A Troubling Discovery in the Deepest Ocean Trenches

In the Mariana Trench, the lowest point in any ocean, every tiny animal tested had plastic pollution hiding in its gut.

Alan Jamieson remembers seeing it for the first time: a small, black fiber floating in a tube of liquid. It resembled a hair, but when Jamieson examined it under a microscope, he realized that the fiber was clearly synthetic—a piece of plastic. And worryingly, his student Lauren Brooks had pulled it from the gut of a small crustacean living in one of the deepest parts of the ocean.

For the past decade, Jamieson, a marine biologist at Newcastle University, has been sending vehicles to the bottom of marine trenches, which can be as deep as the Himalayas are tall. Once there, these landers have collected amphipods—scavenger relatives of crabs and shrimp that thrive in the abyss. Jamieson originally wanted to know how these animals differ from one distant trench to another. But a few years ago, almost on a whim, he decided to analyze their body for toxic, human-made pollutants such as polychlorinated biphenyls, or PCBs, which have been banned for decades but which persist in nature for much longer.

The team found PCBs galore. Some amphipods were carrying levels 50 times higher than those seen in crabs from one of China’s most polluted rivers. When the news broke, Jamieson was inundated with calls from journalists and concerned citizens. And in every discussion, one question kept coming up: What about plastics?

The world produces an estimated 10 tons of plastic a second, and between 5 million and 14 million tons sweep into the oceans every year. Some of that debris washes up on beaches, even on the world’s most isolated islands. About 5 trillion pieces currently float in surface waters, mostly in the form of tiny, easy-to-swallow fragments that have ended up in the gut of albatrosses, sea turtles, plankton, fish, and whales. But those pieces also sink, snowing into the deep sea and upon the amphipods that live there.

Brooks eventually found plastic fibers and fragments in 72 percent of the amphipods that the team collected, from all six trenches that they had surveyed. In the least polluted of these sites, half of the amphipods had swallowed at least one piece of plastic. In the 6.8-mile-deep Mariana Trench, the lowest point in any ocean, all of the specimens had plastic in their gut.

Does a single fiber really matter amid all the sediment and detritus that amphipods regularly swallow? Jamieson thinks so. For a start, PCBs and other toxins can stick to plastic, turning fibers into sinks for other contaminants. Also, many of the pieces that his team found were relatively huge. “The worst example I saw was a purple fiber, a few millimeters long, tied in a figure-of-eight in an animal no longer than a centimeter,” Jamieson says. “Imagine if you swallowed a meter of polypropylene rope.”

If trenches from places as distant as Japan, Peru, and New Zealand can be contaminated, it’s likely that humanity’s plastic fingers have stretched into every part of the ocean, including habitats we have barely begun to understand. No marine ecosystem is untouched. “It builds upon a growing body of evidence suggesting that the deep sea, by far the largest habitat on the planet, may very well be the largest reservoir of plastic waste on the planet,” says Anela Choy from the University of California at San Diego.

“It’s not a good result,” Jamieson adds. “I don’t like doing this type of work.”

When he submitted his findings to a scientific journal, the researchers who reviewed the paper reasonably asked how he could tell that the fibers were actually plastic. “Our response was, ‘Some of it’s purple!’ ” Jamieson says. “There’s bits of pink in there. This doesn’t come from animals.” To satisfy the critics, his team chemically analyzed a subset of the fibers and found that all of it was synthetic.

They also took steps to ensure that they hadn’t inadvertently introduced plastic into the trenches. The landers that they used to collect the amphipods have some plastic parts, but they are all bright green and yellow, and no such colors were found in the specimens. Even if the amphipods had eaten plastic from the landers (or from the bait used to attract them), the team only dissected the last of the creatures’ several stomachs to avoid sampling their most recent meals. And they performed those dissections within a special chamber, where continuously rising air stops fibers from their equipment or clothes from settling in the samples. Given these precautions, Jamieson is confident that the fibers he found had sunk into the abyss on their own.

Learn more at The Atlantic.

Kate McCartyenvironment, water