Since the Mariana Trench is the deepest part of the ocean, you might guess that it is safe from the impact of humans, but you would be wrong. Scientists have found that, despite its depth and remoteness, the deep sea contains levels of toxins that match some of the most polluted marine systems on earth.
According to a new study just published in the journal Nature Ecology and Evolution, man-made pollutants have reached the depths of two of the world's deepest ocean trenches -- the Mariana Trench in the North Pacific and the Kermadec Trench in the South Pacific, which are each miles deep and are separated by thousands of miles.
For the study, researchers from Newcastle University, the University of Aberdeen and the James Hutton Institute sent deep-sea landers to collect samples of small organisms living in the deepest level of the trenches and found troubling levels of toxic pollutants in small crustaceans, or amphipods.
The level found wasn't the only concern. The types of toxins they found are considered persistent organic pollutants (POPs) that are known for staying in the environment for a long time. In this case, the two most prevalent ones were Polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs).
Even though PCBs have been banned and PBDEs are heavily restricted, they're still clearly a pervasive environmental problem that are making their way through the food chain.
In the Mariana trench alone, the highest concentrations of PCBs found were approximately 50 times greater than the levels that have been found in crabs living near the Liaohe River, one of most polluted waterways in China.
"The fact that we found such extraordinary levels of these pollutants in one of the most remote and inaccessible habitats on earth really brings home the long term, devastating impact that mankind is having on the planet," said Dr. Alan Jamieson, lead author of the study, who is based in the School of Marine Science and Technology at Newcastle University. "It's not a great legacy that we're leaving behind."
It's not exactly clear how these pollutants made their way to the depths of the trenches, but scientists speculate that they came from contaminated plastic debris floating at the surface -- possibly from the Great Pacific Garbage Patch -- and from animals who have died and sank to the bottom, where they are consumed by amphipods, who are later consumed by larger animals. Scientists also hope to see more research into how these pollutants will impact the entire ecosystem, but for now it's a harsh reminder about how we're negatively affecting the planet.
To get a sense of the depth of Mariana Trench, consider that Mount Everest would fit into it with over a mile to spare. Alluding to that imagery, Dr. Jamieson wrote:
Of course, the pressure and depth are immense, which do require incredible physiological adaptations for survival, and equally clever engineering solutions for exploration, but the 11km that so easily swallows Mount Everest is still only 11km. Think of it like this: 11km is only half the length of Manhattan Island, I could legally drive it in less than six minutes, and Mo Farah could run it in less than 30 minutes.
The reality is that the deep sea just isn't that remote, and the great depth and pressures are only an imaginary defence against the effects of what we do "up here." The bottom line is that the deep sea -- most of planet Earth -- is anything but exempt from the consequences of what happens above it, and it's about time we appreciated that.