Very high levels of man-made pollutants and toxic chemicals — including polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs) — have been found in animals living in some of he deepest oceanic trenches in the world, according to brand new as yet unpublished research.

The work involved the collection of small shrimp-like creatures, including Hirondellea gigas (shown), from the Mariana Trench in the western Pacific Ocean, and from the Kermadec Trench near New Zealand — at depths of 7,000 to 10,000 meters. The Mariana Trench is of course actually the deepest trench in the world — meaning that man-made persistent organic pollutants (POPs) are now accumulating en masses even in the most remote parts of the ocean.

The collections were part of a 2014 US National Science Foundation sponsored research program focused on deep-sea ecosystems.

“We often think deep-sea trenches are remote and pristine, untouched by humans,” commented Alan Jamieson, a deep-ocean researcher at the University of Aberdeen, UK. But the research shows clearly that that simply isn’t the case. A great deal of earlier research conducted in less-remote parts of the ocean painted a similar picture though — with the great prevalence of plastic debris on the ocean floor being a common finding.

“It’s really surprising to find pollutants so deep in the ocean at such high concentrations,” stated Jeffrey Drazen, a marine ecologist at the University of Hawaii in Honolulu.

An article on the findings published in Nature provides more, stating that in “both trenches, the amphipods contained polychlorinated biphenyls (PCBs) — used to make plastics and as anti-fouling agents to stop barnacles growing on ships’ hulls — and polybrominated diphenyl ethers (PBDEs), which are used as flame retardants. Both chemicals are man-made and belong to a category of carbon-based compounds called persistent organic pollutants (POPs) because they are hard to break down. Production of PCBs — which are carcinogens — has been banned in many countries since the late 1970s; PBDEs, which animal studies suggest may disrupt hormone systems and interfere with neural development, are only now being phased out.”

The part that’s particularly interesting though is that the concentrations of PCBs in the amphipods studied that came from the Mariana Trench were incredibly high — somehow even 15 times higher than those collected from the Kermadec Trench.

“It’s even higher than in the estuaries of two of the most polluted rivers — the Pearl River and the Liao River — in China,” stated Jamieson.





Continuing: “By contrast, the Kermadec Trench contains PBDEs at concentrations 5 times greater than the Mariana — and at a level that is higher than in the coastal waters of New Zealand’s North Island, the study finds. The researchers suspect that the proximity of the Mariana Trench to large plastic manufacturers in Asia, as well as to a long-term US military base on the island of Guam, may have contributed to its high PCB levels. The waters above the trench are also part of the North Pacific gyre, a system of strong swirling ocean currents that might be sucking materials on the surface down into the deep sea. Both the Mariana and Kermadec trenches are around 11 kilometers deep.”

“The take-home message is that when you dump rubbish into the sea, it will ultimately sink. When (pollutants) fall into the trenches, they have nowhere else to go. So they’re just going to keep building up,” noted Jamieson.

The researcher also noted that the trenches will no doubt end up being home to far higher levels of pollutants than estuaries, as they are essentially the end of the line.

“It sounds quite deep, but it’s not in terms of pollutant transport,” Jamieson stated.

What affect will these extremely high levels of man-made pollutants have on the life that’s local to these trenches? And, on a broader level, what state will the planet’s oceans be in following another century or so of (growing) industrial activity and consumer culture?