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Human Exposure and Atmospheric Sciences

Investigating the Human Exposome

Environmental exposures are complex and involve thousands of chemicals, a multitude of sources, and different exposure pathways. Exposures generally occur at low levels and varying timeframes over a lifetime. According to recent research, 70-90 percent of long-term latent and chronic human diseases like cancer, cardio-vascular, Parkinson's, and Alzheimer's disease, emphysema, asthma, and diabetes are attributable to the interaction of environmental and human genome factors. As such, EPA scientists are evolving their research from a targeted "one exposure, one adverse effect" approach towards a broader "discovery" approach that incorporates the concept of the human "exposome" as the counterpart to the human genome.

The human exposome is defined as all of the environmental chemicals, human metabolites, chemical metabolites, metabolic reaction products, as well as the byproducts and biochemistry of the symbiotic microorganisms in our gut.

The ever-changing exposome
In short, the exposome represents everything that is "not the genome" in human systems biology. The challenges we encounter with the exposome concept are in the levels of complexity. Unlike the human genome, which stays essentially unchanged from birth to death, the exposome changes constantly in response to the environment around you, your health state and activity, diet, and metabolic processes.

Also, the compounds that make up the exposome fall into many different categories. They can be small reactive gases and volatile organic compounds in breath from internal biology or from environmental sources like water disinfection, exhausts and fuels, and consumer products (e.g. spray cans). They can also be bigger organic molecules in urine and blood that come from the environment like pesticides, fire retardants, perfluorinated compounds, and their metabolites. And, they can include all kinds of internal chemicals that the human body uses to operate our life cycles like proteins and enzymes. Measuring all these different kinds of chemicals requires different sampling and analytical techniques.

EPA exposome research
EPA scientists are working on a series of stratified exposure experiments for cataloguing components of the human exposome in different biological media like blood, breath, and urine using different kinds of sampling methods and analytical laboratory techniques. These include Gas Chromatography-Mass Spectrometry, Liquid Chromatography-Mass Spectrometry, and immunochemistry. As such, the scientists are developing and cataloging environmental and human biomarker measurements and their cumulative impacts on human systems biology.

The ultimate goal of these investigations is to develop a knowledge base of human exposome chemicals that can be used to assess what is "normal" in the human population, and then contrast distributions and variance statistics to results from biomarker studies of sub-populations that may be affected by specific environmental stressors.

Diagnosing with the exposome
In the long run, scientists hope to be able to "diagnose" the environmental effects on human systems biology much like your personal physician diagnoses your health state.

In the case of the exposome, the perturbations of the exposome would be diagnosed across a community or sub-population (children, pregnant mothers, elderly, ethnic groups, etc.) and then compared to the expected range. If the exposome appeared to be disturbed, then further environmental and biological analytical study would be indicated to figure out the cause of this effect.

Although this approach would work at the individual person level, the true power will come from the statistical interpretations that can applied across many people and so more broadly provide the diagnostic tools to protect public health.

Publications

Technical Contact
Joachim D. Pleil, Ph.D.
EPA National Exposure Research Laboratory
pleil.joachim@epa.gov

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