Plastic proliferates at the bottom of world's deepest ocean trench

Yet again, plastic is proving to be everywhere in the sea. During a dive to the bottom of the Mariana Trench that purportedly reached 35,849 feet, Dallas businessman Victor Vescovo claims to have found a plastic bag. And it's not even the first time: It's the third time plastic has been documented in the deepest explored part of the ocean.

Vescovo made his dive in a submersible on April 28 as part of his "Five Deeps" Expedition, which involve journeys to the deepest points in each of Earth's oceans. During the four hours Vescovo spent at the bottom of the Mariana Trench, he observed several marine creatures—one of which is a potentially new species—a plastic bag, and candy wrappers.

Few people have reached such extreme depths. Swiss engineer Jacques Piccard and U.S. Navy Lieutenant Don Walsh were the first in 1960. National Geographic explorer and movie director James Cameron then made a dive to the depths in 2012. Cameron logged 35,787 feet on his dive, just shy of the 62 feet that Vescovo claims to have reached.

Unlike humans, plastic seems to descend with ease. Earlier this year, a study sampled amphipods in six deep-sea trenches, including the Mariana, and found all were ingesting microplastics.

Deep plastic

A study released in October 2018 documented what is still the deepest known piece of plastic—a flimsy shopping bag—found at a depth of 36,000 feet inside the Mariana Trench. Scientists found it by looking through the Deep-Sea Debris Database, a collection of photos and videos taken from 5,010 dives over the previous 30 years.

Of the classifiable debris logged in the database, plastic was the most prevalent, and plastic bags in particular made up the greatest source of plastic trash. Other debris came from material like rubber, metal, wood, and cloth.

A whopping 89 percent of the plastic in the study was single use, the type that's used once and then thrown away, like a plastic water bottle or disposable utensil.

The Mariana Trench is no dark, lifeless pit; it has plenty of residents. NOAA's Okeanos Explorer vessel searched the region's depths in 2016 and found diverse life-forms, including species like coral, jellyfish, and octopus. The 2018 study also found that 17 percent of the images of plastic logged in the database showed interactions of some kind with marine life, like animals becoming entangled in debris.

Where did the plastic come from?

Single-use plastics are virtually everywhere, and they may take hundreds of years or more to break down once in the wild. The Mariana Trench has higher levels of overall pollution in certain regions than some of the most polluted rivers in China, according to a study in February 2017. The study's authors theorized that the chemical pollutants in the trench may have come in part from the breakdown of plastic in the water column.

While plastic can enter the ocean directly, such as trash blown from a beach or discarded from ships, a study published in 2017 found that most of it flows into the sea from 10 rivers that run through heavily populated regions.

Discarded fishing gear is also a major source of plastic pollution, and a study published in March 2018 found that the material comprised the bulk of the Texas-size Great Pacific Garbage Patch floating between Hawaii and California.

While the ocean clearly contains much more plastic than a single plastic bag, the item has now gone from a wind-flung metaphor for listlessness to an example of how deep an impact humans can have on the planet.