Where does the Pyrenean snow plastic come from?

Industrial plastic pellets polluting the Atlantic coast are currently in the news. But microplastics are everywhere. In Occitania they can be found in the snows of the Pyrenees, in the air of the Pic du Midi and in the waters of the Garonne. “In 2019, we tested whether they are present in the upper atmosphere and found that some of them are present in snow and rain,” says Jeroen Soncke, who studies atmospheric pollutants at Pic du Soleil.

Based on this observation, a researcher at the Toulouse Geosciences Laboratory (GET) and his colleague Gael Le Roux, a researcher at the Laboratory for Functional Ecology and Environment (LEFE), embarked on a more ambitious project to try to understand the importance of the atmospheric cycle. in major plastic cycles, from large objects to microplastics, with the help of the Institute for Environmental Geosciences (IGE) in Grenoble.

Through literature synthesis work over the past twenty years, researchers were initially able to come up with an initial estimate of the amount of plastic in various ecosystems. “What is especially interesting is that we find a lot of them in the depths of the ocean, about 300 times more than on the surface, while we talk a lot about the famous 7th continent,” Jeroen Sonke alerted. But this is only 3% of the plastic that can be found on the continents. »

Vicious circle

Based on these figures, and using emission and atmospheric deposition fluxes, ocean deposition rates, and plastic degradation rates, the CNRS teams were able to create the first comprehensive mathematical model of the life cycle of plastics. “The dispersion of plastics is mainly due to the rivers that carry them to the oceans. It was also understood that there were land-based and marine releases to the atmosphere. Specifically, plastics from the continents that are found, for example, in agricultural soils using sewage sludge, are carried by winds or rivers and end up in the oceans.

But due to their long settling times, they can be carried back to the continents by sea breezes, for example, which explains their presence in the Pyrenees, as well as at the two poles or in the Himalayas. “This is a vicious circle. And the smaller the particles, the more dangerous they are for the entire ecosystem,” insists Jeroen Sonke.

A model that, given the amount of plastic being fragmented across the continents, is not going to break. The CNRS researcher assures us that, based on a scenario of ending plastic pollution in 2025, “it could go on for millennia.” “Instead of focusing on cleaning up the surface of the oceans, we should restore everything on earth before it ends up in the oceans,” says Jeroen Sonke, who believes in possible solutions, in particular through microbiology.