Levels of certain pollutants considered safe are now linked to changes in the brain function of children, which can increase their risk of developing cognitive and emotional problems later, according to an alarming study.

The study, published in the journal Environment International, used brain scan data from more than 9,000 children aged 9 and 10. 

Children exposed to more pollutants showed changes in connectivity between various brain regions. In some areas, they had more connections than normal; in other areas, they had fewer.

"A deviation in any direction from a normal trajectory of brain development -- whether brain networks are too connected or not connected enough -- could be harmful down the line," said Devyn L. Cotter, a doctoral candidate in neuroscience at the University of Southern California’s Keck School of Medicine.

Communication between regions of the brain helps us navigate virtually every moment of our day, from the way we take in information about our surroundings to how we think and feel. 

Many of those critical connections develop between the ages of 9 and 12 and can influence whether children experience normal or atypical cognitive and emotional development.

"Air quality across America, even though 'safe' by EPA standards, is contributing to changes in brain networks during this critical time, which may reflect an early biomarker for increased risk for cognitive and emotional problems later in life," said Megan M. Herting, Associate Professor of population and public health sciences at the Keck School.

In the study, the team analysed the salience, frontoparietal and default-mode brain networks, as well as the amygdala and hippocampus  -- key regions of the brain known to be involved in emotion, learning, memory and other complex functions.

Next, the researchers used EPA and other data to map air quality at each child's residence, including levels of fine particulate matter (PM2.5), nitrogen dioxide (NO2) and ground-level ozone (O3). 

They then used advanced statistical tools to investigate whether young brains develop differently when they are exposed to more pollution.

The results showed that greater exposure to PM2.5 was linked to relative increases in functional connectivity between regions, while more exposure to NO2 predicted relative decreases in connectedness. 

Exposure to higher levels of O3 was associated with greater connections within the brain's cortex, but fewer connections between the cortex and other regions, such as the amygdala and hippocampus.

The findings could prompt regulators to consider brain health, in addition to lung and cardio metabolic health, when they set or adjust recommendations for air quality.