Canadian study offers new clues about how digestive systems handle microplastics

As plastic pollution continues to spread across the planet due to a quarter of the over 450 million tons produced plastic ending up in the environment, eventually to turn into microplastic, scientists have unveiled a breakthrough technique that offers one of the clearest views yet of what happens to these microscopic plastic particles after they are swallowed.

Researchers from the University of Guelph in Canada have developed a new imaging method that allows scientists to locate microplastics inside an organism without cutting it open, which, according to an article published on an American news platform for engineers, has been a longstanding obstacle in understanding how these tiny particles move through living bodies.

The technique has already produced a surprising finding. Rather than readily passing through the gut wall into surrounding tissues, microplastics remained confined within the digestive tract of earthworms, suggesting the gut may provide a stronger protective barrier than previously thought.

Each year, humanity produces hundreds of millions of tons of plastic, with nearly one-quarter eventually escaping into the environment. Over time, much of that waste breaks down into microscopic fragments that are now found in soil, rivers, oceans, food and drinking water, making exposure almost unavoidable for wildlife and humans alike.

One of the biggest unanswered questions has been whether these tiny plastic particles simply pass through the digestive system before being excreted or whether they can penetrate the intestinal lining and accumulate in other organs.

Studying that process has proved exceptionally difficult because the particles capable of crossing biological barriers are extremely small—less than 83 micrometres** across, roughly 10 times smaller than the head of a sewing pin.

Until now, researchers have largely relied on dissecting animal tissues to search for the particles. However, because microplastics are already widespread in laboratories and the surrounding environment, dissected samples can easily become contaminated, making it difficult to determine whether plastics found inside tissues were genuinely present or introduced during analysis.

The Canadian team overcame this challenge by using microcomputed tomography, a high-resolution three-dimensional imaging technique capable of revealing microplastics inside intact organisms.

Unlike conventional X-rays, the technology produces detailed 3D images in which microplastics appear as bright particles against darker surrounding tissues, allowing researchers to precisely map their location without dissection.

The researchers tested the technique on earthworms, which are considered ideal study organisms because they constantly ingest soil—where microplastics are increasingly accumulating—and play a vital role in maintaining healthy ecosystems.

Their observations showed that microplastic particles measuring between **5 and 53 micrometres** remained inside the worms' digestive tract rather than crossing into other tissues.

While the findings are limited to earthworms, the researchers say they offer valuable insight into how digestive systems may act as natural barriers against indigestible particles.

"While we need to be careful about extrapolating our research on earthworms to other species, our study does suggest we may need to give our digestive tract more credit for its ability to act as a barrier to components of our food that cannot be digested," the researchers note.

Beyond its biological findings, the new imaging technique could help scientists better investigate how microplastics behave across a wide range of animals without the contamination risks associated with traditional dissection methods, potentially advancing research into one of the world's fastest-growing forms of pollution.

By Nazrin Sadigova