How Does Wildfire Smoke Impact Mortality in Washington State?

Doubleday et al. Environmental Health (2020) 19:4 https://doi.org/10.1186/s12940-020-0559-2

Anyone who saw the movie Bambi as a child understands the destructive potential of wildfires. While images of burning logs and raining ash certainly give a healthy fear of flames, they can overshadow an overlooked wildfire danger: smoke. Researchers at the University of Washington recently studied the impact of wildfire smoke exposure on mortality in Washington State. Their findings suggest wildfire smoke could contribute to an increased number of deaths in Washington State.

Wildfire smoke contains harmful compounds

Wildfire smoke contains harmful compounds known to negatively impact human health, including particulate matter (tiny inhalable particles composed of acids, metals, dust, and other materials), carbon monoxide, and benzene (which can cause cancer). Unlike flames, which are primarily a concern for those who are directly adjacent or engulfed to a fire, smoke can spread thousands of kilometers away in plumes and expose many people to the toxic compounds it carries. We know there’s a risk potential from exposure to wildfire smoke, and we know people are being exposed, but the exact nature of the health effects of exposure and the scale of the problem is not yet well understood. To better understand the link between wildfire smoke and mortality, researchers sifted through data from 2006-2017 on non-traumatic deaths, like those due to cardiovascular or respiratory causes and the location of a deceased’s home and compared it to outdoor particulate matter concentration data. By tying these two datasets together the team was able to compare mortality trends with spikes and lulls in air quality.

What did the research show?

In Washington State there were 170,985 non-traumatic deaths during wildfire season from 2006-2017. Among these deaths, there was evidence of a small increase, just over 1%, in the likelihood of death on both the day someone was exposed to wildfire smoke and also on the day after. This increase in odds of death) was observed across all ages. Findings also suggest that people who already have an underlying respiratory issue, like chronic obstructive pulmonary disorder (COPD) or asthma, are at greater risk.

What are the limitations of the research?

One of the challenges was trying to limit the exposure data to just the particulate matter from wildfire smoke, and not from other sources of pollution. Trying to estimate the impact specifically from wildfire smoke can be difficult in urban areas because of its pollution, which can muddy the air quality signal. Even after a lot of fancy statistics to try to limit this issue, some misclassification likely exists. Another question is whether the pollution levels measured near someone’s home truly reflect their exposure level – what if that person spends most of their day inside? Public health research often relies on sophisticated statistics and models to assess impacts because controlled experiments would be some combination of impractical, expensive, and/or unethical. Although these research methods are imperfect, the results are still meaningful.

Why does it matter?

Because wildfires in Washington and elsewhere (Northern California, Australia, etc.) are expected to increase in size, frequency, intensity, and duration with climate change. It is estimated that the area burned by wildfires in the western United States approximately doubled from 1984-2015, and that trend is likely to continue with climate change. That could leave a lot of people facing exposure to wildfire smoke – Washington had a population of about 7.5 million people in 2018. As we start to grasp the scope of the problem, studies like this can provide some guidance for local and state public health officials on how to advise populations that are at risk of wildfire smoke exposure. The researchers recommend that these agencies use risk messaging that targets people with underlying health conditions (particularly respiratory problems) during times of increased wildfire smoke to prevent exposure. Further study is needed to more fully understand the impact of wildfire smoke, including on less dramatic outcomes like hospitalizations and emergency room visits.

Reviewed by: Laura Schifman