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.