Decades after manufacturers have stopped producing a class of harmful chemicals once used in electrical equipment, traces of these chemicals have found in a deep sea trench.
In a study published in Nature Communications, researchers report detecting PCB chemicals at the bottom of the Atacama Trench off the coast of South America. During an expedition in 2018, a team retrieved sediment cores from five locations along the trench. The depths for these samples ranged from 2,500 meters (3 km) to 8,000 meters (8 km). “We found PCBs in sediment across all sites in all of the 50 sediment layers,” the study authors wrote.
PCBs, or polychlorinated biphenyls, are synthetic chemicals that were once widely used in appliances and building materials. People were often exposed by eating animals and plants that contained PCBs, and communities located near superfund sites can be exposed, too, according to the Centres for Disease Control and Prevention. PCB chemicals make up more than 200 substances and were banned throughout the world in the 1970s and 1980s. Researchers have since linked PCBs to health concerns like immune system and hormonal disruptions. Some PCBs can break down in the environment, according to the National Oceanic and Atmospheric Administration. However, how they break down depends on the environment the chemicals are in and the chemical makeup of the particular PCBs. Hence why scientists are able to find these chemicals in sediments the bottom of the ocean more than 30 years after they were banned.
Ronnie N. Glud, one of the study authors and director of the Danish Centre for Hadal Research at the University of Southern Denmark, said the amount of PCBs detected in the Atacama Trench are not extremely high. Other bodies of water, like the Baltic Sea, have concentrations at 300 times higher. However, the location is what alarmed researchers. “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. No one would expect to find pollutants in such a place,” Glub said in a press release.
This also alarmed researchers because PCB chemicals do not easily break down in water, according to the study. The chemicals bind to organic material that eventually sinks to the ocean floor. This has allowed the toxins to accumulate in the trench.
There isn’t a lot of information about pollutants in deep sea trenches, and the scientists involved in the new study want to keep analysing pollutant concentrations in the ocean. One of the researchers involved is planning to travel to Japan to deploy samplers in the Japan Trench.
“In future studies, we will also study the uptake in bottom-dwelling animals to try to understand how pollutants spread and can affect the food web in the deep sea trench. We will also study how the microbial community in the deep sea trench may contribute to the degradation of certain pollutants,” said Anna Sobek, lead author of the study.
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