Ocean’s Silent Plastic Invasion: Marine Mammals Now Carry Microplastics Within

Research Suggests That Microplastics, Once Ingested, Move Into the Fat and Internal Organs of Whales

Microscopic plastic remnants have been detected in the blubber and lungs of over 65% of the marine mammals examined in a graduate student’s investigation into ocean microplastics. The discovery of polymer fragments and fibers in these creatures indicates that microplastics can migrate beyond the digestive system and embed in their tissues.

The research, set to be published in the October 15 issue of Environmental Pollution, was recently published online.

Harms that embedded microplastics might cause to marine mammals are yet to be determined, but plastics have been implicated by other studies as possible hormone mimics and endocrine disruptors.

“This is an extra burden on top of everything else they face: climate change, pollution, noise, and now they’re not only ingesting plastic and contending with the big pieces in their stomachs, they’re also being internalized,” said Greg Merrill Jr., a fifth-year graduate student at the Duke University Marine Lab. “Some proportion of their mass is now plastic.”

The samples in this study were acquired from 32 stranded or subsistence-harvested animals between 2000 and 2021 in Alaska, California, and North Carolina. Twelve species are represented in the data, including one bearded seal, which also had plastic in its tissues.

Why Marine Mammals Are Especially Vulnerable

Plastics are attracted to fats – they’re lipophilic – and so are believed to be easily attracted to blubber, the sound-producing melon on a toothed whale’s forehead, and the fat pads along the lower jaw that focus sound to the whales’ internal ears. The study sampled those three kinds of fats plus the lungs and found plastics in all four tissues.

Plastic particles identified in tissues ranged on average from 198 microns to 537 microns – a human hair is about 100 microns in diameter. Merrill points out that, in addition to whatever chemical threat the plastics pose, plastic pieces also can tear and abrade tissues.

“Now that we know plastic is in these tissues, we’re looking at what the metabolic impact might be,” Merrill said. For the next stage of his dissertation research, Merrill will use cell lines grown from biopsied whale tissue to run toxicology tests of plastic particles.

Polyester fibers, a common byproduct of laundry machines, were the most common in tissue samples, as was polyethylene, which is a component of beverage containers. Blue plastic was the most common color found in all four kinds of tissue.

Plastic Pollution in Marine Food Chains

A 2022 paper in Nature Communications estimated, based on known concentrations of microplastics off the Pacific Coast of California, that a filter-feeding blue whale might be gulping down 95 pounds of plastic waste per day as it catches tiny creatures in the water column. Whales and dolphins that prey on fish and other larger organisms also might be acquiring accumulated plastic in the animals they eat, Merrill said.

“We haven’t done the math, but most of the microplastics probably do pass through the gut and get defecated. But some proportion of it is ending up in the animals’ tissues,” Merrill said.

“For me, this just underscores the ubiquity of ocean plastics and the scale of this problem,” Merrill said. “Some of these samples date back to 2001. Like, this has been happening for at least 20 years.”

Reference: “Microplastics in marine mammal blubber, melon, & other tissues: Evidence of translocation” by Greg B. Merrill, Ludovic Hermabessiere, Chelsea M. Rochman and Douglas P. Nowacek, 2 August 2023, Environmental Pollution.
DOI: 10.1016/j.envpol.2023.122252

This work was supported by the National Science Foundation, the North Carolina Wildlife Federation, and North Carolina Sea Grant (2018-2791-17).

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