How Plastic Gets Inside Us

Plastic is no longer just in the environment. It is entering the human body.

In this episode of The Plastic Age, Dr. Elie explores the two major routes of exposure: what we eat and drink, and what we breathe. Drawing on published human, animal, and laboratory studies, we examine micro- and nanoplastics in bottled water, food containers, household air, human stool, lung tissue, and blood.

But exposure is not the same as absorption. The crucial question is what happens when the smallest particles cross biological barriers and enter circulation.

This episode marks the beginning of a new chapter in the series: following plastic from the world around us into the tissues, organs, and systems of the human body.

Transcript

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Hello, hello, welcome to Beyond Plastic, where science meets consciousness. I'm your host, Dr. Ellie, and here we explore the ideas that shape our health, our lives, and ultimately our humanity. Our first series, The Plastic Age, is a journey through the remarkable story of how plastic transformed our world, entered our bodies, and became one of the defining challenges of our time. In our last episode, we followed plastic after we throw it away. We followed it into landfills, rivers, and oceans. We watched larger objects fragment into microscopic particles. We followed those particles into soil, marine organisms, and even under experimental conditions through the roots and vascular systems of plants. And we ended with a realization that changes the direction of our story. There was never a place called away. The environment in which we released plastic is the same environment from which we build ourselves. The water outside outside of us becomes the water inside us. The air around us enters our lungs thousands of times each day. The soil grows the plants and feeds the animals that eventually become our food. So today we cross a threshold. For the first four episodes we followed plastic across the world. Now we are going to follow it into the human body. And before we ask what plastic may be doing once it gets inside, we need to answer a more fundamental question. How does it get inside us in the first place? There are two routes that matter most. We ingest it and we breathe it. There may also be exposure through the skin, particularly to very small particles, or through hair follicles, damaged skin and certain occupational environments. But compared with ingestion and inhalation, the evidence that intact human skin represents an important pathway for plastic particles themselves remains much less established. So let us begin with something we do every day without thinking about it. Eating and drinking. For years, scientists have reported microplastic particles in seafood, salt, drinking water, and other foods. But determining exactly how many particles people consume has been surprisingly difficult. One widely cited study published in Environmental Science and Technology in 2019 attempted to estimate human intake using the available literature at the time. The researchers calculated that Americans might consume roughly 39,000 to 52,000 microplastic particles per year from food and beverages, with estimates rising when inhalation was included. But there was an enormous limitation in this study. The foods included in the analysis represented only about 15% of caloric intake. And perhaps even more importantly, most analytical methods at the time could not reliably see the smallest particles. So those numbers were never a precise measurement of what enters the average human body. They were an early estimate based upon what the instruments at that time were capable of detecting. And then our instruments got better. So in 2024, researchers published a remarkable study in the proceedings of the National Academy of Sciences. They developed a technique called stimulated Raman scattering microscopy that allowed them to identify plastic particles at sizes far below those detected in most earlier bottled water studies. They examined three commercially available brands of bottled water in the United States. What they found changed the scale of that conversation. On average, approximately 240,000 detectable micro and nanoplastic particles were found in a single liter of bottled water. The concentration varied substantially between samples, but approximately 90% of the detected particles were in the nanoplastic size range. That distinction matters enormously. A microplastic is generally defined as a plastic particle smaller than 5 millimeters. But 5 millimeters is enormous compared with a human cell. The particles that concern biologists most are at the opposite end of this scale. Nanoplastics. Nanoplastics are measured not in millimeters but in nanometers. To put it in perspective, a nanometer is one billionth of a meter. At those dimensions, a plastic particle is no longer merely a tiny version of a bottle or a bag. It begins to enter the scale at which biology itself operates. Cell membranes, proteins, intracellular structures, and potentially biological barriers. The bottled water study did not demonstrate that 240,000 particles enter the bloodstream every time someone drinks a liter of water. That would be an entirely different claim. But it did demonstrate exposure. The particles were present in something humans consume every day. What happens after we swallow them is the next question. And bottled water is only one example. Plastic food containers themselves can shed particles. In 2023, researchers publishing in Environmental Science and Technology examined plastic containers and reusable food pouches under different conditions. They found that heating was particularly important. Under some of their experimental conditions, three minutes of microwave heating released as many as 4.2 million microplastic particles and more than two billion nanoplastic particles from a single square centimeter of plastic surface. These numbers are astonishing to me. Subsequent work has suggested that much of this increased shedding may be driven by the high temperatures reached during heating rather than something unique to microwave radiation itself. That distinction matters because the lesson is not simply that microwaves are dangerous, it is that heat and plastic can be a problematic combination. And again, we have to be scientifically careful. These were laboratory