Underwater landscape, seabed carved by swell into the reef, Huah

Pollution Has Been Discovered Even In The World’s Deepest Ocean Trenches

High levels of persistent organic pollutants, including polychlorinated biphenyls (PCBs), were found in crustaceans living in some of the planet’s most remote areas – the Mariana Trench above Australia and the Kermadec Trench off the northeastern tip of New Zealand. The discovery, published in the journal Nature Ecology & Evolution, “brings home the long-term, devastating impact” that humans are having on the environment.

“It’s not a great legacy we’re leaving behind,” said biologist Alan Jamieson from Newcastle University. “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.”

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The findings were made during a study conducted by Jamieson and a team of Scottish researchers, who used a mechanical deep-sea lander to collect samples from these relatively unexplored parts of the ocean. After the lander resurfaced with small amphipods in the traps, Jamieson thought the creatures might be worth examining, so he brought them to an environmental scientist.

“He came back and said these are really badly contaminated,” Jamieson said in an interview with NPR. “Every sample we had, had contaminants in it at very high or extraordinarily high levels.”

In fact, some of the more contaminated crustaceans from the Mariana Trench contained PCB levels 50 times greater than the levels found in crabs from China’s most polluted river system. Jamieson attributed this extreme level of pollutants to the Mariana Trench’s proximity to the North Pacific Subtropical Gyre, known as the Great Pacific Garbage Patch.

According to Jamieson, it’s possible that these pollutants make their way to the trenches by attaching to plastic discarded into the ocean, or absorbed by plants and fish. When these plants, animals, and bits of garbage die or become waterlogged, they sink to the bottom of the ocean and collect in the deepest crevices – like the Mariana and Kermadec Trenches.

fourty metres

“There’s nowhere else for it to go, because there’s no mechanism to put it back to the surface again,” Jamieson said. “We’ve got to remember, planet Earth is mostly deep sea, and to think that it’s just okay to ignore it is a little bit irresponsible.”

While PCBs were banned in the 1970s after studies linked these coolants and lubricants to a higher risk of cancer, the amphipods also showed moderate concentrations of polybrominated diphenyl ethers (PBDEs), flame-retardant chemicals which are still in production today. These pollutants break down very slowly, and can be transported easily through soil, water, and air – meaning they accumulate easily in the environment.

Marine biologist Katherine Dafforn, with the University of New South Wales, said it’s “disturbing” to find pollutants like these in the trenches – especially at such high levels. In an opinion piece accompanying the study, she said many chemicals have “far-reaching impacts” that we may not even be aware of, yet. Jamieson said further studies will be necessary to see what implications these findings may have for the wider ecosystem.

“(The study has) provided clear evidence that the deep ocean, rather than being remote, is highly connected to surface waters and has been exposed to significant concentrations of human-made pollutants,” Dafforn said. “(These) findings are crucial for future monitoring and management of these unique environments.”

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