Project Summary Anxiety and depression are among the most debilitating disorders worldwide and increase the risk for later-life adverse health outcomes including chronic anxiety and depression, substance abuse and suicide. Anxiety and depression are also the most common psychiatric disorders among adolescents with symptoms presenting as early as 4-5 years of age. Yet, we still have a poor understanding of the etiology of anxiety and depression in youth and the mechanisms involved. Air pollutants are widely recognized for their ability to affect the central nervous system and adversely impact neurodevelopment during childhood. The epigenome is particularly sensitive to environmental stimuli and studies targeting inflammatory and oxidative stress pathways have identified DNA methylation changes resulting with exposure to air pollutants. Oxidative stress and inflammation, however, are not the only pathways involved in air pollution neurotoxicity or the pathophysiology of mental health disorders. Thus, utilizing an epigenome- wide platform may help identify novel biomarkers of exposure and effect which may otherwise be overlooked with a targeted approach. The goal of this proposal is to determine whether exposure to fine particulate matter (PM2.5) and traffic-related air pollution (TRAP) during childhood and adolescence impacts the epigenome and whether changes in DNA methylation can be used to identify children at increased risk for anxiety and depression. Using the Cincinnati Childhood Allergy and Air Pollution Study (CCAAPS) and Health Outcomes and Measures of the Environment (HOME) study birth cohort, we will: 1) conduct an unbiased epigenome-wide search for DNA methylation biomarkers associated with PM2.5 and TRAP exposure prenatally through age 12 years (n=500) and 2) identify unique and pollution-related DNA methylation signatures associated with anxiety and depression. In addition, we will replicate our findings in a third, independent birth cohort, Project Viva (n=652), with similar sociodemographic characteristics and available air pollution and neurodevelopmental outcome data. The study design, based on three well-established birth cohorts with nearly two decades of follow-up, will allow for longitudinal and cross-sectional analyses of air pollution, DNA methylation, and mental health assessments all of which will increase the rigor and generalizability of our study.