Surface-Specific Retention and Biointeraction of Xenobiotic Airborne Particulate Matter on Adaxial and Abaxial Leaf Surfaces of Ruscus aculeatus

Airborne particulate matter (PM) represents a complex class of environmental xenobiotics composed of mineral particles, heavy metals, persistent organic compounds, and environmentally persistent free radicals that pose significant risks to ecosystems and human health. Vegetation functions as a biological interface where these xenobiotic particles are intercepted, retained, and potentially transformed through physicochemical interactions, surface adsorption, and biological processes occurring at the phyllosphere. Understanding surface-specific plant–xenobiotic interactions is therefore critical for predicting contaminant fate, residence time, and exposure mitigation in urban environments. This study evaluates the surface-specific retention of xenobiotic PM on the adaxial and abaxial leaf surfaces of Ruscus aculeatus, a low-stature urban shrub exposed to near-road emissions. Particulate deposition was quantified using a modified gravimetric filtration protocol separating coarse (10–100 μm), fine (2.5–10 μm), and ultrafine (0.2–2.5 μm) particle fractions. The species accumulated a total particulate load of 54.8 μg.cm⁻², with significantly higher retention on the abaxial surface (30.3 μg.cm⁻²) compared with the adaxial surface (24.5 μg.cm⁻²). Coarse particles dominated total mass accumulation, whereas fine particles exhibited enhanced stabilization on the sheltered abaxial surface. Microstructural leaf features, including grooves and vein networks, promoted mechanical trapping, reduced resuspension, and increased particle residence time, suggesting enhanced potential for biointerface interactions and transformation processes. These findings highlight the importance of leaf surface morphology in regulating plant–xenobiotic interactions, influencing environmental fate, and reducing near-ground exposure risks. The results support the strategic use of shrub vegetation as a complementary biological filter for mitigating airborne xenobiotic contamination in urban landscapes and provide a mechanistic basis for plant selection in nature-based air quality management strategies.