Microplastics pass through earthworms without accumulating in body tissues, study shows

As much as 40 million tonnes of microplastics are released into the environment globally every year. These tiny pieces of plastic come from larger plastic items that break down or are shed by products such as clothing, paints, and cosmetics.

Despite how widespread this waste has become, scientists still don’t fully understand whether the particles can move from the digestive system into other body tissues, where they could cause long-term harm.

To explore that question, researchers used the Canadian Light Source (CLS) at the University of Saskatchewan to track how microplastics move through earthworms. Earthworms play a key role in improving soil structure and are considered a good indicator of what happens when living organisms ingest tiny plastic particles.

The research team, from the University of Guelph, put earthworms in soil containing far more plastic particles than they would normally be exposed to in the environment. The microplastics were made of polyethylene, one of the world’s most common plastics, in sizes ranging from five to 20 microns—smaller than a human red blood cell.

In lab tests, the scientists found the earthworms quickly ingested microplastics along with soil, reaching a consistent level in their systems within about two weeks. When the worms were transferred to clean soil, they seemed to eliminate nearly all the microplastics within a single day, suggesting the particles did not accumulate in their bodies.

To confirm this, the team used the CLS’s high-intensity X-rays to see where the microplastics went once they were inside the earthworms. The microplastics were coated with barium, which made them appear as bright white particles in the scans.

The researchers mapped approximately 2,500 individual microplastic particles inside the earthworms; the imaging clearly showed that all the particles remained inside the gut and didn’t cross into internal tissues. The team recently published their findings in the journal Environmental Toxicology and Chemistry.

“These results are good news for earthworms,” says Nicholas Letwin, PhD candidate and lead author on the paper. “The plastics are ingested and then simply pass through. They don’t stay in the body indefinitely, which would be very detrimental for worms or any organism.”

“The CLS was instrumental in allowing us to map the plastics within earthworm tissue, which is something that you can't really do anywhere else,” he adds.

Beyond earthworms, the study demonstrates a powerful proof of concept. The imaging technique makes it possible to visually track microplastics inside organisms with unprecedented precision.

The researchers say that the findings raise questions about whether humans need to be concerned about digesting microplastics.

“I think we need to give our bodies more credit,” says Ryan Prosser, associate professor and co-author on the project. “Humans unintentionally eat all kinds of different things that would not be considered nutritious. Scientists have studied the amount of dirt humans eat and that stuff isn't moving out of our gut and into our bloodstream or other tissues.”

“At least in this case, we confirmed with the worms that their digestive track is selective enough to not allow microplastics to move into their body beyond the gut,” says Prosser.

The team says further research needs to be done to inform regulations related to microplastics in the environment and to assess the health risks to other organisms and humans.

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Letwin, Nicholas V., Jarvis A. Stobbs, Juliska Princz, Gladys L. Stephenson, Adam W. Gillespie, Moira M. Ijzerman, and Ryan S. Prosser. "Assessing the accumulation of microplastics in earthworms (Eisenia fetida) using traditional bioaccumulation modeling and synchrotron-based microcomputed tomography." Environmental Toxicology and Chemistry (2026): vgag072. https://doi.org/10.1093/etojnl/vgag072 

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