MAKING SENSE OF WILDFIRE SMOKE Ted Schettler, MD, MPH Record-setting drought and heat in the West, driven in large part by climate change, set the stage for an early start to the 2021 wildfire season. By early July fires had engulfed more than twice the acreage that burned this time last year, the largest wildfire season recorded in California history. Although wildfires are natural features of this landscape, their increased intensity in prolonged seasons with more people living in the wildland-urban interface has deepened and widened their destructive impacts. Deaths and injuries to residents and firefighters, catastrophic property loss, socio-economic upheaval and forced displacement of people from their homes are the most wrenching, long-lasting consequences where the fires burn. But health impacts extend far beyond, primarily due to hazardous smoke that spreads over vast regions, sometimes for many days or weeks.
Wildfire Smoke Characteristics
Wildfire smoke is physically and chemically complex. Its composition, formation, behavior, aging, and dispersion are influenced by the fuel mix, kind of fire, rate of fuel consumption, meteorological conditions, and landscape features. The primary emissions from wildfires are coarse and fine particulate matter (PM), including aerosols; gases such as carbon monoxide, hydrogen cyanide, methane, nitrous oxide, nitrogen oxides, other volatile organic carbon compounds, including benzene, formaldehyde and acrolein; trace metals; polycyclic aromatic hydrocarbons (PAHs) and other toxicants. Some of the gases form secondary pollutants including organic aerosols and ozone when they photo-react in the atmosphere. Particulate matter is typically divided into sub-types by size. Particles less than 10 microns in diameter (PM10) are inhalable; those between 2.5-10 microns are largely confined to the upper airways. Smaller particles (< PM 2.5) can penetrate more deeply into lungs and ultrafine particles can pass into the general circulation. Wildfire-related PM 2.5 is often used as a metric of exposure but is only a surrogate for the complex mix of particles, gases, and hazardous air pollutants unique to each fire.
Health Effects of Wildfire Smoke
Well-established health effects of exposure to wildfire smoke range from eye and respiratory tract irritation to reduced lung function, bronchitis, pneumonia, exacerbation of asthma and COPD, and premature death—similar to impacts of urban PM. Even children without asthma show a decline in lung function. A causal association between general particulate air pollution 24
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and cardiovascular morbidity and mortality is well established. Data linking wildfire smoke exposure to cardiovascular mortality and morbidity are mixed but most studies find increased risks of adverse cardiovascular events, especially among susceptible populations. Young and healthy people can also develop biological responses including systemic inflammation and vascular activation. Inconsistencies in study findings may be due to differences in exposure and outcome assessment methods, considerations of lag times, and variability in smoke composition. Very close to the fire, carbon monoxide concentrations can be high enough to be an acute health threat causing headache, weakness, dizziness, confusion, visual impairment, coma, and death. In addition to impaired lung function, firefighters are at increased risk of several kinds of cancer, plausibly because of repetitive exposures to a variety of carcinogens associated with products of combustion. Cancer risk associated with exposure to wildfire smoke in the general population, however, is uncertain. There is growing interest in learning more about what happens when smoke blankets communities sometimes for weeks at a time, since wildfire smoke waves, events lasting more than two days, have increased sharply in recent years. Birth outcomes, mental health, cognitive impacts, and cancer have not been sufficiently studied although some evidence shows an increased risk of low birth weight or preterm birth with wildfire smoke exposure during pregnancy. Children, pregnant women, people with pre-existing respiratory disease and the elderly are especially vulnerable to smoke exposure and should take particular care to limit exposures to wildfire smoke.
Personal and Public Health Protection
Officials from the U.S. Environmental Protection Agency, U.S. Forest Service, Centers for Disease Control and Prevention, and California Air Resources Board have prepared Wildfire Smoke: A Guide for Public Health Officials, which contains a wealth of information useful to all stakeholders, including clinicians who will periodically be advising patients on best practices for minimizing smoke exposure and health risks. Another guide from the CDC summarizes recommendations succinctly for the general public. Health care professionals, health care systems, public health officials, city planners, schools and businesses should all be involved in implementing solutions to mitigate adverse impacts of wildfire smoke. WWW.SFMMS.ORG
