With the city once again blanketed in wildfire smoke, experts are warning that long-term exposure to air pollution can lead to higher risk of heart failure.
Environment Canada issued a special air quality statement on Sunday night due to wildfire smoke from northern Ontario pushing Toronto’s Air Quality Health Index to 10+, classified as “very high risk.” Poor air quality was expected to persist Monday and possibly into Tuesday.
The effects of air pollution on the heart are underscored in a recent study, which found that long-term exposure to air pollution, in particular fine particulate matter, was linked to higher levels of diffuse myocardial fibrosis, a type of heart scarring that can lead to higher risk of heart failure.
Students from Toronto say they are finding refuge from the extreme heat and poor air quality by staying indoors and out of direct sunlight. Environment Canada has issued an air quality warning for the city as wildfire smoke affected much of southern Ontario.
(July 14, 2025 / The Canadian Press)According to air quality tracker IQAir, Toronto had the second-worst air quality in the world on Monday morning, with PM2.5 (a measurement of fine particulate matter) concentration at 17.3 times the World Health Organization annual guideline value. It later improved to sixth-worst.
The study, published in the medical journal Radiology and led by University Health Network clinician-scientist Dr. Kate Hanneman, used an advanced imaging technique called cardiac MRI on 694 participants in Ontario who were exposed to fine particulate matter over one year.
Heart damage was observed even when levels were below global air quality guidelines, and there is no safe exposure limit for air pollution, according to the research.
“Even in patients that are largely from Toronto and outside of Toronto, in Ontario, where our quality is much better than other areas of the world … We’re still seeing this association,” Hanneman said.
Fine particulate matter, or PM2.5, refers to fine particles that are inhaled by the lungs and can cause respiratory problems, especially among people with pre-existing conditions such as asthma.
They are released by natural sources, such as wildfire smoke, as well as human activities, including burning fossil fuels. Fine particulate matter is also present in smog and is released in fireworks. Climate change is causing wildfires to become more frequent, last longer and burn more intensely, according to scientists.
Much of Central Canada, Manitoba and Saskatchewan have been placed under special air quality statements or warnings due to smoke from wildfires, as Environment Canada advised residents to limit time outdoors and watch for smoke exposure symptoms.
(July 14, 2025 / The Canadian Press)The study focused on cardiovascular effects from long-term cumulative exposure, so one or two days of wildfire smoke wouldn’t be a factor. However, sustained exposure, such as what was seen in the summer of 2023, could pose serious health risks, Hanneman said. Sustained exposure could be days to weeks.
According to a bulletin from Toronto Public Health, 2023 was the first time wildfire smoke had a significant impact on Toronto’s air quality, lasting 12 days.
There are steps individuals can take to protect themselves from air pollution, including limiting outdoor activity on smoky days, closing windows, installing a high-efficiency particulate air filter in the home, and wearing a mask if going outside can’t be avoided.
Living in a large city centre like Toronto is a risk factor because of emissions from cars and factories, which include fine particulate matter as well as other pollutants like nitrogen dioxide.
“That kind of exposure is largely dependent on where you live, being in a city, or living right next to some sort of refinery or something that’s burning fossil fuels,” Hanneman said.
The study found that the greatest health effects were in women, smokers and patients with hypertension. It included 493 patients with dilated cardiomyopathy, which weakens the heart’s ability to pump blood, as well as 201 healthy individuals.
Fine particulate matter is associated with increased risk of cardiovascular diseases, including heart failure and stroke, the study said. An estimated 31 per cent of cardiovascular disease is attributable to environmental factors such as air pollution, according to the World Health Organization.
Wildfire season is upon us, and smoke is reducing air quality through swaths of the country. Environment Canada suggests people check the Air Quality Health Index daily to determine how much time to spend outside. Here's how to interpret the index.
(July 14, 2025 / The Canadian Press)
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