1877 to 1988.
The first step in this project was to create a research platform for investigating relationships between employment in the Ontario mining industry and occupational disease. The research platform was developed by using the Mining Master File (MMF) to create a retrospective cohort of mine workers from various mines in Ontario. The health risks for these workers were then evaluated by linking the cohort to a number of administrative health databases that provided information on health outcomes, including: Ontario Health Insurance Plan’s Registered Persons Database (RPDB), the Ontario Health Insurance Plan (OHIP) Claims database, the Discharge Abstract Database (DAD), the National Ambulatory Care Reporting System (NACRS), and the Ontario Cancer Registry (OCR). The cancer incidence and mortality experience of this cohort were compared to the general Ontario population by calculating standardized mortality (SMR) and incidence (SIR) ratios. Respiratory disease incidence risk was examined in relation to occupational variables (e.g., job categories, duration of employment, mine types).
The final cohort file consisted of 61,397 male and 161 female workers employed in Ontario mines between 1928 and 1988 and successfully linked to Ontario’s health databases. Due to small numbers, female workers were excluded from further analyses.
Compared to the general population, workers in the MMF had higher risk of silicosis and lung cancer. Lung cancer incidence was higher among underground and surface miners compared to the Ontario population. Lung cancer incidence was also notably higher among gold, uranium, and to a lesser extent nickel miners. There was an increased risk of pulmonary fibrosis and silicosis among all job categories employed more than five years but no clear pattern or trend. Miners had higher risks for silicosis and pulmonary fibrosis with increasing duration of surface mining employment while miners had higher COPD risks at all durations of underground mining employment. There was also an increased risk of silicosis and COPD with increasing number of different ores mined.
The findings of this study confirm the increased risk of respiratory diseases and cancers among mine workers. Compared to the rest of Ontario, miners in this cohort experienced a statistically higher burden of silicosis and lung cancer, and respiratory diseases were clearly associated with duration of mining employment and experience with mining multiple ores over a career.
While this study confirmed results found in previous research, it also uncovered some new findings that require further investigation. The research platform created in this project will provide opportunities to test new hypotheses, including the impact of combined exposures among miners of multiple ore types.
This study was funded by a grant from the Ontario Ministry of Labour, Training and Skills Development’s Research Opportunities Program.
O6B.2 Cancer risk by ore type in a mixed miners cohort