About 40 million tonnes of microplastics enter the environment globally each year, originating from the breakdown or shedding of common plastic products.
Despite widespread microplastic contamination, it remains unclear whether these particles migrate from the digestive system into other tissues, potentially causing long-term harm.
To investigate this issue, researchers utilized the Canadian Light Source (CLS) at the University of Saskatchewan to monitor the movement of microplastics through earthworms. Earthworms contribute to soil structure and serve as key indicators of the effects of ingesting microplastic particles in living organisms.
A research team from the University of Guelph exposed earthworms to soil containing higher concentrations of plastic particles than typically found in natural environments.
The team employed polyethylene microplastics, one of the most prevalent plastics globally, with particle sizes ranging from five to 20 microns, which is smaller than a human red blood cell.
Laboratory experiments demonstrated that earthworms rapidly ingested microplastics along with soil, reaching a stable concentration in their systems within approximately two weeks.
Upon transfer to uncontaminated soil, the earthworms expelled nearly all microplastics within one day, indicating that the particles did not accumulate in their bodies.
To validate these observations, the team employed high-intensity X-rays at the CLS to trace the distribution of microplastics following ingestion by earthworms. The microplastics were coated with barium, which rendered them as bright white particles in the resulting scans.
The researchers mapped approximately 2,500 individual microplastic particles within the earthworms; the images clearly showed that all particles remained within the gut and did not 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.
“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 things that are not 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.
Beyond the findings in earthworms, this study provides a robust proof-of-concept. The imaging technique allows for highly precise visual tracking of microplastics within biological organisms.
These findings indicate that humans are exposed to microplastics during digestion, raising important questions regarding the potential health implications of such exposure.
Further research is necessary to inform regulatory decisions and to evaluate health risks for humans and other organisms.
The Canadian Light Source (CLS) is a national research facility of the University of Saskatchewan and one of the largest science projects in Canada’s history. More than 1,000 academic, government, and industry scientists from around the world use the CLS every year in innovative research on health, agriculture, the environment, and advanced materials.