Russia Today reported that researchers recently discovered man-made pollutants in the deepest and most remote places on Earth – the Atacama Trench, which descends 8,000 meters into the Pacific Ocean.

The presence of PCBs in such a remote location confirms an important fact: no place on Earth is free from pollution.

PCBs were produced in large quantities from the 1930s to the 1970s, mostly in the Northern Hemisphere, and were used in electrical equipment, paints, refrigerants, and many other products.

By the 1960s it had become clear that they were harmful to marine life, leading to an almost universal ban on their use in the mid-1970s.

However, because they take decades to break down, PCBs travel long distances, spreading far away from where they were first used, and continue to spread through ocean currents, wind and rivers.

Our study took place in the Atacama Trench, which covers nearly 6,000 kilometers (3,728 miles) of South America’s coastline.

The researchers collected sediment from five locations in the trench at different depths ranging from 2,500 to 8,085 meters.

Each sample was divided into five layers, from surface sediments to deeper clay layers, in each of which PCBs were found.

In this part of the world, ocean currents bring cold, nutrient-rich water to the surface, which means plenty of plankton — tiny organisms at the bottom of the ocean food web.

When plankton die, their cells sink to the bottom, carrying with them pollutants such as PCBs. But PCBs don’t dissolve well in water and instead prefer to bind to fatty tissues and other living or dead organisms such as plankton.

Because oceanic sediments contain many remains of dead plants and animals, they act as an important sink for pollutants such as PCBs. About 60% of PCBs released during the 20th century are stored in deep ocean sediments.

A deep trench, like an atacama, acts as a funnel, collecting parts of dead plants and animals that fall into the water.

There is a lot of life in the trench, so microbes work to break down the organic carbon in the coastal mud.

Organic carbon in the deeper parts of the Atacama Trench was found to be more decomposed than in the shallower parts. At deeper depths, the sediment also had higher concentrations of PCBs per gram of organic carbon.

Organic carbon in sludge degrades more easily than PCBs, which may remain and build up in landfills.

Storing pollutants means that ocean sediments can be used as a rear-view mirror in the past. It is possible to determine when a layer of sediment accumulated on the ocean floor, and by analyzing the pollutants in different layers, information can be obtained about their concentration over time.

In the Atacama Trench, PCB concentrations were high in surface sediments, which contrasts with what we typically find in lakes and oceans.

In general, higher concentrations are observed in the lower layers of deposited sediments from the 1970s to the 1990s, followed by decreasing concentrations toward the surface, reflecting the inhibition and reduction of PCB emissions.

Now, we still don’t understand why the Atacama is so different. We did not look closely enough at the sediment to detect small differences in PCBs, nor did the concentrations peak yet in this deep trench.

These concentrations are still very low, hundreds of times lower than in areas near sources of human pollution, such as the Baltic Sea. But the fact that we didn’t detect any pollution indicates the extent of humanity’s impact on the environment.

It is safe to say that the more than 350,000 chemicals currently in use worldwide come at the cost of polluting the environment and ourselves. Pollutants have now been discovered buried beneath one of the world’s deepest ocean trenches – and they’re not going anywhere.

The report was prepared by Anna Sobek, Professor of Environmental Chemistry and Chair of the Department of Environmental Sciences at Stockholm University. (Russia Today)