Fine particulate matter relates to white matter microstructure alterations in U.S. children

Abstract

BACKGROUND AND AIM: Recent epidemiological findings have increased concern that exposure to fine particulate matter air pollution (aerodynamic diameter ≤2.5 µm; PM2.5) may be neurotoxic, even at low levels. Earlier human MRI and animal studies suggest that PM2.5 may impact white matter, yet questions remain about potential localized effects on microstructure. The goal of the current cross-sectional study was to examine how PM2.5 exposure relates to white matter microstructure in a large, diverse sample of children. METHODS: We examined the associations between annual average outdoor PM2.5 exposure and white matter microstructure in 7,602 9-10 year-old children from the landmark Adolescent Brain Cognitive Development study. Diffusion Tensor Imaging was used to characterize white matter microstructure using fractional anisotropy (FA). Annual average PM2.5 concentrations were assigned to the primary residential address at the baseline visit in 2016-2018 using an ensemble-based model approach. RESULTS:After correcting for multiple comparisons and adjusting for study site (n=21), socio-demographics, and MRI-related covariates, residential PM2.5 exposure (mean 7.65; range 1.72–15.90 ug/m3) was found to have significant non-linear associations with FA in multiple tracts. Increasing exposure to PM2.5 was associated with bilateral increases in FA in the uncinate fasciculus, superior longitudinal fasciculus, and inferior longitudinal fasciculus and bilateral decreases in the cingulate cingulum. PM2.5 exposure from 1.72 to 7.5 ug/m3 was also positively associated with increases in the left hemisphere fornix and right hemisphere anterior thalamic radiation. CONCLUSIONS:White matter microstructure in today’s developing youth may be affected by ambient fine particulate matter. Different patterns were observed in the left and right hemispheres and along specific white matter tracts. Our findings suggest that annual average PM2.5 exposure may relate to greater restricted diffusion as indexed by FA in tracts important for motor, emotion, and attention, which may reflect a combination of alterations in myelination, microarchitecture, and/or packing density. KEYWORDS: Air pollution, Particulate matter, Neurodevelopmental outcomes, Children's environmental health