PCB, an environmental toxin discovered in a deep-sea trench.

PCB has been banned in most countries since the 1970s, but that doesn’t mean it’s no longer there. Now, deep sea researchers report that they have found PCBs at the bottom of the Atacama Trench in the Pacific Ocean.

During their expedition to the deep sea trench, the research team retrieved sediment samples and analyzed them for PCB presence at five different locations in the trench. All surface sediment samples analyzed contained PCBs.

The study, which was led by Professor Anna Sobek of the Department of Environmental Sciences at Stockholm University and Professor Ronnie N. Glod, Director of the Danish Center for Hadal Research at the University of Southern Denmark, is published in the journal. Nature Communications.

Polychlorinated biphenyls is short for Poly-Chlorinated Biphenyls, which covers 209 different substances. They were introduced in the 1930s and were mainly used in building materials and technical components, but are now banned in most countries and classified as highly persistent environmental toxins. PCBs can be carcinogenic and cause reproductive harm.

Although world production of PCBs decreased dramatically in the 1970s, these materials still pose an environmental threat. In 2018, researchers reported, for example, that half of the world’s population of killer whales is weakened by PCBs.

Another study found that deep-sea amphibian waste contains large amounts of PCBs.

Professor Rooney N. Glod, who has taken part in more than 10 expeditions to deep-sea trenches around the world, says.

These expeditions helped dispel the myth that deep-sea trenches are unaffected by what happens on the surface and provided insight into the surprisingly rich, vibrant, and diverse life in the ocean depths. Studies have also shown that deep-sea trenches accumulate large amounts of organic matter, which contributes to the ocean’s ability to absorb carbon released into the atmosphere through the burning of fossil fuels.

However, not only organic matter accumulates in deep-sea trenches, which are also called Hadal trenches. For example, the Danish Center for Hadal Research reported in 2021 that Mercury also accumulates in trench sedimentsAnd in 2022, a similar announcement was made for black carbon, particles formed primarily from the combustion of fossil fuels.

The concentration of PCBs in samples from the Atacama Trench is not alarmingly high, according to Ronnie N. He notes that much higher concentrations have been found in places like the Baltic Sea, the North Sea and Tokyo Bay. Concentrations 300 – 1,500 times higher have been measured in the Baltic Sea.

“These are places with a lot of human activity, so one would expect that. The Atacama samples don’t show very high concentrations, but given that they were recovered from a deep-sea trench bottom, they are relatively high. One would expect to find contaminants in Like this place.”

PCBs are hydrophobic, which means they are insoluble in water. Instead, they bind to organic matter that sinks to the bottom.

“The Atacama Trench is located in an area of ​​relatively high plankton production in the surface waters. When the plankton die, they sink to the ocean floor,” explains Anna Sobek.

In addition, large amounts of material are transported down steep slopes and deposited in the deepest areas.

Some of the organic material that reaches the bottom of the Atacama Trench is eventually decomposed by microorganisms and, as a result, PCBs build up in sediment.

PCBs are stable compounds that slowly re-deposit over time, which is why increased concentrations can be found in inaccessible areas such as the Hadal Trenches, despite being largely banned around the world in the 1970s.

“Unlike coastal regions where PCB concentrations are usually higher in the deeper sediment layers deposited 50 years ago, the PCB concentrations in the Hadal sediment are higher in the upper sediment layers, indicating that PCBs have not reached We have only recently reached deep trenches and concentrations have not yet peaked: we may see even higher concentrations in a few years,” says Rooney N. skins.

Deep sea trenches are home to many different microorganisms and animals that have adapted to the harsh living conditions. It may also be home to organisms that can metabolize pollutants that are deposited there.

This is one of the focuses of the Danish Center for Hadal Research, and for this research, the center has a robust inventory of frozen sediment samples collected from expeditions to various deep sea trenches in 2021 and 2022.

Ronnie N says: Glud.

Deep sea trenches are located in the Hadal region of the ocean, which lies at depths of 6-11 km. There are about 27 trenches in the deep sea, also called Hadal trenches, which are named after the Greek god Hades, who ruled the underworld.