Tire wear particles drive size-dependent loss of freshwater bacterial biofilm diversity

Tire wear particles (TWPs) represent a significant, yet understudied, source of anthropogenic pollution in aquatic environments, contributing to microplastic contamination and potentially altering microbial ecosystems. As TWPs are continuously released through abrasion during vehicle use, they accumulate in rivers and sediments, where they can act as surfaces for microbial biofilm formation. In this study, we investigated how TWP characteristics - particle size (small & large), wear condition (unused & used), and vehicle type (car & truck) - affect microbial biofilm composition after four weeks of exposure in the River Rhine, compared to natural sediment. Using 16S rRNA amplicon sequencing, we found that TWP-associated biofilms harboured significantly lower bacterial diversity than natural sediment biofilms. While a substantial number of OTUs were shared between both habitats, TWPs exhibited increased richness but decreased overall diversity, indicating selective enrichment of specialised taxa. Larger particles further reduced diversity, and specific genera such as Aquabacterium and Ketobacter were highly enriched on TWPs, indicating selective microbial colonization. These findings reveal the effects of TWPs on microbial biofilm communities, emphasizing their potential role in altering freshwater microbial ecosystems. Given the widespread release of TWPs, understanding their ecological impact is crucial for assessing their role in aquatic pollution and ecosystem functioning.