A Hirondellea gigas specimen collected at a depth of 35,820 feet in the Mariana Trench's Challenger Deep. A study in 2016 found high levels of organic pollutants in amphipods collected at 7,000–10,000 metres depth. Photo: JAMSTEC

By Jane Qiu
20 June 2016

(Nature) – Toxic chemicals are accumulating in marine creatures in Earth’s deepest oceanic trenches, the first measurements of organic pollutants in these regions have revealed.

“We often think deep-sea trenches are remote and pristine, untouched by humans,” says Alan Jamieson, a deep-ocean researcher at the University of Aberdeen, UK. But Jamieson and his colleagues have found man-made organic pollutants at high levels in shrimp-like crustaceans called amphipods that they collected from two deep-ocean trenches, he told a conference on deep-ocean exploration in Shanghai on 8 June 2016.

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

Before this work — which has not yet been published — the study of pollutants in deep-sea organisms had been limited to those that live at depths of 2,000 metres or less. The latest research tested for levels of organic chemicals in amphipods collected at 7,000–10,000 metres depth, from the Mariana Trench in the western Pacific Ocean — the world’s deepest trench — and from the Kermadec Trench near New Zealand.

The creatures were captured during two international expeditions in 2014, when researchers lowered uncrewed landers into the trenches as part of a research programme to study deep-ocean ecosystems, sponsored by the US National Science Foundation.

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 concentrations of PCBs in the amphipods from the Mariana Trench were particularly high, and 15 times greater than those found in the Kermadec. “It’s even higher than in the estuaries of two of the most polluted rivers — the Pearl River and the Liao River — in China,” says Jamieson. [more]

Man-made pollutants found in Earth's deepest ocean trenches

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