Workers Health & Safety Centre

Research questions ‘safe’ level of exposure to diesel engine exhaust

New research suggests exposure to diesel engine exhaust, at levels lower than previously considered acceptable, can significantly contribute to the burden of cancer.

Diesel engine exhaust — hazards and health impacts

Diesel engine exhaust (DEE) is a complex mixture of particulates and gases many small enough to be inhaled deep into the lungs. Diesel is often used to power on-road and off-road vehicles from trucks, buses, trains and ships to various heavy equipment used in industry and construction.

By 2012, sufficient research evidence led the International Agency for Research on Cancer (IARC) to reclassify DEE from a probable to a definite human carcinogen (Group 1). DEE causes lung cancer and growing evidence suggests it causes bladder cancer. It is also associated with respiratory and cardiovascular health effects.

Given that large populations of workers are exposed to diesel engine exhaust and that urban populations are exposed to low levels of diesel engine exhaust in the environment, the potential occupational and public health impact of diesel engine exhaust exposure may be considerable.

Assessing the research evidence

Existing epidemiological studies have provided information on the risk of lung cancer by estimating DEE exposure levels expressed as elemental carbon, a primary component of DEE, and often used as a surrogate to measure DEE.

At a recent seminar in Toronto, guest lecturer Dr. Roel Vermeulen, Professor of Environmental Epidemiology and Exposome Science, Utrecht University, the Netherlands, reviewed his current research on DEE.

Vermeulen’s research involves performing analyses to derive an exposure–response estimate for cumulative elemental carbon and lung cancer mortality. This was then used to estimate excess lifetime lung cancer mortality for environmental and occupational exposures and attributable lung cancer deaths due to diesel engine exhaust.

His research found acceptable risk and maximum tolerable risk would be near 0.01 µg/m3 elemental carbon and 1 µg/m3 elemental carbon, respectively well below current occupational exposure levels, and, according to Vermeulen, even below some environmental exposure levels.

Based upon these findings, Vermeulen concludes:
  • Occupational Exposure Limits (OEL) need to be set which better reflect the hazards
  • We should question if diesel engines using older technologies should be used in workplaces at all
  • New technology diesel engines will reduce elemental carbon emissions, and its introduction into the workplace must be expedited
  • Where new technologies exist, elemental carbon may no longer provide adequate surrogate measures to monitor exhausted materials and additional new hazards may emerge.

Towards a prevention plan

Diesel engine exhaust is considered a priority carcinogen according to the 2017 Burden of Occupational Cancer in Ontario report. It concludes some 301,000 Ontario workers, nearly five per cent of the working population, are exposed to DEE every year accounting for 170 lung and 45 bladder cancer cases.

The report points to a significant regulatory gap in Ontario, a lack of occupational exposure limits (OEL) for whole diesel exhaust or diesel particulate matter. Exposure limits for elemental carbon have been implemented in Finland at an OEL of 100 µg/m3 elemental carbon. The Finnish Institute for Occupational Health however recommends a more protective elemental carbon OEL of 20 µg/m3 for the mining industry and 5 µg/m3 for other workplaces. This latest research would question whether even these levels are sufficiently protective.

Related resources:
Download and review Dr. Vermeulen's presentation
Learn more about the OEH Seminar Series 2017-2018
Review CAREX Canada Diesel Engine Exhaust exposure profile
Want to read more about diesel engine exhaust from WHSC?
Groundbreaking report focuses on occupational cancer prevention in Ontario
Cancer burden of diesel exhaust steep for exposed workers
The Workers Health & Safety Centre assists workplace parties through training programs and information services. WHSC offers hazard awareness training on vehicle emissions and has a hazard resource bulletin on diesel engine exhaust. All of these resources are aimed at raising awareness about hazardous exposures and targeting prevention at the workplace level.

To learn more: 
Call:   1-888-869-7950 and ask to speak with a training services representative