Project Summary The study of chemical mixtures is a high priority as mixtures represent the real-life exposure scenarios that impact health. Mixtures are methodologically similar to studying the exposome (i.e. the study of all health relevant exposures) and research on new methods to measure and analyze higher order mixtures will inform future exposomic research. We have developed a tooth-based exposure biomarker that measures prenatal and childhood exposure to elements and organic environmental chemicals that reduces exposure misclassification and can accurately estimate both dose and timing of exposure. In our first grant cycle we established the biomarker for a mixture of Pb, Mn, Zn, As and Cd in predicting neurodevelopment. In this renewal we will longitudinally assess additional metals and more than 100 organic environmental chemicals over the prenatal and early childhood periods. These early life stages are comprised of critical windows of susceptibility when individuals are particularly vulnerable to chemical exposures. Current knowledge on the effects of fetal exposure to chemical mixtures is limited. In reality, humans are exposed to a large number of organic and inorganic toxicants simultaneously, but most studies only focused on one chemical at a time, and while we know that elements and organic pollutants can interact biochemically, there are a lack of comprehensive data on organic-element interactions. In addition, our biomarker can uniquely identify critical windows that define heightened susceptibility with greater precision than blood or urine-based biomarkers. Prospective birth cohorts that collect biomarkers during pregnancy and follow offspring into childhood can provide evidence to assess the impact of exposures during key developmental windows, but this approach can miss critical windows if biological sampling is mistimed. We propose to overcome these limitations by applying precise tooth matrix-based biomarkers of organic chemical and elemental exposures at specific life stages that comprehensively assess the prenatal and early childhood periods. Our overarching aim is to study the risk of neurodevelopmental deficits due to high dimensional mixtures of elements and organic chemicals using a single toxicant exposure biomarker. We will leverage 3 established and richly characterized birth cohorts in a discovery–replication design. Our discovery cohort (called PROGRESS) and our 2 replication cohorts (called ELEMENT and PRISM) were all recruited during early pregnancy and followed through late childhood. Two are based in Mexico City, have similar designs and have multiple overlapping neurodevelopmental test data. The 3rd is based in New York City and allows us to better generalize results to the U.S.; thus, we replicate at multiple levels. Finally, in preparation for this highly innovative proposal, we have collected deciduous teeth for biomarker analysis in all 3 cohorts (80% of teeth are already collected) and have extensive r...