Polychlorinated biphenyls (PCBs) are tough chemicals. Created mainly for electrical equipment, and also during waste incineration, their production was banned starting in 1979 due to cancer risk and other health worries. But PCBs have resisted degradation and spread far and wide, reaching the Arctic and Antarctic. Now, researchers report finding PCBs in crustaceans living in two of the deepest trenches in the ocean. During two expeditions in 2014, an international team collected wildlife from the Mariana Trench in the North Pacific and the Kermadec Trench in the South Pacific. When they analyzed small, shrimplike crustaceans called amphipods (pictured), they detected “extraordinary” levels of many kinds of PCBs, exceeding those of polluted waters at the surface. The most contaminated samples from the Mariana Trench—a long submarine canyon, south of Japan, nearly 11 kilometers deep—had concentrations 50 times greater than crabs studied in a highly polluted Chinese river, the team reports this week in Nature Ecology & Evolution. The amphipods also contained polybrominated diphenyl ethers, another type of persistent pollutant widely used as flame retardants. The toxic chemicals most likely sink into the trenches in decaying bits of carrion or with bits of plastic; the Mariana Trench sits under a huge collection of trash known as the Great Pacific Garbage Patch. Bottom line: Even the bottom of the ocean isn’t safe from human pollution.
Correction, 14 February 12:10 p.m.: This story has been updated to reflect that PCBs aren’t a by-product of electrical equipment and that the Mariana Trench is located under garbage patch in the western Pacific; the “Great Pacific Garbage Patch” generally refers to another patch in the eastern Pacific.