Humans and animals are constantly exposed to a complex assortment of microplastics (MPs) suspended in indoor air and the external atmosphere, but the deposition, retention and fate of these particles in the respiratory system remain poorly constrained. This systematic review identifies and critically evaluates original studies that have detected and characterised MPs in human and animal airways using autopsy, surgery, bronchoalveolar/bronchial lavage, sputum, saliva, nasal lavage, inhalation-exhalation and mucociliary-clearance approaches. The operational definition adopted here is plastic particles below 5 mm, with the practical lower size bound determined by the detection limits of each study; particles below 1 µm were not part of the primary MP evidence base and are noted only as a separate future research need. MPs or plastic-like particles have been reported in all respiratory matrices examined, with fibres often, but not universally, dominant and with reported sizes ranging from about 1 µm to several millimetres. However, the apparent heterogeneity in abundance, size, shape and polymer type is confounded by differences in sampling representativeness, digestion and density-separation methods, spectral confirmation, blank correction, recovery testing and size-detection limits. Therefore, the current evidence supports airway deposition and retention of MPs but is not yet sufficient for quantitative risk assessment or for robust comparison among organs, populations or species. Stronger future studies require harmonised reporting units, explicit LOD/LOQ procedures, procedural blanks, positive controls, recovery tests, fibre-diameter measurements, validated spectral libraries and transparent quality/risk-of-bias assessment. Potential health effects, including inflammation, oxidative stress, impaired clearance, additive leaching and translocation, are biologically plausible but remain insufficiently linked to environmentally realistic airway burdens.
Piroozfar et al. (Mon,) studied this question.