Canada finalizes indoor air quality guidelines for xylenes

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Canada has finalized its Residential Indoor Air Quality Guidelines for xylenes in terms of health effects, pollutant sources, and exposure limits, according to the Canada Gazette.

While most sources of xylene pollution come from petroleum refineries, chemical plants and the combustion of fuels in motor vehicles, the new guideline examines risks that could occur with indoor concentrations.

“In Canadian homes the indoor xylene concentrations are at least three-fold greater than outdoor concentrations, indicating a predominance of indoor sources,” states the new guideline under Health Canada.

In a residential setting, building and renovation products, such as caulking, coatings and stains, as well as smoking in the home, can contribute to indoor xylene concentrations.

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Xylene (or dimethylbenzene) is an aromatic hydrocarbon with three isomers (p-xylene, m-xylene, and o-xylene). They are colourless, volatile, flammable, sweet-smelling liquids naturally found in petroleum products, particularly as an additive to gasoline during blending to enhance fuel’s octane rating. They are also widely used in paints, varnishes, pesticides, vitamins, pharmaceuticals, printing inks, dyes, adhesives, sealants, cleaning agents, degreasing agents, paint removers, and for chemical extractions.

Xylenes also form during combustion of organic materials, such as forest, grass and other biomass fires.

Canada’s National Pollutant Release Inventory indicates that from 2015 to 2017 the annual on-site releases of xylenes from all industrial facilities totalled over 3,200 tonnes. The majority of xylene releases (97%–99%) were to the air, with the remainder going to water and land.

In terms of risk management recommendations for indoor settings, the guideline suggests that homes should ensure adequate ventilation. The garage is a prime culprit, and should not be used to store gasoline or other chemicals, the guideline warns. If there are no other options, homeowners should tightly seal the products, use garage exhaust fans, and ensure the interface between the attached garage and the home is properly sealed.

Additionally, homeowners should avoid idling cars, snowblowers, lawnmowers, or any gas-powered equipment in the garage, even with the garage door open.

“Many of these items have been shown to release xylenes in chamber tests, even when properly sealed and when not in operation,” states the new guideline.

The intent of the new guideline is also to present short-term and long-term exposure limits for xylenes. In recent years, Health Canada has conducted exposure studies in multiple Canadian cities including Edmonton, Halifax, Windsor, Regina, Ottawa, Montreal, and a First Nations reserve in Manitoba. The studies conducted in those cities during the winter and summer from 2005 to 2014 showed median indoor xylene levels ranged from 2.0 to 11.1 µ g/m3, or one-millionth of a gram per cubic metre of air. However, the 95th percentiles in this study ranged from 15.6 to 212.7 µ g/m3.

Under the new guideline, the short-term (or one-hour) exposure limit for xylenes is 7,200 µg/m3 and the long-term exposure limit (based on a 24-hour average) is 150 µg/m3. These limits apply to all three isomers in any combination, states Health Canada.

The major symptoms of acute human exposure to xylenes, through inhalation, include irritation of the nose, throat, eyes and central nervous system, causing headaches, nausea, dizziness, difficulty concentrating, impaired memory, and slurred speech, among many other challenges. Notably, hearing disorders have been also linked to xylene exposure.

Most research indicates that available data has been considered inadequate to determine the carcinogenicity of xylenes.

The final guidelines for xylenes can be downloaded here.

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