Size-Dependent Pulmonary Toxicity and Whole-Body Distribution of Inhaled Micro/Nanoplastic Particles in Male Mice from Chronic Exposure

The ubiquitous presence of micro/nanoplastics (MP/NP) in the atmosphere has raised significant concerns about their potential health risks through inhalation, yet the effects of natural respiratory exposure remain underexplored. This study addresses this critical knowledge void by utilizing a whole-body inhalation exposure system to investigate the distribution, accumulation, and pulmonary toxicity of polystyrene MP/NP (1.5 × 10⁵ particles/m³) in male ICR mice (n = 16/group). Fluorescently labeled MP/NP revealed the highest particle accumulation in the lungs, followed by the bloodstream and spleen, with minimal detection in the brain. Unsurprisingly, 80 nm nanoplastics displayed greater intertissue transport efficiency than 1 μm microplastics. Chronic exposure to both microplastics and nanoplastics disrupted oxidative balance and exacerbated oxidative stress within the extracellular environment of the lungs. The impaired antioxidant defenses and disrupted intra- and extracellular metabolism led to inflammation, apoptosis, and fibrosis. Intriguingly, 1 μm microplastics induced more severe pulmonary toxicity than their smaller counterparts, promoting epithelial-mesenchymal transition and fibrosis. These findings underscore the need for a nuanced understanding of size-dependent toxicities of inhalable plastic particles and highlight the health risks posed by airborne MP/NP.