Book Excerpt: The Unknown Risks of Microplastics in Indoor Air

Visual: Amy Bader/Getty Images

Take a look around. If you’re on a bus or train, you’re likely sitting on a plastic seat surrounded by people in synthetic clothing, all of it shedding particles as they move. If you’re on the couch or in bed, you’re sunk into the embrace of microfibers. The carpet underneath you is probably plastic, as is the coating of a hardwood floor. Curtains, blinds, TVs, coasters, picture frames, cables, cups — all of it's either wholly plastic or coated in plastic.

Whereas the takeover of packaging was a conspicuous revolution for plastic bags and bottles, the material's infiltration of every other aspect of our lives has been a quiet coup. While scientists have been untangling the complex dynamics of microplastics in the atmosphere, others have turned their attention to how the omnipresent plastic products around us are bastardizing our indoor air.

The accompanying article is excerpted and adapted from "A Poison Like No Other: How Microplastics Corrupted Our Planet and Our Bodies," by Matt Simon (Island Press, 252 pages).

In 2015, researchers sampled the living rooms of two apartments near Paris, each home to two adults and a child, as well as a university office where three people worked. They only sampled air when people were present in the rooms, both at a height of about 4 feet to gather what the subjects are breathing, and a half inch off the ground to determine the deposition rate of dust. The researchers also took samples from vacuum cleaner bags the occupants had used in the two apartments.

In the apartments, they counted about half a fiber floating in a cubic foot of air; in the office, it was a little under two. Based on the number of particles they caught near the floor, the researchers calculated that up to a thousand fibers are deposited per square foot each day, which matched with the number of fibers they found in the vacuum bags.

Overall, two-thirds of the fibers they tallied were made of natural materials like cotton and wool, while the remaining third were plastic. Polypropylene fibers were particularly prominent, and indeed one of the occupants clued the researchers in on the fact that they’d been sampling a room adorned with a large polypropylene carpet.

Moving over to the West Coast, another team tested indoor and outdoor air on the California State University Channel Islands campus. They found a similar concentration of microfibers suspended in the air indoors and found that microplastic fragments had become airborne as well. The more foot traffic the area had, the higher the microfiber count.

"Fibers from the synthetic clothing of students and staff passing through could easily contribute to microfiber loading of the inside air," the researchers wrote in a paper. They collected more than six times the number of microfibers indoors as they did outdoors: With little airflow inside, the particles suspend in the air, waiting to be breathed in, whereas outdoors plentiful airflow dilutes the particles.

We are all, then, like Pig-Pen from the Peanuts comics, who swirls with a perpetual aura of dust, only we’re depositing our microfibers wherever we go. As you abrade a synthetic fabric — putting it on or walking around in it or sitting on the couch — its fibers "fibrillate," meaning that instead of always breaking neatly in two, fibers also shed clones of themselves, known as fibrils. Under the microscope, the fiber looks like a giant mother surrounded by tiny, curled-up offspring. One experiment found that abrading an ounce of fleece produced 60,000 microfibers, but also 170,000 fibrils that were significantly shorter and thinner than their parents, and therefore more liable to get suspended in the air around us, à la Pig-Pen.

To be clear, that was done with a standard testing machine the textile industry uses on new materials, not on humans walking around a room. To test this directly, another set of scientists recruited four volunteers to move around a space wearing four different kinds of synthetic garments. After counting the microfibers from petri dishes left in the room, they arrived at a stunning figure: Each year, you might shed a billion polyester microfibers into the air just by moving around, which would explain why all these studies find so much microplastic deposited on floors. This is based on those four specific garments, though, so your results may vary — if you wear a lot of cheap, fast fashion, you may be shedding more.

Another study in 2020 confirmed the findings from these indoor air surveys, and on longer timescales to boot. In Shanghai, researchers sampled a dorm room, an office, and a corridor of a lecture building. In the dorm, they counted up to roughly 7,000 particles deposited per square foot of floor each day, 1,200 in the office, and 1,600 in the corridor. Like the Paris study, they found that about a third of the particles were plastic, while the rest were natural fibers like cotton. But because these researchers were sampling continuously for three months, they could chart how deposition rates changed day to day: The particle counts tripled on weekends in the dorm and doubled on weekdays in the office, while the counts in the corridor remained relatively stable over time.

