Abstract
Airborne microplastics (MPs) are increasingly recognised as a prominent environmental and public health concern, with evidence of human inhalation. However, their behaviour and fate within the respiratory system remain poorly understood. This review synthesises current knowledge on the mechanisms of MP inhalation and deposition in the respiratory tract, with particular emphasis on their interactions with the respiratory epithelial barrier. Physiochemical properties influencing MP deposition such as size, shape, density, and surface charge are discussed, alongside host-related factors including airway geometry, breathing patterns, and the influence of environmental humidity. The contributions of mucociliary clearance and macrophages as frontline defence against these pollutants are also reviewed. Critical evaluation of in vitro and in vivo experiments indicates that MPs cause epithelial barrier dysfunction, highlighting instances of endoplasmic reticulum stress, oxidative stress, mitochondrial dysfunction, inflammation, and disturbances to tissue repair and development that could potentially aggravate respiratory diseases. Despite growing evidence of adverse effects, significant deficiencies remain in the existing scope of research, particularly on the chronic health consequences of airborne MP exposure. This review necessitates the need for long-term inhalation studies, more diverse representative particle models, and mechanistic investigations to clarify the long-term implications of airborne MP exposure on human health.
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