Wildfire smoke exposure linked to mental health issues

A recent study of 10,000 nine to 11 year olds has found that each additional day of exposure to wildfire smoke and other types of extreme forms of air pollution raises the risk of mental health issues in children.

“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 lead author Harry Smolker, a research associate at CU Boulder Institute of Cognitive Science.

This study, published in the journal Environmental Health Perspectives, was published at the same time as smoke from Southern California wildfires covers much of the Western U.S., extending as far away as Las Vegas and some parts of Colorado. 

Severe levels of particulate matter

Although annual average air quality has improved in recent decades due to limits on greenhouse emissions from combustion engines, more frequent wildfires have led to a new critical problem: a larger number of days with severe levels of 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,” Smolker said. “We need to understand what these extreme events are doing to young people, their brains and their behavior.”

Wildfire smoke and mental health

Although scientists have already known that air pollution can harm the lungs and the heart, they have only recently started to explore its impact on mental health.

Studies have shown that PM 2.5 (particulate matter with a diameter of less than 2.5 micrometers), is small enough to cross the blood-brain barrier, leading to inflamed tissue, damaged cells, and immune responses which can trigger both acute and long-term brain changes.

Experts have previously found that hospital admissions for depression, psychosis, and suicide attempts increase in adults on days with a high level of air pollution.

When pregnant women are exposed to high levels of particulate matter, their children are at a higher risk of developing motor deficits and cognitive impairments later in life. 

However, this new study is among the first to examine potential impacts on young people, whose brains are in a process of continuous development.

Wildfire smoke exposure

The scientists analyzed data from 10,000 pre-teens participating in the Adolescent Brain Cognitive Development (ABCD) Study – the largest longitudinal study of brain development and children’s health conducted in the U.S. 

To determine how many days in 2016 children were exposed to PM2.5 levels exceeding the level the Environmental Protection Agency (EPA) considers safe (35 micrograms per cubic meter), the researchers examined participant addresses and historical air quality data.

The investigation revealed that approximately one-third were exposed to at least one day above the EPA standard, with one participant exposed to unsafe levels for 173 days. The highest level of exposure was 199 micrograms per cubic meter, which is over five times the level deemed safe.

Mental health impacts of wildfires

The experts looked at parent questionnaires at four time points during three years. They discovered that, across both genders, each additional day of exposure to unsafe levels of PM2.5 increased the probability of an adolescent developing symptoms of depression, anxiety and other mental health issues up to one year later.

These findings came after taking into account a wide variety of possibly confounding factors, such as race, socioeconomic status and, most importantly, parental mental health. Even when parents did not report any symptoms of mental illness, their children frequently did.

“This suggests that PM2.5 exposure may have specific impacts on youth distinct from impacts on their parents,” Smolker said.

Repeated exposure is most damaging 

Repeated high levels of PM2.5 exposure had a larger influence on risk than annual averages or maximum levels did, an alarming finding suggesting that each additional day of exposure counts.

For each day of unsafe exposure, risk increased up 0.1 points on average on a scale from 1 to 50.

“This is relatively small, but not trivial,” Smolker said, emphasizing that PM2.5 is only one of the large variety of pollutants in the “exposome,” the collection of environmental exposures which shape children’s development. “Collectively they can add up.” 

Cognitive impacts of air pollution

Some children may be genetically predisposed to be even more vulnerable to the cognitive impact of air pollution

Although PM2.5 can arise from many sources, including traffic and industry, the experts suspect that most of the exposures in the study were due 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,” said co-author Colleen Reid, a geographer at CU Boulder.

“The current study concluded that the number of days of PM2.5 exposure above US EPA standards during late childhood was associated with higher concurrent levels of internalizing symptoms across females and males, even after considering effects of other temporal patterns of exposure,” wrote the study authors. 

“Notably, this association remained when accounting for parental psychopathology, suggesting PM2.5 exposure may have specific impacts on youth distinct from impacts on their parents.”

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