Any plastic product you interact with, be it a trash can or coffee maker or lamp, is jettisoning little bits of itself as it ages.

That tracks with the behavioral patterns of students spending more time at home over the weekend but more time in classrooms and offices during the week. The researchers also futzed with the air conditioning in the dorm and found that having it on at any speed significantly increased the number of microfibers deposited, as vigorous air flow picked up particles that’d settled on furniture. AC units themselves both capture and release additional microplastics: They’re snagging particles when air passes through their filters, sure, but those filters are also made of plastic that sheds fibers, which are then blasted around the room in the cold air.

The flow of human bodies through a room or hallway generates still more airflow, churning up microfibers that had settled on the floor and other surfaces. That's likely why the air in busy rooms consistently tests for more microplastics, says Paris-East Créteil University environmental scientist and chemist Rachid Dris, who did the Paris study. "We notice always that it's the ones where there are more people coming and going, we will have higher concentration than the ones where there isn't lots of movement. And that is probably due to this resuspension effect."

Scientists aren't just finding plenty of textile microfibers in indoor dust — polymers like polypropylene and polyester and polyamide, from clothes and rugs and couches — but polyvinyl microplastics (PVC is polyvinyl chloride) as well.

Neda Sharifi Soltani, an environmental scientist at Macquarie University in Sydney, led a 2021 study of indoor air in Australian households, where she found roughly similar microplastic deposition rates as Dris did in Paris. But in households without carpet, she found that polyvinyl, a polymer used in linoleum and wood flooring finishes, was the dominant plastic microfiber. Polyvinyl was twice as prevalent, in fact, in homes with carpet.

"When I look at the samples under the microscope, it is really, really surprising — lots of fibers we are exposed to every day," says Soltani. (Religiously vacuuming, then, will go a long way in reducing microplastics in your home, whether you have carpets or not. Just be careful when disposing of the dust so you’re not flinging the particles into the air again. Sweeping will be less effective, since that mechanical action resuspends some of the microplastics.)

So then, how many of these particles are we breathing? We’ve got these consistent tallies of microplastics swirling in the air and collecting as dust on the floor. We know how much air a typical human breathes each year, and we know that people in high-income countries spend approximately 90 percent of their time indoors, where microplastic pollution is far worse than outdoors. We’ve also got a good amount of complicating factors, of course, like how many sources of microfibers are in a room and how big the room is and what the airflow's like.

But we’ve got enough data to ballpark it: By Soltani's estimate, we inhale 13,000 microfibers a year. Other scientists’ estimations have quadrupled that figure. Another rather quirky experiment used a mannequin connected to mechanical lungs to calculate that an adult male might inhale up to 272 particles a day, or 100,000 in a year.

But in 2021, Fay Couceiro claimed a much, much higher estimate. She visited a home and gathered airborne microplastics with a pump (sans mannequin) that approximated human inhalation, then used micro-Raman spectroscopy — a particularly sensitive version of the microplastic-counting technique — to detect particles between 1 micrometer and 10 micrometers, the size of a single bacterium. Her tally: We’re inhaling up to 7,000 microplastics a day, or 2.5 million annually.

The average human takes about 20,000 breaths a day, which would mean that with every third breath you inhale a microplastic. Couceiro did this experiment in a bustling home with two children, so there was ample opportunity for particles — especially at the tiny size she was looking for — to resuspend in the air. "I have kids myself — I’ve seen what my kids do," says Couceiro. "They jump up and down on the bed and hit each other with pillows. You can see a lot of particles in the air when you walk into the room. And that was what I wanted to show, that if you were in that kind of environment, you would be breathing in a lot more than perhaps we thought we were."

Physiologically speaking, though, children likely inhale fewer microplastics than adults because they’re smaller. But from a behavioral standpoint, they may be inhaling more: Kids are up to the aforementioned shenanigans, and toddlers spend a lot of time crawling on the floor, where microfibers accumulate — thousands of particles per square foot each day.

Toddlers also gnaw on plastic toys and may ingest particles that way too. Crawling children, plus adults and pets shuffling around, will stir up particles, resuspending them for everyone in the room to breathe.

