From Roadside Air to the Soil Interface: Atmospheric Deposition and Subsequent Environmental Behavior of Tire Additives

Tire additives are released during tire wear and can enter roadside air with fresh or resuspended particles and, for some compounds, through volatilization. Once airborne, they may partition between gas and particle phases, undergo atmospheric transformation, and reach terrestrial surfaces through dry and wet deposition. However, how much atmospheric deposition contributes to the transfer of tire additives from roadside air to soils and plants remains unclear. This review traces major tire additives and their transformation products from their occurrence, phase partitioning, and transformation in the atmosphere, through deposition, to their subsequent fate at the soil–plant interface. Available evidence shows that these processes are strongly compound-specific. Some additives remain mainly particle-associated, whereas others have substantial gas-phase fractions, and environmental aging can further change both parent compounds and transformation products before deposition. Field studies confirm the deposition of tire and road wear particles and selected tire additives, while controlled soil and plant experiments show retention, transformation, release, and plant uptake after environmental entry. However, the contribution of atmospheric deposition to additive burdens in field soils and crops is still difficult to separate from runoff, irrigation, road splash, and other rubber-related sources. Acute toxicity of N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine quinone (6PPD-Q) is well established in highly sensitive aquatic species, whereas risks associated with atmospheric deposition in terrestrial systems and humans remain poorly characterized. Overall, atmospheric deposition represents a possible pathway by which tire additives are transferred from roadside air to terrestrial environments. Quantifying its contribution will require phase-resolved measurements, robust source attribution, and coordinated monitoring across air, deposition, soil, and plants.