experiments using water and food simulants. They tell us that certain plastic materials can shed enormous numbers of particles under particular conditions. They do not tell us that every heated plastic container releases the same amount or that every released particle is absorbed into the body. Another striking illustration came from infant feeding bottles. Polypropylene is one of the most widely used plastic in the world and is commonly used in baby bottles. In a study published in Nature Food in 2020, researchers tested polypropylene infant feeding bottles during formula preparation. They found that sterilization and exposure to hot water dramatically increased particle release, with some tested bottles releasing as many as 16 million microplastic particles per liter. Think about this paradox. The product, the baby bottle, is perfectly fulfilling the function for which plastic became indispensable. It's lightweight, durable, shadow resistant, it's sterilizable and convenient, and yet the very processes required to use it, which are heating, sterilization, and repeated mechanical contact, can gradually liberate particles from its surface. And heat is particularly important. Surfaces become altered, repeated washing creates also abrasion, ultraviolet light, aging, and mechanical stress gradually change materials that may appear completely intact to the human eye. The container does not need to visibly melt for microscopic pieces to leave it. Researchers demonstrated the same phenomenon rather dramatically with plastic teabags. In a 2019 environmental science and technology experiment, steeping a single plastic teabag at approximately 95 degrees Celsius released billions of micro and nanoparticles into the water. Again, that does not establish toxicity, but it demonstrates something important about exposure. Plastic does not have to become visible debris before it begins interacting with what we consume. Sometimes the fragmentation is occurring directly on the objects sitting in our kitchen, and eventually some of those particles reach the gastrointestinal tract. One of the first direct clues came from a small human study published in Annals of Internal Medicine in 2019. Researchers collected stool samples from eight healthy individuals living in Europe and Asia. Microplastic particles were detected in every participant. Nine different types of plastic were identified. Now, eight people is obviously not enough to tell us the exposure of humanity, but the importance of this study was conceptual. Plastic was not simply in seafood, water, or salt anymore. It had passed through the human digestive system. And this brings us to one of the most important distinctions we will make throughout this entire series. Being exposed to something is not the same as absorbing it. Your gastrointestinal tract is technically continuous with the outside world. That may sound strange, but think about it. When you swallow food, it enters a long muscular tube running from your mouth to the anus. Until something crosses the intestinal wall and enters your tissue or circulation, it remains, biologically speaking, outside the internal environment of your body. That intestinal wall is one of the great biological borders of human life. It must perform an almost impossible task. So it has to be permeable enough to allow water, electrolytes, amino acids, sugars, fats, vitamins, and other nutrients to enter us. But at the same time, it must prevent bacteria, viruses, toxins, foreign particles, and you know any unwanted toxin or material from doing the same thing. It accomplishes this through layers of mucus, of epithelial cells joined by what we call tight junctions, immune cells, digestive secretions, and an enormous community of microorganisms that collectively help maintain the intestinal barrier. So, what happens when plastic arrives? Well, for many of the larger particles, the most likely fate is relatively straightforward. They remain within the lumen of the gastrointestinal tract and eventually leave the body in the stools. However, as particles become progressively smaller, the biology changes. And this is where we must be very precise about the evidence. We do not yet possess experiments in healthy living humans in which scientists administer known doses of nanoplastics and then track exactly what percentage crosses the intestine. You know, such experiments would probably raise obvious ethical and technical problems. Much of our mechanistic understanding, therefore, comes from animal studies and laboratory models of human intestinal cells. In mice, researchers have demonstrated that orally administered micro and nanoplastic particles can move beyond the gastrointestinal tract and appear in other tissues. A frequently cited 2017 experiment exposed mice to 5 and 20 micrometer polystyrene particles. Investigators subsequently reported particle accumulation in tissues, including the liver, kidney, the gut, with biological effects differing according to particle size and exposure. More recent animal experiments using particles in the nanometer range have reinforced the same fundamental principle, which is size matters. Smaller particles can interact with biological tissues in ways that larger particles cannot. There are several possible biological doors through which they enter. Particles may be taken up through specialized immune surveillance structures in the intestine, including the M cells associated with pairs patches. Very small particles may also be internalized by intestinal epithelial cells through processes such as endocytosis, which is the cellular machinery cells use to bring material across their membranes. And when the intestinal barrier is experimentally disrupted, that passage may increase even further. Human intestinal cell cultures have shown that plastic particles can interact with and sometimes enter epithelial cells, while animal studies have reported changes in mucus production, in the tight junction proteins, inflammation, and the gut microbiome under various exposure conditions. But I want to emphasize those words: the animal studies and cell studies. These experiments are essential because they reveal mechanisms. They tell us what is biologically possible. They do not automatically tell us what happens at typical environmental exposures in a healthy human being over decades or over years. That question remains under investigation. And there