Extraordinary levels of pollution 10km deep in the Mariana trench, say scientists

The Guardian reports, 13th February 2017: Scientists have discovered “extraordinary” levels of toxic pollution in the most remote and inaccessible place on the planet — the 10km deep Mariana trench in the Pacific Ocean.

Small crustaceans that live in the pitch-black waters of the trench, captured by a robotic submarine, were contaminated with 50 times more toxic chemicals than crabs that survive in heavily polluted rivers in China.

“We still think of the deep ocean as being this remote and pristine realm, safe from human impact, but our research shows that, sadly, this could not be further from the truth,” said Alan Jamieson of Newcastle University in the UK, who led the research.

“The fact that we found such extraordinary levels of these pollutants really brings home the long-term, devastating impact that mankind is having on the planet,” he said.

Jamieson’s team identified two key types of severely toxic industrial chemicals that were banned in the late 1970s, but do not break down in the environment, known as persistent organic pollutants (POPs

The research, published in the journal Nature Ecology and Evolution, suggests that the POPs infiltrate the deepest parts of the oceans as dead animals and particles of plastic fall downwards. POPs accumulate in fat and are therefore concentrated in creatures up the food chain. They are also water-repellent and so stick to plastic waste.

The very bottom of the deep trenches like the Mariana are inhabited by incredibly efficient scavenging animals, like the 2cm-long amphipods we sampled, so any little bit of organic material that falls down, these guys turn up in huge numbers and devour it,” said Jamieson.

The level of one type of POP, called polychlorinated biphenyls (PCBs), was only equalled anywhere in the northwest Pacific in Suruga Bay in Japan, an infamous pollution blackspot. The researchers also found severe contamination in amphipods collected in the Kermadec trench, which is 7,000km from the Mariana trench. The pollution was ubiquitous, found “in all samples across all species at all depths in both trenches”, the scientists said.

PCBs were manufactured from the 1930s to the 1970s, when their appalling impact on people and wildlife was realised. About a third of the 1.3m tonnes produced has already leaked into coastal sediments and the open oceans, with a steady stream still thought to be coming from poorly protected landfill sites.

The results are both significant and disturbing, said the marine ecologist Katherine Dafforn at the University of New South Wales in Australia and not part of the research team: “The trenches are many miles away from any industrial source and suggests that the delivery of these pollutants occurs over long distances despite regulation since the 1970s.


Source: The Guardian, 13th February 2017. For the full details, see www.theguardian.com/environment/2017/feb/13/extraordinary-levels-of-toxic-pollution-found-in-10km-deep-mariana-trench


Marinet observes: The levels of toxic chemicals in marine life at such depths may seem surprising, and the explanation offered by these scientists is plausible. However there is an alternative explanation.

Prior to 1975 a very wide range of toxic waste (chemicals and nuclear materials) were dumped at sea. A favourite location for this dumping were the ocean trenches, “abyssal depths” as they are also termed, which are deep trenches/valleys in the ocean floor. One such trench lies off the SW approaches to the UK in the Atlantic, and the UK used to dump considerable amounts of nuclear waste in this “abyssal depth” in the belief that it would never be disturbed and was so deep that no life could exist there. We now know differently, and life abounds as such depths.

The dumping of these wastes was first forbidden by the “Convention on the Prevention of Marine Pollution by Dumping of Wastes and Other Matter 1972”, known as the London Convention, which came into force in 1975. It has been signed by 87 States, including the United States and the UK.

In 1996 the Convention was modernised and, eventually in 2006, came into operation being known as the “London Protocol”. The Protocol is far stronger than the Convention in its terms, taking the precautionary approach which prohibits all dumping except for a “reverse list” of materials (see below). The London Protocol has been signed by 48 States, but not by the United States.

Materials which can gain exemption from dumping by the 48 States include dredged material, sewage sludge (beyond 3 nm if pulverized and beyond 12 nm if not), organic material of natural origin, fish wastes, vessels and platforms, inert inorganic geological material (mining waste), bulky items of iron/steel/concrete, and carbon dioxide streams for sequestration. Of course for those States which have not signed the London Protocol (e.g. United States) these limitations do not apply.

It is therefore distinctly possible that the high levels of PCBs (polychlorinated biphenyls, a toxic chemical liquid used as a lubricant and insulator in large electrical equipment) and the other toxic chemicals found in the marine life in the Mariana trench are due to historical dumping activities by industrialised nations in the Pacific area who saw the Mariana trench as a “suitable abyssal depth” for their disposal needs.

Fortunately such toxic dumping is now outlawed, but the environmental life of these toxic chemicals is very long-lived, and because they accumulate in fatty material in an animal’s body they are passed up the food chain, e.g. from lower forms of life to the body of their predators.

As the levels of PCBs and other toxic chemicals are so high in the Mariana trench and far higher than elsewhere, it therefore seems probable that the trench has been used in the past for the dumping of toxic chemical wastes.

The UK has signed the London Protocol, and it is time the United States did so too along with all the other countries who have not, see list here.


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