An emerging role of microplastics in the etiology of lung ground glass nodules

Background: Microplastic pollution has become a serious global environmental threat. The abundance of microplastics in the air is an order of magnitude higher than that in other media, which means that all living animals breathing with lungs (including humans) cannot escape the fate of inhaling microplastics. However, there is no direct evidence to demonstrate what type and abundance of microplastics exist in lung tissue. In addition, whether the retention of microplastics and the long-term friction between microplastics and lung tissue are related to some respiratory diseases is largely unknown. Ground glass nodules (GGNs) are areas of lesions of homogeneous density and with hazy increase in density in the lung field that do not obscure the bronchovascular structure, which have been increasingly identified in past decades. Although their etiology is broad, the correlation of microplastics with GGNs remains elusive. Results: In this study, we identified the presence of 65 microfibers, including 24 microplastics (>20 mu m) in 100 human lung tissues with mu-FTIR. The detection rate of microfibers in tumor was 58%, higher than that in normal tissue (46%), and 2/3 of microplastics were found in tumor. Microfibers seemed to be embedded in lung tissues, which was suggested by the in situ observation via LDIR. Additionally, sub-micron-sized plastic particles were also detected in some lung tissues with Raman. The abundance of microfibers in lung tissue gradually accumulated with the increase of age. Moreover, the detection rate in tumor of patients with higher microfiber exposure risk history was significantly higher than those with a relatively lower one, implying microfiber inhalation could be related to the formation of GGN. Further, serious weared surface of microfibers isolated from lung tissue emphasized a possible link of surface roughness to the disease progression. Conclusions: Collectively, the existence of microplastics in human lung tissues was validated, and their correlation with GGN formation was preliminarily explored, which laid a foundation for future research on microplastic exposure in the etiology of lung cancer and other related respiratory diseases.