From the street into the river: microplastics from the abrasion of car tires can get to nearby waters via the air and rain. This has consequences for the microorganisms living therein, as studies in the Rhine have shown. Accordingly, microbial biofilms form on the abrasion particles in the river water. But their bacterial composition differs from natural biofilms on stones and co and thus confuses the entire river ecosystem.
Micro and nanoplasty are now omnipresent. Almost everywhere in nature, these tiny plastic particles, which come from plastic waste and many of our everyday objects, can be found and spread over wind and rain in the environment. This also includes the abrasion of car tires, which causes about a quarter of all microplastics. In addition, there are deliberately produced plastic particles such as peeling balls in cosmetics or plastic granules from industry that end up in nature through waste water.
It is known from previous studies that the sea and rivers are heavily contaminated with such microplastics and that different types of bacteria can settle on the plastic particles. This also applies to the Rhine, as the latest analyzes of the State Office for Nature, Environment and Climate North Rhine-Westphalia showed. But what are the consequences for the microbial communities in the river?
Plastic -client microbes in the Rhine
Researchers around Dana Bludau from the University of Duisburg-Essen have now systematically examined this using tire abrasion. To do this, they deliberately poured small amounts of tire particle mixtures into the Rhine near Cologne. The particles were either a few hundred micrometers or over 1000 micrometers in size and came from new and old tires of cars and trucks. This reflects the real variety of abrasion particles. It is known that the abrasion is mainly deposited in the river sediment and only a small part of the current is driven away. The biologists therefore placed their abrasion samples in special research channels and boxes in the Rhine, which are naturally washed up by the current. Four weeks later, they removed the rehearsals and examined the microorganisms located therein.
The result: The plastic particles are not equally attractive for all water -living microbes. Representatives of aquabacterium and ketobacter had particularly frequently settled there, with the former preferred small and latter large particles. “We were able to show that certain types of bacteria particularly like to settle on tire abrasion, while the general variety of microorganisms decreases on it,” reports Bludau. Accordingly, thin biofilms from different microorganisms form on the particles. But their diversity and composition differ significantly from the natural biofilms that cover stones, sediments and other materials in the river. “Especially the biofilms on larger particles of older tires differed significantly from those on natural particles of the river,” said Bludau. Abriting of truck tires also had a particularly low and unnatural biodiversity.
Changed microbes communities
The researchers suspect that the types of bacteria found on the abrasion particles have an adapted metabolism through which they can break down chemicals from the tire material. “The ability to metabolize hydrocarbons such as gasoline, diesel and kerosene that occur in tires, offers a possible explanation for the observed spread of aquabacterium,” the team gives an example. For many other microbes that occur naturally in the Rhine water, tire ingredients such as alkanes, plasticizers or heavy metals can be useless or even toxic, which is why they do not settle on the tire particles.
Overall, the tire abrasion introduced promoted bacterial species that specialize in the reduction of environmental pollutants, thereby changing the natural microbe composition in the Rhine. That could have far -reaching consequences for the river. Because microbes are central actors in aquatic ecosystems: they break up organic material, control nutrient circuit and form the basis for food chains. “If tire abrasion changes the composition of these biofilms, this concerns the entire river system,” emphasizes Bludau.
Source: University of Duisburg-Essen; Specialist articles: Environmental Pollution, DOI: 10.1016/J.ENVPol.2025.127004
