Martin Wagner was annoyed that his colleagues were always talking about microplastics in the ocean. It was 2010 and the Great Pacific Garbage Patch had been headline news. Here was this massive gyre, formed by circular ocean currents in the Pacific Ocean, reportedly brimming with plastic particles, killing sea turtles and seagulls. Wagner, a professor of biology at the Norwegian University of Science and Technology, whose lab focuses on the impact of plastics on human and ecosystem health, felt like scientists were pointing to marine systems as the main repository of these tiny plastic particles. But wouldn’t it make sense for them to exist in other systems as well? “It was like, wait a second, it must be in freshwater too,” Wagner says today. He set out to search for microplastics elsewhere.
As we know, plastic is omnipresent. Plastic is cheap and easy to make and mold. We use this miracle polymer to store and transport food, make our clothes and cosmetics, cars and boats, detergents and fertilizers, transfuse our blood and floss our teeth. But it also takes between 20 to 500 years to break down a single piece of plastic in a landfill. Those bagged salad containers will be with us for generations to come.
When it comes to the environment, plastic is a scourge. We’ve seen the images of marine animals entangled in fishing lines and six-pack holders, beaches piled with plastic items like shopping bags, water bottles, and old toothbrushes. But it’s microplastics that increasingly have been the focus of environmentalists and scientists. Microplastics are plastic debris less than five millimeters long. They enter the environment from the natural decomposition of plastic or by being shed by the countless products that contain plastic chemicals.
Microplastics have been found in places as remote as Antarctica1 and the summit of Mount Everest,2 in fish guts, and in honeybees.3 Researchers recently found tiny plastic particles in the lungs of surgical patients, the blood of donors, and the placentas of unborn babies.4 We can breathe in polyethylene from our T-shirts because wastewater plants can’t fully filter them out. Microplastics are in our food—carried into the food chain by water or plankton—and in our toothpaste and dental floss.
When it comes to eating microplastics, scientists have documented plastic particles in about 40 percent of the human diet, including beer, honey, salt, and seafood. A graduate student in the United Kingdom collected mussels from different parts of the country and predicted that consumers ingest 70 microplastic particles for each 100 grams of mussels.5 Meanwhile, another study showed beer samples had about 28 particles per serving.6 People may be eating as much as a credit card’s worth of plastic each week7—or more, because scientists still haven’t figured out how to reliably determine microplastic levels in meat, vegetables, grains, or packaged foods, which means we still don’t know how much plastic we actually eat.
Yet despite all the new knowledge about microplastics and the even tinier nanoplastics, smaller than a millimeter, that enter the human body through ingestion or inhalation—available in a dizzying array of sizes, colors, and chemical makeups—there remains a gaping question. What exactly does it mean for human health?
We do know for certain that, in principle, plastics in our system can be bad for us. One of the earliest bodies of research on the impact of plastic particles on humans examined the so-called “flock worker’s lung,” a condition developed by employees of a Rhode Island plant that processed nylon flock, short fibers cut from cables of synthetic monofilaments to produce velvet-like materials used in upholstery, blankets, and clothing.8 The factory had almost no ventilation, and epidemiologists found that workers there had levels of lung cancer that were three times higher than among the people in the area who didn’t work in the factory. At first, they suspected the workers were inhaling chemicals, but when they studied the lungs of some of the workers who had died, they found nylon fibers lodged in the lung tissue. “This was significant,” says Scott Coffin, a research scientist who leads California’s development of regulations for microplastics in drinking water. “It was the late 1990s, and this was the first case that showed microplastics causing cancer in humans.”
Scientists have documented plastic particles in about 40 percent of the human diet.
The finding was buried in scientific literature for 15 years, Coffin says, mostly because of terminology: The reports used the term “nylon flocking” instead of “microplastics.” Scientists have worked to clarify that kind of distinction. For example, researchers quantified how many microfibers we set loose when we wash a fleece jacket.9 A 2022 study10 led by the City University of Hong Kong found that a clothes dryer releases up to 561,810 microfibers during 15 minutes of use, and Coffin says it’s likely that the burst of fine particle pollution11 released when we clean the lint from the dryer vent is many times higher than the U.S. Environmental Protection Act’s recommendations for occupational exposure to inhaling particles. “You might notice there’s a small cloud of dust. That’s trillions of nano sized plastic fibers you’re inhaling,” says Coffin. “It’s only a momentary exposure, but no one warns you about that.”
Even some of the most essential ways that we protect our health can expose us to microplastics. Wearing masks is universally recognized as the most effective protection against contracting and disseminating Covid-19, but a study by Chinese scientists found that nearly all types of masks also increased the intake of microplastic fibers.12 When they did experiments using simulated breathing and seven masks, all except for the KN-95 produced more fibers than they filtered out.
