Want a side of plastic with your fresh-caught salmon?

About a quarter of fish samples from markets in Indonesia and fresh off the boat in California are filled with plastic and debris such as clothing fibers, scientists at the University of California, Davis, have found.

While other research has found plastics in the bellies of popular dinner-plate items such as tuna and swordfish, this is the first study to link marine plastic ingestion directly to fish sold for human consumption.

“We knew fish ingest plastic, but we wanted to see if it was getting to consumers’ plates,” said Susan Williams, an ecology professor at UC Davis and a coauthor of the study.

The team looked at the guts and gastrointestinal tracts of 76 fish bought in markets in Makassar, Indonesia, and 64 fish bought from local fishers at the docks of California’s Pillar Point Harbor and Half Moon Bay fish markets south of San Francisco.

“In Indonesia, they sell the fish whole, and consumers eat the fish whole, guts and all,” Williams said. “In the U.S., the fish are often cleaned and fileted before they are sold, so we had to get them from the fishermen.”

Students help pick up plastic from an Indonesian beach. (Photo: Dale Trockel/UC Davis)

Scientists found plastics and synthetic fibers in more than 28 percent of the fish bought in Indonesia and 25 percent of the fish tested in California—including oysters, Pacific anchovies, chinook salmon, striped bass, and other dinner-plate mainstays. Researchers found plastic trash in six of 11 Indonesian fish species tested and eight of 12 species examined in the U.S.

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The main difference between the two locations—which are some 8,000 miles apart—was the type of debris discovered. In Indonesia, all of the items found in fish were marine plastics, ranging from tiny fragments to plastic foam to monofilament fishing line. But in California, only 20 percent of debris was identified as plastic trash. The remaining material found in fish bellies came from clothing fibers—a result, Williams said, determined by each country’s waste management system and laundry habits.

“When you walk down the beach in Indonesia, you can be up to your knees in plastic debris,” said Williams, who has focused her work on marine biodiversity in that country. The lack of clean drinking water there only exacerbates the problem, as residents have few options to drink purified water outside of bottled water.

In the U.S., most plastic waste makes its way to recycling plants and landfills, but a love of blended synthetic fabrics and washing machines could be the driving force behind an ocean of fibers making its way into fish bellies.

“Washing machines agitate clothing much more than the hand washing they traditionally do in Indonesia, and the materials we use don’t break down as quickly as cotton does,” Williams said.

So what do plastic- and fiber-filled fish guts mean for human health? Scientists aren’t yet sure.

For starters, the debris the team found was all stuck in the fishes’ guts and intestinal tracts—both parts typically removed before consumption in the U.S. But in Indonesia, where fish are eaten whole, residents are almost certainly ingesting plastic debris with their dinner.

The next level of testing will seek to find out whether the plastic and synthetic materials are leaching into other parts of the fish, and whether there are health effects to humans from ingesting plastic.

Lead author Chelsea Rochman of UC Davis has already shown that a blend of polyethylene (the most common plastic in the world) and other common chemical pollutants found in plastics can lead to liver toxicity in fish.

“We know that plastics are a problem for the fish themselves, but we don’t know if those health issues transfer to humans who are consuming fish that have eaten plastic,” Williams said.