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We’ve long known that the fish we eat are exposed to toxic chemicals in the rivers, bays and oceans they inhabit. The substance that’s gotten the most attention – because it has shown up at disturbingly high levels in some fish – is Mercury.

But mercury is just one of a slew of synthetic and organic pollutants that fish can ingest and absorb into their tissue. Sometimes it’s because we’re dumping chemicals right into the ocean. But as a study published recently in
Nature, Scientific Reports helps illuminate, sometimes fish get chemicals from the plastic debris they ingest.

“The ocean is basically a toilet bowl for all of our chemical pollutants and waste in general,” says Chelsea Rochman , a postdoctoral researcher at the University of California, Davis, who authored the study. “Eventually, we start to see those contaminants high up in the food chain, in seafood and wildlife.”

For many years, scientists have known that chemicals will move up the food chain as predators absorb the chemicals consumed by their prey. That’s why the biggest, fattiest fish, like tuna and swordfish, tend to have the highest levels of mercury, polychlorinated biphenyls (PCBs) and other dioxins. (And that’s concerning, given that canned tuna was the second most popular fish consumed in the U.S. in 2012, according to the National Fisheries Institute.)

What scientists didn’t know was exactly what role plastics played in transferring these chemicals into the food chain. To find out, Rochman and her co-authors fed medaka, a fish species often used in experiments, three different diets.