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Deep sea littered with plastic debris

Deep-sea sediments are accumulating tiny fragments of plastic in surprisingly high concentrations, scientists have discovered. The accumulations represent a previously unknown repository of global plastic waste.

Marine plastic debris in surface waters and coastal sediments is already a significant problem, affecting wildlife, tourism and shipping. And now the discovery of plastics in the deep sea, including particles found on corals, poses another potential threat to marine life.

The new study, published today in Royal Society Open Science, reveals around four billion microscopic plastic fibres could be littering each square kilometre  of deep sea sediment around the world.

The discovery was made by scientists from the Museum, the University of Oxford, the Scottish Association for Marine sciences, the University of Plymouth and the University of Barcelona.

Where has all the plastic gone?

Plastic production has increased exponentially in the last couple of decades, but this has not led to a rise in plastic waste in surface waters and coastal sediments.

Oceanographers have long wondered where all the extra plastic is going. The discovery of plastic debris in deep-sea sediments explains where all this missing plastic waste has gone.

The deep-sea plastics are in the form of microplastic fibres – microscopic fragments. They can be small by design or formed by the breakdown of larger pieces.

Over half of the fragments recovered by the team were bits of the semi-synthetic fibre rayon, used extensively in clothing.

Surprising find

The researchers analysed samples of deep-sea sediment from locations across the Mediterranean, the northeast Atlantic, and the southwest Indian Ocean.

Museum marine biologist Dr Lucy Woodall spotted bright blue and red fibres in the cores of sediment she had extracted as part of a project to study seamounts in the southwest Indian Ocean.

She began to systematically pick through her samples for plastic fragments, sending them to the University of Plymouth for chemical analysis. A quick search showed that deep-sea microplastics have previously been undocumented in scientific literature.

Unknown impact

As part of the seamount project Dr Woodall also took samples of corals, and she was surprised to find that they also hosted microplastics.

‘It is alarming to find such high levels of contamination, especially when the full effect of these plastics on the delicate balance of deep-sea ecosystems is unknown,’ Dr Woodall said.

Few studies have looked at the impact of microplastics, but it is known that they can absorb pollutants and even be ingested by organisms.

Prof Richard Thompson from Plymouth University said: ‘The deep sea habitat extends to more than 300 million square kilometres globally, so the discovery of previously under-reported microplastics suggests there may be even greater accumulation than was previously suspected.’

‘The discovery of substantial quantities in deep-sea sediments is of considerable relevance to our understanding of the potential of these particles to cause harm in the marine environment.’

The great ocean bottom garbage patch?

A vast accumulation of plastic particles including microplastics in the surface waters of the north Pacific, known as the Great Pacific garbage patch, had previously brought the world’s attention to the problem of plastics in the marine environment.

However, the recent discovery of the previously unknown microplastic fibres found in deep-sea sediments may be a much bigger problem – the concentrations found by researchers are considerably larger than those found in the Great Pacific garbage patch.