For Dick Vethaak, the “aha” moment came when microplastics were discovered in the air. It was 2015, and the ecotoxicologist and professor emeritus at VU Amsterdam had known that the minuscule pieces of plastic could be found in the ocean and in seafood like fish and mussels. But then researchers found microplastics floating in the air on a rooftop of a Paris university.
Humans, it became clear, were not only consuming small amounts of microplastics: They might also be breathing them in. Vethaak’s team began looking for microplastics in the human body — in blood, organs, tissues.
“The results were quite shocking,” he said.
Scientists have found microplastics — or their tinier cousins, nanoplastics — embedded in the human placenta, in blood, in the heart and in the liver and bowels. In one recent study, microplastics were found in every single one of 62 placentas studied; in another, they were found in every artery studied.
But even amid all this research, scientists still don’t have a clear sense of what these materials are doing to the human body. Microplastics could be making us more vulnerable to cancer, heart disease and kidney disease; they could be factors in Alzheimer’s disease or affecting fertility. At the moment, however, scientists just don’t know — and they are in a race against time. And as hundreds of millions of tons of plastics enter the environment every year, it’s a race they might be losing.
“I hate to say it, but we’re still at the beginning,” said Phoebe Stapleton, a professor of pharmacology and toxicology at Rutgers University.
Over many decades, scientists have linked things like DDT, cigarette smoke and air pollution to cancer, heart disease, respiratory problems and much more. Those efforts took years of careful science and analysis that many scientists say pale in comparison with the challenge of decoding microplastics.
“Cigarettes are definitely easier than microplastics,” said Sherri Mason, director of sustainability at Penn State Behrend in Erie, Pa.
Part of the problem is that there is no one type of microplastic. The tiny plastic particles that slough off things like water bottles and takeout containers can be made of polyethylene, or polypropylene, or the mouth-twisting polyethylene terephthalate. They might take the form of tiny spheres, fragments or fibers.
Then there are the chemical additives that help to make plastic flame-retardant, flexible or more easily degradable. In a 2021 study, researchers in Switzerland identified more than 10,000 chemicals used in the manufacture of plastic — of which over 2,400 were potentially “of concern” for human health. Plastics can also carry other chemicals not involved in their production: “hitchhikers” absorbed onto plastics and later potentially released into the human body.
“What you have is an absolute unknown cocktail of chemicals that are on these microplastics,” said Frederick vom Saal, a professor emeritus of biology at the University of Missouri.
The challenge for scientists, then, is to find a connection between microplastics and human health for a dizzying array of substances: potentially for each combination of chemical additives, plastic material, shape, size, and organ of the body.
“To be able to say we have a health impact, we need to have a direct correlation between a product and a health outcome,” Stapleton said. “It’s very narrow, that straight line. And there’s so many different health outcomes there could be, and we’re finding these particles in so many different tissues.”
Researchers are still refining their techniques to even find plastics — particularly nanoplastics — in the body. Scientists have to shine light on the tiny particles and, based on the light that scatters off them, determine what material they are looking at. But identifying the particles is only half the battle — researchers then have to know how many there are, how long they linger in the body, and what chemicals they might carry with them. Only then can they start to try to connect those particles with human diseases.
“This is where it gets so frustrating,” Mason said.
Microplastics are also complicating things that scientists thought they knew. The health risks of air pollution, for example, have been well documented for years, but now, researchers are realizing that microplastics are in air pollution, too. One study from 2019 suggested that people could inhale up to 272 pieces of microplastic in a 24-hour period. “We didn’t even have this on our radar screen,” said Lukas Kenner, a professor of pathology at the Medical University of Vienna.
Scientists do have some evidence that microplastics could make us sick. In lab settings, microplastics added to human cells have been found to trigger cell death, tissue damage and allergic reactions. In a study released last week, researchers in Naples found that heart disease patients with microplastics in their tissues were twice as likely to suffer a heart attack or stroke, or to die within three years. In another study, mice exposed to microplastics exhibited “dementia-like” behavior changes.
Many of the chemicals in plastics also can cause cancer or disrupt hormones. “We know with certainty that there is an extensive human literature on the effects of phthalates, BPA, PCBs and flame retardants,” vom Saal said. “We know enough about some of the really bad players.”
But scientists say that laboratory research on microplastics using mice or human cells isn’t the same as understanding how the tiny pieces of plastic move and accumulate throughout the body. “Probably over the next decade we’ll get a lot of good data,” Mason said. “But we’ll never have all of the answers.”
Kimberly Wise White, vice president of regulatory and scientific affairs at the American Chemistry Council, an industry trade group, said these lab studies “have limitations in their applicability to humans in the real world.”
“Understanding the potential impact of microplastics to human health is especially complicated due to the challenges of confounding variables, such as a person’s diet, behaviors and potential exposures to known environmental stressors,” she added.
Plastics present scientists with an almost impossible task — a quest to understand the health outcomes of thousands of different chemicals, shapes and sizes while they continue to accumulate in the environment. In 1950, the world produced 2 million metric tons of plastic; in 2019, that number had grown to a staggering 460 million tons. And when that plastic breaks down, it splits into tinier and tinier pieces that can slide more easily into the human body.
“It’s almost like a generational accumulation,” Stapleton said. “Forty years ago we didn’t have as much plastic in the environment as we do now. What will that look like 20 years from now?”
Vom Saal says that agencies such as the Food and Drug Administration need to act more quickly, to limit the amount of diverse chemicals going into things like food packaging. The FDA recently announced that companies are voluntarily phasing out the use of “forever chemicals” in food packaging made to be resistant to grease, oil and water, which could take more than 18 months.
“There’s no way for people like me to try to track down thousands and thousands of chemicals in products,” vom Saal said. “You cannot have safety if you have complete ignorance.”
Scientists say that governments should start to put the brakes on plastics — even if their full health consequences aren’t yet known. “I’m a doctor, and we have our principle: ‘Don’t harm anybody,’” Kenner said. “If you just spill plastics everywhere, and you have no idea what you’re doing, you’re going exactly against this principle.”
Mason, the Penn State scientist, said she believes we can now justify starting to slow the flow of plastics into the environment. “I think we have enough data to start to take a precautionary approach,” she said.
But she worries that, as in the case of cigarettes, industry voices and doubters may push back, slowing the pace of regulation and allowing plastics to continue to pollute the environment — and enter human bodies — for years and years. “We need to act before we have all the answers,” she said. “But I’m not sure that we will.”
