The bright red weather station on the summit of the Hoher Sonnblick in Austria can hardly be overlooked, even from afar. However, what is happening in the snow next to it cannot even be seen with the help of a microscope. Almost every day, many billions of plastic particles that are smaller than 200 millionths of a millimeter and thus as tiny as viruses land on one square meter of winter white. This is the conclusion reached by an international team that has developed a new detection method for the nanoplastic content. According to the study most plastic debris is blown from cities, many over hundreds of miles, from London, Paris and Amsterdam.
Nanoplastics are formed when plastics continue to crumble under the influence of UV light, wind and weather. It is the final stage of plastic decomposition, so to speak, whether it started with a toothbrush, garden furniture or fishing net, abrasion from car tires or fibers from fleece jackets. Because the nanoparticles are similarly small to biomolecules, they are considered to be of particular concern. They can be inhaled or swallowed, possibly spread throughout the body and, according to laboratory experiments, even penetrate cell membranes – with unclear consequences for humans and nature.
Considerable amounts of microplastics were found in the Swiss Alps two and a half years ago, i.e. particles with diameters between one thousandth and five millimeters. However, the detection of the smaller nanoplastic particles is considered to be particularly difficult and was not the focus of science for a long time. The researchers led by Rupert Holzinger from Utrecht University in the Netherlands originally had other plans when, a few years ago, they shoveled snow into small bottles next to the weather station every day for six weeks. “Actually, we wanted to examine the samples for particulate matter using a new measurement method. At first, the nanoplastic was just a by-catch,” says Holzinger.
But the researchers couldn’t let go of the topic and they developed a new analysis method. To do this, they thawed the Sonnblick snow samples in the laboratory, filtered out all particles smaller than 200 nanometers, heated this mixture to up to 300 degrees Celsius and analyzed the vapor in a mass spectrometer. They looked for characteristic patterns of different types of plastic in the measurement signals – and found what they were looking for. After that, the plastics PET (polyethylene terephthalate) and PP (polypropylene) were the most common in the snow. Tire abrasion, on the other hand, which accounts for the lion’s share of microplastics, was hardly found. The team has not yet given an explanation for this.
“We also measured the total mass of the nanoplastic mixtures in one milliliter of melted snow and derived deposition rates from this,” says Holzinger. The amounts of plastic that entered fluctuated greatly, but increased even when it had not snowed. Apparently, the plastic crumbs trickled to the ground even when the sun was shining. Roughly estimated, almost one milligram of nanoplastic fell on one square meter of snow in one week, which corresponds to at least 200 billion particles. Of course, this number sounds much more dramatic, the researcher admits. “How it is to be evaluated ultimately depends on whether it actually causes damage. And we just don’t know that.”
North Pole, South Pole, mountain peaks: the plastic particles have spread all over the world
The researchers, on the other hand, see the origin of the particles more clearly. Because the tiny particles behave like a gas that flows with the air, the team was able to use weather models to trace the paths of so-called air parcels. “We calculated, so to speak: where and for how long was an air parcel that ultimately lands on the Sonnenblick previously in contact with surfaces in Europe,” says Dominik Brunner from the EMPA research institute in Switzerland, who was responsible for the simulations. Accordingly, the longer the corresponding air packet had previously hung over urban areas, the more nanoplastic was found on the Sonnblick. Some could even have been blown into the Alps from the Atlantic.
Ulrike Braun from the Federal Environment Agency thinks it’s good that the air is getting more attention as a source of small plastic particles. “For a long time, no one really had the air transport path on their radar, because it was clear that nanoparticles were the main en route there. And up until now, you couldn’t map them well,” she says. The new procedure is sound and the quantities determined are plausible. The only question is whether the method is also suitable for routine measurements. “We simply no longer need the one spectacular measurement that shows that there are a great many plastic particles in the air. We already know that they are everywhere, at the North Pole, the South Pole and of course also in the Alps. What we need is 100 Measurements in one place, reliable monitoring,” says Braun. However, such a thing is still pending when it comes to microplastics, partly because there are no standards for sampling.
“We’re still at the very beginning,” admits Holzinger. Although the new analysis method only takes a maximum of two hours, it is still too time-consuming for routine measurements. In addition, there were no reference particles with which the measuring instruments could be calibrated. “We now have to make the methods more robust, more accurate and also more user-friendly,” emphasizes the researcher. If this succeeds, it may soon be possible to answer other open questions, for example how many plastic particles are hanging in the air elsewhere. Because one thing is certain: a plastic breeze is not only blowing in the Alps.