Long-term effects unknown
When it comes to the long-term effects of wildfire smoke on human health outcomes, much less is known. In a recent literature review, Colleen E. Reid, PhD, and Melissa May Maestas, PhD, found only one study that investigated long-term respiratory health impacts of wildfire smoke, and only a few studies that have estimated future health impacts of wildfires under likely climate change scenarios (Curr Opin Pulm Med. 2019 Mar;25:179-87).
Dr. Colleen E. Reid
“We know that there are immediate respiratory health effects from wildfire smoke,” said Dr. Reid of the department of geography at the University of Colorado Boulder. “What’s less known is everything else. That’s challenging, because people want to know about the long-term health effects.”
Evidence from the scientific literature suggests that exposure to air pollution adversely affects cardiovascular health, but whether exposure to wildfire smoke confers a similar risk is less clear. “Until just a few years ago we haven’t been able to study wildfire exposure measures on a large scale,” said EPA scientist Ana G. Rappold, PhD, a statistician there in the environmental public health division of the National Health and Environmental Effects Research Laboratory. “It’s also hard to predict wildfires, so it’s hard to plan for an epidemiologic study if you don’t know where they’re going to occur.”
Dr. Ana G. Rappold
Dr. Rappold and colleagues examined cardiopulmonary hospitalizations among adults aged 65 years and older in 692 U.S. counties within 200 km of 123 large wildfires during 2008-2010 (Environ Health Perspect. 2019;127[3]:37006. doi: 10.1289/EHP3860). They observed that an increased risk of PM2.5-related cardiopulmonary hospitalizations was similar on smoke and nonsmoke days across multiple lags and exposure metrics, while risk for asthma-related hospitalizations was higher during smoke days. “One hypothesis is that this was an older study population, so naturally if you’re inhaling smoke, the first organ that’s impacted in an older population is the lungs,” Dr. Rappold said. “If you go to the hospital for asthma, wheezing, or bronchitis, you are taken out of the risk pool for cardiovascular and other diseases. That could explain why in other studies we don’t see a clear cardiovascular signal as we have for air pollution studies in general. Another aspect to this study is, the exposure metric was PM2.5, but smoke contains many other components, particularly gases, which are respiratory irritants. It could be that this triggers a higher risk for respiratory [effects] than regular episodes of high PM2.5 exposure, just because of the additional gases that people are exposed to.”
Another complicating factor is the paucity of data about solutions to long-term exposure to wildfire smoke. “If you’re impacted by high-exposure levels for 60 days, that is not something we have experienced before,” Dr. Rappold noted. “What are the solutions for that community? What works? Can we show that by implementing community-level resilience plans with HEPA [high-efficiency particulate air] filters or other interventions, do the overall outcomes improve? Doctors are the first ones to talk with their patients about their symptoms and about how to take care of their conditions. They can clearly make a difference in emphasizing reducing exposures in a way that fits their patients individually, either reducing the amount of time spent outside, the duration of exposure, and the level of exposure. Maybe change activities based on the intensity of exposure. Don’t go for a run outside when it’s smoky, because your ventilation rate is higher and you will breathe in more smoke. Become aware of those things.”