Recent trends in respirable crystalline silica and elemental carbon exposure in the Ontario, Canada mining industry.

Introduction: Mining is a high-hazard industry with significant occupational disease risks. Despite this there is limited data describing current exposure conditions. The aim of this short communication is to share recent exposure data from underground mines in Ontario, Canada.

Methods: Data from underground mines were accessed through a freedom of information request. Data were cleaned and standardized. Data contained measurements of several hazards from 2013 to 2018; analysis focused on personal samples for respirable crystalline silica (RCS) and elemental carbon (EC) from 2014 to 2018. Descriptive statistics were calculated overall and by sampling year; comparisons were made to current occupational exposure limits. Linear regression models were constructed to examine time trends.

Results: EC exposures decreased significantly, ~10% per year over the measurement period (2014 to 2018). Overall 14% of EC measurements were above the current mining exposure limit (0.12 mg/m3 EC) in Ontario, Canada. Results for silica did not show a statistically significant trend but did suggest a reduction of ~1.8% per year. Almost one-third of the RCS measurements were above the American Conference of Governmental Industrial Hygienists (ACGIH) recommended threshold (0.025 mg/m3).

Conclusions: Current exposure data is needed to understand workers' exposure and support occupational disease prevention. Recent data from the Ontario mining industry suggests that exposure to elemental carbon decreased significantly from 2014 to 2018, but the annual reduction for silica exposure was not nearly as substantial. Mining workers continue to be exposed to levels of EC and RCS that are hazardous to health.