Simple, lightweight silicone wristbands are giving researchers a new window on people’s environmental exposures to toxic organic chemicals. They sequester and concentrate organic compounds, with a chemical absorption profile similar to that of human cells. And unlike other devices for tracking chemical exposure, the wristbands are comfortable to wear. Read on to find out how scientists are using them to explore links between disease and exposure to pesticides, flame retardants, fragrances, and endocrine disruptors.
For one week, 92 preschool-aged children in Oregon sported colorful silicone wristbands provided by researchers from Oregon State University. The children’s parents then returned the bands, which the researchers analyzed to determine whether the youngsters had been exposed to flame retardants. The scientists were surprised to find that the kids were exposed to many polybrominated diphenyl ethers (PBDEs), chemicals that are no longer produced in the U.S., as well as to organophosphate flame retardants, which are widely used as substitutes for PBDEs.
The results from that wristband study (Environ. Res. 2016, DOI: 10.1016/j.envres.2016.02.034) remain qualitative—they tell parents whether their child has been exposed to a particular chemical but don’t provide information regarding the amount of exposure. The researchers, led by environmental chemist Kim Anderson, are now working on ways to extract quantitative exposure data from the bands.
The work by Anderson’s team is one of several projects evaluating the effectiveness of silicone wristbands to record exposure to organic chemicals in air, water, and personal care products. Interest in using the bands as personal exposure monitors has been growing since Anderson’s team described the technology in a 2014 Environmental Science & Technology study (DOI: 10.1021/es405022f). Increasing demand for the wristbands recently led Anderson to cofound MyExposome, a company that hopes to put the tool into the hands of the public.
Silicone wristbands are easy to slip on, lightweight, and comfortable to wear compared with traditional personal air monitoring devices that rely on bulky air pumps, filters, and electronics. Study participants wear the bands for a specific amount of time—typically a day, a week, or a month. They keep the bands on at all times during the study—while sleeping, showering, jogging, swimming, eating, working, petting the dog, or reading their favorite magazine.
While they are being worn, the bands passively absorb a wide range of organic chemicals from the participants’ surroundings, trapping them within the silicone polymer matrix. After participants return the bracelets, researchers extract chemicals from them using various solvents or thermal desorption methods.
They identify the substances using analytical methods such as gas chromatography/mass spectrometry. Anderson’s team has developed a GC/MS screening method that detects 1,400 organic chemicals from wristbands, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls, pesticides, flame retardants, fragrances, and endocrine-disrupting chemicals such as bisphenol A, phthalates, and nonylphenol. The number of chemicals that the method detects keeps growing, Anderson says.
The screening method provides qualitative information on whether the chemicals are present in the wristband. It does not provide information on the amount of each chemical. But Anderson and colleagues are working to change that. They have already developed quantitative methods for analyzing certain classes of chemicals, including PAHs, pesticides, and flame retardants, absorbed into the wristbands.
Anderson got interested in silicone wristbands after decades of work in the environmental field developing passive sampling technologies. Such technologies measure how much of an environmental pollutant is likely to end up in an organism, rather than how much of the substance is in water, sediment, or air. Merely determining the concentration of chemicals in the environment “is a poor surrogate for understanding the chemical load in organisms,” she says.
While attending a football game years ago, Anderson noticed that several athletes and fans were wearing silicone wristbands. “I knew that was a material that I could adapt to be a passive sampler,” she says.
Her research group had previously tried to make a passive sampler necklace. It was effective in some regards, but wasn’t amenable to some job environments in which workers could be endangered by an item dangling around their necks. It also wasn’t expected to be something men would be willing to wear, Anderson notes. So she and her colleagues began developing gender-neutral wristbands out of various carbon- and silicone-based polymers.
Silicone polymers are an attractive material for wristbands because they are more elastic than polymers made from carbon, Anderson says. Silicone polymers are also good mimics of bioavailability because they contain long chainlike structures that form spaces similar in size—about 1 nm in diameter—to pores created by biological polymers in a human cell membrane, she says.
