In the summer of 2016, 100 teenage girls in the Salinas Valley slipped silicone bracelets onto their wrists and kept them there for a week.
Around the same time, 92 preschoolers in Oregon accessorized the same way.
The bands also found their way onto the wrists of farmworkers in Peru as well as Houston residents working to rebuild after Hurricane Harvey. Aside from the color, the wristbands looked like the yellow Livestrong bracelets popularized by cyclist Lance Armstrong in the early 2000s.
But this was not some fashion trend. The wristbands were research tools whose porous silicone made them ideal for soaking up chemicals in their surroundings. All were worn as part of a growing effort to understand what’s present in different environments and how those “exposures” — be they pesticides, smoke, floodwater contaminants or just the day-to-day contents of a preschool classroom — can affect our health.
In homes, on buildings, from satellites and even in apps on the phones in our pockets, tools to monitor the environment are on the rise. And they are fueling a new movement to track something called the “exposome” — the sum of all environmental exposures over a lifetime.
A growing number of scientists believe that if we knew every substance that someone was exposed to at every moment of his or her life, it could give rise to dramatic improvements in the understanding of the causes and risk factors for disease.
That goal, its architects will readily admit, is absurdly ambitious — even impossible. But even imperfectly realized, the approach may be what’s needed to finally understand why one person develops a disease and another doesn’t, which environmental exposures are the most worrying — and if there are windows of vulnerability during the times of life when exposures may be especially harmful.
“We think about all health and illness as a combination of genes and the environment,” said Julia Brody, a toxicologist affiliated with Brown University and the leader of the Silent Spring Institute, which studies environmental links to breast cancer. “And now it really is time to fill out the environment side of that equation.”
Salinas resident Carmen Ramirez was 15 when she joined the CHAMACOS Youth Council, a group of local students who helped carry out the study in which 100 Salinas Valley teens wore silicone wristbands for seven days. Ramirez helped with data collection, explained the bracelets to the girls and interviewed them about their lifestyles and exposure to pesticides.
“My friends were thinking things like, ‘I hope I pass my math test,’ and I was thinking, ‘I hope we get funding for the study,’” said Ramirez, who recently completed her sophomore year at CSU Monterey Bay.
That study is one of several related to pesticide exposure in the Salinas Valley. For 18 years, UC Berkeley epidemiologists have worked with local residents to study the physical effects of chemicals used in Salinas Valley homes and in agriculture.
“Agriculture is different everywhere in California, but a lot of the pesticides and the pesticide mixtures being used are similar,” said Kim Harley, the study’s lead scientist and an associate adjunct professor at UC Berkeley’s School of Public Health.
Harley said the study found higher pesticide levels in the bracelets of girls who lived near agricultural fields, but also concluded that the simple acts of placing a doormat at the entrance to homes and cleaning homes more frequently resulted in lower pesticide levels.
Concern over such exposures and myriad others was what led British cancer researcher Christopher Wild to coin the word “exposome” in 2005. He had closely followed the race to sequence the human genome and was worried that the world, in its eagerness to advance genetics, had forgotten the importance of environmental exposures to health.
Such a sentiment has grown stronger in recent years as genetics has failed to yield clear links to many cancers and other diseases. A recent study looked at the prevalence of 28 chronic conditions in twins and found that genetics explained less than 20 percent of the risk in most of the illnesses examined.
Even in the case of asthma — which ranked highest in terms of genetic contribution — genetics explained less than 50% of the risk. For leukemia — on the other end of the rankings — genetics explained only 3%.
“I was excited about the genetics,” said Wild, who formerly directed the World Health Organization’s International Agency for Research on Cancer. “But I felt it was an Imbalance. … If we can’t measure this other component, we’re not going to get to the bottom of the problem.”
Slowly, his colleagues have begun to rally around the idea. Efforts to develop sophisticated devices that sample the world around us are now on the rise. And new research groups are forming around the world to bring together the technology and expertise to process the vast amounts of data that will come from exposomics projects.
One example is the Children’s Health Exposure Analysis Resource, a network of U.S. laboratories and other resources that was established by the National Institute of Environmental Health Sciences. CHEAR and its successor program, which also includes research on adults, allow scientists to examine more chemicals that people may be exposed to — sometimes thousands at one time — than is done in traditional studies.
Researchers continue to select bits and pieces of lifetime exposures to put under the microscope, and they continue to discuss how to collect and examine information in a meaningful way and make real progress with such an ambitious task. Some scientists advocate for more air monitors in cities and homes. Others are developing wearable monitors that soak up pieces of the environment as people move through their day.
Some are trying to match tracking data from cell phones to satellite indicators of air quality, helping to assess individual exposures based on a person’s locale and movements. Still, other researchers are looking inside the body, hoping to identify chemical footprints that distinct exposures may have left behind.
Blood in particular holds clues, said Dean Jones, a biochemist at Emory University in Atlanta and co-author of a 2019 article about the promise of exposome research in the Annual Review of Pharmacology and Toxicology. For example, scientists can look for metabolites, small molecules broken down or created by body processes, and learn what happened internally following various exposures.
Though varied, the approaches share the goal of adding breadth to traditional studies in exposure science, which have historically focused on linking a single disease to one or more suspicious exposures, often as cases build up over time.
A history of poisoned lead workers dating back to the time of the Romans, for example, led modern researchers to show that even low levels of lead from automobile exhaust posed a serious public health risk. And a startling spike in lung cancer cases alongside increased smoking popularity drove researchers in the mid-20th century to study the dangers of cigarettes.
But many potentially harmful exposures could be far less obvious. The air you breathe, the food you eat, the products you use, the medicines you take, the surfaces you touch — all may contain multitudes of invisible chemicals (many naturally occurring, others not) and microbes you never know you’ve contacted.
Exposome scientists want to capture as broad a picture as possible. They want to ask not only if certain chemicals or microbes can harm health, but also if certain substances are dangerous in particular combinations during particular times — such as pregnancy — or to particular groups of people. They are, however, still a long way from tracking even a fraction of the potential threats that surround us.
For her part, Ramirez, the CSUMB student, is proud to have made her own contribution to the exposome effort.
The youth council she served on partnered with Hijos del Sol (Children of the Sun), the noted after-school arts program based in East Salinas, to create a mural depicting steps that protect against pesticide exposure, such as washing produce and using doormats. Some students on the council put on puppet shows for Salinas Valley children, while others created short radio novella episodes about the results of the study, educating communities through stations in California, Washington and Oregon.
“Issues like these aren’t just adult issues,” Ramirez said. “It’s the children who are growing up with this.”
Lindzi Wessel is a freelance journalist. Erin Malsbury, a former Monterey Herald intern, is a recent graduate of UC Santa Cruz’s Science Communication Program. A version of this article first appeared in Knowable Magazine from Annual Reviews, based in Palo Alto. (www.knowablemagazine.org).
