Extremely high levels of pollution have been found in two of the Earth’s deepest oceanic trenches, reports a paper published online this week in Nature Ecology & Evolution. The study suggests that such high levels of pollution in trenches over 10 kilometres deep, which are far from industrial zones and nearly 7,000 km apart, is evidence that anthropogenic surface pollution can reach the farthest corners of the earth.
Alan Jamieson and colleagues find that amphipod crustaceans - which live 10,000 m below sea-level - contain similar levels of contamination to Suruga Bay, one of the most polluted industrial zones of the northwest Pacific. They used deep-sea landers able to plumb the depths of the Pacific Ocean’s Mariana and Kermadec trenches in order to bring up samples of the organisms that live in the deepest levels of the trenches. They found extremely high levels of persistent organic pollutants (POPs) in the fatty tissues of the amphipods, including polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) which are commonly used as dielectric fluids and flame retardants, respectively.
The authors suggest that the pollutants most likely found their way to the trenches through contaminated plastic debris and carrion-fall sinking to the bottom of the ocean, where they are then consumed by amphipods.
In an accompanying News & Views article, Katherine Dafforn writes: "Jamieson et al. have provided clear evidence that the deep ocean, rather than being remote, is highly connected to surface waters and has been exposed to significant concentrations of human-made pollutants."