The wristbands are being promoted to the public by the Environmental Defense Fund (EDF), an environmental group that teamed up with MyExposome on a small project last year. EDF recruited 28 volunteers, mostly EDF staff and board members, to wear the bands for one week. Participants filled out a short activities survey. MyExposome analyzed their bands qualitatively for the suite of 1,400 chemicals.
EDF reported 57 chemicals were found in the bands, including PAHs, pesticides, plasticizers, phthalates, fragrances, preservatives, and flame retardants. Each band contained at least 10 and as many as 27 of the screened chemicals, with an average of 15.
The environmental group has since recruited a more geographically diverse group of volunteers, representing all 50 states and some international regions, to further test the wristbands. “We have now about 5,000 people who have signed up,” says Sarah Vogel, vice president of health programs at EDF.
The bands have already made a difference for roofers in western Oregon, Anderson tells C&EN. A small group of the roofers wore the wristbands while working as part of a pilot project conducted by Anderson and colleagues at Oregon State to determine whether the bands can be worn comfortably by workers who are physically active on the job.
When the researchers analyzed the chemicals in the bands, they discovered that roofers at a training location were exposed to higher levels of harmful PAHs than roofers at a job site. Even though it was just a small demonstration project, the data were compelling, Anderson says. The researchers communicated the information to the roofers’ union, which prompted changes in how the workers set up tar kettles—a source of PAHs—and how the training site is ventilated.
The bands are also helping researchers examine whether there is a link between prenatal exposure to hazardous PAHs and asthma in children. Anderson is collaborating with Julie Herbstman, an epidemiologist at Columbia University, on a project with pregnant women in New York City.
“We put the wristbands on the women in their last trimester,” Anderson says, and later follow their children’s health for asthma and other adverse effects. The pregnant women also provide urine samples and wear conventional backpack polyurethane foam air samplers to monitor their exposure to PAHs.
The project just started last year, so it is too soon to tell if prenatal exposure to PAHs is associated with asthma in children. “You can’t really diagnose asthma until children are two to three years old,” Anderson notes. But the wristband results do seem to correlate well with PAH metabolites found in urine, Anderson says. The wristbands are more comfortable to wear, have lower cost, and are less of a burden to set up and operate than the backpacks.
In other work Anderson and colleagues are conducting, exposure data from silicone wristbands are integrated with location data from a smartphone’s GPS and measurements of lung function taken with a pocket-sized spirometer. The studies aim to associate exposures to toxic PAHs with decreased lung function.
In one study, 10 adults with asthma in Eugene, Ore., each wore a wristband for one day and then wore a second band for one week. The smartphone pinged them three times a day as a reminder to take a lung function measurement with the spirometer, which was connected by Bluetooth to the phone. Afterward, researchers at Pacific Northwest National Laboratory downloaded the data and integrated them with chemical data from the wristbands.
Preliminary results suggest that lung function decreases on days associated with exposure to high levels of PAHs, Anderson says. But in some cases, the effect lags. “What you are exposed to the day before affects your lung function the next day,” she notes.
Silicone wristbands are also helping researchers study the link between flame retardants found in electronics, furniture, and textiles, and adverse health effects, particularly in children. Heather M. Stapleton and colleagues at Duke University have been exploring such associations for more than a decade by measuring chemicals in the air and in house dust. They have also used hand wipes to examine hand-to-mouth exposure and dermal contact. When the researchers learned about the wristbands, they put them to the test to see how they compare with the hand wipes. The results were published last month in Environmental Science & Technology (2016, DOI: 10.1021/acs.est.6b00030).
