Analysis of the Ontario Ministry of Labour’s MESU exposure database


Analyzing past exposure data can give us important information on which occupations and industries were overexposed in the past and may continue to be overexposed in the future, where there are gaps in our knowledge, and where intervention efforts should be targeted. Moreover, exposures that occurred 15 to 40 years ago are highly relevant in terms of current cancer risks.

The Ontario Ministry of Labour collected exposure measurements to determine compliance with occupational exposure limits between 1981 and 1996. There are approximately 300,000 measurements in the MESU database, many of which are for known or suspected carcinogens.


The goal of this project is to analyze a series of priority workplace carcinogens and produce reports on exposure to these substances in Ontario, based on the MESU dataset. Exposures of interest were based on the CAREX Canada priority list occupational carcinogens.

In collaboration with CAREX Canada, the data will also be used to create exposure matrices that can be used for cancer surveillance and future research.


Exposure measurements were taken in a variety of workplaces by the Ministry of Labour from 1981 to 1996. Data for individual carcinogens is extracted from the database, and statistical analyses are performed to determine the level of exposure, and the occupations and industries most affected by the substance.


The time period of the data collection, approximately 15 to 30 years ago, makes the MESU dataset highly relevant for determining current cancer risks. The analyses will also lead to important information on overexposed worker populations and areas to target for future intervention efforts.

Current status:

The dataset has been received from the Ministry of Labour and analyses are underway. Initial exposures of interest include:

  • wood dust
  • perchloroethylene
  • trichloroethylene
  • nickel
  • isocyanates

A study of health and safety in high school shops, and teachers’ exposure to wood dust, formaldehyde and welding fumes was published in the Journal of the Ontario Occupational Health Nurses Association: Kubrak O, Arrandale V, Chenard A, Nichol K. Health and Safety in High School Shops. Journal of the Ontario Occupational Health Nurses Association 2013, 32(2): 33-38.


Paul Demers (Occupational Cancer Research Centre and Cancer Care Ontario) (PI)
Victoria Arrandale (Occupational Cancer Research Centre)
Kate Jardine (Occupational Cancer Research Centre)
Garthika Navaranjan (Occupational Cancer Research Centre)
Joanne Kim (Occupational Cancer Research Centre)
Cheryl Peters (CAREX Canada)
Chun-Yip Hon (Ryerson University)