is another doorway into the body that may be just as important. Your lungs. The average adult moves thousands of liters of air through the lungs every day, with the amount varying according to body size and physical activity. We tend to imagine air as empty space. It isn't. Every breath carries particles. There's dust, pollen, combustion products, even biological materials, there's fibers, and increasingly researchers have demonstrated that some of those airborne particles are plastic. Indoor air is particularly interesting because modern humans spend most of their lives inside environments filled with synthetic materials. Carpets, curtains, furniture, foams, paints, household plastics, and perhaps most importantly clothing. Polyester, nylon, acrylic, and other synthetic textiles continuously release microscopic fibers during manufacture, during washing, drying, and even ordinary wear. We usually associate textile microfibers with washing machine and oceans, but fibers leave clothing while we are wearing it as well. They become part of household dust, they settle onto our floors, furniture, and some remain suspended in the air. A 2024 study examined indoor air from 30 homes and 30 workplaces in Birmingham and the United Kingdom. Using active air sampling, researchers measured an average of approximately 15.6 microplastic particles per cubic meter of air in homes and 13.1 per cubic meter in workplaces. Those numbers should not be treated as universal. Concentrations can vary enormously between different environments, and studies use different sampling techniques and detection limits. But the important point is simpler. Synthetic particles are present in the air people breathe. That's it. And now we have direct human evidence that some make it into the respiratory system. In a 2022 study published in Environmental Science and Technology, investigators examined sputum from 22 patients with various respiratory diseases. Microplastics were detected in every sputum sample examined. Twenty-one different polymer types were identified. The same year, a separate study published in the Science of the Total Environment analyzed human lung tissue obtained during surgery. Thirteen lung tissue samples were examined. Guess what? Microplastics were identified in 11 out of that 13 samples. 39 particles were detected altogether, including polypropylene, polyethylene terphthalate, polymers commonly used in packaging and textiles. Perhaps most surprising was where some of the particles were found. They were not simply in the upper respiratory tract, they were detected deep in the upper, middle, and lower regions of the lung. And the investigators actually found the greatest concentrations in samples from the lower lung. Other human studies have since reported microplastics and respiratory samples, including broncho-alveolar lavage fluid and pleural fluid, further strengthening the evidence that inhalation is a genuine route of exposure. Again, finding a particle in the lung does not tell us that it caused disease, but it tells us something fundamental that our respiratory defenses are not perfect. The human respiratory tract is remarkably good at removing foreign particle and foreign material. The nose filters many larger particles. Mucus traps others. Tiny hair-like structures called cilia continuously move mucus upward through the bronchial tree toward the throat, where material can be swallowed or expelled. Deep within the lungs, macrophages from our immune system, they patrol the alveoli and engulf foreign particles. But particle size once again changes the equation. Larger inhaled fibers may become trapped and cleared, but smaller particles can travel deeper into the respiratory tree, and nanoparticles can approach the dimensions of the extraordinarily thin membrane separating air inside the alveoloia alveoli from blood flowing through the pulmonary capillaries. Consider that delicate thin membrane and boundary for a moment. Every second of your life, oxygen crosses it, carbon dioxide crosses it in the opposite direction, so we can expel it. The barrier has evolved to be extraordinarily thin because gas exchange must occur rapidly. That efficiency may also create a vulnerability. Can very small plastic particles in the nanorange cross it? In experimental animals, the evidence suggests that sufficiently small particles can move beyond the lungs. Studies in mice and rats have demonstrated pulmonary deposition, inflammation, and under some experimental conditions, distribution beyond the respiratory system with effects depending upon particle size, polymer, the dose, and duration of exposure. But once again, translating those exposures directly into everyday human risk would be irresponsible. Experimental animals are often exposed to specific polymers at controlled and sometimes relatively very high concentrations so that scientists can identify biological mechanisms. What these studies establish is biological possibility. They do not yet establish the long-term dose response relationship in the general human population. And then came a discovery that made all of these questions much harder to dismiss. Scientists found plastic associated material in human blood. In 2022, researchers in the Netherlands published a study in Environmental International examining whole blood from 22 healthy adult volunteers using pyrolysis gas chromatography mass spectrometry, they measured several common plastic polymers and particles above the method size threshold. Polyethylene terephthalate, the plastic commonly known as PET, was among the most frequently detected along with polyethylene and polymers of styrene. The mean concentration of the sum of quantifiable plastic polymers was approximately 1.6 microgram per milliliter of blood. Now this was a small study, and measuring tiny quantities of plastic in biological tissue is very, very difficult. Plastic is everywhere in laboratories, in the tubing, the gloves, containers, airborne, sample processing equipment, so the possibility of contamination must be controlled obsessively. Different analytical technologies also measure different things. Some identify individual particles, others, including pyrolysis-based methods, heat a sample and identify the chemical signatures of polymers. Their detection limits differ dramatically. That is why concentrations reported by different studies cannot always be directly compared. This