And the usual caveat applies here: Even with micro-Raman spectroscopy, researchers can only quantify particles down to a certain size, so the smallest are escaping detection. Actual plastic particle counts in indoor air and dust are likely much higher — consider the millions of nanoplastics falling on your head if you’re standing outside in the Alps. Given how difficult and expensive it is to test for nanoplastics, though, that remains an assumption. "But it's a very reasonable one," says Dris.

So unless you work in a factory making synthetic textiles, the most polluted place you frequent may be the room you’re sitting in right now. (Wearing face masks during the Covid-19 pandemic has had contradictory effects here. The synthetic material keeps out both the virus and microplastics swirling in indoor air but also sheds fibers for us to inhale. Don't get me wrong — that is far and away a better outcome than eschewing masks and getting Covid. But disposable masks are now all over the environment: A report released by OceansAsia, a marine conservation organization, estimated that in 2020 alone, 1.5 billion masks may have entered the oceans, and another study found that one of those masks releases 1.5 million microplastics as it decomposes.)

All of it's coming from the towels we wipe our hands with and the clothes we wear and the couches we plop down on and the carpets we tread — just look at the sunlight coming in through a window and you can watch airborne microfibers dance in the beam. (I also find them — as I write this sentence — stuck to the lenses of my glasses.) Any plastic product you interact with, be it a trash can or coffee maker or lamp, is jettisoning little bits of itself as it ages. Rub against lacquered furniture, and off come microplastics. Cutting open a single-use plastic bag produces particles as the material shears, and ripping one open adds extra energy to fling microplastics into the air.

Same goes for breaking the seal on a plastic bottle cap. Whenever you run your clothes dryer, microfibers tear loose and accumulate in the lint trap. When you clean out the filter to keep your house from burning down, you’re holding concentrated microplastic, which flies into the air of your laundry room.

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And into the environment too. In one clever experiment, scientists dried pink polyester fleece blankets in two homes after a fresh snowfall, allowing them to easily scour the area around the dryer vent for fibers of the same color. They took each sample from a square foot of snow at different distances out to 30 feet, both laterally and straight back from the houses, 14 plots total in each yard. They found an average of 400 fibers per plot in one yard and 1,200 in the other. The most fibers accumulated closest to the vents, but the researchers did find that many had made it out to 30 feet.

And they weren't sampling for nanoplastics, which would more easily slip through the lint filter and take to the air. A separate study that tested polyester clothes estimated that your dryer could be emitting 120 million microplastics into the outdoor air every year. And keep in mind that the air coming out the dryer vent is hot, so it rises and boosts the particles into the atmosphere.

So we have yet another source of microfibers into the environment: high heat and friction in a dryer conspiring to brutalize the plastics in our clothes. And as more people around the world ascend into the middle class, more washers and dryers are coming off production lines. Which is not to say line-drying is any better, or worse, than using a machine — it's just that no one has yet quantified the microfibers released. A clothesline has no filter, while a dryer's lint filter does a so-so job of snagging microfibers to keep them out of outdoor air, though obviously many are slipping through. And when you remove that accumulated lint and throw it in the trash, that's no guarantee the fibers won't take to the air at some point in the waste management process.

So, to add it all up: How many total microplastics might we be consuming a year by eating, drinking, and breathing? Every human will differ, and there's no way of knowing exactly how many particles go into your body. But according to a 2021 study, which aggregated all kinds of data about known human exposure to microplastics, the median intake for a child is 553 particles per day, or 202,000 per year. For adults, it's 883 per day, or 322,000 per year.

They were only able to account for a fifth of food consumption, given the lack of data on so many products. And once again we have a discrepancy here, because stool samples suggest we excrete up to 1.5 million particles a year, and if Fay Couceiro is correct, we may be inhaling millions more.

Whatever the number ends up being, it's going to be big, and day by day it gets bigger as the production of plastic accelerates. Scientists aren't waiting around for a definitive answer — they are now racing to understand what microplastics are doing to our bodies.

Matt Simon is a science journalist at Wired magazine, where he covers the environment, biology, and robotics. He's the author of two previous books, "Plight of the Living Dead: What Real-Life Zombies Reveal About Our World — and Ourselves" and "The Wasp That Brainwashed the Caterpillar: Evolution's Most Unbelievable Solutions to Life's Biggest Problems." He enjoys long walks on the beach and trying not to think about all the microplastics there.