We used to think microplastics stayed in a fish’s guts. Chilling new research suggests the tiny particles migrate into its flesh.

Nearly 50 years ago, scientists studying the North Atlantic Ocean started noticing that tiny fragments of plastic were turning up in their plankton and seaweed samples. The microparticles, they found, absorbed toxic chemicals and were then eaten by flounder, perch, and other fish. Until recently, though, researchers thought these ingested plastics stayed in a creature’s guts and possibly its liver. Removing a fish’s entrails before serving it up appeared to eliminate the risk of eating plastic.

But recent research suggests that these tiny bits of plastic move into fish flesh. And now seafood, a recent study found, is the third-largest source of chemical-laden “microplastics” of sources analyzed so far for the average American consumer, behind bottled water and air. “Plastic is now part of our food system,” says Kieran Cox, a marine ecologist and PhD candidate at the University of Victoria in British Columbia who led the study.