Distance-Dependent Transport of Tire and Road Wear Particles along the Road-to-Indoor Gradient and Implications for Human Exposure

Abstract

Tire and road wear particles (TRWPs) are ubiquitous in urban environments and represent a potential pathway for human exposure to microplastics, yet knowledge of their transport across multimedia and the associated exposure implications remains scarce. Here, we investigate the road-to-indoor transport of TRWPs and evaluate human exposure in road-adjacent and indoor scenarios using a multicompartment nationwide data set. Lateral and vertical transport analysis showed clear attenuation with increasing road-to-building distance and sampling height, following the relationships y = 1.62x–0.384 and y = 1.16e–0.023x, respectively. Particle size played a dominant role in transport, with finer particles showing greater indoor penetration. In contrast, aspect ratio varied little among compartments and exerted limited influence. Wind speed further affected TRWP transport, showing a positive correlation with lateral transport (r = 0.398) but a negative correlation with vertical transport (r = −0.512). Moreover, TRWPs contribute to daily intake in both outdoor and indoor environments, with dust ingestion being the predominant pathway. Notably, indoor exposure exceeded outdoor exposure, with median estimated daily intakes of 12 300 and 928 ng (kg of body weight)−1 day–1 for children and adults, respectively. This study provides new insights into the transport patterns of TRWPs and highlights their substantial contribution to human exposure in road-to-indoor environments.