Traffic Exposure From Freeways as a Risk Factor for Autism

Background: The prevalence of autism spectrum disorders (ASDs) has increased over the last 10 years. The ASDs are heterogenous with many genetic and environmental factors likely contributing to their origins. Examination of regional pollutants has suggested the importance of air toxics in autism etiology, yet little research has examined local level air pollution exposure beyond measures of roadway proximity.  Specifically, living near a freeway has been associated with increased autism risk. 

Objectives:  In this study we investigate the relationship between traffic related air pollution (TRP) exposure and autism. 

Methods:  This study analyzed data on 303 autism cases and 259 typically developing controls enrolled in the Childhood Autism Risks from Genetics and the Environment (CHARGE) Study. Autism diagnosis was confirmed based on evaluations conducted at the M.I.N.D. Institute using both the ADOS and ADIR while controls were those that scored below the cut-off of 15 on the Social Communications Questionnaire and who did not meet criteria for developmental delay using the Mullen's Scales of Infant Development and the Vineland Adaptive Behavior Scales.  The mother’s address from the birth certificate and trimester specific addresses derived from a residential history questionnaire were geo-coded and TRP estimates assigned to each location using the CALINE4 line-source air-quality dispersion model. Logistic regression models were fit comparing estimated trimester- and birth-specific pollutant levels for cases with autism vs. typically developing controls. Analyses included adjustment for pertinent covariates including child's gender, maternal age, and other demographic and socio-economic related characteristics.

Results:  Cases were more likely to live at residences with the highest TRP exposure during the first year of life, as compared to controls (OR 2.02, 95%CI 1.25-3.28).  Exposure during the third trimester was associated with increased autism risk even after adjusting for exposure during other trimesters.

Conclusions:  Exposure to traffic related air pollution during the third trimester of pregnancy and early life was associated with increased autism risk. Further examination of specific air pollution measures is needed to better understand this association.