In a first, scientists discover banned toxic chemicals in deepest reaches of ocean

Image credit: Dr Alan Jamieson

New Delhi: High levels of human-made pollutants, including chemicals that were banned in the 1970s, have been found lingering in the tissues of marine creatures that dwell in the deepest oceans of the Earth.

As per a new study, this is the first time that scientists have uncovered the evidence that man-made pollutants have now reached the farthest corners of our Earth.

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

Sampling amphipods from the Pacific Ocean's Mariana and Kermadec trenches - which are over 10 kilometres deep and 7,000 km apart – scientists were stunned to find extremely high levels of Persistent Organic Pollutants (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.

"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 Alan Jamieson, from the Newcastle University in the UK.

"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," said Jamieson, who led the study.

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 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 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 humankind is having on the planet," said Jamieson.

Oceans comprise the largest biome on the planet, with the deep ocean operating as a potential sink for pollutants and litter that are discarded into the seas.

These pollutants then accumulate through the food chain so that by the time they reach the deep ocean, concentrations are many times higher than in surface waters.

"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," said Jamieson.

“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,” he added.

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 findings were published in the journal Nature Ecology and Evolution.

(With PTI inputs)