Exposure to Ambient Fine Particulate Matter and Cortical Thinning in Adolescents

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Introduction Exposure to ambient air pollutants, including PM2.5 (particulate matter with aero-diameter < 2.5 μm) is associated with neurodevelopmental delays and increased behavioral problems. Recent studies suggested that air pollutants may alter white matter structure and global functional connectivity in young children, but little is known about the exposure effects on adolescent brain. Methods We studied 108 adolescents (50% girls) from an urban-dwelling twin cohort in Southern California. Individual-level exposure to PM2.5, based on residential histories and a spatiotemporal model of monthly ambient concentrations, was estimated and aggregated to one-year average during pre- (9-10), early- (11-13), and mid-adolescence (14). High-resolution T1-weighted MRI images were acquired at age 14 to estimate cortical thickness using FreeSurfer. Sex-stratified mixed-effects models were constructed to assess the effect of PM2.5 on cortical thickness while controlling for within-family correlation, race/ethnicity, and socioeconomic status. Results We found generally consistent patterns of cortical thinning in the prefrontal cortex to be associated with exposure to PM2.5 across pre-, early- and mid-adolescence. The exposure effects are most prominent in the inferior frontal and anterior cingulate cortex in girls, whereas the effects are most prominent in left lateral temporal cortex and right lingual gyrus in boys. However, the results did not survive correction for multiple comparisons (FDR). Conclusions The accelerated cortical thinning associated with PM2.5 exposure may be due to earlier synaptic pruning or over-pruning, rendering slower maturing brain regions (e.g., lateral prefrontal and temporal surfaces) more vulnerable to such effects. Large-sample studies are needed to confirm this initial evidence for adverse effects of PM2.5 on cortical brain development in adolescents and to understand the functional implications and underlying mechanisms.