Banned chemicals from the 70s found in the deepest reaches of the ocean

The ultra-deepwater amphipod Hirondellea gigas from the deepest depths of the Mariana Trench in the Northwest Pacific Ocean. This species is known to inhabit depths of 6000 to nearly 11,000m. Photo by Dr Alan Jamieson

A study, from the University of Aberdeen and Newcastle University has uncovered the first evidence that man-made pollutants have now reached the farthest corners of our earth.

Sampling amphipods from the Pacific Ocean’s Mariana and Kermadec trenches - which are over 10 kilometres deep and 7,000 km apart - the team found extremely high levels of Persistent Organic Pollutants - or POPs - in the organism’s fatty tissue. These include polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) which are commonly used as electrical insulators and flame retardants.

Publishing their findings today in Nature Ecology & Evolution, the study team say the next step is to understand the consequences of this contamination and what the knock-on effects might be for the wider ecosystem.

Lead author Dr Jamieson from Newcastle University, and honorary lecturer at the University of Aberdeen, said: “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.

“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.

“What we don’t yet know is what this means for the wider ecosystem and understanding that will be the next major challenge.”

To find these levels of contamination in different species of amphipod from different trenches and at different depths really highlights how much this pollution has spread and managed to accumulate." Professor Stuart Piertney

Professor Stuart Piertney from the University of Aberdeen added: “To find these levels of contamination in different species of amphipod from different trenches and at different depths really highlights how much this pollution has spread and managed to accumulate.”

From the 1930s to when PCBs were banned in the 1970s, the total global production of these chemicals was in the region of 1.3million tonnes.

Released into the environment through industrial accidents and discharges and leakage from landfills, these pollutants are invulnerable to natural degradation and so persist in the environment for decades.

The research team used deep-sea landers - designed by Dr Jamieson while still at the University of Aberdeen - to plumb the depths of the Pacific Ocean in order to bring up samples of the organisms that live in the deepest levels of the trenches.

The authors suggest that the pollutants most likely found their way to the trenches through contaminated 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.

“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,” added Dr Jamieson, who is now based in the School of Marine Science and Technology at Newcastle University. “It’s not a great legacy that we’re leaving behind.”