Survival of the fittest in the depths of the sea likely includes plenty of its own inherent challenges, but now it's got a man-made one to add to the list. A research team out of Scotland's University of Aberdeen has discovered high concentrations of human-created organic pollutants in crustaceans gathered from two deep-ocean trenches, putting to rest any hope that people haven't managed to muck up even the world's most far-flung locations. "We often think deep-sea trenches are remote and pristine, untouched by humans," lead researcher Alan Jamieson tells Nature, which notes he delivered his announcement about the find at a deep-sea exploration conference in China on June 8 and that the research has yet to be published. The work involved scientists lowering two unpeopled landers about 6 miles deep in 2014: one into the Mariana Trench in the western Pacific Ocean, and the other into the Kermadec Trench near New Zealand.
They then tested the amphipods—tiny crustaceans that resemble shrimp—they found down there and discovered the creatures had polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), both hard-to-break down, carbon-based compounds used to make plastics and as flame retardants. The PCB concentration in Mariana Trench amphipods was especially stunning—15 times that of the crustaceans in the Kermadec. Researchers believe the high PCB levels may be due to the Mariana Trench's relative closeness to Asian plastic manufacturers. "The take-home message is that when you dump rubbish into the sea, it will ultimately sink," Jameieson says. "When [pollutants] fall into the trenches, they have nowhere else to go. So they’re just going to keep building up." (Plastic is also floating around the ocean via human feces.)