The majority of the plastic pollution in the ocean, by volume, comes in the form of tiny confetti-sized particles, which, as anyone who's ever kept a pet fish can attest, resemble fish food.
And fish are fooled as well.
More than 40 species of fish, globally, are known to consume plastic.
"It's available for almost any marine animal of any size to eat, making this material available to go up the food chain," said Chelea Rochman, the lead author of a new paper from the journal Nature, Scientific Reports. Rochman is a post doctoral researcher at the University of California Davis School of Veterinary Medicine.
There is no doubt among scientists that animals are eating marine plastic, but much less is known about what happens to animals when the plastic gets into their bodies.
Rochman analyzed the fish after two months to test their levels of persistent organic pollutants like PCBs, flame retardants and polyaromatic hydrocarbons.
"We did find that the chemicals do transfer from the plastic to the fish," Rochman says, "and we saw a greater concentration in the fish that ate the plastic that had been in the ocean than the fish that had eaten the controlled diet or the clean plastic diet."
As plastic floats around in the ocean, or polluted waterways, it acts like a sponge for heavy metals and persistent organic pollutants. That, Rochman says, could explain why the fish fed the San Diego Bay plastic showed higher levels of those chemicals in their bodies.
The chemicals didn't kill the fish, Rochman said, but some funky things happened to their livers.
"We did see an increase in glycogen depletion in our fish fed both the virgin plastic and our fish fed the plastic that had been in the ocean for 3 months," Rochman said.
Our bodies store glycogen in our livers as a reserve energy source if we're under stress.
In Rochman's experiment, fish that ate plastic had less glycogen. They also had excess fat cells in their livers, or lipidosis, an indication of the beginnings of fatty liver degeneration. The fish fed virgin polystyrene showed elevated levels of lipidosis when compared to the control group, but the fish fed dirty plastic had significantly higher levels than the other two groups of fish.