Seal Feces Reveals Microplastics Are Traveling Up the Food Chain

Over 9 billion tons of plastic have been produced since the 1950s, and about 7 billion tons have ended up as waste, much of it in pieces smaller than 5 millimeters.

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Tiny pieces of plastics are turning up in the feces of seals that feed on whole fish, demonstrating how seaborne contamination can move up the food chain, British researchers report.

The researchers studied a group of grey seals at the Plymouth Marine Sanctuary in southwestern England. The seals live on a diet of mackerel caught in the Atlantic Ocean.

Lead author Sarah Nelms and her colleagues dissected 31 of the mackerel collected for the seals and found 10 of them had plastic fibers or fragments in their gastrointestinal tracts. Meanwhile, just under half the seal scat samples they collected contained bits of plastic.

Nelms, a Ph.D. researcher at the University of Exeter, said the study grew out of her sense of alarm at how much plastic has been washing ashore.“The initial point of concern was the amount of plastic I was seeing on beaches,” Nelms told Seeker. Her interest was further piqued by a lecture and video presentation on ocean plastics being consumed by plankton — the tiny organisms at the bottom of the food chain. “That really shocked me,” she said.

Environmental Pollution

Microplastics are a growing problem in the world’s oceans. They originate largely with packaging and drink bottles and break up into tiny pieces in the environment. Of the 9 billion-plus tons of plastic produced since the 1950s, about 7 billion have ended up as waste, much of which ends up in pieces smaller than 5 millimeters (about 3/16 of an inch), according to the US Environmental Protection Agency.

The findings — published March 5 in the research journal Environmental Pollution — show that microplastics can pass up the food chain, from fish to a mammalian predator. And those findings raise questions for human health, the authors concluded.

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Microplastics have turned up in seafood like shellfish, which humans consume whole — and the authors of the new study say more study needs to go into how ingesting those substances affect people. Nelms said that’s the planned follow-up to her seal study.

"Given that most of our food is packaged in plastic, it is highly likely we are consuming small amounts of plastic as a result of contamination on a regular basis,” Nelms said. By comparison, the amount of plastic humans end up eating directly through their food “probably makes up a small proportion of the plastic we eat.” But she said even if animals eventually pass the plastic, long-lived toxins can latch onto the particles and enter the body.

“Persistent chemicals, such as PCBs, are known to adhere to the surface of microplastics,” she said. “They can cause endocrine disruption and alterations to immune system function if ingested.” Those chemicals “are more of a concern than the particles themselves,” she said.