Highest-ever concentration of microplastics found on seafloor: scientists

This file photo shows microplastic particles swirling around in the ocean. (EXTREME-PHOTOGRAPHER / Istock.com)

TORONTO — Scientists say they have discovered the highest levels of microplastics ever recorded on the seafloor.

As part of an international research project led by the University of Manchester, scientists were able to uncover a staggering 1.9 million pieces of microplastics in a single square-metre of the ocean’s floor in the Mediterranean.

In a study, published in the journal “Science” on Thursday, the researchers showed how deep-sea currents act as conveyor belts to transport and deposit tiny plastic fragments and fibres across the seafloor.

As a result of these currents, “microplastic hotspots” or large accumulations can occur in certain locations, the study said.

“Almost everybody has heard of the infamous ocean ‘garbage patches’ of floating plastic, but we were shocked at the high concentrations of microplastics we found in the deep seafloor,” Ian Kane, the study’s lead author and an earth scientist at the University of Manchester, said in a press release.

“We discovered that microplastics are not uniformly distributed across the study area; instead, they are distributed by powerful seafloor currents which concentrate them in certain areas.”

While people often think of microplastics as tiny pieces of plastics in exfoliants, detergents, and glitter; the deposits found in the study area of the Tyrrhenian Sea, which is part of the Mediterranean Sea, consisted primarily of fibres from textiles and clothing.

These types of microplastics can easily enter rivers and oceans because they’re not effectively filtered out in domestic waste water treatment plants, the researchers said.

According to the scientists, more than 10 million tons of plastic waste enter the oceans each year.

And although there has been much attention given to floating debris, such as plastic drinking straws and bags, which are visible on the surface, it only accounts for one per cent of the plastic that enters the world’s oceans.

The other 99 per cent of plastic waste is believed to be somewhere below the surface in the depths of the oceans.

The difficulty for scientists, however, has been locating where exactly all that plastic waste has wound up in the oceans.

That is why the international team set out to determine how deep ocean currents affects the location of microplastic hotspots. To do this, they collected sediment samples from the seafloor of the Tyrrhenian Sea and combined them with calibrated models and deep ocean currents and detailed mapping of the seafloor. They then analyzed all the samples using infra-red spectroscopy to determine the different plastic types.

“Our study has shown how detailed studies of seafloor currents can help us to connect microplastic transport pathways in the deep sea and find the ‘missing’ microplastics,” Mike Clare, a co-lead on the project and a researcher at the National Oceanography Centre, said.

The researchers said understanding where the microplastic hotspots are is vital because deep ocean currents carry oxygenated water and nutrients, which means these areas are also likely to house important ecosystems with marine life that can consume or absorb the harmful plastics.

“The results [of the study] highlight the need for policy interventions to limit the future flow of plastics into natural environments and minimize impacts on ocean ecosystems,” Clare said.