The study, which explores how particulate pollution impacts the adolescent brain, involves 10,000 youth and is among the first of its kind.
According to a recent study by the University of Colorado Boulder, which analyzed 10,000 children aged 9 to 11, each additional day of exposure to wildfire smoke and other severe air pollutants slightly increases the risk of mental health issues in young people.
“We found that a greater number of days with fine particulate air pollution levels above EPA standards was associated with increased symptoms of mental illness, both during the year of exposure and up to one year later,” said first author Harry Smolker, a research associate with CU’s Institute of Cognitive Science.
The study, published in Environmental Health Perspectives, comes as smoke from Southern California fires blankets much of the West, thickening skies as far away as Las Vegas and parts of Colorado. While annual average air quality has generally improved in recent decades due to limits on emissions from combustion engines, more frequent fires have created a new problem: more days with severe levels of tiny particles of burnt things —a.k.a. particulate matter—in the air.
“We are entering a new age in which we are experiencing unprecedented levels of exposure to particulates multiple times a year,” said Smolker. “We need to understand what these extreme events are doing to young people, their brains, and their behavior.”
The pollution and mental health link
While scientists have known for years that air pollution can harm lung and heart health, they’ve only recently begun to explore its impact on cognition and behavior.
Some studies show that PM 2.5, particulate matter with a diameter of less than 2.5 micrometers, may be small enough to slip across the blood-brain barrier, inflaming tissue, damaging cells, and igniting an immune response that can fuel both acute and longer-term brain changes.
Hospital admissions for depression, suicide attempts, and psychotic episodes have been shown to increase in adults on high-pollution days. And when pregnant people are exposed to high levels of particulates, their children are more likely to have motor deficits and cognitive impairments later in life, studies suggest.
Smolker’s study is among the first to look at potential impacts on adolescents, whose brains are still developing.
The team analyzed data from 10,000 pre-teens participating in the ongoing Adolescent Brain Cognitive Development (ABCD) Study— the largest long-term study of brain development and child health ever conducted in the United States. CU Boulder is one of 21 ABCD research sites.
They looked at participant addresses and historical air quality data to determine how many days in 2016 youth were exposed to PM2.5 levels above 35 micrograms per cubic meter (35ug/m3) – the level the Environmental Protection Agency deems unsafe.
About one-third were exposed to at least one day above the EPA standard. One participant was exposed to unsafe levels for 173 days. The highest level of exposure reported was 199 micrograms/m3 – more than five times the level deemed safe.
When looking at parent questionnaires at four-time points over three years, the researchers found that, across both genders, each additional day of exposure at unsafe levels boosted the likelihood of a youth having symptoms of depression, anxiety, and other “internalizing symptoms” up to one year later.
This was after accounting for a wide variety of potentially confounding factors, including race, socioeconomic status and, notably, parental mental health. Even when parents did not report symptoms, their children often did.
“This suggests that PM2.5 exposure may have specific impacts on youth distinct from impacts on their parents,” Smolker said.
Each day counts
Repeated high levels of exposure had a far greater influence on risk than annual averages or maximum levels did, suggesting that each additional day of breathing poor air counts.
For each day of unsafe exposure, risk went up .1 points on average on a scale of 1 to 50.
“This is relatively small, but not trivial,” Smolker said, noting that PM2.5 is just one of the myriad pollutants in the “exposome” — the collection of environmental exposures that shape children’s development. “Collectively they can add up.”
Some youth may be genetically predisposed to be even more vulnerable to the cognitive and behavioral impacts of air pollution, he notes.
While particulate matter can emerge from many sources, including traffic and industry, study co-author Colleen Reid, a geographer with the Institute for Behavioral Science at CU Boulder, suspects that most of the exposures in the study were due at least in part to wildfire smoke.
“Wildfire smoke events are becoming more and more common, and this study adds to a growing body of evidence that they can impact our health,” Reid said.
Reference: “The Association between Exposure to Fine Particulate Air Pollution and the Trajectory of Internalizing and Externalizing Behaviors during Late Childhood and Early Adolescence: Evidence from the Adolescent Brain Cognitive Development (ABCD) Study” by Harry R. Smolker, Colleen E. Reid, Naomi P. Friedman and Marie T. Banich, 6 August 2024, Environmental Health Perspectives.
DOI: 10.1289/EHP13427
The study was funded by the National Institutes of Health.
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1 Comment
I am a medical anthropologist. There is no mention of the psychological impact of being near enough to a wildfire to smell smoke. There is a natural repulsion to wildfire, and smoke can cause an instinctive psychological response. This article focuses solely on the chemicals/particulates in smoke as air pollution, and is thinking of the impact of wildfire smoke on children in chemical terms, with these particulates hypothetically entering the brain. It is much easier to understand why kids smelling high levels of smoke from wildfires are depressed, anxious and upset. Wildfires are dangerous, and we instinctively know that, even children. Perhaps talking with the kids about natural wildfire disasters would help them identify this as a source of their mental discomfort when smelling smoke.