PCB has been found at the bottom of the Atacama Trench in the Pacific Ocean. PCBs, or polychlorinated biphenyls, are industrial products or chemicals. They have been banned in most countries since the 1970s.

Although banned, previous use of them means they can still be found polluting our environment.

PCBs can be found worldwide. In the 1960s, when initial research results were released, traces of PCBs could be detected in people and animals around the world – not only in heavily populated areas such as New York City, but also in remote areas as far as the Arctic. These findings of such widespread and persistent contamination contributed to the banning of the chemical in 1979.

What are PCBs?

And now deep sea researchers from Denmark have found PCB in the Atacama Trench.

The Danish Center for Hadal Research reported in 2021 that mercury also accumulates in the trenches’ sediments, and in 2022, a similar announcement was made about black carbon, which is particles that are mainly formed by the combustion of fossil fuels.

Professor Ronnie N. Glud, director of the Danish Center for Hadal Research at the University of Southern Denmark explained:

“The Atacama samples do not show very high concentrations but considering that they were retrieved from the bottom of a deep-sea trench, they are relatively high. A priori no one would expect to find pollutants in such a place.

“Unlike coastal areas where PCB concentrations are typically higher in deeper sediment layers deposited 50 years ago, PCB concentrations in hadal sediments are highest in the upper sediment layers, indicating that PCBs have only recently reached the deeper trenches and that concentrations have not yet peaked: We may see higher concentrations in a few years.”

PCBs were made for things such as microscope oils, electrical insulators, capacitors, and electric appliances such as television sets or refrigerators. PCBs are hydrophobic, meaning they are not very soluble in water. Instead, they bind to organic material that sinks to the bottom.

Professor Anna Sobek from the Department of Environmental Science at Stockholm University explained:

“The Atacama trench is located in an area with relatively high production of plankton in surface waters. When the plankton dies, it sinks to the bottom of the ocean.” Some of the organic material that reaches the bottom of the Atacama trench is eventually decomposed by microorganisms, and as a result, PCBs accumulate in sediment.

Click on this link to access, Organic matter degradation causes enrichment of organic pollutants in hadal sediments, published in Nature Communications.