“We examined how the levels of organophosphate flame retardants on hand wipes and wristbands compared to urinary metabolites of those compounds,” says Stephanie C. Hammel, a graduate student in Stapleton’s group at Duke. The study involved 40 participants who wore the wristbands for five consecutive days and collected urine samples on days one, three, and five. They used hand wipes on day five. Urine samples were pooled across the three days and analyzed for metabolites of four organophosphate flame retardants: tris(1,3-dichloroisopropyl) phosphate (TDCIPP), tris(1-chloro-2-propyl) phosphate (TCIPP), triphenyl phosphate (TPHP), and monosubstituted isopropylated triaryl phosphate (mono-ITP).
“For the compounds where we saw a significant correlation, the wristbands were more highly correlated to the urinary metabolites than the hand wipes,” Hammel says. “We believe that the wristbands work better as a more time-integrated measure of exposure—or at least in this case a period of five days—whereas hand wipes might reflect more recent exposures,” Stapleton adds.
Silicone wristbands absorb organic chemicals from the environment. The bands can be worn at all times and continue to record a person’s chemical exposure even as they sleep, shower, jog, swim, eat, work, pet a dog, or perform any other activity.
Silicone polymers mimic the way human cells absorb organic chemicals because they contain long chainlike structures that create channels similar in size (about 1 nm) to pores created by biological polymers in a human cell membrane. The wristbands take up polycyclic aromatic hydrocarbons, polychlorinated biphenyls, pesticides, flame retardants, fragrances, endocrine-disrupting chemicals, and many other persistent pollutants. The chemicals can be extracted from the bands and analyzed, providing a snapshot of an individual’s chemical exposure over a particular time period.
The wristbands have caught the attention of researchers around the world. Projects are under way in Africa, Asia, Europe, and the U.S. to evaluate the bands for use in monitoring farm and worker-related chemical exposures, Anderson says.
Paul Jepson, director of the Integrated Plant Protection Center at Oregon State, and scientists in Anderson’s group are collaborating to help residents of a rural farming community in Senegal learn about their chemical exposures.
“We’ve been working with the community for about a decade or more with stationary air monitors,” Anderson says. “They had heard about the wristband and asked us if they could wear them as part of a study.”
The Oregon State researchers recruited 35 men and women from the community to each wear a band for five days. Afterward, they were given a second band to wear for another five days. The researchers then analyzed the bands quantitatively for 63 pesticides. Each person’s band had two to 10 pesticides, but no two individuals had the same profile. The amounts of pesticides in the bands within the same individual were consistent from the first week to the second.
Differences such as this in pesticide exposure from one individual to the next are not captured by stationary air monitors, which are often used to calculate exposures, Anderson stresses. On the basis of the information provided by the wristbands, she says it may be important to customize advice to individual farmers about how to reduce their exposure to pesticides.
Although this was a small study, it demonstrates the eagerness of people to use this technology, Anderson says. The researchers observed 100% compliance—participants wore the bands as they were instructed. That’s not been the case with conventional personal-backpack monitors, she says.
Scientists at the U.S. Environmental Protection Agency are excited about the flurry of research under way using silicone wristbands for monitoring everyday exposures to chemicals. EPA and the world’s other regulatory agencies need both exposure and toxicity information to assess the risk of a chemical. But there are many chemicals for which exposure data simply don’t exist.
“If we can identify hundreds or thousands of chemicals in a wristband that we didn’t know people were being exposed to, that is a treasure trove,” says John Wambaugh, a physical scientist with EPA’s Office of Research & Development.
Wambaugh sees one limitation to the wristbands: They provide only a record of a person’s cumulative exposure over time. “You lose some of the notion: Did they get one big exposure at one point, or have they been gradually getting exposure?” he says.
Still, he is excited to examine how the wristbands could complement an ongoing EPA effort to develop computer models that generate high-throughput exposure predictions for thousands of chemicals. Initially, the models were based on data about how chemicals are used, says Kristin Isaacs, an EPA scientist who works with Wambaugh.
