Plastic pollution is one of the great challenges of the 20th century. We already know that microplastics, those tiny synthetic particles with a very low capacity to degrade, are everywhere: in water, in Arctic ice, in the salt with which we season our food and, of course, also in the air. Through the atmospheric global circulation, plastic debris can travel long distances and end up being deposited in places very far from the origin, as has been analyzed in a work that has just been published in PNAS magazine.
Road microplastics
The authors, from different universities in the US and Europe, have studied how these invisible pieces enter the atmosphere, how long they remain in the air and where in the global system are the hot spots of deposition of microplastics. The results show how, on the west coast of the United States, the main source of deposition is the so-called “road microplastics”, which come from the wear of tires, brakes and other parts of the vehicles or the road itself. A few months ago, a study published in the journal Nature Communications revealed that this source of contamination is not negligible: they constitute 30% of microplastics in oceanic and freshwater ecosystems.
On the other hand, the ocean waves are loaded with insoluble plastic particles that were once food wrappers, soda bottles or plastic bags and that move towards the upper layer of the water. There they are stirred by the waves and the wind and catapulted into the air. Another important source of re-emission of plastics is the dust produced in agricultural fields. In addition, the wind can be another important factor in the vicinity of population centers. “Once in the atmosphere, plastics can stay in the air for up to 6.5 days, long enough to cross a continent, ” explains Natalie Mahowald, co-author of the article.
Where are they deposited?
The results of the model revealed that the Pacific Ocean and the Mediterranean Sea are hot spots for deposition of plastic waste, but that the continents are also large receptors and, in fact, receive more net plastics from polluted ocean sources than they send. The US, Europe, the Middle East, India and East Asia would also be hot spots on the mainland.
The most relevant sources of contamination are also variable depending on the region. Thus, on the coasts oceanic sources are more important, in North Africa and Eurasia the main origin is found in agricultural residues, while sources produced by roads had a great impact in densely populated regions around the world.
For the authors, this study is important but it is only the beginning and it is necessary to analyze much more how the transport and deposition of plastic pollution works in humid climates versus dry climates, mountains versus plains, etc. The world hasn’t slowed down its production and use of plastics, which is why these questions become more urgent with each passing year.
