Concern over unknown long-term effects of wildfire smoke

(Image Credit: AdobeStock/Erin)

With 2023 officially being the worst wildfire season ever in Canada, ophthalmologists are urging for more awareness on the long-term effects wildfire smoke can have on the eye.

Wind has pushed the wildfire smoke across Canada and several states in the United States, causing major dips in air quality – at one point New York City had the worst air quality on the planet due to the wildfire smoke.

There are currently over 1000 active wildfires burning in Canada, with 740 of them being labeled as “out of control” by the Canadian Interagency Forest Fire Centre (CIFFC). Over 5000 wildfires have started in Canada this year, according to the CIFFC.¹

In 2023, Canada has seen over 13 million hectares (HA) burned by wildfire – Almost double the previous high of 7.1 million HA in 1995.¹

With this increase in wildfires, the Canadian Broadcasting Corporation (CBC) reports eye health experts are worried on the long-term impacts the smoke could have on the eye.

"There's particulate matter, volatile organic compounds," said Marisa Sit, MD, FRSCS, a Toronto ophthalmologist with the University Health Network's Comprehensive Ophthalmology Unit at the Donald K. Johnson Eye Institute. "These are things [in the smoke] that can irritate our eyes."

According to Vancouver ophthalmologist Briar Sexton, MD, eye symptoms such as dry, itchy, red, painful, watery and gritty eyes can happen before the smoke is even noticeable.

"When I first moved to [British Columbia] and started practicing in 2006, we weren't talking about wildfires anywhere near the way that we are now," said Sexton. "The amount of exposure any single individual would get was actually quite minimal compared to [what] they are getting in hot spots these days."

Sexton told the CBC that she has had numerous patients complaining about irritated eyes, and that she is not clear what lasting damage the wildfire smoke could have on the eye.

CBC spoke with numerous doctors who studied pollutants with similar components to wildfire smoke. These doctors mentioned that cigarette smoke has been found to be a risk factor for macular degeneration and an increased risk of cataracts.

"If I had a magic crystal ball, I do think those are things we're unfortunately going to see being linked to wildfire regions in higher incidences in the future," Sexton said to the CBC.

A recent review on the wildfires that swept across Australia in 2020 concluded that “there is strong evidence that wildfire smoke and other air pollution sources have harmful effects on ocular surface, causing eye symptoms and changes to normal function of the ocular surface.” However, the same review stressed that “it is not yet known whether repeated or long-term smoke exposure carries an increased risk long term of ocular surface disease.”²

One of the authors of the review, Suki Jaiswal, MOptom, an optometrist in Sydney, Australia, has decided to conduct further studies on the impact of wildfire smoke on the eyes.

Jaiswal is looking at the short and long-term impacts wildfire smoke can have on each individual part of the eye and how long recovery takes. She is taking a larger focus on groups like firefighters that are frequently exposed.

Jaiswal uses a pair of goggles that release small amounts of smoke and wants to identify who is most at risk and whether any of the damage incurred is reversible.

"If we don't have a uniform understanding of how we should protect the eyes and how we should manage any eye disease that does occur from wildfire exposure, I think our patients are going to suffer," Jaiswal said.

VSP Vision has listed ways to limit exposure to wildfire smoke and prevent eye irritation:³

• Use lubricating eye drops or artificial tears to keep your eyes refreshed and help get rid of dust and particles that can irritate eyes.
• Don’t rub your eyes. You might transfer dust and ash from your hands or face to your eyes and that could scratch or irritate them. It’s also helpful to wash your hands regularly.
• Keep windows and doors closed to keep the air indoors clean. Running your air conditioner may also help but be sure to keep the fresh air intake closed and the filter clean to prevent bringing in additional smoke. However, if it’s too warm to stay indoors with the windows and doors closed and you do not have air conditioning, the Center for Disease Control (CDC) recommends seeking shelter elsewhere.
• The CDC also recommends limiting indoor air pollution by refraining from using anything that burns, like fireplaces, gas stoves and candles. Vacuums can also stir up dust already present in your home. Air filters are also recommended for those with respiratory conditions.

What makes wildfire smoke so toxic?

Wildfire smoke comprises of thousands of compounds including solid matter (particles, embers, heavy metals, organic microorganisms), water vapor and a complex mix of gaseous compounds.

"Wildfire smoke itself is quite a complex mixture and it's made up of fine particles … and a number of other gases, which are toxic, mainly due to the fact that wildfires burn everything so more toxic than household fires because everything has been burned," Kimberly Humphrey, MD, MPH, a climate change and human health fellow at the Center for Climate, Health, and the Global Environment at Harvard T.H. Chan School of Public Health, told ABC News.

Particulate matter (PM_2.5 and PM₁₀) is a key component of wildfire smoke. PM_2.5 refers to particles smaller than 2.5 μm in size and PM₁₀ refers to particles smaller than 10 μm in size. PM_2.5 is considered to be proxy measure for air pollution.²

Because these particles are too small to be seen with the naked eye, they can easily enter the nose and throat and can travel to the lungs, with some of the smallest particles even circulating in the bloodstream, according to the Environmental Protection Agency.⁵

A study from California in 2021, found that PM_2.5 particles from wildfires can be up to 10 times more harmful than the same type of air pollution coming from combustion activity.⁴

References:

1. Canadian Interagency Forest Fire Centere Inc. CIFFC. Accessed August 7, 2023. https://ciffc.net/

2. Sukanya Jaiswal, Isabelle Jalbert, Katrina Schmid, Natasha Tein, Sarah Wang, Blanka Golebiowski, Smoke and the eyes: A review of the harmful effects of wildfire smoke and air pollution on the ocular surface, Environmental Pollution, Volume 309, 2022, 119732, ISSN 0269-7491, https://doi.org/10.1016/j.envpol.2022.119732.

3. Vision Care. Protect your eyes from wildfire smoke. Accessed August 7, 2023. https://www.vsp.com/eyewear-wellness/eye-health/eye-diseases/wildfire-smoke-pro

4. Aguilera, R., Corringham, T., Gershunov, A. et al. Wildfire smoke impacts respiratory health more than fine particles from other sources: observational evidence from Southern California. Nat Commun 12, 1493 (2021). https://doi.org/10.1038/s41467-021-21708-0

5. Environmental Protection Agency. EPA. Why wildfire smoke is a health concern. Accessed August 7, 2023. https://www.epa.gov/wildfire-smoke-course/why-wildfire-smoke-health-concern