Chemicals banned in 1970s discovered in deep ocean fauna

Not even the world's deepest ocean trenches are free of pollution, scientists discover

All of this is to say that "our proximity to these extreme locations is far from remote, which is why even the deepest chasms of the ocean are no longer pristine", the authors note in the paper.

To collect samples in each of these remote trenches, in 2014 the researchers used a deep-sea lander operated remotely from the surface and baited traps to collect tiny crustaceans.

Rather, they had similar contamination levels to crustaceans in Japan's Suruga bay, which is one of the most contaminated industrial zones of the northwest Pacific.

Sampling amphipods from the Marianas and Kermadec trenches, Newcastle University's Dr Alan Jamieson led a study that found extremely high levels of pollution in the organism's fatty tissue.

Wherever humans go, we usually leave a trail of pollution behind, and it seems this applies even to the road untraveled, like unexplored parts of the ocean's deepest trenches.

The researchers, from the University of Aberdeen and the James Hutton Institute in the United Kingdom, focused on two specific types of chemical pollutants: polychlorinated biphenyls, or PCBs, and polybrominated diphenyl ethers, or PBDEs, both of which may cause a variety of adverse health effects, including neurological, immune and reproductive issues and even cancer (in humans). But researchers estimate 1.3 million tonnes of PCBs were produced worldwide.

"We're very good at taking an "out of sight, out of mind" approach when it comes to the deep ocean but we can't afford to be complacent", he added.

"What we don't yet know is what this means for the wider ecosystem, and understanding that will be the next major challenge".

As indicated by their name, POPs do not degrade easily and are believed to be able to persist in the environment for decades at least.

It also shows a strong connection exists between surface and deep-sea waters and suggests a need for better management and monitoring of these unique environments.

The PCBs and flame retardants found in the trenches can have "devastating effects on the hormonal, immune and reproductive systems", wrote Katherine Dafforn, an ecotoxicologist at the University of New South Wales, in an article accompanying the study.

"Despite temperatures that hover around 1C and pressures over 1,000 times greater than at the surface, deep sea trenches ... support significant endemic biodiversity", she wrote.

The findings of Dr Jamieson's team were, she said, "disturbing".

"However, there is increasing evidence that the unique marine creatures in these trenches are threatened by human-made pollution". In fact, in the Mariana trench, the highest observed concentrations of PCBs were about 50 times greater than the levels that have been found in crabs living near China's Liaohe River, one of that nation's most polluted waterways.

"Manufactured chemicals such as DDT, originally used in pesticides, are part of an extensive group of carbon-based substances now classified as POPs".

Banned in the 1970s, PCBs were once widely used as dielectric and coolant fluids in transformers, capacitors and other electrical devices. The chemicals bond with bits of plastic and other kinds of organic debris, and are transported in air, soil and coastal waters.

These pollutants then accumulate through the food chain so that by the time they reach the deep ocean, concentrations are many times higher than in surface waters.

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