What docs should know: Why wildfire smoke is a 'different beast' from other air pollution

Wildfire smoke is a significant and growing threat to air quality and has been associated with a wide range of acute respiratory and other health endpoints—and more research into the chronic effects is urgently needed, said a leading epidemiologist at the Canadian Thoracic Society’s recent 16th Annual Canadian Respiratory Conference in Toronto. “In high-income countries, especially in North America, we are moving into a new air pollution regime and that regime is going to be dominated by wildfire smoke,” said Sarah Henderson, scientific director of environmental health services at the BC Centre for Disease Control (BCCDC) in Vancouver.Wildfire season exploded a year ago, noted Henderson, and unlike other years, in 2023 the fires and smoke were countrywide, not isolated to one area. “It took off like we have never seen before, and then it just kept going like we have never seen before.”With climate change, drought and lack of forest management/fire suppression (which focus on protecting communities and the forestry industry, but can ultimately lead to more sources of ignition) blamed for the increased fire activity, Canadians can expect more days of air quality warnings and smoke-blanketed cities this summer in at least some provinces.In Western North America, studies show wildfire smoke exposure is starting to dominate people's lifetime exposure to air pollution. “In prior years, it would've been industry and traffic, but while we down-regulate those sources, we're seeing growing contribution from this other source. And this one, we don't get to regulate,” said Henderson, a public health professor at the University of British Columbia. Henderson talked to the respirologists and other healthcare providers at the conference about how wildfire smoke differs from other types of air pollution.A key component of wildfire smoke is fine particulate matter or particles less than 2.5 microns in diameter. They have a very high surface-area-to-volume ratio and the microscopic soot particles can be inhaled deep into the lungs.The smoke is a complex mixture of gases and particles that stick together, interact and change as they move away from the fire. Of all the pollutants in wildfire smoke, fine particulate matter (PM2.5) is thought to pose the greatest risk to human health.However, PM2.5 is only one component of wildfire smoke, and there are hundreds of volatile organic and inorganic materials and gasses, said Henderson. “We generally do not measure those gases because they are very challenging to measure and measuring them would not be useful from a health perspective because you can go to a fire, grab a sample of the air, analyze it, grab a sample of the air an hour later, analyze it again, and the gas is going to be very different. That's because fires are highly dynamic and what's coming off of them depends on the fuels that are burning, the temperature at which those fuels are burning, and what the weather is doing. It's a really complex system.”“We have anthropogenic materials also burning and caught up in the wildland fire smoke. Those anthropogenic materials we can almost guarantee are more toxic than the wildland fire smoke itself. And the wildland fire smoke is plenty toxic.”As with other air pollution, wildfire smoke impacts the respiratory and cardiovascular systems, with the respiratory effects being more significant.“When we're talking about acute respiratory health, wildfire smoke is a different beast from other forms of air pollution."When the particles travel deep into the lung, down to the alveolar region, they cause irritation and an immune response that leads to local inflammation and often more systemic inflammation. "The smallest particles can also translocate across the alveoli into the bloodstream and start circulating to have access to every organ system in the body, including the brain. Like other forms of air pollution, it affects the entire body."But said, Henderson, “The glaring difference is that there is a much stronger respiratory effect (than other kinds of air pollution), especially for people with obstructive respiratory conditions, asthma, COPD. They are very sensitive to wildfire smoke and those airways can close up pretty quickly when it's smoky outside.“If we have 100 micrograms per meter cubed of smoke per day in the province, we can expect a doubling in all respiratory outcomes. The cardiovascular effects are much smaller than the respiratory effects, and this is getting very clear in the wildfire smoke literature.”Rapid onsetA UBC study Henderson was involved in looked at air quality and ambulance dispatches for breathing problems in particular areas. The results showed that increased PM2.5 during wildfire seasons was associated with some respiratory and cardiovascular outcomes within as little as one hour following exposure. “The effect is highest in the first hour and it starts going down in 48 hours.”Another study showed that, counterintuitively, the relationship between PM2.5 concentrations and acute respiratory outcomes is nonlinear, with steeper slopes at lower concentrations and a plateau at higher concentrations, Henderson explained to the audience and in an article in the BC Medical Journal. “This nonlinear concentration-response relationship is likely due to biological saturation of the cellular processes that cause health harms at high concentrations.”She further noted that wildfire smoke gets a lot of public and media attention when PM2.5 concentrations are extreme, but it causes much more harm at lower concentration levels that occur more frequently and might be disregarded. In B.C., concentrations over 100 micrograms per metre cubed are responsible for less than 20% of asthma-related visits attributable to wildfire smoke. However, more than 35% occur at concentrations between 10 and 30 micrograms per metre cubed, she said.In utero studiesHenderson and her team have been studying data from infants who were in utero during recent B.C. summers of extreme forest fire smoke. The results show that there is a significant risk of stillbirth, extreme preterm birth, and very preterm birth; and an elevated risk of preterm birth for infants in utero for high-exposure summers. Another study looked at the otitis media by age one among infants, those with in utero high exposure versus those without, and found a relationship, with the critical exposure time being the second trimester. (See also “What are the effects of in utero and neonatal wildfire smoke exposure on birth outcomes and health in early life?”)One thing that is not clear is whether the chronic effects of wildfire smoke exposure are similar to those of other types of air pollution, nor whether being exposed to air pollution in a highly polluted city daily is worse or better than getting a big dose of wildfire smoke over several summers. This is among the topics the BCCDC will be studying in the coming years.“Does smoke exposure induce asthma in children? Does smoke exposure damage the respiratory health of children in a way that's going to affect their health over the entire life course? We don't know," said Henderson. "We know that the acute respiratory effects are higher (than other air pollution) but we have to be prepared for a world where the chronic respiratory effects are also higher.”Henderson urged healthcare providers to consider another aspect of smoky air—the psychological toll. “It's very hard on people's psyches and probably very hard on the operation of their brain because of that ability for smoke to cross that blood-brain barrier. So, people find it very upsetting, and that is part of the overall health impact of smoke exposure.”In conclusion, Henderson spoke about the importance of further research, particularly into the chronic effects of wildfire smoke, and of arming patients with knowledge and the tools to protect themselves. She advocates for in-home filtering systems, whether purchased air purifiers or do-it-yourself purifiers using fans and furnace filters. She also advocates for indoor air quality sensors in homes and for patients to “take it easy” and wear quality masks outdoors on smoky days.“Last year was not a one-off unfortunately, and we are going to have to deal with this for the rest of our lives. The more you reduce your exposure the more you reduce your risk. So I'm encouraging people to calmly and rationally say, 'What am I breathing right now? What can I do to reduce exposure?"

What docs should know: Why wildfire smoke is a 'different beast' from other air pollution

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