Discovery of microplastics in humans raises tough questions about health implications | To research

Microplastics have been detected in the lungs of living people for the first time. The lung tissue samples were taken from 11 people who had surgery at a hospital in Hull, UK.

The finding adds to concerns about microplastic contaminants in the environment, but it was no surprise to researchers in the field. In 2021, Brazilian pathologists found polymeric particles and fibers in the lung tissue of 13 out of 20 adults undergoing autopsy in São Paulo. And in February, researchers in the Netherlands reported plastic pollutants in the blood of healthy volunteers.

Microplastics form from the fragmentation and disintegration of plastics in furniture, packaging, clothing, disposable items, electronics, etc. Usually defined as particles smaller than 5mm, these can be inhaled and potentially harmful. The most frequently detected polymers in the Brazilian study were polyethylene (PE) and polypropylene (PP).

In 11 of the 13 UK patients, microparticles – 39 in total – were detected by infrared spectroscopy. Twelve types of polymers have been recorded, with PP, polyethylene terephthalate (PET) and resin being the most abundant.

“We identified microplastics in all regions of the lungs,” says Laura Sadofsky, a respiratory biologist at Hull York Medical School at the University of Hull, who led the study. “We expected to find microparticles in the lung tissue, but not the larger sizes further down the airways.”

Airborne polymers

That expectation stemmed from studies she and others had conducted that showed microparticles were in the air we breathe — in quantities that at first surprised Sadofsky. In 2021, his team found an average of 1400 microparticles per day, mostly PET, in the air of 20 households. In a later study outdoors, the researchers detected an average of more than 3,000 microparticles per day – especially PE and nylon – for every square meter of soil sampled. The team concluded that people were exposed to significantly higher concentrations inside their homes than outside.

Textiles are a source of household plastic microparticles. Each garment is valued to release thousands of fibers per wash. Airborne microplastics are so ubiquitous that they contaminate samples even in controlled laboratory environments. “We struggle so much in the lab to keep things clean and free of microplastics because they float around and fall off people,” says Stephanie Wrightmicroplastics researcher at Imperial College London, UK.

But the crucial questions of whether the type and amount of particles present in human lung tissue can cause damage remain unanswered. Wright notes that decades of air pollution research indicate that certain size fractions are important, namely PM2.5 and PMten (defined as particles with a diameter of 2.5 and 10 µm, respectively). Exposure to these pollutants is related to premature death.

There is also connections between the inhalation of synthetic fibers in textile workers and lung diseases. “About 30% of people who work in the nylon flocking industry have respiratory problems, lung disease,” says immunologist Barbro Melgert at the University of Groningen, the Netherlands.

In the Dutch study, blood samples taken from 22 healthy volunteers revealed an average of 1.6 µg of plastic particles per milliliter of blood. It is possible that the particles moved into the bloodstream from the gut. In Wright’s opinion, the average concentration is surprisingly high given that animal studies suggest that only 0.4% of ingested particles can cross the gut-blood barrier.

But Marja Lamoree at the Vrije University of Amsterdam in the Netherlands, who led the study, advises caution when interpreting the results, as these are the first measurements of a small number of individuals. “This can be interpreted as an estimate of what might be expected in future studies and as a useful starting point,” she says.

Pioneering studies

For now, the field is full of questions, not answers. “We don’t know if microplastics cause problems in our lungs,” Melgert says. In recent experiences, which have not yet been peer-reviewed, she added nylon and polyester fibers to lung organoids and saw signs that they had an impact on stem cell development pulmonary. Melgert suggests that developing lungs or healing airways might be more affected.

Early last year, a group in Italy detected the first evidence microplastics in human placentas using Raman spectroscopy. About ten fragments of microplastics, including three in pigmented PP, were found in four out of six placentas.

Since, Phoebe Stapleton and his colleagues at Rutgers University in New Jersey, USA, inserted polystyrene particles in the lungs of pregnant rats. 24 hours later, the particles had entered the animals’ placentas, lungs, hearts and spleens, as well as the livers, lungs, kidneys and brains of fetuses. Although the dose of infused particles is high, Stapleton thinks people are no less sensitive.

Studies show that as the size of microplastic particles decreases, their relative abundance in the environment increases, meaning there are many more tiny particles around. And these are viewed with concern. “The smaller the particle, the more likely it is to bypass epithelial barriers or interact with cells,” says Wright. “But they are obviously also the hardest to detect.”

Hull’s study had a size limit of 3 μm, close to the detection limit for infrared spectroscopy. “The numbers in most studies are greater than 10 microns, simply because the analytical method used didn’t allow for anything smaller,” says Wright. No studies have looked at particles in the nanometer range

Once the particles get deep into the lungs, they are difficult to clear. They can be engulfed by immune cells, but not consumed like microbes are. ‘For microplastics, I think they will never be digested [by cells] because we just don’t have the enzymes or the machinery to get rid of it,” Melgert says. This means that they can accumulate over time.

An added complication is that the particles contain plasticizers and other compounds, including known endocrine disruptors. They may also be coated with bacteria, viruses, metals, or organic matter, which could add to the toxicity. “These particles had a life before entering the lungs and may have absorbed different chemicals on their surface,” says Stapleton.

Melgert isn’t surprised by reports of microplastics in human tissue. “On a sunny day, look out the window and you’ll see the amount of dust in the air. There must be microplastics entering your lungs.

She suggests keeping dust at home to a minimum, vacuuming well, and letting in fresh air. In the meantime, she plans many more studies on microplastics and their impact on people.

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