“We needed information about what chemicals are in consumer products and at what concentrations,” Isaacs says. So a few years ago, the EPA scientists began collecting data for about 2,000 chemicals that are listed on product material safety data sheets made publicly available by retail giant Walmart. They then merged that information with what they could find in scientific literature about how people use consumer products.
EPA has entered into collaborations to get more data on consumer product use. For example, EPA scientists have access to product-use questionnaires for 50,000 women enrolled in the National Institutes of Health’s Sister Study—a study following the health of women whose sister had breast cancer.
EPA also has an agreement with Nielsen, a company that provides information on what television shows consumers watch and what they buy. The company provided EPA with a year’s worth of data from 60,000 households involved in a project in which people record every product they bring into their homes. “We are analyzing those data to see if we can predict what people are buying based on demographics,” Wambaugh adds.
Although EPA now has more data than ever on chemicals in consumer products, the agency still lacks information about thousands of substances. In a recent test, EPA scientists ground up 100 consumer products, including upholstery, breakfast cereals, and baby toys, and tried to extract every chemical they could.
-Heather Stapleton, Duke University
The researchers found 3,800 different chemicals, and only 200 of those were ones that they already knew were in consumer products, Wambaugh says. The unidentified substances might not raise concerns, however. “Unless you are grinding your baby toy up in a blender and extracting it with dichloromethane, you are not necessarily being exposed,” he says. “But the potential is there.” The wristbands could help EPA identify whether people are actually being exposed to any of the chemicals.
Identifying chemicals in pulverized consumer products, house dust, silicone wristbands, or any other matrix can be challenging if researchers don’t know what they are looking for. Advances in high-resolution mass spectrometry, coupled with more data on how people use various consumer products, however, are facilitating the process.
High-resolution MS has been a boon to exposure science over the past few years, Wambaugh says. “It allows you to try to identify everything in the sample,” he notes. In the past, scientists would analyze a sample, such as blood, urine, or dust, for a specific chemical. That work was predicated on researchers knowing which substance they were looking for.
But even with high-resolution MS, identifying specific chemicals can be tricky. That’s because different molecules can consist of the same atoms combined in disparate arrangements.
EPA scientists recently ran into that situation when trying to identify chemicals in house dust from dozens of homes across the U.S. The researchers detected a compound with the molecular formula C17H19NO3 in 75% of the dust samples. Initially, they thought they had uncovered a huge heroin problem because the molecular formula matches that of morphine, a component of heroin. But the formula also matches piperine, the alkaloid that gives black pepper its pungency.
The EPA scientists then examined information about how each of these two chemicals is used and combined those data with exposure predictions from high-throughput models. “We decided that most of those matches were actually the black pepper ingredient rather than the heroin component,” Wambaugh says, because many more people use black pepper than heroin.
EPA scientists are currently working with university researchers and technology companies to develop methods for screening blood samples for new chemical signatures using nontargeted high-resolution MS. Silicone wristbands could simplify the analysis.
“It is much easier to analyze a wristband for a wide range of chemicals than it is to analyze a blood sample for a wide range of chemicals,” Stapleton says. “The matrix isn’t as complicated.”
Wambaugh sees great potential in people using silicone wristbands to record their chemical exposure. He acknowledges that the bands are an imperfect tool, but he says they have fewer limitations than other methods routinely used to evaluate risk, such as toxicity tests on laboratory rats.
Consumers who want to learn about their everyday exposures to chemicals can try out the wristbands by joining projects such as those conducted by EDF. MyExposome eventually hopes to market the bands directly to the public. But for now, the company only offers them to groups of 20 people or more, at a cost of about $1,000 per person.
Anderson is hoping to get funding for a citizen science project using the wristbands. “You don’t have to wait for a disaster like a Flint” for people to get interested about their chemical exposures and want to wear the band, she says, referring to the lead-in-drinking-water crisis in Flint, Mich. “We have developed a technology that inspires people to think about science and their environment and hopefully even act about their environment.”