The route taken by small pieces of plastic after being deposited into the sea by northern European rivers is more complicated than you might think.

It is estimated that about 8 to 12 tons of plastic ends up in the sea every year, a large part of it via rivers. Half of that plastic consists of pieces smaller than half a millimeter – in other words: from microplastic. Mats Huserbruten from the Institute for Marine Research in Bergen, Norway and colleagues now have figured out which floating microplastic particles take off when they are discharged into the sea by Northern European rivers. They also pointed out a number of places where this plastic accumulates.

Two main routes

For their study, Huserbråten and his team simulated how the Rhine, Meuse and 19 other rivers in Northern Europe and the Arctic cause microplastics to end up in the sea every day, and how it moved through the sea in subsequent years. They also looked at the amount of plastic particles in seawater samples they collected from the Norwegian coast in 2017 and 2018.

This research shows that the plastic follows two main routes. The first, which is taken up by almost two thirds of the plastic particles, leads along the Norwegian coast to the laptevzee, north of Russia. Then the plastic crosses the North Pole, to frame street – between Greenland and Spitsbergen – to leave the Arctic Sea.

Roughly a third of the plastic also first moves north along the Norwegian coast, but then goes straight through Framstraat. This plastic then moves south along the Greenland and Canadian coasts.

Big consequences

Now it is not the case that all plastic leaves the polar region again via one of these two routes. The stuff appears to accumulate in particular between Iceland and Spitsbergen, in the Nansen basin (a deep part of the polar sea north of the island of Nova Zemlya), in the Barents Sea (west of Novaya Zemlya) and in the already mentioned Laptev Sea.

As for the researchers, their study shows that “floating microplastics and other synthetic particles can spend decades in the surface waters of the Arctic.” And according to Huserbråten and his team, that can have major consequences, for example for all kinds of animals that ingest the plastic.

Outdated data

Tim van Emmerik, who conducts research into plastic waste in rivers at Wageningen University and Research, notes that the Norwegian researchers do partly rely on outdated data. For the amount of plastic that ends up in the sea from rivers, they base themselves on a study from 2017† Last year, however, new estimates published. A difference between the two studies, explains Van Emmerik, is that in 2017 we still thought that the plastic mainly ends up in the sea via a small group of large rivers. But according to the latest insights, many more rivers are responsible for this.

Furthermore, says Van Emmerik, less plastic ends up in the sea via rivers than appears from these types of worldwide studies. “New findings suggest that most plastic doesn’t end up in the sea at all, but lingers in the rivers† A large part of the plastic that has reached the sea also quickly washes up on beaches.” In short, the question is whether there really is that much plastic from rivers in the Arctic.