In the 1980s, Health Canada and the Federal-Provincial Advisory Committee on Occupational and Environmental Health (CEOH) developed a series of indoor air quality guidelines that were published in 1987 in a report entitled Exposure Guidelines for Residential Indoor Air Quality (CEOH 1989). Limit values for formaldehyde, carbon monoxide, carbon dioxide, nitrogen dioxide, sulfur dioxide, ozone, and particulate matter provided in this document were based on the scientific evidence available at the time the document was prepared. For formaldehyde, target and action levels were set at 60 μg/m3 (50 ppb) and 120 μg/m3 (100 ppb), respectively. The 120 μg/m3 value was one tenth of the lowest value concentration found to cause irritation symptoms following controlled exposure (1,200 μg/m3 ). However, since then, a significant amount of research has been carried out and published on the health effects of some of these substances, warranting a reassessment of the scientific basis of the guidelines and potentially a revision of the guidelines themselves.
In the late 1990s, formaldehyde was assessed under the Canadian Environmental Protection Act (1999) (CEPA 1999). Formaldehyde was found to be a sensory irritant and a potential carcinogen; however, the risk of cancer associated with the exposure of the Canadian population to formaldehyde was estimated to be "extremely low," and the major health concern was that "in some indoor locations, concentrations may approach those associated with eye and respiratory tract sensory irritation in humans" (Environment Canada, Health Canada 2001). Formaldehyde was therefore declared "toxic," as it is "entering the Canadian environment in a quantity or concentration that constitutes or may constitute a danger for the environment on which life depends and a danger in Canada to human life or health" (Environment Canada, Health Canada 2001).
The purpose of this document is to revisit the guidelines developed for formaldehyde in view of epidemiological and toxicological studies published since 1987. Epidemiological studies relevant for setting indoor air quality (IAQ) guidelines (i.e. in which the only route of exposure to formaldehyde was inhalation) were reviewed. Studies of workers handling formaldehyde or formaldehyde-containing products (e.g. pathologists, embalmers, painters) were excluded from the review as immunologic sensitization from dermal contact may modify or confound the effect of formaldehyde inhalation. Toxicological studies have been extensively reviewed as part of the CEPA assessment mentioned above and in the Toxicological Profile prepared by the U.S. Agency for Toxic Substances and Diseases Registry (ATSDR 1999); only the key inhalation studies cited in these documents were reviewed.