Smog in downtown Los Angeles as seen from a nearby freeway
Credit: Aliazimi/Wikimedia, CC BY-SA 3.0

There is a mental health crisis brewing among children and teens, and new evidence has suggested that exposure to air pollution could be one of many risk factors. In a recent study, researchers found that adolescents living in areas with relatively high levels of ozone experienced a significant uptick in depressive symptoms, such as sadness, loneliness, and feelings of self-hate.

“One of the things that I’m pretty startled by is that we’re seeing these effects over 2- and 4-year periods.”

And this change in mental health can come about rather quickly, explained the study’s lead author, Erika Manczak, an assistant professor of psychology at the University of Denver. “One of the things that I’m pretty startled by is that we’re seeing these effects over 2- and 4-year periods.” Perhaps even more unexpected: All of the study’s 213 participants lived in neighborhoods where average ozone concentrations were below the National Ambient Air Quality Standards. “Even though these were objectively low levels of average ozone exposure, we are nonetheless seeing these effects.”

To conduct this study, Manczak and colleagues analyzed mental health data of children between the ages of 9 and 13 collected at several points over a 4-year period. They then compared these figures with air quality monitoring data that roughly corresponded to each participant’s home address. After accounting for a range of compounding factors—like age, gender, and socioeconomic status—the researchers found that even slightly elevated ozone levels corresponded to an increase in depressive symptoms over time.

“They were able to show really clean linear symptom trends in folks exposed to high levels [of ozone] that are basically absent in folks not exposed to high levels,” said Aaron Reuben, a postdoctoral scholar in neuropsychology at Duke University who was not involved in the study. “For people concerned about understanding individuals’ risk for depression, I think this paper adds a lot of new value.”

“Humans Are Messy Subjects”

Scientists have long known that air pollution exposure can lead to a slew of negative health impacts, but “it was assumed for many years that air pollution mostly harmed the lungs,” explained Reuben. Even today, ozone is frequently said to contribute to pulmonary issues like asthma and respiratory infections, “which it does, but then we realized: Maybe it could also harm organ systems closely associated with the lungs.”

That, it turns out, includes the brain and central nervous system. “There seems to be some evidence in animal models to suggest that exposure to ozone and other forms of pollution can affect the activity of various neurotransmitters, as well as can encourage the expression of inflammatory proteins in the brain,” explained Manczak.

All of those things have been separately implicated in the formation and development of mental disorders, said Omar Hahad, a psychologist and researcher at the University Medical Center Mainz in Germany who was not involved in the study.

Animal-based research can tell scientists only so much. After all, depression in a rat will look very different from depression in a human being. That’s why these findings are often used in conjunction with observational studies, like Manczak’s, to understand how these physiological mechanisms could affect people, especially vulnerable populations like children.

It’s not a perfect science, though. For one, “humans are messy subjects,” explained Reuben. “Almost everything in human toxicology studies is going to be correlational.”

There also could be other factors coming into play that researchers cannot easily control for. “In highly urbanized areas, it’s more likely that there are colocalizations of other environmental factors such as noise exposure, light, or temperatures, which we know affect mental health,” explained Hahad.

Taking Precautionary Action

Nevertheless, the research by Manczak and colleagues adds to the growing list of evidence that highlights air pollution’s negative effect on mental health. “I think replicating the study in a much larger sample and in different parts of the world would be really an important next step to help us be a little bit more confident in these associations,” Manczak said.

In addition, more work is also needed to understand how different mixtures of pollutants might alter these effects. “We don’t know if the effects of these air pollutants are additive or synergistic,” said Hahad.

Despite these outstanding questions, the public can still take precautionary actions, researchers said. “I’m a really big believer in paying attention to what your local air quality is and using that information to inform how you behave across the day,” said Manczak, whether that be rescheduling outdoor activities on high-pollution days or donning N95 masks.

That said, individual efforts can get us only so far. “What is really lacking [are] the political actions to really address this problem,” said Hahad.

Reuben agreed. “Fundamentally, when we talk about air quality, water quality, things that influence health and longevity of all of us, it has to be a societal response. You just can’t do it alone.”

—Krystal Vasquez (@caffeinatedkrys), Science Writer

Citation: Vasquez, K. (2022), Air pollution linked to adverse mental health effects, Eos, 103, Published on 5 May 2022.
Text © 2022. The authors. CC BY-NC-ND 3.0
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