Risk Assessment Prioritization Process for Indoor Air Contaminants


Canadians spend approximately 90% of their time indoors and are exposed to a large number of indoor air contaminants. In many cases, these indoor air contaminants are known to cause or exacerbate health effects, such as asthma, allergies, chronic obstructive pulmonary disease and other respiratory diseases. Some indoor air contaminants are found, or are expected to be found, in Canadian homes at a level that could pose an elevated health risk to Canadians.

Health Canada conducts health risk assessments for indoor air contaminants and develops Residential Indoor Air Quality Guidelines (RIAQG), which are issued as voluntary objectives under the Canadian Environmental Protection Act, 1999 (CEPA). RIAQG summarize the health effects of inhalation exposure to specific indoor air contaminants, provide information on exposure and sources in Canadian residential environments, derive recommended short- and/or long-term exposure limits, and give recommendations on ways to reduce exposure in an effort to keep indoor air levels below these exposure limits. When a recommended exposure limit cannot be derived from the available scientific evidence, a guidance document is developed that focuses on recommendations to control sources or other actions to reduce exposure.

Health Canada also establishes Indoor Air Reference Levels (IARL) which are screening values derived for contaminants for which there is no RIAQG or guidance. Health Canada does not perform new risk assessments to develop an IARL, but rather evaluates assessments from internationally recognized health and environmental organizations, and selects the most appropriate previously-derived reference level for Canadian homes. The IARL represent concentrations that are associated with acceptable levels of risk following long-term exposure, as determined by the organization that performed the risk assessment.

Health Canada's health risk assessments are used as the scientific basis for actions to reduce exposure to indoor contaminants and help protect human health. They are developed to support the needs and activities of provinces, territories, municipalities, and other federal agencies and departments. They are also used for risk management activities, including the development of standards and regulations related to indoor air quality.

Prioritization of indoor air contaminants

Health Canada has developed a process to prioritize contaminants for assessment, to be conducted approximately every three years. It assigns greater priority to contaminants for which there is new information suggesting a health concern due to inhalation exposure at levels that may be found in indoor air. The risk assessment prioritization process has four steps described in Figure 1.

Figure 1. Overview of the risk assessment prioritization process for indoor air contaminants
Figure 1. Text version below.
Figure 1 - Text description

Figure 1 shows an overview of the risk assessment prioritization process for indoor air contaminants, with the four steps indicated in four boxes, that are divided in two (left and right sides). The first box contains "Developing the priority list of indoor air contaminants (ongoing)" on the left and "The list of indoor air contaminants for consideration is developed from results of previous risk assessments from other jurisdictions, research, and inquiries directly from Canadians, as well as through input from provinces, territories and other government departments, internal and external partners, international actions and priorities, and new science. More specifically, the priority list of contaminants is influenced by:

  • the need to update existing RIAQG or IARL;
  • new evidence linking specific indoor air contaminants and adverse health effects; and
  • new or emerging indoor air contaminants identified by internal or external partners or international agencies." on the right.

There is an arrow pointing towards the second box, which contains "Reviewing recently published literature" and "Comparing results with exposure data" on the left, and "Health Canada conducts a review of literature for each contaminant, to identify relevant, recently published literature on health effects of inhalation exposure, including assessments from other jurisdictions. Health Canada then identifies potential hazard values from key studies. For each contaminant, indoor air exposure data are compared to existing health-based exposure limits or potential hazard values. Health Canada uses its own indoor air exposure data, when available, or exposure data from published literature." on the right.

There is another arrow pointing towards the third box containing "Risk-based prioritization" on the left and "The contaminants on the list are prioritized according to risk to human health, and based on whether:

  • exposure levels approach or exceed an established health-based value or potential hazard value from new literature;
  • recently published health effects data could result in a change in the existing guidelines or provide justification for development of new guidelines; and
  • new information is available indicating possible increased exposure compared to previous studies." on the right.

Finally, another arrow points towards the fourth box, which contains "Determination of action for priority contaminants" on the left and "The contaminants that are determined to be moderate or high risk are grouped for further action, taking into consideration data gaps, stakeholder requests, partner needs and other government activities.

Outcomes from this step will determine, for each contaminant, whether Health Canada proceeds with development of a RIAQG, proposes an IARL, conducts further indoor air exposure studies, or does not need to take any action and can re-evaluate a contaminant in subsequent prioritization exercises." on the right.

Additional Information

If you would like more information on Health Canada's risk assessment prioritization process for indoor air contaminants or have any questions about indoor air contaminants, please contact us at HC.air.SC@canada.ca.

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