Man-Made Pollution Found in Deepest Ocean Trenches

Even the deepest reaches of the ocean aren’t immune from human pollution, discovered during two deep-sea expeditions.

At a conference on deep-ocean exploration held in Shanghai on June 8th, a team of scientists announced a shocking discovery. Man-made pollution exists even in the ocean’s deepest and most inaccessible underwater trenches. Two deep-sea expeditions, carried out in 2014 by an international team sponsored by the U.S. National Science Foundation, reported the findings.

Man-Made Pollution Found in Deepest Ocean Trenches

“We often think deep-sea trenches are remote and pristine, untouched by humans,” said Alan Jamieson, one of the participating scientists and an expert deep-ocean researcher at the University of Aberdeen in Scotland. Researchers proved this assumption incorrect after identifying extraordinarily high levels of man-made pollutants in deep-dwelling crustaceans called amphipods.

Scientists took the amphipods from two of the deepest points on Earth, the Kermadec Trench near New Zealand and the Mariana Trench in the western Pacific. Previously, scientific studies had only examined pollutant levels in marine organisms living at 6,500 feet (2,000 m) or shallower. Jamieson and his team collected amphipods at incredible depths of between 23,000 and 33,000 feet (7,000 and 10,000 m).

The study found that varying levels of polychlorinated biphenyls (PCBs) and polybrominated biphenyl ethers (PBDEs) contaminated amphipods from both trenches. Companies use PCBs in plastic production and as an anti-fouling agent for ships, and PBDEs as flame retardants. Both chemicals are notoriously long-lasting, and several countries ban or strictly regulate them.

What did they find?

Mariana Trench amphipods contained higher PCB levels than those from the Kermadec Trench. Kermadec Trench amphipods showed higher levels of PBDEs. Both areas suffered from more contamination compared to other similarly-tested areas, including estuaries and tracts of open ocean. The Mariana Trench tested higher for PCBs than China’s Pearl and Liao Rivers, two of the most polluted rivers on the planet.

Jamieson explains this phenomenon by pointing out that the sea dilutes chemicals dumped into estuaries. On the other hand, he says, “when you dump rubbish into the sea, it will ultimately sink. When [pollutants] fall into the trenches, they have nowhere else to go. So they’re just going to keep building up.” Ocean currents may also draw surface pollution into the depths.

The trench’s proximity to Asian plastic manufacturers and a long-term U.S. military base in Guam might explain the high PCB levels in Mariana Trench amphipods. Deep-sea microbiologist Douglass Bartlett is concerned about whatever is causing the pollution. “[It] hits home very dramatically that the trenches are not that remote after all, and [that] the world is all connected,” he says.

Because the study of pollutants at such depths is so new, the ramifications are unclear. However, experts worry that as-yet-undiscovered resources (including organisms that could contribute to the development of life-saving drugs) may be at risk. Scientists are also concerned that the contamination could affect the deep-ocean trenches function as a valuable carbon sink.