When we consider how indoor environments influence our health, we often think first of how those environments change our lifestyle, encouraging us to be more sedentary or less social. But there’s another way our time indoors affects our biology: by determining what substances we come in contact with.
In a paper published in the journal Environmental Science and Technology, researchers at Virginia Tech introduce a conceptual engineering model for studying how the indoor environment influences the “exposome.”
“The exposome is the aggregate of all the chemicals, microbes, and radiation you’re exposed to in the water you drink, the food you eat, the air you breathe, and objects you touch,” said Linsey Marr, a professor of civil and environmental engineering in the College of Engineering and an author of the paper. “It’s everything your body comes in contact with.”
In the indoor, or “built” environment, design; building materials; heating, cooling, and ventilation systems; plumbing — even factors like the choice of hand soap — all affect that set of exposures.
Understanding those influences is a step toward eventually designing buildings that have a positive impact on human health.
The research team has also founded an interdisciplinary center within the Institute for Critical Technology and Applied Science to tackle these questions. Called the ICTAS Center for Science and Engineering of the Exposome, the group includes Amy Pruden, the W. Thomas Rice Professor of Civil and Environmental Engineering; Marc Edwards, the Charles P. Lunsford Professor of Civil and Environmental Engineering and a University Distinguished Professor; professor of civil and environmental engineering Peter Vikesland; Marr; and research scientists Dongjuan Dai and A.J. Prussin.
“We’re trying to raise some of the fundamental questions that we need to address when we look at the exposome of the built environment,” said Prussin, the center’s associate director.
The Centers for Disease Control estimate that environmental factors may be responsible for up to 90 percent of human disease. For most Americans, who spend about 90 percent of their time indoors, the environment likely to have the biggest health impact is the one created by buildings like offices and homes, where the exposome is very different than it is outside.
In their paper, the researchers describe the indoor exposome in terms of chemicals, particles, and microbes in the air, in drinking water, or on surfaces. And they emphasize that one of the keys to studying the exposome accurately is to recognize that these substances and exposure routes are interdependent.
When we breathe in dust, we also acquire the microbes and chemicals clinging to those particles. Disinfectants added to drinking water to alter its microbial communities also create chemical byproducts.
And while it’s usually clear whether a substance enters your body from the air, the water, or a surface, the path it takes to get to that point of contact can be complex.
Substances in the water can be aerosolized into the air, and then settle on surfaces; particles resting on surfaces can be blown into the air or washed into the water.
For example, Legionella is a pathogen found in potable water, but the human exposure route is airborne: The bacteria cause disease when aerosolized water droplets are breathed in.
“It’s not simple; we cannot simply focus on the water issue,” said Dai, the paper’s lead author. “The water and the air actually influence each other.”
Engineering controls can alter the exposome and improve health — radon mitigation systems are one common example. But before engineers can determine which plumbing materials or ventilation systems or types of paint are most beneficial, they must identify precisely how each of those things influences the indoor exposome, and the health impact of that change.
The growing recognition of the significant impact of the environment on human health parallels the advent of germ theory in the late 19th century, when the connection between microbial pathogens and human disease won widespread acceptance.
But investigating the connection between health and the exposome is more complicated. Instead of identifying a single pathogen responsible for a specific disease, researchers must consider a network of thousands of interrelated exposures and their combined contributions to conditions like asthma and obesity, complex conditions in their own right with dozens of potential causes.
Scientists and engineers with different backgrounds will need to work together to tease apart that web of influences.
“The exposome problem, by its nature, requires an interdisciplinary collaborative approach,” Marr said. “No one person has enough expertise to tackle the whole thing.”
The exposome center brings together experts in environmental engineering working on microbial communities, drinking-water quality, airborne pollutants, and other specialties.
The group’s research symposium in the spring attracted faculty and students from an even wider range of fields, including English and history.
This kind of interdisciplinary collaboration will be one of the keys to untangling the complex influence of the indoor exposome on human health. Another will be finding ways to deal with the huge amounts of data generated by tracking indoor exposures and health metrics for large populations.
But the rapid development of data science and proliferation of sensors, such as those in smartphones and watches, may give researchers the tools to first measure and then reveal that complexity.
In addition, the researchers say, involving citizens in the research process may be one way to address the exposome problem.
“In order to get some of these large data sets, we’re really going to need a lot of citizen scientists out there,” Prussin said.