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Did you know that Canada has no clear legal standards for indoor air quality in homes? Yet most people spend at least 90% of their time indoors, and indoor air is often more contaminated than outdoor air.

What are some indoor air pollutants?

There are three main groups of indoor air pollutants:

  •         Biological – eg. mites, bacteria, mould. Bacteria can grow when filters or steam- or mist-producing devices (e.g., humidifiers, shower heads) aren’t kept clean. Mould grows when water infiltrates building materials such as drywall.
  •         Physical – e.g. dust, small particles, asbestos (especially if friable or flaking)
  •         Chemical – e.g. combustion products (i.e., wood or cigarette smoke, carbon monoxide, nitrogen dioxide), household products (i.e. paint strippers and cleaning products), and ozone (i.e., from  electronics like printers, copiers and fax machines).  As well, chemicals like formaldehyde, volatile organic compounds and plastics may “off-gas” from paints, floor finishes, glues, recently dry-cleaned clothing, room deodorizers, and household furnishings.


Some contaminants enter homes from outdoors, such as radon from soil, vapours from contaminated subsurface groundwater or soil, air emissions from nearby roads and industries, and particles carried in on clothes and shoes. A study published in January’s Pediatrics warns of the hazards of third-hand smoke, namely chemicals that cling to smokers’ hair and clothes and to surfaces like furniture and carpets.  Infants and children can breathe or ingest these particles when crawling or playing on the floor.


Poor air circulation in a house can exacerbate poor IAQ.


So what?


Contaminants in indoor air may lead to nonspecific respiratory and neurologic symptoms (e.g., rhinitis, otitis media, respiratory infections, headaches), as well as allergies, asthma, heart disease and, in extreme cases, some types of cancer.


How much is too much?

Canadian provinces do have some regulations on indoor air quality to protect workers when they are at work. These occupational exposure limits are designed for healthy adults working a 40 or so hour week, and are usually a compromise between health-based limits and available control technology. Occupational limits are not designed to protect children, seniors, and other vulnerable people, nor for homes, hospitals, and other locations that are occupied 24/7. Nor do occupational limits cover all contaminants.


Ministry of the Environment standards are much more stringent than occupational standards, but they usually don’t apply to indoor air.


Health Canada has recommendations (not laws) for indoor air exposure limits for some contaminants. Unfortunately, they aren’t always based on current science. The comprehensive Health Canada Guideline, Exposure Guidelines for Residential Indoor Air Quality, was last revised in 1989.  Acceptable exposure ranges are provided for carbon monoxide, nitrogen dioxide, ozone, fine particulate matter, sulphur dioxide, and carbon dioxide.  Occasionally, Health Canada issues new (2007) IAQ guidelines for individual contaminants, usually at much lower levels. For example, the 2007 guideline for radon is one-quarter of that recommended in 1989.  


There are recent Residential IAQ guidelines for moulds (2007) and formaldehydes (2006).  Health Canada recognizes that mould exposure may be hazardous, but did not set exposure limits, due to the number of species and strains as well as significant variability in human response to moulds.  


What can we do about it?


Most people have lots of options to improve IAQ. For example:

  •         Don’t wear outside shoes indoors (they carry particles of dirt, bacteria, etc.)
  •         Don’t smoke inside
  •         Ensure good ventilation
  •         Keep indoor spaces clean
  •         Keep ventilation equipment and mist-producing devices clean
  •         Change to greener cleaning products
  •         Don’t use smelly chemicals, such as paint removers, indoors.
  •         Keep smoke alarms, carbon monoxide detectors in working order
  •         Grow green plants (to remove toxins)
  •         Use an air cleaner with a HEPA/ carbon filter
  •         Vacuum with a HEPA filter
  •         Change filters regularly
  •         Wait a few days before bringing recently dry-cleaned clothes into the house; alternatively, switch to eco-friendly dry-cleaners
  •         Remove any visible mould with bleach
  •         Tape up or remove flaking asbestos

In more serious cases:

  •         Increase air changes, perhaps with heat recovery
  •         Remove dust catchers like carpets
  •         Change to greener furniture/fabrics/draperies
  •         In some areas, it may be wise to test basement radon levels (check with your local Medical Officer of Health to find out whether this is a concern in your municipality)


How much you decide to do may depend on whether IAQ is causing a problem, such as respiratory symptoms or headache.  You may want to take more care to protect vulnerable individuals, such as young children, the elderly and those with impaired immune systems.


There are many unknowns about indoor contaminants, especially the health risks of chronic exposure to low concentrations of a variety of chemicals.  We also know little about the health impact of new technologies, such as nanoparticles.

Someday, labelling requirements for consumer products may require manufacturers to warn of IAQ hazards- but that’s a long way off.






Radon in buildings



Dales et al. Quality of indoor residential air & health (CMAJ 2008; 179(2):147-52)



Health Canada Indoor Air Quality guidelines



IAQ guidelines for radon – 2007


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