Deleterious effects of microplastics and nanoplastics on rodent lungs: a systematic review

<bold>Background:</bold> Microplastics (MP) and nanoplastics (NP) precipitate in the atmosphere and can be inhaled. Furthermore, they have been identified in human lung tissue. However, the pulmonary consequences of exposure to these particles remain poorly understood. <bold>Objectives:</bold> To investigate the deleterious effects of MP and NP on rodent lungs. <bold>Methods:</bold> A systematic search was conducted in PubMed and Embase up to February 2024. Animal studies evaluating the effects of exposure to MP and/or NP on rodent lungs were included. The outcomes were synthesized narratively. The study protocol was registered in PROSPERO (CRD42024539770). <bold>Results:</bold> A total of 46 studies were included from 702 records. Most studies investigated polystyrene as the type of micro-nanoplastic (MNP) (n=28) and single exposure as the exposure pattern (n=24). The most frequently evaluated outcome was histopathological analysis of rodent lungs (n=29). The results indicate a dose-dependent association between MNP exposure and lung changes. Several studies identified inflammatory cell infiltration in the lungs (n=15), including peribronchial, perivascular, bronchiolocentric, in the parenchymal space, and in the alveolar space. Other reported findings were alveolar wall thickening (n=8), clusters of macrophages (n=5), fibrosis (n=6), granulomatous lesions (n=4), blood vessels congestion (n=2), edema in the alveolar wall and alveolar space (n=3), and pulmonary hemorrhage (n=2). Only two studies reported no lung changes. <bold>Conclusions:</bold> The included studies suggested a dose-dependent association between exposure to MNPs and lung changes in rodents, with inflammatory cell infiltration as the most commonly observed change.