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Study Monitors Exposure of Individuals to Airborne Biologics, Chemicals

NEW YORK (GenomeWeb) – People are exposed to a wide range of bacteria, viruses, and chemicals as they go about their daily lives, a new study has shown.

Researchers led by Stanford University School of Medicine's Michael Snyder gave a wearable device to 15 individuals to collect air samples for varying lengths of time. As they reported in Cell today, they found that people were exposed to thousands of different species and chemicals. Their so-called 'exposomes' also varied by geographical location and season.

The researchers said that further study of these exposures could provide insight into how the environment impacts human health at an individual level.

"Human health is influenced by two things: your DNA and the environment," Snyder, chair of the department of genetics and director of the Center for Genomics and Personalized Medicine, said in a statement. "People have measured things like air pollution on a broad scale, but no one has really measured biological and chemical exposures at a personal level. No one really knows how vast the human exposome is or what kinds of things are in there."

He and his colleagues re-engineered air-monitoring devices that participants could wear on their upper arms. These devices simultaneously collected abiotic and biotic compounds that were later analyzed by either LC-mass spectrometry, for the abiotic compounds, or next-generation sequencing, for the biotic compounds. Fifteen individuals wore these devices, though three participants were tracked more intensively. One participant — Snyder himself — wore the device for more than two years.

The researchers extracted DNA and RNA from these samples and generated a total of 42.9 billion DNA reads and 30.4 billion RNA reads. They then compared these reads against a database they developed that contains more than 40,000 species belonging to all domains of life. In all, they identified 2,560 species, and found that Snyder was exposed to 2,378 species during the course of 24 months of monitoring, while another participant was exposed to 1,357 species during 12 months, and a third to 1,009 species during three months. These samples were dominated by a few phyla, such as Basidiomycota, Streptophyta, and Firmicutes, among others. The researchers also picked up reads from the participants' dogs, cats, and pet guinea pig, as well as evidence of eucalyptus exposure.

These exposomes, the researchers noted, are highly dynamic, diverse, and varied by geographical location and time of year.

Samples collected when the participants were in similar locations were more similar to each other than to samples collected at different sites.

Still, even participants who lived close by geographically had quite different exposomes. In particular, they tracked four individuals in the San Francisco Bay Area closely for three weeks, though one had a trip to Washington, DC, during that time frame. Where in the region the participants were and their travel pattern —such as their commute to and from work — influenced their exposome profiles. The individuals with geographically constrained routines had exposomes that clustered more tightly, while one individual with a long commute and the individual with an out-of-state trip had more varied exposomes.

Exposures to certain phyla, genera, and species were more likely at certain times of the year, the researchers added. For instance, individuals were more likely to be exposed to pine trees during the summer or fruit green mold during the summer or autumn.

At the same time, participants were also exposed to a host of chemicals. The researchers identified 3,299 chemical features, which they tentatively annotated to 972 compounds. They confirmed eight of these using references standards, including insect repellent DEET and carcinogen DEG. Exposures to chemical likewise varied by place and season.

Overall, each individual had a distinct environmental exposome, the researchers reported. "The bottom line is that we all have our own microbiome cloud that we're schlepping around and spewing out," Snyder said.