Associations of Autism Spectrum Disorder with PM_2.5 Components: A Comparative Study Using Two Different Exposure Models

This retrospective cohort study examined associations of autism spectrum disorder (ASD) with prenatal exposure to major fine particulate matter (PM_2.5) components estimated using two independent exposure models. The cohort included 318 750 mother-child pairs with singleton deliveries in Kaiser Permanente Southern California hospitals from 2001 to 2014 and followed until age five. ASD cases during follow-up (N = 4559) were identified by ICD codes. Prenatal exposures to PM_2.5, elemental (EC) and black carbon (BC), organic matter (OM), nitrate (NO₃^-), and sulfate (SO₄^2-) were constructed using (i) a source-oriented chemical transport model and (ii) a hybrid model. Exposures were assigned to each maternal address during the entire pregnancy, first, second, and third trimester. In single-pollutant models, ASD was associated with pregnancy-average PM_2.5, EC/BC, OM, and SO₄^2- exposures from both exposure models, after adjustment for covariates. The direction of effect estimates was consistent for EC/BC and OM and least consistent for NO₃^-. EC/BC, OM, and SO₄^2- were generally robust to adjustment for other components and for PM_2.5. EC/BC and OM effect estimates were generally larger and more consistent in the first and second trimester and SO₄^2- in the third trimester. Future PM_2.5 composition health effect studies might consider using multiple exposure models and a weight of evidence approach when interpreting effect estimates.