field is still developing and refining its measurement standards, but the blood study posed a biological question that could no longer be avoided. If plastic associated particular material is present in human blood, then some fraction of what we encounter has somehow crossed one of the body's external barriers, the intestine, the lung, or potentially another route of exposure. And once a particle reaches the bloodstream, the geography of the human body changes completely. The bloodstream is the great transportation network of our biology. So a red blood cell leaving your heart can travel through arteries into vessels so narrow that it must deform to pass through them, release oxygen into tissues and return through the veins remarkably quickly. Anything that enters that circulation potentially gains access to an extraordinary vascular network connecting nearly every organ in the body. But here too, size matters. A large plastic fragment does not simply float through capillaries like a bottle traveling down a river. Particles interact with biology almost immediately. In biological fluids, nanoparticles can become coated by protein and lipids, forming what scientists call a protein corona. That coating can change the way a particle behaves and how cells recognize it. Macrophages, one of the immune cells, may engulf it, the liver or spleen may remove some particles from circulation, some may eventually be excreted, others may enter tissues, and the smallest may potentially cross barriers that larger particles cannot. This is where the story becomes far more complicated than simply saying, hey, there's plastic in us. There isn't one plastic. There are thousands of plastic formulations, and there isn't one particle size. There is a continuum from fragments visible to the naked eye down to particles smaller than many viruses. And there isn't one shape. There are fibers, spheres, shards, there are irregular fragments. There isn't either one surface chemistry. The particles weather, they oxidize, they interact with molecules in their surroundings. And plastic themselves contain additives like plasticizers, stabilizers, pigments, flame retardants, and you know countless other chemicals which introduce an entirely separate layer of toxicology that we will explore later, maybe in the series. This is why two plastic particles of equal mass may behave very differently inside biology. And it is why the science of nanoplastics may ultimately prove more important than the science of the larger particles we first learned to measure. For years we studied what our instruments allowed us to see. But nature does not stop existing at the detection limit of our instruments. The smaller the particle becomes, the harder it is to measure, and potentially the more capable it becomes of interacting with cells and biological barriers. That creates one of the great scientific challenges of the plastic age. The particles most capable of moving through biology may also be the particles we have historically been worst at detecting. Which brings us back to the question we started with. How does plastic get inside us? We eat and drink particles present in food and water or released from materials that contact them. We inhale particles and fibers suspended in indoor and outdoor air. Many larger particles are probably cleared or excreted. Our bodies are not passive containers. We have sophisticated defense systems built over hundreds of millions of years of evolution. The mucus, cilia, intestinal barriers, immune cells, liver, kidney, lymphatic systems. But those defenses evolved in a world without the enormous modern burden of synthetic polymer particles, including particles at the nanoscale. And the accumulating evidence tells us that at least some fraction of these materials can move beyond the surfaces where exposure begins. We have detected microplastics in humans tool, in spurum, in lung tissue, and plastic associated material has been measured in blood. As scientists have begun looking more carefully, they have also reported micro and nanoplastics in an expanding list of human tissues, liver, kidney, heart, blood vessels, reproductive tissues, placenta, and even the human brain. Some of those newer measurements, including measurements in the brain, remain the subject of active scientific discussion about analytical methods, contamination control, and exactly how concentrations should be interpreted. That is how a young field of science progresses, the methods improve, findings are challenged, experiments are repeated, and the evidence becomes stronger or sometimes changes. Those findings do not mean that every detected particle is causing the disease. That distinction is essential. Presence is not toxicity, association is not causation. An elaboratory mechanism is not automatically a clinical outcome. But something historically unprecedented has clearly occurred. A family of materials invented little more than a century ago has fragmented into particles small enough to enter the same biological spaces occupied by our own healthy cells. Synthetic polymers created by human industry are now being detected within the biology of the species that invented them. And now we have to ask the question that matters most. What happens next? If these particles reach the bloodstream, what happens when they encounter the lining of an artery? What happens when immune cells recognize them? Can they contribute to inflammation? Can they become incorporated into disease tissue? And could their presence have anything to do with the diseases that physicians like me spent our lives trying to prevent and treat? That is where we are going next. And because I am a cardiologist, the next part of this journey takes us into territory particularly close to me: the blood vessels, the arteries, and the human heart. In our next episode, we are going to examine some of the most consequential human evidence published so far on micro and nanoplastics, including research that found them within human atherosclerotic plaque, and then followed those patients to see what happened to them. For more than a century, plastic transformed the world outside us. Now we are beginning to understand what happens when that world enters the circulation. If this episode changed the way you see the world, share it with someone you care about. Awareness is where transformation begins. Until next time, thank you for listening.