Environmental Exposures - broadly defined as originating from external sources (air, water, diet, infection, radiation, stress, etc.) and internal sources (inflammation, lipid peroxidation, the microbiome, preexisting disease, among others)1 - are important determinants of human health. Although chronic diseases are thought to result from the combination of environmental exposures and human genetics, the environmental determinants are poorly understood in comparison to the genetic factors. For example, epidemiologists are now able to conduct genome wide association studies (GWAS) with relative ease, but they still rely upon self-reported questionnaires to characterize environmental exposures. This disparity in data quality between genetic and environmental risk factors spawned the concept of the exposome representing all environmental (i.e. non-genetic) contributors to disease - from both external and internal sources - received by an individual during life. By measuring individual exposomes, environment wide association studies (EWAS) can be conducted which simultaneously test disease associations with thousands of environmental exposures.

What types of measurements are best suited for characterizing individual exposomes? On one hand, a top-down approach would combine biospecimens, like blood or urine, with new -omics technologies to profile subjects' internal levels of metabolites, metals, macromolecular adducts, serum proteins, and persistent organic compounds. On the other hand, a bottomup approach would exploit advances in sensor and cell-phone technologies to measure multiple personal exposures to external pollutant levels, as well as host of factors as physical activity, diet, and hormone levels among others. The integration of these two approaches promises to enable us to zero in on important environmental factors and to interleaf EWAS with GWAS.

This workshop will take a close look at emerging technologies that can be used to gather individual exposure information based upon external and internal measurements. Presentations and discussions will explore which of the technologies are "ready now" and which are still "emerging" for use in environmental health research. Particular attention will be paid to the relative advantages and disadvantages of external and internal measurements for characterizing individual exposomes and for performing EWAS. Recent proof of- concept studies will be highlighted and bioinformatic tools will be discussed. This synthesis should inform researchers and policy makers about the critical roles that the exposome concept and new technologies can play in understanding the origins of human diseases.