Plastic pollution is everywhere - including where you would least expect it, especially when it's in tiny particle form. Today, scientists are working to measure the consequences of this contamination.
There's the pollution you can see - on the beach, on the roadside and in open-air landfills. And then there's the pollution you can't - on the peak of Mount Everest, deep inside the Mariana Trench, in clouds, in buildings, and in our water supply, food, blood and brain. Just about everything on the planet has been contaminated with plastic, from our ecosystems to our very own bodies. Every time scientists look for it, they find it.
The problem with plastic waste is that the particles get smaller and smaller without ever really disappearing. They're formed from the 52 million metric tons of global plastic waste emitted annually, as well as from the wear and tear of everyday items such as tires and clothing, not to mention personal care products. These particles come in two main types: microplastic, a broad category of particles measuring between 5 mm and 1 micron (a strand of human hair has a diameter of 100 microns); and nanoplastic, or particles measuring less than 1 micron. "Nanoplastic is impossible to get rid of, even if you have the best water purification systems in the world, like those in Europe," says Florian Breider, the head of EPFL's Central Environmental Laboratory. "For instance, a water purification plant can become overwhelmed during very heavy rainfall, so some of the rainwater is diverted to a reservoir, kind of like a bypass, which discharges the water directly into the environment."
This means we unknowingly ingest nanoplastic on a regular basis: when we bite into a piece of lettuce, drink a glass of water or - further downstream in the process - sip coffee from a plastic-lined paper cup or eat lasagna that was reheated in a plastic container. We're also exposed to nanoplastic in the air we breathe. Here, particle size is a determining factor: "Nanoplastic can penetrate deep within the bodies of some organisms, passing through the cell walls and lodging inside the muscles," says Breider. "Microplastic, on the other hand, tends to accumulate in the digestive or respiratory tract."
Just how dangerous is that? "It's really hard to measure how plastic contamination affects ecosystems and humans because the equation is extremely complicated," says Breider. "There are many different kinds of polymers, and they're sometimes mixed together. What's more, manufacturers often throw in additives. If you combine that with the myriad metabolites and byproducts from polymer degradation and transformation, then you've got thousands of different variables and possible combinations."
Nanoplastic is impossible to get rid of, even if you have the best water purification systems in the world, like those in Europe.
A formidable challenge
Plastic pollution is essentially just another form of chemical pollution. In addition to the polymers themselves, plastic contains various additives that give it a particular color or texture, prevent it from aging or make it more flexible - that's what phthalates do, for example. "Once these chemicals are released into the environment or a living organism, they tend to spread well beyond the plastic," says Breider. "And we know that some phthalates are endocrine disruptors, for example. The antioxidants that protect plastic from UV-induced degradation aren't necessarily toxic themselves, but when they're metabolized, the resulting metabolites could be."
Compounding the problem is the fact that product labeling is often patchy and loosely regulated. "Sometimes the information given about a product is inaccurate and all the additives aren't listed," says Breider. "That makes things hard for scientists because it puts the burden on us to identify them. In short, I'd say plastic pollution is a formidable challenge: it comes from many different sources and from products used in many different ways, there's a wide range of polymers along with an array of additives and byproducts, and we don't really know how the chemicals behave in the environment or what their lifespan is."
Targeted, limited studies
All this limits the extent of research that can be done. "We can only run highly targeted studies in well-defined contexts, with results that aren't always clear and that can't be applied more broadly," says Breider. "And we often can't establish direct cause and effect because we're exposed to so many other things too." Research on humans is even more complicated because scientists have fewer samples to work with and the analytical methods used on other organisms, such as fish, can't be employed on people. "In many cases, we're also missing baseline data or a reference point," says Breider. "That's why it's so important to develop technology that lets us take these measurements as well as strategies for carrying out studies in an ethical way."
Despite these headwinds, scientists are forging ahead. For instance, Breider's research group is studying the absorption of plastic through the respiratory tract. They've teamed up with the Swiss Centre for Applied Human Toxicology to investigate how plastic and additives that end up in the lungs are metabolized and affect lung tissue. "This is research we can conduct in vitro, which means we can avoid a lot of issues related to ethics and finding study participants."
Tire tread is a classic example
In 2020, a study published in Science made the headlines: tire-tread particles were found to induce acute mortality in Coho salmon in the US Pacific Northwest. A chemical called 6PPD-quinone, which is an oxidation product of an additive that protects tire rubber from the ozone in city air, turned out to be toxic to some living organisms. "The particles released by tire wear - long overlooked by researchers - account for 30% of the microplastic in Lake Geneva," says Breider, whose research group has carried out several studies on this additive. This percentage is consistent with the levels found globally.
Tire-tread particles, unlike those from packaging, are released directly into the environment, and in significant amounts. Scientists estimate that between 800 grams and 1 kilogram of tire particles are emitted per person per year in Switzerland. "These particles are found in cities, of course, but unfortunately also in high-altitude lakes far from any roads," says Breider. "They're carried by the wind and rainstorms."
His research group, in association with colleagues from the University of Geneva, has analyzed the tire-wear residue contained in Lake Geneva sediment. They collected samples from the LéXPLORE floating research platform run jointly by EPFL, the University of Lausanne, the University of Geneva, Switzerland's Eawag research institute and the CARRTEL research center. "We extracted data on registered vehicles in Switzerland since 1900, and - using past nuclear testing and the Chernobyl disaster as time markers - were able to measure changes in the sediment concentration of new tire ingredients over time," says Breider. "We found that these changes were significantly correlated with the number of vehicles on the road."
Pollution from tire wear is a critical issue. Humans are heavily exposed to these chemicals, and we don't fully know how they affect our health. In the wake of the Science study, the Swiss Federal Council issued its own report in 2023, concluding that a better understanding is needed of the risks to the environment and human health and that solutions must be found to limit the impact of tire-tread particles. Manufacturers are seeking alternatives but haven't yet found anything suitable. "The trick is to change the composition of tires without altering their properties," says Breider. "Tire companies also have to ensure that whatever they come up with doesn't actually make the situation worse."
"Tire pollution is a particularly interesting problem," he adds. "In developed countries, the pollution stems mainly from particle emissions during use. But used tires are often sent to Africa, where they're used initially on cars, and when they're no longer suitable for the road, turned into sandals or other handmade items. Some old tires also get dumped in open-air landfills. In Vietnam, old tires from two-wheeled vehicles are used as a substitute for concrete substrate in oyster farms. We need to think broadly about how this kind of plastic is used and recycled."
