Sublethal effects of road dust particles in the yellow mealworm beetle Tenebrio molitor

High-traffic areas generate road dusts (RD) including tyre road wear particles (TRWPs), a significant source of microplastics in the environment. These particles, which persist in sediments, soil, and vegetation, can adsorb pollutants such as heavy metals and hydrocarbons, facilitating their widespread dispersal. Despite concerns about their potential ecotoxicity, their effects on soil organisms remain underexplored. This study investigated the impact of oral exposure to RD on Tenebrio molitor (Coleoptera, Tenebrionidae). Road dust was collected from roadsides and analysed for morphology and composition by scanning electron microscopy/energy dispersive X-ray spectroscopy, revealing TRWPs of variable size entrapping trace elements such as Fe, Al, and Si. Newly emerged adult beetles were exposed to contaminated flour with 5 % and 10 % RD for 20 days post-metamorphosis. The transfer of particles from the gut to beetle tissues was assessed by μFT-IR (Fourier Transformed Infrared Microscopy), showing that most TRWPs remained in the gut and were excreted, thus suggesting limited translocation to tissues. Nevertheless, exposure induced notable physiological and immune responses. While RD exposure did not affect survival, it induced body mass loss, increased haemocyte density and phenoloxidase enzyme activity. These responses varied according to sex and age, underscoring individual sensitivity. and indicate potential metabolic and inflammatory stress and transient nutritional deficiencies. Although specific exposure effects of TRWPs could not be isolated from those of other RD components, this study supports the use of T. molitor in standardized assays and emphasizes the ecological relevance of assessing complex pollutant mixtures. Our findings contribute to understanding the biological risks of RD in terrestrial organisms.