Clean air is becoming a key factor in choosing a location

Microplastics do not simply remain on the roadside or in water bodies. The wind carries the finest particles through the atmosphere and disperses them across the whole of Switzerland. A systematic study carried out for the first time by Empa, Eawag and Agroscope now reveals the extent of the problem. Every year, around 219 tonnes of microplastics are deposited on the ground and in water bodies in areas below 2,000 metres.

Around 78 tonnes of these plastic particles fall directly onto agricultural land every year. A further ten tonnes end up directly in lakes and rivers. In total, around two-fifths of the atmospheric microplastic load therefore ends up on particularly sensitive areas. These figures highlight what was previously almost impossible to measure. Plastic breaks down into ever smaller pieces under the influence of UV radiation, precipitation, ozone and mechanical stress. The wind stirs up these particles, carries them further afield and then disperses them back onto the Earth’s surface via rain, snow or as dry deposits.

Not just a problem for cities
Over the course of a year, the research team collected samples in Zurich, Dübendorf, Magadino, Payerne and on the Chaumont in the Jura. Particles with a diameter of between 20 and 215 micrometres were analysed.

Zurich had the highest concentration, with an average of 881 microplastic particles per square metre per day. This is consistent with dense population, traffic and plastic consumption in urban areas. A closer look at the other measurement sites reveals a more surprising picture. Dübendorf, Magadino, Payerne and Chaumont recorded significantly lower levels, ranging from 249 to 331 particles, but the figures were close to one another. This suggests that microplastics in the atmosphere are not solely an urban phenomenon. The particles also reach rural regions, agricultural land and bodies of water far from major centres.

PET dominates the particle
The researchers determined not only the quantity but also the types of plastic. They found PET most frequently, accounting for 31 per cent. This was followed by polyethylene at 26 per cent and polypropylene at 21 per cent.

PET is best known for its use in drinks bottles, but is also found in the polyester fibres of clothing. Polyethylene and polypropylene are found in packaging, films, containers and many everyday products. However, the study cannot directly attribute individual particles to a specific source. Tyre wear was also recorded in a separate, ongoing investigation.

Rain washes it away, dry conditions cause it to settle
Microplastics return from the air to the ground in two ways. Rain and snow wash particles out of the atmosphere. In addition, in dry weather they settle under the influence of gravity. In Switzerland, around 60 per cent of the deposited microplastic mass originates from this dry deposition.
Measured against the total mass of all airborne particles, the proportion remains small. It ranges between 0.02 and 0.12 per cent. However, the ongoing deposition over large areas results in significant quantities. Microplastics do not degrade, or do so only very slowly, and therefore remain a long-term problem in soils, water bodies and food chains.

Precaution rather than displacement
Much remains unclear regarding the long-term consequences for the environment and health. What is clear, however, is that pollution does not arise solely from wastewater or visible littering. The air is a significant transport route that disperses plastic particles far beyond their original point of origin.

The researchers do not derive a simple, single solution from this. They refer to the precautionary principle: preventing littering, using plastics more deliberately and closing material cycles. What does not enter the environment cannot later settle as invisible plastic debris on Swiss fields, lakes and in Swiss towns and cities.