The good news, scientists say, is that the majority of microplastics don’t stick around—we exhale or excrete them. But Coffin and other researchers admit that they have no idea how much exactly that “majority” is—intestinal absorption is estimated to be around 0.3 percent, he says, though he also says that’s probably an underestimate.13 And some debris—especially long and skinny fibers—do end up in the deepest part of the lungs.
In March, 2022, a lab in the Netherlands published research that examined lung tissue from eight volunteers and found plastic fibers in 80 percent of them.14 Jeanette Rotchell, an aquatic toxicologist at the University of Hull who was an author of the study, says she was less surprised than her land-oriented colleagues to find plastic in those hard-to-reach places. That’s because, with a background in marine ecology, she had seen the inflammation in fish gills and guts from microplastics. The biggest particles were about the length of a sesame seed, but long and thin, and they were wedged deep in the deepest part of the lungs. Still, Rotchell cautions about making a leap from animal to human studies. “You can see inflammation effects in mussels and fish,” she says. “But I think for humans, we don’t have enough data yet with environmentally relevant levels and types of plastics.”
Coffin, who is trying to figure out how much microplastics humans are exposed to, and what that means, says we still don’t fully understand how the size, shape, color, and chemical makeup of plastics influences their health impact. Most plastics appear to have a similar effect on the human body, says Coffin, except for polyurethane, a flexible foam commonly found in furniture, bedding, and carpets, which may be twice as toxic as other types, though few studies have compared polymer toxicities in mammals.
Scientists do know some of what happens when these particles enter the body, says Wagner. The body produces an inflammatory response, which happens when damaged cells release chemicals to isolate the foreign substance. This response can trigger oxidative stress. “Some papers suggest that actually, nanoplastics could interfere with the energy production and mitochondria and that might induce oxidative stress,” which essentially means that the body’s ability to repair damage in itself is thrown out of whack, he says. “But we’re really in the dark about how that happens.”
Particles that end up in our bloodstream or tissue first need to cross a physical barrier in the gut or in the lung, Wagner says. Animal studies show that if particles are small enough, they can pass through tissue and end up in the bloodstream or in other organs directly.15 “And then what happens after is not very well known,” says Wagner. “Does it get excreted? Is there some way of getting rid of those particles? There’s really not a lot of experimental work being done on that.”
Microplastics can also carry micropollutants into the body,16 says Andrey Rubin, a doctoral student at Tel Aviv University’s Porter School for Environmental Studies. Pesticides, drugs, hormones, even heavy metals can interact with and get absorbed by microplastics. Chemicals added to plastics really drive toxicity, and household exposures can come from unexpected places, Coffin says. “If you are eating microplastics that are shed from food safe materials, those chemicals are less likely to cause harm than inhaling microplastics from something that is never supposed to enter the human body, like fibers from rugs or furniture.” Additionally, a study published this April showed how waterborne germs can catch a ride on plastic particles and travel through the environment to find new hosts to sicken.17
As Wagner points out, studies on animals have shown microplastics can disrupt endocrine functions,18 or hormonal systems, which regulate biological processes such as body growth, energy production, and reproduction. Many chemicals are used to make plastics, and one, bisphenol A, found in plastic containers and bottles, is a notable endocrine disruptor. In lab studies, scientists have found that bisphenol A mimics the hormone estrogen and can lead to damage in sperm development.19 Further research has shown that microplastics, and not just those with bisphenol A, can cause damage to the testes and lead to the production of deformed sperm cells that have a harder time reaching eggs.20 Microplastics can also have effects on female reproductive health, such as inflammation in the ovaries and lower-quality egg cells. “I’m seeing a very consistent picture that there’s actually some reproductive health effects that nanoplastics and microplastics can induce,” says Wagner.
What amount of microplastics disrupt human reproduction? Too early to say. “We know how many [bits of plastic] it takes to impact the reproduction of rodents, but we can’t compare exposure numbers to people,” Coffin says, in part because of the difference in body size proportionate to the plastic particles and the ability of rodents to reproduce easily. Coffin expects more solid data within the next three years.
So, can regulators advise an allowable daily dose of microplastics? “We will eventually have a recommended level,” Coffin says. “It would be based on an idea of a threshold,” which would draw a clear line between the safe and unsafe amounts of debris. In the past few years, driven by public concern, the amount of research papers on microplastics has been growing exponentially. “But even as we have produced a lot of research as a community,” Wagner says, “I think the knowledge really hasn’t increased at that kind of rate.”
The rate that has increased is plastics production: 367 million metric tons of plastics were manufactured in 2020. That amount is predicted to triple by 2050.
Katharine Gammon is a freelance science writer based in Santa Monica, California who writes about environment, science, and parenting. You can find her at the beach or on twitter @kategammon.
Lead art: Orakunya / Shutterstock
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