High Levels Of Toxic Chemicals Contaminate Marine Animals In Deepest Ocean Trenches

14 Février, 2017, 15:01 | Auteur: Ludovic Moineau
  • Man-made pollutants have been found in a shrimp-like creature Hirondellea gigas from the deepest part of the ocean more than 10,000 metres deep in the Mariana Trench in the Northwest Pacific Ocean

Reaching down to a depth of around 11km, the Mariana Trench is the most unexplored part of the planet and contains unknown marine life.

The researchers found that both the Mariana and Kermadec trenches were full of polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) - two chemicals banned by the United States in 1979 and the Stockholm Convention on Persistent Organic Pollutants in 2001.

Between the 1930s to the 1970s, when they were banned, the total global production of PCBs was about 1.3 million tonnes.

The situation with PBDEs, which continue to be used as flame retardants, is even worse.

"PCBs and PBDEs were present in all samples across all species at all depths in both trenches", the researchers wrote.

"The spotlight has hovered over these pollutants due to their capacity to remain viable over long time periods and for long-range transport in material such as soil, water and air". They also have a tendency to "bioaccumulate", meaning they can build up in marine organisms over time.

Researchers checked for the presence of PCBs and PCDEs in the Mariana Trench in the Western Pacific and the Kermadec trench north of New Zealand.

The research was carried out in the ocean's hadal zone, between six and 11 km deep, and comprised of deep trenches in the sea floor caused by tectonic plate activity.

The researchers used deep-sea landers to comb the Mariana and Kermadec trenches for amphipods, and tested their fatty tissues for signs of pollutants called Persistent Organic Pollutants (POPs).

Hirondellea gigas are voracious scavengers, known to consume nearly any organic material that descends from the surface waters, including any pollutants that come with it.

An expedition conducted by the US National Oceanic and Atmospheric Administration past year also found various manmade items on the slopes leading to the Sirena Deep, part of the Mariana trench, and the nearby Enigma Seamount.

"Contamination was sky high": two commensal amphipods on a sponge stalk in the Mariana trench.

A robotic submarine dispatched to the Marina trench in the Pacific Ocean found in the pitch black water tiny crustaceans that were contaminated with 50 times more toxic chemicals than crabs that live in very polluted rivers in China, The Guardian reports.

Scientists discovered that these two banned chemicals among others do not break down or degrade in the environment, so they ultimately find their ways into the waters where marine creatures absorb them.

And when we say "extremely high", that's even compared to some of the most polluted places in the world.

The results are both significant and disturbing, said the marine ecologist Katherine Dafforn at the University of New South Wales in Australia and not part of the research team: "The trenches are many miles away from any industrial source and suggests that the delivery of these pollutants occurs over long distances despite regulation since the 1970s".

What remains unclear is exactly how the contaminants got into the trenches - and why their levels are so high in the Mariana.

But the Mariana Trench is polluted. Chemical pollutants in that region could easily cling to plastic waste as it drops through the water column toward the bottom of the ocean. She said the new research showed that the deep ocean trenches are not as isolated as people imagine.

"We still think of the deep ocean as being this remote and pristine realm, safe from human impact".