Airborne Microplastics in Indoor Environments of Nanjing, China: Characteristics and Inhalation Exposure

Airborne microplastics (MPs) have emerged as a growing concern in indoor air quality, whereas quantitative evidence on inhalation exposure remains limited. This study investigated the abundance, physicochemical characteristics, and inhalation exposure of airborne microplastics across functionally representative campus locations with an outdoor site as reference. Microplastics were universally present, with indoor concentrations (679 ± 229 MPs·m −3 ) substantially exceeding outdoor levels (149 ± 27 MPs·m −3 ). Fragments and fibers dominated across all environments, with more than 69% of microplastics were below 50 μm, indicating the predominance of fine microplastics capable of remaining airborne for extended periods. Polyamide (PA) was the most frequently detected microplastics indoors, while garages displayed greater microplastic diversity associated with traffic-related sources. By integrating zone-specific concentration data with time activity patterns, the highest estimated daily inhalation exposure within commonly occupied indoor environments reached 100.9 ± 35.2 MPs·kg BW −1 ·day −1 , highlighting zone-dependent exposure risks that challenge the conventional use of uniform indoor averages. Overall, this study provides an exposure relevant characterization of indoor airborne microplastics, emphasizing the importance of partitioning indoor spaces for precise risk assessment and management, and highlights the importance of integrating environmental measurements with human activity patterns when evaluating potential health implications.