Story At A Glance

  • Even low levels of air pollution have been associated with neurological effects.
  • Small particles are known to be able to reach the brain.
  • A new study links short-term increases in particulate matter to psychiatric problems in children.

Every year, exposure to outdoor air pollution leads to about 4.2 million deaths around the world, according to the World Health Organization. Air quality is linked to lung cancer, stroke and heart disease to name a few. Researchers have known for quite some time that air pollution can also affect the health of children starting in utero. For example, even though air quality in places like Los Angeles have improved tremendously in the last few decades, recent research still shows effects on babies like preterm births and low birth weights. Some studies have linked emergency department visits for depression in adults to air pollution. New research is now showing that in children.

In a new paper published in Environmental Health Perspectives, a group of researchers have linked short-term increases in air pollution to emergency department visits for psychiatric purposes in children. They looked at data for air pollution at the home addresses of children in their cohort and paired that with emergency department (ED) visits at Cincinnati Children’s Hospital Medical Center between 2011 and 2015. The children were in the ED for psychiatric reasons like anxiety, suicidality, bipolar disorder, PTSD, as well as others.

The researcher compared the patients to themselves as a control so that each ED visit could be compared to a period of time when they didn’t visit the ED. They also tried different lengths of lag time from same day to three days after increased exposure to particulate matter smaller than 2.5 μm in diameter (PM 2.5). “When we're talking about higher exposures, we're talking relative to each other,” says coauthor Patrick Ryan in the division of Biostatistics and Epidemiology at Cincinnati Children’s Hospital Medical Center. “Most of the days of exposure...are underneath the U.S. EPA national ambient air quality standards. So we're not talking about super high levels.”

The researchers found that for every increase of 10 μm per cubic meter of PM 2.5 there was about a 7 percent increase in psychiatric emergency departments visit risk. “In this case, particulate matter, these very small particles in the air, can be associated with these emergency department psychiatric visits in children...which is I think a very serious finding,” says Wilma Zijlema, an epidemiologist based at ISGlobal studying how green spaces affect health.

Particulate matter in the body

So how is air pollution affecting the mental health of children? Scientists aren’t 100 percent certain about what these particles do in our bodies, but they have a few ideas. “There's a couple potential broad categories of how we think air pollution might be affecting the central nervous system in the brain,” says Ryan. One potential direct mechanism has to do with the fact that the particles are so small, especially ultrafine particles that are less than 0.1 μm in diameter, that they can actually cross the olfactory bulb and be directly deposited in the brain. Another important thing to note here is that these particles are “not just one inert piece of dirt or something like that,” according to Ryan. The particles may have chemical compounds attached to their surface that are toxic, Ryan adds.

A potential indirect mechanism that particulate matter can affect your health is that whenever you breathe air pollution into your body, your body reacts to it with an inflammatory response. “From the studies that we've done with the more long-term, chronic exposures, we think...this constant inflammatory state of the brain...might lead to the anxiety and the depression developing,” Ryan tells Changing America.

One way researchers are trying to understand the mechanisms of air pollution is by studying animals like rats or mice. For example, in research by Lucio Costa at the University of Washington, he exposes animals to diesel exhaust to see how it affects their neural development. “A lot of these disorders for development and aging do not have a very strong genetic component,” says Costa. “So we thought there...must be something in the environment, which causes this effect or contributes to these effects.” 

In one study of mice, Costa and collaborators found that prenatal and early-life exposure to diesel exhaust led to autism-like behavior. More studies in animals might be able to help us understand how the particulate matter is affecting development and brain function.

Confounding factors

Another thing Ryan and collaborators found was that there could be an interaction between what they call “community deprivation” and the effects of air pollution. And other experts think that this could be an important angle to investigate. “There could be an interaction between exposure to high air pollution and other situations that the child might go through [like] difficult home situations, other diseases, difficulties [at school],” says Costa.

“Some of the interesting things that we have yet to explore on this might be looking more at who it is who's most susceptible,” says Sara Adar, an epidemiologist at the University of Michigan who studies the health effects of air pollution in elderly adults. So if not all children are equally susceptible, how do we identify who is more at risk than others? And if there are community interventions that could help lower that risk, more research could be done to understand what those might be.

What are acceptable levels of air pollution?

Several experts tell Changing America that this study is concerning because the levels of air pollution were not considered to be very high. The air pollution was below the Environmental Protection Agency’s national air standard threshold for the amount of acceptable air pollution considered safe. And it’s not like we’re breathing air coming directly out of a tailpipe. “These are all levels that people would not recognize that they're being exposed [to],” says Adar. “Our air pollution is relatively invisible to us [in the United States].”

“It makes you think about these levels, about these limits,” says Zijlema. “It's an important point to make that health effects can appear below these levels, so that there's basically no safe level of air pollution.”

Published on Nov 18, 2019