Microplastics have not yet earned their bad reputation
In 2018 a team of Austrian scientists discovered tiny fragments of plastic, known as microplastics, in stool samples from people in several countries. Since then, such particles have been found in human blood as well as organs, including the lungs, liver, kidneys, heart and even the brain. They have also turned up in the placenta and breast milk. And, according to some recent studies, the amount making its way into the body is increasing.
A barrage of papers tentatively suggests these foreign bodies may play a role in a wide range of diseases. A study of about 250 patients in America, published in 2024 in the New England Journal of Medicine, linked the presence of microplastics in arterial plaque with a higher risk of heart attack and stroke. A small study published in Nature Medicine in February reported that the brains of people with dementia had much higher amounts of microplastics than the brains of those without. In studies conducted with human tissues in the lab, microplastics have been found to trigger inflammation (the basis for many chronic diseases), fuel the growth of cancer and reduce the efficacy of antibiotics.
These findings have raised alarm bells. But the true impact of microplastics on human health remains hard to determine. For one thing, the field is so new that few of the headline-grabbing studies have been replicated. Questions of contamination and accuracy also loom large: the brain study in Nature Medicine, for example, suggests that as much as 7 grams of plastics may accumulate in the brain, roughly the weight of a disposable plastic spoon. Others find that figure unrealistically high.
More pressing, most research thus far on the health effects of microplastics has been conducted on human cells in Petri dishes or in animal models such as mice, rather than on groups of people. That is, in large part, because researchers have lacked the tools to conduct the large-scale population studies and randomised trials necessary to establish any definitive causal effects. This is now starting to change.
Containing multitudes
Part of the problem has been the mind-boggling non-uniformity of microplastic particles. Some come from disintegrating rubbish; others result from the wear and tear of everyday products like synthetic textiles, car tyres, paints, toys, utensils and packaging. Their composition is no less varied. A wide range of polymers, such as nylon and polypropylene, are used to make plastics, along with over 10,000 chemical additives (including at least 2,400 of potential health concern).
What is more, plastics do not remain factory-fresh forever. As they circulate in the environment, microplastics pick up contaminants such as heavy metals, as well as viruses, bacteria and moulds (collectively known as their “corona”). And they come in all sorts of shapes—from fibres and spheres to needles and shards—as well as carrying different electrical charges.
All this matters because microplastic particles with different properties can have dramatically different effects. Several research groups have found that chemical and biological contaminants in the corona affect how the particles interact with cells involved in inflammation. Research on other nanoparticles, including those of carbon and silver, has shown that jagged or elongated shapes are more likely to damage cells, says Virissa Lenters of Vrije University, in Amsterdam. And the strength of the electrical charge that a given microplastic particle possesses can change how easily it can enter a given cell.
Thus far, however, most lab studies have used a single, sterile type of microplastic particle: the smooth polystyrene beads that are the only ones available for laboratories to buy. This has led some research groups to develop their own microplastic particles with different charges, compositions, shapes and sizes, for use in studies. These are then exposed to processes that simulate natural wear and tear (one group, for example, has aged its microplastic fragments by dousing them in water from the Rhone river) so that they more closely resemble microplastics found in the world outside the lab.
The process is painstaking. Lukas Kenner from the Medical University of Vienna says that it has taken his colleagues around two years to work out how to make particles of PET (polyethylene terephthalate), a plastic found in everyday products such as disposable water bottles, that suitably replicate those found in the environment. The particles are then given fluorescent labels so they can be tracked inside tissue. Such work is a necessary step towards achieving the replicable conditions required in experiments, says Dr Kenner. “We can’t just take particles from the street.”
Another problem facing researchers is working out how high a dose of microplastics to administer to their subjects. Up until now, says Juliette Legler at Utrecht University, the doses associated with negative effects in cell cultures and animal studies have been far higher than the amounts likely to be found in living human bodies.
But knowing what amount is realistic remains elusive. That is because scientists lack tools to both accurately and speedily measure the quantity of microplastics found in human bodies. The usual method, which involves inspecting biological tissue with a specialised microscope, is not sensitive enough to detect the smallest microplastics. For more sensitivity, scientists turn to chemical detection, which destroys the sample (meaning that information about the cell types that contain the particles gets lost) and is prone to confusing plastics with biological molecules such as lipids. Those methods also require samples to be elaborately prepared prior to testing, which slows down the analysis.
The expensive and laborious nature of measurement means that studies on specific health consequences, such as, for example, the correlation between microplastics in stool and irritable bowel syndrome, have been limited to a few dozen people. For reliable conclusions to be reached, that number would need to be far higher.
Promising solutions to these measurement hurdles are coming along at a fast clip. Dr Kenner’s group has come up with a new, laser-based method to determine the composition of microplastics without damaging their host tissue. This allows the researchers to better assess the biological effect of the microplastics, as well as allowing the tissue samples to be reused in future research. It is a “game-changer”, he says, enabling work that would have been unthinkable just a year ago.
A group at the University of Applied Sciences and Arts of Western Switzerland, for their part, have adapted existing spectroscopy software with machine-learning techniques to detect smaller and more complex particles, and to do so automatically—which makes analysis faster, more accurate and more thorough, capturing 15% more particles. Others, such as Douglas Walker and his team at Emory University, are seeking to minimise the chemical misidentification of plastics.
Wrapping up
Such advancements mean that larger and more comprehensive studies are finally becoming possible. One group of researchers is using these new methods to study 800 mother-and-child pairs in Belgium and Spain, looking for links between microplastics in placenta, urine and blood and health outcomes such as premature birth and early child development.
In another study, which involves 100 Dutch women, researchers are tracking microplastics in household dust and in participants’ urine. They are trying to understand how various sources of the particles compare and whether certain lifestyle habits, such as vacuuming more often, make a difference. Austrian scientists are looking at the same issue with a “plastic fasting” study (in which volunteers reduce their use of plastics for a week) to find out how it changes the amount of microplastics in their blood and stool.
All being well, results from these studies should start coming in by the end of 2025. But many more such studies will be needed to reach definitive conclusions about what microplastics do to human bodies. With each generation exposed to ever greater amounts from the day they are born, says Dr Legler, convincing answers are urgently needed.