Plastic waste is abundant thoughout all oceans of the world. Plastic particles are ingested by marine animals. Most of them are excreted lateron, but a small portion can pass through the intestinal wall and enter the bloodstream.
Analyzing plastic nanoparticles is a challenge
While macro- and microplastic particles are easier to detect and their concentrations are easier to determine, quantitative data of particles smaller than 1 µm have been scarce. This is due to their size and the fact that standard measuring methods often fail in distinguishing between plastic and environmental particles.
In their 2020 expedition aboard the RV Pelagia, the largest Dutch vessel and flagship of the NIOZ, researchers from the UFZ and Utrecht University recorded the occurrence of nanoplastic along a transect from the European continental shelf to the subtropical North Atlantic Gyre. Samples were taken at 12 measuring points: in the uppermost water layer at around 10 m, in the intermediate layer at around 1,000 m, and 30 m above the seabed.
Dušan Materic / UFZ (left) and Helge Niemann (NIOZ) taking samples in the North Atlantic
„With the data from these measuring points, we can make statements about the vertical and horizontal distribution of nanoplastic in the North Atlantic“, says Dr Dušan Materic, chemist at the UFZ and lead author of the study.
Analysis method
For analyzing the amounts of nanoplastic the scientists used a high-resolution proton transfer mass spectrometer (PTR-MS) coupled with thermal desorption (TD). With this system, the plastic particles are combusted. In this process, gases are released that can be quantified in the mass spectrometer.
Dušan Materic developed this method while working at Utrecht University. According to him each polymer produces a distinct chemical fingerprint in the mass spectrometer, which allows to reliably determine its identity and concentration.
Nanoplastic in all depths
The researchers detected nanoplastic at all depths analysed across the 12 measurement sites.
„They are present everywhere in such large quantities that we can no longer neglect them ecologically“, says Materic.
The plastic nanoparticles found mostly were from polyethylene terephtalate (PET; polystyrene (PS) and polyvinyl chloride (PVC). These polymers are commonly used in disposable and reusable plastic bottles, films, drinking cups, and cutlery.
At nearly all measuring points, the reserachers detected these types of plastic in the uppermos water layer. „This is because, on the one hand, the redistribution from the atmosphere occurs via the sea surface and, on the other hand, a lot of
plastic is introduced via the estuaries of rivers“, says Materic.
The intermediate layer (i.e. the layer between the oxygen-rich surface water and the oxygen-depleted deep water) is dominated by PET
nanoparticles. According to Materic, a higher concentration of nanoplastic was found in the North Atlantic subtropical gyre, an area
where surface microplastics are known to accumulate because of ocean currents.
The lowest nanoplastic concentrations were detected near the sea floor. PET nanoparticles were found at any measuring point there, even at depths of more than 4,500 m. But the researchers did not find PP or PE nanoparticles in these depths. The researchers assume that the PE and PP nanoplastic may be minderalized or molecularly altered, so that they are no longer detected as plastic by the PTR-MS, or there might be some other dynamic processes that they were not aware of.
Even nanoparticles add up to tons of material
The scientists extrapolated the mass of nanoplastic in the North Atlantic from the concentration measurements. Based on these results, around 27 million tonnes of nanoplastic – 12.0 million tonnes of PET, 6.5 million tonnes of PS, and 8.5 million tonnes of PVC – are stored in the uppermost water layer of the North Atlantic, up to 200 m deep, from the temperate to the subtropical zone.
„This is in the same order of magnitude as the estimated mass of macro- and microplastics for the entire Atlantic“, says Materic.
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