Globally, humanity now produces a staggering 450 million tonnes of plastic every year. From food and drink containers to cosmetics packaging, sewage pipes, window frames and polyester clothing, we use plastics in almost every area of life. And nearly one-quarter of them end up in the environment, where they very slowly degrade into microscopic pieces.

These microplastics—particles between 1 micrometer and 5 millimeters wide—have been found in the deepest parts of the oceans, at the top of the tallest mountains, at the sparsely populated poles and even inside the human body.

It is very difficult for living organisms, including humans, to avoid ingesting microplastics. If these microplastics cross the lining of the digestive tract to enter the bloodstream or other tissues, they will persist in the body. Until now, it has been difficult for researchers to accurately assess whether this is happening.

Our research team has developed a new technique to identify the location of microplastics within an organism without dissecting it. We tested it on earthworms and discovered that microplastics ranging in size from 5 to 53 micrometers do not readily cross the lining of the gut to enter other tissues in the worms...