According to studies, we are bombarded by thousands of species and various chemicals

We are all exposed to a vast and dynamic cloud of microbes, chemicals and particles that, if visible, could make us look like Pig-Pen from Peanuts.

Using a redesigned air monitoring device, scientists at Stanford University School of Medicine examined this plume and discovered a multitude of biological and chemical details that swirl around us. Their discoveries show, in unprecedented detail, the variety of bacteria, viruses, chemicals, plant particles, fungi and even tiny microscopic animals that enter our personal space – a bombardment known as the "bombardment". human exposome.

"Human health is influenced by two things: your DNA and the environment," said Michael Snyder, Ph.D., professor and chair of genetics at Stanford. "People have measured things like large-scale air pollution, but no one has really measured biological and chemical exposure on a personal level." Nobody really knows how much Human exposome is vast or what are the things. "

According to Snyder, this curiosity – to see, for the first time, what an individual's exposure looks like at an individual level and how much it varies by people – motivated the study. But the study of the exposome also offers an opportunity to clarify factors of environmental influence of human health that are otherwise obscure, he said. For example, rather than simply blaming the pollen, people with seasonal allergies would be able to identify exactly what they are allergic to by monitoring their exposure data and their symptoms throughout of the year.

The results of the study also reveal information on chemical and household peaks and weather trends, and also show the wide range of chemical and biological particles that can be found between individuals, even in a relatively small geographic area like San Francisco Bay Area.

The study will be published online on September 20 at Cell. Snyder is the main author. Postdoctoral researcher Chao Jiang, Ph.D .; research scientist Xin Wang, Ph.D .; research associate Xiyan Li, Ph.D .; and postdoctoral researchers Jingga Inlora, Ph.D., and Ting Wang, Ph.D., are co-principal authors.

"About 70 billion readings"

For two years, scientists collected data from 15 participants who went through more than 50 different locations. Some people were monitored for a month, some for a week and one (Snyder) for two full years. To capture fragments of each individual's exposome, a small device attached to the participant's arm "breathes" tiny bursts of air – about one-fifteenth of the volume of a medium human breath.

The device, the size and shape of a large box of matches, accompanies participants everywhere and is equipped with a sub-micron filter that traps particles in the body. ;apparatus. The data – bacteria, viruses, chemicals, mushrooms and other objects sucked by the device – are brought back to Snyder's laboratory and extracted for DNA and RNA sequencing, as well as chemical profiling for identify all organisms and chemicals collected. exposed to.

This idea – of siphoning parts of an individual's exposome and systematically classifying what it contains – is pretty new, Snyder said. And Jiang needed to put together an entirely new database.

"Scientists have collected separate databases on bacteria, viruses or fungi, but to fully decode our environmental exposures, we have created a pan-domain database covering more than 40,000 species," Jiang said. It includes information about bacteria, viruses, fungi, animals, plants and others all organized in a single searchable database.

"We sequenced these samples with incredible detail," said Snyder, who is also Professor Stanford W. Ascherman, FACS, professor of genetics. "Nobody has ever done a study as thorough before, we have about 70 billion readings."

Particle analysis

Between the participants, Snyder and Jiang found that the exposures could be very different, even in a relatively small geographic area – in this case, San Francisco Bay. Snyder cited a particularly well-controlled part of the study, in which four participants, including Snyder, were closely monitored for a month, for example.

Each person lived in a separate area of ​​the San Francisco Bay Area: Palo Alto, Sunnyvale, Redwood City and San Francisco (although the person who lived in Redwood City crossed the bay for his work). "It turns out that, even at very close distances, we have very different exposure profiles or signatures," said Snyder. These personal signatures are essentially traces of specific fungi, plants, chemicals and bacteria, visible regularly on or around a single person, but which vary from person to person. Many environmental aspects contribute to this microscopic amalgam: domestic animals, household chemicals, flowers in bloom and even rain.

"In the end, we all have our own microbiome cloud that we design and broadcast," Snyder said.

Specific and unique signatures were captured for each individual (although Snyder added that DEET, an insect repellent, as well as several carcinogens were found in just about every chemical sample). For example, the San Francisco resident has shown high levels of "slime bacteria" or bacteria that are commonly found in wastewater and sewage treatments. Snyder constantly had fungal exposures at home because of what he suspected was the use of "green" paint. "The guy who painted my house was an ecologically and ecologically friendly person, and he avoided using paints containing a substance called pyridine," Snyder said. Pyridine, which was a popular additive for indoor paints, has an inverse relationship with fungi, that is, less pyridine, plus there are fungi.

Snyder's profile was the most diverse, as he took the camera wherever he went, nationally and internationally, for two years, trading his filters for each new location. Apart from exhibits of his pet (Snyder has a cat, a dog and a guinea pig), his signature also showed signs of eucalyptus in early spring, providing nuanced information about what could cause his allergies d & # 39; in April.

Connect to human health

In addition to the four highly controlled participants, a dozen participants were added at different times of the year, helping Snyder to grasp the exposures brought by weather, seasons and location.

"There are many results that have not been described before – all kinds of seasonal patterns of fungi, bacteria and plants," Snyder said. The device can even capture viral / bacterial signatures and carcinogenic particles in the air. Although the devices have detected potentially pathogenic viral and bacterial sequences, it can be difficult to distinguish a threatening pathogen from one of its near innocuous relatives.

With regard to carcinogens, it is also more complicated than just detecting them in the device. "We measure individual exposures, not absolute levels," he said. "So, at this point, the data is not generalizable enough to make general statements."

But that does not mean that one day it will not be. Snyder said the study only scratches the surface of human exposure data and its link to health, and that his team's future goals are to better understand exposure to human health. "We want to measure more people in more diverse environments," said Snyder. "We also want to simplify the technology, to the point that everyone can measure their personal exposures, perhaps a bit like an exposure-sensing smartwatch."

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