Pollutants banned in the 1970s are STILL damaging marine life today

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

However, samples taken from the area, which lies east of the Philippines reveal high levels of pollutants banned 40 years ago have contaminated the bodies of creatures living there.

This includes polychlorinated biphenyls (PCBs) which have been defined as carcinogens and do not break down for decades.

Revealed this afternoon, the findings are now being reported across the world.

HOW DO WE KNOW THIS?

Researchers from Aberdeen and Newcastle universities and Scotland’s James Hutton Institute examined the fatty tissue of scavengers living more than 10km down to gain the results.

Similar to sand hopping insects, the amphipods measure just 2-3cm and were collected from both the Mariana Trench and the Kermadec Trench, which sits 7,000km away north of New Zealand.

WHAT HAPPENED?

The experts, who used a robotic submarine to collect the creatures, were shocked to find they contained ten times the level of industrial pollution than the average earthworm.

They also held 50 times more toxic chemicals than the crabs that withstand China’s chemical-doused rivers and the levels were comparable to that found in creatures from dirty waters of Suruga Bay in Japan - some of the worst in the Pacific region.

Dr Alan Jamieson, of Newcastle University, said the findings reveal new insight into the impact of human activity on the natural world. He 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 north west Pacific.”

WHAT ARE PCBS?

Once commonly used in industry, the chemicals can be deployed as heating or cooling fluids and in a range of other uses. However, tests established them as definite carcinogens.

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

But industrial accidents and leakage from landfill have seen them released into the sea and they are extremely slow to break down.

It is understood that the pollutants may have been carried to the trenches through contaminated plastic debris and dead animals sinking to the ocean floor, where amphipods have then consumed them.

Polybrominated diphenyl ethers, which were once used as flame retardants and are known to reduce fertility, were also detected in the marine life.

Jamieson said: “When it gets down into the trenches, there is nowhere else for it to go. The surprise was just how high the levels were. The contamination in the animals was sky high.”

WHAT ARE THE IMPLICATIONS FOR THE FUTURE?

According to Jamieson, they’re not good. He said: “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. It’s not a great legacy that we’re leaving behind.”

As well as chemical ingress, Jamieson says humanity’s footprint on the sea bed includes a Canadian beer can found lying 6,500m under the waters off the New Zealand coast and a raincoat discovered 10,800m down the Mariana Trench. A Spam tin was also discovered almost 5,000m below the surface, with plastic bags adding to the undersea litter.

Jamieson said: “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.

“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.”

The findings are published in the journal Nature Ecology & Evolution.