Scientists have found that crustaceans from the deepest ocean trenches contain ten times the level of industrial pollution than the average earthworm.

The Pacific Ocean’s Mariana and Kermadec trenches are over 10 kilometers deep and separated by roughly 7,000 kilometers. For instance, the United States Center for Coastal & Ocean Mapping measured the depth of the Mariana Trench’s Challenger Deep in 2010, finding that it was 10,994 meters (36,070 feet) below sea level. In fact, if Mount Everest were place at this location it would be covered by over one mile of water, according to Geology.com. That’s deep!

The Kermadec Trench — while slightly less impressive but astonishing all the same — reaches a depth of 10,047 meters (32,963 feet) and is noted for its very abrupt slope. Also notable is a 2014 incident in which an unmanned research submarine operated by the Woods Hole Oceanographic Institution was destroyed by a “catastrophic implosion” at a depth of 9,990 meters while exploring the trench.

At depths such as these, one would think that these areas would be invulnerable to anthropogenic (man-made) phenomena. But you would be wrong.

Case in point: In 2016, NOAA and Oregon State researchers learned that Challenger Deep is a surprisingly noisy place. “This should be one of the quietest places in the world, but it was a lot noisier than we expected,” said Oregon-based oceanographer Robert Dziak, who led the project for the NOAA at the time of this discovery. “There really is almost constant sound from natural and man-made sources.”

Now, it appears that noise isn’t the only issue plaguing the deepest parts on Earth: man-made pollutants that were banned in the 1970s have also made an appearance, according to a team of scientists led by Newcastle University’s Dr. Alan Jamieson.

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Hirondellea gigas are voracious scavengers that consume anything that comes down from the surface. Credit: Dr. Alan Jamieson, Newcastle University

While sampling crustaceans from both trenches using deep-sea landers, they found extremely high levels of Persistent Organic Pollutants — or POPs — in the creatures’ fatty tissues. According to a statement from the researchers, the POPs include polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) which are commonly used as electrical insulators and flame retardants.

“We still think of the deep ocean as being this remote and pristine realm, safe from human impact, but our research shows that, sadly, this could not be further from the truth,” said Dr. Jamieson, lead author of a study on the findings published in the journal Nature Ecology & Evolution. “In fact, the amphipods we sampled contained levels of contamination similar to that found in Suruga Bay, one of the most polluted industrial zones of the northwest Pacific.”

NOTE: In recent years, Suruga Bay has suffered from severe industrial pollution, with surveys of local sea life in the mid-2010s showing intense PCB and PBDE contamination.

PCBs were banned in the 1970s, but their use began as early as the 1930s. During that short time, the total global production of these chemicals was in the region of 1.3 million tons. Before they were banned, these toxic chemicals were released into the environment through industrial accidents and discharges and leakage from landfills. The problem is, these pollutants are immune to natural degradation. Therefore they tend to persist in the environment for decades.

The scientists suggest that the pollutants most likely found their way to the trenches through contaminated anthropogenic plastic debris and dead animals sinking to the bottom of the ocean, where they are then consumed by amphipods and other fauna, which in turn become food for larger fauna still. See Also: Microplastics, Pollution, And Broken Records: Opinion.

“The fact that we found such extraordinary levels of these pollutants in one of the most remote and inaccessible habitats on earth really brings home the long term, devastating impact that mankind is having on the planet,” said Dr. Jamieson, who is based in the School of Marine Science and Technology at Newcastle University. “It’s not a great legacy that we’re leaving behind.”

The study team — from Newcastle University, UK, University of Aberdeen and the James Hutton Institute — says the next step is to understand the consequences of this contamination and what the knock-on effects might be for the wider ecosystem.

“We’re very good at taking an ‘out of sight out of mind’ approach when it comes to the deep ocean but we can’t afford to be complacent,” Dr. Jamieson added. “This research shows that far from being remote the deep ocean is highly connected to the surface waters and this means that what we dump at the bottom of the sea will one day come back up in some form another.”

Top Image – Pixabay

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