Classifying Carcinogens
CAREX Canada classifies carcinogens based on evaluations made by the International Agency for Research on Cancer (IARC). IARC has classified more than 900 agents into different groups based on their carcinogenicity to humans. These agents include pure chemicals and chemical mixtures, occupational exposures, physical agents, biological agents, and lifestyle factors.
The most important IARC carcinogen categories for CAREX Canada are Group 1 and Group 2A. Group 1 agents were evaluated by IARC as “carcinogenic to humans” based on “sufficient evidence of carcinogenicity in humans.” Carcinogens such as asbestos, benzene, wood dust, and diesel exhaust are Group 1 agents. The Group 2A category includes agents that are “probably carcinogenic to humans” based on “limited evidence of carcinogenicity in humans and sufficient evidence of carcinogenicity in experimental animals.” Carcinogens/exposures such as shiftwork, creosotes and acrylamide are Group 2A agents.
IARC Group 2B agents are “possibly carcinogenic humans” for which there is “limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals.” Some pesticides used in Canada, such as Chlorothalonil and MCPP, fall into this category.
Prioritizing Canadians' Exposures to Carcinogens
Overall, CAREX Canada aims to determine where Canadian exposures to carcinogens are occurring, the number of Canadians exposed to different carcinogens and their levels of exposure. One of our first tasks was to prioritize which agents to focus on, as many IARC classified agents occur in environmental and occupational settings in Canada.
CAREX Canada categorized IARC agents into four priority groups: immediate high priority; possible high priority; moderate priority with further substantial investigation warranted; and low priority with no evidence of use in Canada. There were three criteria considered in this prioritization process:
- The carcinogenicity and other toxic properties of the agent.
- The prevalence of exposure in Canada.
- The feasibility of assessing exposure in Canada.
Two documents, one for environmental and one for occupational carcinogens, have been produced to summarize the prioritization methods and results in detail: