More plastic in oceans than previously thought

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The amount of plastic in the oceans may have been significantly underestimated to date. When measuring plastic particles in the nanometer range, a research team discovered that their mass is probably greater than that of visible plastics and microplastics combined.

The measurement data comes from twelve locations in the North Atlantic, from coastal marine areas to the deep sea, and from temperate climates to the subtropics. The study by the research team led by Dušan Materić from the Helmholtz Centre for Environmental Research (UFZ) in Leipzig has now been published in the journal Nature.

For the uppermost layer of water, which is penetrated by sunlight and mixed by the wind, the team has extrapolated a mass of 27 million tons for the North Atlantic alone. “That is roughly the same order of magnitude as the estimated mass of macro- and microplastics for the entire Atlantic,” Materić is quoted as saying in a statement from his institute.

Upper layers are more polluted than lower layers

The UFZ chemist developed a special method for analyzing the water samples: a mass spectrometer that can precisely measure the concentrations of organic trace gases. When burned, the individual types of plastic leave behind a typical “chemical fingerprint.”

The researchers took samples from the top layer using an excellent filter at a depth of ten meters and five to 30 meters above the seabed and in the open ocean at a depth of 1,000 meters. In general, the pollution with nanoplastics was greater in the higher layers than in the deeper ones and greater in coastal areas than in the open North Atlantic.

The oceans contain more than just plastic waste visible to the naked eye

The research team was surprised to find that they could not detect the standard plastics polyethylene (PE) and polypropylene (PP) in the samples. “There is a lot of PE/PP microplastic on the ocean surface, but we did not find any PE/PP nanoparticles that could have been created as a result of solar radiation or abrasion by waves, for example,” said Materić.

Instead, they found polyethylene terephthalate (PET), polystyrene (PS), and polyvinyl chloride (PVC), all commonly used plastics found in disposable and reusable plastic bottles, films, disposable cups, and disposable cutlery, for example. Only PET was found in the deep sea.

Some zones are known as enrichment zones

The first five measurement sites were located in the vast North Atlantic subtropical gyre that surrounds the Sargasso Sea. Four other sites stretched between the gyre and the European mainland, and three sites were located near the coast, from the French to the Dutch Atlantic coast.

On average across all measurement sites, the study authors found 18.1 milligrams of nanoplastics per cubic meter of water at a depth of ten meters and 25 milligrams near the coast. Near the seabed, the average was 5.5 milligrams per cubic meter. In the upper layer, there was little difference between the measurement sites inside and outside the North Atlantic Gyre.

At a depth of 1,000 meters, the concentration within the gyre was 13.5 milligrams, almost twice as high as outside the gyre (7.5 milligrams). Due to ocean currents, the gyre is known as an accumulation zone for microplastics on the surface.