PCB traces found deep in the Atacama Trench reveal how pollution travels far from its source
Wastes from human activity are souring air, soil, rivers, and seas. Are there any pristine corners left on the planet. Even the deepest, darkest depths where sunlight never reaches show signs of contamination. A team of scientists has detected PCBs, or polychlorinated biphenyls, in sediments more than 8,000 meters below the ocean surface, confirming that these toxins remain a global challenge and can be carcinogenic.
The study, recently published in Nature Communications, shows traces of these organoflorine compounds in buried plant material and in sediment layers. The Atacama Trench is the world’s deepest trench, stretching about 5,900 kilometers off the coasts of Peru and Chile in the Pacific Ocean.
Researchers collected samples at multiple depths and found PCB traces across the spectrum, including at 8,085 meters below sea level.
“The Atacama Trench sits in a zone of relatively high surface plankton productivity, which drives the export of organic material to the seafloor as plankton dies,” explains Anna Sobek, the study’s lead author. “As plankton and other organic matter sink, they bind pollutants to lipids and organic carbon and transport them downward.”
The bottom of the trench acts as a sink for dead organic matter from both the water column and landslides on the seafloor, the researchers note.
“In deep-sea trenches, a large pool of organic carbon accumulates in the deepest zones, where dead plankton and a busy microbial community drive the decomposition process,” the authors elaborated. “In our measurements, sediment from the trench’s deepest parts contained a lower percentage of readily degradable organic carbon, yet higher concentrations of PCBs per gram of organic carbon in deeper sediments. The longer-lived PCBs remain after the organic carbon degrades, leading to accumulation.”
However, the authors caution that PCB levels in the Atacama Trench are not alarmingly high. As Professor Ronnie N. Glud, director of the Danish Hadal Research Center at the University of Southern Denmark and a study author, notes, much higher concentrations have been observed in places like the Baltic Sea, the North Sea, or Tokyo Bay.
The study’s images show that the trench’s bottom hosts PCB residues in notable amounts, despite the remote location and the protective depth that might seem to shield it from pollution.
“These sites experience substantial human activity nearby, so some level of contamination was anticipated. While Atacama samples do not show extreme concentrations, they are significant given their deep-water burial,” Glud adds.
There is limited data on pollutants in deep-sea trenches. Earlier work reported surprisingly high levels of PCBs and similar contaminants in sediments-dwelling organisms. The researchers conclude that future work will track how pollutants move through bottom-dwelling animals and how they might alter the ocean’s food web in trench ecosystems. They also plan to study how microbial communities in abyssal trenches contribute to breaking down certain pollutants.
In Japan’s Trench, new efforts will measure environmental pollutants at depths from 100 meters to 9,000 meters, a range never explored before, to understand the extent of contamination and possible degradation pathways through microbes in extreme environments.
Exposure to high PCB levels is linked to a range of health and biological effects. Skin issues, neurological and immune changes in children, and various cancers observed in animal studies are among the risks. In humans, occupational exposure has been associated with liver and biliary tract cancers. PCBs, due to their fire resistance and insulating properties, have historically been used in transformers, capacitors, sealants, inks, and other electrical components. They travel easily through air, water, and soil, and older equipment or fluorescent tubes may still harbor these chemicals. Experts emphasize that there are no natural sources of PCBs.
Overall, the research underscores how persistent pollutants travel through sea life and sediments, reaching even the most remote trenches. The work adds compelling evidence of the enduring footprint of industrial chemistry on global ecosystems and serves as a reminder of the need for continued monitoring and mitigation strategies. [Citation: Nature Communications study, attribution to the researchers involved]
Additional context is drawn from the broader body of literature on halogenated organics and deep-sea chemistry, highlighting the interconnectedness of ocean processes and human activity. The field continues to evolve as new methods reveal the hidden journeys of pollutants from their sources to the most distant corners of the planet.